Skeletal muscle fiber-type distribution and habitual physical activity in daily life

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The capacity to perform physical activity largely depends on physical fitness. Muscle fiber-type distribution (MuscleFTD) is associated with physical fitness and may influence the capacity to perform physical activity. The purpose of this study was to determine whether habitual physical activity in daily life (PADL) and MuscleFTD are related. Thirty-eight healthy non-athletes (31 women, 7 men) were recruited. PADL was measured twice for 14 days using a tri-axial accelerometer for movement registration (Tracmor). From Tracmor output, the proportion of time subjects were physically active at low, moderate, and high intensities was determined (%Low, %Moderate, and %High, respectively). A total activity index (PAindex) and sub-scores on work, leisure-time and sports were obtained using the Baecke questionnaire. MuscleFTD was determined using immuno-fluorescence against respective myosin heavy chain isoforms. No relationship was observed between PADL and MuscleFTD. %Low, %Moderate, and %High, as well as PAindex and its sub-scores, were not related to MuscleFTD either. The time spent on sports was associated with the proportion of type I and IIX fibers (P=0.06 andP<0.01, respectively). In conclusion, MuscleFTD probably cannot explain why some people are more prone to engaging in physical activities than others.

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