Mr. McCutchen describes "Shoulder Crunch," "Elbow Crunch," and "Wrist Crunch" as the results of excess centripetal force exerted by the arm when the racquet slows down upon meeting the ball, and he points out that the arm must exert more centripetal force on a racquet with greater angular momentum (generally the result of more weight toward the head).
This makes sense, but a racquet with more angular momentum would slow down less upon meeting the ball, thus reducing the excess centripetal force. This seems to be reflected in his formula "Shoulder Crunch = (2/R)(Shock) (where R = distance of the racquet's mass center from the axis of reference, here the shoulder)." If you increase R (put more weight toward the racquet head) in this formula (keeping other factors constant), you get less Crunch. (The formulas for Elbow Crunch and Wrist Crunch are the same, except for measuring R from those other joints, respectively.) In other words, at a given overall racquet weight, head-heavy balance causes less Crunch. This seems to contradict the point Mr. McCutchen is trying to prove, unless more angular momentum increases "Shock" enough to outbalance the effect of increasing R in the Crunch formula. This leads us to try to determine whether his conclusions about Shock are correct:
Mr. McCutchen uses a complicated formula for Shock, which he defines as follows: "Shock loading of the racquet results from a sudden change in the racquet's kinetic energy on impact, which produces an internal energy load on the racquet, which is expressed as frame vibration." His argument that a heavier racquet undergoes less Shock makes good sense, and it's also sensible to assume that a heavy racquet will be more maneuverable if it is balanced head-light. The question arises though: At a given weight, shouldn't a racquet with head-heavy balance suffer less Shock, because having more mass in the head and thus more angular momentum enables it better to dominate the collision with the ball and thus slow down less? The change in kinetic energy is proportional to the square of the change in velocity, so a racquet that slows down less should experience a smaller change in kinetic energy.
Racquet Research evidences a lot of effort with no apparent financial reward to its author, so he can't be faulted for not setting up a lab to actually measure impact shocks. He does take into account flex ratings provided by the USRSA, but his racquet rankings do not take into account, probably because the data are unavailable, the effect of shock-damping technologies built into racquet frames. Some of these damping systems make a significant difference. Whether Racquet Research's Shock rankings have a sound theoretical basis may be questionable. A difference between theoretical rankings and actual performance, taking into account shock-damping technologies, seems fairly certain.
