If you glance in the mirror after doing a set of push-ups or curling a set of weights, it might look like you managed to build muscle instantly. But that short-term pump is temporary, thanks to increased circulation in your muscles. Building permanent, measurable muscle gains takes a few weeks.
You may notice your weight-training exercises getting easier within a few weeks, thanks to neural adaptation. But real, long-term gains in muscle mass usually take about two months of consistent training.
Your Short-Term Muscle Gain
As you start lifting weights, you may notice two types of short-term "gains." The first is the aforementioned pump that comes when your muscles are temporarily engorged with blood. The impressive effects of that short-term pump are why male actors may drop and do a set of push-ups before doing a shirtless scene: It makes their pecs and arms temporarily look bigger and beefier than they really are.
The second, but not-quite-as-instant type of short-term muscle gain you might notice is actually neural adaptation. As exercise physiologist Len Kravitz, Ph.D., at the University of New Mexico explains, when you first begin a strength-training program the initial gains in strength you notice aren't due to increases in muscle size or power. Instead, they're the result of neural adaptation, as your nervous system essentially rewires the muscles to work efficiently.
The gains from neural adaptation typically show within two to eight weeks of a strength-training program. But as Kravitz goes on to explain, the long-term muscle gains that come from hypertrophy — or an increase in muscle size — take about 16 workouts to show.
Because the rest time between strength-training workouts is as critical for building muscle as the workouts themselves, that works out to about eight weeks of twice-weekly training for most people. By no coincidence, that frequency of training also parallels the Department of Health and Human Services guidelines for optimal health. Remember, even if you're building muscle for aesthetic reasons, doing regular resistance training provides some very real health benefits too.
How Your Body Builds Muscle
Muscle growth isn't a magical result of staring at dumbbells or weight machines. Instead, it's your body's response to the structural damage caused by a resistance training workout. The word "damage" might sound bad, and it can be if you've decided to go full-on Schwarzenegger and started lifting too much weight too soon. But if you're lifting appropriate amounts of weight, that damage is the natural result of your muscle fibers contracting to overcome the resistance you're exposing them to.
Once that damage is done, it stimulates a repair response that essentially rebuilds your muscle fibers; this mechanism is also what creates muscular hypertrophy, or long-term growth in muscle size (as opposed to that temporary pump). Metabolic fatigue — or essentially, working your muscles to the point of fatigue — also promotes hypertrophy but, as the American Council on Exercise points out, it's not entirely clear which mechanism plays a greater role in hypertrophy.
Here's the quick takeaway: If you want to build muscle, you need to work out consistently, using levels of resistance that either create the short-term structural damage of a tough resistance-training workout or bring your muscles to the point of metabolic fatigue.
But you also need adequate rest between workouts, because that rebuilding and repair process — which ultimately creates your bigger, stronger muscles — happens during the rest periods between workouts, not during the workouts themselves.
Your Rate of Muscle Growth
As the American Council on Exercise goes on to explain, each body responds differently to strength-training stimulus — so unfortunately, once you're into the world of long-term muscle growth, there's no single rate that applies to everyone.
Just a few of the factors that you can't control that influence your rate of muscle growth include your age, gender, hormone levels and overall genetic makeup. Some people really are genetically predisposed to put on muscle quickly, while for others it's a struggle.
ACE gives the example of a person with near-optimal conditions for building muscle: In a perfect world, a 20-year-old young man with a large percentage of fast-twitch muscle fibers (which respond best to growth stimulus) and a strong genetic predisposition toward building muscle could gain about 2 pounds of muscle mass per month.
But for most people, that rate will be a little slower. Perhaps you're a woman, with the different hormonal makeup that entails; you've started strength-training a little later in life, and you have a lower percentage of fast-twitch muscle fibers or you simply aren't genetically predisposed to building muscle easily.
All of those factors are out of your control — but happily, there are quite a few things you can control to help your body build muscle. More on that in a minute. First, keep in mind that for some people, seeing real long-term adaptation to strength-training — that is, muscle growth — can take as long as three to six months. So even if you don't see a lot of growth right away, as long as you're training sufficiently to exhaust your muscles, those muscle gains are on the way.
Factors You Can Control
Although you can't change your genetic makeup and the enormous role it plays in strength-training, you can make exercise and lifestyle choices that increase your odds for quick, healthy muscle growth. These include eating a healthy diet with enough calories and the right macronutrient balance to promote hypertrophy, staying properly hydrated, getting plenty of sleep and maintaining appropriate training volume.
According to a meta-analysis published in a November 2016 issue of the New Zealand journal Sports Medicine, that ideal training volume is twice a week. Training once a week also created muscular hypertrophy, but strength-training twice weekly produced significantly better results.
There's no scientific proof or consensus about whether training a muscle group three times a week is even better and, given the importance of the rest periods between workouts, this is one case where you can't assume that more is automatically better.
Aside from consistently hitting the gym, there are a few other techniques you can use to appropriately exhaust your muscles or, as strange as it may sound, damage them to the point of inducing hypertrophy — which is absolutely not the same thing as injuring them. In fact, appropriate weight training practices will help you avoid injury as you tone your body.
These techniques include:
- Always warm up the muscles you're going to train with five to 10 minutes of light activity.
- Start with weight you can manage while using good form.
- Gradually increase the resistance or number of sets as your muscular strength and endurance improve.
- Do slower repetitions to promote muscle growth by increasing the muscles' time under tension.
- Switch your workouts up periodically; this decreases the risk of overuse injuries while promoting muscle growth.
- Stay hydrated, get plenty of sleep, and stretch after your workouts to promote flexibility in those new muscles you're building.
- University of New Mexico: "Resistance Training: Adaptations and Health Implications"
- American Council on Exercise: "How Muscle Grows"
- Health.gov: "Dietary Guidelines for Americans, 2015-2020: Appendix 1. Physical Activity Guidelines for Americans"
- Mayo Clinic: "Strength Training: Get Stronger, Leaner, Healthier"
- American Council on Exercise: "7 Techniques for Promoting Muscle Growth"
- Sports Medicine: "Effects of Resistance Training Frequency on Measures of Muscle Hypertrophy: A Systematic Review and Meta-Analysis"