Zachary Conroy

Astronauts often suffer from reductions in cardiorespiratory and muscle endurance associated with microgravity. To combat these reductions in fitness, astronauts utilize fitness equipment on the International Space Station on longer stays at the station. Dietary supplementation in combination with exercise could further benefit astronauts, and recent evidence suggests vitamin D plays a critical role in increasing cardiorespiratory and muscle endurance by supporting cardiac and skeletal muscle function. Astronauts also get inadequate sunlight, so they commonly face Vitamin D deficiency. Our lab has previously found that Vitamin D supplementation enhanced muscle growth and strength in a mouse model of strength training, but it is unknown if vitamin D increases the volume of endurance exercise or enhances the cardiorespiratory/muscle endurance adaptations to the training. Endurance training often has greater impacts on cardiovascular and respiratory systems than strength training. Ultimately, investigating these impacts are important for the health of astronauts exposed to prolonged microgravity and vitamin D deficiency. We have hypothesized that vitamin D supplementation will positively impact the ability of the cardiorespiratory and muscular systems to effectively respond to endurance testing in mice. The success of this hypothesis will be assessed in several ways. Mice will be given access to running wheels as a model of endurance training, and changes in cardiorespiratory/muscle endurance will be measured via maximal treadmill tests. Lastly, cellular mechanisms contributing to the physical adaptations will be observed by measuring critical growth hormones, insulin-like growth hormone, and vascular endothelial growth factor in the heart and muscles with ELISA assays.