Using percentages of 1RM ignores the big differences between individuals and exercises
We are all used to seeing workout programs that specify a particular percentage of one repetition-maximum (1RM) as the weight to be used, often for a set number of reps.
Such workout programs are often used when we are *not* training to failure. Their purpose is to provide guidance regarding the number of reps, so we know when to stop the set.
Yet, the number of reps we can do to failure with a given percentage of 1RM can vary depending on several factors.
What factors affect the number of reps we can do with a given percentage of 1RM?
The number of reps we can do with a given percentage of 1RM varies depending on:
- Training history — athletes who have a background in endurance sports can do more reps with a given percentage of 1RM than strength athletes. In one study, endurance athletes did 20 reps with 80% of 1RM on the leg press, while weightlifters only managed 12 reps with the exact same percentage of 1RM.
- Exercise —on some exercises, we can perform quite a lot of reps with a given percentage of 1RM, while on other exercises the number is much lower. In one study, strength-trained individuals did 18 reps with 80% of 1RM on the leg press, but only 8 reps with 80% of 1RM on the seated row.
- Tempo — when we lift with a slow tempo, we can perform fewer reps with a given percentage of 1RM than when we lift with a fast tempo. In one study of the bench press, strength-trained subjects managed 7 reps with 65% of 1RM with a slow tempo (3-second lifting and lowering phases), but managed 12 reps when using a fast tempo (1-second lifting and lowering phases).
Hopefully, these examples show that the differences can be very large!
And if we add them together, the differences could be enormous. For example, an endurance-trained individual working on the leg press with a fast bar speed would surely be able to perform many, many more reps with a given percentage of 1RM than a strength-trained athlete working on the seated row with a slow tempo.
Why does this matter?
If we follow a prescription to do a certain number of reps with a percentage of 1RM, then its purpose is to allow a sufficient stimulus to the high-threshold motor units of the targeted muscle, while also stopping the set before we reach muscular failure (usually 1–2 reps beforehand).
In principle, this can be a good thing, since training to failure is not a good idea for athletes, since it seems to accelerate the conversion of fast twitch muscle fibers to slow twitch muscle fibers, and the accumulation of fatigue contributes to muscle damage, which slows recovery.
The problem is that the prescription may not work.
If you follow a program that prescribes a percentage of 1RM for a given exercise, there are three possible outcomes:
- You follow the prescribed number of reps, but have to stop before you reach the target number because you reach muscular failure, which was not the goal of the workout. This could easily happen if you came from a powerlifting background, and started a bodybuilding program.
- You follow the prescribed number of reps, but have to stop before the set really gets hard, which means you probably don’t get recruit all of the high-threshold motor units of the targeted muscle. This could happen if you came from a bodybuilding background, and started a powerlifting program.
- You follow the prescribed number of reps, and stop just at the right point, which is one or two reps before failure. You get all the benefits of hitting full motor unit recruitment, without the detrimental side effects that come with accumulating lots of fatigue.
Whether you hit the sweet spot depends on how close you personally are on the exercise/tempo you are using to the standard tables that the coach writing the program referred to, when writing your program.
What can you do instead?
Ultimately, setting the percentage of 1RM is a way of setting the proximity to failure. Ideally, we want to get close enough to failure to ensure that we have recruited all the high-threshold motor units, but we don’t really want to accumulate too much fatigue.
Fortunately, we can achieve the same goal more accurately in at least three other ways.
- Using repetition maximums — we can test “repetition maximums” for a number of reps, and then subtract 1 or 2 reps to reach our intended target. For example, if we want an athlete to do 3 sets of 8 reps, we would test their 10RM, and then prescribe their 3 sets of 8 reps with that weight.
- Using repetitions in reserve — we can guess the approximate load that the athlete can lift for a number of reps, then subtract 1 or 2 reps to reach our intended target, then ask them to stop 1 or 2 reps before reaching failure. For example, if we want an athlete to do 3 sets of 8 reps, we would guess their 10RM, and then prescribe 3 sets of 8 reps with that weight. In practice, they may only manage 3 sets of 6 reps, or they may achieve 3 sets of 10 reps, but the proximity to failure will be correct either way.
- Using bar speed — we can guess the approximate load that the athlete can lift for a number of reps, monitor their bar speed during the set, and ask them to stop once bar speed drops below a certain level. Monitoring bar speed during any set to failure will show you the bar speeds that correspond to 1 or 2 reps prior to failure.
What is the takeaway?
Coaches often write percentages of 1RM to help athletes decide what load they should use for a set of reps, when not training to failure. Yet, when using this approach, it is easy to perform too many or too few reps, depending on your training history, and the exercise/tempo. In such cases, the workout either fails to produce the right stimulus (insufficient recruitment of high-threshold motor units) or causes the wrong stimulus (too much fatigue).