Co-contraction training, muscle explosive force and associated electromyography activity.

BACKGROUND: The effects of a six-week Maximal isometric voluntary co-contraction (MIVCC) training program of the elbow flexor and extensor muscles on maximal and explosive muscle strength have been studied.

METHODS: Ten active men underwent 6-week MIVCC. Maximal rate of force development (MRFD) of the elbow flexor (MRFDflex) and extensor (MRFDext) were measured in addition to maximal voluntary contraction (MVC) of these muscles (MVCflex and MVCext) before (T0), after 4-week (T1) and 6-week (T2) MIVCC training program. During each test session, integrated electromyographic activity (iEMG) of agonistic and antagonistic muscles during MVC, MRFD, submaximal contractions (30% and 60% MVC) and MIVCC of the elbow flexor and extensor muscles were measured.

RESULTS: At T2, MVCflex (13.3±11.7%) and MVCext (22.5±6.1%) increased significantly (P<0.001). Similarly, iEMG of agonists muscles during MVC increased significantly for flexor (+29.9%) and extensor (+29.6%) muscles (P<0.001) without changes of antagonists co-activation. The increases in MRFDflex (+12.5%), MRFDext (+9.2%) and iEMG at MRFD were not significant.

CONCLUSIONS: MIVCC training can simultaneously improve strength of antagonistic muscles without inducing an alteration of MRFD or an increase in muscles co-activation during contractions of the agonist muscles. Interestingly, the improvement of estimated forces during MIVCC after 6-week-training suggested that the higher level of MIVCC previously observed in bodybuilders could be the result of specific training exercises (posing). The fact that MIVCC training did not alter "explosive" force production, which is important in optimal design of sports-specific resistance training as well as in rehabilitation programs.