Variability in Estimating Eccentric Contraction-Induced Muscle Damage and Inflammation in Humans

Abstract

We studied five young healthy volunteers who performed a "damage protocol" consisting of 240 (24 sets x 10 repetitions/set) maximal isokinetic eccentric muscle contractions (30°/s) on each leg one week apart. Biopsies were taken from the vastus lateralis on two occasions. Two biopsies were taken from within the same muscle 24 h following the damage protocol. On a second occasion a single biopsy was taken from the contralateral leg at 24 h following the same damage protocol. Biopsies at all three sites showed Z-band disruption, much greater (i.e., ∼14-fold) than is typically observed in resting biopsies, with no significant differences (ANOVA) according to site location (within legs or between legs). The within-leg coefficient of variation (CV) was, however, 41 ± 30%, and the between-leg CVs were 57 ± 36% and 68 ± 36%. Macrophage cells were also detected within the muscle, and cell numbers were not statistically different between biopsy sites. However, the within-biopsy CV = 52 ± 19% and the between-biopsy CVs of 34 ± 24% and 48 ± 27%. We conclude that eccentric contraction-induced Z-band streaming and inflammatory cell response, as detected in muscle biopsy samples from humans, is highly variable with a CV of 40-70%. Key words: muscle damage; eccentric exercise; biopsy; coefficient of variation