Why burpees and jumping rope?

No matter what, your body starts to lose strength as you age. Most people reach their strength peak around age 25, and some research shows marathon runners tend to be fastest at 28, though, of course, this is going to vary from person to person. If you started strength-training after 25 and hadn't before, your peak would come later.

But if you want to truly stay fit, you're going to need to keep building strength to combat your body's natural loss of muscle mass. It's worth it to do so, and it may be the thing that keeps you young longest. As Joyner wrote for Outside Magazine, "study after study is showing that simple tests of physical performance are highly predictive of future mortality." To achieve peak physical performance at any age, you need to go beyond endurance to build strength.

You can build strength in a lot of ways — lifting weights and adding intervals to endurance workouts both work. But these two workouts will build both your endurance and your strength, all at once.

"On hard days, I'll sometimes alternate a minute of burpees with sets using a weighted jump rope," Joyner tells us.

Ouch.

How to do these workoutsIt's worth starting slow with burpees, just to make sure you get the form right. If you start standing, you'll then squat down until you can put your hands on the ground. Kick back into plank position, do a push-up, then kick your legs back into your squat position. Then jump.

Here's a GIF to show you how it works, from this YouTube video by ScottHermanFitness:

This video by XHIT Daily on YouTube is also useful, showing burpees done with a wider stance, which can be more stable for someone not accustomed to the exercise.

Jumping rope with a weighted rope is obviously a more straightforward exercise. You can find a variety of recommended workouts, but generally (once you get up to speed), you'll want to do a series of sets, perhaps alternating with another exercise. If you're feeling tough, you can try alternating with burpees, like Joyner.

Just remember this, though: These workouts are going to be hard. It's great to push yourself, and there's plenty of research showing strong benefits for vigorous exercise. But it takes time to build up to these kinds of exercises (and practice to get them right), and you should talk to your doctor first if you're worried you might injure yourself.

Anyone who wants to attempts these intense workouts also needs to remember to rest. Most trainers recommend alternating between hard days and easy days.

"Make your hard days hard and your easy days easy," says Joyner. "Control your pace or it will control you."