Does the Use of a Light Discus Modify the Throwing Pattern? A Study of Kinematical and Electromyographical Data of the Throwing Arm

Abstract : Seven high-level discus throwers (best performance 57 ± 3 m) participated to the present study. During the same session, they performed 12 throws (6 with a 1.7 kg discus and 6 with a 2 kg discus) in a random order. The throwing distance was computed from the velocity vector (magnitude, direction, height) at ejection. Kinematical data were collected by means of 3 video-cameras and a 3-D modelling of the throwing movement was processed according to the DLT method. Surface electromyograms (sEMG) of 6 arm-and-shoulder muscles of the throwing arm [Biceps brachii; Pectoralis major; Deltoideus pars superior; Trapezius pars medialis; Deltoideus pars medialis; Latissimus dorsi] were recorded by means of a portable device. Thereafter, sEMG was integrated (iEMG) and related to the iEMG recorded during a maximal effort against an external resistance. Computed distance with a light discus was significantly longer and was the result of a faster discus speed at ejection. This was probably the result of an enhanced increase in discus velocity during the last throwing phase (Δt2da). There was no significant difference in the duration of the four preceding phases with 1.7 kg compared to 2 kg discus. The total duration of the throwing movement was not significantly different between 1.7 and 2 kg discus. The EMG patterns of the different muscles were similar with both discuses when the beginning and the end of the muscle activity were considered. There was no significant difference between discuses when iEMG was summated on the whole throwing movement and related to the iEMG previously recorded during a maximal effort. These results suggest that the lighter discus might be used for high level training without kinematical alteration of throwing.