The effects of 8-weeks unilateral resistance training on strength, time to task failure, and synergist co-activation of elbow flexor Muscles in trained and untrained limbs

The effect of cross training to improve endurance and its mechanism is not fully understood. The purpose of this study was to determine the effects of 8-weeks unilateral resistance training on strength, time to task failure, neuromuscular fatigue and synergist muscles co-activation in trained and contralateral untrained limbs. 20 healthy female students were randomly assigned to either a training or a control group. The experimental group performed unilateral resistance training on non-dominant elbow flexors, 3 days per week for 8 weeks. The surface electromyography signal that was recorded from elbow flexor muscles during submaximal and maximal voluntary contraction(MVC) of both trained and untrained limb, were computed as Root Mean Square(RMS), mean power frequency(MPF) and integrated electromyography (IEMG) data in pre and post test. The result indicated a significant increase in elbow flexor MVC and time to failure in submaximal isometric task in trained and contralateral untrained limb. There was a significant difference between groups in RMS and MPF of biceps brachii in trained and untrained limb. However, this differences were not significant for brachialis and triceps in contralateral limbs. Also, after resistance training, there is a significant difference in the IEMG ratio of the muscles among blocks of submaximal contraction in trained and untrained limb, indicating a tendency to alternation in synergistic muscles activity. Cross transfer effect of unilateral resistance training on time to task failure might be explained, at least partly by the mechanism of synergistic alternate activity pattern.