Relationship between Force and Histological Changes in Mouse Anterior Crural Muscles Following Eccentric Exercise

The purpose of this study was to determine the relationship between mononuclear cell number and maximal isometric force (Po) following active lengthening exercise. The tibialis anterior muscles (TA) of mice were actively lengthened 120 times from a dorsiflexed to plantarflexed position in 300 ms while stimulating the peroneal nerve (100 Hz, 310 ms). Po at 150 Hz was measured immediately before and after,10 min, 3 and 10 days after exercise and the total number of mononuclear cells per field of view (MN) for the TA muscles were counted. Po declined to 55% of the baseline value both immediately and 10 min after exercise, declined further to 25% at 3 days, and was still significantly reduced at 10 days following exercise. TA muscles at 3 and 10 days post-exercise showed marked increases in MN, however, the only significant relationship between Po and MN was at 3 days following exercise (r = -0.64). The results of this study do not support the use of Po following active lengthening exercise to either predict the extent of subsequent injury, or estimate the concurrent degree of histological damage.