What Happens to 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.

Row of weights (Image: jdwfoto/iStock/Getty Images)

Microscopic Tears

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.

Rebuilt Muscles

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.


The soreness that occurs 24 to 72 hours or more after workouts was once believed to occur from the buildup of lactic acid, which the muscles produce as they use energy, but it is now believed that the soreness is the direct result of muscle tearing. This soreness is known as delayed onset muscle soreness, or DOMS for short.

Types of Pain

DOMS can potentially cause stiffness, swelling, strength loss and pain. This is different from the burn of a workout or the deep lingering pain of an injury which may prevent basic activity or routine tasks. Injuries can be the product of over-worked muscles and large, unhealthy tears. DOMS, on the other hand, is a sign of progress and proper weight training.


The most painful soreness occurs frequently in veterans who begin a new routine, or in beginners. In other words, the most significant number of healthy and productive tears will usually form in a muscle that is not fully acclimated to the intense training of a strenuous workout. With enough training the muscle will gain endurance, but your training should always remain one step ahead of a comfortable workout and quick, painless recovery.

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