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

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.

KEYWORDS:

• Delayed onset muscle soreness
• lengthening contractions
• oxygen consumption
• repeated bout effect

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

PO_max = concentric maximal power output

PPT = pain pressure threshold

VO_2peak = 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.

Additional information

Funding

This work has been funded as part of the research grant FONDECYT 11150293 from CONICYT, Chile, and from an internal institutional grant from Universidad Finis Terrae.