Aerobic exercise is a type of physical activity that increases the heart rate and breathing rate to improve cardiovascular fitness. Isometric exercise is a type of strength training in which the joint angle and muscle length do not change during contraction. Situps are a type of abdominal exercise that involve lying on the back with the knees bent and lifting the upper body towards the knees. All three of these exercises are types of physical activity that can help improve overall health and fitness.