ABSTRACT
Purpose: This study aimed to examine the changes in skeletal muscle (SM) α-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 α-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 α-actin levels increased at 0.5, 3, and 24–72 h after ECC1 (26.1–47.9%), and SM α-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 α-actin, Mb and HP levels. Conclusion: Our results indicate that α-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.
Abbreviations
MVIC = maximal voluntary isometric contraction
DOMS = delayed-onset muscle soreness
RBE = repeated bout effect
CK = creatine kinase
Mb = myoglobin
SM = skeletal muscle
HP = hydroxyproline
HL = hydroxylysine
ECC1 = initial eccentric cycling bout
ECC2 = secondary eccentric cycling bout
POmax = concentric maximal power output
PPT = pain pressure threshold
VO2peak = peak oxygen consumption
Rpm = revolutions per minute
VAS = visual analogue scale
VM = vastus medialis
VL = vastus lateralis
ASIS = anterior superior iliac spine
RF = rectus femoris
EDTA = Ethylenediaminetetraacetic acid
ELISA = enzyme-linked immunosorbent assays
Acknowledgments
We would like to thank the Functional Molecular Biology Laboratory and Dr. Keith Baar from the University of California, Davis, for their assistance in HP analysis.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Availability of data and material
Data is available upon request.
IRB approval
This study was approved by the Universidad Finis Terrae Ethics Committee.