Hit the weight room for a couple of hard workouts and a funny thing may happen: your muscles get bigger. It's like an infomercial come true – and it's the topic of an ongoing debate among exercise scientists trying to figure out exactly how long it takes to build new muscle.
For decades, researchers have assumed that gains made in the first few weeks of training are an illusion. Swelling caused by muscle damage makes muscles seem bigger and "neuromuscular" adaptations – better signalling from the brain to the muscles – allow you to increase your strength before you've actually built any muscle. For real improvements, according to the National Strength and Conditioning Association (NSCA), you have to wait at least six to eight weeks.
But a new study from a team of researchers at Texas Tech University and other institutions challenges that timeline, using a modified training program that minimizes the effects of muscle damage. The results, published in the European Journal of Applied Physiology, revive the claim that true muscle growth can occur in less than four weeks.
"The fact that neural adaptations are taking place does not mean that muscle growth isn't occurring as well," says Matt Stock, the lead author of the new study and currently an assistant professor at the University of Central Florida. "Some people may be surprised by our results, but they are fairly consistent with several other recent publications."
Back in 2011, as a doctoral student at the University of Oklahoma, Stock was a co-author on a surprising study that observed a remarkable 3.5-per-cent increase in muscle size (as measured by cross-sectional area with a CT scanner) after just two workouts.
That initial increase was probably a result of swelling, the researchers acknowledged – but muscle size kept increasing in subsequent weeks, when the damage and swelling triggered by unfamiliar exercise would be expected to subside. They concluded that real gains in muscle size and strength could occur within three to four weeks of twice-a-week workouts.
That conclusion was controversial and, in 2015, researchers from the University of Sao Paulo's School of Physical Education and Sport in Brazil published a response. Before, during and after a 10-week training program, they used ultrasound to measure muscle size and used a related ultrasound technique known as "echo intensity" to estimate how much swelling was present. Sure enough, the apparent muscle gains after three weeks appeared to be associated with damage-induced swelling.
Stock's new study attempts to eliminate the confounding effects of swelling by having his subjects use only "concentric" muscle contractions, in which the muscle shortens. When doing biceps curls, for example, the subjects lifted the weight upward, then an experimenter took the weight, lowered it for them and handed it back for the next repetition. This avoided the "eccentric" contractions that are thought to induce most training-related muscle damage.
With this training technique, the subjects showed no signs of muscle damage or swelling – but still had statistically significant increases in muscle size and weight after seven workouts in 3-1/2 weeks.
Not everyone is convinced by the new findings. One problem, according to Felipe Damas, the lead author of the Brazilian study, is that despite their bigger muscles, the subjects in the new study didn't increase the maximum force they could generate. This suggests that any early gains are perhaps not practically relevant.
In addition, not everyone saw similar improvements: Just 10 of the 13 subjects had significant gains in muscle size, or "hypertrophy," after four weeks.
According to Stuart Phillips, a leading expert in muscle physiology at McMaster University who collaborated on the Brazilian study, Stock's results would be stronger if muscle size was measured with more accurate techniques such as MRI or a direct muscle biopsy. Still, he says, "I would agree that hypertrophy starts earlier than we perhaps originally thought."
How early? That depends on factors such as genetics and nutrition, as well as how hard you train, says Stock, "but I don't think it is unrealistic to expect to see changes within six to eight workouts."
Damas's estimate is similar – though translating those results to the real world is another question. All of the studies seeing early muscle gains involved very hard workouts. In Stock's study, the subjects did five or six sets each of biceps curls and shoulder presses, with each set of eight to 12 repetitions performed to voluntary failure and 90 seconds of rest between sets. A more realistic timeline for most people, Damas suggests, is still the six to eight weeks suggested by the NSCA.
Nonetheless, there's something encouraging about the idea that you're already making gains – near-invisible though they may be – after less than a month of strength training. If you think you see early changes, don't let the skeptics convince you otherwise. Celebrate it – and keep training.
Alex Hutchinson's latest book is Which Comes First, Cardio or Weights? Follow him on Twitter @sweatscience.