Consecutive postural adjustments (CPAs): A kinetic analysis of variable velocity during a pointing task

Relationship Between Mandibular Position, Activation of the Masticatory Musculature and Free-Throw Accuracy in Female Basketball Players

BACKGROUND

Current research relates jaw clenching to athletic performance, in terms of force and agility. However, the impact of jaw clenching on sports accuracy is unclear.

OBJECTIVES

To analyse the impact of jaw position and chewing type on free-throw accuracy and electromyographic (EMG) activity of masticatory muscles during free-throws.

METHODS

Cross-sectional study with 25 female basketball players aged 18-44. Each participant executed 18 free-throws under three different jaw conditions: mandibular rest, maximum intercuspation, and with interdental cotton rolls, in randomised order.

RESULTS

Chewing type and jaw position were not associated with shooting accuracy (p = 0.106; p = 0.778). There was a positive correlation between EMG activity of the right masseter and free-throw accuracy at maximum intercuspation (rs = 0.402; p = 0.046). In contrast, negative correlations were found with other muscles when the occlusal vertical dimension was altered (rs = -0.619, p = 0.001; rs = -0.490; p = 0.013; rs = -0.534; p = 0.006). The chewing type affected the EMG of the left masseter in the altered occlusal vertical dimension (H = 6.969; p = 0.031). Significant differences in EMG recordings were observed across different mandibular positions during free-throws (p < 0.001).

CONCLUSIONS

While jaw positioning and chewing type do not impact free-throw accuracy in amateur female basketball players, the EMG activity of masticatory muscles is linked to shooting performance. This highlights the need for further research on motor behaviour of masticatory muscles in precision sports, especially for athletes using intraoral devices.

The role(s) of "Simultaneous Postural Adjustments" (SPA) during Single Step revealed with the Lissajous method

Dynamical phenomena in the postural chain occur before, during and after the voluntary movement. These phenomena correspond to anticipatory (APA), simultaneous (SPA), and consecutive (CPA) postural adjustments, respectively. APA and, more recently, CPA, have been extensively investigated in the literature. SPA have surprisingly received much less attention. The aim of the present study was to examine the role(s) of SPA associated with a single step task (SST). Ten healthy young adults performed series of SST on a force-plate. A 2-DOF mechanical model was used to separate the dynamics of the swing leg and the dynamics of the rest of the body, corresponding to the focal and the postural component of the SST, respectively. The postural component was plotted against the focal one during SPA (from heel-off to foot-contact), and this plot was modelled as a Lissajous ellipse. Result showed that this ellipse systematically ran through the same three quadrants of the diagram. For each of these quadrants, the role of the postural component in regards to the focal one was interpreted according to the relative orientation of the postural and focal dynamics. Results thus showed that SPA ensured the following successive roles: counter-perturbation of swing leg dynamics following heel-off, propulsion of swing leg, counter-perturbation of swing leg dynamics again, and then braking swing leg movement. These new findings contribute to a better knowledge of postural adjustments properties, and may provide new insights for understanding balance troubles with aging and in neurological patients (e.g. people with Parkinson's disease).