Metabolic stress is when the metabolic waste products such as lactate and a lowered pH that accumulate faster in your muscles than your body can deal with them. This is what produces the familiar “burning” sensation in your muscles during the last few reps of your set when you are lifting weights.
The theory is that the more metabolic stress you can create for your muscles, the more anabolic (i.e., muscle building) hormones will be released, such as testosterone and growth hormone.
Does less rest equal more muscle?
In other words, the more work and less rest you give your muscles, the more metabolic stress will be created, which will supposedly lead to a surge in muscle building hormones.
Research has found, however, that lactate may take much longer to clear the body than we initially thought. This means that it doesn’t really matter if we rest 30 seconds or two minutes between sets because our body will not be able to clear the lactate in that short amount of time.
In fact, it has been discovered that the typical half-life of lactate in the blood is about 20 minutes so fretting about whether you should rest 30 seconds or 3 minutes in between sets seems kind of pointless.
The good news, however, is that lactate is no longer believed to be the cause of fatigue in the muscle.
So instead of focusing on lactate and this whole idea of “metabolic stress,” we should probably focus on a few things that do significantly change with shorter or longer rest periods — things such as ATP resynthesis and muscle pH recovery.
Without falling too far down the scientific rabbit hole here, all we need to know is that ATP is the energy a muscle uses to contract, and the level of muscle pH (acidic or basic) affects how strongly the muscle is able to contract.
Unlike lactate, the majority of ATP used is replaced within a few minutes. Full muscle pH recovery, however, takes about five minutes. What this means is that the difference between resting 30 seconds in between sets and resting 3 minutes between sets can make a big difference in your workout. Not in the amount of metabolic stress (lactate) you have, but in the amount of work you will be able to do the following set.
Everything comes with a price
This is the tradeoff with short rest periods and fast circuit training type workouts. Yes, you may be able to keep your heart rate up in the magical “orange” zone for a bit longer, but you won’t be able to lift as much weight as many times.
Ultimately, less overall training volume (reps & sets) means less muscle.
This is why most powerlifters and strength athletes rest 3-5 minutes or more in between sets, so they are fully recovered for their next set.
Does this mean everyone should be resting 3-5 minutes in between sets?
Unless you are a competitive powerlifter or attempting a new personal best, resting this long in between every set is probably unnecessary.
Also, certain exercises will naturally require different amounts of recovery time.
Full body heavy compound movements like a squat or deadlift will typically require longer rest periods than an isolated single-joint exercise like a bicep curl or a leg extension.
Finding a balance between volume and recovery
Here’s the thing, unless you are lifting near your maximum capacity, you don’t need to be 100% recovered from the last set in order to do the next one.
You just need to be recovered enough.
So how do you know when you’ve rested enough?
This is the intuitive part of lifting, where you know from both experience and your current state or recovery when you are ready for the next set. Not because the timer on your phone tells you you’re ready, but because you feel you’re ready to go.
I think we have all had those workouts where everything is going great. The right machines are opening up at the right times, we are feeling well-rested and motivated, and the weights seem lighter than usual.
Unfortunately, most of us have also all had those workouts when we are exhausted, our muscles are still sore from yesterday, and we feel like we are simply going through the motions.
Because each workout brings its own unique set of physical, mental, and emotional baggage, we have to be willing to adjust our workout accordingly—including our rest periods.
So what’s the deal?
On the one hand, we are told that we should set a timer to keep things moving and to get in as much work as possible. While on the other hand, we are told that we should simply listen to our body and rest as long as we need between each set.
What’s even more annoying is the fact that they are both right.
Timing rest periods vs. Self-monitoring recovery
Setting a timer can be a form of external motivation like a coach who is there to push you, keep things moving, and prevent you from getting distracted along the way.
At the same time, you also need to listen to what your body is telling you. Some sets (and days) are just harder than others, and you may need a little more or less recovery time despite what your coach or the annoying beeping timer may be telling you.
I’ll be honest with you. I use a timer that automatically starts when I log my last set, but most days, I use it more as a suggestion to keep moving rather than a requirement.
I’ve tried purely self-monitoring my rest periods in the past, but too often, I found myself getting distracted, checking my phone, and losing track of time. Before I knew it, my 1-3 minute rest period had turned into 5-7 minute breaks which not only lengthened my workout, but also got me more than a few dirty looks from the guy waiting to use the machine behind me.
The bottom line…
Research has shown that there is no magic rest period length that is going to give you a surge in hormones and blow up your muscles. In the end, your level of muscle growth is still going to come down to the amount of weight you lift and how many times you lift it.
Multiple studies have shown that your muscle’s ATP and pH will recover almost fully after 3-5 minutes depending upon the nature and intensity of the set.
That doesn’t mean that you should necessarily have to wait that long in between each set if you feel rested enough to continue.
However, because you are not increasing or decreasing your metabolic stress (i.e., lactate concentration) by shortening your rest periods to 30-60 seconds as many bodybuilders believe, there is little reason not to rest at least 1-3 minutes in between sets.
Whether or not you decide to use a timer or choose to self-monitor your rest breaks, should not make a significant difference to your overall results in the gym. Although I have found that I benefit from having a ticking clock telling me to keep moving and not get distracted, that could just be me.
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