What Happens to Your Muscles When You Lift Weights?

Lifting weights improves strength and increases muscle density.
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Lifting weights is a common form of strength training, but when lifting you may find yourself wondering exactly how your reps translate to muscle development and toning. Understanding what happens to your muscles when you lift weights not only gives you an idea of how muscle development occurs but also explains some of the pains and risks associated with lifting.

Muscle Damage

    Lifting weights and performing other strenuous exercise causes microscopic tears and other damage in the tissue of your muscles. Though it might sound like a reason for concern, this damage is actually a key component of muscle development. The damage that your muscles receive while lifting weights triggers the healing process and also prompts the body to try and adapt itself to prevent this type of damage in the future.

Muscle Fiber Growth

    As your body heals the damage that lifting weights caused in your muscles, specialized cells known as satellite cells begin fusing together and attach themselves to the damaged tissue to promote the healing process. These satellite cells begin fusing with the muscle fibers themselves, increasing their cross-section thickness. Eventually these fused cells transition into new protein strands within the fibers, and components of the cells are used by the muscles to create additional strands as well. These strands increase both the size and the strength of the muscle fibers, resulting in the increase in muscle mass and muscular strength that you experience when lifting weights regularly.

Lactic Acid Buildup

    When you lift weights or perform other strenuous exercise, lactic acid starts building up in your muscles. While lactic acid was once believed to be a waste product that was detrimental to the muscles, more modern research performed by Dr. George Brooks and others has found lactic acid to actually be beneficial during exercise. The muscles use lactic acid as fuel during your workout, burning it to produce energy when they need more energy than they can produce through standard cellular respiration.

The Pump

    As you lift weights, your muscles perform a series of intense contractions to lift and lower the weights in a controlled fashion. These contractions place pressure on the blood vessels that provide blood flow to the muscles, increasing blood pressure within the muscles themselves. This increase in blood pressure causes some blood plasma to leak from the capillaries in the muscles into the surrounding tissue. This leakage causes the "pump" effect, creating larger, swollen muscles that remain pumped for approximately 15 to 30 minutes after you finish lifting.

The Burn

    The burning sensation you feel while lifting weights is caused by the build up of an acidic byproduct of the energy production process within the muscles themselves. The body uses a process known as anaerobic glycolysis to convert carbohydrates to energy when there isn't enough oxygen present in the blood to meet the energy needs of your muscles through normal respiration; this process produces water and free hydrogen ions as a result, changing the pH of the muscles and making them more acidic. A component of lactic acid binds with the hydrogen ions to remove them, but as more ions build up the lactic acid can't remove them all and they begin accumulating around nerve endings. When you stop lifting the ions can be flushed from the muscles, explaining why the burn you feel fades soon after you stop working out.

Delayed-Onset Muscle Soreness

    Delayed-onset muscle soreness or DOMS is the aching you feel in your muscles in the days following your lifting session. This soreness is sometimes incorrectly attributed to the build up of lactic acid in the muscles during exercise, but by the time DOMS sets in, most if not all lactic acid has been removed from the muscles by blood circulation. The real culprit when it comes to DOMS is the damage done to the muscles while lifting; soreness can remain until the microscopic tears and other damage to the muscle tissue has healed, a process that can take several days depending on the severity of the damage.

Muscle Injury

    While the damage done to muscles while lifting weights is beneficial in the long run, too much damage can result in muscle injuries that can sometimes take weeks or longer to recover from. Overtraining and improper lifting techniques can cause muscle injuries such as muscle strain, larger muscle tears and damage to the ligaments and other connective tissues that bind muscles to bone and muscles to each other. While pushing your limits is important if you're trying to increase your strength and muscle mass, you should always listen to your body and stop lifting if you feel sharp or sudden pains beyond the burning sensation you normally experience. Don't try to lift if you've recently experienced muscle injury, as this can cause further damage to the muscles and connective tissues, and consult your doctor or a physical therapist if you suspect an injury or aren't sure whether a previous injury is healed enough for you to start lifting again.

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