2. Arms: Modified push-up
3 x 10 reps, 15 seconds rest between sets

Kneel on hands and knees, and then walk hands forward until they are placed directly beneath the shoulders, with the body in a straight line from shoulders to knees. With hands facing forwards, bend elbows to the side and lower the body until it's almost touching the ground. Ensure the back stays in a straight line by gently squeezing your bottom together, and stopping your chest from sagging. Press to straighten the arms back to the starting position. Repeat.

Why it works: This activity is easier than a traditional push-up, which means you can do more sets for longer endurance and longer heart rate elevation. It's also less strain on the back, which is good for injury prevention, while still working some of the major muscles of the chest and arms.