The effect of marker placement around the elbow on calculated elbow extension during bowling in cricket.

The elbow extension angle during bowling in cricket may be calculated from the positions of markers attached around the shoulder, elbow and wrist using an automated laboratory-based motion analysis system. The effects of two elbow-marker sets were compared. In the first, a pair of markers was placed medially and laterally close to the condyles while in the second a triad of markers was placed on the back of the upper arm close to the elbow. The root mean square (RMS) difference in elbow extension angle between the two methods at four key instants was 8° for 12 fast bowlers and 4° for 12 spin bowlers. When evaluated against video estimates of the elbow extension angle for the fast bowlers, the elbow extension angle calculated using the pair method had an RMS error of 2° while the triad method had an RMS error of 8°. The corresponding errors for the spin bowlers were 3° and 5°, respectively. It is thought that the greater errors associated with the triad is a consequence of soft tissue movement in this dynamic activity. This is consistent with the finding of greater error for the fast bowlers compared with the spin bowlers.