This Is What Happens to Your Body When You First Start Working Out

If you’ve ever started lifting weights again after a long time off, you may remember that time as a magical period where your body reacted extraordinarily to the stresses put on it, and seemingly began to pile on muscle like crazy. (And if you’ve never experienced this phenomenon, add it to the list of reasons to reup your gym membership and proceed straight to the weight rack.) Often referred to as “newbie gains,” the effect is not purely psychological, experts say—there really are benefits that newcomers enjoy over more seasoned gym rats.

“The nice part about that beginning stage is that you don't have to get it perfect,” says Erik Hanson, an assistant professor in the Department of Exercise and Sports Science at the University of North Carolina at Chapel Hill. “You can make real, strong gains without having everything completely dialed in.” Figuring out exact numbers of repetitions and sets and nailing down your nutrition becomes important later, he says, but not yet. Any disruption from your normal non-exercising routine is going to stimulate growth.

Muscle grows when we stress the muscle fibers, throwing the body out of the predictable state it likes to be in. The body works hard to maintain a stable internal environment called homeostasis. From the moment you begin resistance training, you're going to stimulate muscle breakdown, Hanson says, but you also stimulate protein synthesis that rebuilds muscle—and leaves you with bigger, stronger muscles.

In other words, that temporary damage has to occur in order to convince the body to rebuild muscles stronger and bigger so that they handle future work more efficiently, and without taxing the body so heavily. “Whenever you have a new stimulus, an unaccustomed stress, the body responds very well to that,” Hanson says. “New exercise is going to cause the most stress, and also produce a strong adaptive response.” He says it takes about a month to see noticeable muscle mass added to your body after you begin exercising seriously, but after your second weightlifting session, you could already feel stronger.

The reason isn’t that you’ve actually piled on a ton of muscle mass in the two days since your first workout. Even in the newbie gains period, lean mass accumulates incrementally, Hanson says. Your early strength gains are due to an improvement in your nervous system: “There are two components to it,” Hanson says. “A neurological component that happens very, very quickly, and then the actual accretion of muscle tissue, which takes a little bit longer to manifest itself in results you can see.” These "neuro-gains" happen almost immediately, and at about the time they start to level off, you begin seeing an increase in lean muscle mass that allows you to keep progressing, he says. How long muscle gains last depends on the individual.

As time goes on, these exercises become less disruptive to your muscle fibers. You may get still tired, you may see incremental gains, but the body by now has prepared itself to handle these repeated bouts of exercise better, and be more able to maintain a state closer to homeostasis even as you work out, Hanson says. Instead of freaking out and responding with frantic attempts to build as much muscle as it can, your muscle fibers take the workload in stride, and gains become more incremental as they become used to the stresses you put on them.

If you step away from the gym for a while, though, and find that your fitness level has slipped far enough away, you can relive this period of rapid growth—and it could go faster the second time around, Hanson says. “Following a de-training period, the ability to recoup the previous gains is actually enhanced because your body has already achieved and been to that (level of fitness) before.” It’s known as muscle memory, the ability for the body to reawaken its knowledge of how to efficiently respond to exercise.

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If you’re motivated enough to consistently hit the gym week after week, there’s only one downside: Becoming fitter is only going to get more difficult. “Our bodies are unbelievably well-adapted to conserve, and if we are not continually urging our muscles to grow through workout modifications, then the gains start to diminish,” says Eric Holder, a physical medicine and rehabilitation physician at the Yale School of Medicine. After your newbie gains period, your routine will have to become a science of specific workouts, reps, sets, and calorie counting, and you’ll have to vary your workouts to prevent your muscles from getting too used to them.

Most people who work out consistently—and with increasing intensity—would be fortunate if they put on half a pound of muscle a month, writes strength coach and fitness author Eric Bach. Beginners, however, might expect to gain five to 10 pounds of lean muscle in three to four months if they take their training seriously, Hanson says. Ten pounds would be very impressive, but not unreasonable, he adds.

Effective routines for newcomers include Stronglifts 5x5, a popular modern variation of the workout Arnold Schwarzenegger used in his early days. Five-by-five programs have been a staple of weightlifting since the mid 20th century, when bodybuilding pioneers such as Reg Park, Mark Berry, and Bill Starr began to advocate five sets of five reps for a workout comprised of compound lifts—movements that work several muscle groups at once—such as squats, deadlifts, rows, and shoulder presses. That also means you won't have to overload yourself mentally by having to learn a ton of exercises and figuring out how many sets and reps to do.

Closed-kinetic-chain exercises like these, in which your hands or feet are in a position fixed against resistance, such as having your feet flat on the floor, also tend to be well-tolerated by beginning lifters and act as a primer for full-body strength development, Holder says. Compound exercises utilizing free weights, such as the barbell, also target smaller supporting muscles that are crucial for using your strength in practical real-world situations and prevent muscle imbalances, in which some of your muscles become well-developed but others remain underdeveloped, he adds.

Having the best routine in the world, however, won’t be a mean a thing if you don’t give your muscles the right amount of fuel. Researchers disagree over how much protein your body needs, but most recommend you get at least 0.7 grams of protein per pound of body weight if you’re serious about growing your muscles, while acknowledging there may be benefits to having more. You can get an estimate of your caloric needs through a Total Daily Exercise Expenditure (TDEE) calculator, and track your intake through a meal logger, such as the free version of MyFitnessPal. (Don’t forget to calculate roughly how many calories you burn during workouts, too, and replenish that in addition to your baseline needs.)

Initially, you'll want to give yourself enough sleep and rest days for your muscles to recover. Any decent workout program will pilot you through your introductory period as long as you stay consistent. Sleep enough, eat enough, and learn the proper techniques, and you're bound to see results.

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