Non-Invasive Method on Slow-Twitch Quadriceps Muscle Fibers Dominate a High Level of Fitness

Abstract

Abstract: Previous studies have proved that there is a linear correlation between VO2max and slow-twitch fibers in athletes. These studies were done using biopsy, the invasive method, to estimate the muscle fiber type. There is also a non-invasive method, which is convenient to use and not conflicted by ethical law in Indonesia. However, further study regarding muscle fiber shifting and its correlation with the level of fitness using a non-invasive method to estimate muscle fiber is still lacking. This research aims to determine the distribution and correlation between level of fitness and muscle fiber type in non-athletes estimated by a non-invasive method. Muscle fiber type in the quadriceps muscle group and level of fitness were determined in 33 untrained male students with an average age of 20.5 y.o. Muscle fiber type was determined by a non-invasive method by counting the maximal repetition with 80% 1RM weight. The level of fitness was determined a week later by the Astrand ergoc ycle method. The slow-twitch muscle fibers dominated a high fitness level (p=0.002). However, the correlation test between muscle fiber types and fitness level was not significant (p=0.551). This result showed that a high fitness level, which has a higher oxygen consumption, has numerous slow-twitch muscle fibers. It is rich in myoglobin delivering oxygen to maintain the aerobic activity. Yet there is no correlation between the level of fitness and muscle fiber type as estimated by a non-invasive method in quadriceps. Further studies are needed to analyze several factors that may contribute to it.