Ah, the push-up. While lunges are a unilateral exercise, push-ups are a compound exercise. Compound exercises use several muscle groups at once. This classic move engages your core, biceps, triceps, deltoids, and lower body—and that’s just to keep you stabilized. Using this many muscle groups at once causes your heart to work harder to get oxygen-rich blood to your muscles. So, in short, push-ups can also be a form of cardiovascular exercise that increases heart health.
Most people find they can't do a full minute of press-ups without their muscles giving in to begin with. If your muscles fail on you, don't think of it as a point of no return. Instead, take a moment to rest and continue with the exercise for as long as possible, just as you did the abdominal plank. Bit by bit, you'll find your press-up stamina improving.

The skin also serves as a release point for heat. (See “Why Does My Face Turn Red When I Exercise?” for more on that.) When you exercise, your muscles generate a lot of heat, which you have to give up to the environment so your body temperature doesn’t get too high, Hackney says. The heat in the muscle transfers to the blood, which shuttles it to the skin; it can then escape into the atmosphere.