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Recommendations for endurance exercise prescription are often based on percentages of heart rate (HR) or the volume of oxygen consumption ( V ˙ O2) maximum or reserve that is extrapolated to a power output (P) or velocity. Previous work has demonstrated dissociations of the expected responses to exercise anchored to the critical heart rate (CHR) compared with the P associated with CHR. However, it is unclear if similar dissociations due to reductions in P to maintain the designated intensity would be present during exercise anchored to the V ˙ O2 associated with CHR ( V ˙ O2CHR). The purpose of this study was to examine the patterns in physiological ( V ˙ O2, HR, P, respiration rate [RR], muscle oxygen saturation [%SmO2]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP, MMG AMP], mean power frequency [EMG MPF, MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise at V ˙ O2CHR ( V ˙ O2-clamp). On separate days, ten participants (age: 25 ± 4 yr) performed a graded exercise test and four constant P trials at 85–100% of peak P (PP) to derive CHR and V ˙ O2CHR. Responses were recorded during a trial to exhaustion at V ˙ O2CHR (32.86 ± 7.12 mL·kg−1·min−1; TLim = 31.31 ± 21.37 min) and normalized in 10% intervals of TLim to their respective values at PP. The one-way repeated-measures ANOVA with post hoc, Bonferroni-corrected, pairwise comparisons indicated differences (p < 0.001) from baseline for HR (mean ± SD %change = 8 ± 3%), RR (43 ± 38%), P (−15 ± 5%), EMG MPF (10 ± 8%), and RPE (65 ± 38%), but no differences (p = 0.077–0.955) for %SmO2 (−17 ± 53%), EMG AMP (−3 ± 16%), MMG AMP (40 ± 61%), and MMG MPF (1 ± 7%). The loss in performance observed during V ˙ O2-Clamp exercise may provide a quantification of the inefficiency associated with the V ˙ O2 slow component phenomenon. The neuromuscular responses suggested constant muscle excitation despite the reductions in P, but the metabolic and perceptual responses suggested a combination of feedforward and feedback mechanisms regulating TLim. Future studies should further examine responses to the V ˙ O2-Clamp exercise at a uniform threshold. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to examine differences in heart rate recovery (HRRec) and oxygen consumption recovery (VO2 recovery) between young healthy-weight children and children with obesity following a maximal volitional graded exercise test (GXTmax). Method: Twenty healthy-weight children and 13 children with obesity completed body composition testing and performed a GXTmax. Immediately after the GXTmax, HRRec and VO[subscript 2] recovery were measured each minute for 5 consecutive minutes. Results: There were no statistically significant group differences in HRRec for the 5 min following maximal exercise, Wilks's Lambda = 0.885, F(4, 28) = 0.911, p = 0.471, between the healthy-weight children and children with obesity despite statistically significant differences in body fat percentage (BF%; healthy-weight children, 18.5 ± 6.1%; children with obesity, 41.1 ± 6.9%, p < 0.001) and aerobic capacity relative to body mass (VO[subscript 2] peak; healthy-weight children, 46.8 ± 8.2 mL/kg/min; children with obesity, 31.9 ± 4.7 mL/kg/min, p < 0.001). There were statistically significant differences in VO[subscript 2] recovery for the 5 min following exercise, Wilks's Lambda = 0.676, F(4, 26) = 3.117, p = 0.032. There were no statistically significant correlations between HRRec and body mass index (BMI), BF%, VO[subscript 2] peak, or physical activity. Conclusions: In a healthy pediatric population, obesity alone does not seem to significantly impact HRRec, and because HRRec was not related to obesity status, BMI, or BF%, it should not be used as the sole indicator of aerobic capacity or health status in children. Using more than one recovery variable (i.e., HRRec and VO[subscript 2] recovery) may provide greater insight into cardiorespiratory fitness in this population.

Background: Diffusion tensor imaging (DTI) parameters correlate with muscle fiber composition, but it is unclear how these relate to in vivo contractile function. Purpose: To determine the relationship between DTI parameters of the vastus lateralis (VL) and in vivo knee extensor contractile. Methods: Thirteen healthy, premenopausal women underwent magnetic resonance imaging of the mid‐thigh to determine patellar tendon moment arm length and quadriceps cross‐sectional area. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD) of the VL were determined using diffusion tensor imaging (DTI). Participants underwent an interpolated twitch (ITT) experiment before and after a fatiguing concentric‐eccentric isokinetic knee extension (60°·s−1). During the ITT, supramaximal electrical stimuli were delivered to elicit twitch responses from the knee extensors before, during, and after a maximal voluntary isometric contraction (MVIC). Knee extensor‐specific tension during twitch and MVIC were calculated from isometric torque data. Pearson's correlations were used to determine the relationship between muscle contractile properties and DTI parameters. Results: MD and RD were moderately correlated with peak twitch force and rate of force development. FA and AD were moderately inversely related to percent change in MVIC following exercise. Conclusion: MD and RD are associated with in vivo quadriceps twitch properties but not voluntary strength, which may reflect the mechanical properties of constituent fiber types. FA and AD appear to relate to MVIC strength following fatiguing exercise. [ABSTRACT FROM AUTHOR]

Critical power (CP) and anaerobic work capacity (AWC) from the CP test represent distinct parameters related to metabolic characteristics of the whole body and active muscle tissue, respectively. Purpose: To examine the contribution of whole-body composition characteristics and local lean mass to further elucidate the differences in metabolic characteristics between CP and AWC as they relate to whole body and local factors. Methods: Fifteen anaerobically trained men were assessed for whole-body (% body fat and mineral-free lean mass [LBM]) and local mineral-free thigh lean mass (TLM) composition characteristics. CP andAWCwere determined from the 3-min all-out CP test. Statistical analyses included Pearson product--moment correlations and stepwise multiple-regression analyses (P ≤ .05). Results: Only LBM contributed significantly to the prediction of CP (CP = 2.3 [LBM] + 56.7 [r² = .346, standard error of the estimate (SEE) = 31.4W, P = .021]), and only TLM to AWC (AWC= 0.8 [TLM] + 3.7 [r² = .479, SEE = 2.2 kJ, P = .004]). Conclusions: The aerobic component (CP) of the CP test was most closely related to LBM, and the anaerobic component (AWC) was more closely related to the TLM. These findings support the theory that CP and AWC are separate measures of whole-body metabolic capabilities and the energy stores in the activated local muscle groups, respectively. Thus, training programs to improve CP and AWC should be designed to include resistance-training exercises to increase whole-body LBM and local TLM. [ABSTRACT FROM AUTHOR]

The effects of increased muscle temperature via continuous ultrasound prior to a maximal bout of eccentric exercise were investigated on the symptoms of delayed onset muscle soreness (DOMS) of the elbow flexors. Perceived muscle soreness, upper arm circumferences, range of motion (ROM), and isometric and isokinetic strength were measured over 7 days on 14 college-aged men (n = 6) and women (n = 8). Ten minutes of continuous ultrasound (ULT) or sham-ultrasound (CON) were administered. Muscle temperature was measured in the biceps brachii of both arms. Muscle temperature increased by 1.79[degrees] [+ or -] 0.49[degrees]C (mean [+ or -] SD) in the experimental arm of the ULT group. Muscle soreness was induced by a single bout of 50 maximal eccentric contractions. The ULT group did not differ significantly (p < 0.05) from the CON group with respect to perceived muscle soreness, upper arm circumference, ROM, and isometric and isokinetic strength. In conclusion, increased muscle temperature failed to provide significant prophylactic effects on the symptoms of DOMS. KEY WORDS. muscle soreness, eccentric exercise, ultrasound, DOMS prevention