What Really Happens to Your Muscles During a Workout

Maybe you want to up your cardio game, build muscle, or simply live a healthier lifestyle, but whatever the reason, the result is the same: You want to start working out. Great job! But just what happens to our muscles when we work out, especially during strength-based training? And what happens to our bodies as we build muscle mass? Can testosterone really help build muscle mass? And will some warm-up stretches actually HURT your muscles more than help? Fear not, fellow gym-goers, as we have the answers.

The human body has three types of muscles: cardiac, smooth, and skeletal. The cardiac muscle makes up the heart’s wall, responsible for the heart’s contractions. This is how we have blood pumping through it. Smooth muscles form the wall of the intestine, uterus, blood vessels, and internal muscles of the eye. Right now, we’re focusing on the third type of muscle, the skeletal muscles. Skeletal muscles make up the majority of your muscles, and they’re around 30 to 40% of your total body mass, so it goes without saying that it’s important to take good care of them if you want to live a healthy and happy life.

Skeletal muscles are attached to your bone by tendons, which are tough bands of fibrous connective tissue. And if you break one, hoo boy, you’re gonna have a bad time. You’ve probably heard trainers or exercise enthusiasts talk about shoulder muscles, hamstrings, and abdominal muscles. All of those are skeletal muscles. They’re composed of thread-like myofibrils and sarcomeres that come together as muscle fiber. Motor neurons communicate to your muscles when to contract, and the better those signals are at telling the muscles to contract, the stronger a person can get. And there are a lot of skeletal muscles in the body. There are at least over 650 named skeletal muscles, although that number may even go up to 840. Why is it so unclear? Well, the dissension comes from how to count complex muscles. The biceps brachii is one of those complex muscles that’s difficult to categorize. It has two heads and two different origins, but they are insert on the radial tuberosity. Therefore, doctors and scientists argue whether to count it as one muscle or two. 

The science of good exercise can be surprisingly complex in that way. When you exercise, you’re forcing your muscle fibers to contract and stretch repeatedly. Muscle contraction is when the muscles tighten, shorten, and lengthen during physical activity. It can happen when you do something as simple as pick something up or stretch. After the muscle contracts, it returns to its normal state of muscle relaxation. When your muscles contract, they offer stability for your joints and connective tissue. Sometimes, your muscles will contract involuntarily. Our body needs our muscles to contract in order to be able to move. It also produces heat to maintain your body temperature, hence why you heat up so much during exercise. Did you know that around 40% of your body’s temperature converts into muscle movement? One prime example is that, whenever someone feels cold, they might shiver.

It’s your body’s way of activating your skeletal muscles to help warm you up. Your muscles also help you maintain your posture, which can be as simple as standing up or sitting down. Your muscles do a lot in day-to-day life, so what are they doing when you hit the bench press or elliptical? First, let’s talk about the different ways that muscles contract. The first is isometric or stationary contraction. The muscle contracts, but the length doesn’t change, and it doesn’t really go anywhere. During isometric exercises, the joint also doesn’t move. It can be used to help build strength, but it’s not the most efficient way to go about it. Two examples of isometric exercises would be a leg lift or plank. Since you don’t move during these exercises, it will only improve your muscle strength in that one position.

The second is concentric, which is when the muscle gets shorter. It’s the one we’re most used to. One example of a concentric contraction is the upward movement you would perform during a bicep curl. The third is eccentric, where the muscle gets longer as tension is produced, like when you’re lowering your arm during a bicep curl. When your muscle contracts during a workout, it causes tiny tears within the muscle fibers. The size of these tiny tears in the muscle varies based on the intensity of your workout. That’s what causes that sore feeling after you’re worked out. Your body is getting to work repairing those muscles. If this is causing you to freak out about your exercise habits, don’t panic about tearing your muscles! These tears are absolutely normal and are essential to building  muscle. 

It’s only a problem if you over-exercise. Over-exertion can lead to much larger tears and injuries like muscle strain. The duration and intensity influence the effect it has on your body. Endurance training can make your muscles stronger and less likely to wear out. That means focusing on things like running or cycling. It can help enlarge your heart for better blood flow, too! It can help you increase lung capacity, improve your metabolism, and buff your coordination. That being said, if you’re looking to build muscle through aerobic exercise or cardio, you’re barking up the wrong tree. For those of you hitting the gym who want to build up your muscles, look for a sign that says “strength training,” that’s where you need to go. It’s strength training that will help lead to muscle building if that’s your health goal. If you can’t afford to head to the gym, you can easily do this alone and in the comfort of your home.

All you need is repetitive resistance exercises. You can use weights, resistance bands, or even your own body weight. You’ll be able to force your muscle to contract and increase the contractile filaments within your muscle. Sometimes, you can even use certain forms of swimming to help build muscle, as long as it involves resistance against the water. Your muscle size will increase if you continue to challenge your muscles to deal with higher levels of resistance or weight. This is known as muscle hypertrophy, which occurs when the fibers of muscles sustain damage or injury. It can help improve muscle endurance, build muscle mass, burn fat, and build strength. As the body repairs the damage, it increases the mass and size of the muscle. This might be the one time your doctor will recommend tearing something.

Just be sure not to go overboard with it. Hormones, like testosterone, can also stimulate muscle growth. They can improve how the body processes proteins, stimulate anabolic hormones, and activate satellite cells, a type of stem cell that helps muscle development. Strength and resistance training can help with the release of growth hormone from the pituitary gland. It can also stimulate testosterone release, which will encourage muscle growth, and it improves the sensitivity of the muscles to testosterone. Once you finish exercising and cool down, your body will return to homeostasis. The amount of time you’ll need to recover will depend on how intense and how long your workout is. It can also be impacted by your underlying physical fitness or how accustomed your body is to exercise. On top of all that, a working knowledge of satellite cells is important for discussing what happens to muscles during exercise. So, let’s look a little deeper into just what satellite cells are. Satellite cells are myogenic stem cells that help with muscle regeneration. 

They’re located between the external lamina and sarcolemma, the transparent tubular sheath around the fibers of the skeletal muscles. We talked about creating tears in the muscles while working out, but what happens after that? It’s the satellite cells that repair those tears in the muscles. They replicate, mature, and fuse to your damaged muscle fibers. This allows them to form a new muscle protein strand. During this process, your muscles will increase in size and strength. But is the process created equal across all people? A study revealed that there are moderate responders and extreme responders when it comes to muscle growth. Modest responders with about 28% muscle growth were found to have about 19% activation in their satellite cells. Extreme responders who saw 58% myofiber hypertrophy had 23% activation in their satellite cells.

In the study, there was also a group of people who were labeled as “non-responders” who had 0% growth and 0% activation in their satellite cells. But how do you get these satellite cells to activate so that you’ll increase your muscle growth? That’s where muscle tension, muscle damage, and metabolic stress occur. Muscle tension can be the act of lifting progressively heavier weights. The tension helps change the chemistry of the muscle, which helps along the process of activating the satellite cells. Muscle damage releases inflammatory molecules and immune system cells. Those are what help activate the satellite cells. You’ll know you’ve had metabolic stress if you’ve ever felt a burning sensation after an exercise. Metabolic stress causes cell swelling around the muscle. This contributes to muscle growth, but it won’t necessarily increase the size of your muscle cells.

This is known as sarcoplasmic hypertrophy. While it can make your muscles look larger, it won’t necessarily increase your actual strength. It’ll be all looks and no substance. After a workout, one of the best things you can do is allow your muscles to recover. But what can you do to help further along your recovery time? Rest up, of course! You’ll want to get more sleep, for starters. Your heart will have a chance to rest as you sleep. This gives the cells time to grow and muscles to repair. So maybe try getting a bit more sleep after a workout, especially an intense one. Make sure you eat well. You may have heard from a doctor or personal trainer how important a balanced diet is to your health and longevity, and they weren’t lying. Eating well is the key to muscle recovery. Protein helps rebuild muscle fibers, while carbohydrates restore depleted glycogen levels. 

Glycogen is a form of glucose. Glucose is one of the main sources of energy for your body. When your body doesn’t need to use the glucose you’re eating immediately, it’ll store it in your muscles and liver. So, while there is a lot of hype around low-carb diets, your body needs carbohydrates to help you form glucose and glycogen. The process of your body turning glucose into glycogen is known as glycogenesis. Doctors recommend a diet rich in antioxidants, complex carbohydrates, and lean protein to help build muscle. These can help make the right changes to your body between workouts and give it the strength it needs to keep improving. Staying hydrated will also help with muscle repair, especially during hot weather or in a sweaty environment like a gym. Your body will lose a lot of water through your sweat and breathing. If you’re dehydrated, your muscles won’t be able to repair themselves as efficiently.

That’s why you’ll need plenty of drinking water. Even minor dehydration can have a negative impact on muscle performance and function. If your muscles are dehydrated, you increase the risk of injury. You need to hydrate so that your muscles are lubricated. When they aren't lubricated, they’re not able to contract properly. Dry muscles can make you feel fatigued, too. And it doesn’t just impact your athletic performance, but it can negatively impact your regular everyday movements as well. There are several signs that your body gives you that you’re dehydrated. A dry mouth, lips, or eyes can indicate you haven’t been getting enough water. Headaches, feeling tired, and dry skin are also signs of dehydration. Prolonged dehydration is particularly worrisome. If you notice the signs of severe dehydration, you’ll want to find medical help. This can include hot, red, dry skin, nausea, seizures, loss of cognitive abilities, hallucinations, dizziness, loss of consciousness, lack of sweating, and a body temperature higher than 103 degrees. 

It can potentially help to drink tart cherry juice. Tart cherry juice has a lot of antioxidant and anti-inflammatory polyphenol compounds. It helps lessen pain, and it quickens strength recovery. Not all studies agree that cherry juice helps as much as some research suggests, but if you do enjoy drinking cherry juice, it might still be nice to incorporate it into your routine. Just make sure to drink plenty of water along with it. If cherry juice isn’t for you, you can feel secure knowing that drinking water is just fine. Hydration is the ultimate goal to help with recovery! If you had an intense workout, you might want to give yourself a few days to recover and let your muscles heal as well. If you work out daily, it might be best to start with light workouts as you build your muscle strength.

If you’re feeling sore after a workout, you can do quite a few things to help relieve the discomfort. Make sure you always stretch before and after a workout. Stretching before your workout will help reduce the risk of injury and may help reduce soreness afterward. It’ll help your muscles loosen up and increase your range of motion while working out. When you stretch after your workout, you’re engaging in maintenance stretches. It’ll decrease soreness, move lactic acid out of your muscles, and help your blood flow return to normal. All of this aids your body in recovery, and it can help lessen how sore you feel after. However, an important note you may not have known about is that dynamic stretches are the most effective - These are stretches that entail compound movements, otherwise known as keeping yourself mobile while you stretch.

Think lunges, air-squats, and hip circles. Static stretching - Just stretching out your body parts while standing still - has actually been proven to have negative effects on the body. Experts have discovered that it can lead to fatigue and even muscle damage if overused. But let’s say you have damaged your muscles and want to get better. How would you go about doing that, you’re probably wondering? Low-intensity and low-impact exercise that encourages blood flow can also help in muscle recovery. Dr. Nicole Belkin, an orthopedic surgeon at New York-Presbyterian at Columbia University Irving Medical Center, states, “If you’re feeling fatigued from strength training, engage in a lower intensity cardiovascular bike ride or walk, which enables your body to circulate waste products caused by the rigorous activity.” Something as simple as yoga can be used to help in muscle recovery. 

Aside from rest, hydration, and stretching, there are a few things you can do to help with soreness. Ice can help reduce inflammation, or heat can be used to increase blood flow to your muscles. This can be just taking a warm shower or bath. Some people enjoy taking Epsom salt baths to help relax muscles and loosen joints. Studies on Epsom salt haven’t proven it can help, but it also doesn’t hurt. So, if you enjoy a nice warm Epsom salt bath, let yourself enjoy it. At the very least, the warm water should help soothe your sore muscles. But, at the end of the day, the best thing for your body after a workout, easy or intense, is to just let yourself rest and drink plenty of water. As exercise stops and we enter the cool-down period, our bodies gradually return to homeostasis, and normal operation is resumed.

Recovery time depends on the intensity, type, and duration of exercise as well as your underlying physical fitness. It can also be dependent on age. Children, teenagers, and older adults often require more post-workout recovery than young or middle-aged adults. People new to exercising or just out of shape in general may also need more time to recover from working out. They may even want to engage in passive recovery to repair their muscles and rebuild energy, like sleeping and drinking plenty of water. However, just because you're fit doesn’t mean you won’t need plenty of recovery time. If you’re used to more intense workouts, you’ll need to let your body rest and recover from them. For example, let’s say you go to the gym four or five days a week. If you’re mixing high-intensity workouts, cross-training routines, and active recovery days, you’ll most definitely want to take two to three days off to really recover. Regardless of who you are or where you are in your health journey, rest is as important as training itself, as this is where muscles are rebuilt and grow back bigger.

Pushing yourself may be important to achieve your goals, but pushing too far will have the opposite effect. Recovery looks different for everyone, so be sure to show yourself kindness as well. For someone who is an elite marathon runner, they may be able to engage with a 4 or 5-mile run as an active recovery workout.