On heavy lifting days, it’s wise to take your time between each set. It’s not uncommon for coaches to have you pair up with a fellow athlete of similar size and strength to make the weight transitions easier. One person lifts, the other rests. Reverse and repeat as necessary. Most people will have an internal clock in their bodies that determines when they’ve had enough rest and their muscles are ready to work against a load. But what is that optimum time? And why is it so important that we use it to recover?

The body’s primary energy resource for ANY muscle contraction/force exertion is from a molecule called adenosine triphosphate (ATP). Now, there is a lot of science that goes into understanding ATP, but the simplified version for the understanding of this piece is that the body has a limited supply of ATP, and it must be replenished for work to continue. With that being said, the amount of rest taken in between sets is directly related to how much energy will be available to the muscles for the following set.

Now, there are three energy systems that produce ATP: ATP-PC (high power, short duration), glycolytic (moderate power/short duration), and oxidative (low power/long duration). All three systems are readily available and ‘initiated’ at the outset of any activity. The type of activity is what dictates which system(s) are used.

So, in the case of heavy lifting (think 1-3 rep max attempts), ATP-PC is utilized to generate immediate power. However, we only have this system for around 10-15 seconds of maximum output. ATP that is already present in the muscle is used and recycled by breaking down creatine phosphate. Once we have depleted our ATP (through a 1 rep max attempt, for example), it takes at least 3 minutes of rest for muscles to recover the maximum amount possible of ATP and creatine phosphate. After at least 3 minutes have elapsed, your ATP-PC system will be ready for explosive movements again. Therefore, it’s quite obvious that if you attempt to lift again within these 3 minutes you will struggle to get the same results from a prolonged rest.

If you have exhausted your ATP-PC system, but continue to workout (think heavy metcons or AMRAPS), then the glycolytic system kicks in. When this happens, the anaerobic energy system (the glycolytic system) breaks down elements of our muscle glycogen to form more ATP. Our muscles get more fuel, but we also have negative kickbacks in the form of lactate and hydrogen ion (acid) secretion. We are all very familiar with the burn we experience during AMRAPS and metcons, and we can thank the buildup of these ions for that, as they are preventing further muscle contractions at high levels. Though you are able to perform for longer in this zone versus the ATP-PC system, you can’t lift as heavy. However, a useful side effect from the lactate and hydrogen ion secretion is improved human growth hormone secretion, which is a reason slightly higher reps are beneficial for increasing muscle mass (to a certain level).

It’s therefore important to understand just what your muscles need in terms of adequate rest time when heading into your workout. It goes without saying that you should take your time with heavy lifts, but hopefully now you have a deeper understanding and appreciation for the process your body is going through. So next time you fail on that 1RM back squat, ask yourself if you were giving your legs a long enough break.

William Imbo
William Imbo is an Associate Editor at BoxLife magazine, CrossFit Level 1 Trainer and holds an MPS in Sports Industry Management from Georgetown University. He is an avid CrossFitter and loves film, music and travel, thanks to having grown up across Europe. A fan of the New Orleans Saints and Newcastle United, Will's favorite CrossFit girl is Helen-least favorite being Isabel.


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