Anyone who has ever watched Ronnie Coleman’s DVDs knows that Ronnie trained only one-way: heavy. But there’s a thin line between training hard and running your nervous system into oblivion so you can’t recuperate. Some bodybuilders mix heavy and light training.

Scientists tested the “training balls-to-the-wall” theory by comparing it to a mixed training system that included both heavy and lightweights. Subjects were divided into two groups: a combined training group (heavy and light training) and a normal group (heavy training only). For the first six-week block, both groups performed a standardized training program. For the remaining four weeks, the groups performed different training programs: The combined group performed five sets of 90% of 1RM with three minutes of rest between sets, plus one set at 50% of 1RM. The normal group performed just five sets of 90% of 1RM with three minutes of rest between sets. The only difference between the two programs was the addition of a single set at 50% of 1RM after the main sets, which was completed until muscular failure.

The researchers reported that, as expected, the size of the participants’ thigh muscles in both the combined and normal training groups significantly increased during the first six weeks (the hypertrophy phase). However, they also reported that in the following four weeks (the test phase), only the combined group increased muscular size, while the normal group actually trended toward losing a small amount of size. They also found that the combined four-week training program led to a larger increase in 1RM leg press than the simpler four-week strength program followed by the normal group.

The study suggests that a variation in sets and reps can produce greater hypertrophy than continuous heavy training.