High intensity eccentric exercise induces muscle fiber damage and associated delayed-onset muscle soreness (DOMS) resulting in an impaired ability of the muscle to generate voluntary force. This study investigates the extent to which DOMS, induced by high intensity eccentric exercise, can affect the activation and performance of the non-exercised homologous muscle of the contralateral limb. Healthy volunteers performed maximal voluntary contractions of knee extension and sustained isometric knee extension at 50% of maximal force until task failure on both the ipsilateral exercised limb and the contralateral limb. Surface electromyography (EMG) was recorded from the ipsilateral and contralateral knee extensor muscles (vastus medialis, rectus femoris, and vastus lateralis). Maximal isometric knee extension force (13.7% reduction) and time to task failure (38.1% reduction) of the contralateral non-exercised leg decreased immediately after eccentric exercise, and persisted 24 h and 48 h later (p < 0.05). Moreover, the amplitude of muscle activity recorded from the contralateral knee extensor muscles was significantly lower during the post exercise maximal and submaximal contractions following high intensity eccentric exercise of the opposite limb (p < 0.05). Unilateral high intensity eccentric exercise of the quadriceps can contribute to reduced neuromuscular activity and physical work capacity of the non-exercised homologous muscle in the contralateral limb.

No abstract

Background:The purpose of this study was to investigate the effects of 9 weeks' resistance training utilizing a daily undulating periodization (DUP) program versus a linear periodization (LP) program on concentric and isometric muscle strength and neuromuscular function of the quadriceps muscle.Material and methods: 30 male subjects (age = 21.7 ±2.5 yr, body mass = 71.4 ±11.9 kg, height =1.77 ±0.09 m) participated in the study. Subjects were randomly divided into DUP and LP training groups. Both the DUP and LP training group performed leg press exercise 3 times per week. Volume and intensity were equated for each training program. However, the periodization type was different between the two groups. Additionally, the maximal isometric voluntary contraction (MIVC) of the quadriceps muscle and the associated electromyography (EMG) activity were recorded before and after 9 weeks of the DUP and LP training programs. Results:The DUP training program resulted in a greater increase (50.1% ±10.1) in quadriceps isometric strength compared with the LP training program (35.5% ±7.3; F = 7.6, p < 0.025). Accordingly, EMG activity of the quadriceps muscle after 9 weeks of the DUP training program was significantly larger than that observed after the LP training model (F = 7.5, p < 0.05). Conclusions:Resistance training using a DUP program is more effective than a LP program to elicit neuromuscular activity and muscle strength.

No abstract

-Aims: Cross-training is the process whereby training of one limb gives rise to enhancements in the performance of the opposite, untrained limb and may be dependent on type of muscle contractions performed. The aim of this study was to investigate whether unilateral resistance training using eccentric contraction is more effective than concentric resistance training to improve time to task failure in the contralateral untrained limb. Methods: Subjects completed 12 weeks of resistance training consisting of 36 sessions, using unilateral leg exercise. Sustained isometric knee extension performed at 50% of maxmal force until task failure for the contralateral untrained leg. Surface electromyography (EMG) signals were simultaneously recorded from contralateral untrained quadriceps (vastus medialis, rectus femoris, and vastus lateralis). Results: Time to task failure of the contralateral untrained leg and associated EMG activities significantly increased after 12 weeks of unilateral resistance training (p<0.05). However, percent increase in time to task failure and EMG amplitude after eccentric resistance training was significantly higher than concentric resistance training (p<0.05). Conclusion: This study concluded that unilateral eccentric resistance training is superior to concentric resistance training to increase time to task failure in the contralateral untrained limb.