To Örebro University

Introduction: It is well-established that regular exercise training alters the characteristics of skeletal muscle. Thus, this cross-sectional study reports the skeletal muscle characteristics of long-term trained (>15 years) endurance- (ET) and strength (ST) athletes compared with healthy controls (C). The aim was to compare fiber cross-sectional area (CSA), citrate synthase activity (CS), myonuclei content and myosin heavy chain (MyHC)-proportions between groups.

Materials and methods: A total of twenty-three male subjects (41.7 ± 4.2 years) qualified for the study based on self-reported activity and performance testing. Performance testing consisted of a VO2peak test and a maximal isokinetic knee extension test. Skeletal muscle characteristics were assessed from muscle biopsies using immunohistochemistry, an enzymatic activity-assay and a polyacrylamide separation gel. Muscle biopsies were taken from the m. vastus lateralis at rest.

Results: ST men had higher myonuclei content and a larger fiber CSA compared with C. ET subjects demonstrated a higher CS-activity compared with both C and ST. However, no differences were found in CS-activity between C and ST subjects. Finally, ET subjects demonstrated a significantly higher proportion of the MyHC I-isoform compared with C and ST. However, C subjects displayed a higher proportion of MyHC IIx compared with ET and ST.

Conclusion:We show that endurance-trained individuals display a great oxidative capacity, demonstrated by enhanced CS-activity, higher proportion of slow myosin heavy chain content and greater VO2peak. Additionally, we conclude that the greater strength output in strength-trained individuals compared with control is related to larger fiber CSA and higher myonuclei content.