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Investigations of training effects on exercise energy cost have yielded conflicting results. The purpose of the present study was to compare quadriceps energy cost and oxidative capacity between endurance-trained and sedentary subjects during a heavy dynamic knee extension exercise. We quantified the rates of ATP turnover from oxidative and anaerobic pathways with (31)P-MRS, and we measured simultaneously pulmonary oxygen uptake in order to assess both total ATP production [i.e., energy cost (EC)] and O(2) consumption (O(2) cost) scaled to power output. Seven sedentary (SED) and seven endurance-trained (TRA) subjects performed a dynamic standardized rest-exercise-recovery protocol at an exercise intensity corresponding to 35% of maximal voluntary contraction. We showed that during a dynamic heavy exercise, the O(2) cost and EC were similar in the SED and endurance-trained groups. For a given EC, endurance-trained subjects exhibited a higher relative mitochondrial contribution to ATP production at the muscle level (84 +/- 12% in TRA and 57 +/- 12% in SED; P < 0.01) whereas the anaerobic contribution was reduced (18 +/- 12% in TRA and 44 +/- 11% in SED; P < 0.01). Our results obtained in vivo illustrate that on the one hand the beneficial effects of endurance training are not related to any reduction in EC or O(2) cost and on the other hand that this similar EC was linked to a change regarding the contribution of anaerobic and oxidative processes to energy production, i.e., a greater aerobic energy contribution associated with a concomitant reduction of the anaerobic energy supply. [ABSTRACT FROM AUTHOR]

During ramp exercise the deoxy[Hb + Mb] pattern follows a sigmoid model [f(x) = f (0) + A/(1 + exp(-(-c +dx))], indicating a non-linear muscle blood flow (Qm)/oxygen uptake (VO25)-relationship. We hypothesised that in trained cyclists the sigmoid would display a rightward shift, due to an increased oxidative capacity and/or higher percentage of slow-twitch fibres. A total of 10 cyclists and 11 physically active students (PA students) performed a relative ramp exercise (+/-12 min) and a ramp25-exercise (25 W min(-1)). Deoxy[Hb + Mb] was measured at the M. Vastus Lateralis by NIRS, normalized to the total amplitude of the response and expressed as a function of absolute and relative (%peakP) work rate. The work rate corresponding to c/d (i.e.50% of the amplitude of the deoxy[Hb + Mb] response) was the only parameter of the sigmoid that differed significantly between cyclists (57.9 +/- 4.4% and 60.1 +/- 4.1%peakP in the relative and ramp25, respectively) and PAstudents (49.6 +/- 4.2% and 48.2 +/- 5.1%peakP, respectively), indicating a rightward shift of the sigmoid in the cyclists. These results suggest a change in the time course of C((a-v))O(2) as a function of aerobic fitness status. [ABSTRACT FROM AUTHOR]

This study evaluated energy cost and energy sources of a ballet exercise ( grand adage) in young female dancers with different technical ability, and then related the energy sources to the subject’s $$ \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{2\max }} $$ and anaerobic threshold (IAT). Twenty-five dancers (13–16 years) were divided into two different technical ability groups: low-level ( n = 13) and high-level ( n = 12). The overall energy requirement of dance exercise ( VO2eq) was obtained by adding the amount of VO2 during exercise above resting (aerobic source or VO2ex) to the VO2 up to the fast component of recovery (anaerobic alactic source or VO2al) and to the energy equivalent of peak blood lactate accumulation (anaerobic lactic source or $$ V\text{O}_{\text{2la}^{-}} $$ ) of recovery. VO2eq of exercise amounted to 81 ± 10 and 94 ± 9 ml kg−1 in low-level and high-level groups, respectively. VO2ex represented the higher fraction (65 ± 4% and 77 ± 5%) in low-level and high-level groups, respectively, of VO2eq in both the groups. In the low-level group the remaining fractions were: 23 ± 2 % for VO2al and 12 ± 1% for $$ V\text{O}_{\text{2la}^{-}} $$ . In high-level group the remaining fractions were: 18 ± 2 % for VO2al and 4 ± 1% for $$ V\text{O}_{\text{2la}^{-}} $$ . Between two groups, significant differences were found in VO2ex ( P < 0.01), $$ V\text{O}_{\text{2la}^{-}} $$ ( P < 0.01), and VO2al ( P < 0.05). IAT was 55 and 60% of $$ \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{2\max }} $$ for low-level and high-level dancers, respectively. Low-level dancers performed more exercise above IAT than high-level. For these reasons, it should be better to define exercise intensity according to the IAT parameter and not only to $$ \ifmmode\expandafter\dot\else\expandafter\.\fi{V}{\text{O}}_{{2\max }} . $$ [ABSTRACT FROM AUTHOR]

To further understand the mechanism(s) explaining the faster pulmonary oxygen uptake $$(p{\dot{V}}\hbox{O}_{2})$$ kinetics found in children compared to adults, this study examined whether the phase II $$p{\dot{V}}\hbox{O}_{2}$$ kinetics in children are mechanistically linked to the dynamics of intramuscular PCr, which is known to play a principal role in controlling mitochondrial oxidative phosphorylation during metabolic transitions. On separate days, 18 children completed repeated bouts of moderate intensity constant work-rate exercise for determination of (1) PCr changes every 6 s during prone quadriceps exercise using 31P-magnetic resonance spectroscopy, and (2) breath by breath changes in $$p{\dot{V}}\hbox{O}_{2}$$ during upright cycle ergometry. Only subjects ( n = 12) with 95% confidence intervals ≤±7 s for all estimated time constants were considered for analysis. No differences were found between the PCr and phase II $$p{\dot{V}}\hbox{O}_{2}$$ time constants at the onset (PCr 23 ± 5 vs. $$p{\dot{V}}\hbox{O}_{2}\ 23 \pm 4\,\hbox{s}, P=1.000)$$ or offset (PCr 28 ± 5 vs. $$p{\dot{V}}\hbox{O}_{2}\ 29 \pm 5\,\hbox{s},\, P=1.000)$$ of exercise. The average difference between the PCr and phase II $$p{\dot{V}}\hbox{O}_{2}$$ time constants was 4 ± 4 s for the onset and offset responses. Pooling of the exercise onset and offset responses revealed a significant correlation between the PCr and $$p{\dot{V}}\hbox{O}_{2}$$ time constants ( r = 0.459, P = 0.024). The close kinetic coupling between the $$p{\dot{V}}\hbox{O}_{2}$$ and PCr responses at the onset and offset of exercise in children is consistent with our current understanding of metabolic control and suggests that an age-related modulation of the putative phosphate linked controller(s) of mitochondrial oxidative phosphorylation may explain the faster $$p{\dot{V}}\hbox{O}_{2}$$ kinetics found in children compared to adults. [ABSTRACT FROM AUTHOR]