Non-invasive estimation of muscle fiber typology in various disciplines of professional cycling

INTRODUCTION: Classic muscle biopsy studies demonstrated that elite endurance athletes exhibit a high proportion of slow-twitch (ST) fibers, while elite sprinting athletes benefit from a predominant fast-twitch (FT) fiber profile (1). Muscle carnosine quantification by proton magnetic resonance spectroscopy (1H-MRS) was developed as a non-invasive method to estimate muscle fiber type composition (2). The validity was initially demonstrated in track-and-field, where muscle carnosine levels in elite athletes gradually decrease with increasing running distance discipline (2). Also in cycling, it is anticipated that the various disciplines span a range of muscle typology requirements, but solid data are scarce. Therefore, the aim of this study was to compare muscle carnosine levels between professional cyclists excelling in different cycling disciplines. METHODS: The muscle carnosine content of 29 male and 9 female elite Belgian cyclists (5 road climbers, 8 classic road cyclists, 3 road sprinters, 8 mountain bikers, 10 track-fond cyclists, 3 BMX riders and 1 track-sprint cyclist) was measured in the gastrocnemius medialis muscle by 1H-MRS on a 3-T whole body MRI scanner (Siemens Trio). Z-scores of muscle carnosine were calculated for each cyclist relative to a reference population with same age and sex (163 men, 112 women). Independent sample T-tests were used to compare the carnosine concentrations between the reference population and the different cycling disciplines. RESULTS: BMX riders (z=+1.61; range:+1,17 to +2.28; p=0.007) and the track-sprint athlete (z=+3.86) show higher carnosine levels compared to reference population, characteristic for a higher proportion of FT fibers. Road sprinters (z=-0.21; range:-0.41 to +0.11) and trackfond riders (z=-0.51; range:-1.64 to +0.89) have an intermediate profile, slightly below population average. Mountain bikers (z=-1.17; range:-2.05 to -0.14; p(men)=0.034; p(women)=0.048), classic road cyclists (z=-1.30; range:-2.24 to -0.55; p=0.001) and road climbers (z=-2.21; range:-2.57 to -1.78; p<0.001) exhibit significantly lower carnosine levels suggesting a higher proportion of ST fibers than population average. No sex differences were found in muscle profile within the same discipline. CONCLUSION: Prominent differences in muscle carnosine levels exist between elite cyclists of various disciplines, in line with the expectations and their respective functional demands. Road cyclists and mountain bikers display typical slow-twitch profile, whereas riders from BMX and track sprint have a dominant fast-twitch profile. The non-invasive character and the high intra-individual stability of the method open opportunities for application in cycling talent orientation. REFERENCES: 1. Gollnick, P. (1972). J. Appl. Physiol, 33, 312–319. 2. Baguet, A. (2011). PLoS One, 6, 1–6.

Jaar van publicatie:2019