Student: Mckenzie Temperly, Undergraduate Student in Health Sciences, Drake University
Research Mentor: Dr. Kimberly Huey
Effects of Vitamin D Supplementation on Muscular and Cardiorespiratory Adaptations to Strength and Endurance Training in Mice
Astronauts’ health is significantly threatened due to the negative consequential effects of being subjected to a microgravity environment, especially as mission durations increase and future explorations to Mars are developed. The adverse outcomes are associated with reductions in muscle strength and cardiorespiratory fitness, which are further enhanced because of the increased likelihood of astronauts having a vitamin D deficiency. This is because these individuals receive inadequate sunlight exposure and undergo changes in their nutritional diet. Ultimately, performing simple tasks when returning to the Earth’s surface become much more difficult. To promote overall muscle health and cardiorespiratory fitness, individuals concurrently perform both strength and endurance exercise. Recent evidence has suggested vitamin D stimulates muscle growth and supports optimal muscle function and cardiorespiratory fitness. Previously, our laboratory reported vitamin D supplementation enhanced muscle growth in a mouse model of strength training. However, it is unknown as to whether the benefits of vitamin D increase in combination with concurrent exercise training as compared to strength training alone. This project aims to determine whether vitamin D supplementation positively impacts the ability of skeletal muscle and the cardiorespiratory system to effectively respond to concurrent training. In order to mimic strength training, the mice undergo functional overload surgery, in which the gastrocnemius and soleus are removed to overload the plantaris muscle resulting in muscle growth and increased strength. The mice then also have access to a running wheel, or they remain sedentary while receiving either a daily placebo or vitamin D injection for two weeks. Changes in cardiorespiratory endurance are being evaluated through differences in maximal treadmill test times from pre to post-concurrent training. Afterward, the plantaris is tested for strength and fatigue using a dual-mode footplate system to measure plantar flexor force. Following muscle testing, muscle tissues are isolated for cellular ELISA assays to measure levels of several growth factors and contractile proteins, such as insulin-like growth hormone (IGF-1), fibroblast growth factor (FGF), and vascular endothelial growth factor (VEGF). The results from this project may be useful for developing training programs and supplementation therapies for astronauts prior, during, and post-mission to prevent muscular atrophy.