The 72-Hour Rule for Building Muscle | Dr. Andy Galpin
In a Nutshell
Train each muscle group every ~72 hours to create mechanical tension, the primary driver of muscle growth. Load can be heavy (5 reps) or light (up to 30 reps) as long as sets approach failure within 1–3 reps. Track progress by adding weight, reps, sets, or range of motion every 2–3 weeks to ensure progressive overload.
These notes were generated by AI and may contain inaccuracies.
All we're trying to do is increase muscle size. What this generally takes is what's called mechanical tension. This is primarily driven by volume. You need to put some sort of load on the muscle, and you got to do it kind of often.
The 72-hour rule states that every 72 hours or so, try to put a stimulus on the muscle you want to grow. Some training protocols will break that rule, but the rule is to learn the rules first before worrying about all the exceptions.
72 hours might mean something like body part split training where you train arms one day and then back another day and quads another day. Or you could do whole body every day and train every third day. What you'll see consistently among all those effective programs is that most of the time, every 72 hours or so, they're trying to get your muscle to work a little bit.
More recently, the research has been really clear that mechanical tension tends to be the driver that is heavyish lifting weights. You can go kind of on the heavier side of the spectrum. This might look like something where it's kind of as heavy as you can go for as low as five repetitions per set. Or it can go the other end of the direction, which is light and a lot of repetitions. There is excellent research showing even up to 30 repetitions per set can give you equal muscle growth as five to six repetitions per set. Plenty of studies on this.
What that should tell you is it's not about the repetitions per set. It's about some underlying physiological principle and that is what's called mechanical tension.
If you like to go to the gym often and you want to use a routine that requires you to be in there five or six days a week, great. If you're the person who goes, I got two days a week to lift, awesome. We could do it differently. If you want to be in there every single day, then maybe think about something like a body part split. So one day for your shoulders, the next day for your calves, the next day for your hamstring. In those days, you're going to do more focused work and you're probably going to lift harder.
If you want to get some muscle growth and you got two days a week, then a more full body routine is recommended so that even if you're lifting say Monday and Thursday or Tuesday and Saturday, every 72 hours, every muscle or most of them gets some sort of mechanical tension placed on it.
You can use barbells, dumbbells, your body weight, bands, machines, kettle bells. All of it is fine. They're just different ways to put tension on the tissue. They're not all exactly the same. The reason they all do work, and there are plenty of randomized control trials and other types of research on these, and they all show that they work, is because they're fundamentally getting to the same stimuli in the tissue.
You can go light, you can go heavy. How much rest you take in between sets, you can do either. If you rest a small amount of time, then you'll have to go lighter. That's fine. You can rest a lot, say two, three, four minutes in between. This allows you lot to recover a lot. In fact, more recent research suggests this is potentially even better. Either one is fine.
Exercise choice includes machines or barbells or free weights, isolation work. All of it's fine. All of it is possible. When we would differentiate these are when we have more specific information about you, such as how many days you want to be in the gym, is it a particular body part you want to have larger, do you have any injuries, what's your history, what exercise equipment do you have available.
Other things to think about are whether to emphasize the eccentric portion, go slow with repetitions or go fast. All of them work.
You have to try hard. As long as you reach pretty close to failure, then it's fine. More recent research indicates you don't have to go all the way to failure. Most people are going to say something like within one to three repetitions to failure, at least by your last set. If you feel like you could have got one more rep done, but that's it, you're probably in a good spot. If you feel like you could have done five or six or eight more reps, that's probably not enough tension to drive a ton of hypertrophy.
If you're thinking about your program and you're like, "Man, I'm trying to gain muscle," if you're checking all those boxes, then you're probably in a good spot. If you're not growing, then we would need to think about other things like: Are you being consistent enough? Are you progressively overloading? Are you sleeping, eating, and all the other variables go into it.
With progressive overload specifically, all we're referring to here is some sort of increased stimuli. You can get this by adding a little bit of weight or load. The next time you come to the gym, you add a couple of more pounds. That's the easiest one to describe, but it's honestly not super realistic. It's quite difficult to just continue to add load. It only lasts four or five weeks, then eventually you just can't keep adding load.
The more common ways are to progress with something like adding a few more repetitions per set. You go to the gym and you pick a certain weight. Last time you did 50 lbs for this given exercise and you did it for eight repetitions and now this week you try to get it to nine repetitions and then the next week 10, 11 and so forth. You're going to hit a limit there at some point, but that's another style or option.
You could add more sets. You did two sets this week of that exercise. Now you do three sets next week. You could do a combination. You could add a little bit of load and a little bit of reps or a little bit of reps and a set. All of these represent progressive overload.
You can increase the range of motion that you're using. You can increase the frequency so you train that muscle three times in a week instead of twice in a week. There's lots and lots of ways you can progress.
There are some nuances within it of course, but at some level you have to add insult. You have to add challenge or hypertrophy will be limited most of the time. The single largest reason people get plateaued or don't see any progress is they don't have any sort of structured progressive overload. This is where you'll see a significant difference between making up your workouts as you go and having a plan.
Even if that plan is not great, when you have a plan in place, you will see more results. Period. It's easier to track. It's easier to monitor. And you can make very simple things like okay did I do a little bit more work this week than I did last week.
Realistically, even colloquially, week by week progress is not realistic. Even if you progress every two weeks or every 3 weeks that's still fine. That may be more realistic. You don't necessarily have to literally try to get better every single time or to lift more load or more repetitions every single week. That will last for a few weeks, few months at most and then you'll not be able to progress anymore.
Just think of it conceptually. What did I do last time? Try to match that or do a little bit better one way or the other. That would represent your progressive overload.
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