News & Views from the Editor-in-Chief: Andrew M. Jones
In my News & Views piece to accompany the October issue of MSSE, I've chosen to highlight three papers which focus on basic and fundamental issues relating to skeletal muscle adaptation, damage, and fatigue.
In conventional resistance exercises, coupled concentric and eccentric contractions (CON-ECC) are performed, but performing eccentric-only contractions (ECC) is also possible. ECC induce muscle damage, but less is known about muscle damage induced by CON-ECC. In their paper entitled 'Comparison between Eccentric-only and Coupled Concentric-Eccentric Contractions for Neuromuscular Fatigue and Muscle Damage', Ruas et al. compared ECC (6 sets of 8 contractions) and CON-ECC (6 sets of 8 concentric-eccentric contractions) of the knee extensors for changes in several parameters relating to neuromuscular fatigue and muscle damage before, immediately after and 1-3 days post-exercise in 20 young adults. They found that neuromuscular fatigue and muscle damage were similar between ECC and CON-ECC, despite twice as many contractions performed in CON-ECC with the ECC intensity. This suggests that eccentric contractions are mainly responsible for the fatigue and damage observed in conventional resistance exercises.
The capillary network is key for delivery of oxygen and nutrients and for removal of metabolites in the working skeletal muscle. Since the early 1970's it has been known that exercise training increases muscle capillarization but the best training regime for increasing muscle capillarization is an open question. In the meta-analysis completed by Liu et al. ('Effects of Exercise Training Intensity and Duration on Skeletal Muscle Capillarization in Healthy Subjects: A Meta-analysis'), 57 trials with a clearly defined training intervention were included to measure the effects of low-, moderate- and high intensity and sprint interval training on capillarization. High intensity training was shown to be most effective in improving capillarization in previously untrained subjects, whereas training volume was less important. In already trained subjects, training interventions of 2-12 weeks duration does not change capillarization but in athletes with years of training, capillarization is already very high. The authors conclude that capillary growth occurs rapidly (within weeks) and continues at a slower pace over years of training.
In 'Prior Involvement of Central Motor Drive does not Impact Performance and Neuromuscular Fatigue in a Subsequent Endurance Task', Laginestra et al. aimed to isolate the effects of the involvement of central motor drive on high-intensity endurance performance. Ten young healthy individuals performed a single-leg constant-load exhaustive test after either a voluntary (i.e., involving central motor drive) or an electrically-evoked (i.e., no central motor drive) fatiguing task. No differences were found in endurance performance time, nor in neuromuscular fatigue development between modalities even though these two bouts required an overall different level of central motor drive. This suggests that high-intensity endurance exercise is primarily limited by mechanisms related to intramuscular metabolic perturbations rather than factors associated with voluntary drive. These findings provide insights into mechanisms of fatigue and highlight the importance of mitigating peripheral fatigue as a strategy to improve performance in this type of exercise.
Andrew M. Jones
University of Exeter