Most people think of intensity as how hard you’re working on a particular exercise, but in the strict definition, that’s not true.
Intensity actually refers to the percentage of your maximum you’re lifting at. So if your 1-rep max on a squat is 150kg (330 lbs) and you’re doing sets with 135kg (297 lbs), that’s 90%, which is a fairly high-intensity.
For the purposes of this article though, we’ll use this strict definition, but also the one most people mean when they use the phrase intensity, as in their level of perceived exertion.
Basic Intensity Recommendations
The American College of Sports Medicine recommendations state that for those wishing to gain strength, most training should be conducted with between 80-100% of 1RM. Those looking to build muscle should lift in the 70-85% range, and those training for muscular endurance shouldn’t exceed 70% of their 1RM. (1)
These guidelines aren’t a bad starting point, as, while they may be slightly more simplistic than we’d like, they appear to make sense, and most lifters do train in these ranges when they’re training for the corresponding goals.
When you consider that typically you’ll be performing fewer than 8 reps per set for strength, between 8 and 12 for hypertrophy, and 12 plus for endurance, these loading parameters fit.
Intensity and Rep Ranges Dictate Adaptations
In order to make progress, training needs to be tough, but reps still need to be completed with good form.
Taking the above rep ranges into consideration as a rough guide, it’s obvious that a strength or power athlete would need to use above 80% for most of his or her sets, as anything lighter wouldn’t be challenging enough if they were performing fewer than 8 reps.
The person chasing hypertrophy likely wouldn’t be able to go much heavier than 85% while still keeping their reps above 8, and the endurance athlete wouldn’t be able to keep hitting the higher-rep sets using much more than 60% 1RM.
The main reason we want to stick primarily to these rep ranges (and by proxy to these loads/ intensities,) is to do with training adaptations.
The body has two main types of muscle fibre - slow twitch and fast twitch. Slow twitch play a bigger role in endurance activities, and respond better to longer sets with lighter loads/ intensities, while fast twitch are used more for strength and power activities, and adapt to higher loads/ intensities. (2,3.)
Additionally, heavier loads will place a greater demand on the Central Nervous System, which is vital in strength and power development. So actually, while there is a little more to it than just saying - “Use above 80% for strength, 70-85% for muscle growth, and under 70% for endurance” - by and large, it’s not a bad recommendation.
If you were to only pick one intensity category, it’s likely best you stick to what’s outlined above.
However, there can certainly be times when training with lower or higher intensities can be beneficial.
A powerlifter, for example, would want to mostly train with low reps and a high intensity, but could definitely benefit from using higher reps at a lower intensity if they wanted to build some muscle in a certain body part, were recovering from an injury, on a deload, or felt their conditioning needed more work.
Likewise, a bodybuilder or endurance athlete could benefit from a strength phase as a change in stimulus from their usual moderate intensity, higher rep programming.
It’s important we don’t stick solely to one range, all the time. There needs to be some consistency, but variety is crucial, too.
RPE - A Different Kind of Intensity
RPE, or Rate of Perceived Exertion is closer to what most people think intensity is, as it refers to how hard you feel you’re working.
RPE is based off the original Borg Scale, which asked participants to subjectively measure their level of exertion on a scale of 6 to 20. (4)
An RPE scale looks along the lines of -
- RPE 10 = An all-out maximum effort lift, with questionable form.
- RPE 9.5 = A very difficult lift. Form was good, but there’s no way another rep could be done.
- RPE 9 = Tough, but one more rep was doable.
- RPE 8 = Still tough, but there were 2 more reps in the tank.
- RPE 7 = 3 reps left.
- RPE 6 = Not so tough. Still slightly challenging, but 4 reps left.
An alternative to RPE is RIR, or Reps In Reserve, which is what you'll find in all of the MyPhysique training programs in one capacity or another.
- RER 1 = 1 rep left. (Similar to RPE 9.)
- RER 2 = 2 reps left. (Same as RPE 8,) and so on.
Both these methods, while not technically monitoring intensity from a percentage point of view, can be very useful for gauging training effort and progress.
For any goal, your RPE should usually fall somewhere between a 7 and 9.
Any lower than RPE 7 (with the exception of very high-rep endurance work and warmups,) and you’re probably not working hard enough to cause muscular or neural adaptations, and any higher than an RPE means you’re likely using sub-par form, and risk overreaching or burning out.
The Best System?
Neither a percentage-based intensity system or an RPE-style system is necessarily best, and both have their time and place.
If you’re training purely for strength, then it may make sense to use percentage intensities for your big lifts - the squat, bench and deadlift. Whereas for more of a muscle-building routine, and for accessory exercises, an RPE approach will likely work better. This is why the POWER program deals with a lot of percentage-based movements.
As with every other training variable though, your MyPhysique program has been designed with both of these in mind. You may do some percentage-based work, you may do some RPE-based work, but regardless of goals, most of your sets will be between about 65-90% of your 1 rep max, and between an RIR 1-3.