Short vs. long length of rectus femoris during eccentric exercise in relation to muscle damage in healthy males

BACKGROUND: We investigated the effects of short vs. long length of rectus femoris during eccentric exercise of similar range of motion on selected muscle damage indicators. METHODS: Using an isokinetic dynamometer at 1.05 rad/s, 12 healthy male [mean (standard deviation), 21 (2) years] volunteers randomly underwent two exercise sessions, one on each leg, 14 days apart. During each session, subjects had to accomplish 12 sets of 10 maximal voluntary efforts in seated and prone positions to achieve short and long length of rectus femoris, respectively. Muscle damage indicators [serum creatine kinase activity, delayed onset muscle soreness, range of motion, eccentric peak torque, concentric peak torque and isometric peak torque] were assessed pre-exercise and 24, 48, 72 as well as 96 h post-exercise. FINDINGS: Compared to baseline data, creatine kinase, delayed onset muscle soreness, and range of motion disclosed significant changes at all time points after both exercise sessions (P<0.05). However, these muscle damage indicators demonstrated greater changes following exercise at short compared to long length of rectus femoris (P<0.05). Torque assessments also revealed that nine out of 12 and only two out of 12 measurements decreased significantly following short and long length eccentric exercise of rectus femoris, respectively (P<0.05). Short length eccentric exercise resulted in greater torque declines compared to long length during concentric and isometric evaluations (P<0.05). No such differences were observed when torque changes were evaluated eccentrically. INTERPRETATION: Short length of rectus femoris eccentric exercise induces greater muscle damage and peak torque declines than the corresponding long length in healthy adults.