Jumping: Power or Impulse?

Dear Editor-in-Chief: I write in response to the manuscript by Canavan and Vescovi (2) that revisited attempts to predict power output on the basis of height achieved during vertical jumping. Adamson and Whitney (1) and Smith (4) indicated that such approaches are misguided. Moreover, the misapplication of mechanical constructs in the context of exercise was highlighted in this journal by Knuttgen (3). The warnings have gone largely unheeded, and the infatuation with power as a mechanical construct, supposedly to indicate maximal intensity exercise performance, persists. The ability to jump either horizontally or vertically is dependent principally on the velocity at takeoff. From Newton’s second law of motion, this velocity is attributable to the preceding impulse and is enshrined in the impulse–momentum relationship. It is muscle’s capability to develop impulse not its ability to generate power that is the point at issue. The force–time history can be explored by considering characteristics of the profile or area under the force–time curve. It is the interaction of force development and its manipulation over time that explains rather than simply describes performance. Integration of the force–time history can be used to provide a velocity–time profile of the body’s center of mass and so provide a basis for calculations of the products of force and velocity. Ostensibly, these provide instantaneous values of power output that are seductive. The failings of this approach were demonstrated by Adamson and Whitney (1) and Smith (4). Attempts to justify the use of “power” to explore jumping are often based on the strong relationship between this supposed measure and height jumped. Indeed, this is the approach taken by Canavan and Vescovi (2), who use jump height and body mass as predictors for an R2 of 0.92; they compound matters by claiming that there is no probability that their result could have occurred by chance. Such a relationship might well be simply fortuitous; the relationship between impulse and jump height is perfect; that is, 1. Efforts to explain jumping in the context of power are at best misguided and a distraction and at worst a misrepresentation of the mechanical constructs involved. Such approaches probably reveal more about investigators’ understanding of underlying mechanics than they do about explanations rather than simple descriptions of performance. Edward M. Winter The Centre for Sport and Exercise Science Sheffield Hallam University Sheffield, United Kingdom