Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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Short rest period between sets stimulates anabolic hormones only briefly

If you train with short rest periods between the sets, your body produces more anabolic hormones than if you take longer rest periods between sets. But this effect wanes after a month, according to an American study of twelve [what else?] untrained male students. Researchers at the University of Nebraska published the results of their research in the Journal of Strength & Conditioning Research.

The researchers got their test subjects to do weight training four days a week for ten weeks. In two training sessions the subjects exercised all muscles in their body. One group took 2.5 minute rests between the sets [LR] and the other took 1 minute rests [SR].

When the researchers examined the students' blood during the first week of the experiment, the analyses confirmed the results of previous studies: that training sessions with short rest periods increase the production of anabolic growth hormone and testosterone [structure above]. But by week 5 the effect had declined considerably, and by week 10 it had disappeared.

The figure below shows the effect on the testosterone level. The figure is based on measurements done on samples taken ten minutes after the training session.

Short rest period between sets stimulates anabolic hormones only briefly

The figure that shows the effect of the training schedules on growth hormone production is almost the same.

Short rest period between sets stimulates anabolic hormones only briefly

The effects of the two different training schedules were also pretty similar. In terms of strength and muscle circumference, the schedule with the 2.5 minute rest periods was slightly better. But in terms of body weight, body fat and fat free mass, the schedule with the 1 minute rest periods seemed better.

Short rest period between sets stimulates anabolic hormones only briefly

The researchers stress that the study is very small and that there were large individual differences between the students' responses. But bearing these ifs and buts in mind, the researchers suggest that the positive effect of short resting periods is apparently temporary. This would have consequences for the way in which strength athletes can get the most out of their strength training.

"If it is true that the concentrations of endogenous anabolic hormones are determinants of long-term muscle growth, then regular alterations in training protocol (i.e., periodization) may contribute to maximizing results by eliciting greater hormonal responses", the researchers write.

So you could train with a short rest period for a few weeks, and then with a longer rest period for a few weeks.

We, the nitpicking compilers of Ergo-Log, have another theory. The researchers asked the students to use short or long rest periods. They didn't use a trainer and didn't check what happened. Training with short rest periods is heavy going. The students in the SR group may have lengthened their rest periods. In the beginning they may well have followed the researchers' instructions obediently, but after a while they started to be a little easier on themselves.

We'll be keeping to short rest periods between our sets. At least: we'll try to do so. Really.

J Strength Cond Res. 2009 Jan;23(1):62-71.