A New Model for Non-invasive Estimation of Muscle Composition in Team Sport Athletes

Abstract

ABSTRACT: The fiber type composition of the athletes can be studied by muscle biopsy. However, it is an invasive, thus discouraged procedure. We standardized a method to non-invasively estimate the area occupied by type II fibers (FTII) in the vastus lateralis muscle (VLM) based on the quantification of intramuscular carnosine by proton magnetic resonance spectroscopy (1H MRS). Carnosine is enriched in FTII in athletes.

PURPOSE: To develop a simple and easy-to-apply model for estimating muscle fiber types composition in team sports athletes using 1H MRS as gold standard.

METHODS: Cross-sectional study with 51 high-performance, young athletes (20.6 ± 2.9 years, 58% women), of team sports (26% handball, 22% basketball, 22% floor volleyball, 18% softball, 8% beach volleyball, 6% indoor soccer). The area occupied by FTII in the VLM was estimated by quantifying carnosine by 1H MRS in a 3 T scanner using a surface coil. Field tests (speed, jump, maximum oxygen uptake), anthropometric measurements and demographic variables were obtained. A multiple linear regression model was built based on biological plausibility and Hosmer-Lemeshow criterion. The model with the highest R2 and the lowest value of the Akaike Information Criterion was selected. The assumptions of normal distribution of the errors were verified using the Shapiro-Wilk test, homoscedasticity with the Breusch-Pagan test, and non-correlation with Durbin-Watson d statistic.

RESULTS: The population had an FTII of 32.9 ± 8.9%, speed of 7.3 ± 0.5 m/s, counter movement jump (cmj) of 34.0 ± 7.3 cm and body fat percentage of 16.7 ± 6.3%. Men had a higher FTII (38.3 ± 8.8%) than women (29.1 ± 6.9%) (p < 0.001). A significant correlation of the FTII with speed (r = 0.528; p < 0.001), cmj (r = 0.509; p < 0.001) and body fat percentage (r = -0.335; p = 0.019) was found. The model complied with the assumptions and has a predictive scope: FTII (%) = 3.04 + 2.30*(speed in m/s) + 0.56*(cmj in cm) + 0.58*(body fat in %)-0.92*(age in years) + 7.68*(sex; male = 1; female = 0).

CONCLUSION: The selected independent variables explained by 42% the variability of the area occupied by FTII in team sport athletes. This new model for estimating the composition of skeletal muscle fibers depends on field tests, anthropometric measurements and demographic variables that are very easy to obtain in clinical practice.