To develop scientifically-valid tools to monitor performance in practice, a critical question is what to measure. On pommel horse, the importance of fundamental skills called circles is uncontroversial, and one of the key performance qualities of circles is the amplitude of the movement. Previous studies have used joint angles or the magnitude of a body part`s trajectory to evaluate the amplitude, but we hypothesized that the distance between two points, namely a head and toes might be substituted despite its relative simplicity. This study examined the use of Head-Toe Distance (HTD) normalized by the gymnast`s body height as a simple variable to potentially evaluate the amplitude of circles. The kinematic data of circles performed by 18 elite gymnasts were collected with a Qualisys motion capture system operating at 100 Hz. HTD and its horizontal component, HTDh, were computed along with their relationships to the outcome scores given by the official judges, as well as the other amplitude variables: the horizontal diameters of shoulder and ankle trajectories; the body flexion angle; and in the rear support position, the shoulder extension angle and the head position. The results supported HTDh, rather than HTD, for its potential usage as a single variable to evaluate the amplitude of circles. The benefits of HTDh compared to the other variables lies in its potential validity despite its relative simplicity in assessment. Because computing HTDh requires only the positional data of the head and toes, it may have greater practical applications as an evaluative tool in gymnastics.
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