So, we’ve talked about the importance of muscle strength previously and also the consequences of muscle weakness on function, QoL, potential resilience to injury etc. These things, in part, make restoration of strength an important parameter of many rehabilitation (or prehabilitation) programmes. But just as we need to get the characteristics of the intervention right, we need to make sure there’s adequate recovery time.

Planning and designing a resistance training program for muscular strength development requires manipulation of variables that include exercise selection, training volume, training intensity, movement velocity, and importantly rest

During our programme design, we’re aiming to recruit as much as possible the fast twitch motor units (a motor nerve and the muscle fibres that it innervates); the associated muscle fibres are characteristically strong, powerful, and have fast twitch abilities … however, as you probably remember from 1st year physiology, they’re also very fatiguable. So just as we need to optimise the intensity of muscle activation to recruit these units, we need to ensure that we’re not encountering diminishing returns with repeated efforts i.e. compromising the ability to sustain the high force ‘conditioning’ muscular contractions required to promote muscular strength adaptations.

How Much Rest Should We Give?

The time pressures of clinical practice and the need to ‘persuade’ the novel exerciser of the benefits of going to the gym, it becomes a reality of weighing up getting a decent amount of conditioning work done within a limited time (let’s face it, it’s an easier sell to tell a novice exerciser it’s only 30 mins of hard work, versus and hour!) against the potential for muscle fatigue…
So how much rest is sufficient between sets?

Let’s simplify the problem a little and focus our intervention on muscle strength.

Rest Between Sets

How much do you think?  You may say it’s anywhere between 30s to 2 minutes+ if you read the methodologies of RCTs that investigate the effect of strength training on any particular variable or condition, which isn’t helpful. I’ve always plumped for 1.5 minutes, which is partly based on the findings of the literature and partly based on my experience observing the 100s of recovery profiles following strength testing and high-intensity exercise.

Can we be more specific? A really nice systematic review, published last year (Grgic et al 2018) attempted to answer this question. They noted that the current recommendations by the American College of Sports Medicine stating that

‘…extended rest interval duration should be utilized when the goal is to increase muscular strength”

are based on “level 4 category of evidence which is ‘‘expert [opinion] level,’’ not on level 1 evidence (which is systematic review), hence the purpose of their review.

So what did they find from the literature?

Resistance-Trained

Broadly speaking, an inter-set rest interval of >2 mins is likely to be required for optimal strength gains. However, several of the studies included in the review demonstrated significant strength gains with shorter time intervals. So it’s a case of weighing up the pros and cons. As the authors rightly point out, Robinson et al (1995) showed that during a training protocol of 4 x per week for 5 weeks, an inter-set rest interval of 3 mins was associated with greater strength gains compared to 1.5 minutes…but there was only 1% difference between groups. So, in a cost-benefit analysis, what’s more important, saving time or a further 1% improvement?

Also there may be a difference between young and old, with older adults perhaps requiring shorter inter-set rest intervals compared to  younger adults, albeit their being considerably less research on resistance-trained older adults.

Untrained

For those unaccustomed to resistance training, it appears from the limited research available that short to moderate rest intervals (1 – 1.5 mins) is sufficient to enable significant strength gains.

So that’s it, or is it?  Maybe not.  There are just a couple of things I want to point out here.  First, sifting through the studies included in the excellent review by Grgic et al (2018), most interventions used a rep range that exceeded 8 RM, with the majority of studies using 10-12.  Thus we could argue, that certainly towards the 12RM +, we might be working more towards muscle endurance, recruiting fewer fast twitch motor units and thus require less rest to recover.  If you’re using a more ‘intense’ approach, i.e. 5RM, you may want to consider a longer rest period, for example > 1min between sets.  We want to avoid fatigue and compromising the ability to sustain the high force ‘conditioning’ muscular contractions throughout each set.

Secondly, it’s probably wise that, whilst discussing the topic of rest, that we address another important variable: inter-session recovery i.e. the carry-over effects of a prior session on the next.  However, I think we’ll do that next week.

How Much Rest Then?

Well, first, broadly plan out the progressive resistance training/rehabilitation plan you want your patient to complete (how many sessions, how many exercises, how many sets etc.). Then add in the variables like time (or perceived lack of), training history, propensity to do what you ask (and all the other moderating psychological factors that influence buy-in) and then see what you’re left with to get the work ‘done’. A high-intensity (5RM) intervention with a trained young person might require at least 2 mins of rest between sets, whereas in the first few weeks of a similar programme with a un-trained older adult, you might get away with 1.5 mins, or less, between sets.

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References
Grgi et al (2018) Effects of Rest Interval Duration in Resistance Training on Measures of Muscular Strength: A Systematic Review Sports Med. 48:137–151

Robinson et al. (1995). Effects of different weight training exercise/rest intervals on strength, power, and high intensity exercise endurance. J Strength Cond Res. 9(4):216–21.