Concentric and eccentric shoulder rehabilitation biomechanics

The use of an impulse-momentum (IM) exercise technique was investigated for end-stage shoulder rehabilitation. The objectives of this study were to: (a) quantify the net shoulder joint forces and moments while using an IM system and (b) test the influence of gender and muscle loading type (concentric or eccentric) on kinetic and kinematic parameters. Fourteen healthy adults (eight males, six females) performed a repeated measures experiment on an instrumented device utilizing a cabled shuttle system. While maintaining 90° of shoulder abduction and 90° of elbow flexion, the subjects externally rotated their upper arm from 0° to 90° (concentric acceleration) and then internally rotated their upper arm back from 90° to the 0° position (eccentric deceleration). Shoulder joint forces and moments as well as rotational work and power were calculated using inverse dynamics (free-body forces and moments calculated at intersegmental joint centres). Overall concentric peak forces and moments were greater than eccentric peak forces and moments (P<0.0001). Joint forces and moments reached a maximum during the initial phase of concentric loading (0° to 45°) compared with any other rotational position in the loading cycle (concentric 45° to 90° or eccentric 90° to 0°). The results also indicate that males experienced higher (P<0.0001) average resultant peak joint forces (concentric 0° to 45° = 108.0 N and eccentric 90° to 45° = 87.2 N) than females (concentric 0° to 45° = 74.7 N and eccentric 45° to 0° = 56.0 N). In addition, males experienced higher (P<0.0001) average resultant peak joint moments (concentric 0° to 45° = 30.4 N m and eccentric 45° to 0° = 21.0 N m) than females (concentric 0° to 45° = 30.4 N m and eccentric 45° to 0° = 12.8 N m).