Everyone lifting light weights during exercise workouts will be heartened by a study that found that lifting light weights (many times) is just as good as lifting heavy weights in building muscle strength and size. 49 young men, who had been resistance training for at least 2 years, were randomly assigned to either the light weight or heavy weight group and followed for 12 weeks. All of the men gained muscle strength and size, and these gains were almost identical, whether they lifted heavy or light weights.
The researchers decided that the key to getting stronger was muscle fatigue - they had to weight lift until they had almost total muscle fatigue, which researchers refer to as "volitional failure". Whether it was with light or heavy weights didn't make a difference. From Science Daily:
New research from McMaster University is challenging traditional workout wisdom, suggesting that lifting lighter weights many times is as efficient as lifting heavy weights for fewer repetitions. It is the latest in a series of studies that started in 2010, contradicting the decades-old message that the best way to build muscle is to lift heavy weights. "Fatigue is the great equalizer here," says Stuart Phillips, senior author on the study and professor in the Department of Kinesiology. "Lift to the point of exhaustion and it doesn't matter whether the weights are heavy or light."
Researchers recruited two groups of men for the study -- all of them experienced weight lifters -- who followed a 12-week, whole-body protocol. One group lifted lighter weights (up to 50 per cent of maximum strength) for sets ranging from 20 to 25 repetitions. The other group lifted heavier weights (up to 90 per cent of maximum strength) for eight to 12 repetitions. Both groups lifted to the point of failure.
Researchers analyzed muscle and blood samples and found gains in muscle mass and muscle fibre size, a key measure of strength, were virtually identical....While researchers stress that elite athletes are unlikely to adopt this training regime, it is an effective way to get stronger, put on muscle and generally improve health.
Another key finding was that none of the strength or muscle growth were related to testosterone or growth hormone, which many believe are responsible for such gains."It's a complete falsehood that the short-lived rise in testosterone or growth hormone is a driver of muscle growth," says Morton. "It's just time to end that kind of thinking."