Impact of heat therapy on skeletal muscle structure and function

Skeletal muscle occupies approximately 40 to 50 percent of body mass and is responsible for respiration, postural control, and locomotion and plays a pivotal role in regulating glucose, lipid, and protein metabolism. Acute muscle trauma and chronic disease conditions such as muscular dystrophies are associated with structural abnormalities, enhanced fatigability and impaired metabolism and consequently lead to exercise intolerance and poor quality of life. Despite the clinical importance and a number of studies on the treatment of muscle damage, few modalities have shown to elicit beneficial effects. Heat treatment has been used for a long time to treat soft tissue injuries in the field of physical therapy and sports medicine. However, the underlying mechanisms by which heat treatment accelerates muscle recovery following injury are not clear.

The primary aim of my dissertation studies was to determine the impact of heat therapy on skeletal muscle structure and function in humans and animals. In Chapter 2, we report that a single session of local heat treatment promotes the expression of angiogenic and myogeneic mediators including vascular endothelial growth factor (VEGF) and angiopoietin 1(ANGPT1) in healthy human skeletal muscle. In Chapter 3, we report repeated exposure to heat therapy stimulates factors involved in muscle repair process and accelerates functional recovery from exercise-induced muscle damage. In Chapter 4, we show that 8 weeks of local heat therapy improves muscle strength of knee extensor and increases skeletal muscle capillarization in type II muscle fibers. In Chapter 5, we describe the effects of heat therapy in a mouse model of ischemia induced-muscle damage. Animals that were exposed to heat therapy at 39°C had improved maximal absolute force and relative muscle mass in the soleus muscle. These observations reveal that the beneficial effects of heat therapy are muscle fiber type specific and dependent on the treatment temperature. In Chapter 6, we review and summarize the outcomes described in Chapters 2-5 and provide a general conclusion as well the clinical implications of our findings.