The Development of Musculoskeletal Disorders

The article “Sex differences in kinematic adaptations to muscle fatigue induced by repetitive upper limb movements” discusses about the development of musculoskeletal disorders that may be caused by repetitive muscles movements that create muscle fatigue. When it comes to muscle fatigue men and women manage to respond differently during isometric single joint efforts. However, sex difference when doing multiple joint task has not yet been identified. In this study both men and women must adapt their upper body (kinematics) during a RPT (repetitive pointing task). The study included 40 men and 41 women performing various muscle movements using their dominant arm and had to reach a level of perceived exertion of 8/10. It started where the participants repeatedly moved there dominant arm, at a proximal and distal target.

In the article it claims, “They maintained a rhythm of one movement per second (2 s for a cycle) set by a metronome” (Fuller et al). The metronome is used to provide auditory feedback in order to help the participants maintain their pace. Additionally, to make sure the participants elbow’s were elevated, a mesh barrier was added and positioned under their elbow motion trajectory. The tasks were done until the participants reach an RPE of 8/10. Data was required for the upper body and trunk. This was done by using a six-camera motion capture system. There were reflective markers placed on the upper arm, trunk, forearm. Furthermore, before performing the RPT, the participants must be in anatomical position. The variables being analyzed during this study, are the trunk-global, humero thoracic, elbow, as well as the joints in the wrist and hand.

In this study, both sex group performed the RPT for the same amount of time. Many similarities as well as differences were found between the men and women in this study. Some similarities that were found was their endurance time as well as their kinematic adaptations during RPT. Additionally, for both the men and women, it seemed that there trunk range of motion increased with fatigue,while their shoulders and elbow’s decreased.

During the study, the men had more of a decrease than the women when it came to their humero thoracic elevation. However, the women manage to increase their humero thoracic elevation when doing movement to movement variability. These differences help show that the men’s humero thoracic elevator muscles managed to be more fatigued than the women. This could be because the women’s muscles managed to adapt better than the men’s. Men (7.4 ± 3.2 min) and women (8.3 ± 4.5 min) performed the repetitive pointing task for a similar duration. For both sex groups, trunk range of motion increased with fatigue while shoulders and elbows decreased. Moreover, participants modified their trunk posture to compensate for the decreased humero thoracic elevation. Movements at all joints also became more variable with fatigue. However, of the 24 joint angle variables assessed, only two Sex × Fatigue interactions were observed.

Although average humero thoracic elevation angle decreased in both subgroups, thisdecrease was greater in men (standardized response mean [SRM] − 1.63) than in women (SRM − 1.44). Moreover, the movement-to-movement variability of humerus thoracic elevation angle increased only in women (SRM 0.42 elevator muscles were more fatigued than women’s despite a similar perceived exertion or that they adapted differently to a similar level of muscle fatigue. Finally, different pre-fatigue movement parameters are related to endurance time in men vs women. Those results highlight the complexity of the phenomenon of fatigue and its impact on motor behavior.