This study aims to investigate the effects of different exercise time (ET) on energy consumption and physical fitness of adolescents at 60% THR exercise intensity.

  Method:  146 healthy pupils were divided into low (LET), middle (MET), and high (HET) ET groups, along with a control group (CET).The exercise intensity and energy consumption of these groups were respectively assessed using Polar Team OH1 and ActiGraph wGT3X-BT triaxial accelerometers.

  Results:  After modeling energy consumption patterns with these four ET groups, this study concludes that there were no statistically significant main effect of periods or interaction effect of "periods×group".The interaction effect of "energy consumption×group", however, did prove to be statistically significant.The main effect, in BMI changes, as well as improvement in the shuttle run, the 50 meter dash, and the sit and reach test, was statistically significant.Lastly, the interaction effect of "gender×group" on the improvement of lung capacity and rope skipping ability was statistically significant.There were no statistically significant differences in "group×gender" or groups or gender in sit-up test performance.

  Conclusions:  The combination of 60% THR exercise intensity and 36% 74% ET is the minimum threshold for maintaining basic bodily fitness for adolescents; and 55% 74% ET is the minimum threshold for BMI decline and skipping rope improvement (however, this does not apply to males) among females; 75% ET is the minimum necessary to promote bodily fitness and the overall improvement of exercise capacity.