Muscular strength is a measure of how much force a muscle can exert in a single effort, while muscle endurance describes the ability of muscles to contract repeatedly over time. Muscle strength and endurance develop together: that is, building muscle strength also helps build endurance and vice versa. However, some exercises and activities are best for developing muscle strength and others for muscle endurance. Both muscular strength and endurance are important components of health-related fitness.
Overtraining or staleness occurs when an athlete ignores the signs of overreaching and continues to train. Many athletes believe that weakness or poor performance signals the need for even harder training. So, they continue to push themselves. This only breaks down the body further.