How Long Does It Take for Muscles to Grow After Working Out?

How long does it take to build muscle? Is it one month, five months or longer? Muscle growth, or hypertrophy, depends on a multitude of factors, including the age when you start working out, as well as workout frequency, duration and training techniques.

Each of these factors — and others — influence your ability to build lean mass. Your diet is just as important. What you eat can make or break your gains. For this reason, it's essential to prioritize pre- and post-workout nutrition.

Whether you're just starting to work out or setting new fitness goals, you might be asking yourself — how long does it take to see muscle growth? First, make sure you understand how this process occurs.

Regular exercise, especially strength training, causes an increase in the size of individual muscle fibers. This process is called muscular hypertrophy, explains the University of New Mexico. The key to muscle growth is to gradually increase the stress on your muscles by lifting heavier weights, performing more reps, trying new exercises and so on.

Simply put, muscle growth occurs in response to progressive overload. If, say, you begin to lift heavier in the gym, the size and amount of contractile proteins will increase over time. This helps your muscles adapt to the extra load and sustain your workouts. Likewise, you can do more sets or reps, experiment with new lifting techniques or switch between free weights and gym machines to keep your muscles guessing.

Read more: 10 Workout Shortcuts to Build Muscle and Burn More Calories

According to the American Council on Exercise, it's easier to build mass when you're just getting started with strength training due to the initial recruitment of motor units. As you progress, your nervous system adapts and hence more motor units are recruited during training. However, this doesn't indicate an increase in muscle size but rather a physiological adaptation to exercise.

As with most things, consistency is crucial to achieving your fitness goals. If you stick to your workouts, your muscles will continue to adapt and grow. How long it takes to get noticeable results depends on several factors, including your genetics. Most people can expect to see improvements in muscle size and strength within three to six months, states the American Council on Exercise.

As discussed earlier, your ability to build muscle depends on a number of factors. Your genetics, for example, play a key role in muscle growth and development. Although you have no control over this factor, you can continuously improve your workouts to get better results. Other key aspects involved in muscle development include:

• Training load, duration and frequency
• Recovery from exercise
• Hormone levels
• Hydration
• Diet (energy intake and macronutrient ratios)
• Age at which you start training

An individual who starts training is his early 20s and maintains this habit over the years will likely build more mass by age 40 than someone who begins training in his 30s. But this may not always be the case.

Nutrition, recovery, genetics and hormone levels are just as important as exercise. Consistency matters too. Someone who starts training later in life might be more motivated and work harder than those who begin training at a younger age but take frequent breaks, have a bad diet or skimp on sleep. Therefore, the rate at which muscle growth occurs varies greatly from one person to another.

A February 2012 review featured in the Journal of Sports Medicine & Doping Studies notes that it's possible to increase lean mass by 5 percent or more in nine to 12 weeks. Strength training plays a key role in this process, but you can only build muscle up to a point due to the fixed size of your tendons, neural limitations and other factors.

Read more: Can I Start Bodybuilding in My 50s?

Furthermore, your ability to build mass may decrease as you age. As the scientists point out, aging causes a gradual decrease in lean mass. This effect is more pronounced after 45. Additionally, the strength of your bones and tendons tends to decline over time, limiting the maximal attainable hypertrophy.

Considering these facts, it's hard to say how long it takes to build mass. Each of the factors listed above plays a role. If you work out hard and watch your diet, you should see results within two months or so. However, if you're a former athlete or getting back into exercise after a break, you may progress at a faster rate due to the so-called muscle memory.

Not all exercises are created equal when it comes to building muscle. If you're trying to put on mass, it's important to prioritize strength training.

According to the University of New Mexico, resistance training activates the satellite cells in muscle tissue, facilitating hypertrophy. This form of exercise causes micro-tears in the muscle fibers. As a result, satellite cells begin to multiply and fuse to the existing muscle fibers, helping them recover from trauma. These cells play a crucial role in skeletal muscle growth and repair.

Strength training also boosts the release of insulin-like growth factor (IGF-1), testosterone and other muscle-building hormones in response to progressive overload.

You also need to consider the number of reps and sets. It's one thing to train for strength or endurance, and another thing to train for hypertrophy. The American Council on Exercise recommends performing three to six sets of six to 12 reps per exercise for hypertrophy. Rest intervals between sets should not exceed 30 to 90 seconds.

Cardiovascular training may induce hypertrophy under certain conditions, explains a research paper published in Exercise and Sport Sciences Reviews in April 2014. To obtain this effect, it's important to strike the right balance between training duration, frequency and intensity. Working out at high intensity for 30 to 45 minutes four to five times per week may help you build muscle and torch fat.

High-intensity interval training, or HIIT, is best known for its ability to burn fat and preserve lean mass. What you may not know is that it may also promote muscle growth.

For example, a small study has found that subjects who followed a HIIT program combining leg cycling and arm-cranking experienced hypertrophy in leg and trunk muscles within four months. These findings were published in the Open Access Journal of Sports Medicine in November 2014.

Another small study, which appeared in the International Journal of Exercise Science in January 2017, indicates that a HIIT running protocol may increase quadriceps size in as little as 10 weeks. As expected, subjects also experienced improvements in cardiorespiratory fitness.

An April 2018 meta-analysis published in the Journal of Sports Sciences assessed the effects of resistance training versus concurrent HIIT and resistance training for hypertrophy. After analyzing several studies, researchers concluded that combining the two training methods may lead to similar improvements in muscle size and strength as resistance training alone.

Read more: The Truth Behind 5 Common Myths About HIIT

According to the Gatorade Sports Institute, HIIT has negligible effects on hypertrophy when compared to heavy weight training. However, it may increase muscle size after several months of exercise. The research is conflicting, so you may want to experiment with different training styles to see what works best for you.

All in all, HIIT is unlikely to hurt your gains. Do it after strength training or on your off-training days to burn fat and boost your cardiovascular fitness. Consider incorporating free weights or other types of resistance into your HIIT workouts to build lean mass.

Whether you're just getting started or trying to get faster results, there are some ways to maximize hypertrophy. First of all, make sure you're using the right amount of weight. According to a small study featured in the Journal of Sports Science & Medicine in December 2016, moderate load training is more effective for muscle growth than heavy load training. The latter is a better choice for those looking to gain strength.

Workout frequency matters too. There is a dose-response relationship between training volume and hypertrophy, states a small study published in Medicine and Science in Sports and Exercise in January 2019. Simply put, the more often you work out, the greater your gains will be over time.

The American Council on Exercise recommends lifting weights with a slow, controlled motion to increase the time under tension and reach metabolic fatigue. For example, if you're doing biceps curls, lift and then lower the barbell or dumbbells slowly instead of rushing through the movement. Hold the contraction at top of the movement, squeezing your biceps.

Also, consider alternating between low- and high-intensity strength workouts with different loads. Perform more reps with lighter weights and fewer reps with heavier loads to keep your muscles guessing and prevent plateaus.

If, say, you're training legs twice a week, perform a heavier workout at the beginning of the week and a lighter one a few days later. The heavier workout may include compound movements like squats, deadlifts and leg presses, while the lighter one may consist of donkey kicks, glute bridges, walking lunges, jump squats and so on.

More advanced lifting techniques, such as drop sets, giant sets and supersets, can maximize hypertrophy and help you break through plateaus. Drop sets, for instance, require gradually reducing the load from one set to the next until you reach muscle fatigue.

For example, when performing biceps curls, you may start with a 20-pound barbell and perform as many reps as possible without comprising form. As soon as you feel that you can't do any more reps, switch to lighter weights (like a 15-pound barbell) and continue. Do it again and again until you reach absolute fatigue.

Over time, this lifting technique may improve muscle size and definition, notes the American Council on Exercise. For best results, perform drop sets at the end of your workout. If you start with drop sets, you may not have enough energy left for other exercises.