Eight male subjects were asked to swim 25 m at maximal velocity while the use of the arm(s) and legs was alternately restricted. Four situations were examined using one arm (1A), two arms (2A), one arm and two legs (1A2L) and both arms and legs (2A2L, normal swim) for propulsion. A significant mean increase of 10% on maximal velocity was obtained in 1A2L and 2A2L compared to 1A and 2A. A non-significant 4% effect was obtained in 1A. This study focused on the actual contribution of leg kick in the 10% gain in maximal velocity. It was clear that the underwater trajectory of the wrist was modified by the action of the legs (most comparisons P < 0.001). Therefore it was thought that the legs enhanced the generated propulsive force by improving the propulsive action of the arm. The arm action was quantified by selecting typical phases from the filmed trajectory of the wrist, namely forward (F), downwards (D) and backwards (B). Although there was a tendency for individual changes in kinematic parameters (F, D and B) to occur with individual changes in velocity when 2A was compared to 2A2L, no relationship was found between the relative changes in F, D and B and relative changes in velocity. This was illustrated by describing the responses of three individuals who could represent three patterns of contribution by legs and arms to propulsion in high speed swimming.

With aging, most skeletal muscles undergo a progressive loss of mass and strength, a process termed sarcopenia. Aging-related defects in mitochondrial energetics have been proposed to be causally involved in sarcopenia. However, changes in muscle mitochondrial oxidative phosphorylation with aging remain a highly controversial issue, creating a pressing need for integrative approaches to determine whether mitochondrial bioenergetics are impaired in aged skeletal muscle. To address this issue, mitochondrial bioenergetics was first investigated in vivo in the gastrocnemius muscle of adult (6 months) and aged (21 months) male Wistar rats by combining a modular control analysis approach with 31P magnetic resonance spectroscopy measurements of energetic metabolites. Using this innovative approach, we revealed that the in vivo responsiveness (‘elasticity’) of mitochondrial oxidative phosphorylation to contraction-induced increase in ATP demand is significantly reduced in aged skeletal muscle, a reduction especially pronounced under low contractile activities. In line with this in vivo aging-related defect in mitochondrial energetics, we found that the mitochondrial affinity for ADP is significantly decreased in mitochondria isolated from aged skeletal muscle. Collectively, the results of this study demonstrate that mitochondrial bioenergetics are effectively altered in vivo in aged skeletal muscle and provide a novel cellular basis for this phenomenon.

To determine whether power-velocity relationships obtained on a nonisokinetic cycle ergometer could be related to muscle fibre type composition, ten healthy specifically trained subjects (eight men and two women) performed brief periods of maximal cycling on a friction loaded cycle ergometer. Frictional force and flywheel velocity were recorded at a sampling frequency of 200 Hz. Power output was computed as the product of velocity and inertial plus frictional forces. Force, velocity and power were averaged over each down stroke. Muscle fibre content was determined by biopsy of the vastus lateralis muscle. Maximal down stroke power [14.36 (SD 2.37)W.kg-1] and velocity at maximal power [120 (SD 8) rpm] were in accordance with previous results obtained on an isokinetic cycle ergometer. The proportion of fast twitch fibres expressed in terms of cross sectional area was related to optimal velocity (r = 0.88, P < 0.001), to squat jump performance (r = 0.78, P < 0.01) and tended to be related to maximal power expressed per kilogram of body mass (r = 0.60, P = 0.06). Squat jump performance was also related to cycling maximal power. expressed per kilogram of body mass (r = 0.87, P < 0.01) and to optimal velocity (r = 0.86, P < 0.01). All these data suggest that the nonisokinetic cycle ergometer is a good tool with which to evaluate the relative contribution of type II fibres to maximal power output. Furthermore, the strong correlation obtained demonstrated that optimal velocity, when related to training status, would appear to be the most accurate parameter to explore the fibre composition of the knee extensor muscle.

A friction loaded cycle ergometer was instrumented with a strain gauge and an incremental encoder to obtain accurate measurement of human mechanical work output during the acceleration phase of a cycling sprint. This device was used to characterise muscle function in a group of 15 well-trained male subjects, asked to perform six short maximal sprints on the cycle against a constant friction load. Friction loads were successively set at 0.25, 0.35, 0.45, 0.55, 0.65 and 0.75 N.kg-1 body mass. Since the sprints were performed from a standing start, and since the acceleration was not restricted, the greatest attention was paid to the measurement of the acceleration balancing load due to flywheel inertia. Instantaneous pedalling velocity (v) and power output (P) were calculated each 5 ms and then averaged over each downstroke period so that each pedal downstroke provided a combination of v, force and P. Since an 8-s acceleration phase was composed of about 21 to 34 pedal downstrokes, this many v-P combinations were obtained amounting to 137-180 v-P combinations for all six friction loads in one individual, over the widest functional range of pedalling velocities (17-214 rpm). Thus, the individual's muscle function was characterised by the v-P relationships obtained during the six acceleration phases of the six sprints. An important finding of the present study was a strong linear relationship between individual optimal velocity (vopt) and individual maximal power output (Pmax) (n = 15, r = 0.95, P < 0.001) which has never been observed before. Since vopt has been demonstrated to be related to human fibre type composition both vopt, Pmax and their inter-relationship could represent a major feature in characterising muscle function in maximal unrestricted exercise. It is suggested that the present method is well suited to such analyses.

To investigate the different ways of assessing the running velocity at which maximal oxygen uptake (VO2max) occurs, or maximal aerobic velocity (vamax), 32 well-trained runners (8 female and 24 male) were studied. The vamax and the running velocity corresponding to a blood lactate concentration of 4 mmol.l-1 (vla4) were measured during a progressive treadmill session. Within the week preceding or following the treadmill measurement the subjects completed a Université de Montreal Track-Test (UMTT). The velocity corresponding to the last stage of this test (vUMTT) was slightly higher than vamax: 6.08 m.s-1, SD 0.41, vs 6.01 m.s-1, SD 0.44 (P less than 0.03) but these two velocities were strongly correlated (r = 0.92, P less than 0.001). The heart rate values corresponding to these velocities were similar and well correlated (r = 0.79, P less than 0.01); the corresponding blood lactate values had similar mean values: 10.5 mmol.l-1, SD 2.7 vs 11.8 mmol.l-1, SD 2.5, but were not correlated. Both vamax and vUMTT correlated well with the best performance sustained over 1500 m during the season. These results suggest that the UMTT provides a value of vamax as accurately as a treadmill measurement and that either could be used to measure the running velocity corresponding to VO2max. The v1a4 was 86.6%, SD 2.6 of vamax; these two velocities correlated strongly. Thus, in well trained runners, v1a4, when measured with a well-defined procedure, corresponds to a constant fraction of vamax and depends then on VO2max and the energy cost of running.

This suggests that there is a decrease in coactivation as agonist force is lost. This decrease in coactivation under fatigue conditions has not been previously reported and is probably due to the training status of the subjects. Subjects may have learned to better use their antagonist muscles to efficiently transfer force and power to the rotating pedal. This coordination can be adapted to cope with fatigue of the power producer muscles.

Diolez P, Deschodt-Arsac V, Raffard G, Simon C, Dos Santos P, Thiaudière E, Arsac L, Franconi J-M. Modular regulation analysis of heart contraction: application to in situ demonstration of a direct mitochondrial activation by calcium in beating heart.

The present study aims to assess energy demand and supply in 100-m sprint running. A mathematical model was used in which supply has two components, aerobic and anaerobic, and demand has three components, energy required to move forward (C), energy required to overcome air resistance (Caero), and energy required to change kinetic energy (Ckin). Supply and demand were equated by using assumed efficiency of converting metabolic to external work. The mathematical model uses instantaneous velocities registered by the 1997 International Association of Athletics Federations world champions at 100 m in men and women. Supply and demand components obtained in the male champion were (in J/kg) aerobic 30 (5%), anaerobic 607 (95%), C 400 (63%), Caero 83 (13%), Ckin 154 (24%). Comparatively, a model that uses the average velocity of the male and female 100-m champions overestimates Ckin by 37 and 44%, respectively, and underestimates Caero by 14%. We argued that such a model is not appropriate because Ckin and Caero are nonlinear functions of velocity. Neither height nor body mass seems to have any advantage in the energetics of sprint running.