What happens to your muscles after lifting weights?
Before a muscle can grow stronger, it will incur microscopic damage in the course of a difficult workout or resistance training. The process of healing can last a week or longer and possibly overlap with the next workout. The type of soreness and pain you feel is an important aspect that will help you judge how to continue your workout.
During a workout, intense lifting causes microscopic tears to form in the fiber and connective tissue of muscles. These tears fatigue the muscles and accumulate in large number. With proper rest and sufficient nutrients the muscles are slowly rebuilt over the following days, but full repair can take a week or more. For healing and growth, it is essential to eat a meal of carbohydrates, protein and some fat immediately after a workout.
The ability of the body to rebuild its muscles also increases size, strength and muscle capacity. Ordinarily old tissue is discarded before new tissue is synthesized. The digestion of protein provides the raw material that can be used to synthesize new muscle.