Validity of an iPhone application (Gymnastics - The Giant) for evaluating giant’s performance
M. Maggio, V. Muollo, F. Fontana, P. Zamparo1
1 Department of Neurological and Movement Sciences, University of Verona, Verona, Italy
Aim: The giant is an artistic gymnastics skill in which a gymnast rotates of 360° around an axis while in a fully extended position. The gymnast begins in a handstand position (0°); on the upswing (from 180° to 270°) the abdominal muscles are engaged to slightly arch the body and prevent anterior pelvic tilt (which would adversely affect the strength of the swing). When the giant is properly performed (no pelvic tilt) a brisk change in the angular speed of the CM occurs at about 230° (Cheetham 1984); in correspondence of this angle the angular velocity of the tight is maximal (TAVmax). An un-correct performance can thus be detected by a shift of TAVmax at smaller or larger angles. Acceleration data can be recorded by means of an iPhone embedded accelerometer (it allows to determine TAVmax because it is associated with a brisk change in velocity: before TAVmax the body accelerates and after TAVmax it decelerates) and the angle at which the TAVmax occurs could be recorded by means of the iPhone gyroscope. Our aim was to validate an iPhone application by comparing the data of angle at TAVmax with those assessed by kinematic analysis in young elite gymnasts (National Italian Team).
Methods: Ten gymnasts (8F/2M, 13±3 years, 39± 13 kg, 1.44±0.17 m) with 8±4 years of experience, participated to this study. The iPhone was fixed on the lateral side of the right thigh; the gymnasts were asked to repeat the giant 5 times while being video recorded (Casio Exilim, ex-zr1000, 120Hz). Video clips were analysed with an open source software (Kinovea): the angle corresponding to TAVmax was calculated and compared to that derived from the iPhone application.
Results: The iPhone angle at which TAVmax occurs was 215±3° and not significantly different (paired t-test: p=0.15, N=50) from that determined with kinematic analysis (214±4°).
Conclusions: The angle at TAVmax is the same when calculated by kinematic analysis or with the iPhone application; in elite gymnasts, this angle is close to the angle at which the TAVmax should occur (230°). This app can thus be utilized for training purposes since its output (the angle at TAVmax) allows discriminating a good form a bad performance.
Cheetham P.J. (1984) Horizontal bar giant swing center of gravity motion comparisons. 2nd Int. Symposium on Biomechanics in Sports, Colorado Springs (US)