CHANGES IN RECIPROCAL AND TRANSJOINT INHIBITION INDUCED BY MUSCLE FATIGUE IN MAN

The effects of localised muscle fatigue on group I reflex pathways wer e studied in the human upper limb. Activation of group I afferents ori ginating from biceps and extensor carpi radialis (ECR) resulted in an inhibition of flexor carpi radialis (FCR) motoneurones, probably throu gh a disynaptic pathway. Reciprocal inhibition (from ECR to FCR) and t ransjoint inhibition (from biceps to FCR) were compared before and dur ing localised fatigue induced in the muscle from which group I afferen ts originated. Fatigue of wrist extensors did not modify the reciproca l inhibition, while during fatigue of elbow flexors the transjoint inh ibition was less pronounced. This striking difference between reciproc al and transjoint inhibition is discussed in relation to the pattern o f diffusion of voluntary contractions during fatigue in the human uppe r limb.