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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:

Pumping iron: Lighter weights just as effective as heavier weights to gain muscle, build strength

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." 

Another popular view bites the dust.From the NY Times:

Why Antioxidants Don’t Belong in Your Workout

Antioxidant vitamins are enormously popular with people who exercise. The supplements are thought to alleviate muscle damage and amplify the effects of exercise. But recent studies have raised questions about whether antioxidants might be counterproductive for runners and other endurance athletes. And now a cautionary new experiment adds to those doubts by finding that antioxidants may also reduce the benefits of weight training.

 Both aerobic exercise and strength training lead to the production of free radicals, molecules that in concentrated amounts can cause tissue damage. Antioxidants sop up and neutralize free radicals. So, the thinking goes, taking antioxidant should lessen some of the damage and soreness after exercise and allow people to train harder.But recent experiments with endurance athletes have found that consuming large doses of vitamins C and E actually results in a slightly smaller training response. 

So for the new study, which was published online this month in The Journal of Physiology, scientists at the Norwegian School of Sports Sciences in Oslo and other institutions, some of whom previously had studied aerobic exercise and antioxidants, set out to repeat those experiments in a weight room.

They began by recruiting 32 men and women who had at least some experience with weight training. They measured the volunteers’ muscular size and strength.Then they randomly divided them into two groups. Half were asked to start taking two antioxidant vitamin pills each day, one before and one after exercising. The total daily dosage amounted to 1,000 milligrams of Vitamin C and 235 milligrams of Vitamin E, which “is high but not higher than athletes commonly use,” ...The other group did not take any supplements.

All of the volunteers then began the same resistance-training regimen, consisting of four fairly rigorous training sessions each week. As the exercises grew easy, weights were increased, with the aim of pumping up the size and strength of the volunteers’ muscles.The program lasted 10 weeks. 

In general, people’s muscles had increased in size to the same extent, proportionally. The group that had taken the vitamins now had larger muscles. So did the group that had not. But there were subtle but significant differences in their strength gains. Over all, the volunteers who had taken the antioxidants had not added as much strength as the control group. Their muscles were punier, although they had grown in size.

The differences continued beneath the skin, where, as the muscle biopsies showed, the volunteers taking the vitamins had reduced levels of substances known to initiate protein synthesis. Protein synthesis is necessary to repair and strengthen muscles after weight training. So the volunteers taking the vitamins were getting less overall response from their muscles, even though they were following the same exercise program.

Exactly how antioxidant pills change muscles’ reactions to weight training is still unknown. But Dr. Goran and his colleagues speculate that, by reducing the number of free radicals after exercise, the vitamins short-circuit vital physiological processes. In this scenario, free radicals are not harmful molecules but essential messengers that inform cells to start pumping out proteins and other substances needed to improve strength and fitness. Without enough free radicals, you get less overall response to exercise.

The upshot is that whether you lift weights or jog, Dr. Goran would advise “against the use of high-dosages of concentrated antioxidant supplements.”