When we think of quality training, we usually think of high intensity exercise. Pushing hard, going all out and barely surviving our workouts. While this, on occasion, can be a great way to ensure progress, the truth is that for long term, SUSTAINABLE progress, you'll likely want to train with lower intensities the majority of the time.
How do we define training intensity?
Two common methods of defining training intensity is either as a percentage of one rep max lifted or proximity to failure. For the context of this article, we are defining intensity as proximity to failure. The closer you train to failure during a set, the higher the intensity and vice versa.
Two methods of determining and tracking the intensity of a set are using the RIR or RPE scales. RIR stands for Reps In Reserve and refers to how many reps you have left in you when you stop a set. RPE stands for Rate of Perceived Exertion and refers to how difficult you find a set on a scale from 1-10. A set that you stop when you have 1 rep left in you would count as an RIR of 1 or an RPE of 9, for example.
So what does "lower" intensity refer to?
"Lower intensity" refers to an RIR of 4-2 or an RPE of 6-8. Anything lower than this and the training stimulus is so weak that it might as well be considered a warm up. Anything more than this and it falls under "high intensity" training. Ultimately, though, this range can be considered moderate intensity training.
The closer you train to failure, the more training fatigue you accumulate. Some of this fatigue can be felt immediately, while overall fatigue lingers even after a workout. If your training intensity is too high, not only does it impair your ability to recover between sets or exercises, but it also can cause recovery problems between training sessions. If you train a muscle group Monday and Wednesday, but your Monday session is filled with very high intensity training, you may not actually fully recover before your Wednesday session arrives, hindering your ability to train frequently and consistently.
By training with a slightly lower intensity and allowing yourself to have more reps in reserve, you can more easily recovery between sets and exercises as well as much more easily recover between sessions. This allows you to go into the gym every session unhindered and able to perform well enough to cause an adequate training stimulus.
Easier Volume Accumulation
Hypertrophy has a very strong dose-response relationship with volume (total sets done). The more volume you can perform in a given time frame, the more hypertrophy you will cause (up to a point). Because lower intensity training is better at facilitating recovery, it's much easier to accumulate higher training volumes when most of your sets are lower intensity.
If you were to perform a very high intensity set of an exercise, it becomes much more difficult to continue performing sets afterwards due to the fatigue generated, and the total number of sets you can perform in that session with suffer. Lowering the intensity of your sets in order to perform more total volume is a trade off that is typically worth it if you want to build muscle.
Lower Injury Risk
Many injuries occur due to ego lifting. Ego lifting comes in different forms, but it's typically seen as either lifting more weight than you can actually handle safely or going too close to failure or beyond by allowing your form to break down in order to continue performing repetitions. Both result in injuries due to form breakdown, which puts your body in a compromised position.
By using a weight that you know you can handle and allowing yourself to keep reps in reserve, you are far less likely to have form breakdown and therefore far less likely to get injured. A set where you leave a couple of reps in the tank will feel pretty difficult, but not so much so that you'll need to allow your form to break down to complete the repetitions or use momentum to get the weight up.
Many trainees become intimidated by sets where they know they'll need to push extremely hard, which can sometimes negatively impact their performance during a set due to inhibitions holding them back from pushing as hard as they actually could. The mental aspect of training is very important and can truly impact your performance. This is far less common with lower intensity training. Since lower intensity training is less intimidating, most go into them with confidence and are more likely to perform at their peak, finishing the set with very good form. This may lead to a more consistent pattern of performance that is more predictable.
Utilizing lower intensity training is a good strategy for new lifters who are intimidated by resistance training. It's a good idea to start them with easier intensities and slowly introduce them to higher intensities as they get more comfortable under the bar and their form becomes better. Going straight into high intensity training before their form is perfected can be a risk injury.
Lower intensity facilitates higher frequency training
Similar to how lower intensity training can allow you to perform more total sets in a given session, it can also allow you to train more frequently due to better recovery between sessions. This can be helpful for volume accumulation and routine design flexibility. Because you have the option of training more frequently, you can design more complex routines that may be better suited to your individual needs. Rather than train a muscle only twice a week, perhaps you could train it 3, 4 or even 5 times a week if you were to train with lower intensities.
High frequency training can be a great way to spread out high volume training to make each session more manageable. Performing 25 sets of chest is much easier if you train chest three times a week as opposed to only twice and will result in much more manageable per session volumes.