J. D. MacDougall

Effect of strength training upon motoneuron excitability in man.

Two healthy females and twelve healthy males, aged 19-24 yr, underwent strength training for periods of 9-21 wk. The muscles trained included extensor digitorum brevis (N = 3), soleus (N = 7), brachioradialis (N = 4), and the hypothenar muscles (N = 3). The effect of training on motoneuron excitability was measured as the degree to which two reflex responses (V1 and V2) were potentiated by voluntary effort. Strength training was found to increase V1 and V2 potentiation by 49.7 and 38.9%, respectively, (P less than 0.01) for pooled muscle comparisons with the exception of the soleus V2 wave, which was rarely seen and excluded from this analysis. There was a positive correlation (r = 0.83, P less than 0.01) between the change in the V1 and V2 potentiation. It was argued that strength training may cause an increased ability to raise motoneuron excitability during voluntary effort.

Postactivation potentiation in endurance-trained male athletes.

PURPOSE The purpose of the study was to determine whether postactivation potentiation (PAP) was enhanced in the trained muscles of male endurance athletes. METHODS Triathletes (TRI), distance runners (RUN), active controls (AC), and sedentary control subjects (SED) (N = 10 per group) performed 10-s maximal isometric contractions (MVC) of the elbow extensor and ankle plantarflexor muscles. Maximal twitch contractions were evoked (percutaneous stimulation) before and during a 5-min period after the MVC. PAP was measured as the percentage change in peak twitch torque post-MVC. RESULTS TRI, who train both upper and lower limb muscles, had enhanced (relative to SED) PAP in both elbow extensor and plantarflexor muscles. In RUN, who train only the lower limbs, enhanced PAP was restricted to the plantarflexors. AC, whose main activity was upper and lower limb weight training, also had enhanced PAP in both muscle groups, although the enhancement in the plantarflexors was not as great as in TRI and RUN. CONCLUSION PAP is enhanced in endurance athletes. Enhanced PAP may counteract fatigue during endurance exercise. The mechanism(s) responsible for the enhanced PAP remain to be determined.

Neuromuscular function in weight-trainers

Electrophysiologic measurements were made on the median-innervated thenar muscles and triceps surae in 17 weight-trainers (bodybuilders and weight-lifters) and in control subjects. In the median-innervated thenar muscles, the weight-trainers presented normal values for motor unit counts, reflex potentiation, and twitch contractile properties; however, the weight-trainers possessed a significantly greater (8%) median motor nerve conduction velocity. In the triceps surae, the weight-trainers exhibited significantly greater reflex potentiation (70%), which was interpreted as an increased ability to activate motor units during maximal voluntary contractions. Peak twitch tension (16%) and twitch contraction time (20%) of the triceps surae were significantly greater in the weight-trainers, whereas their twitch half-relaxation time and soleus motor unit counts were not significantly different from control values. The observed difference may reflect a combination of genetic endowment and the effects of training.