Variation in cycling exercise mechanical efficiency in the <scp>HERITAGE</scp> Family Study

The objectives of the study were to assess the effects of cycling endurance exercise training and sex on cycling exercise mechanical efficiency (ME) and to explore its associations with body composition, glycemic profile, and skeletal muscle characteristics. Subjects were males (n = 371) and females (n = 465) of European (ED) and African descent (AD) of the HERITAGE Family Study. The measurements were repeated after a 20-week controlled endurance exercise program. A substudy involving 78 participants from 19 ED families was used to evaluate associations between skeletal muscle traits and variations in ME. An increase in ME of 4%-5% was induced by training and was comparable between sexes. Higher values of ME were associated with reduced body weight and fatness and fasting plasma glucose and insulin, both before and following endurance training, independently of cardiorespiratory fitness. There was no association between muscle fiber type or capillarity and ME. There was also no consistent muscle glycolysis and oxidative enzymatic profile associated with ME. The results of this study show that cycling exercise ME is trainable in nonathletes. ME variations in the sedentary state and in response to an exercise training program are associated with favorable body composition and glycemic profiles. Further research is needed to better understand its biological determinants.