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Rating Our Perceived Exertion: Some Physiological Qualifiers

Rating Our Perceived Exertion: Some Physiological Qualifiers

Measuring one's exercise intensity is probably the best way to move, in actuality, from the realm of intention to reality.  How many times have we 'gone out too fast' only to 'bonk' when the test of endurance is in force?  In other words, we may set decide to engage a 30-minute lactate threshold workout, or perhaps a 60-90 minute endurance workout, only to fall short of our expectations.

So much in the Spinning® program, as well as the vast majority of claims throughout the world of cardiovascular training, strongly suggests that heart rate monitors be worn in order to measure exercise intensity.  I wear mine faithfully in my classes, and I have always recommended my students do the same.  After I was given a spot on the Master Instructor Team, I still encouraged all who attended my workshops to embrace the reality that, without heart rate monitors; our exercise intensity measurements via perceived exertion alone are somewhat to very imprecise.  Conversely, though, another pitfall is to assume that a certain heart rate value is the only variable that matters – due to its objectivity.  For example, due to energy requirements versus where a body is in terms of storage or other factors, a rider may not always be able to endure for the same timeframe at a given heart rate.  Perceived exertion, then, for this reason must be paired with heart rate as a consideration. 

It seems to me that, at this point, the time has come to revisit some of the simplest indicators that we reference as we evaluate where our bodies are functioning physiologically along the intensity spectrum – or simply to explore what the body feels at certain verbal ratings of perceived exertion (RPE).  As we consider RPE, though, let us pair the RPE with plausible heart rate monitor readings; this method is really the best means of triangulating a more complete picture of exercise intensity.  Our goal is to link the subjective to the objective.

The RPE scales in most common numerical use are the 1-10 scale and the Borg scale.  The Borg model has the distinction of being specifically based upon a 30-year-old male subject and the heart rates he experienced ranging between very, very light to very, very hard intensities.  On page 1.25 of the Spinning® Instructor Manual, there is a chart verbally ranging from easy to very hard, along with how each of the five Energy Zones aligns with said range, and said chart simply provides qualifiers such as easy and hard.  Here we shall focus in depth upon the verbal references.

Ultimately, it would seem that the authors of the Manual realized that, whether we use numbered ratings or not, we really do have to find ways to qualify our perceived exertion.  In other words, the number 6 (out of 10) and/or the number 13 (on the Borg scale) must have certain meaning to the frequent user of each scale.  So what exactly are we weighing when we evaluate, or qualify, perceived exertion?

Breathing is probably the most observable qualifier from within and without.  A sharp instructor may even use the Spinning® eye to notice signs of changes in participants’ work output.  Whoever is observing, whether that be the rider him/herself or the instructor, we frequently categorize these two basic realities of breathing: (1.) breathing rate accelerates with increases in effort or exertion, but it decreases when effort is lowered; and (2.) breathing will change location with significant increases in effort (in the vast majority of cases).  Let us focus on this latter idea.  Breathing during warm-up and low-end aerobic effort, or 50-65% MHR and an RPE of very easy to easy, breathing most often occurs nasally for the entire respiration cycle (in and out).  Moving toward a more mid-level aerobic level, or 70-75% MHR and an RPE of somewhat hard, there is often a shift to at least semi-regular and perhaps slow expirations through the mouth.  (This is not always the case, however.  Some are able to continue nasally through most of this range.)  The next point upward along the intensity continuum is highly consistent across most participant fitness levels, though: at LT (lactate threshold), commonly identified to be 80-85% MHR along with an RPE of hard, oral exhalations become virtually compulsory along with a noticeably faster breath cycle.  In addition, what was at lower intensities a largely effortless or even passive exhalation now becomes focused, purposeful, and active.  As effort level surpasses LT, to the point of 85-92% MHR and an RPE of very hard to very, very hard, the pace of the breath cycle quickens even more; it becomes still more active; and even the inspiration of air occurs orally.

What might be a second indicator of perceived exertion?  The clearest candidate is probably the slight drop in blood pH (i.e., more toward acidic side of spectrum), leading to a burning sensation, which intensifies gradually as one approaches lactate threshold.  In most cases, only the rider may directly observe this change; the instructor notices changes that are inextricably linked to this burn.  Up to LT, where lactate production equals elimination, said burn due to the drop in blood pH is tolerable, even if uncomfortable at lactate threshold in particular.  After :15 (seconds) to 3:00 (minutes) of exposure to an intensity of 85-92%, and an RPE of very hard to very, very hard, one becomes too fatigued to continue at that pace; a recovery then becomes necessary.  Worth qualifying here, too, is that burn in the muscle is typically first noticeable, even if to a minor degree, at an intensity just shy of 70% MHR and right around a somewhat hard perceived exertion.  Some would refer to the sensation at that point as not a burn per se, but more of a warmth or heat in the affected muscles.  As intensity is elevated, the heat is advanced in nature until the burn becomes unbearable, even leading to muscle failure at the end of the interval.  Some have even referenced a burning in the lungs at extremely very, very hard intensities such as sprints at 92% of maximal heart rate.  A low-high continuum might look like this: warmth in the muscle, some highly endurable heat in the muscle, intense but tolerable burn in the muscle, very intense and almost unbearable burn in the muscle, and finally burn in the lungs at maximal effort.

Thirdly, we have postural change and biomechanical changes.  These are again matters that both rider (from perspective of within) and instructor (from perspective of without) may plainly observe, is postural change.  Most riders, including some fairly accomplished ones, betray signs like elevated shoulders, tense arms, facial color change, and tension in facial or neck muscles.  The actual pedaling technique becomes quite forced as well, given a high enough intensity for the right timeframe.  Of course, highly trained riders are quite practiced at countering these affects and maintaining their calm and composure; however, every rider ultimately has that breaking point where a relaxed technique gives way to stress response signals.

Hopefully you have found this brief flyover useful when perceived exertion, and how it relates to the more objective heart rate readings, is in view.  For more information about perceived exertion in particular, please do consult the Spinning® program CED entitled ‘Rating of Perceived Exertion: It’s More than a Feeling.’  In particular, this study further explores the psychology of RPE as well as more about the numeric scales designed to enumerate it.




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