Shorter rest-periods for hypertrophy
Do shorter rest periods impair hypertrophy?
If you have ever done back-to-back “hard” sets, you would know shorter rest periods between sets increases the “burn” of muscles, increases your heart rate significantly higher and often can cause you to run out of breath, whereas a longer rest periods can often relieve these issues. These “issues” are just some examples of fatigue mechanisms.
Shorter rest periods reduce the hypertrophy stimulus and shorter rest periods reduce the number of your reps you can achieve before reaching failure. The reps we lose out on are our “stimulating reps”. The closer we can get to failure WITHOUT an excessive accumulation of fatigue mechanisms, the better the hypertrophy stimulus.
As we start any exercise session, regardless of type (cardio, strength or hypertrophy) we begin a cascade of fatigue mechanisms e.g.increase heart rate, increased body temperature, increased sweat production, increased sodium loss, increased calcium and hydrogen ions (the burn), an increase in other metabolites, increased breathing and so on. The longer we continue exercise, the higher the contribution and accumulation of these fatigue mechanisms.
When we take a break between sets the body begins to buffer (reduce in number) of some of these fatigue mechanisms. The shorter our rest periods, the less of these fatigue mechanisms we can buffer. You will sometimes hear coaches explain this as Central Nervous System (CNS) fatigue, but often many don’t quite understand exactly what this means. No rest between sets or a very short rest between sets will involve high levels of CNS fatigue in subsequent muscular contractions due to these fatigue mechanisms.
One of the most important elements of CNS fatigue is supra-spinal CNS fatigue, which exists in the brain and is involved between the motor cortex (produces the central motor command that creates motor unit recruitment) and the sensory part of the brain (which is what generates our perception of effort).
When we experience an increase in the fatigue mechanisms, we increase our perception of effort closer to the maximum tolerable limit, leaving less capacity to generate the central motor commands and therefore motor unit recruitment. The higher the accumulation of fatigue mechanisms, the higher the perceived exertion of a set or exercise. If the rest periods are too short the accumulation of fatigue becomes so great that even training to failure might not achieve stimulating reps in order to gain muscle as our perceived exertion is being influenced by excessive metabolites and other fatigue mechanisms.
This is where training smart and not hard is a good idea. I often get clients saying to me “I didn’t even break a sweat in that session, and I feel great” or “I don’t have any DOMS after that session”. This is because you do NOT need to break yourself to make gains.
You will often hear even PhD’s, in hypertrophy, preach that higher volumes are equal to lower reps and I agree. However, these PhD’s also mention that you can make equal hypertrophy gains with 45 second breaks compared to longer rest periods but they do not explain context as this cannot be beneficial WITH higher volume sets. What happens in research cannot always be practiced in reality, but some things are just not possible. In higher volume studies, participants very often are also untrained, which opens a lot of questions around relevance of the study. Un-trained individuals, oddly, often recover faster than trained individuals so can handle more volume and can, pretty much, make gains on anything they touch. The more trained you are, the less you need to do because you have the ability to isolate muscles more effectively creating a far greater stimulus. It is due to this ability to isolate the muscles more effectively that trained individuals need to rest as there is less compensatory mechanisms in lifts. Lower volume sessions, with 90-180 second rest periods are potentially better because of the reduced accumulation of fatigue mechanisms described in this article whilst also making time in the gym more effective. These fatigue mechanisms can sometimes last days to recover from, reducing the quantity of stimulating reps (reps closer to failure which cause hypertrophy) that you can achieve in sessions in following days.
It is important to remember, listen to your body, evaluate progress and adjust as needed. Having said all of this, you don’t have to everything I say here regarding “what works”. Try things out yourself. We are all different. Perhaps mix your training with higher vs lower volume and shorter or longer rest periods. Listen to your body –adjust your programming depending on how you feel works best. If you feel awful from doing shorter rest periods, your recovery is reduced, or you aren’t seeing results then increase rest periods and mix up volumes. Perhaps do a de-load, but if you need a de-load you probably are doing too much volume. There’s no point doing a de-load and then doing the same programming again, because you will land up at the same point. Reduce your volume a bit and see if you can see progress. If you aren’t seeing progress still, reduce volume further and overtime start reintroducing volume as you make an increase in reps and load overtime.