Rest Periods For Strength Development
KEY POINTS:
1) If you have the time then rest until you feel ready for your next set. If it doesn't compromise volume too much then longer rests will lead to better strength development.
2) The studies on rest periods and muscle growth are pretty split. Some show shorter rests are correlated with greater gains in muscle, and some show longer rest periods are more effective. Looking at the mechanisms of muscle growth and my personal experience of training has me pretty convinced that longer rests are better all round where possible.
3) If you are continuously unable to get enough volume in due to resting too long between sets then rather than shortening the rest periods perhaps look towards zig zagging between two exercises which train completely different muscle groups.
How long to rest between sets is a big practical considerations for people looking to build as much strength as possible. Generally I think the fatiguing nature of the main exercises that strength trainee's use dictate the rest periods anyway, and I tend to have my clients autoregulate their rest periods (so they go into the next set when they feel ready to do so rather than monitoring their rests with a stopwatch).
The questions regarding rest periods that I'm most commonly asked are along the lines of "should I try to reduce the duration of my rest periods as I'll often take five minutes between a sets of squats?", or "if I'm pushed for time should I focus on cutting my rest periods a bit to get everything in?". These are great practical questions which will be answered in this article. Whilst I find the theory of what causes fatigue to build up during a strength training session interesting it doesn't really matter as far as the practical application goes, after all if you're fatigued then you're fatigued. Knowing the reason behind it isn't going to allow you to take a shorter rest period however like I said I do find it interesting so I'm going to briefly summarise what causes this fatigue. If you're completely disinterested then skip this next section and check out the more relevant practical recommendations.
What Causes The Fatigue?
The fatigue that builds up as you progress through a strength training workout is compromised of some level of CNS related fatigue as well as peripheral fatigue (within the muscle). We know that some level of CNS related fatigue occurs during a training session which reduces the ability to activate the muscles resulting in drops in force production. We also know that CNS fatigue dissipates extremely quickly when you finish training (as quickly as 20 minutes or so) so longer rest periods are almost certainly going to minimise CNS fatigue going into the next set versus shorter rest periods.
Some researchers propose that shorter rest periods associated with higher levels of metabolite accumulation may also result in reduced force production due to afferent feedback. This would be a case of the higher levels of discomfort associated with metabolite accumulation (the 'burn') causing a signal to be sent to your spinal cord requesting a reduction in muscle activation.
The muscle itself is also experiencing fatigue as you progress through a workout. Here we have a reduced ability to both activate individual muscle fibers (eg a reduction in calcium ion release) and for individual fibers to produce force (which is often associated with the production of inorganic phosphate and ADP). So even if there's no CNS fatigue present these factors will still reduce force thus the weight you're able to load on the bar. Fow what it's worth I think processes within the muscle along with it being harder to get 'amped up' for sets as a workout progresses are the main factors.
How Long Should I Actually Rest Between Sets?
This is going to be dependant on what kind of weight you're using relative to your max, how strong you are, and which exercise you're performing (you could maybe make an argument for how aerobically fit someone is as well but I don't think it's particularly relevant unless someone is way way out of shape). For someone who's extremely strong and performing multiple doubles at 90% 1RM on deadlifts they may need >8minutes rest between sets. A weaker less experienced lifter may only need 2-3 minutes. The key is to take long enough between sets so you're mentally focused and ready to perform well again. We aren't necessarily looking to completely maintain force production as that would involve a ridiculously long training session but we are trying to avoid large drop offs in strength from set to set which compromises the training adaptations.
Firstly think about what you want to achieve in the session. As a strength athlete I'd suggest that intensity is more important than volume (although volume is still a very important factor and shouldn't be overlooked). I'll give an example of how I mean this. Imagine your session consists of 4 sets x 5 reps at 85% 1RM. How hard this is will vary quite a bit between individuals with absolute strength being an important factor but let's say that this person could hit 7 reps if they performed an AMRAP set at 85%. This means that 4x5 at that intensity is going to be extremely hard work which will require rest periods of likely 4-5 minutes for the average intermediate level lifter. If they decided to repeat each set after 2 minutes and wanted to maintain the five rep sets it's likely going to look something like 85% x 5 reps, 85% x 5 reps, 80% x 5 reps, 78% x 5 reps. The point being that they've sacrificed weight on the bar just to get the sets in faster. The adaptations will be better if they rested longer and hit all sets at 85% simply because the level of stress is higher and heavier lifting is more specific to getting better at lifting heavy things. (Caveat - this can vary between individuals but it's generally the case playing the averages).
So with the shorter rests the volume has been maintained as far as hitting 4x5 but it's been done in a way that's suboptimal. If the lifter in this example was in a rush to get through all of their programmed work in a session then my suggestion would usually be to still take the longer rest periods on the main work (ie the big compound lifts) to keep the quality and loading high, then reduce rest periods a bit on the 'easier' assistance based exercises.
With these kind of exercises (such as leg extensions for example) I think resting on the longer side is beneficial but taking shorter rests and just getting the work in will often be the best route if you're in a rush. Any reduction in muscle activation may not be as much of a problem as we might think because even though some fibers aren't recruited they'll still feel tension due to most of the force being transmitted laterally across the muscle. It could be a reasonable proposition that this will lead to at least some sort of hypertrophic response even in the fibers not recruited. I don't think it's likely as ideal but I think there could be some sort of response that makes it a better option than getting in way less volume (because the reason for doing leg extensions in the first place is likely for a hypertrophic response). However on the main lifts keeping intensity up should be more of a priority than volume unless it's going to result in a drastic difference such as only fitting in two sets instead of five sets. In that case a heavy top set followed by load reductions in subsequent sets with shorter rest periods would probably be more beneficial.
The main take away there is that if you have the time to rest until you feel well recovered and still get your full session in then take it. If your reps are dropping off rapidly set to set (or each set feels way harder than the last) then I'd suggest extending your rest periods if they're on the short side (<2mins). If you're in a rush and won't have time to get everything in without short rest periods then get the main work in at a high quality and if you can't get all the assistance work in once in a while I wouldn't stress too much.
If Longer Rest Periods Aren't Viable
If you're constantly pushed for time and need to take short rest periods each session just to get the training in then I'd suggest zig zagging exercises and adjusting your programming accordingly. The idea here would be to work between two completely different exercises such as squats and pull ups, or a deadlift variation and OHP. If you took two minute rests after performing each exercise you'll be taking more like five minute rests between the exercise that hits the same muscle group when you take into account the time to set up and perform the lift. This means that you'll be working at a similar pace as usual so won't sacrifice volume but you'll be able to get in more high quality work because you're giving each muscle group more time to recover. With isolation type exercises this same principle can be applied and the rest after each exercise can be reduced due to the less fatiguing nature of these types of exercises.
This is also why I believe peripheral fatigue seems to play a bigger part than CNS fatigue. High levels of CNS fatigue would suggest that you'd still struggle to train a completely different exercise after a two minute rest because the activation of all muscles would be reduced and not just the ones you're working. For example if you were performing bent over rows and built up CNS fatigue then you'd also find that your strength on triceps extensions took a hit which doesn't seem to happen, at least not to a notable extent.
I feel like I've stumbled through this article a bit (my kids are nagging me to go out on the trampoline with them) but I hope it had the information that you were looking for!