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BACKGROUND: A plateau in oxygen consumption (VO2) is the primary means of confirming that maximal oxygen uptake (VO2max) is attained during incremental exercise to fatigue. However, it is still unresolved what causes expression of a plateau in VO2 at the end of incremental exercise. OBJECTIVES: To elucidate incidence and identify determinants of the VO2 plateau in subjects of varying fitness. METHODS: Thirty subjects (mean (SD) age and VO2max 26.9 (9.8) years and 3.4 (0.8) litre/min respectively) were separated into three groups: endurance trained (ET; n = 9), recreationally active (Rec; n = 11), and strength/sprint trained (STR; n = 10). During three separate visits, subjects completed incremental treadmill exercise during which breath by breath gas exchange data were obtained. Body composition was measured using a three site skinfolds model. Force production of the knee extensors and flexors was assessed using isokinetic dynamometry. RESULTS: VO2max was significantly higher (p < 0.05) in the ET group vs STR and Rec. The change in VO2 (DeltaVO2) at VO2max was not different (p > 0.05) in the ET group (33.0 (27.3) ml/min) compared with the Rec group (30.3 (24.1) ml/min) and the STR group (44.4 (23.8) ml/min). No correlations (p > 0.05) were evident between DeltaVO2 at VO2max and VO2max (r = 0.05), fat-free mass (r = 0.12), and muscular strength (r = -0.12). CONCLUSIONS: The incidence of a plateau in VO2 at VO2max (from correlation data) is not due to factors related to training status or physical fitness of subjects, but is altered by analysis and interpretation of gas exchange data. [ABSTRACT FROM AUTHOR]

Adults who have had an amputation face barriers to having an active lifestyle which attenuates cardiorespiratory fitness. Prior studies in amputees typically involve treadmill walking or arm ergometry, yet physiological responses to bilateral leg cycling are less understood. This study assessed the hemodynamic and metabolic responses to moderate and vigorous cycle ergometry in men who have had a transtibial amputation (TTA). Five men who had had a unilateral TTA (age = 39 ± 15 yr) and six controls (CONs) without an amputation (age = 31 ± 11 yr) performed two 20 min bouts of cycling differing in intensity. Cardiac output (CO), stroke volume (SV), and oxygen consumption (VO 2 ) were measured during moderate intensity continuous exercise (MICE) and high intensity interval exercise (HIIE) using thoracic impedance and indirect calorimetry. In response to MICE and HIIE, the HR and VO 2 levels were similar ( p > 0.05) between groups. Stroke volume and CO were higher ( p < 0.05) in the CONs, which was attributed to their higher body mass. In men with TTAs, HIIE elicited a peak HR = 88%HRmax and substantial blood lactate accumulation, representing vigorous exercise intensity. No adverse events were exhibited in the men with TTAs. The men with TTAs show similar responses to MICE and HIIE versus the CONs.

Arm cycling ergometry (ACE) leads to a lower maximal oxygen uptake (VO 2 max) than cycling which is related to a smaller active muscle mass. This study compared estimates of fat and carbohydrate oxidation (FOx and CHOOx) between progressive exercise protocols varying in stage duration in an attempt to create a standard exercise protocol for determining substrate metabolism using ACE. Four men and seven women (age = 24 ± 9 yr) unfamiliar with ACE completed incremental exercise to determine peak power output and VO 2 peak. During two subsequent sessions completed after an overnight fast, they completed progressive ACE using 3- or 5-min stages during which FOx, CHOOx, and blood lactate concentration (BLa) were measured. Results showed no difference (p > 0.05) in FOx, CHOOx, or BLa across stage duration, and there was no difference in maximal fat oxidation (0.16 ± 0.08 vs. 0.13 ± 0.07 g/min, p = 0.07). However, respiratory exchange ratio in response to the 3 min stage duration was significantly lower than the 5 min duration (0.83 ± 0.05 vs. 0.86 ± 0.03, p = 0.04, Cohen's d = 0.76). Results suggest that a 3 min stage duration is preferred to assess substrate metabolism during upper-body exercise in healthy adults.

Background and Aim: A plateau in oxygen uptake ([Formula: see text]) during an incremental cardiopulmonary exercise test (CPET) to volitional exhaustion appears less likely to occur in special and clinical populations. Secondary maximal oxygen uptake ([Formula: see text]) criteria have been shown to commonly underestimate the actual [Formula: see text]. The verification phase protocol might determine the occurrence of 'true' [Formula: see text] in these populations. The primary aim of the current study was to systematically review and provide a meta-analysis on the suitability of the verification phase for confirming 'true' [Formula: see text] in special and clinical groups. Secondary aims were to explore the applicability of the verification phase according to specific participant characteristics and investigate which test protocols and procedures minimise the differences between the highest [Formula: see text] values attained in the CPET and verification phase., Methods: Electronic databases (PubMed, Web of Science, SPORTDiscus, Scopus, and EMBASE) were searched using specific search strategies and relevant data were extracted from primary studies. Studies meeting inclusion criteria were systematically reviewed. Meta-analysis techniques were applied to quantify weighted mean differences (standard deviations) in peak [Formula: see text] from a CPET and a verification phase within study groups using random-effects models. Subgroup analyses investigated the differences in [Formula: see text] according to individual characteristics and test protocols. The methodological quality of the included primary studies was assessed using a modified Downs and Black checklist to obtain a level of evidence. Participant-level [Formula: see text] data were analysed according to the threshold criteria reported by the studies or the inherent measurement error of the metabolic analysers and displayed as Bland-Altman plots., Results: Forty-three studies were included in the systematic review, whilst 30 presented quantitative information for meta-analysis. Within the 30 studies, the highest mean [Formula: see text] values attained in the CPET and verification phase protocols were similar (mean difference = -0.00 [95% confidence intervals, CI = -0.03 to 0.03] L·min-1, p = 0.87; level of evidence, LoE: strong). The specific clinical groups with sufficient primary studies to be meta-analysed showed a similar [Formula: see text] between the CPET and verification phase (p > 0.05, LoE: limited to strong). Across all 30 studies, [Formula: see text] was not affected by differences in test protocols (p > 0.05; LoE: moderate to strong). Only 23 (53.5%) of the 43 reviewed studies reported how many participants achieved a lower, equal, or higher [Formula: see text] value in the verification phase versus the CPET or reported or supplied participant-level [Formula: see text] data for this information to be obtained. The percentage of participants that achieved a lower, equal, or higher [Formula: see text] value in the verification phase was highly variable across studies (e.g. the percentage that achieved a higher [Formula: see text] in the verification phase ranged from 0% to 88.9%)., Conclusion: Group-level verification phase data appear useful for confirming a specific CPET protocol likely elicited [Formula: see text], or a reproducible [Formula: see text], for a given special or clinical group. Participant-level data might be useful for confirming whether specific participants have likely elicited [Formula: see text], or a reproducible [Formula: see text], however, more research reporting participant-level data is required before evidence-based guidelines can be given., Trial Registration: PROSPERO (CRD42021247658) https://www.crd.york.ac.uk/prospero., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Costa et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

We hypothesized that slowed oxygen uptake ( V ˙ O 2 ) kinetics for exercise transitions to higher power outputs (PO) within the steady state (SS) domain would increase the mean response time (MRT) with increasing exercise intensity during incremental exercise. Fourteen highly trained cyclists (mean ± standard deviation [ SD ]; age (39 ± 6) years [yr]; and V ˙ O 2 peak = (61 ± 9) mL/kg/min performed a maximal, ramp incremental cycling test and on separate days, four 6-min bouts of cycling at 30%, 45%, 65% & 75% of their incremental peak PO (Wpeak). SS trial data were used to calculate the MRT and verified by mono-exponential and linear curve fitting. When the ramp protocol attained the value from SS, the PO, in Watts (W), was converted to time (min) based on the ramp function W to quantify the incremental MRT (iMRT). Slope analyses for the V ˙ O 2 responses of the SS versus incremental exercise data below the gas exchange threshold (GET) revealed a significant difference ( p  = 0.003; [0.437 ± 0.08] vs. [0.382 ± 0.05] L⋅min -1 ). There was a significant difference between the 45% Wpeak steady state V ˙ O 2 (ss V ˙ O 2 ) ([3.08 ± 0.30] L⋅min -1 , respectively), and 30% Wpeak ss V ˙ O 2 (2.26 ± 0.24) ( p  < 0.0001; [3.61 ± 0.80] vs. [2.20 ± 0.39] L⋅min -1 ) and between the iMRT for 45% and 30% Wpeak ss V ˙ O 2 values ([50.58 ± 36.85] s vs. [32.20 ± 43.28] s). These data indicate there is no single iMRT, which is consistent with slowed V ˙ O 2 kinetics and an increasing V ˙ O 2 deficit for higher exercise intensities within the SS domain., Competing Interests: No author of this manuscript has direct or indirect interests that are in direct conflict with the conduction of the study., (© 2024 Chengdu Sport University. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.)

Increases in power output and maximal oxygen consumption ( V ˙ O 2 max) occur in response to sprint interval exercise (SIE), but common use of "all-out" intensities presents a barrier for many adults. Furthermore, lower-body SIE is not feasible for all adults. We compared physiological and perceptual responses to supramaximal, but "non-all-out" SIE between leg and arm cycling exercise. Twenty-four active adults (mean ​± ​ SD age: [25 ​± ​7] y; cycling V ˙ O 2 max: [39 ​± ​7] mL·kg -1 ·min -1 ) performed incremental exercise using leg (LCE) and arm cycle ergometry (ACE) to determine V ˙ O 2 max and maximal work capacity (Wmax). Subsequently, they performed four 20 ​s bouts of SIE at 130% Wmax on the LCE or ACE at cadence ​= ​120-130 ​rev/min, with 2 ​min recovery between intervals. Gas exchange data, heart rate (HR), blood lactate concentration (BLa), rating of perceived exertion (RPE), and affective valence were acquired. Data showed significantly lower ( p  ​< ​0.001) absolute mean ([1.24 ​± ​0.31] L·min -1 vs. [1.59 ​± ​0.34] L·min -1 ; d  ​= ​1.08) and peak V ˙ O 2 ([1.79 ​± ​0.48] L·min -1 vs. [2.10 ​± ​0.44] L·min -1 ; d  ​= ​0.70) with ACE versus LCE. However, ACE elicited significantly higher ( p  ​< ​0.001) relative mean ([62% ​± ​9%] V ˙ O 2 max vs. [57% ​± ​7%] V ˙ O 2 max, d  ​= ​0.63) and peak V ˙ O 2 ([88% ​± ​10%] V ˙ O 2 max vs. [75% ​± ​10%] V ˙ O 2 max, d  ​= ​1.33). Post-exercise BLa was significantly higher ([7.0 ​± ​1.7] mM vs. [5.7 ​± ​1.5] mM, p  ​= ​0.024, d  ​= ​0.83) for LCE versus ACE. There was no significant effect of modality on RPE or affective valence ( p  ​> ​0.42), and lowest affective valence recorded (2.0 ​± ​1.8) was considered "good to fairly good". Data show that non "all-out" ACE elicits lower absolute but higher relative HR and V ˙ O 2 compared to LCE. Less aversive perceptual responses could make this non-all-out modality feasible for inactive adults., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 Chengdu Sport University. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.)

Purpose: The postural transition from sitting to standing is a moment of dysautonomic occurrence in individuals with Spinal Cord Injury (SCI). Different tools can be used to minimize this event, such as virtual reality. Thus, we aimed to analyze cardiac autonomic modulation in individuals with SCI during postural transition from the sitting to orthostatism position using a cognitive virtual reality (VR) task., Methods: Individuals with and without SCI were positioned on the Easy Stand® device, sitting at rest, at 0° considering the angle between the seat and the floor, elevation at 45°, and orthostatism at 90°, for 5 minutes in each position. Heart rate variability (HRV) measures of sympathovagal balance were collected (heart rate receiver: Polar V800). The groups were subdivided into two groups, one that performed VR as an intervention during the postural angle changes and another group that did not perform VR., Results: We evaluated 76 individuals, 40 with a medical diagnosis of SCI and 36 who composed the able-bodied control group without SCI, matched by age and sex. The HRV results showed that the SCI group who performed the task in VR demonstrated no significant difference in parasympathetic activation and global variability between the sitting versus 90° positions. There was better sympathovagal balance in SCI and able-bodied control groups who performed the VR task between the sitting versus 90° positions., Conclusion: The use of a VR task seems to contribute to better sympathovagal balance, with the potential to reduce dysautonomia during postural changes., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Papa et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Introduction: High-intensity interval training and sprint interval training significantly increase maximal oxygen uptake (V̇O 2max ), which enhances endurance performance and health status. Whether this response is due to increases in central cardiovascular function (cardiac output (CO) and blood volume) or peripheral factors is unknown., Purpose: This study aimed to conduct a systematic review and meta-analysis to assess the effects of high-intensity interval training and sprint interval training (referred to as intense interval training) on changes in central cardiovascular function., Methods: We performed a systematic search of eight databases for studies denoting increases in V̇O 2max in which CO, stroke volume (SV), blood volume, plasma volume, end-diastolic/systolic volume, or hematocrit were measured., Results: Forty-five studies were included in this analysis, comprising 946 men and women of various health status (age and V̇O 2max , 20-76 yr and 13-61 mL·kg -1 ·min -1 ) who performed 6-96 sessions of interval training. Results showed an increase in V̇O 2max with intense interval training that was classified as a large effect ( d = 0.83). SV ( d = 0.69), and CO ( d = 0.49) had moderate effect sizes in response to intense interval training. Of 27 studies in which CO was measured, 77% exhibited significant increases in resting CO or that obtained during exercise. Similarly, 93% of studies revealed significant increases in SV in response to intense interval training. Effect sizes for these outcomes were larger for clinical versus healthy populations. Plasma volume, blood volume, and hematocrit had small effect sizes after training ( d = 0.06-0.14)., Conclusions: Increases in V̇O 2max demonstrated with intense interval training are attendant with increases in central O 2 delivery with little contribution from changes in hematocrit, blood volume, or plasma volume., (Copyright © 2022 by the American College of Sports Medicine.)

Context: Persons with spinal cord injury (SCI) present with low fat oxidation that is associated with poor cardiometabolic health. This study compared changes in fat and carbohydrate (CHO) oxidation during moderate intensity continuous exercise in persons with SCI and able-bodied adults (AB)., Design: Repeated measures, within-subjects study., Setting: University laboratory in San Diego, CA., Participants: Nine men and women with SCI (age and time since injury = 32 ± 11 yr and 7 ± 6 yr) and 10 AB adults (age = 25 ± 8 yr)., Interventions: To assess peak oxygen uptake (VO 2 peak) and peak power output (PPO), participants performed progressive arm ergometry to volitional exhaustion. Subsequently, they completed 25 min of continuous exercise at 45%PPO., Outcome Measures: Respiratory exchange ratio (RER), fat and CHO oxidation, and blood lactate concentration (BLa) were assessed., Results: Data showed a similar RER ( P  = 0.98) during exercise in SCI (0.97 ± 0.04) versus AB (0.97 ± 0.03) reflecting high CHO use and no differences in BLa (3.5 ± 1.1 and 3.0 ± 0.9 vs. mM, P  = 0.56) or fat and CHO oxidation between groups ( P  > 0.05). However, participants with SCI exercised at a higher relative intensity ( P  < 0.01, 84 ± 7 vs. 75 ± 7%HRpeak) versus AB., Conclusion: Data confirm high reliance on CHO during arm ergometry in persons with SCI. To better compare substrate utilization to AB adults, we recommend that exercise be prescribed according to peak heart rate due to differences in cardiorespiratory fitness between groups.

Purpose: To compare the metabolic, cardiorespiratory and perceptual responses to three isoenergetic high-intensity interval exercise (HIIE) protocols of different bout duration and an isoenergetic continuous exercise protocol., Methods: Eleven healthy males (age, 28 ± 6 yr) performed four 20-min cycling trials of equal mean power output 1 wk apart. Participants cycled either continuously (CON) or intermittently with 10 s (HIIE10), 30 s (HIIE30), or 60 s (HIIE60) bouts at intensities corresponding to 49% (CON) or 100% of power at peak oxygen uptake (V̇O2peak). Recovery intervals during the HIIE trials were 15, 45, and 90 s, respectively., Results: Average V̇O2 was similar in the HIIE trials (2.29 ± 0.42, 2.20 ± 0.43, and 2.12 ± 0.45 L·min-1, for HIIE10, HIIE30, and HIIE60, respectively), whereas in CON (2.02 ± 0.38 L·min-1), it was lower than HIIE10 (P = 0.002) and HIIE30 (P = 0.043). Average pulmonary ventilation (VE) was higher in HIIE60 compared with HIIE10, HIIE30, and CON (75.8 ± 21.8 L·min-1 vs 64.1 ± 14.5 L·min-1, 64.1 ± 16.2 L·min-1, and 54.0 ± 12.5 L·min-1, respectively, P < 0.001). The peak values and oscillations of V̇O2 and VE in HIIE60 were higher compared with all other trials (P < 0.001). Blood lactate concentration was higher in HIIE60 compared with HIIE10, HIIE30, and CON from the fifth minute onward, reaching 12.5 ± 3.5, 7.2 ± 2.1, 7.9 ± 2.9, and 4.9 ± 1.6 mmol·L-1, respectively, at the end of exercise (P < 0.001). RPE was higher and affective responses were lower in HIIE60 compared with all other trials toward the end of exercise (P < 0.001)., Conclusions: These findings highlight the importance of bout duration in HIIE, since shorter bouts resulted in attenuated metabolic and cardiorespiratory responses, lower RPE and feelings of displeasure compared with a longer bout, despite equal total work, duration, and work-to-recovery ratio. These results may have implications for the prescription of HIIE in various populations., (Copyright © 2022 by the American College of Sports Medicine.)

This study examined the effects of a resistance-type high-intensity interval training (RHIIT) matched with the lowest velocity that elicited V . O 2peak (100% v V . O 2peak ) in well-trained kayak sprint athletes. Responses in cardiac structure and function, cardiorespiratory fitness, anaerobic power, exercise performance, muscular strength, and hormonal adaptations were examined. Male kayakers ( n = 24, age: 27 ± 4 years) were randomly assigned to one of three 8-wk conditions ( N = 8): (RHIIT) resistance training using one-armed cable row at 100% v V . O 2peak ; paddling-based HIIT (PHIIT) six sets of paddling at 100% v V . O 2peak ; or controls (CON) who performed six sessions including 1-h on-water paddling/sessions at 70-80% maximum HR per week. Significant increases ( p < 0.05) in V . O 2peak , v V . O 2peak , maximal cardiac output, resting stroke volume, left ventricular end-systolic dimension, 500-m paddling performance were seen pre- to post-training in all groups. Change in V . O 2peak in response to PHIIT was significantly greater ( p = 0.03) compared to CON. Also, 500-m paddling performance changes in response to PHIIT and RHIIT were greater ( p = 0.02, 0.05, respectively) than that of CON. Compared with pre-training, PHIIT and RHIIT resulted in significant increases in peak and average power output, maximal stroke volume, end-diastolic volume, ejection fraction, total testosterone, testosterone/cortisol ratio, and 1,000-m paddling performance. Also, the change in 1,000-m paddling performance in response to PHIIT was significantly greater ( p = 0.02) compared to that of CON. Moreover, maximum strength was significantly enhanced in response to RHIIT pre- to post-training ( p < 0.05). Overall, RHIIT and PHIIT similarly improve cardiac structure and hemodynamics, physiological adaptations, and performance of well-trained kayak sprint athletes. Also, RHIIT enhances cardiorespiratory fitness and muscular strength simultaneously., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Sheykhlouvand, Arazi, Astorino and Suzuki.)

Responses to sprint interval exercise (SIE) are hypothesized to be perceived as unpleasant, but SIE protocols are diverse, and moderating effects of various SIE protocol parameters on affective responses are unknown. We performed a systematic search to identify studies (up to 01/05/2021) measuring affective valence using the Feeling Scale during acute SIE in healthy adults. Thirteen studies involving 18 unique trials and 316 unique participant (142 women and 174 men) affective responses to SIE were eligible for inclusion. We received individual participant data for all participants from all studies. All available end-of-sprint affect scores from each trial were combined in a linear mixed model with sprint duration, mode, intensity, recovery duration, familiarization and baseline affect included as covariates. Affective valence decreased significantly and proportionally with each additional sprint repetition, but this effect was modified by sprint duration: affect decreased more during 30 s (0.84 units/sprint; 95% CI: 0.74-0.93) and 15-20 s sprints (1.02 units/sprint; 95% CI: 0.93-1.10) compared with 5-6 s sprints (0.20 units/sprint; 95% CI: 0.18-0.22) (both p < 0.0001). Although the difference between 15-20 s and 30 s sprints was also significant ( p = 0.02), the effect size was trivial ( d = -0.12). We observed significant but trivial effects of mode, sprint intensity and pre-trial familiarization, whilst there was no significant effect of recovery duration. We conclude that affective valence declines during SIE, but the magnitude of the decrease for an overall SIE session strongly depends on the number and duration of sprints. This information can be applied by researchers to design SIE protocols that are less likely to be perceived as unpleasant in studies of real-world effectiveness., Systematic Review Registration: Open Science Framework, https://osf.io/sbyn3., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Metcalfe, Williams, Fernandes, Astorino, Stork, Phillips, Niven and Vollaard.)

Introduction: The characterization of immune and oxidative stress responses to acute and chronic exercise training is important because it may aid in the safety and dose-response prescription of resistance training (RT) in many populations. Purpose: The present study compared changes in acute oxidative stress and markers of apoptosis in immune cells before and after 8 weeks of low-load RT with total or partial blood flow restriction (BFR) versus high-load traditional RT. Methods: Twenty-seven untrained men were randomly divided into three groups: traditional RT [75% one-repetition maximum (1-RM)], RT with partial (20% 1-RM), and total BFR (20% 1-RM). Over an 8-week period, participants performed six sets of arm curls until failure with 90 seconds of recovery for 3 days/week. Blood samples were obtained before and after the first and last training sessions. Results: Data indicated that all training groups showed similar increases in muscular strength ( p < 0.001), reduction in mitochondrial membrane potential (MMP) after exercise in neutrophils ( p < 0.001), and increase in caspase-3 activity after exercise ( p < 0.001). Traditional RT and total BFR showed increased plasma lipid peroxidation ( p < 0.001) and protein carbonyls ( p < 0.001) and lower levels of reduced glutathione (GSH) ( p < 0.001) after exercise. No change was observed in oxidative stress biomarkers in response to partial BFR ( p > 0.05). Conclusion: Data show that RT with partial BFR can increase muscular strength but still does not augment biomarkers of oxidative stress in untrained men. In addition, RT with total BFR promoted similar responses of oxidative stress and markers of immune cell apoptosis versus traditional RT., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 de Lima, Marin, Ferreira, Sousa Filho, Astorino, Prestes, Marquezi and Otton.)

This study compared changes in oxygen uptake (VO 2 ), heart rate (HR), blood lactate concentration (BLa), affective valence, and rating of perceived exertion (RPE) between sessions of high intensity interval exercise (HIIE) performed on the arm (ACE) and leg cycle ergometer (LCE). Twenty three active and non-obese men and women (age and BMI=24.7±5.8year and 24.8±3.4kg/m 2 ) initially underwent graded exercise testing to determine VO 2 max and peak power output (PPO) on both ergometers. Subsequently on two separate days, they performed 10 1min intervals of ACE or LCE at 75 %PPO separated by 1min of active recovery at 10 %PPO. Gas exchange data, HR, and perceptual responses were obtained continuously and blood samples were acquired pre- and post-exercise to assess the change in BLa. VO 2 max and PPO on the LCE were significantly higher ( p <0.001) than ACE (37.2±6.3 vs. 26.3±6.6ml/kg/min and 259.0±48.0 vs. 120.0±48.1W). Mean VO 2 (1.7±0.3 vs. 1.1±0.3L/min, d =2.3) and HR (149±14 vs. 131±17 b/min, d =2.1) were higher ( p <0.001) in response to LCE vs. ACE as was BLa (7.6±2.6 vs. 5.3±2.5mM, d =2.3), yet there was no difference ( p =0.12) in peak VO 2 or HR. Leg cycling elicited higher relative HR compared to ACE (81±5 vs. 75±7 %HRmax, p =0.01), although, there was no difference in relative VO 2 (63±6 vs. 60±8 %VO 2 max, p =0.09) between modes. Affective valence was lower during LCE vs. ACE ( p =0.003), although no differences in enjoyment ( p =0.68) or RPE ( p =0.59) were demonstrated. Overall, HIIE performed on the cycle ergometer elicits higher relative heart rate and blood lactate concentration and a more aversive affective valence, making these modes not interchangeable in terms of the acute physiological and perceptual response to interval based exercise., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Astorino and Emma.)

Spinal cord injury (SCI) results in a multitude of metabolic co-morbidities that can be managed by exercise. As in the non-injured population, manipulation of exercise intensity likely allows for fruitful optimization of exercise interventions targeting metabolic health in persons with SCI. In this population, interventions employing circuit resistance training (CRT) exhibit significant improvements in outcomes including cardiorespiratory fitness, muscular strength, and blood lipids, and recent exploration of high intensity interval training (HIIT) suggests the potential of this strategy to enhance health and fitness. However, the neurological consequences of SCI result in safety considerations and constrain exercise approaches, resulting in the need for specialized exercise practitioners. Furthermore, transportation challenges, inaccessibility of exercise facilities, and other barriers limit the translation of high intensity "real world" exercise strategies. Delivering exercise via online ("virtual") platforms overcomes certain access barriers while allowing for broad distribution of high intensity exercise despite the limited number of population-specific exercise specialists. In this review, we initially discuss the need for "real world" high intensity exercise strategies in persons with SCI. We then consider the advantages and logistics of using virtual platforms to broadly deliver high intensity exercise in this population. Safety and risk mitigation are considered first followed by identifying strategies and technologies for delivery and monitoring of virtual high intensity exercise. Throughout the review, we discuss approaches from previous and ongoing trials and conclude by giving considerations for future efforts in this area., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 McMillan, Astorino, Correa, Nash and Gater.)

Maximal oxygen uptake (VO 2 max) is strongly associated with endurance performance as well as health risk. Despite the fact that VO 2 max has been measured in exercise physiology for over a century, robust procedures to ensure that VO 2 max is attained at the end of graded exercise testing (GXT) do not exist. This shortcoming led to development of an additional bout referred to as a verification test (VER) completed after incremental exercise or on the following day. Workloads used during VER can be either submaximal or supramaximal depending on the population tested. Identifying a true VO 2 max value in unhealthy individuals at risk for or having chronic disease seems to be more paramount than in healthy and active persons, who face much lower risk of premature morbidity and mortality. This review summarized existing findings from 19 studies including 783 individuals regarding efficacy of VER in unhealthy individuals to determine its efficacy and feasibility in eliciting a 'true' VO 2 max in this sample. Results demonstrated that VER is a safe and suitable approach to confirm attainment of VO 2 max in unhealthy adults and children, as in most studies VER-derived VO 2 max is similar of that obtained in GXT. However, many individuals reveal higher VO 2 max in response to VER and protocols used across studies vary, which merits additional work identifying if an optimal VER protocol exists to elicit 'true' VO 2 max in this particular population.

The aim of this study was to compare the acute responses to three time-matched exercise regimens. Ten trained adults (age, maximum oxygen consumption (VO 2max ), and body mass index (BMI) = 25.9 ± 5.6 yr, 50.9 ± 5.4 mL·kg -1 ·min -1 , and 22.1 ± 1.8 kg·m -2 ) completed sprint interval training (SIT) requiring 14 × 5 s efforts with 35 s of recovery, high-intensity interval training (HIIT) consisting of 18 × 15 s efforts at ~90% of peak heart rate (HR peak ) with 15 s of recovery, and vigorous continuous training (CT) consisting of 8.75 min at ~85 %HR peak , in randomized order. Heart rate, blood lactate concentration, rating of perceived exertion, affective valence, and enjoyment were monitored. Moreover, indices of neuromuscular function, autonomic balance, diet, mental stress, incidental physical activity (PA), and sleep were measured 24 h after each session to analyze the magnitude of recovery. Both HIIT and CT exhibited a greater %HR peak and time ≥ 90 %HR peak than SIT ( p < 0.05). Blood lactate and rating of perceived exertion were higher in response to SIT and HIIT vs. CT ( p < 0.05); however, there were no differences in enjoyment ( p > 0.05). No differences were exhibited in any variable assessed along 24 h post-exercise between conditions ( p > 0.05). These data suggest that HIIT and CT accumulate the longest duration at near maximal intensities, which is considered a key factor to enhance VO 2max .

This study compared changes in substrate metabolism with high intensity interval training (HIIT) in women of different ethnicities. Twelve Caucasian (C) and ten Hispanic women (H) (age = 24 ± 5 yr) who were inactive completed nine sessions of HIIT at 85 percent peak power output (%PPO). Pre-training, changes in fat oxidation (FOx) and carbohydrate oxidation (CHOOx) during progressive cycling were measured on two days to compute the minimum difference (MD). This test was repeated after the last training session. Between baseline tests, estimates of FOx and CHOOx were not different ( p > 0.05) and were highly related (intraclass correlation coefficient equal to 0.72 to 0.88), although the coefficient of variation of maximal fat oxidation (MFO) was equal to 30%. Training significantly increased MFO ( p = 0.03) in C (0.19 ± 0.06 g/min to 0.21 ± 0.06 g/min, d = 0.66) and H (0.16 ± 0.03 g/min to 0.19 ± 0.03 g/min, d = 1.3) that was similar ( p = 0.92) between groups. There was a significant interaction for FOx ( p = 0.003) as it was only increased in H versus C, although both groups exhibited reduced CHO oxidation ( p = 0.002) with training. Use of MD revealed that only 3 of 22 women show meaningful increases in MFO (>0.08 g/min). The preliminary data reveals that a small dose of low-volume HIIT does not alter fat and CHO oxidation and there is little effect of ethnicity on the response to training.

Implementing permissive dehydration (DEH) during short-term heat acclimation (HA) may accelerate adaptations to the heat. However, HA with DEH may augment risk for acute kidney injury (AKI). This study investigated the effect of HA with permissive DEH on time-trial performance and markers of AKI. Fourteen moderately trained men (age and VO 2max = 25 ± 0.5 yr and 51.6 ± 1.8 mL . kg -1 . min -1 ) were randomly assigned to DEH or euhydration (EUH). Time-trial performance and VO 2max were assessed in a temperate environment before and after 7 d of HA. Heat acclimation consisted of 90 min of cycling in an environmental chamber (40 °C, 35% RH). Neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) were assessed pre- and post-exercise on day 1 and day 7 of HA. Following HA, VO 2max did not change in either group ( p = 0.099); however, time-trial performance significantly improved (3%, p < 0.01) with no difference between groups ( p = 0.485). Compared to pre-exercise, NGAL was not significantly different following day 1 and 7 of HA ( p = 0.113) with no difference between groups ( p = 0.667). There was a significant increase in KIM-1 following day 1 and 7 of HA ( p = 0.002) with no difference between groups ( p = 0.307). Heat acclimation paired with permissive DEH does not amplify improvements in VO 2max or time-trial performance in a temperate environment versus EUH and does not increase markers of AKI.

Background: The 'verification phase' has emerged as a supplementary procedure to traditional maximal oxygen uptake (VO2max) criteria to confirm that the highest possible VO2 has been attained during a cardiopulmonary exercise test (CPET)., Objective: To compare the highest VO2 responses observed in different verification phase procedures with their preceding CPET for confirmation that VO2max was likely attained., Methods: MEDLINE (accessed through PubMed), Web of Science, SPORTDiscus, and Cochrane (accessed through Wiley) were searched for relevant studies that involved apparently healthy adults, VO2max determination by indirect calorimetry, and a CPET on a cycle ergometer or treadmill that incorporated an appended verification phase. RevMan 5.3 software was used to analyze the pooled effect of the CPET and verification phase on the highest mean VO2. Meta-analysis effect size calculations incorporated random-effects assumptions due to the diversity of experimental protocols employed. I2 was calculated to determine the heterogeneity of VO2 responses, and a funnel plot was used to check the risk of bias, within the mean VO2 responses from the primary studies. Subgroup analyses were used to test the moderator effects of sex, cardiorespiratory fitness, exercise modality, CPET protocol, and verification phase protocol., Results: Eighty studies were included in the systematic review (total sample of 1,680 participants; 473 women; age 19-68 yr.; VO2max 3.3 ± 1.4 L/min or 46.9 ± 12.1 mL·kg-1·min-1). The highest mean VO2 values attained in the CPET and verification phase were similar in the 54 studies that were meta-analyzed (mean difference = 0.03 [95% CI = -0.01 to 0.06] L/min, P = 0.15). Furthermore, the difference between the CPET and verification phase was not affected by any of the potential moderators such as verification phase intensity (P = 0.11), type of recovery utilized (P = 0.36), VO2max verification criterion adoption (P = 0.29), same or alternate day verification procedure (P = 0.21), verification-phase duration (P = 0.35), or even according to sex, cardiorespiratory fitness level, exercise modality, and CPET protocol (P = 0.18 to P = 0.71). The funnel plot indicated that there was no significant publication bias., Conclusions: The verification phase seems a robust procedure to confirm that the highest possible VO2 has been attained during a ramp or continuous step-incremented CPET. However, given the high concordance between the highest mean VO2 achieved in the CPET and verification phase, findings from the current study would question its necessity in all testing circumstances., Prospero Registration Id: CRD42019123540., Competing Interests: The authors have declared that no competing interests exist.

Data obtained in primarily Caucasian (C) and African American adults show that ethnicity does not mediate responsiveness to exercise training. It is unknown if Hispanics (H), who face elevated health risks and are less active than C, exhibit a similar response to exercise training. This study compared cardiorespiratory and hemodynamic responses to high intensity interval training (HIIT) between C and H women. Twelve C and ten H women ages 19-35 yr who were non-obese and inactive completed nine sessions of HIIT over a 3 wk period. Maximal oxygen uptake (VO2max) was assessed twice at baseline during which thoracic impedance was used to evaluate heart rate (HR), stroke volume (SV) and cardiac output (CO). Habitual physical activity was assessed using accelerometry. Results showed a significant main effect of training for VO2max in C and H (F = 13.97, p = 0.001) and no group by training interaction (p = 0.65). There was a main effect of training for CO and SV in C and H (F = 7.57, p = 0.01; F = 7.16, p = 0.02), yet post hoc analyses revealed significant increases were only exhibited in C. There was a tendency for a group by training interaction for a-VO2diff (F = 1.32, p = 0.054), and a large effect size was seen in H (d = 1.02). Overall, data show no effect of ethnicity on changes in VO2max with low-volume HIIT, yet C and H may achieve this outcome differently. Longer studies in similar populations are needed to verify this result., Competing Interests: The authors have declared that no competing interests exist.

Spinal cord injury (SCI) leads to loss of sensory and motor function below the level of injury leading to paralysis and limitations to locomotion. Therefore, persons with SCI face various challenges in engaging in regular physical activity, which leads to a reduction in physical fitness, increases in body fat mass, and reduced physical and mental health status. Moderate intensity continuous training (MICT) is recommended to enhance physical fitness and overall health status in this population, but it is not always effective in promoting these benefits. High intensity interval training (HIIT) has been promoted as an alternative to MICT in individuals with SCI due to its documented efficacy in healthy able-bodied individuals as well as those with chronic disease. However, the body of knowledge concerning its application in this population is limited and mostly composed of studies with small and homogeneous samples. The aim of this review was to summarize the existing literature regarding the efficacy of HIIT on changes in health- and fitness-related outcomes in this population, denote potential adverse responses to HIIT, describe how participants perceive this modality of exercise training, and identify the overall feasibility of interval training in persons with SCI.

Incidence of obesity is increasing worldwide which is deleterious to health due to its association with increased risk of cardiovascular disease, diabetes, and some cancers. Completion of regular physical activity in individuals with obesity increases maximal oxygen uptake (VO 2 max). However, whether individuals with obesity can exhibit 'true' VO 2 max is unresolved. This study examined efficacy of verification testing (VER) to identify 'true' VO 2 max in 17 inactive women with obesity (age, body fat, and VO 2 max = 37 ± 10 yr, 48.7 ± 3.5 %, and 19.4 ± 3.0 mL/kg/min, respectively). They performed ramp exercise (RAMP) to volitional fatigue followed by VER at 105 percent peak power output (%PPO) at baseline and after 3 and 6 wk of high intensity interval training. Results showed no difference in ramp and verification-derived VO 2 max (1.99 ± 0.37 L/min vs. 1.98 ± 0.32 L/min, 2.00 ± 0.40 L/min vs. 2.04 ± 0.38 L/min, and 2.08 ± 0.34 L/min vs. 2.08 ± 0.32 L/min at 0, 3 and 6 wk of training), although in 40 % of VER tests, VO 2 max was greater than the RAMP value. Overall, verification testing may be adopted as an additional approach to confirm 'true' VO 2 max attainment in obese women as ramp exercise frequently underestimates VO 2 max in this population.

High intensity interval training is frequently implemented using the 4 × 4 protocol where four 4-min bouts are performed at heart rate (HR) between 85 and 95% HR max. This study identified the HR and power output response to the 4 × 4 protocol in 39 active men and women (age and VO 2 max = 26.0 ± 6.1 years and 37.0 ± 5.4 mL/kg/min). Initially, participants completed incremental cycling to assess VO 2 max, HR max, and peak power output (PPO). They subsequently completed the 4 × 4 protocol, during which HR and power output were monitored. Data showed that 12.9 ± 0.4 min of 16 min were spent between 85 and 95% HR max, with time spent significantly lower in interval 1 (2.7 ± 0.6 min) versus intervals 2-4 (3.4 ± 0.4 min, 3.4 ± 0.3 min, and 3.5 ± 0.3 min, d = 2.4-2.7). Power output was highest in interval 1 (75% PPO) and significantly declined in intervals 2-4 (63 to 54% PPO, d = 0.7-1.0). To enhance time spent between 85 and 95% HR max for persons with higher fitness, we recommend immediate allocation of supramaximal intensities in interval one.

Background In this Position Statement, the International Society of Sports Nutrition (ISSN) provides an objective and critical review of the literature pertinent to nutritional considerations for training and racing in single-stage ultra-marathon. Recommendations for Training. i) Ultra-marathon runners should aim to meet the caloric demands of training by following an individualized and periodized strategy, comprising a varied, food-first approach; ii) Athletes should plan and implement their nutrition strategy with sufficient time to permit adaptations that enhance fat oxidative capacity; iii) The evidence overwhelmingly supports the inclusion of a moderate-to-high carbohydrate diet (i.e., ~ 60% of energy intake, 5-8 g·kg - 1 ·d - 1 ) to mitigate the negative effects of chronic, training-induced glycogen depletion; iv) Limiting carbohydrate intake before selected low-intensity sessions, and/or moderating daily carbohydrate intake, may enhance mitochondrial function and fat oxidative capacity. Nevertheless, this approach may compromise performance during high-intensity efforts; v) Protein intakes of ~ 1.6 g·kg - 1 ·d - 1 are necessary to maintain lean mass and support recovery from training, but amounts up to 2.5 g.kg - 1 ·d - 1 may be warranted during demanding training when calorie requirements are greater; Recommendations for Racing. vi) To attenuate caloric deficits, runners should aim to consume 150-400 Kcal·h - 1 (carbohydrate, 30-50 g·h - 1 ; protein, 5-10 g·h - 1 ) from a variety of calorie-dense foods. Consideration must be given to food palatability, individual tolerance, and the increased preference for savory foods in longer races; vii) Fluid volumes of 450-750 mL·h - 1 (~ 150-250 mL every 20 min) are recommended during racing. To minimize the likelihood of hyponatraemia, electrolytes (mainly sodium) may be needed in concentrations greater than that provided by most commercial products (i.e., > 575 mg·L - 1 sodium). Fluid and electrolyte requirements will be elevated when running in hot and/or humid conditions; viii) Evidence supports progressive gut-training and/or low-FODMAP diets (fermentable oligosaccharide, disaccharide, monosaccharide and polyol) to alleviate symptoms of gastrointestinal distress during racing; ix) The evidence in support of ketogenic diets and/or ketone esters to improve ultra-marathon performance is lacking, with further research warranted; x) Evidence supports the strategic use of caffeine to sustain performance in the latter stages of racing, particularly when sleep deprivation may compromise athlete safety.

The present study examined the effect of meal intake on physiological and psychological indices during self-selected high intensity interval exercise (HIIE). Seventeen active men and women (age = 26.4 ± 5.8 yr) completed ramp cycle ergometry to determine maximal oxygen uptake and peak power output. On two subsequent days, they performed a session of self-selected HIIE consisting of ten 1 min bouts separated by 1 min recovery in the fed or fasted state, whose order was randomized. Meal intake consisted of a banana and a Zone™ bar containing 315 kcal, which were ingested 2 h pre-exercise, and the fasted state required no food for > 12 h pre-exercise. Participants ingested an identical meal the evening before each session. Heart rate (HR), oxygen uptake (VO 2 ), blood glucose and blood lactate concentration, rating of perceived exertion (RPE), affect, and enjoyment were measured during exercise. Irrespective of fed state, both bouts elicited intensities equal to 94% HRmax which represents HIIE. Our results showed no difference in HR (174.0 ± 13.5 vs. 173.2 ± 12.9 b/min in fed and fasted state, p = 0.17), VO 2 (2.43 ± 0.54 vs. 2.40 ± 0.52 L/min in fed and fasted state, p = 0.14), RPE (p = 0.44), affect (p = 0.79), or enjoyment (103 ± 14 vs. 101 ± 13, p = 0.77) between the fed and fasted state. Despite its high reliance on carbohydrate, performance and perception of low-volume HIIE are not altered by ingestion of a meal before exercise., Competing Interests: The authors declare that there is no conflict of interest in completion of this study., (Copyright © Biology of Sport 2019.)

Background: There is individual responsiveness to exercise training as not all individuals experience increases in maximal oxygen uptake (VO 2 max), which does not benefit health status considering the association between VO 2 max and mortality. Approximately 50% of the training response is genetic, with the other 50% accounted for by variations in dietary intake, sleep, recovery, and the metabolic stress of training. This study examined if the blood lactate (BLa) response to high intensity interval training (HIIT) as well as habitual dietary intake and sleep duration are associated with the resultant change in VO 2 max (ΔVO 2 max)., Methods: Fourteen individuals (age and VO 2 max = 27 ± 8 years and 38 ± 4 mL/kg/min, respectively) performed nine sessions of HIIT at 130% ventilatory threshold. BLa was measured during the first and last session of training. In addition, sleep duration and energy intake were assessed., Results: Data showed that VO 2 max increased with HIIT ( p = 0.007). No associations occurred between ΔVO 2 max and BLa (r = 0.44, p = 0.10), energy intake (r = 0.38, p = 0.18), or sleep duration (r = 0.14, p = 0.62). However, there was a significant association between training heart rate (HR) and ΔVO 2 max (r = 0.62, p = 0.02)., Conclusions: When HIIT is prescribed according to a metabolic threshold, energy intake, sleep status, and BLa do not predict ΔVO 2 max, yet the HR response to training is associated with the ΔVO 2 max.

Context/Objective: Maximal oxygen uptake (VO 2 max) is a widely used measure of cardiorespiratory fitness, aerobic function, and overall health risk. Although VO 2 max has been measured for almost 100 yr, no standardized criteria exist to verify VO 2 max attainment. Studies document that incidence of 'true' VO 2 max obtained from incremental exercise (INC) can be confirmed using a subsequent verification test (VER). In this study, we examined efficacy of VER in persons with spinal cord injury (SCI)., Design: Repeated measures, within-subjects study., Setting: University laboratory in San Diego, CA., Participants: Ten individuals (age and injury duration = 33.3 ± 10.5 yr and 6.8 ± 6.2 yr) with SCI and 10 able-bodied (AB) individuals (age = 24.1 ± 7.4 yr)., Interventions: Peak oxygen uptake (VO 2 peak) was determined during INC on an arm ergometer followed by VER at 105 percent of peak power output (% PPO)., Outcome Measures: Gas exchange data, heart rate (HR), and blood lactate concentration (BLa) were measured during exercise., Results: Across all participants, VO 2 peak was highly related between protocols (ICC = 0.98) and the mean difference was equal to 0.08 ± 0.11 L/min. Compared to INC, VO 2 peak from VER was not different in SCI (1.30 ± 0.45 L/min vs. 1.31 ± 0.43 L/min) but higher in AB (1.63 ± 0.40 L/min vs. 1.76 ± 0.40 L/min)., Conclusion: Data show similar VO 2 peak between incremental and verification tests in SCI, suggesting that VER confirms VO 2 max attainment. However, in AB participants completing arm ergometry, VER is essential to validate appearance of 'true' VO 2 peak.

Nutritional status has numerous effects on exercise metabolism and psychological responses. The effect of fed state on changes in affective valence; however, are unknown. Thus, the present study examined how fed state influenced self-selected exercise intensity, affective responses during exercise, and exercise enjoyment when exercise was completed following physical activity guidelines for public health. In a repeated-measures crossover design, 25 recreationally active men and women (age and BMI = 22.0 ± 2.0 yr and 24.3 ± 3.3 kg/m 2 ) performed a single 30 min session of treadmill exercise at a Rating of Perceived Exertion (RPE) equal to 13 on the Borg 6-20 scale following an overnight fast (FAST) or 30 minutes after a small meal (FED). Affective valence was recorded every 3 minutes during exercise. Heart rate and gas exchange data were measured continuously using a metabolic cart, blood glucose and blood lactate concentration were measured pre/post-exercise, and enjoyment was measured 15 minutes post-exercise. There was no effect of condition on affective valence, enjoyment, or self-selected intensity (all p>0.05 ). However, pre-exercise blood glucose was higher in FED pre-exercise, but higher post-exercise in FAST ( p <0.05). Blood lactate concentration was also higher in FAST ( p <0.05). Our results reveal minimal effects of a small, high-carbohydrate pre-exercise meal on in-task and post-task affective responses, exercise enjoyment, and self-selected intensity. These data suggest that an overnight fast does not alter affective valence or reduce enjoyment of continuous exercise.

Study Design: Repeated measures within-subjects crossover study., Objectives: High intensity interval exercise (HIIE) elicits higher oxygen consumption (VO 2 ) and heart rate (HR) versus moderate intensity continuous exercise (MICE) in men with spinal cord injury (SCI). No study has compared hemodynamic responses to HIIE versus MICE in SCI. In this study, we determined hemodynamic and cardiorespiratory responses to different bouts of arm cycling in men with SCI., Setting: Human Performance Laboratory, San Diego, CA., Methods: Five men (age and injury duration = 42.6 ± 16.1 yr and 9.9 ± 7.6 yr) with SCI participated in the study. VO 2 peak and peak power output were initially assessed. Subsequent visits included MICE, HIIE, sprint interval exercise (SIE), and a no-exercise control (CON). Energy expenditure was matched across modes and equal to 100 ± 10 kcal. During the bouts, cardiac output (CO), stroke volume (SV), HR, and VO 2 were measured., Results: Heart rate, SV, and CO increased in response to all exercise bouts and were higher during exercise versus CON. During HIIE and SIE, heart rate approached 90% of maximum, and stroke volume increased by 40% which was higher ( p  < 0.05) versus MICE and CON. In addition, exercise led to a two (MICE) to threefold increase in CO (HIIE and SIE) although it was not different from CON. VO 2 during SIE and HIIE was higher ( p  < 0.05) versus MICE., Conclusions: Similar to results in non-disabled populations, HIIE and SIE elicit near-maximal values of SV and CO., Competing Interests: Compliance with ethical standardsThe author declares that he has no conflict of interest.

Background: High intensity interval training (HIIT) is a robust and time-efficient approach to improve multiple health indices including maximal oxygen uptake (VO 2 max). Despite the intense nature of HIIT, data in untrained adults report greater enjoyment of HIIT versus continuous exercise (CEX). However, this has yet to be investigated in persons with spinal cord injury (SCI)., Objective: To examine differences in enjoyment in response to CEX and HIIT in persons with SCI., Design: Repeated measures, within-subjects design., Setting: University laboratory in San Diego, CA., Participants: Nine habitually active men and women (age = 33.3 ± 10.5 years) with chronic SCI., Intervention: Participants performed progressive arm ergometry to volitional exhaustion to determine VO 2 peak. During subsequent sessions, they completed CEX, sprint interval training (SIT), or HIIT in randomized order., Outcome Measures: Physical activity enjoyment (PACES), affect, rating of perceived exertion (RPE), VO 2 , and blood lactate concentration (BLa) were measured., Results: Despite a higher VO 2 , RPE, and BLa consequent with HIIT and SIT (P < 0.05), PACES was significantly higher (P = 0.03) in response to HIIT (107.4 ± 13.4) and SIT (103.7 ± 12.5) compared to CEX (81.6 ± 25.4). Fifty-five percent of participants preferred HIIT and 45% preferred SIT, with none identifying CEX as their preferred exercise mode., Conclusion: Compared to CEX, brief sessions of submaximal or supramaximal interval training elicit higher enjoyment despite higher metabolic strain. The long-term efficacy and feasibility of HIIT in this population should be explored considering that it is not viewed as more aversive than CEX.

Increases in maximal oxygen uptake (V˙O2max) frequently occur with high-intensity interval training (HIIT), yet the specific adaptation explaining this result remains elusive., Purpose: This study examined changes in V˙O2max and cardiac output (CO) in response to periodized HIIT., Methods: Thirty-nine active men and women (mean age and V˙O2max = 22.9 ± 5.4 yr and 39.6 ± 5.6 mL·kg·min) performed HIIT and 32 men and women (age and V˙O2max = 25.7 ± 4.5 yr and 40.7 ± 5.2 mL·kg·min) were nonexercising controls (CON). The first 10 sessions of HIIT required eight to ten 60 s bouts of cycling at 90%-110% percent peak power output interspersed with 75 s recovery, followed by randomization to one of three regimes (sprint interval training (SIT), high-volume interval training (HIITHI), or periodized interval training (PER) for the subsequent 10 sessions. Before, midway, and at the end of training, progressive cycling to exhaustion was completed during which V˙O2max and maximal CO were estimated., Results: Compared with CON, significant (P < 0.001) increases in V˙O2max in HIIT + SIT (39.8 ± 7.3 mL·kg·min to 43.6 ± 6.1 mL·kg·min), HIIT + HIITHI (41.1 ± 4.9 mL·kg·min to 44.6 ± 7.0 mL·kg·min), and HIIT + PER (39.5 ± 5.6 mL·kg·min to 44.1 ± 5.4 mL·kg·min) occurred which were mediated by significant increases in maximal CO (20.0 ± 3.1 L·min to 21.7 ± 3.2 L·min, P = 0.04). Maximal stroke volume was increased with HIIT (P = 0.04), although there was no change in maximal HR (P = 0.88) or arteriovenous O2 difference (P = 0.36). These CO data are accurate and represent the mean changes from pre- to post-HIIT across all three training groups., Conclusions: Increases in V˙O2max exhibited in response to different HIIT regimes are due to improvements in oxygen delivery.

Exercise adherence is affected by factors including perceptions of enjoyment, time availability, and intrinsic motivation. Approximately 50% of individuals withdraw from an exercise program within the first 6 mo of initiation, citing lack of time as a main influence. Time efficient exercise such as high intensity interval training (HIIT) may provide an alternative to moderate intensity continuous exercise (MICT) to elicit substantial health benefits. This study examined differences in enjoyment, affect, and perceived exertion between MICT and HIIT. Twelve recreationally active men and women (age = 29.5 ± 10.7 yr, VO2max = 41.4 ± 4.1 mL/kg/min, BMI = 23.1 ± 2.1 kg/m2) initially performed a VO2max test on a cycle ergometer to determine appropriate workloads for subsequent exercise bouts. Each subject returned for two additional exercise trials, performing either HIIT (eight 1 min bouts of cycling at 85% maximal workload (Wmax) with 1 min of active recovery between bouts) or MICT (20 min of cycling at 45% Wmax) in randomized order. During exercise, rating of perceived exertion (RPE), affect, and blood lactate concentration (BLa) were measured. Additionally, the Physical Activity Enjoyment Scale (PACES) was completed after exercise. Results showed higher enjoyment (p = 0.013) in response to HIIT (103.8 ± 9.4) versus MICT (84.2 ± 19.1). Eleven of 12 participants (92%) preferred HIIT to MICT. However, affect was lower (p<0.05) and HR, RPE, and BLa were higher (p<0.05) in HIIT versus MICT. Although HIIT is more physically demanding than MICT, individuals report greater enjoyment due to its time efficiency and constantly changing stimulus., Trial Registration: NCT:02981667., Competing Interests: The authors have declared that no competing interests exist.

Sprint interval training (SIT) elicits comparable long-term adaptations versus continuous exercise training (CEX) including increased maximal oxygen uptake (VO 2 max) and fat utilization. However, there is limited research examining acute hemodynamic responses to SIT. The aim of this study was to examine hemodynamic responses to low-volume SIT. Active men (n=6, VO 2 max = 39.8 ± 1.7 mL/kg/min) and women (n=7, VO 2 max = 37.3 ± 5.7 mL/kg/min) performed a ramp-based VO 2 max test (RAMP) to determine workload for the SIT session. Subjects returned within 1 wk and completed a session of SIT consisting of six 30-s bouts of "all-out" cycling at 130% maximal workload (Wmax) interspersed with 120 s of active recovery. Continuously during RAMP and exercise and recovery in SIT, VO 2 was obtained and thoracic impedance was used to estimate heart rate (HR), stroke volume (SV), and cardiac output (CO). Results revealed no significant differences in COmax (p = 0.12, 19.7 ± 2.4 L/min vs. 20.3 ± 1.8 L/min) but lower SVmax (p = 0.004, 110.4 ± 15.7 mL vs. 119.4 ± 15.5 mL) in RAMP versus SIT. HRmax from SIT (179.0 ± 11.8 b/min) was lower (p = 0.008) versus RAMP (184.4 ± 7.9 b/min). Peak VO 2 (L/min) was lower (p < 0.001) in response to SIT (2.43 ± 0.82 L/min) compared to RAMP (2.84 ± 0.82 L/min). Hemodynamic variables increased linearly across SIT bouts and remained significantly elevated in recovery. Sprint interval training consisting of 3 min of supramaximal exercise elicits similar CO yet lower VO 2 compared to RAMP.

Unlabelled: Techniques including direct Fick and Doppler echocardiography are frequently used to assess hemodynamic responses to exercise. Thoracic impedance has been shown to be a noninvasive alternative to these methods for assessing these responses during graded exercise to exhaustion, yet its feasibility during supramaximal bouts of exercise is relatively unknown. We used thoracic impedance to estimate stroke volume (SV) and cardiac output (CO) during the Wingate test (WAnT) and compared these values to those from graded exercise testing (GXT). Active men (n = 9) and women (n = 7) (mean age = 24.8 ± 5.9 yr) completed two Wingate tests and two graded exercise tests on a cycle ergometer. During exercise, heart rate (HR), SV, and CO were continuously estimated using thoracic impedance. Repeated measures analysis of variance was used to identify potential differences in hemodynamic responses across protocols., Results: Maximal SV (138.6 ± 37.4 mL vs. 135.6 ± 26.9 mL) and CO (24.5 ± 6.1 L·min(-1) vs. 23.7 ± 5.1 L·min(-1)) were similar (p > 0.05) between repeated Wingate tests. Mean maximal HR was higher (p < 0.01) for GXT (185 ± 7 b·min(-1)) versus WAnT (177 ± 11 b·min(-1)), and mean SV was higher in response to WAnT (137.1 ± 32.1 mL) versus GXT (123.0 ± 32.0 mL), leading to similar maximal cardiac output between WAnT and GXT (23.9 ± 5.6 L·min(-1) vs. 22.5 ± 6.0 L·min(-1)). Our data show no difference in hemodynamic responses in response to repeated administrations of the Wingate test. In addition, the Wingate test elicits similar cardiac output compared to progressive cycling to VO2max. Key pointsMeasurement of cardiac output (CO), the rate of oxygen transport delivered by the heart to skeletal muscle, is not widely-employed in Exercise Physiology due to the level of difficulty and invasiveness characteristic of most techniques used to measure this variable.Nevertheless, thoracic impedance has been shown to provide a noninvasive and simpler approach to continuously measure CO at rest and during exercise.Results show that measurements of CO are not different and highly reliable in response to repeated administrations of the Wingate test.Despite vastly different intensities and durations, maximal CO was similar between the Wingate test and graded exercise to VO2max.

Unlabelled: Spinal cord injury (SCI) induces dramatic changes in body composition including reductions in fat-free mass (FFM) and increases in fat mass (FM)., Objective: To examine changes in body composition in response to chronic activity-based therapy (ABT) in persons with SCI., Design: Longitudinal exercise intervention., Methods: Seventeen men and women with SCI (mean age=36.1±11.5 years) completed 6 months of supervised ABT consisting of load bearing, resistance training, locomotor training, and functional electrical stimulation. At baseline and after 3 and 6 months of ABT, body weight, body fat, and FFM were assessed using dual-energy X-ray absorptiometry, and fasting blood samples were obtained to assess changes in insulin-like growth factor-I (IGF-I), adiponectin, and myostatin., Results: Across all subjects, there was no change (P>0.05) in body weight, percent body fat, or FFM of the leg, arm, or trunk, whereas whole-body FFM declined (P=0.02, 50.4±8.4 to 49.2±7.4 kg). No changes (P=0.21-0.41) were demonstrated in IGF-I, adiponectin, or myostatin during the study., Conclusions: Chronic ABT focusing on the lower extremity does not slow muscle atrophy or alter body fat, body mass, or regional depots of FFM in persons with SCI. Further, it does not induce beneficial changes in adiponectin, myostatin, or IGF-I. Alternative exercise-based therapies are needed in SCI to reverse muscle atrophy and minimize the onset of related health risks.

To examine the effect ("cross-tolerance") of heat acclimation (HA) on exercise performance upon exposure to acute hypobaric hypoxia (4350 m). Eight male cyclists residing at 1600 m performed tests of maximal aerobic capacity (VO2max) at 1600 m and 4350 m, a 16 km time-trial at 4350 m, and a heat tolerance test at 1600 m before and after 10 d HA at 40°C, 20% RH. Resting blood samples were obtained pre-and post- HA to estimate changes in plasma volume (ΔPV). Successful HA was indicated by significantly lower exercise heart rate and rectal temperature on day 10 vs. day 1 of HA and during the heat tolerance tests. Heat acclimation caused a 1.9% ΔPV, however VO2max was not significantly different at 1600 m or 4350 m. Time-trial cycling performance improved 28 sec after HA (p = 0.07), suggesting a possible benefit for exercise performance at acute altitude and that cross-tolerance between these variables may exist in humans. These findings do not clearly support the use of HA to improve exercise capacity and performance upon acute hypobaric hypoxia, however they do indicate that HA is not detrimental to either exercise capacity or performance.

Spinal cord injury (SCI) results in a loss of motor and sensory function and is consequent with reductions in locomotion, leading to a relatively sedentary lifestyle which predisposes individuals to premature morbidity and mortality. Many exercise modalities have been employed to improve physical function and health status in SCI, yet they are typically expensive, require many trained clinicians to implement, and are thus relegated to specialized rehabilitation centers. These characteristics of traditional exercise-based rehabilitation in SCI make their application relatively impractical considering the time-intensive nature of these regimens and patients' poor access to exercise. A promising approach to improve physical function in persons with SCI is exposure to acute intermittent hypoxia (IH) in the form of a small amount of sessions of brief, repeated exposures to low oxygen gas mixtures interspersed with normoxic breathing. This review summarizes the clinical application of IH in humans with SCI, describes recommended dosing and potential side effects of IH, and reviews existing data concerning the efficacy of relatively brief exposures of IH to modify health and physical function. Potential mechanisms explaining the effects of IH are also discussed. Collectively, IH appears to be a safe, time-efficient, and robust approach to enhance physical function in chronic, incomplete SCI.

Alterations in maximal oxygen uptake (VO2max), heart rate (HR), and fat oxidation occur in response to chronic endurance training. However, many studies report frequent incidence of "non-responders" who do not adapt to continuous moderate exercise. Whether this is the case in response to high intensity interval training (HIT), which elicits similar adaptations as endurance training, is unknown. The aim of this retrospective study was to examine individual responses to two paradigms of interval training. In the first study (study 1), twenty active men and women (age and baseline VO2max=24.0 ± 4.6 yr and 42.8 ± 4.8 mL/kg/min) performed 6 d of sprint interval training (SIT) consisting of 4-6 Wingate tests per day, while in a separate study (study 2), 20 sedentary women (age and baseline VO2max=23.7 ± 6.2 yr and 30.0 ± 4.9 mL/kg/min) performed 12 wk of high-volume HIT at workloads ranging from 60-90% maximal workload. Individual changes in VO2max, HR, and fat oxidation were examined in each study, and multiple regression analysis was used to identify predictors of training adaptations to SIT and HIT. Data showed high frequency of increased VO2max (95%) and attenuated exercise HR (85%) in response to HIT, and low frequency of response for VO2max (65%) and exercise HR (55%) via SIT. Frequency of improved fat oxidation was similar (60-65%) across regimens. Only one participant across both interventions showed non-response for all variables. Baseline values of VO2max, exercise HR, respiratory exchange ratio, and body fat were significant predictors of adaptations to interval training. Frequency of positive responses to interval training seems to be greater in response to prolonged, higher volume interval training compared to similar durations of endurance training.

Background: Caffeine (CAF) has been shown to improve performance during early phase of repeated sprint exercise; however some studies show that CAF also increases the magnitude of physical stress represented by augmented blood lactate, glucose, and cortisol concentrations during latter phase of repeated sprint exercise. No studies have investigated the efficacy of combined carbohydrate (CHO) and CAF consumption during repeated sprint exercise (RSE) in female athletes. Thus, the purpose of this study was to investigate the effects of CAF with CHO supplementation on RSE and agility., Methods: Eleven female athletes completed four experimental trials performed 7 d apart in a double-blind, randomized, and counter-balanced crossover design. Treatments included CAF + PLA (placebo), CAF + CHO, PLA + CHO, and PLA + PLA. Participants ingested capsules containing 6 mg · kg(-1) of CAF or PLA 60-min prior to RSE, and 0.8 g · kg(-1) of CHO solution or PLA immediately before the RSE, which consisted of ten sets of 5 × 4-s sprints on the cycle ergometer with 20-s active recovery. The agility T-test (AT-test) was performed before and after the RSE. Blood samples were acquired to assess glucose, lactate, testosterone, and cortisol., Results: During Set 6 of RSE, peak power and mean power were significantly higher in PLA + CHO than those in CAF + PLA and PLA + PLA, respectively (p < .05). Total work was significantly increased by 4.8% and 5.9% with PLA + CHO than those of CAF + CHO and CAF + PLA during Set 3. PLA + CHO also increased total work more than CAF + PLA and PLA + PLA did during Set 6 (p < .05). No significant differences in AT-test performance either before or after the RSE were occurred among treatments (p > .05). Blood lactate and glucose concentrations were significantly higher under CAF + CHO, CAF + PLA, and PLA + CHO versus PLA + PLA (p < .05), but no differences in testosterone or cortisol levels were found (p > .05)., Conclusions: Findings indicate that CAF + PLA or CAF + CHO ingestion did not improve repeated sprint performance with short rest intervals or agility. However, CHO ingested immediately prior to exercise provided a small but significant benefit on RSE performance in female athletes.

Background: Activity-based therapy (ABT) focuses on regaining motor and sensory function below the level of the lesion in persons with a spinal cord injury (SCI). This is accomplished through repetitive training of specific motor tasks. Research has shown that ABT may increase neuroplasticity in the rat and human spinal cord., Objective: The primary aim of this study was to examine acute alterations in neuroplasticity-related proteins during ABT in persons with SCI., Methods: Volunteers were current participants in an ABT program and consisted of 12 men and 3 women (age, 31.8 ± 10.9 years) with chronic SCI (injury duration, 63.9 ± 54.4 months). A single 2-hour bout of ABT consisted of standing load bearing, body weight-supported treadmill training, whole body vibration, and functional electrical stimulation. Blood samples were obtained at baseline and immediately after completion of each modality to determine serum levels of brain-derived neurotrophic factor (BDNF), prolactin, and cortisol., Results: One-way analysis of variance (ANOVA) with repeated measures was used to examine differences in proteins over time. Results revealed baseline levels of BDNF (2.37 ± 1.41 ng/mL) that were lower than previous research has demonstrated in persons with SCI. No change in BDNF or cortisol was found, although prolactin was significantly reduced in response to ABT., Conclusion: Despite the length of the bout, acute changes in BDNF were not observed. Whether different intensities or modalities of ABT may promote acute increases in serum BDNF in individuals with SCI remains to be determined and further study is merited.

Introduction: The primary aim of the current study was to determine the effect of two doses of chronic high-intensity interval training (HIT) on changes in maximal fat oxidation (MFO) and body composition., Methods: Sedentary women (N = 23, age and V˙O2max = 24.2 ± 6.2 yr and 30.3 ± 5.2 mL·kg-1·min-1, respectively) completed either high (HI) (80%-90% maximal workload) or moderate (MOD) intensity (60%-80% maximal workload) HIT on a cycle ergometer 3 d·wk-1 for 12 wk consisting of 6-10 sixty-second bouts interspersed with active recovery. Seven women of similar age and fitness level served as controls. Every 3 wk, substrate oxidation was assessed during progressive exercise via indirect calorimetry to determine MFO and minimum fat oxidation, and body composition was assessed every 6 wk. Repeated-measures ANOVA was used to examine changes in substrate oxidation in response to training, with training group used as a between-subjects variable., Results: Results revealed improved MFO (P = 0.04, 19%-25%) and minimum fat oxidation (P = 0.001, 22-24 W) in response to HIT, yet the magnitude of improvement was similar (P > 0.05) between training paradigms. No change (P > 0.05) in body weight, percent body fat, or waist-hip circumference was revealed with training., Conclusion: These data suggest that 12 wk of either moderate or more strenuous interval training similarly enhance fat oxidation in sedentary women but do not alter body weight or body composition.

An emerging trend in sports nutrition is the consumption of energy drinks and "energy shots". Energy shots may prove to be a viable pre-competition supplement for runners. Six male runners (mean ± SD age and VO2max: 22.5 ± 1.8 years and 69.1 ± 5.7 mL·kg-1·min-1) completed three trials [placebo (PLA; 0 mg caffeine), Guayakí Yerba Maté Organic Energy Shot™ (YM; 140 mg caffeine), or Red Bull Energy Shot™ (RB; 80 mg caffeine)]. Treatments were ingested following a randomized, placebo-controlled crossover design. Participants ran a five kilometer time trial on a treadmill. No differences (p > 0.05) in performance were detected with RB (17.55 ± 1.01 min) or YM ingestion (17.86 ± 1.59 min) compared to placebo (17.44 ± 1.25 min). Overall, energy shot ingestion did not improve time-trial running performance in trained runners.

Energy drinks are frequently consumed by athletes prior to competition to improve performance. This study examined the effect of Red Bull™ on repeated sprint performance in women athletes. Fifteen collegiate soccer players participated, with mean age, height, and body mass equal to 19.5±1.1 year, 168.4±5.8 cm, and 63.4±6.1 kg, respectively. After performing a familiarization trial, subjects performed three sets of eight bouts of the modified t test after ingestion of 255 mL of placebo or Red Bull 1 h pre-exercise in a randomized, placebo-controlled crossover design. Throughout testing, sprint time, heart rate (HR), and rating of perceived exertion (RPE) were continuously obtained. Repeated measures analysis of variance was used to examine differences in variables between drink conditions. Across athletes, t test time ranged from 10.4 to 12.7 s. Mean sprint time was similar (p>0.05) between Red Bull (11.31±0.61 s) and placebo (11.35±0.61 s). HR and RPE increased (p<0.05) during the bouts, but there was no effect (p>0.05) of Red Bull on either variable versus placebo. Findings indicate that 255 mL of Red Bull containing 1.3 mg/kg of caffeine and 1 g of taurine does not alter repeated sprint performance, RPE, or HR in women athletes versus placebo. One serving of this energy drink provides no ergogenic benefit for women athletes engaging in sprint-based exercise.

Objective: To examine acute energy costs of multi-modal activity-based therapy (ABT) in men and women with spinal cord injury (SCI)., Study Design: Descriptive case series., Setting: An outpatient center in California., Participants: Seven men and women (age = 28.3 ± 11.6 years; duration of injury = 4.3 ± 2.5 years) with injury levels ranging from C5 to T8., Intervention: Activity-based therapy., Outcome Measures: Oxygen uptake (VO(2)), energy expenditure (kcal/minute), SCI Metabolic Equivalent of Task (MET) (1 MET = 2.7 ml/kg/minute)., Results: Oxygen uptake (VO(2)) during ABT ranged from 5.10 to 8.62 ml/kg/minute, with VO(2) consistently higher during modalities involving load bearing versus non-load bearing (P = 0.08). SCI MET values ranged from 1.89 to 3.24 and were significantly higher in subjects with mid-thoracic injury versus low-cervical injury (P = 0.01)., Conclusion: Data reveal that multi-modal ABT increases VO(2) in persons with SCI, but energy expenditure is relatively low. Strategies must be identified to optimize energy expenditure in the SCI to reduce health risks. Modalities involving load bearing seem to be superior to non-load-bearing activities. VO(2) was greater in response to load-bearing modalities than non-load-bearing modalities. It remains to be determined whether chronic ABT enhances cardiovascular fitness and reduces disease risks in this population.

Unlabelled: Studies provide equivocal results regarding the ergogenic properties of caffeine during high-intensity exercise., Purpose: The primary aim of this study was to examine the effects of two doses of caffeine on peak/average torque, power output, and total work of the knee extensors and flexors during two bouts of high-intensity exercise., Methods: Fifteen active men (mean age = 26.4 ± 3.9 yr and body mass = 82.7 ± 2.9 kg) initially completed a familiarization bout on the isokinetic dynamometer, followed by three subsequent trials separated by at least 48 h. Exercise consisted of two bouts of 40 repetitions of maximal knee extension and flexion of the dominant leg at a contraction velocity equal to 180°·s. Before each trial, subjects abstained from caffeine intake and intense exercise for 48 h. Treatment order (5 and 2 mg·kg of anhydrous caffeine or placebo) was randomly assigned to subjects using a single-blind, randomized, counterbalanced, crossover design. A 3 (treatment) × 2 (sets) ANOVA with repeated measures was used to detect differences in performance across treatment and time., Results: Compared with placebo, caffeine significantly (P < 0.05) enhanced peak knee flexion torque, knee extension/flexion total work, and knee extension/flexion power in bout 1 with no effect in bout 2. Only the 5-mg·kg dose of caffeine improved performance, with the magnitude of performance improvement ranging from 5% to 8%., Conclusions: Data suggest that a relatively high (5-mg·kg body weight) but not low (2-mg·kg body weight) caffeine dose is ergogenic for maximal knee extension/flexion exercise.

Background/objective: Regular exercise is required in persons with spinal cord injury (SCI) to reduce the deleterious effects of chronic paralysis. The primary aims of the study were to examine responses to passive and active exercise on a new rehabilitative device for persons with SCI and to examine reliability of these responses over 2 days of testing., Methods: Nine men and women with chronic SCI completed the study, 2 with a complete injury and 7 with an incomplete injury. The level of injury ranged from thoracic (T4-T6 and T10) to cervical (4 with C5-C6 and 3 with C6-C7 injuries). They completed 2 30-minute sessions of active lower-body and passive upper-body exercise, during which heart rate (HR), blood pressure (BP), gas exchange data, rating of perceived exertion (RPE), and oxygen-hemoglobin saturation were continuously assessed., Data Analysis: One-way ANOVA with repeated measures was used to examine differences in all variables over time., Results: Results demonstrated significant increases (P < 0.05) in HR, systolic BP, RPE, and oxygen uptake (V(O2)) from rest to exercise. No change (P > 0.05) in diastolic BP or oxygen-hemoglobin saturation was evident. Cronbach's alpha values for HR, systolic BP, and V(O2) recorded over both days of testing ranged from 0.79 to 0.97, indicating adequate consistency., Conclusions: Data demonstrated that exercise on this device significantly increases HR, V(O2), and systolic BP compared to rest. However, its efficacy for long-term rehabilitation, especially in regular exercisers with SCI, is unknown.