After a strength-training workout, your muscles need time to rest and recover. You’ve probably heard that you shouldn’t rework the same muscle group again until at least 48 hours have elapsed. That’s because your muscles need that time to recover and repair. But what’s really going on beneath the surface concerning muscle repair and how does it lead to growth?
Muscle Repair and Injury
When you lift weights, it injures the contractile filaments called actin and myosin. It’s these filaments that form cross-bridges that allow a muscle fiber to contract. The stress of training also damages the membrane that surrounds each muscle cell. This damage allows calcium to enter the cell. Calcium acts as a signaling molecule that activates enzymes that clean up the damaged contractile filaments. At the same time, white blood cells arrive at the scene. Some of the white blood cells called macrophages, being the “hungry” cells that they are, eat up the damaged filaments and other debris. As they do this, they release free radicals. What you end up with is a localized inflammatory response.
We think of inflammation as being a bad thing, but when it comes to muscle repair, it’s a necessity. In fact, you must have an inflammatory response for muscles to grow. It’s the inflammatory response that activates satellite cells that help your muscles increase in size. Satellite cells are precursor cells that are capable of giving rise to new skeletal muscle cells. During adulthood, these cells are inactive until muscle cells are injured or stressed. One way muscle cells are stressed is through heavy resistance training. This triggers the whole cascade of events discussed above.
To summarize, you stress muscles by forcing them to contract against heavy resistance. This damages the actin and myosin filaments and the membrane that surrounds the muscle cells. Calcium leaks into the muscle cell and turns on the inflammatory response. In turn, enzymes clean up the damage as satellite cells enter the scene.
How DO satellite cells trigger muscle growth? When a muscle cell is damaged, these cells, on the outside of muscle fibers, divide. One cell develops into a new muscle cell or fiber, and the other remains a satellite cell. The cells that become new muscle cells or fibers fuse with existing muscle fibers. Once this fusion takes place, the muscle cells form new myofibrils. As new myofibrils are built the muscle fiber increases in thickness and the muscle cells grow in size. Since they also have more myofibrils, the muscle also gains strength.
Feed Your Muscles
How can you optimize this process? Satellite cells need good nutrition and an anabolic environment for repair and growth. That’s where balanced macronutrients, sufficient calories, and enough protein come into play. Protein supplies the amino acids muscle cells require to rebuild damaged muscle fibers. You also need enough of a training stimulus to cause injury. Lifting light weights may not damage the muscle fibers enough to lead to significant muscle growth or strength gains.
Muscle Repair, Soreness, and NSAID
We talked about the role inflammation plays in muscle growth and repair. When you have an inflammatory response, the muscles that are damaged become stiff and sore. No wonder! The white blood cells called to the scene of the damage release chemicals that cause swelling. The swelling stimulates the nerve endings and you feel pain. You might be tempted to grab a bottle of ibuprofen to relieve the discomfort of delayed-onset muscle soreness or DOMS. Don’t do it! Ibuprofen and other NSAID block the inflammatory response. Without the inflammatory response, you don’t activate satellite cells and you don’t have the same potential for muscle growth.
Whether NSAID limit muscle growth in practice is still unclear. Studies are conflicting. Some research shows no reduction in muscle hypertrophy in people taking NSAID and at least one study shows a slight increase. Still, it’s not clear what effect taking these medications has on muscle growth longer term. It may depend on how long you take them and at what dose. It makes sense that they would limit muscle growth based on what we know about muscle damage and repair. Why take a chance? Remember, delayed-onset muscle soreness is limited and will go away on its own. NSAID also have significant side effects, especially if you take them regularly.
Helping Your Muscles Repair
As you can see, muscle repair is closely tied to muscle growth. If you don’t have the right conditions for muscle repair, you’ll limit the ability of your muscles to grow and become stronger. First, you need to stress your muscles enough to cause microscopic damage to the muscle fibers. Without this, you won’t trigger the cascade of events you need for growth and repair.
Plus, you need to give your muscles adequate macronutrients to help it repair. Protein is important but you also need carbohydrates after a workout. Without carbohydrates, you don’t get post-workout insulin. You need insulin to send amino acids, from the protein you eat, into muscle cells. Your muscles are hungry for building blocks (amino acids) and you need a way to get those amino acids into the interior of muscles cells. That comes from insulin.
In addition, don’t interfere with the repair process by taking NSAID, even if you feel sore. Finally, don’t forget that rest is an important part of the equation. The repair and muscle building process takes place in-between workouts when you’re resting. You can overwhelm your body’s ability to repair by overtraining. Don’t train the same muscle groups until at least 48 hours have passed.
Sleep is imperative as well. Lack of sleep boosts the release of cortisol, a stress hormone that interferes with muscle repair and actively breaks down muscle tissue. If you do intense workouts, you may need a little more sleep time than the average person due to the stress you’re placing on your body. Aim for at least 7 hours but 8 is better.
The Bottom Line
Now you know how your muscles repair and how this repair is related to muscle growth. Train hard but give your muscles enough rest and good nutrition as well. Then, be patient. It takes time to see the fruits of your hard work – but they’ll come.
Int J Biochem Cell Biol. 2003 Aug;35(8):1151-6.
Appl Physiol Nutr Metab. 2008 Jun;33(3):470-5. doi: 10.1139/H08-019.
EuroStemCell “Satellite cells are vital for muscle repair and replacement”
Med Sci Sports Exerc. 2006 May;38(5):840-6.
Michigan State University Extension. “The importance of rest and recovery for athletes”
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