Non-invasive Estimation Of Muscle Fiber Type Composition In Elite Athletes

Abstract

It has been established that excellence in sports with short and long exercise duration requires a high proportion of fast and slow twitch muscle fibers, respectively. Until today, the muscle biopsy method is still accepted as gold standard to measure muscle fiber type composition. Because of the invasive nature and high sampling variance of a muscle biopsy, it would be useful to develop a non-invasive alternative, which can be used as a tool for talent identification. PURPOSE: To develop a new and non-invasive estimation method of the fiber type composition in human muscles, based on proton magnetic resonance spectroscopy (1H-MRS) measurement of muscle carnosine content, a typical fast twitch metabolite. METHODS: A total of 160 healthy subjects volunteered to participate in this cross-sectional study. The 4 subgroups consisted of 83 untrained control subjects (47 males and 36 females), 12 talented young male track-and-field athletes, 51 active elite athletes (40 males and 11 females) and 14 male ex-athletes. The carnosine content was measured in the gastrocnemius medialis muscle by 1H-MRS. RESULTS: The muscle carnosine content was ∼30 % higher in explosive athletes (6.58 ± 0.92 mM), such as sprint runners, compared to a reference population (4.94 ± 1.43 mM), whereas it was ∼20 % lower than normal in typical endurance athletes (3.98 ± 0.64 mM), such as 3,000-marathon runners. Decathletes showed intermediate carnosine levels (5.32 ± 0.72 mM). When active elite runners were ranked according to their best running distance, a negative sigmoidal curve (R2=0.9874) was found between the logarithm of running distance and muscle carnosine content. Noteworthy is that the muscle carnosine concentration remained significantly different between ex-sprinters and ex-endurance athletes (5.11 ± 1.07 vs. 3.61 ± 0.81 mM; p=0.012), who had discontinued training for many years already. Moreover, a similar difference was observed in young talents between explosive (7.04 ± 2.49 mM) and endurance (4.90 ± 0.93 mM) athletes. This suggests that the muscle carnosine content is probably genetically determined. CONCLUSION:1H-MRS based muscle carnosine quantification is a new non-invasive method for the estimation of muscle fiber type composition. Supported by Research Foundation - Flanders (FWO 1.5.149.08)