Influences of chemically-induced muscle pain on power output of ballistic upper limb movements

Objective: To analyse the conditioning effects of localised acute muscle pain on power output during ipsi- and contra-lateral ballistic arm extensions. Methods: Eight male subjects performed right arm (ipsilateral) and left arm (contra-lateral) bench press movements. The power output (and force and velocity) of the concentric phase of movement was measured before and during muscle pain induced by a standardised intramuscular injection of levo-ascorbic acid in the right pectoralis major muscle (prime mover muscle) and in the lateral head of the right triceps brachii muscle (synergist). Results: The power output of ipsi- and contra-lateral arm bench press movements was significantly decreased during pain of the right pectoralis major muscle, but not during pain of the right lateral triceps muscle. The velocity and force were both affected and contributed to the decrease in power output. Conclusions: Acute muscle pain of a prime mover muscle reduces ipsi- and contra-lateral motor performance of ballistic upper limb extension. This is not a generalised or non-specific inhibitory effect on the motor system, since pain failed to modify motor performance when applied to a synergist, non-prime mover, muscle. A basically bilateral executive cortical plan for ballistic upper limb extension could explain the conditioning effect of muscle pain on both ipsi- and contra-lateral arm. Significance: The results presented here contributes to the understanding of the conditioning effects of muscle pain on movement performance. (C) 2004 Published by Elsevier Ireland Ltd on behalf of International Federation of Clinical Neurophysiology.