You may be lifting weights, doing bodyweight exercises, running on the roads and trails or the treadmill, pedaling your heart out, stepping endlessly on some cardio machine… even if you're doing all of this training, you may still be missing out.

Truth is, after our teens or early twenties, most of us quit doing high intensity sprinting and jumping. This is a huge mistake. Here's why:

You see, there are actually 3 different types of muscle fiber in your body. The first is slow-twitch or Type I and it makes up about 40% of your total muscle tissue.

The other two types are both fast twitch fibers and together make up about 60%. Type IIa is just called fast-twitch. Type IIx is called super-fast.

Now here's the scoop. When you stop doing fast, explosive type training, you lose fast twitch muscle fiber. If you're not doing this type of training, up to 60% of you muscle tissue is being ignored. Ouch.

Even if you do slow cardio, long distance running, non-explosive strength training, etc. you're only maintaining the other 40%. You're letting the other 50 or 60 percent literally waste away.

So, how can you avoid this atrophy?

Well, the good news is that you can stop the loss of muscle tissue - and even gain it back. Yes, actually reverse the muscle loss.

And the best way to do it is to run sprints (to develop Type IIx muscle) and do explosive plyometric type movements (to get back your Type IIa)

But, wait you say... aren't sprinters ignoring the slow-twitch 40%? Well, it turns out that they're not. Studies show that sprinters generally have more overall muscle (including slow twitch) and a much higher percentage of super-fast twitch. Doesn't seem like their training is creating fast twitch fibers at the expense of slow twitch.

So, when you're ready to get back to working your fast fibers, increase your intensity gradually so you don't put yourself at risk for injury. But, if you do it smart, you can boost your fast twitch muscle tissue (and ultimately your total muscle tissue) no matter what your age or what shape you're currently in.

And remember, more muscle tissue also means a higher metabolism... you'll be burning more calories and fat - even when you're just sitting around.

Anyway, if you've been ignoring a large part of your muscle by avoiding high intensity exercise, then I'm sure this advice won't fall on deaf ears. Start getting your muscle back NOW. Reverse the old-aging and the middle-aging processes. Get jumping and sprinting right now.