The kip maneuver is one of the principal skills of apparatus exercise at the horizontal bar, but it is difficult for beginners to execute the maneuver. Most of the studies on the kip maneuver compared successful trials with unsuccessful ones, or the trials of skilled subjects with that of unskilled ones. Although skill training is mandatory for beginners to successfully complete the kip maneuver, there is no study on the process of learning and the effect of skill training on the changes in biomechanical parameters in the kip maneuver. The purpose of this study was to investigate effects of skill training for the kip maneuver on the shoulder and hip joint torques in the learning process. The kip maneuver of ten male varsity club gymnasts was videotaped and analyzed two-dimensionally to make the motion model of the kip maneuver of the skilled subjects. Three male subjects with no experience of performing the kip maneuver were selected as unskilled subjects. They participated in skill training for 5 to 12 days to learn the kip maneuver. All trials of the unskilled subjects were videotaped during the training. We selected every five trials to analyze changes in joint angles, torques of the shoulder and hip joints, and mechanical work done by the joints.
The number of trials the unskilled subjects needed to successfully complete the kip ranged from 47 to 108. Movements of the shoulder and hip joints in the trials in the second half of training were similar to those of the successful trials of all unskilled subjects. The range of the hip movement gradually increased with the number of trials. In the skilled subjects, immediately after the reversal point of the swing, i.e. the forward to the backward swing, the shoulder extension torque was increased rapidly with the extension of the shoulder joint, while the hip extension torque was exerted continuously in the same phase. This may indicate that the skilled subjects extended the shoulder joint strongly and intentionally. In the first trial of the unskilled subjects, the shoulder joint torque had three peaks. The hip extension torque was very small, whereas in the trials from the midpoint of the training, one of the peaks of the shoulder joint torque disappeared and hip extension torque was developed during the backward swing. In the unskilled subjects, the maximal hip extension torque significantly related to the number of trials in subjects B (y = 158.5 + 0.99 x, p < 0.05, where y is the maximal hip extension torque and x is the number of trials) and C (y = 145.3 + 1.09 x, p < 0.05, y and x respectively). The mechanical work done by the shoulder joint showed no significant relation to the number of trials in all subjects. Although the mechanical work done by the hip joint significantly related to the number of trials (subj. A: y = 150.2 + 2.15 x, p < 0.05; subj. B: y = 164.3 + 1.30 x, p < 0.05; subj. C: y = 196.7 + 1.22 x, p < 0.05, where y is the mechanical work and x is the number of trials). These results may suggest that it is essential for the unskilled subjects of the kip maneuver to increase the hip extension torque and the mechanical work done by the hip joint as well as to exert the shoulder extension torque.
