<Li> In the 1990s Billy Blanks's Tae Bo helped popularize cardio - boxing workouts that incorporated martial arts movements </Li> <Ul> <Li> Stair climbing </Li> <Li> Elliptical trainer </Li> <Li> Indoor rower </Li> <Li> Stairmaster </Li> <Li> Stationary bicycle </Li> <Li> Treadmill </Li> <Li> Aerobic gymnastics </Li> </Ul> <Ul> <Li> Walking </Li> <Li> Cycling </Li> <Li> Running </Li> <Li> Cross-country skiing </Li> <Li> Cross-country running </Li> <Li> Nordic walking </Li> <Li> Inline skating </Li> <Li> Rowing </Li> </Ul> <Ul> <Li> Swimming </Li> <Li> Kickboxing </Li> <Li> Skipping rope or jump rope </Li> <Li> Circuit training </Li> <Li> Jumping jacks </Li> <Li> Water aerobics </Li> <Li> Jogging </Li> </Ul>

Which of the following activities requires the highest level of aerobic fitness