Plasma α-Actin as an Early Marker of Muscle Damage After Repeated Bouts of Eccentric Cycling

Purpose: This study aimed to examine the changes in skeletal muscle (SM) alpha-actin, myoglobin (Mb) and hydroxyproline (HP) in plasma and other indirect markers of muscle damage after repeated bouts of eccentric cycling. Methods: Ten healthy men (23.3 +/- 2.8 years) performed two 30-min eccentric cycling bouts at 100% of maximal concentric power output (230.7 +/- 36.9 W) separated by 2 weeks (ECC1 and ECC2). Maximal voluntary isometric contraction (MVIC) peak force of the knee extensor muscles, muscle soreness (SOR), pain pressure threshold (PPT) and plasma levels of SM alpha-actin, Mb, and HP were measured before, 0.5, 3, 24-168 h after each cycling bout. Results: MVIC peak force decreased on average 10.7 +/- 13.1% more after ECC1 than ECC2. SOR was 80% greater and PPT was 12-14% lower after ECC1 than ECC2. Plasma SM alpha-actin levels increased at 0.5, 3, and 24-72 h after ECC1 (26.1-47.9%), and SM alpha-actin levels at 24 h after ECC1 were associated with muscle strength loss (r = -0.56, P = .04) and SOR (r = 0.88, P = .001). Mb levels increased at 0.5, 3, and 24 h after ECC1 (200-502%). However, Mb levels at 24 h after ECC1were not associated with muscle strength loss and SOR. HP levels remained unchanged after ECC1. ECC2 did not increase SM alpha-actin, Mb and HP levels. Conclusion: Our results indicate that alpha-actin could be used as a potential marker for the early identification of SM damage due to its early appearance in plasma and its association with other indirect markers of muscle damage.

Automated summary

This study examined the changes in markers of muscle damage after repeated bouts of eccentric cycling. The results suggest that alpha-actin could be a potential marker for the early identification of muscle damage.