ToolBox: Feeling Fast
Ratings of Perceived Exertion – The past quarter century has seen the rise of “scientific” training, led by the introduction of heart rate monitors and now power monitors. How do these modern tools stack up against the traditional subjective ratings of perceived exertion, and does there remain value in understanding and appreciating perceptual responses to exercise?
The History of Training Monitoring
The legendary cyclist Francesco Moser, along with his trainer Francesco Conconi, revolutionized the entire field of sports training in the early 1980s. While aerodynamic improvements certainly helped substantially, the systematic training was what really ignited the field of sport science since that 1984 record. With their detailed and scientific approach to preparing Moser for shattering the Hour Record, they redefined training from a somewhat random ride at various intensities to systematic efforts using heart rate as a defining parameter.
The rest is pretty much history in the public domain. From Moser’s clunky model, heart rate monitors were popularized by Polar, which now dominates the market. During my move last summer, I came across my first generation Polar HRM from about 1988, featuring a wired cable from the chest band to a wrist unit that makes even the largest techno-watch today seem svelte and sleek in comparison!
Concurrently in the mid-1990s, two other lab-based instruments made the initial jump to portable accessibility for the masses. We all know about the SRM and the PowerTap for power monitoring. The other testing tool is the hand-held lactate measuring units such as the AccuSport and the Lactate Pro, which require only a finger-prick blood sample and can deliver results within 60 s of measurement. This has come to replace expensive and after-the-fact lab-based lactate measurement techniques, and swimming is especially notable as a sport that has used lactate monitoring extensively.
But How do you Feel?
All of these tools are fantastic, and it’s almost inconceivable for many of us to go for any “decent” ride without at least a bike computer and HRM on the bike. Yet it is also important to remember that one of the fundamental uses of all monitoring devices is to help you learn how to “feel” and gauge your efforts better. That is, one important goal is to provide objective quantification of your effort and then match or correlate that to your perceptual sensations of effort. That’s why many experienced endurance athletes can gauge their interval intensity or even their breakaway efforts mainly by feel rather than blindly keeping pegged to a certain number.
So of course, as with any tool used for research, the question becomes: “How do we quantify our perceptual sensation of effort, and how accurate and reliable is this measure?”
Borg’s Ratings of Perceived Effort
For perceived effort, the gold standard is Dr. Gunnar Borg’s classic “Ratings of Perceived Exertion” or RPE scale, first introduced in the 1970s and formally published in 1982 (1). The classic Borg scale (see Figure 1) rates your perceived effort on a scale from 6-20, with 6 being “no exertion at all,” to 13 being “somewhat hard,” 17 being “very hard,” through to 20 being “maximal exertion.”
When using the scale, it is important to remember that “This feeling should reflect how heavy and strenuous the exercise feels to you, combining all sensations and feelings of physical stress, effort, and fatigue. Do not concern yourself with any one factor such as leg pain or shortness of breath, but try to focus on your total feeling of exertion.” (Quote taken from Center for Disease Control website). So it is not just focusing on sore legs or localized effort, but your overall sensation of how hard the workload is.
Another important consideration is that this is not meant to be compared across individuals. It is not a contest to “tough it out” and rate a hard effort as easy. Garbage in, garbage out! The focus is on comparing your honest responses to workloads over time, just like tracking long-term changes to your training or fitness from your training diary.
One thing may strike you as strange about this scale – why does the scale go from 6-20? This may lead you to consider another “coincidence,” namely how a prototypical heart range capacity ranges from resting of 60 to a maximum of 200. This isn’t a coincidence at all, as research has demonstrated that there is a very close correlation between heart rate and perceived effort!
Even still, for the lay public, a scale from 6-20 isn’t overly intuitive to grasp, such that another version of the Borg scale runs from 1-10, and this is what many coaches prescribe to their athletes for ease of understanding.
RPE Clamp Protocol
The Borg scale or its variants is commonly employed as a research tool for gauging perceived effort, and also for secondary support for a tool such as a HRM or power monitor. However, one interesting flip on the question is this, ”How constant is my workload if I try to maintain a set perceived effort?” In other words, if I went out and did a time trial at a RPE of 16 (between “Hard” and “Very Hard”), does my power output fluctuate over time?
Such a question is of interest both to physiologists and to coaches and athletes. For physiologists, it gets at the central question of “What is the drive for exercise and fatigue?” For coaches and athletes, it helps to calibrate our objective tools like power monitors with individual sensations, helping in turn to adjust training.
This question was again nicely designed and tested by my colleagues at the University of Cape Town from Dr. Tim Noakes’s laboratory. His Ph.D. student Ross Tucker published a 2006 study using a RPE clamp protocol (2), wherein he had subjects ride at their own self-selected power output at a constant RPE = 16. No power, time, cadence, heart rate, or distance cues were given at any stage of the test, and subjects were told simply to maintain RPE of 16 and adjust wattage (they couldn’t see the wattage) as needed. They had subjects do this in 15, 25, and 35 degrees Celsius, but I won’t go into detail with those findings.
What they did find was that, in all three environmental conditions, the self-selected power progressively decreased over time in a fairly linear fashion. See Figure 2 for data from my own RPE clamp ride, done on the Pro300 PT indoor ergometer from CycleOps.
Red is HR, green is cadence, and yellow the power output. Interesting things to note from this recording of my power files is that the wide fluctuation in power. From the initial first few minutes, my power was about 275 W, then down to about 230, then another prolonged duration at 250 W. Then from there, it gradually and steadily tailed off, with the final drop down to about 180-190 W. The final spike was from a 30 s all-out (self-paced) effort. The other interesting thing was that each of these levels were sustained for a fair amount of time and was quite steady until the final precipitous drop over the final 10 min. Total RPE effort time was 42 min before I dropped to 70% of my initial power levels.
Rubber on the Road
So what does a simple but interesting protocol tell us about our drive to exercise and fatigue?
• We aren’t stable in our perception of effort! This certainly highlights that we might not want to solely rely on our perceived effort to gauge the intensity of intervals or time trials. As if there aren’t enough excuses to spring for a power monitor!
• The voluntary drive for exercise remains an important determinant of how hard and fast you can go. One theory is that your brain is deliberately lowering or putting a ceiling on your exercise to prevent you from damaging yourself. However, it can fool you into underestimating your capacity. As the final sprint and spike in power output suggests, you’ve still got a fair bit of neuromuscular capacity within you even at the point of voluntary exhaustion.
• The above can especially be used during the late stages of a race when the hammer is about to drop. At that point, as REM sings, ”Everybody Hurts, but realize that you still have a capacity for burning one more match, and this is exactly the best time to do it when everyone else is mentally suffering.
1. Borg GA. Psychophysical bases of perceived exertion. Medicine and Science in Sports and Exercise 14: 377-381, 1982.
2. Tucker R, Marle T, Lambert EV, and Noakes TD. The rate of heat storage mediates an anticipatory reduction in exercise intensity during cycling at a fixed rating of perceived exertion. Journal of Physiology (London) 574: 905-915, 2006.
Stephen Cheung is a Canada Research Chair in Kinesiology at Brock University, with a research specialization in the effects of thermal stress on human physiology and performance. He can be reached for comments at [email protected].