How Muscles Get Big

The science behind muscle soreness and building muscle mass.

Article By: Leanna Carpenter

We’ve always said that combining an active lifestyle with healthy eating makes you more likely to lose weight and keep it off. So now you’re thinking about hitting the gym and maybe even building up some muscle. Well, we’ve enlisted two fitness experts to help you understand how muscles get big. And believe it or not, it’s by carefully overworking them. We said carefully. So read on to find out how.

Though it may seem a little counterintuitive, Michael Moses, a team doctor for the Marine Corps Marathon, the Washington Redskins and the Washington Wizards cheerleaders, helps explain the process.

“When muscles are overloaded during weight lifting, little tears are made in the muscle itself,” he says. “This microtrauma may sound harmful but is in fact the natural response of your muscles when they experience work. The muscle repairs these tears when you're resting, and this helps muscles grow in size and strength.”

So when you lift weights, you’re actually slightly damaging your muscles by allowing them to lift more weight than they would in normal daily life.

And that damage is why you wake up sore the next day. To think of it in simple terms, you’re nursing an injury, and the pain is telling you no más. Some guys who work out say the muscle soreness is actually worse the second day after working out. This pain is caused by minute tears in the fibers of the connective tissues in your body—the ligaments that connect bones to other bones, and the tendons that connect muscles to bones.

“This is known as delayed onset muscle soreness (DOMS), and researchers think it could be caused by microscopic tears in the muscles fibers following a bout of exercise,” says Michael Wood, CSCS, a nationally recognized personal trainer.

“Muscles become sore after training because of the microscopic tear. This kind of soreness is OK and might even feel worse two to three days after the workout but will go away,” says Moses.

While soreness after working out is normal, it illustrates the need to get enough rest between workouts because your muscles need ample time to get stronger, bigger and firmer. Not resting each body part for at least two days can set you up for an injury.

So when you’re doing an exercise that actually hurts you on a minor level, you need to take measures so that you’re doing controlled damage to your body. This means warming up before lifting weights. “The main benefit to warming up is injury prevention because blood will be pumping to an area, lowering the chance of a muscle pull or joint injury,” Moses says. 

While you may be sore for a couple of days after working certain muscles, there are other things you can do to help stimulate muscle-building. The first: Eat something. “There is about a 60-minute time frame after you work out when your body can most benefit from a decent meal — and don't be afraid of carbs,” Moses says.

Wood says eating within 30 minutes can be even more beneficial, suggesting a balanced meal with carbs and protein. “You should focus on post-workout nutrition and proper recovery,” he says. “Once the muscle has been overloaded, it is then necessary to focus on the nutritional component followed by adequate sleep to ensure optimal results.”

By the same token, stretching the muscles after exercise will help with muscle recovery, as will sitting in the hot tub at your gym, if it has one. These activities lower the risk of injury after a workout by allowing the muscle to keep from tightening up.

Generally speaking, bigger muscle groups (legs, back and chest) will take longer to recover than smaller ones, and working out these larger muscle groups will also burn the most calories in your workout.

However, you should ask yourself why you’re working the muscles. Are you trying to build strength or athletic endurance? “The key is trying to find the right intensity (load) for weight lifting,” says Wood. “If you’re still very sore a few days following a workout, the load was most likely too heavy. Remember, heavier is not necessarily better.”

The rate at which your muscles recover can be influenced by your diet and sleep patterns. A good diet and a full night’s sleep (seven to eight hours) will help muscles recover. While everyone’s body is different, Moses says it’s relatively safe to work muscle groups twice per week to give ample recovery time. But even that is a loose guideline. You should always check with your doctor to make sure you’re not doing too much. 

When you decide to build muscle, Moses says it’s important to know when to say when. “You should exercise to the point of fatigue but not pain,” he says. If you notice any swelling or inflammation in your muscles or joints before or after lifting, Moses says to stop until things return to normal or check in with your doctor. And be sure to listen to your body. 

“Never ignore numbness or tingling,” Moses says. "Such sensations are often related to nerve compression, and these warning signs may indicate serious injury that should always be examined by a physician.”

Remember, even though you're making a decision to lift weights for health reasons, you don’t want to push your body too far. Building muscle, endurance and strength takes time. And just like weight loss, it’s best to do it slowly and safely. Lifting too much weight or not giving your muscles enough healing time can result in an injury and actually hinder your goals. Always listen to the messages your body is sending.

“To experience soreness in muscle is one thing, but to experience soreness in joints, ligaments or tendons is another thing,” says Wood.