This study makes no claims. But I bet other people will.

In the fitness industry, everyone’s trying to get or stay ahead. And while there are lots of ways to do that, tapping into published research is one of the more common ways to “reveal” something new and come across as being more leading edge than the next guy/girl.

I would argue that most people who post links to PubMed haven’t read the actual study, but are just browsing abstracts. I’ve written about what abstracts are good for in the past. But it’s been a while since I’ve really taken the theme up.

This paper piqued my interest because I think it’s interesting and because it generates a new host of questions about what we don’t understand. But it’s also a great illustration of how discordant the abstract is from the full paper, and how it could be used as a great marketing gimmick.

Villanueva MG et al. Influence of rest interval length on acute testosterone and cortisol responses to volume-load-equated total body hypertrophic and strength protocols. Journal of Strength and Conditioning Research, 26(10):2755-2764, 2012.

There’s something about testosterone that gets every male fitness-freak all excited. It’s like the magical essence of muscle; the philosopher’s stone of size. There’s a whole nation of it. My buddy Brad Pilon even wrote a massive review on it. We actually still understand very little about it, except that given in larger-than-normal-production doses, it makes guys more muscular. Research on testosterone manipulation without an external source, however, remains fairly infantile; possibly because it’s fairly difficult to study it without being able to control it externally.

We know that increasing serum concentrations of testosterone via aromatse-inhibitors doesn’t necessarily translate to more size. In fact, increasing them to four-times baseline with an aromatase-inhibitor doesn’t seem to translate, on average, to more size.

These researchers set out to figure out whether the time you take between sets makes a difference in your testosterone and cortisol production.

Here’s the abstract:

We hypothesized that total body strength (S) and hypertrophic (H) resistance training (RT) protocols using relatively short rest interval (RI) lengths between sets will elicit significant acute increases in total testosterone (TT) and cortisol (C) in healthy young men. Six men, 26 (±2.4) years, completed 4 randomized RT sessions, after a control session (R). The S and H protocols were equated for volume load (sets × repetitions × load); S: 8 sets × 3 repetitions at 85% 1RM, H: 3 sets × 10 repetitions at 70% 1RM, for all exercises. The RI used 60 seconds (S60, H60) and 90 seconds (S90, H90). Blood was drawn preexercise (PRE), immediately postexercise (POST), 15 minutes postexercise (15 MIN), and 30 minutes postexercise (30 MIN). The H60 elicited significant increases in TT from PRE (7.32 ± 1.85 ng·ml) to POST (8.87 ± 1.83 ng·ml) (p < 0.01), 15 MIN (8.58 ± 2.15 ng·ml) (p < 0.01), and 30 MIN (8.28 ± 2.16 ng·ml) (p < 0.05). The H90 also elicited significant increases in TT from PRE (8.37 ± 1.93 ng·ml) to POST (9.90 ± 1.25 ng·ml) (p < 0.01) and 15 MIN (9.46 ± 1.27 ng·ml) (p < 0.05). The S60 elicited significant increases in TT from PRE (7.73 ± 1.88 ng·ml) to 15 MIN (8.35 ± 1.64 ng·ml) (p < 0.05), and S90 showed a notable (p < 0.10) difference in TT from PRE (7.96 ± 2.29 ng·ml) to POST (8.75 ± 2.45 ng·ml). All the protocols did not significantly increase C (p > 0.05). Using relatively short RI between RT sets augments the acute TT response to hypertrophic and strength schemes. Shortening RI within high-intensity strength RT may lead to concomitant enhancements in muscle strength and size over a longer period of training.

The abstract sounds awesome, doesn’t it? Decrease my rest interval to 60 seconds and get HY-UGE. That’s what I want. Not just huge, but strong at the same time. Bonus. If I didn’t think it was unscrupulous, I’d be publishing my own e-book right now (or at the very least, a free secret report).

As a whole, the paper is not as well-written as I’d like (but I’ve just come to terms with my own neuroses about it–i.e. it’s do-able, but hardly anyone does it). As usual, there are far too many tests of significance that are unadjusted. But on the whole, the design was okay (randomized order using random number tables), and the study falls short on generalizability (which is not a _study_ flaw, but rather, an interpretation limitation.)

The catch-phrase in the abstract however, is the kicker, “Shortening rest interval within high-intensity strength resistance training may lead to concomitant enhancements in muscle strength and size over a longer period of training.” This is, in actuality, short form for, “If we did this experiment again and again over the period of a few months to years, we MIGHT see gains in strength and size. Does anyone want to do this study? Because we didn’t.”

In fact, there are several sentences in the full paper that emphasize the exploratory nature of the experiment:

1) “Because this was a pilot study…”
2) “Although the mechanism(s) underlying acute bout hormonal responses leading to chronic improvements in muscle size and strength remain to be fully clarified…”
3) “Nevertheless, the precise mechanism for this upregulation are not fully understood…”
4) “Even though a causative link between increased muscle activity and the acute increases in testosterone in response to the total body strength protocols examined in the present investigation cannot be made…”

The major flaw in this study is the lack of comparison between the shorter and longer rest interval conditions. There is a virtual wall of text outlining the differences between the shorter rest interval condition and the REST condition, and the longer rest interval condition and the REST condition for both the hypertrophy and strength-based protocols (the REST condition being the one where the subjects sat still for 45 minutes), but nothing on comparing the short to the long rest interval, and nothing on comparing the hypertrophy-based vs strength-based programs.

From an interpretation point of view, the range of increases in testosterone ranged from 12 to 22.5% for each of the rest/protocol combinations (short rest/hypertrophy, long rest/hypertrophy, short rest/strength, long rest/strength). We have seen reports of four-fold increases (i.e. 200%) in serum testosterone not having much of an effect on muscle or fat mass over 8 weeks, so while you _could_ do this study over a longer period of time, it’s hard to say HOW long you would have to do it to start seeing muscle accrual occur in a noticeable and meaningful way.

In the end, the last sentence (which is the most eye-grabbing one of the whole paper and abstract together) is thoroughly unjustified. Not only are the percent increases in testosterone not meaningful for growth, but there were no actual comparisons made between the shorter and longer rest interval conditions within the strength protocol.

So when next you read, “You should keep your rest to 60 seconds between sets because this increases your testosterone and therefore muscle mass–honest, it’s in this study…” in some free (or not free) secret-but-just-for-you-if-only-you’ll-give-me-your-email-address report, you’re probably just as well-off sitting on your ass for at least another 30 seconds if you want to, knowing whoever wrote that sentence didn’t actually read the study, and it’s probably not going to make an iota of difference.

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