Rest Periods
The more we look into rest periods the more we realise the impact it has on performance and overall training in the gym. It is one of those areas that for a lot of people is subject to emotional bias. For instance, we generally do a set when we feel ready, and for all intense and purposes we get the next set out, then the next one and we feel like we progress and think we are going along just fine. But if we actually look at it objectively and try to understand a little bit more about rest periods and fatigue accumulation, we will start to realise a lot of what we might commonly be doing in the gym, in terms of chasing a pump and not letting our body get too cold by taking shorter rest periods, might be counterproductive to our long-term results and progression. With respect to muscle building.
Why Do We Rest?
To start making sense of rest periods and actually deciding how long we should be resting for, we need to ask the question, why do we rest? It sounds like an obvious question but when we start to look into this, we start to open up a lot of ideas to be considering with rest periods and fatigue management. We know we take rest periods because we only have a certain number of resources, and if we are giving maximum effort, there is going to be a point where we run out of the ability to continue to produce enough force to be able to shift the weight. Then we decide to take a rest period to allow those things to dissipate and then comeback and are able to give maximum effort, which would mean more stimulation to the targeted muscle for muscle building.
Short vs Long Rest Periods
When we are talking about short vs long rest periods, we are considering anything below 2min as a short rest period, and anything above 3min + is a long rest period. What we are arguing here is whether it is better to be taking slightly shorter rest periods, where we are more focused on maintaining a pump and blood flow. Or should we take longer rest periods that are more focused around creating better performances, in terms of the amount of weight lifted and the number of reps you might hit in any given set.
When we are looking at identifying what the ideal rest period is we have to look at what it is we are actually trying to anticipate, what is this fatigue that we are talking about. Fatigue has a very clear-cut definition where it is a temporary reduction in ability to produce force. When we look at fatigue being some kind of disturbance in your bodies ability to be able to produce this. Which means despite you getting into your next set, if you don’t have the ability to create force you are going to lose the potential stimulatory affects of that set.
We can broadly categorise fatigue as two different things. Firstly, we have central fatigue which is a reduction in motor unit recruitment. Or your brain’s ability to tell your muscle fibres to contract. Secondly, we have peripheral fatigue which is a reduction in force production in local muscle fibres where there is some kind of disturbance in the actin myosin cross bridges.
Peripheral Fatigue
With Peripheral fatigue we have something going on in the muscle fibre. This could be looking at things like the accumulation of different by products from contracting different mineral. It could be a reduction in available fuel sources, If we look at how your body goes about recruiting motor units, we have low threshold motor units and the high threshold motor units. We want to get those high
threshold motor units recruiting as much as possible when we are in the gym. Because they have the highest potential for force production and for muscle growth. Unfortunately, we can’t just go straight to those muscle fibres cold, the body has to first, in order of sequence go through the low threshold motor units and gradually fatigue and build up to those high threshold motor units.
In this context it might actually be a good thing to be accumulating some of this peripheral fatigue in the low threshold motor units, because eventually once we create all that fatigue, we will eventually get to the high threshold motor units and we will be stimulating them and creating the activation and the force production that we need to build muscle. This is part of why using high reps can still be a very effective stimulus for muscle building.
Say we are doing a set of 50rep max on any exercise, reps 1-10 of that 50 rep max are going to be pretty easy. Because of that low perception of effort and higher contraction speed, there’s not going to be much activation through the high threshold motor units and not much force production through them either. It is all going to come from the low to medium threshold motor units. Then as we approach 20,30,40reps those low threshold motor units start to fatigue. They experience this peripheral fatigue which forces the body to then go to the next level up in motor unit recruitment. Then ultimately by the 45-50reps everything else has been fatigued and the body has no choice but to go to the high threshold motor units and cause them to contract to then be producing force.
This is a useful method for beginners, people overcoming injuries or people who might not be confident using heavy loads in the gym. Now we are not just dealing with peripheral fatigue, we are also dealing with what’s called central fatigue, which is where we are getting this whole motor unit where the brain cell (neuron) is sending an impulse down to muscle fibres telling them to contract.
Central Fatigue
With central fatigue we are getting some kind of disturbance in this message. This becomes very interesting because the body is going to try and work as hard as it can, but due to insufficient rest periods, or due to an overall accumulation of too much central fatigue this message is being interrupted. Which if we are looking at the high threshold motor units, there could be a lot of peripheral fatigue built up and your body should be trying to go to high threshold motor units but if there is too much central fatigue that has been accumulated during the workout, your brain can’t send that message out. For example, say we do a challenging set of 10reps. We hit failure point, then we only take 30sec or maybe even less rest. Then we go into the next set, we are going to be tired and have a really good pump and feel like we have done a lot of work. However, this impulse has been disrupted, we haven’t allowed enough of this central fatigue to dissipate. Then you are going to jump into set 2 or exercise 2 later in the workout and if we have too much of this central fatigue built up that is going to disrupt your body’s ability to actually recruit those high threshold motor units. Instead, the body is going to be left feeling weak, we will feel tired and fatigued and we will end up doing what’s called junk volume. Because it hasn’t been enough to stimulate the high threshold motor units. The only thing that would have allowed that to happen (in terms of the correct stimulation) is if we had taken longer rest periods to allow for this central fatigue to dissipate a little bit more.
When looking at what really causes the most amount of central fatigue, it is anything that is more aerobic based or endurance based in nature. When doing very high reps or having short rest periods in-between all of our exercises and sets. That tends to be more towards aerobic or endurance in nature, compared to taking long rest periods. Why we might get away with it for the first couple of sets and exercises, it will increase a lot through the workout and that’s when you are going to get to say exercise 3 or 4 or sets 3 or 4, and if we are taking short rest periods we are going to be working hard, we are going to feel tired and have some kind of a pump. But we are not going to get the high threshold motor unit recruitment that we need in order to be producing maximum amounts of stimulation. That is part of why it is important to take as long a rest period as needed to allow for this central fatigue to dissipate.
How Long Should We Rest
Most of the literature points towards at least 3mins being the bare minimum of a rest period. When we let people auto regulate their own rest period and just tell them to go when they feel ready, it tends to be more 60-90sec. Which they might feel ready to go, they might feel fresh and ready to do the next set. But within the nervous system, within this motor unit, there is still a diminished response for your body’s ability to recruit and contract muscle fibres. As a result, despite feeling good we are still going to get less stimulation.
As a general rule what is recommended people do is take slightly longer rest periods, say 3mins minimum for most exercises. This is going to vary person to person and exercise to exercise. For example, you need at least 3min when we are looking at big movements like bench press, rows, deadlifts, squats etc. but maybe something like a single arm dumbbell preacher curl, single arm triceps extension, single leg calf raise, anything that’s unilateral and single joint in nature, probably don’t accumulate any where near as much central fatigue as your bigger compound movements, as such need slightly shorter rest periods.
looking at beginners or people who are coming back from injuries, probably aren’t really getting to those true failure points and are not accumulating near as much central fatigue. In that context we probably trend towards slightly lower rest periods. But keep in mind as people get more advanced and as they get better at pushing themselves and as they start using a lot more of these exercises that have good matches with resistance profiles to what you body brings to the table; we are going to create a lot more stimulation overall. As a result, we do need longer rest periods to allow for the muscle fatigue to be dissipating, also within the brain a lot of that fatigue to be dissipating as well. That is what is going to allow us to push a lot harder in each set to get maximum stimulation.
References
- Ganbaru Method, Eugene Teo, Published November 2021, Accessed December 18th Introduction (ganbarumethod.com)
