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Blood properties influence aerobic exercise performance. While vascular volumes and hemoglobin mass (Hb mass ) are elevated in trained individuals, evidence of sex differences in vascular volumes is equivocal due to inadequate matching of aerobic fitness between males and females. This cross-sectional study aimed to compare hematological values normalized to body mass (BM) and fat-free mass (FFM) between males ( n  = 45) and females ( n  = 34) matched for aerobic fitness (V̇O 2 max) normalized to FFM (mL∙kg FFM -1 ∙min - 1 ). Data included body composition measured by dual-energy X-ray absorptiometry (DXA), V̇O 2 max from an incremental test, and hematological values derived from a CO rebreathe test. Fat mass was unrelated to blood volume (BV; R 2  = 0.02, P  = 0.26) and Hb mass ( R 2  = 0.03, P  = 0.16), while FFM was the strongest predictor of both ( R 2  = 0.75 and R 2  = 0.83, respectively, P  < 0.001). Females exhibited higher FFM-normalized BV (+4%, P  < 0.05) and plasma volume (PV) (+14%, P  < 0.001) and lower red blood cell volume (RBCV) (-8%, P  < 0.001) and Hb mass (-8%, P  < 0.001) compared to males. Positive correlations between aerobic fitness and relative Hb mass and BV were observed in both sexes when normalized to BM and FFM (0.48 <  r  < 0.71; P  < 0.003). Stepwise multiple regression models, including FFM, V̇O 2 max, height, and [Hb], provided accurate predictions of Hb mass ( R 2  = 0.91) and BV ( R 2  = 0.85). Overall, sex differences persist in relative Hb mass , BV, PV, and RBCV after matching of aerobic fitness, though relative BV and PV were greater in females. These findings suggest sex-specific strategies in oxygen delivery and/or extraction, and they underscore the importance of carefully selecting normalization practices when assessing sex-based differences in hematological variables., Competing Interests: None of the authors report any conflicts of interest.

Purpose: The aims of the present study were to investigate blood lactate kinetics following high intensity exercise and identify the physiological determinants of 800 m running performance., Methods: Fourteen competitive 800 m runners performed two running tests. First, participants performed a multistage graded exercise test to determine physiological indicators related to endurance performance. Second, participants performed four to six 30-s high intensity running bouts to determine post-exercise blood lactate kinetics. Using a biexponential time function, lactate exchange ability (γ 1 ), lactate removal ability (γ 2 ), and the quantity of lactate accumulated (QLaA) were calculated from individual blood lactate recovery data., Results: 800 m running performance was significantly correlated with peak oxygen consumption (r = -0.794), γ 1 and γ 2 at 800 m race pace (r = -0.604 and -0.845, respectively), and QLaA at maximal running speed (r = -0.657). V ˙ O 2peak and γ 2 at 800 m race pace explained 83% of the variance in 800 m running performance., Conclusion: Our results indicate that (1) a high capacity to exchange and remove lactate, (2) a high capacity for short-term lactate accumulation and, (3) peak oxygen consumption, are critical elements of 800 m running performance. Accordingly, while lactate has primarily been utilized as a performance indicator for long-distance running, post-exercise lactate kinetics may also prove valuable as a performance determinant in middle-distance running., (© 2024. The Author(s).)

We sought to determine the effects of acute simulated altitude on the maximal lactate steady state (MLSS) and physiological responses to cycling at and 10 W above the MLSS-associated power output (PO) (MLSS p and MLSS p+10 , respectively). Eleven (4 females) participants (means [SD]; 28 [4] yr; V̇o 2max : 54.3 [6.9] mL·kg -1 ·min -1 ) acclimatized to ∼1,100 m performed 30-min constant PO trials in simulated altitudes of 0 m sea level (SL), 1,111 m mild altitude (MILD), and 2,222 m moderate altitude (MOD). MLSS p , defined as the highest PO with stable (<1 mM change) blood lactate concentration ([BLa]) between 10 and 30 min, was significantly lower in MOD (209 [54] W) compared with SL (230 [56] W; P < 0.001) and MILD (225 [58] W; P = 0.001), but MILD and SL were not different ( P = 0.12). V̇o 2 and V̇co 2 decreased at higher simulated altitudes due to lower POs ( P < 0.05), but other end-exercise physiological responses (e.g., [BLa], ventilation [V̇e], heart rate [HR]) were not different between conditions at MLSS p or MLSS p + 10 ( P > 0.05). At the same absolute intensity (MLSS p for MILD), [BLa], HR, and V̇ E and all perceptual variables were exacerbated in MOD compared with SL and MILD ( P < 0.05). Maximum voluntary contraction, voluntary activation, and potentiated twitch forces were exacerbated at MLSS p + 10 relative to MLSS p within conditions ( P < 0.05); however, condition did not affect performance fatiguability at the same relative or absolute intensity ( P > 0.05). As MLSS p decreased in hypoxia, adjustments in PO are needed to ensure the same relative intensity across altitudes, but common indices of exercise intensity may facilitate exercise prescription and monitoring in hypoxia. NEW & NOTEWORTHY This study demonstrates the power output and metabolic rate associated with the maximal lactate steady-state (MLSS) decline in response to simulated altitude; however, common indices of exercise intensity remained unchanged when cycling was performed at the work rate associated with MLSS at each simulated altitude. These results support previous studies that investigated the effects of hypoxia on alternative measures of the critical intensity of exercise and will inform exercise prescription/monitoring across altitudes.

Critical power (CP) represents an important threshold for exercise performance and fatiguability. We sought to determine the extent to which sex, hemoglobin mass (Hb mass ), and skeletal muscle characteristics influence CP. Before CP determination (i.e., 3-5 constant work rate trials to task failure), Hb mass and skeletal muscle oxidative capacity (τ) were measured and vastus lateralis (VL) muscle biopsy samples were collected from 12 females and 12 males matched for aerobic fitness relative to fat-free mass (FFM) [means (SD); V̇o 2max : 59.2 (7.7) vs. 59.5 (7.1) mL·kg·FFM -1 ·min -1 , respectively]. Males had a significantly greater CP than females in absolute units [225 (28) vs. 170 (43) W; P = 0.001] but not relative to body mass [3.0 (0.6) vs. 2.7 (0.6) W·kg·BM -1 ; P = 0.267] or FFM [3.6 (0.7) vs. 3.7 (0.8) W·kg·FFM -1 ; P = 0.622]. Males had significantly greater W ' ( P ≤ 0.030) and greater Hb mass ( P ≤ 0.016) than females, regardless of the normalization approach; however, there were no differences in mitochondrial protein content ( P = 0.375), τ ( P = 0.603), or MHC I proportionality ( P = 0.574) between males and females. Whether it was expressed in absolute or relative units, CP was positively correlated with Hb mass (0.444 ≤ r ≤ 0.695; P < 0.05), mitochondrial protein content (0.413 ≤ r ≤ 0.708; P < 0.05), and MHC I proportionality (0.506 ≤ r ≤ 0.585; P < 0.05), and negatively correlated with τ when expressed in relative units only (-0.588 ≤ r ≤ -0.527; P < 0.05). Overall, CP was independent of sex, but variability in CP was related to Hb mass and skeletal muscle characteristics. The extent to which manipulations in these physiological parameters influence CP warrants further investigation to better understand the factors underpinning CP. NEW & NOTEWORTHY In males and females matched for aerobic fitness [maximal oxygen uptake normalized to fat-free mass (FFM)], absolute critical power (CP) was greater in males, but relative CP (per kilogram body mass or FFM) was similar between sexes. CP correlated with hemoglobin mass, mitochondrial protein content, myosin heavy chain type I proportion, and skeletal muscle oxidative capacity. These findings demonstrate the importance of matching sexes for aerobic fitness, but further experiments are needed to determine causality.

Introduction: This study assessed the effect of individualized, domain-based exercise intensity prescription on changes in maximal oxygen uptake (V̇O 2max ) and submaximal thresholds., Methods: Eighty-four young healthy participants (42 females, 42 males) were randomly assigned to six age, sex, and V̇O 2max -matched groups (14 participants each). Groups performed continuous cycling in the 1) moderate (MOD), 2) lower heavy (HVY1), and 3) upper heavy-intensity (HVY2) domain; interval cycling in the form of 4) high-intensity interval training (HIIT) in the severe-intensity domain, or 5) sprint-interval training (SIT) in the extreme-intensity domain; or no exercise for 6) control (CON). All training groups, except SIT, were work-matched. Training participants completed three sessions per week for 6 wk with physiological evaluations performed at PRE, MID, and POST intervention., Results: Compared with the change in V̇O 2max (∆V̇O 2max ) in CON (0.1 ± 1.2 mL·kg -1 ·min -1 ), all training groups, except MOD (1.8 ± 2.7 mL·kg -1 ·min -1 ), demonstrated a significant increase ( P < 0.05). HIIT produced the highest increase (6.2 ± 2.8 mL·kg -1 ·min -1 ) followed by HVY2 (5.4 ± 2.3 mL·kg -1 ·min -1 ), SIT (4.7 ± 2.3 mL·kg -1 ·min -1 ), and HVY1 (3.3 ± 2.4 mL·kg -1 ·min -1 ), respectively. The ΔPO at the estimated lactate threshold ( θLT ) was similar across HVY1, HVY2, HIIT, and SIT, which were all greater than CON ( P < 0.05). The ΔV̇O 2 and ΔPO at θLT for MOD was not different from CON ( P > 0.05). HIIT produced the highest ΔPO at maximal metabolic steady state, which was greater than CON, MOD, and SIT ( P < 0.05)., Conclusions: This study demonstrated that i) exercise intensity is a key component determining changes in V̇O 2max and submaximal thresholds and ii) exercise intensity domain-based prescription allows for a homogenous metabolic stimulus across individuals., (Copyright © 2024 by the American College of Sports Medicine.)

There is renewed interest in the potential for interval (INT) training to increase skeletal muscle mitochondrial content including whether the response differs from continuous (CONT) training. Comparisons of INT and CONT exercise are impacted by the manner in which protocols are "matched", particularly with respect to exercise intensity, as well as inter-individual differences in training responses. We employed single-leg cycling to facilitate a within-participant design and test the hypothesis that short-term INT training would elicit a greater increase in mitochondrial content than work- and intensity-matched CONT training. Ten young healthy adults (five males and five females) completed 12 training sessions over 4 weeks with each leg. Legs were randomly assigned to complete either 30 min of CONT exercise at a challenging sustainable workload (~50% single-leg peak power output; Wpeak) or INT exercise that involved 10 × 3-min bouts at the same absolute workload. INT bouts were interspersed with 1 min of recovery at 10% Wpeak and each CONT session ended with 10 min at 10% Wpeak. Absolute and mean intensity, total training time, and volume were thus matched between legs but the pattern of exercise differed. Contrary to our hypothesis, biomarkers of mitochondrial content including citrate synthase maximal activity, mitochondrial protein content and subsarcolemmal mitochondrial volume increased after CONT (p < 0.05) but not INT training. Both training modes increased single-leg Wpeak (p < 0.01) and time to exhaustion at 70% of single-leg Wpeak (p < 0.01). In a work- and intensity-matched comparison, short-term CONT training increased skeletal muscle mitochondrial content whereas INT training did not., (© 2023 The Authors. Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.)

Purpose: A previously established Step-Ramp-Step (SRS) exercise protocol was able to accurately predict the work rate associated with the maximal metabolic steady state (MMSS) in cyclists. The purpose of this study was to determine whether a modified SRS protocol could predict the running speed and power associated with the MMSS., Methods: Fifteen (8 male; 7 female) runners (V̇O 2max 54.5 [6.5] mL·kg -1 ·min -1 ) were recruited for this investigation composed of four to five visits. In the first visit, runners performed a moderate intensity step (MOD), an incremental exercise test, and a heavy intensity step (HVY), on a motorized treadmill. This SRS protocol was used to predict the running speed and power associated with the MMSS (i.e., the SRS-MMSS), where running power was assessed by a wearable device (Stryd) attached to each runner's shoe. Subsequent visits were used to confirm the maximal lactate steady state (MLSS) as a proxy measure of the MMSS (i.e., the MLSS-MMSS) and to validate the SRS-MMSS speed and power estimates., Results: The estimated SRS-MMSS running speed (7.2 [0.6] mph) was significantly lower than confirmed running speed at MLSS-MMSS (7.5 [0.8] mph; bias = 3.6%, P = 0.005); however, the estimated SRS-MMSS running power (241 [35] W) was not different than the MLSS-MMSS confirmed running power (240 [37] W; bias = -0.6%; P = 0.435). V̇O 2 at SRS-MMSS (3.22 [0.49] L·min -1 ) was not different than respiratory compensation point (3.26 [0.58] L·min -1 ; P = 0.430). Similarly, V̇O 2 at MLSS-MMSS (3.30 [0.54] L·min -1 ) was not different than respiratory compensation point ( P = 0.438)., Conclusions: The SRS protocol allows MMSS, as measured by MLSS, to be accurately determined using running power (Stryd), but not speed, in a single laboratory visit., (Copyright © 2022 by the American College of Sports Medicine.)

Hypoxia negatively impacts aerobic exercise, but exercise testing in hypoxia has not been studied comprehensively. To determine the effects of simulated altitude on the gas exchange threshold (GET), respiratory compensation point (RCP), and maximal oxygen uptake (V̇O 2 max), 24 participants (mean [SD]; 26 [4] years; 171.6 [9.7] cm; 69.2 [11.9] kg) acclimatized to mild altitude (MILD; ∼1100 m) performed three cycling ramp-incremental exercise tests (with verification stages performed at 110% of peak power output (PPO)) in simulated altitudes of 0 m (sea level, SL), 1111 m (MILD), and 2222 m (moderate altitude, MOD), in a randomized order. There were significant effects of condition (i.e., fraction of inspired oxygen [F I O 2 ]) for GET ( p  = 0.001), RCP ( p  < 0.001), V̇O 2 max ( p  < 0.001), and PPO ( p  < 0.001). The V̇O 2 corresponding to GET and RCP (mL·kg -1 ·min -1 ) in MOD (24.1 [4.3]; 37.3 [5.1]) were significantly lower ( p  < 0.05) compared to SL (27.1 [4.4]; 41.8 [6.6]) and MILD (26.8 [5.7]; 40.7 [7.3]) but similar ( p  > 0.05) between SL and MILD. For each increase in simulated altitude, V̇O 2 max (SL: 51.3 [7.4]; MILD: 50.0 [7.6]; MOD: 47.3 [7.1] mL·kg -1 ·min -1 ) and PPO (SL: 332 [80]; MILD: 327 [78]; SL: 316 [76] W) decreased significantly ( p  < 0.05 for all comparisons). V̇O 2 max values from the verification stage were lower than those measured during the ramp-incremental test ( p  = 0.017). Overall, a mild simulated altitude had a significant effect on V̇O 2 max and PPO but not GET and RCP, MOD decreased all four variables, and the inclusion of a verification stage had little effect on the determination of V̇O 2 max in a group of young healthy adults regardless of the F I O 2 . Trial registration: Open Science Framework 10.17605/OSF.IO/ZTC9E.

Brief, intense interval training describes a style of exercise characterized by short bouts of strenuous effort interspersed with recovery periods. The method increases whole body maximal oxygen uptake (V̇o 2max ), but the underlying physiological basis is unclear. V̇o 2max represents the functional limit of the integrative oxygen cascade, which refers to the physiological steps involved in oxygen transport and utilization from atmospheric air to mitochondrial metabolism. There is insufficient evidence to definitively state which steps in the oxygen cascade are responsible for the improvement in V̇o 2max after brief, intense interval training. Studies typically focus on specific physiological variables that are often characterized as "central" or "peripheral" based in part on their location in the body. Recent work suggests that training for ≥6 wk improves V̇o 2max in part by increasing maximal cardiac output and expanding blood volume, responses that are expected to augment central oxygen delivery. Other responses to brief, intense interval training, including increased capillary and mitochondrial density, may contribute to increases in V̇o 2max via enhanced skeletal muscle oxygen extraction and/or increased muscle diffusing capacity. This is especially evident after relatively short-term training and despite no change in central oxygen delivery factors. Mechanistic investigations, particularly employing contemporary technologies, are needed to advance our understanding of the early time course of the V̇o 2max response to brief, intense interval training and the extent to which changes in specific oxygen cascade processes compare with traditional endurance training.

Near-infrared spectroscopy (NIRS) provides a simple and reliable measure of skeletal muscle oxidative capacity; however, its relationship to aerobic fitness and sex are unclear. We hypothesized that NIRS-derived oxidative capacity in the vastus lateralis (VL) and medial gastrocnemius (MG) would be correlated with indices of aerobic fitness and independent of sex. Twenty-six participants (13 males, 13 females) performed ramp- and step-incremental tests to volitional exhaustion on separate days to establish maximal oxygen uptake (V̇o 2max ), peak power output (PPO), lactate threshold (LT), gas exchange threshold (GET), respiratory compensation point (RCP), and maximal fat oxidation (MFO). Data were normalized to lean body mass to account for sex-based differences in body composition. Exercise tests were preceded by duplicate measurements of NIRS-derived oxidative capacity on the VL and MG muscles (i.e., repeated arterial occlusions following a brief set of muscle contractions). Skeletal muscle oxidative capacity for the VL (means ± SD: 21.9 ± 4.6 s) and MG (22.5 ± 6.1 s) were similar but unrelated ( r 2  = 0.03, P = 0.39). Skeletal muscle oxidative capacity for the VL, but not the MG ( P > 0.05 for all variables), was significantly correlated with V̇o 2max ( r 2  = 0.24; P = 0.01), PPO ( r 2  = 0.23; P = 0.01), LT ( r 2  = 0.23; P = 0.01), GET ( r 2  = 0.23; P = 0.01), and RCP ( r 2  = 0.27; P = 0.006). MFO was not correlated with VL or MG skeletal muscle oxidative capacity ( P > 0.05). Females (54.9 ± 4.5 mL·kg LBM -1 ·min -1 ) and males (56.0 ± 6.2 mL·kg LBM -1 ·min -1 ), matched for V̇o 2max ( P = 0.62), had similar NIRS-derived oxidative capacities for VL (20.7 ± 4.4 vs. 23.2 ± 4.6 s; P = 0.18) and MG (24.4 ± 6.8 vs. 20.5 ± 4.8 s; P = 0.10). Overall, NIRS-derived skeletal muscle oxidative capacity in VL is indicative of aerobic fitness and independent of sex in humans. NEW & NOTEWORTHY Near-infrared spectroscopy (NIRS) can be used to measure skeletal muscle oxidative capacity. Here, we demonstrated that NIRS-derived skeletal muscle oxidative capacity of the vastus lateralis was independent of sex, reliable across and within days, and correlated with maximal and submaximal indices of aerobic fitness, including maximal oxygen uptake, lactate threshold, and respiratory compensation point. These findings highlight the utility of NIRS for investigating skeletal muscle oxidative capacity in females and males.

Chan, M, MacInnis, MJ, Koch, S, MacLeod, KE, Lohse, KR, Gallo, ME, Sheel, AW, and Koehle, MS. Cardiopulmonary demand of 16-kg kettlebell snatches in simulated Girevoy Sport. J Strength Cond Res 34(6): 1625-1633, 2020-Kettlebell lifting has become popular both as a strength and conditioning training tool and as a sport in and of itself: Girevoy Sport (GS). Although several kettlebell multimovement protocols have been analyzed, little research has attempted to quantify the aerobic stimulus of the individual events in GS, which could better inform kettlebell-related exercise prescription. The purpose of this study was to quantify the cardiopulmonary demand, assessed primarily by oxygen consumption (V[Combining Dot Above]O2) and heart rate (HR), of continuous high-intensity kettlebell snatches-under conditions relevant to GS-and to compare this demand with a more traditional graded rowing ergometer maximal exercise test. Ten male participants (age = 28.4 ± 4.6 years, height = 185 ± 7 cm, body mass = 95.1 ± 14.9 kg) completed (a) a graded-exercise test on a rowing ergometer to determine maximal oxygen consumption (V[Combining Dot Above]O2max) and maximal heart rate (HRmax) and (b) a graded-exercise test consisting of continuous 16-kg kettlebell snatches to determine peak oxygen consumption (V[Combining Dot Above]O2peak) and peak heart rate (HRpeak) during a simulated GS snatch event. Subjects achieved a V[Combining Dot Above]O2max of 45.7 ± 6.7 ml·kg·min and HRmax of 177 ± 8.3 b·min on the rowing ergometer. The kettlebell snatch test produced a V[Combining Dot Above]O2peak of 37.6 ± 4.4 ml·kg·min (82.7 ± 6.5% V[Combining Dot Above]O2max) and a HRpeak of 174 ± 10 b·min (98.0 ± 3.4% HRmax). These findings suggest that GS kettlebell snatches with 16-kg can provide an adequate aerobic stimulus to improve cardiorespiratory fitness in those with a V[Combining Dot Above]O2max of ≤51 ml·kg·min, according to aerobic training recommendations from the American College of Sports Medicine.

It is typically assumed that in the context of double-leg cycling, dominant (DOM LEG ) and nondominant legs (NDOM LEG ) have similar aerobic capacity and both contribute equally to the whole body physiological responses. However, there is a paucity of studies that have systematically investigated maximal and submaximal aerobic performance and characterized the profiles of local muscle deoxygenation in relation to leg dominance. Using counterweighted single-leg cycling, this study explored whether peak O 2 consumption (V̇o 2peak ), maximal lactate steady-state (MLSS p ), and profiles of local deoxygenation [HHb] would be different in the DOM LEG compared with the NDOM LEG . Twelve participants performed a series of double-leg and counterweighted single-leg DOM LEG and NDOM LEG ramp-exercise tests and 30-min constant-load trials. V̇o 2peak was greater in the DOM LEG than in the NDOM LEG (2.87 ± 0.42 vs. 2.70 ± 0.39 L/min, P < 0.05). The difference in V̇o 2peak persisted even after accounting for lean mass ( P < 0.05). Similarly, MLSS p was greater in the DOM LEG than in the NDOM LEG (118 ± 31 vs. 109 ± 31 W; P < 0.05). Furthermore, the amplitude of the [HHb] signal during ramp exercise was larger in the DOM LEG than in the NDOM LEG during both double-leg (26.0 ± 8.4 vs. 20.2 ± 8.8 µM, P < 0.05) and counterweighted single-leg cycling (18.5 ± 7.9 vs. 14.9 ± 7.5 µM, P < 0.05). Additionally, the amplitudes of the [HHb] signal were highly to moderately correlated with the mode-specific V̇o 2peak values (ranging from 0.91 to 0.54). These findings showed in a group of young men that maximal and submaximal aerobic capacities were greater in the DOM LEG than in the NDOM LEG and that superior peripheral adaptations of the DOM LEG may underpin these differences. NEW & NOTEWORTHY It is typically assumed that the dominant and nondominant legs contribute equally to the whole physiological responses. In this study, we found that the dominant leg achieved greater peak O 2 uptake values, sustained greater power output while preserving whole body metabolic stability, and showed larger amplitudes of deoxygenation responses. These findings highlight heterogeneous aerobic capacities of the lower limbs, which have important implications when whole body physiological responses are examined.

Aims: We investigated whether sprint interval training (SIT) was a time-efficient exercise strategy to improve insulin sensitivity and other indices of cardiometabolic health to the same extent as traditional moderate-intensity continuous training (MICT). SIT involved 1 minute of intense exercise within a 10-minute time commitment, whereas MICT involved 50 minutes of continuous exercise per session., Methods: Sedentary men (27±8y; BMI = 26±6kg/m2) performed three weekly sessions of SIT (n = 9) or MICT (n = 10) for 12 weeks or served as non-training controls (n = 6). SIT involved 3x20-second 'all-out' cycle sprints (~500W) interspersed with 2 minutes of cycling at 50W, whereas MICT involved 45 minutes of continuous cycling at ~70% maximal heart rate (~110W). Both protocols involved a 2-minute warm-up and 3-minute cool-down at 50W., Results: Peak oxygen uptake increased after training by 19% in both groups (SIT: 32±7 to 38±8; MICT: 34±6 to 40±8ml/kg/min; p<0.001 for both). Insulin sensitivity index (CSI), determined by intravenous glucose tolerance tests performed before and 72 hours after training, increased similarly after SIT (4.9±2.5 to 7.5±4.7, p = 0.002) and MICT (5.0±3.3 to 6.7±5.0 x 10-4 min-1 [μU/mL]-1, p = 0.013) (p<0.05). Skeletal muscle mitochondrial content also increased similarly after SIT and MICT, as primarily reflected by the maximal activity of citrate synthase (CS; P<0.001). The corresponding changes in the control group were small for VO2peak (p = 0.99), CSI (p = 0.63) and CS (p = 0.97)., Conclusions: Twelve weeks of brief intense interval exercise improved indices of cardiometabolic health to the same extent as traditional endurance training in sedentary men, despite a five-fold lower exercise volume and time commitment.

Introduction: Altitude and an individual's V˙O2max contribute to a decrease in V˙O2max under hypoxic conditions. The purpose of this study was to update previous reviews with recent research in order to quantitatively determine the individual and interacting effects of altitude and baseline V˙O2max on V˙O2max upon acute exposure to hypoxia while developing a statistical model to predict an individual's V˙O2max under hypoxic conditions., Methods: Meta-regression was conducted on 105 independent groups of participants (n = 958 subjects from 80 different studies). A series of regression models was tested. The final model included altitude, baseline V˙O2max, Alt2, baseline V˙O2max2, and the interaction of altitude with baseline V˙O2max., Results: A curvilinear model provided the best fit for metadata, explaining almost 80% of the variance in the null model. Nonlinear effects of Alt2 (β = -0.078; 95% confidence interval, -0.15 to -0.002) and baseline V˙O2max2 (β = -0.003; 95% confidence interval, -0.004 to -0.001) showed that V˙O2max decreases as altitude increases and that the decrease is greater in individuals with higher aerobic capacities. The interaction of these effects (β = -0.028; 95% confidence interval, -0.042 to -0.015) also showed that the effects of altitude were augmented with higher baseline aerobic capacities. Furthermore, the predictions of the model were fairly accurate in predicting individual decreases in V˙O2max (root-mean-squared error, 3.9 mL·kg(-1)·min(-1))., Conclusions: These data provide a robust quantitative framework for the curvilinear and interacting effects of altitude and baseline V˙O2max in determining an individual's effective V˙O2max at altitude. This predictive model is useful for a priori power calculations, design of future experimental studies, and prediction of aerobic capacity declines in applied settings.

Beetroot juice (BR) has been shown to lower the oxygen cost of exercise in normoxia and may have similar effects in hypoxia. We investigated the effect of BR on steady-state exercise economy and 10-km time trial (TT) performance in normoxia and moderate hypoxia (simulated altitude: ~2500 m). Eleven trained male cyclists (VO 2peak ≥ 60 ml · kg(-1) · min(-1)) completed four exercise trials. Two hours before exercise, subjects consumed 70 mL BR (~6 mmol nitrate) or placebo (nitrate-depleted BR) in a randomized, double-blind manner. Subjects then completed a 15-min self-selected cycling warm-up, a 15-min steady-state exercise bout at 50% maximum power output, and a 10-km time trial (TT) in either normoxia or hypoxia. Environmental conditions were randomized and single-blind. BR supplementation increased plasma nitrate concentration and fraction of exhaled nitric oxide relative to PL (p < .05 for both comparisons). Economy at 50% power output was similar in hypoxic and normoxic conditions (p > .05), but mean power output was greater in the normoxic TT relative to the hypoxic TT (p < .05). BR did not affect economy, steady-state SpO2, mean power output, or 10-km TT completion time relative to placebo in either normoxia or hypoxia (p > .05 in all comparisons). In conclusion, BR did not lower the oxygen cost of steady-state exercise or improve exercise performance in normoxia or hypoxia in a small sample of well-trained male cyclists.

Classical training theory postulates that performance fatigability following a training session should be proportional to the total work done (TWD); however, this notion has been questioned. This study investigated indices of performance and perceived fatigability after primary sessions of high-intensity interval training (HIIT) and constant work rate (CWR) cycling, each followed by a cycling time-to-task failure (TTF) bout. On separate days, 16 participants completed an incremental cycling test, and, in a randomized order, (i) a TTF trial at 80% of peak power output (PPO), (ii) an HIIT session, and (iii) a CWR session, both of which were immediately followed by a TTF trial at 80% PPO. Central and peripheral aspects of performance fatigability were measured using interpolated twitch technique, and perceptual measures were assessed prior to and following the HIIT and CWR trials, and again following the TTF trial. Despite TWD being less following HIIT (P = 0.029), subsequent TTF trial was an average of 125 s shorter following HIIT versus CWR (P < 0.001), and this was accompanied by greater impairments in voluntary and electrically evoked forces (P < 0.001), as well as exacerbated perceptual measures (P < 0.001); however, there were no differences in any fatigue measure following the TTF trial (P ≥ 0.149). There were strong correlations between the decline in TTF and indices of peripheral (r = 0.70) and perceived fatigability (r ≥ 0.80) measured at the end of HIIT and CWR. These results underscore the dissociation between TWD and performance fatigability and highlight the importance of peripheral components of fatigability in limiting endurance performance during high-intensity cycling exercise. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that presleep consumption of α-lactalbumin (LA), a fraction of whey with a high abundance of tryptophan, would improve indices of sleep quality and time-trial (TT) performance in cyclists relative to an isonitrogenous collagen peptide (CP) supplement lacking tryptophan. Using randomized, double-blind, crossover designs, cyclists consumed either 40 g of LA or CP 2 hr prior to sleep. In Study 1, six elite male endurance track cyclists (age 23 ± 6 years, ...O2peak 70.2 ± 4.4 ml⋅kg-1⋅min-1) consumed a supplement for three consecutive evenings before each 4-km TT on a velodrome track, whereas in Study 2, six well-trained cyclists (one female; age 24 ± 5 years, ...O2peak 66.9 ± 8.3 ml⋅kg-1⋅min-1) consumed a supplement the evening before each 4-km TT on a stationary cycle ergometer. Indices of sleep quality were assessed with wrist-based actigraphy. There were no differences between the CP and LA supplements in terms of total time in bed, total sleep time, or sleep efficiency in Study 1 (LA: 568 ± 71 min, 503 ± 67 min, 88.3% ± 3.4%; CP: 546 ± 30 min, 479 ± 35 min, 87.8% ± 3.1%; p = .41, p = .32, p = .74, respectively) or Study 2 (LA: 519 ± 90 min, 450 ± 78 min, 87.2% ± 7.6%; CP: 536 ± 62 min, 467 ± 57 min, 87.3% ± 6.4%; p = .43, p = .44, p = .97, respectively). Similarly, time to complete the 4-km TT was unaffected by supplementation in Study 1 (LA: 274.9 ± 7.6 s; CP: 275.5 ± 7.2 s; p = .62) and Study 2 (LA: 344.3 ± 22.3 s; CP: 343.3 ± 23.0 s; p = .50). Thus, relative to CP, consuming LA 2 hr prior to sleep over 1-3 days did not improve actigraphy-based indices of sleep quality or 4-km TT performance in cyclists. [ABSTRACT FROM AUTHOR]

Purpose: The mean power output (MPO) from a 60-min time trial (TT)—also known as functional threshold power, or FTP—is a standard measure of cycling performance; however, shorter performance tests are desirable to reduce the burden of performance testing. The authors sought to determine the reliability of 4- and 20-min TTs and the extent to which these short TTs were associated with 60-min MPO. Methods: Trained male cyclists (n = 8; age = 25 [5] y; V O 2 max = 71 [5] mL/kg/min) performed two 4-min TTs, two 20-min TTs, and one 60-min TT. Critical power (CP) was estimated from 4- and 20-min TTs. The typical error of the mean (TEM) and intraclass correlation coefficient (ICC) were calculated to assess reliability, and R2 values were calculated to assess relationships with 60-min MPO. Results: Pairs of 4-min TTs (mean: 417 [SD: 45] W vs 412 [49] W, P =.25; TEM = 8.1 W; ICC =.98), 20-min TTs (342 [36] W vs 344 [33] W, P =.41; TEM = 4.6 W; ICC =.99), and CP estimates (323 [35] W vs 328 [32] W, P =.25; TEM = 6.5; ICC =.98) were reliable. The 4-min MPO (R2 =.95), 20-min MPO (R2 =.92), estimated CP (R2 =.82), and combination of the 4- and 20-min MPO (adjusted R2 =.98) were strongly associated with the 60-min MPO (309 [26] W). Conclusion: The 4- and 20-min TTs appear useful for assessing performance in trained, if not elite, cyclists. [ABSTRACT FROM AUTHOR]

Sprint interval training (SIT), repeated bouts of high-intensity exercise, improves skeletal muscle oxidative capacity and exercise performance. β-alanine (β-ALA) supplementation has been shown to enhance exercise performance, which led us to hypothesize that chronic β-ALA supplementation would augment work capacity during SIT and augment training-induced adaptations in skeletal muscle and performance. Twenty-four active but untrained men (23 ± 2 yr; VO2peak =50 ± 6 mL⋅kg-1min-1) ingested 3.2 g/day of β-ALA or a placebo (PLA) for a total of 10 weeks (n = 12 per group). Following 4 weeks of baseline supplementation, participants completed a 6-week SIT intervention. Each of 3 weekly sessions consisted of 4-6 Wingate tests, i.e., 30-s bouts of maximal cycling, interspersed with 4 min of recovery. Before and after the 6-week SIT program, participants completed a 250-kJ time trial and a repeated sprint test. Biopsies (v. lateralis) revealed that skeletal muscle carnosine content increased by 33% and 52%, respectively, after 4 and 10 weeks of β-ALA supplementation, but was unchanged in PLA. Total work performed during each training session was similar across treatments. SIT increased markers of mitochondrial content, including cytochome c oxidase (40%) and β-hydroxyacyl-CoA dehydrogenase maximal activities (19%), as well as VO2peak (9%), repeated-sprint capacity (5%), and 250-kJ time trial performance (13%), but there were no differences between treatments for any measure (p < .01, main effects for time; p > .05, interaction effects). The training stimulus may have overwhelmed any potential influence of β-ALA, or the supplementation protocol was insufficient to alter the variables to a detectable extent. [ABSTRACT FROM AUTHOR]

Commencing some training sessions with reduced carbohydrate (CHO) availability has been shown to enhance skeletal muscle adaptations, but the effect on exercise performance is less clear. We examined whether restricting CHO intake between twice daily sessions of high-intensity interval training (HIIT) augments improvements in exercise performance and mitochondrial content. Eighteen active but not highly trained subjects (peak oxygen uptake [VO2peak] = 44 ± 9 ml/kg/min), matched for age, sex, and fitness, were randomly allocated to two groups. On each of 6 days over 2 weeks, subjects completed two training sessions, each consisting of 5 x 4-min cycling intervals (60% of peak power), interspersed by 2 min of recovery. Subjects ingested either 195 g of CHO (HI-HI group: ~2.3 g/kg) or 17 g of CHO (HI-LO group: ~0.3 g/kg) during the 3-hr period between sessions. The training-induced improvement in 250-kJ time trial performance was greater (p = .02) in the HI-LO group (211 ± 66 W to 244 ± 75 W) compared with the HI-HI group (203 ± 53 W to 219 ± 60 W); however, the increases in mitochondrial content was similar between groups, as reflected by similar increases in citrate synthase maximal activity, citrate synthase protein content and cytochrome c oxidase subunit IV protein content (p > .05 for interaction terms). This is the first study to show that a short-term "train low, compete high" intervention can improve whole-body exercise capacity. Further research is needed to determine whether this type of manipulation can also enhance performance in highly-trained subjects. [ABSTRACT FROM AUTHOR]

To examine whether the menstrual or monophasic oral contraceptive cycle phases affect submaximal (oxygen uptake (V˙O2) kinetics, maximal lactate steady‐state (MLSS)) and maximal (V˙O2max, time‐to‐exhaustion (TTE)) responses to exercise in healthy, active women. During the mid‐follicular or inactive‐pill phase and the mid‐luteal or active‐pill phase of the respective menstrual or oral contraceptive cycle, 15 non‐oral contraceptive users (mean and standard deviation (SD) (±): 27 ± 6 years; 171 ± 5 cm; 65 ± 7 kg) and 15 monophasic oral contraceptive users (24 ± 4 years; 169 ± 10 cm; 68 ± 10 kg) performed: one V˙O2 kinetics test; one ramp‐incremental test; two to three 30‐minute constant‐load cycling trials to determine the power output corresponding to MLSS (MLSSp), followed by a TTE trial. The phase of the menstrual or oral contraceptive cycle did not affect the time constant of the V˙O2 kinetics response (τV˙O2) (mid‐follicular, 20 ± 5 seconds and mid‐luteal, 18 ± 3 seconds; inactive‐pill, 22 ± 8 seconds and active‐pill, 23 ± 6 seconds), V˙O2max (mid‐follicular, 3.06 ± 0.32 L min−1 and mid‐luteal, 3.00 ± 0.33 L min−1; inactive‐pill, 2.87 ± 0.39 L min−1 and active‐pill, 2.87 ± 0.45 L min−1), MLSSp (mid‐follicular, 181 ± 30 W and mid‐luteal, 182 ± 29 W; inactive‐pill, 155 ± 26 W and active‐pill, 155 ± 27 W), and TTE (mid‐follicular, 147 ± 42 seconds and mid‐luteal, 128 ± 54 seconds; inactive‐pill, 146 ± 70 seconds and active‐pill, 139 ± 77 seconds) (P >.05). The rate of perceived exertion (RPE) at minute 30 of the MLSSp trials was greater in the mid‐follicular phase (6.2 ± 1.5) compared with the mid‐luteal phase (5.3 ± 1.4) for non‐oral contraceptive users (P =.022). The hormonal fluctuations between the menstrual and oral contraceptive cycle phases had no detectable effects on submaximal and maximal exercise performance, even when RPE differed. [ABSTRACT FROM AUTHOR]

Purpose: We compared physiological responses to incremental, interval, and continuous counterweighted single-leg and double-leg cycling at the same relative intensities. The primary hypothesis was that the counterweight method would elicit greater normalized power (i.e., power/active leg), greater electromyography (EMG) responses, and lower cardiorespiratory demand.Methods: Graded-exercise tests performed by 12 men (age: 21 ± 2 years; BMI: 24 ± 3 kg/m2) initially established that peak oxygen uptake ([Formula: see text]; 76 ± 8.4%), expired ventilation ([Formula: see text]; 71 ± 6.8%), carbon dioxide production ([Formula: see text]; 71 ± 6.8%), heart rate (HRpeak; 91 ± 5.3%), and power output (PPO; 56 ± 3.6%) were lower during single-leg compared to double-leg cycling (main effect of mode; p < 0.05). On separate days, participants performed four experimental trials, which involved 30-min bouts of either continuous (50% PPO) or interval exercise [4 × (5-min 65% PPO + 2.5 min 20% PPO)] in a single- or double-leg manner.Results: Double-leg interval and continuous cycling were performed at greater absolute power outputs but lower normalized power outputs compared to single-leg cycling (p < 0.001). The average EMG responses from the vastus lateralis and vastus medialis were similar across modes (p > 0.05), but semitendinosus was activated to a greater extent for single-leg cycling (p = 0.005). Single-leg interval and continuous cycling elicited lower mean [Formula: see text], [Formula: see text], [Formula: see text], HR and ratings of perceived exertion compared to double-leg cycling (p < 0.05).Conclusions: Counterweighted single-leg cycling elicits lower cardiorespiratory and perceptual responses than double-leg cycling at greater normalized power outputs. [ABSTRACT FROM AUTHOR]

Objective: To determine the effects of single nucleotide polymorphisms (SNPs) in the adrenergic β2-receptor gene (ADRB2, rs1042713, and rs 1042714) and epithelial Na+ channel gene (SCNN1A, rs2228576) on cycling performance after the inhalation of salbutamol. Design: Randomized double-blind, mixed-model repeated Setting: University Research Setting. Participants: Sixty-nine trained (maximal oxygen consumption: 62.3 ± 7.6 mL⋅kg-1⋅min-1) male and female cyclists, aged 19 to 40 years. Interventions: Participants performed two 10-km time trials 60 minutes after the inhalation of 400 mg of salbutamol or placebo. Subjects were genotyped for the three SNPs (rs1042713: AA 8, AG 30 GG 31; rs1042714: CC 19, CG 35, GG 15; rs2228576: GG: 31 GA: 34 AA: 4). Main Outcome Measures: Forced expiratory volume in 1 second (FEV1) was assessed immediately before and 30 minutes after inhalation. Performance was measured by mean power output maintained over the duration of the time trial. Results: There was a significant increase in FEV1 after the inhalation of salbutamol [mean (SD) = 5.68% (4.7)] compared with placebo [0.84% (2.8); P < 0.001]; however, this did not lead to an improvement in 10-km cycling time trial performance. Neither the bronchodilatory response nor the time trial performance after salbutamol was affected by genotype at any of the 3 SNPs. Conclusions: In cyclists, FEV1 was significantly improved after salbutamol administration regardless of genotypic variation at the ADRB2 (rs1042713 and rs1042714) and SCNN1A (rs2228576) genes. Despite this improvement in lung function, 10-km time trial performance was not altered after the inhalation of salbutamol. Clinical Relevance: Our findings did not show genotype-dependent differences in bronchodilatory responses and athletic performance to inhaled salbutamol, suggesting that genotype-specific drug therapy will not improve asthmatic athletes' care nor athletic performance. [ABSTRACT FROM AUTHOR]

Introduction: Altitude and an individual's V02max contribute to a decrease in V02max under hypoxic conditions. The purpose of this study was to update previous reviews with recent research in order to quantitatively determine the individual and interacting effects of altitude and baseline V02max on V02max upon acute exposure to hypoxia while developing a statistical model to predict an individual's V02raax under hypoxic conditions. Methods: Meta-regression was conducted on 105 independent groups of participants (n = 958 subjects from 80 different studies). A series of regression models was tested. The final model included altitude, baseline V02max, Alt2, baseline V02max2, and the interaction of altitude with baseline V02max. Results: A curvilinear model provided the best fit for metadata, explaining almost 80% of the variance in the null model. Nonlinear effects of Alt2 ()3 = -0.078; 95% confidence interval, -0.15 to -0.002) and baseline V02max2 ()3 = -0.003; 95% confidence interval, —0.004 to -0.001) showed that V02max decreases as altitude increases and that the decrease is greater in individuals with higher aerobic capacities. The interaction of these effects (0 = -0.028; 95% confidence interval, -0.042 to -0.015) also showed that the effects of altitude were augmented with higher baseline aerobic capacities. Furthermore, the predictions of the model were fairly accurate in predicting individual decreases in V02max (root-mean-squared error, 3.9 mL-kg- l -min-1). Conclusions: These data provide a robust quantitative framework for the curvilinear and interacting effects of altitude and baseline V02raax in determining an individual's effective V02max at altitude. This predictive model is useful for a priori power calculations, design of future experimental studies, and prediction of aerobic capacity declines in applied settings. [ABSTRACT FROM AUTHOR]

Purpose: Sprint interval training (SIT) is a time-efficient strategy to improve cardiorespiratory fitness (CRF); however, most protocols have been studied in laboratory settings and require specialized equipment. We investigated the efficacy of brief intense stair climbing as a practical model of SIT to improve CRF. Methods: Two separate studies, each consisting of an acute and chronic phase, were conducted in a total of 31 sedentary women (age = 24 ± 10 yr, body mass index = 23 ± 4 kgIm-2). Results: The acute phase of study 1 established that the mean HR, blood [lactate], and RPE were similar when participants (n = 8) performed an SIT protocol that involved 3 x 20-s "all-out" efforts of either continuously ascending stairs or cycling. The chronic phase demonstrated that CRF, as determined by peak oxygen uptake (...O2peak), increased by 12% or ~1 MET (8.27 ± 1.05 to 9.25 ± 1.01 METs, P = 0.002) when participants (n = 12) performed the 3 x 20-s stair climbing protocol 3 d-wk ' for 6 wk. The acute phase of study 2 established that HR and RPE were similar when participants (n = 11) performed three different stair climbing protocols: the 3 x 20-s continuous ascent model used in study 1 and two 3 x 60-s models of ascending and descending either one or two flights of stairs (P > 0.05). The chronic phase demonstrated that ...O2peak increased by 7% (8.91 ± 1.30 to 9.51 ± 1.52 METs, P = 0.01) when the same group of participants performed the one-flight 3 x 60-s protocol 3 d⋅wk -1 for 6 wk. The Cederholm index determined from an oral glucose tolerance test was 57 ± 17 and 64 ± 21 mg⋅L-2⋅mmol-1⋅mU-1⋅min-1 before and after training, respectively (P = 0.056). Conclusion: Brief, intense stair climbing is a practical, time-efficient strategy to improve CRF in previously untrained women. [ABSTRACT FROM AUTHOR]