Introduction

There's an age old debate about which is more important; training intensity or training volume? Should you focus more on training every set very hard, or should you back off a bit and perform more sets? Perhaps a bit of both would be wise? Before we can answer these questions, we must first understand and agree upon definitions for the terms "intensity" and "volume". Depending on context or the sport being discussed, these terms can have different meanings, and so we need a consistent definition of each before moving forward.

What is training intensity?

Training intensity can be defined in two very different ways. There is "intensity of load" and "intensity of effort". When someone mentions training intensity, it's important to know which definition they're referring to. Intensity of load refers to how much weight you're lifting, while intensity of effort refers to how intense a set feels to you or how close to failure you take that set.

Intensity of Load

Intensity of load refers to the load on the bar and it's relation to your one-rep max, specifically what percentage of your one-rep max is on the bar. The higher the percentage of your one-rep max you have on the bar, the higher the intensity. Lifting 90% of your one-rep max, for example, is considered very high intensity. Each percentage of your one-rep max also correlates to a general rep range; naturally, the higher the percentage of your one-rep max on the bar, the less reps you will be able to perform. So lower rep ranges that use higher percentages of your one rep max are considered higher intensity than lighter rep ranges using a lower percentage.

Intensity of Load is more commonly used in strength sports where load on the bar is very important for getting the desired training stimulus. The higher your intensity of load, the stronger the strength stimulus. In other words, the heavier you train, and thus the lower your rep range, the more strength you will build.

Intensity of Effort

Intensity of Effort refers to how difficult, from a subjective point of view, a set feels. There are two popular methods of rating a set's intensity of effort, the [RPE scale] and the [RIR scale]. Both scales are very useful and which you use will mostly come down to preference.

RIR (Reps in Reserve) refers to how many more reps you could have done when you stop a set. If you do a set of 8 repetitions when you could have gotten 10 repetitions, this would be considered an RIR 2. The lower your RIR (the fewer reps you have left in you) the higher the intensity of effort. Most working sets will fall within an RIR of 4-0, with anything higher acting as a warm-up.

RPE (Rate of Perceived Exertion) refers to how difficult you find a set to be on a scale of 1-10. The higher the rating (the more difficult the set feels), the higher the intensity of effort. Working sets will typically fall within an RPE of 6-10. 

Both scales work very similarly and can sometimes be interchangeable. There are some slight nuanced differences, but ultimately they work to achieve the same goal of helping you manage training intensity. 

According to research, an RIR of 4 or an RPE of 6 is the minimum intensity that is required for an adequate training stimulus. Training with a lower intensity than this can result in very little or no training stimulus at all. This holds true for both hypertrophy and strength. The higher your intensity of effort, the stronger the training stimulus, but the more fatigue you will accumulate as well.

What is training volume?

Training volume is a measurement of how much work you do in a given time period. Most commonly volume is tracked for each workout session as well as total weekly volume. There are two common methods of defining and measuring training volume. We'll explain both below and their applications to training.

Volume Load

Volume load, sometimes referred to as tonnage, is calculated as Reps x Sets x Weight. Performing 3 sets of 10 reps with 100 lbs on the bar would count as 3,000 lbs of tonnage or volume.

This method of defining volume has been around for a very long time and is commonly used in strength sports, but also has applications in hypertrophy. Volume load is best used as a tool to track long term trends of performance in individual exercises more so than tracking overall muscle group volume. Over time, you should be able to lift more weight for more repetitions and/or sets, thus your volume load should steadily increase over your lifting career for each individual exercise.

Increasing volume load slowly and steadily can also be a great way to consistently progress on your lifts to maintain the proper intensity of effort as you get stronger.

Using volume load is a great way to track training volume when lifting very heavy loads below the 5 rep range. When reps are this low, tracking volume load can be a great way to make sure you're doing enough volume to progress. However, as repetitions become higher, there is a potentially more practical method of defining volume when you want to predict training stimulus.

Hard Sets

A recently popular method of defining volume is the total amount of "hard sets" that you do in a given time period. A "hard set" would be defined as any set that meets the intensity of effort threshold previously mentioned. Any set that is done with a minimum intensity of RIR 4 or RPE 6 counts as a "hard set".

This method of defining volume is much more practical to use in order to track total volume for each muscle group. It is also more closely correlated to training stimulus [1][2]. That is, the more hard sets you do, the more stimulus you get for both strength and hypertrophy. Performing 5 hard sets will provide more stimulus than 3 hard sets, regardless of volume load differences.

Because you're tracking only total sets, using this definition of volume is much easier to track and adjust. It also makes it easier to manage fatigue, since all you need to do is adjust the number of sets you perform.

Recommendations for strength goals.

Phew, now that we have all that out of the way, we can move on to actual volume and intensity recommendations. 

For strength-oriented goals, both intensity of load and intensity of effort are important. The closer to your one-rep max you lift, the stronger the strength stimulus. And of course, as we mentioned before, you must train with the correct intensity of effort in order for those heavy sets to count. Make sure all sets have a minimum intensity of RIR 4/RPE 6. There does not appear to be any large benefit to training all the way to failure for strength [3], so it's recommended that on average your training sets be done with an RIR 4-2 / RPE 6-8.

Volume is still important for strength since as volume increases so does the training stimulus achieved. However, heavier sets are more fatiguing than lighter sets, meaning that much of the training done for strength will require that you cut back on total sets done in order to continue training heavy without recovery issues. Because of this, focusing on increasing volume load by doing more reps or more load is more common than trying to push for more total hard sets for strength purposes.

Recommendations for hypertrophy goals.

Hypertrophy has been shown to occur similarly across nearly all loading schemes, meaning intensity of load is mostly unimportant as long as you avoid the extremely heavy rep ranges (<5 reps). And just like strength, intensity of effort is very important. The closer to failure you take a set, the stronger the hypertrophic stimulus. All working sets should be done with a minimum intensity of RIR 4 or RPE 6. It is important to note that the closer to failure you take a set the more fatigue it will generate as well, so make sure to keep this in mind when training, as training to maximize growth is a balancing act between stimulus and fatigue.

In terms of training volume, hypertrophy has been shown to have a very strong dose-response relationship with the total amount of sets done, meaning you should define volume as "total hard sets" for hypertrophy focused training [1]. The more sets you can perform and recover from, the more hypertrophy you can achieve. This also means that because you want to perform as many sets as you can to maximize hypertrophy, most of those sets should not be in the very heavy rep ranges (<5) to facilitate better recovery. It's much easier to perform and recover from 10 sets of a moderate load than it is to recover from 10 sets of a very heavy load. Moderate to light loads will allow steady, long-term progress.

Take Home Points

The intensity vs volume debate is an "either-or" fallacy. You shouldn't look at the two as completely opposing ideas. All training goals will require both to progress optimally, but the balance of each will differ depending on your goals. They are two pieces of the same puzzle, without one, the puzzle is incomplete.

Regardless of whether your goal is strength or hypertrophy, you must train with a minimum intensity of effort of RIR 4/RPE 6. Train with a lower intensity than this and the training stimulus is very weak to non-existent, meaning you won't make progress no matter what your goals are.

For strength, intensity of load is of utmost importance. The closer to your one-rep max you train, the stronger the strength stimulus. Volume load is more important for strength than total hard sets, because total hard sets will be limited due to training with higher percentages of your one-rep max, which are more fatiguing, leading to a necessity to train with fewer sets. Instead of progressing by adding sets, you'll more commonly see a focus on increasing volume load over time through increased reps and/or load on the bar.

For hypertrophy, intensity of load is mostly unimportant, as hypertrophy has been shown to occur at similar levels across nearly all loading schemes. Hypertrophy also has a very strong dose-response relationship with total hard sets done [1], so a heavier focus on doing more sets is more optimal than focusing on volume load. Because you want to maximize the number of hard sets you can perform for hypertrophy, you'll want to avoid extremely heavy rep ranges that hinder your ability to perform a lot of total sets due to fatigue.