SPECIAL COMMUNICATIONS: Letters to the Editor-in-Chief
We welcome the opportunity to respond to Dr. Winter's comments on the terminology used in our recent review (4). Winter contends that the term "critical power" is inappropriate because, in his view, it has no basis in the works of Isaac Newton or in the SI system. While we agree that a rigorous categorization of exercise intensity is essential (3), we strongly disagree with his contention that the term "critical power" be abandoned.
Power is clearly recognized by the SI system as the product of force and velocity and can be quantified in terms of both linear and angular motion. Newton would surely recognize this from his own second law! Moreover, two of the references that Winter cites as being critical of the term "power" actually acknowledge that it is the correct term to use during cycle ergometry (5,6). In our experiments using cycle ergometry, external power is the independent variable and time-to-exhaustion is the dependent variable. The relationship between these variables is hyperbolic, and the asymptote on the power axis is the "critical power" (7,8). When the independent variable is speed (or velocity), force, tension, or torque, it is obvious that these terms should be substituted for power as appropriate (e.g., Burnley (2) and Monod and Scherrer (7)). In our review (4), we repeatedly emphasized the need to use the correct quantity for the specific experimental conditions. Winter's point is therefore moot.
It is true that measures of external power output provide only a partial assessment of the total power output. However, Winter's critique ignores evidence that critical power is sensitive to pedal cadence, whereas the oxygen uptake (V˙O2) at critical power is not (1). Moreover, it is the external power output that dictates performance and is therefore the relevant variable to address (4). The energetics of the entire system cannot be misrepresented if pulmonary V˙O2 is measured concurrently, as we do in all our studies.
Finally, Winter recommends that "critical power" be replaced by "critical intensity." To enact this would be entirely retrograde. First, severe-intensity exercise (performed above the critical power) is non-steady state by definition (3,8), and the "intensity" might therefore be considered to be constantly changing. This is also true for heavy-intensity exercise, while the V˙O2 slow component is still developing (3). Second, we note that the use of "intensity" commits all the errors of which we are accused: it is not recognized by Newton, SI, or the Royal Society and has no established unit of measurement. Science requires that measurements are precisely defined and expressed. In this regard, it is clear that critical power (for cycle ergometry) and critical speed or velocity (for running), for example, are superior to the nebulous term "critical intensity."
In our review (4), the historical, physiological, and mathematical foundations of the critical power concept are comprehensively described, and the important implications for exercise performance are highlighted. We agree that strict adherence to correct terminology is essential in scientific communication. For exactly that reason, we shall continue to use the term "critical power" (or speed, or force, or tension, or torque). We encourage others to do likewise.
Andrew M. Jones, PhD
Anni Vanhatalo, PhD
School of Sport and Health Sciences
University of Exeter
Mark Burnley, PhD
Department of Sport and Exercise Science
R. Hugh Morton, PhD
Institute of Food Nutrition and Human Health
David C. Poole, PhD, DSc
Departments of Kinesiology, Anatomy and Physiology
Kansas State University
1. Barker T, Poole DC, Noble ML, Barstow TJ. Human critical power-oxygen uptake relationship at different pedalling frequencies. Exp Physiol
2. Burnley M. Estimation of critical torque using intermittent isometric maximal voluntary contractions of the quadriceps in humans. J Appl Physiol
3. Jones AM, Poole DC. Oxygen uptake dynamics: from muscle to mouth-an introduction to the symposium. Med Sci Sports Exerc
4. Jones AM, Vanhatalo A, Burnley M, Morton RH, Poole DC. Critical power: implications for the determination of V˙O2max
and exercise tolerance. Med Sci Sports Exerc
5. Knudson DV. Correcting the use of the term "power" in the strength and conditioning literature. J Strength Cond Res
6. Knuttgen HG. Force, work, power and exercise. Med Sci Sports Exerc
7. Monod H, Scherrer J. The work capacity of a synergic muscular group. Ergonomics
8. Poole DC, Ward SA, Gardner GW, Whipp BJ. Metabolic and respiratory profile of the upper limit for prolonged exercise in man. Ergonomics