The Effect of Endurance Training on Muscle Strength and Power

Abstract

<p> In order to investigate possible negative effects of endurance training on muscle strength and power, 10 healthy young men underwent 10 weeks of endurance training. Subjects trained unilaterally on a cycle ergometer so that their opposite leg served as a control. Training consisted of 30 min per day for 3 days per week and progressed to 60 min per day for 5 days per week by the seventh week of training. This volume of endurance training exceeds the upper limits of that normally performed by athletes who compete in power sports. The exercise intensity was initially ~75% of pre-training maximum power output and was increased over time to maintain a training heart rate of 140-160 beats per minute. Endurance, strength, and power variables were assessed in each leg before and after the training period. Measurements included electrically stimulated twitch characteristics of the quadriceps, single-leg V̇O2peak and lactate threshold (Tlac), single-leg take-off vertical jump power indices from a force platform, and maximal leg press strength at a low-(60°/s) and high-velocity (300°/s). Needle biopsies were taken from the quadriceps femoris before and after the training period, and analyzed for fibre-type proportions, fibre area, oxidative enzyme activity and capillary density. Post-training, subjects increased leg V̇O2peak (7%) and Tlac in the trained leg. Leg press strength was unaffected by training. Vertical jump power was not impaired nor were evoked twitches. Following training, there was a decrease in % type IIb and an increase in % type IIa fibres (p<0.05). There were no significant changes in fibre area. Percent fibre area increased for type I and IIa and decreased for type IIb fibres in the trained leg (p<0.05). These data indicate that a 10-week endurance-training program increases aerobic power but does not impair muscle strength or power.</p>