The purpose of this study is to reinterpret the significance of insulin which stimulates production and secretion of leptin, and to check the effects of thermal loading on the stimulation. This study was conducted targeting women in their late thirties who have engaged in tennis club activities on a regular basis for more than two years (age, 37.93±4.53yrs; height, 162.23±4.44㎝; weight, 52.85±4.41㎏). After taking half baths for 30 minutes in hot water of 41℃ to apply thermal loads, the subjects were observed the changes in levels of insulin, glucose, and free fatty acid (FFA) in the blood. The result showed that insulin levels in the blood were increased significantly after thermal loading (P<.01), which means that it is possible to prevent obesity by controlling NPY, one of orexigenic peptides. Also, it seems that significant increase of the levels of glucose (P<.05), FFA (P<.01) and significant decrease weight (p<.001) were caused by hyperfunction of sympathetic nervous system, it is expected that this phenomenon would be effective in improving metabolic rates. Although there are some restrictions in this study as it was conducted targeting females participating in tennis training for a long time, it is determined that the result could be applied positively for subjects with limited physical activities caused by musculoskeletal system disorders, joint damages, and so forth, to prevent or improve obesity.