Discussion on Power in Rowing: one final response

You might have noticed that there is a bit of a discussion going on between Dr Valery Kleshnev, owner of Biorow and author of the rowing biomechanical newsletters, and us.

In his October newsletter, Dr Kleshnev criticizes our recent work on power determination in rowing (recently published in the Journal of Sport Sciences; see below) to which we recently wrote a response. Dr. Kleshnev has now responded to this.

At rowingscience.nl we very much appreciate Dr. Klesnev’s work and recognize its value for the rowing community. However, Dr. Kleshnev and us appear to have fundamentally different interpretations of how classical mechanics should be applied in sport situations such as rowing, and we both believe the other one’s point of view is  flawed.

An extensive continuation of the on screen discussion between us likely is unfruitful and will probably only cause (more) confusion amongst the rowing community. For now, we will restrict ourselves to responding to what we feel are the two main points of criticism, as we have the impression that much of the misunderstandings between Dr. Kleshnev and us stem from us not getting across those two main points.

Our final response:

  1. Kleshnev appears to think that our power equation is fundamentally incorrect. He criticizes us for the fact that we do not determine power production (Prower) directly. Indeed; we (indirectly) derive power production from the power that is transferred to handle and oars and from the rate of change in kinetic energy, since we can measure those. A direct way of determining Prower would be by summing up mechanical power production of the separate muscles. Obviously, such a thing is impossible to do.
  2. Kleshnev states that choice of frame of reference matters. Here, at least, we partially agree. Indeed, except for Prower, all the other power terms depend on the frame of reference, simply because the frame of reference affects the velocity of the point of application of each force (which is defined relative to the frame of reference by definition).  It thus affects the power of this force, and the velocity of all masses and thus the kinetic energy. In the case of Kleshnev’s runner in the train, he is absolutely right that the kinetic energy term of the runner depends on frame-of-reference choice. However, note that the same is true for the power of the horizontal ground reaction force on the runner: this power is zero in a train-bound frame of reference, while it is non-zero in an earth-bound frame. In many cases, the question to be answered leads to a preferred choice of frame of reference. For example, if you want to study overground running performance but your data were gathered in a train moving at constant velocity, it makes sense to use a frame of reference that is moving with the velocity of the train. But if you want to know with how much impact the runner smashes into the wall if the train would abruptly come to a complete stop, it would make more sense to use an earth-bound frame of reference. Please note that while choosing a “logical” frame of reference will most likely make life easier, there is no such thing as a “right” or “wrong” frame of reference (so here we seem to disagree). I.e. overground running performance in the train can also be perfectly studied in an earth-bound frame of reference and if Newton’s laws are consistently applied, the exact same conclusions will be reached!

Hofmijster, M.J., et al., Mechanical power output in rowing should not be determined from oar forces and oar motion alone. J Sports Sci, 2018. 36(18): p. 2147-2153.

Lintmeijer, L.L., et al., Improved determination of mechanical power output in rowing: Experimental results. J Sports Sci, 2018. 36(18): p. 2138-2146.

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