Dynamics of indirect symptoms of skeletal muscle damage after stretch-shortening exercise

Healthy untrained men (age 20.4 ± 1.7 years, n = 20) volunteered to participate in an experiment in order to establish dynamics of indirect symptoms of skeletal muscle damage (ISMD) (decrease in maximal isometric voluntary contraction torque (MVCT) and torque evoked by electrostimulation at different frequencies and at different quadriceps muscle length, height (H) of drop jump (DJ), muscle soreness and creatine kinase (CK) activity in the blood) after 100 DJs from 0.75 m height performed with maximal intensity with an interval of 20 s between the jumps (stretch-shortening exercise, SSE). All ISMDs remained even 72 h after SSE (P < 0.01–0.001). The muscle experienced greater decrease (P < 0.01) in torque evoked by electrostimulation (at low stimulation frequencies and at short muscle length in particular) after SSE than neuromuscular performance (MVCT and H of DJ) which demonstrated secondary decrease (P < 0.01) in neuromuscular performance during the first 48 h after SSE. Within 24–72 h after the SSE the subjects felt an acute muscle pain (5–7 points approximately) and the CK activity in the blood was significantly increased up to 1200 IU/L (P < 0.001). A significant correlation between decrease in MVCT and H of DJ 24–48 h after SSE on the one hand and muscle soreness registered within 24–48 h after SSE on the other was observed, whereas correlation between the other indirect symptoms of skeletal muscle damage was not significant.