I am a nightowl so getting enough sleep is always a challenge for me. Researchers have found that the less sleep the test subjects got, the higher their body mass index. The shorter sleep time altered the subjects hormone levels, energy decreased and appetite increased. And we already knew that decreased energy affects your workout performance. What's enough sleep? The general rule is 8 hours of sleep a night. Some may need more sleep or a little less than 8 hours. Don't sabotage your exercise program and weight loss efforts by not getting enough shut-eye.