Effect of eccentric muscle contractions on Golgi tendon organ responses to passive and active tension in the cat

To investigate the possibility of a peripheral contribution to the perturbations of force sensation reported to occur after eccentric exercise, responses to passive and active tension were recorded from Golgi tendon organs in the medial gastrocnemius muscle of the anaesthetised cat, before and after a series of eccentric contractions. After the eccentric contractions, nearly all tendon organs commenced firing at a shorter muscle length during slow passive stretch than before, probably because of a rise in whole muscle passive tension. There was a small drop in the sensitivity to incremental tension, but no mean change in tension threshold. Following the eccentric contractions, there was a small, but not significant, increase in tendon organ sensitivity to active tension, which was graded using a method of optimised, distributed stimulation of divided ventral roots. Sensitivity was estimated as the mean response over a range of tensions and as the change in discharge rate in response to incremental tension. The experiments provided the opportunity of comparing tendon organ sensitivities to graded passive and active whole muscle tension. In agreement with previous work in which whole muscle nerve stimulation was employed, little difference was found. It was concluded that the peripheral contribution to perturbations of force perception after eccentric exercise is likely to be small and that the centrally derived sense of effort plays the dominant role. Tendon organs appear to be remarkably reliable in signalling whole muscle tension, whether passive or active, and even after the muscle's force production has been disturbed by fatigue or eccentric exercise.