Are you an animal at the gym? Do you push yourself to your physical limits, to the point where it feels like even your teeth are sweating? If so, that's fantastic. But are you still not seeing the gains you've been hoping for? Now for my follow up question: Are you sleeping at night? Because if you're not, it may be what's holding you back.

Researchers at Midwestern State University found that maintaining a sleep debt may impede your fitness progress. This makes sense for many reasons, chief among them being that most muscle repair and growth takes place while we're at rest. So, if you're not sleeping enough, you're not giving your body the time it needs to respond to your hard work.

In the study, male volunteers were kept awake for a full 24 hours and then completed a gym workout. While they were able to finish without any issues, the typical post-workout testosterone spike did not occur. Moreover, researchers posit that a lack of sleep may actually cause testosterone levels to fall over time.