Combination of running and energy restriction impairs bone parameters but does not inhibit endurance adaptations in fast-twitch muscle in young female rats

Low energy availability refers to a state where the body cannot provide sufficient energy to maintain essential physiological functions due to excessive exercise and inadequate energy intake. In athletes, low energy availability impairs bone parameters but may assist muscle adaptation from endurance training. This study was conducted to explore the effect of the combination of running and energy restriction (ER) on bone parameters and muscular endurance adaptations in young female rats. Seven-week-old female rats were divided into four groups: <i>1</i>) sedentary and ad libitum feeding (AL); <i>2</i>) voluntary wheel running and AL; <i>3</i>) sedentary and ER; and <i>4</i>) voluntary wheel running and ER. The experimental period was 11.5 wk. The ER groups were fed a 28% restricted diet compared with the sedentary and AL group. Our results demonstrated that the combination of running and ER decreased the body weight, uterus weight, plantaris and soleus muscle weight, bone mineral density of femur, tibia, and lumbar, and trabecular number of tibia. However, running increased the cross-sectional area (CSA) of type I and IIA fibers and the mitochondrial proteins levels in plantaris muscle under both AL and ER conditions. In the soleus muscle, running exerted no significant main effects on the transition to the myofiber type. ER did not affect the transition to the myofiber type and the mitochondrial protein levels in plantaris and soleus muscles. Our study reveals that the combination of running and ER impairs bone parameters; however, running induces endurance adaptations of plantaris muscle under both AL and ER conditions in young female rats.<b>NEW & NOTEWORTHY</b> Low energy availability impairs bone parameters but may assist muscle adaptation from endurance training. Our study demonstrated that the combination of running and energy restriction (ER) impaired bone mineral density and bone microarchitecture in young female rats. However, running increased the cross-sectional area of type I and IIA fibers, and the levels of mitochondrial proteins in plantaris muscle under both ad libitum feeding and ER conditions in young female rats.