Dr. Feigenbaum,
On a recent Q&A you talked about using a beltless variationas a way to decrease the external load. One may still experience the same internal load though. What are the physiological differences between 2 similar movements (say a squat w/ belt vs a beltless squat) at the same internal load and the same external load? If beltless squats are a way of managing fatigue, but are done at the same RPE despite lower intensity are they contributing the same fatigue as similar RPE squat w/ belt?
Great question. If the external load is substantially less, then we’d expect peripheral fatigue to also be substantially less. Conversely, if the internal load is the same then we’d expect central fatigue to also be about the same- though perhaps for different amounts of time pending the external load.
As far as if beltless squats causing less fatigue when compared to belted squats, yes I think they do as they’re likely to be at a reduced weight and likely produce a reduced internal load due to the lower expectations, arousal, etc. (in most people). I don’t think they’re worlds apart, but if you have many beltless variations, this may add up.
I suspected central vs peripheral would be a difference based on following your content.
Is the bolded part due to programming a lower RPE, as I thought that RPE is the target and therefore the internal load is controlled. Or is internal load broader than RPE of the set?
This brings up an issue with RPE and internal load nomenclature, as internal load really refers to the acute response during the exercise. We’d expect the acute internal load to be the same if the RPE was the same.
That said, the long term effects of exercises with different fatigue potentials is better characterized by rating of fatigue (ROF).
Internal load is a reflection of the psychophysiologic response to a given external load (e.g., weight/sets/reps/duration/etc.) DURING the activity. This is discussed in the first link above, and in other discussions by Impellizzeri.
You are correct that RPE is one potential metric of internal load, and thus, two different exercises each performed to 2 reps in reserve would have the same internal load as measured by RPE.
Fatigue perceptions after the activity, on the other hand, are not the same as internal load (which, to reiterate, can only be determined during the activity itself). This distinction is discussed in the second paper I linked above.
Therefore, you can have 2 different movements/activities performed to the same internal load target (e.g. by RPE, or in endurance contexts by a heart rate target, for example) that have different effects on fatigue afterwards.
At least, this is the state of things based on current definitions and terminology. A lot of this stuff is admittedly still being hashed out (again, as discussed in paper # 2).