Fitness experts say more is not always better and overworking a workout can sap strength and invite injury.

"We have fit people and deconditioned people who overdo it," says Geralyn Coopersmith, national director of the Equinox Fitness Training Institute.

"Exercise is like a drug, if you don't have enough, you get no benefits; if you have too much, you have problems," she says.

Among the common overuse injuries include shin splints, heel spurs and tendonitis.

Coopersmith says among the signs that you've overdone it are extreme fatigue, irritability, moodiness, an elevated resting heart rate, fever and an inability to work your earlier level.