Don’t worry about the number of reps or hormone levels. Just lift until you can’t.


Over the last few years, I’ve written repeatedly about a series of strength-training studies from Stuart Phillips’ group at McMaster University. The basic message of these studies, in my view, has been: stop stressing out about all those training details that people like to stress out about. Strength training is simple—as long as it’s hard.

The group’s latest study is now out in the Journal of Applied Physiology, and it amplifies this message.

In previous studies, they’ve compared the effects of lifting relatively light weights lots of times versus lifting relatively heavy weights fewer times, and found that it makes very little difference to how much muscle and strength you gain. But some of those studies were conducted with untrained volunteers, or with unorthodox training protocols, leaving skeptics unconvinced.

So this time, the study involved 49 volunteers who all had a minimum of two years’ experience in strength training at least three times a week. They underwent a 12-week full-body strength-training program, performing a rotating selection of three sets of five exercises, done four times a week.

Half of the subjects lifted a heavy load of 75-90 percent of one-rep max for 8-12 reps per set; the other half lifted a light load of 30-50 percent of one-rep max for 20-25 reps per set.

The results? For the vast majority of measures, there was no difference between the groups. Muscle mass and muscle fiber cross-sectional area increased to the same degree in both groups. Strength increased to the same degree for all exercises except the bench press, where the heavy weight group had a slight advantage.

The researchers also tested blood samples to assess levels of a variety of hormones: serum total testosterone, free testosterone, cortisol, dihydrotestosterone (DHT), dehydroepiandrosterone (DHEA), luteinizing hormone, insulin-like growth factor 1 (IGF-1), free IGF-1, lactate (mM), and growth hormone. Neither the levels of these hormones nor how much they changed post-workout had any bearing on how much muscle or strength the subjects gained.

Phillips’s view is that muscle recruitment is what matters. If you lift to failure (or near-failure), you’re recruiting essentially all the motor units in a given muscle. That happens relatively quickly with a heavy weight; it takes longer (and more reps) with a lighter weight, but you end up in the same place as far your muscles are concerned.

One point that’s worth noting: previous studies have sometimes compared heavy and light weights by matching “volume.” For example, if you lift 10 pounds 10 times or 20 pounds five times, your total volume is 100 pounds in either case. But that’s a misleading way to do it, because it’s much harder to lift 20 pounds five times than it is to lift 10 pounds 10 times. To inflict the same stress on your muscles, you need to match effort.

Of course, if you compared the effects of lifting a feather a million times versus lifting an anvil once, I expect you’d find some differences. The point here is simply that, within a reasonable range, the effect of program details like number of reps and size of weights is very, very small compared to the effect of how hard you push.

To me, that’s a very liberating message—and while I don’t think you can translate the results directly to endurance sports like running, I do think the general sentiment applies. It’s why, if I’m traveling and happen to have a chance to do a workout with a group of local runners, I seldom stress about the details of the workout. Whether it’s repeat 600s or 1600s, I know that what matters most is how tired I am at the end, and I can reach that goal via many different roads.

A true love for sports

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