Eccentric exercise slows in vivo microvascular reactivity during brief contractions in human skeletal muscle

Unaccustomed exercise involving eccentric contractions results in muscle soreness and an overall decline in muscle function, however little is known about the effects of eccentric exercise on microvascular reactivity in human skeletal muscle. Fourteen healthy men and women performed eccentric contractions of the dorsiflexor muscles in one leg, while the contralateral leg served as control. At baseline, 24h and 48h after eccentric exercise the following were acquired bilaterally in the tibialis anterior muscle: 1) transverse relaxation time (T2)-weighted magnetic resonance images to determine muscle cross-sectional area (mCSA) and T2, 2) blood oxygen level dependent (BOLD) images during and following brief, maximal voluntary contractions (MVC) to monitor the hyperemic responses with participants positioned supine in a 3T magnet, 3) muscle strength, and 4) pain pressure threshold. Compared with the control leg, eccentric exercise resulted in soreness, decline in strength (~20%), increased mCSA (~7%), and prolonged T2 (~7%) 24h and 48h (P<0.05). The BOLD response to a brief MVC was altered 24h and 48h after eccentric exercise, such that time-to-peak (~35%, P<0.05) and time-to-half-recovery (~23%, P<0.05) were prolonged. The altered contraction-induced hyperemic response suggests slowed microvascular reactivity and altered matching of O2 delivery to O2 utilization within muscle tissue showing signs of muscle damage. These changes in microvascular regulation after eccentric exercise may impede rapid adjustments in muscle blood flow at exercise onset and during activities involving brief bursts of muscle activation, which may impair O2 delivery and contribute to reduced muscle function after eccentric exercise.