Intensity in HIT
The “I” in HIT stands for Intensity, which practically speaking means reaching momentary failure (MF). The point at which a load can no longer be lifted, when dynamic movement becomes an isometric contraction, represents 100% intensity: the HIT Gold Standard.
An Agreed Definition of Intensity?
When conversing with a wider audience there can however be a challenge, potential for miscommunication, in the interpretation of the term used. As James Fisher, James Steele and others have pointed out, there are trainers and researchers who associate the term “intensity” with the percentage of a 1 Rep Max (%1RM) being used during exercise. A 1RM is the most weight an individual can lift for one single repetition of an exercise. A percentage of this load is then often used for a given number of reps in research papers and in training routines, such as 80% 1RM x 8 reps.
Load is Not Intensity
You may see researchers and trainers referring to the “intensity” of a set being 80% of a 1RM or 65% of a 1RM and so on. However, the %1RM used in an exercise is not necessarily representative of the actual effort level required to perform a set of that exercise. For example, if a researcher notes that all subjects performed 8 reps of knee extension exercise at 80% of 1RM, it is problematic to say that all subjects trained at 80% intensity. Some subjects may get close to MF at 8 reps with this load, others may be a significant way from reaching MF. The intensity of effort required to perform 8 reps at an “intensity” of 80% of 1RM is variable between individuals- the stimulus level is therefore not equal amongst all individuals.
If instead all subjects were instructed to train through to MF with 80% of 1RM, effort will be the same between all subjects. Effort will be maximal and in HIT terms, intensity will be 100%. Therefore the actual load used in an exercise plays a secondary role to the level of effort required to lift it at the point we terminate the set.1
Effort or Intensity
Perhaps the term “effort” serves us better than “intensity” to help avoid misunderstandings between various camps in the strength training community. When HIT advocates say “high intensity” we mean “high intensity of effort” or simply maximal effort. James Fisher defines effort as “the amount of physical or mental energy being given to a task” and more specifically in the context of resistance training, going to MF means “maximal effort being given to lifting a load… but unable to complete the task.”
MF is of course the classic endpoint goal of a HIT set, but there are other points in a set that can and have been used as endpoints in various approaches to strength training. Let’s take a look at them.
Possible Endpoints to A Set of Exercise
- Nonrepetition Maximum (nRM)– you stop the exercise after a predetermined number of repetitions, despite having the ability to perform more reps.
- Self-determined Repetition Maximum (sdRM)– exercise is stopped when you think you have performed the last full-repetition possible (i.e. you believe you would reach MF on the next rep)
- Momentary Failure (MF)– you cannot complete the current repetition with correct technique
- Momentary Failure Plus Advanced Techniques (MF+)– after MF has been reached the exercise is extended with additional advanced techniques (such as drop sets, forced reps etc.)
According to Steele, Fisher and other researchers, “MF represents the point of maximal effort as it is the point where, despite the greatest effort, a person is unable to meet and overcome the demands of the exercise”. 1 Achieving MF in a set will always represent 100% of possible effort, or put another way maximal effort is achieved by reaching MF in an exercise.2 Which brings to question what level of effort is required to best stimulate hypertrophy and strength increases?
The Best Endpoint?
Exercising to nRM may not provide a strong enough stimulus for the adaptations we seek. Whereas working to sdRM may be, but MF may stimulate better results overall than sdRM, at least within a single-set model. 1 James Fisher notes that it appears advanced trainees do get a greater adaptation in going through a set all the way to MF. He also points out that “True MF may be important because it is difficult to know where else to stop.” It is also worth noting, that MF+ does not appear to stimulate any better physiological results than MF.
James Steele adds that there may be a threshold for optimal results just before MF or just before maximal effort is reached, but research cannot currently define this point if it even exists: his advice is to “Push towards MF… and get there if you can.”
Actual Effort vs. Perception
There is another important issue related to stopping a set before MF has been reached, that of perception. In exercise, there is actual physical effort and then there is your perception of effort and other related feedback, such as perception of load and perception of discomfort. All of which are factors that can impact your performance of an exercise and the actual physical effort level you reach in a set.
James Steele points out that actual effort is “centrally generated by the brain and doesn’t rely on sensation or feedback coming from the muscles.” He elaborates that actual effort relates to a signal from the brain that recruits muscle, whereas “perception is something different and doesn’t necessarily match up with effort.”
This can be problematic in exercise that is stopped at any point prior to MF because we tend not to be very good at matching our perceived effort with actual effort. We may stop a set far further from MF than we believe we have, due for example, to the perception of discomfort. Remember, discomfort is not effort. This brings in to question the validity and value of ratings of perceived exertion (RPE) scales, where an individual is instructed to exercise to a certain level of perceived exertion. 3
Can you predict when you will reach MF?
As trainee’s who have performed HIT for a significant amount of time, you may be better than many at predicting how close you are to failure. However, I’m sure you have had the experience of grinding out more reps than you thought possible, surprising yourself with a couple of extra full reps after thinking the set was done. At the other end of the spectrum too, you may have had the experience of seemingly cruising through a set, surprised when out of the blue you suddenly hit MF prior to your expectation. As seasoned HITers if we can’t accurately predict when MF will occur, what chance does a novice or someone with less experience have?
Velocity Loss as a Marker of Effort
Are there any reliable markers that can tell us we are close to MF prior to it happening? Research led by Paulo Gentil, in which both James Steele and James Fisher were involved, suggests there is: movement velocity loss. This research (3) revealed that when exercising with a 2/2 rep tempo and 75% of 1RM load, velocity loss happens at a specific point in the set- the second from last full repetition.
Penultimate Full Rep- the first rep in which velocity reduces
Ultimate Full Rep- velocity reduces significantly more than in the previous rep
Momentary Failure Rep- movement slows to a halt during the concentric
The researchers point out that the velocity loss observed of ~20% that precedes failure is easily perceptible and that “This kind of velocity loss represents a significant degree of fatigue.” So, under these conditions when the rep perceptibly slows we can know that we are within a rep or two of MF.
A further interesting point to come out of this velocity loss paper is that despite the slowing that was observed in the 75% of 1RM group, there was another group who did not display velocity loss prior to the MF rep. This other group used 50% of a 1RM, it appears that lighter loads may not cause any significant slowing in exercise performance prior to the MF rep itself, which may make going to true MF all-the-more important when using lighter loads.
The Essence of Effort
Maximal effort occurs in strength training when we intend to continue to lift a load at the end of a set but are unable to complete the task with correct technique.
The “High Intensity” in High Intensity Training is equivalent to Maximal Effort and is achieved in continuing an exercise to the point of Momentary Failure.
Simply stating a certain % of a 1RM is used in an exercise is not meaningfully representative of intensity of effort, as load used is not directly indicative of the effort level reached in a set.
Rate of Perceived Exertion scales can be misleading because perception of effort, perception of load and discomfort are not the same as actual effort.
With loads above a certain threshold, notable velocity loss can tell us when we are within a rep or two of Momentary Failure. However Momentary Failure remains the gold standard endpoint of a set and reaching maximal effort may be required for stimulating best results particularly within a single-set approach to exercise and for advanced trainees.