Research Review: Rest intervals affect strength and hypertrophy

By Helen Kollias

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You go to the gym and work out. You do everything to make sure you improve.

You work really hard and you do everything you should be doing, pushing yourself, increase weight when you can, keep good form, follow PN and even keep a workout/diet log, but you don’t time your rest between sets. Why?

Well, that’s anal.

You just feel silly with a timer beeping or staring at the clock.

Anyway, you know how long to rest. Right! Right? You just wait until you feel ready. And really how much does it really matter?

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Research question

How much of a difference is there between, say, a minute rest and 2 ½ minutes? Does it matter to strength gains? Weight loss? Or hormonal response? This week’s study looks at just these questions.

Buresh R, Berg K, French J. The effect of resistive exercise rest interval on hormonal response, strength, and hypertrophy with training. J Strength Cond Res. 2009 Jan;23(1):62-71.

Methods

Participants for this study were twelve young (19-27 years old – average age of 25.3) untrained males with some weight training experience.

None of the participants consistently weight trained for the 3 months before the study. So they had weight trained before, but they weren’t doing much of it now.

The program

During the 10 week training program the only nutritional guideline for the subjects was to consume 1.7 g of protein per kilogram body weight.

For reference, a 75 kg (165 lb) participant would be asked to eat 127.5 g of protein – not a lot.

There were no controls (checks) put in place. So who knows what these guys were actually eating? It’s possible that some guys ate way more protein while others ate less protein than the 1.7g/kg body weight.

Keep this in mind when we get to the results section.

Exercise protocol

There were four weight training sessions a week with two different workouts (1 & 2). A week of training looked like this:

Day 1 – Workout 1

Day 2 – Workout 2

Day 3 – REST

Day 4 – Workout 1

Day 5 – Workout 2

Day 6 – REST

Day 7 – REST

Not a bad 2-day split for the week… if they had used a body split, say, of upper body and lower body, but they didn’t.

Below is a table of the exercise, repetitions and sets for the two workout sessions. Basically, workout 1 was leg/shoulder/abs day and workout 2 was back/chest/arms.

Table 1 – Outline of weight training protocol for Workout 1

Exercise Sets Repetitions
Squat 3 10
Leg curl 3 10
Leg extensions 3 10
Standing heel raises 3 10
Seated dumbbell press 2 10
Dumbbell lateral raises 2 10
Rear delts on pec deck 2 10
Abdominal crunches 2 To fatigue
Lying leg raises 2 To fatigue

Table 2 – Outline of weight training protocol for Workout 2
Exercise Sets Repetitions
Pull-downs 3 10
Machine rows 3 10
Machine bench press 3 10
Pec flyes 3 10
Incline dumbbell curls 2 10
Machine biceps curls 2 10
Dumbbell kickbacks 2 10

A fairly stereotypical beginner program: too much focus on chest, shoulders and arms (4 sets for biceps) with not much for legs (3 sets for hamstrings).

If you’re interested in a more balanced program I would recommend one from the PN Online Resources – Training Programs.

Each participant was instructed on how to do the exercises and supervised for the first session of each workout. While participants were contacted weekly to see how things were going, more of the workouts were unsupervised.

This is pretty much how most exercise studies work: Testing is done, participants are shown how to do the exercise and then they are left pretty much on their own for the rest of the training.

This is far from ideal, since you don’t know if people are actually working out, if they are doing the exercises properly, if they are pushing themselves, etc. So why do most studies follow the self guided exercise program?

Well let’s look at this study: You have 12 participants working out 4 days a week for about 1 hour/day for 10 weeks.

That works out to be 480 hours (48 hours/week). You would need to have more than one full time researcher just to monitor workouts!

Even though it’s better to be supervised, in most cases it just isn’t possible.

The experiment

So far everybody was doing the same thing – same nutrition, same workouts, same exercises, same reps, same sets.

The difference was the rest between exercises: Half (6) of the participants were assigned short rests of 1 minute and half assigned long rests of 2.5 minutes.

Again, I have to mention that the participants weren’t monitored, so how closely these times were actually followed is a huge question.

Measurements

The researchers looked at three areas of exercise response:

  1. Body composition/lean tissue (% body fat & lean body weight): using hydrostatic weighing
  2. Strength: 5 repetition maximum (5RM) for the Smith machine squat (don’t get me started) and the Smith machine chest press
  3. Hormone concentration (the whole point of the study): blood plasma hormone levels of growth hormone, testosterone and cortisol were tested.

Results

Body composition/lean tissue

After 10 weeks of training there was no change in percent body fat in either group, though there was an increase in lean body weight and overall body weight in the short rest group (1 minute rest).

Strength

There were increases in chest press and squat 5RM after 10 weeks of training for both groups.

The long rest group (2.5 minute rest) had a 14.9% increase in 5RM chest press strength and 27.4% increase in 5RM squat strength. Pretty much the same strength increases happened with the short rest group: 10.5% increase in chest press strength (5RM) and 24.0% increase in squat strength (5RM).

This is merely speculation, but I think with more participants there might have been a difference between groups in strength. If there were more participants (increasing the statistical power) in the long rest group, would they have more strength gains compared to the short rest group?

Now you’re thinking: what the____? Either there is a difference or not.

True. But in a study with small groups, any individual differences make it really hard to figure out experimental differences.

In this study with only 6 participants in each group, all you need is one participant that is responding differently (because of genetics, eating more or less protein, or not following the workouts) to mess up the analysis. If there were 20 participants in each group, then differences are more likely to average out. (I’ll stop before I completely go off on a statistical probability lecture.)

Growth hormone, testosterone & cortisol

Despite the small groups, there was a difference in hormone levels between groups after the 1st week: The short rest group had higher testosterone and cortisol compared to the long rest group.

There were no differences in growth hormone, most likely because of limited lactate increases and huge differences between subjects: individual growth hormone levels ranged from 2 ng/mL to 25 ng/mL in the first week of testing in the short rest group!

That’s over 12 times the difference from one person to the next. This variability makes it nearly impossible to figure out differences because of the type of training.

Hormone levels at the halfway point (5 weeks) and at the end (10 weeks) were the same for both groups. No difference in testosterone, cortisol or growth hormone.

Conclusion

What did they find in this study? Well, short rests between sets increase testosterone and cortisol more than long rest between sets in the first week of training and possibly longer.

The similarity in growth hormone between groups could be because of huge individual differences or lack of lactate build-up because of the training.

After 5 weeks any hormonal differences were gone. This finding gives you a really good reason to change your program regularly.

Even with a sub-optimal workout program and no real nutritional changes, you can have increases in strength (in both groups) and lean body mass (short rest group) after 10 weeks of working out. Great!

Sorry, but the workouts didn’t decrease body fat.

Bottom line

A short rest time (1 minute) give you a greater hormonal response initially compared to a long rest time (2.5 minutes), but you should change your workout (rest, sets, reps, entire program) every 3-4 weeks, otherwise you adapt. Oh, 2.5 minute rests are likely to be better for strength than shorter rests.

Learn more

To learn more about making important improvements to your nutrition and exercise program, check out the following 5-day video courses.

They’re probably better than 90% of the seminars we’ve ever attended on the subjects of exercise and nutrition (and probably better than a few we’ve given ourselves, too).

The best part? They’re totally free.

To check out the free courses, just click one of the links below.