Effects of Force and Repetition on Inflammation due to Eccentric Muscle Contractions

Abstract

Recent evidence strongly suggests that force and repetition interact in a consistent manner to affect musculoskeletal disorder (MSD) risk, likely due to an underlying fatigue failure process in affected tissues. This pilot study evaluated whether a force-repetition interaction was present with respect to inflammatory responses of elbow flexor muscles after eccentric exercise. 24 subjects performed eccentric contractions with 6 assigned to each of the following groups: low-force, low-repetition (LFLR), low-force, high-repetition (LFHR), high-force, low-repetition (HFLR) or high-force, high-repetition (HFHR). High- and low-force eccentric contractions were set 120% and 60% of maximum isometric capacity, respectively. Low and high repetition rates were defined as two and eight repetitions/set. A baseline magnetic resonance image (MRI) was taken of their non-dominant arm prior to the eccentric exercise, as were relaxed elbow angle and maximum isometric strength. Dependent measures included MRI data on edema in the muscle (day 2 versus day 0), and relaxed elbow flexion angle and isometric strength (obtained days 0, 1, 2, 4, and 8 post-exercise). Significant force-repetition interactions were found for relaxed elbow angle at days 2 and 4 post-exercise (p < 0.05), and for days 2 and 4 for isometric strength (p < 0.05). MRI data demonstrated a non-significant force-repetition interaction (p > 0.05), but a tendency towards the expected interaction pattern.