Changes in Neuromuscular Performance in Voluntary and Reflex Contraction during Strength Training in Man

Abstract

Eleven male subjects went through heavy resistance strength training 3 times a week for 16 weeks. The training program consisted mainly of dynamic exercise for the knee extensor muscles with loads of 80%-120% of one maximum repetition in the squat lift. The investigation was undertaken to examine effects of strength training on neuromuscular performance both in voluntary and reflex contractions with special interest in their possible relationships. In addition to a large (P less than 0.001) increase in maximal isometric force and a more (P less than 0.05) economical activation of the knee extensor muscles, significant (P less than 0.05) improvements were noted in isometric force-time parameters, which were related (P less than 0.05) to the increase in the fast-twitch/slow-twitch (FT/ST) muscle fiber area ratio. No changes were observed in reflex time components, but the relative change in reflex electromechanical delay (EMD) was related (P less than 0.05) to the relative change in the FT/ST area ratio. A significant (P less than 0.05) decrease in the peak-to-peak amplitude of the reflex electromyogram (EMG), was noted during the training, and a decrease (P less than 0.05) in reflex EMG/force ratio was related (P less than 0.02) to the change in maximal integrated electromyogram (iEMG)/force ratio of the voluntary contraction. The decrease of reflex EMG may indicate a change in sensitivity of the muscle spindle. The interrelationship between the changes in EMG/force ratios of the reflex and voluntary contractions suggests that the mechanical response of individual muscle fibers of the respective motor units has improved.

Resistance training using eccentric overload induces early adaptations in skeletal muscle size

“…It is known that resistance exercise programs accompanied by muscle hypertrophy and task-specific performance may not necessarily increase maximal voluntary isometric strength (Brown et al 1990;Sale et al 1992;Higbie et al 1996), yet a large number of studies have reported such an effect (Hakkinen and Komi 1983;Young et al 1983;Jones and Rutherford 1987). The current finding of a somewhat greater increase in maximal voluntary isometric strength with enhanced eccentric compared with coupled concentric and eccentric resistance training is not at odds and consistent with other reports (Godard et al 1998;Hortobagyi et al 2001).…”

Tibiofemoral contact forces during walking, running and sidestepping

“…To determine the tibiofemoral contact forces for different gait tasks or populations some form of neuromusculoskeletal modelling may be necessary. This is because muscle activation patterns have been shown to be dependent on the control task [12], and to vary with both joint health [13] and training [38]. Thus, it seems unlikely that external measures, when used in statistical models that are inherently linear and non-dynamic, can predict joint contact forces during dynamic locomotor tasks.…”

Paired changes in electromechanical delay and musculo-tendinous stiffness after endurance or plyometric training

“…Kubo et al (2001) reported a decrease in EMD after isometric training, but Zhou et al (1996) found no changes in EMD following sprint training. Similarly Hakkinen and Komi (1983) reported no significant differences in EMD values calculated under reflex contraction before and after 16 weeks of strength training. For healthy adults, data reported in the literature indicate that, for the TS muscle, the EMD value obtained from maximal electrical nerve stimulation are generally between 9.5 and 18.7 ms (Grosset et al 2005;Mora et al 2003;Muro and Nagata 1985;Winter and Brookes 1991).…”