Final answer:
The independent variable in this study is the type of intervention the participants received - high-intensity interval cardiovascular training (HICT) or no exercise training.
Step-by-step explanation:
The independent variable in this study is the type of intervention the participants received. The two groups were randomly assigned, with one group receiving high-intensity interval cardiovascular training (HICT) three times a week for 8 weeks, and the other group serving as a control group, receiving no exercise training. The researchers wanted to investigate the effects of the HICT intervention on sleep and mental health in inactive college students.