Rest Periods In Depth


By Rob Clarke Driven Sports

Having covered load, tension and rep cadence we can move onto rest intervals between sets. This can be a point of contention. Some say rest little, others say rest as long as you need. I’ll return to my discussion of bodybuilders and strength athletes while examining this topic

I should note here that if you haven’t read the previous articles leading up to this, it is probably a good idea.

The composition of muscle | Muscle fiber type and adaptation | All about rep range: bodybuilding vs. powerlifting | The high vs. low reps debate | Workout dynamics part one: load, tension and speed | Workout dynamics part two: “rep-centrics”

Powerlifters and bodybuilders once again…

Powerlifters aim to lift the most weight possible for a single rep in competition. Their training is based largely around this, using low-rep sets as a means to build maximum strength. Some of them tinker with higher reps (relative for them) during some phases of their training, but for the most part this is their training year-round. In training, rest intervals between these heavy-weight low-rep sets can be anywhere upwards of five full minutes. In competition they try and take as long as possible between attempts, stretching the contest’s three minute time limit as much as possible. The idea behind the long rest period is to allow for maximum neuromuscular recovery. 

Obviously after their first working set in training (assuming it’s more than one rep and not a sub-maximal effort) or their first attempt in a contest they will have likely caused some damage to the muscle. This alone could take a few days to recover 100% if they left the gym there and then (or quit the contest), but giving themselves adequate time between sets can go a long way towards allowing the muscle to recovery somewhat extensively. 

Bodybuilding dogma tends to prescribe a fairly short rest interval between sets. In many cases this will be 30-60 seconds at most. Having seen a Jay Cutler DVD or two I can tell you that he barely rests 40 seconds between most sets (the video editing makes this hard to fully assess on his heavier compound lifts, but I’ve no reason to doubt what he says about rest periods when he talks to the camera). The shorter rest can lead to a great pump, excellent mind-muscle connection, and a lot of bodybuilders believe this is superior for fat loss and body compositioning. In fact some old school fat loss programs specify shorter rest periods as a way of increasing the heart rate more, leading to a higher calorie burn. The difference in calorie burn is dubious, and any difference that does exist is marginal at best. I’ve no doubt that people “feel” like they’re burning more though! I do like to go off on a tangent, but I’ll pull it right back to my point – while powerlifters aim to maximize neuromuscular recovery between sets and attempts with prolonged rest intervals, bodybuilders seemingly try to avoid neuromuscular recovery at all costs. There’s a good reason why this can be beneficial.

Muscle fuel

What I mean by neuromuscular recovery is largely based around the metabolic pathways that are used to fuel the muscle fibers. We can find out more about this if we ‘look under the hood’ of each muscle fiber. This shouldn’t be too complex as Fiber types and adaptation has already laid the groundwork into the infrastructure of each fiber. The metabolic pathways are oxidative phosphorylation, glycolysis and the phosphagen (phosphocreatine) system, and each contributes in varying amounts and under very different conditions to the sole aim of generating the “currency” of the cell: adenosine triphosphate, better known as simply ATP.

As you may have guessed, ATP is three phosphates attached to an adenine molecule (there is also a ribose sugar attached). Fundamentally, the way it acts as a currency is by phosphorylating (i.e. donating a phosphate) to other proteins involved in cellular management. By doing this it can switch something ‘on’ or ‘off’, and change the way a protein behaves. This is what fuels everything in your body, including the muscle fibers. 

Slow twitch fibers are fuelled typically by oxidative phosphorylation from the breakdown of fatty acids in the presence of oxygen. This is aerobic (“with oxygen”) respiration, and relatively speaking it is a slow process compared with glycolysis. Glycolysis is the conversion of glucose into pyruvate. It occurs regardless of the presence of oxygen (anaerobic, “without oxygen”), making it ideal for fast twitch fibers to use for ATP generation once their stores of phosphocreatine are depleted. Slow twitch fibers have a very low capacity for glycolysis. This is why a brisk walk is unnoticeable in the calves (which have a fairly high composition of slow twitch fibers) but a set of moderately heavy calf raises for high reps results in a burn like no other. 

The absence of oxygen

The body utilizes glycolysis or the phosphagen system depending upon the effort demanded of the exercise. As I’ve said previously, the type II muscle fibers utilize these metabolic pathways, and to involve them in exercise rapidly, you need to exert the most effort. In other words, heavy loads and explosive movement. The phosphagen system is fuelled by phosphocreatine (PCr), an immediate store of phosphate. Each phosphate donated by PCr goes towards creating ATP from ADP, which then goes on to donate the phosphate where it is needed, becoming ADP again. This ADP is given another phosphate from PCr, and so the cycle continues – at least for as long as you have PCr. During intensive effort, PCr stores of a muscle can be completely depleted within seconds. As you may have guessed, bolstering the store of PCr is one way in which creatine is such an effective ergogenic. 

A single one-rep-max (1RM) set may not be sufficient to deplete the PCr stores completely, but a more exhaustive set certainly will. Replenishment of PCr after an exhaustive set takes a minimum of about four minutes, so you get an idea of where the 3-5 minute rest period suggestion comes from. 

Many articles you will read tend to display the crossover in energy systems in the form of time. I will alternatively attempt to illustrate the crossover by means of reps per set. This won’t be perfect by any stretch of the imagination, but its close and will suffice for future discussion. 

Sets ranging from about 1-3 reps will almost exclusively be fuelled by PCr assuming the load used is one where you’re expecting to get 1-3 reps. 3 reps with a weight you can easily throw up 12 reps with will not challenge your fibers the same way. (This stipulation exists for the rest of these examples.) Sets ranging from 4-6 reps will be fuelled by a combination of PCr and glycolysis. It is likely that the end of this set will have largely depleted PCr stores. Sets ranging from 7-12 will be more or less entirely glycolytic. I have little interest in rep ranges above this as it suggests that you are using a weight that is lower than 65% of your one-rep max – something I stated in the conclusion of the previous instalment to be below the threshold for stimulating adequate growth. The only exception to this, in my opinion, is calf training, which may benefit from high rep training as well as heavy, low rep training. And just for anyone thinking that I am missing 20-rep squats out here, the entire notion of 20-rep squats is that you load your 10-rep max onto the bar and bang out 20 reps with it – no matter how long it takes. That is a HUGE difference from using a weight that is actually your predicted 20-rep max.

Now we know the metabolic pathways we can look into the consequences and what it means for muscle.

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