An investigation into the effect of experimental knee pain on quadriceps muscle torque during different contraction types

Abstract

Reduced isometric and concentric muscle strength during pain is a common finding, however, the few investigations into the effect of eccentric muscle strength during pain report inconsistent findings. Eccentric contractions are innervated by different neural control strategies than concentric and isometric contractions, therefore may not be affected by pain in the same way. The aim of this study was to investigate the effect of experimentally induced knee pain on maximal voluntary eccentric inhibition in comparison to other contraction modes using a repeated measures experimental design. Twenty asymptomatic volunteers completed the study in a physiology laboratory setting. Maximal strength of the quadriceps was assessed using an isokinetic dynamometer. Experimental pain was induced by injecting 1.0ml of 5.8% hypertonic saline into the infrapatellar fat pad. Eccentric strength was reduced immediately with pain for most participants, however the difference was not statistically significant (p = 0.083, z = -1.736, r = 0.39 ‘small’). Eccentric strength was reduced from the baseline to post-pain condition (p = 0.017, z = -2.389, r = 0.53 ‘medium’). In conclusion, eccentric contractions are affected by experimental pain similarly to other contraction types. However, differences exist in the variability of the effect of pain across contraction modes.