The magnitude of muscle damage induced by downhill backward walking.

While various models for exercise-induced muscle damage (EIMD) have been introduced, many of them use maximal voluntary contractions of the elbow flexors and knee extensors performed on isokinetic dynamometers. Few studies have used exercise protocols that attempt to replicate submaximal eccentric muscle actions that commonly occur during daily activities. Downhill backwards walking has been used previously as an EIMD model. However, the common markers of muscle damage have not been systematically examined for this model. The purpose of this study was to determine the magnitude of muscle damage induced by downhill backward walking with regard to changes in commonly-used indirect markers of EIMD. Twenty subjects aged between 19 y and 42 y completed a bout of 60 min of downhill (-15%) backward walking in which a single limb performed submaximal eccentric actions at a stepping rate of 30 - 35 strides per min. A repeated measures ANOVA revealed significant (p < 0.05) increases from baseline for soreness (24 hr- 96 hr), tenderness (24 hr - 96 hr), and plasma creatine kinase activity (0.5 hr - 96 hr), and significant decreases (p < 0.05) in maximal voluntary isometric (approximately 25%) and isokinetic (-15%) strength (0.5 hr - 96 hr) post-walk for the exercised limb. The time course of observed changes in these markers was similar to that reported for EIMD models of the elbow flexors and knee extensors. However, the magnitude of muscle damage appeared more consistent with that demonstrated following submaximal eccentric exercise.