Detraining after tumor-bearing accelerates tumor growth while continuous training decreases tumor growth in mice

Objective:Previous studies have shown that exercise suppresses tumor growth.However,the effects of exercise with different intensities and exercise detraining after tumor-bearing on tumor progression remain unclear.The purpose of this study was to investigate the effects of continuous and disrupted free and exhausted swimming training after tumor-bearing on tumor progression in melanoma B16-F10-bearing C57BL/6 mice.Methods:C57BL/6 mice were subjected to free or exhausted swimming exercise training for 4 weeks prior to the injection of melanoma B16-F10 cells.Subsequently,the B16-F10-bearing mice were maintained with training consisting of free or exhausted swimming or without exercise for 2 weeks during the tumor challenge.Results:The tumor weight was increased by 42%and 109%in mice with 4-week exhausted swimming prior to B16-F10 tumor cells inoculation followed by 2-week training cessation compared with the tumor-bearing control(P<.05)and continuous training groups(P<.01).Tumor weights in groups with exercise detraining after tumor cell inoculation tended to be increased,while the proliferation of splenic T lymphocytes tended to be decreased compared with the group that maintained exercise intensity.After 6-weeks continuous free or exhausted swimming training,the tumor weight of mice was decreased and the proliferation of splenic T lymphocytes was increased compared with the tumor-bearing control group.The frequency of natural killer cells in tumors was increased in all exercise training groups of mice.Conclusions:These results suggest that maintaining exercise intensity after tumor-bearing slows tumor growth in mice,possibly because of the enhanced proliferative activity of splenic lymphocytes rather than natural killer cell infiltration.However,detraining after tumor-bearing might accelerate tumor progression because of the reduced proliferation of splenic T lymphocytes.