Objective:Our aim is to investigate the mechanism of spiral fracture of humeral shaft due to hand grenade throwing and get the key points of prevention by biomechanical analysis of the fundamental rules of throwing.Methods:On military training ground,an orientated and focused camera was applied for filming.Thirty soldiers who practised hand grenade throwing were filmed,Data obtained by filming frontally and laterally were processed by Aijie Analysis System.After that,six soldiers were selected for further testing in a laboratory equipped with Motion Analysis System.Each subject had 14 markers attached to the body in order to be filmed during action.All performances were captured and determined.In addition,when related joints reached peak velocity,the corresponding joint angles,such as arm angle (between upper arm and forearm),shoulder angle (between upper arm and shoulder) and trunk angle (between trunk and upper arm),were also obtained.Data processing was carried out by Kintrak software.