# Do Progressive Sensorimotor Training Devices
## 4 Discussion  
It is well known that introducing instability during static balance increases sensory input, promotes central nervous system processing, as well as motor actions and reactions to moderate motor commands. Neurophysiological studies have demonstrated central adaptations at multiple levels due to exercises using unstable surfaces [25], including increased co-activation of agonist and antagonist muscles that are related to the level of instability [12; 26; 27]. Although coaches and sports trainers generally agree on qualitative ratings of instability devices, objective quantification of the grade of instability and the challenge imposed on postural equilibrium by these devices is currently lacking. The primary purpose of this study, therefore, was to quantify the amount of COM displacement induced by different balance devices commonly used in sensorimotor training in a young athletic population. Consistent with our hypothesis and the findings of [PERSON] et al. [12], mean COM displacement during unipedal stance sequentially increased with progressively unstable balance pads. While unipedal stance alone induced approximately three-fold greater COM displacement than the referent bipedal stance condition, instability balance pads resulted in a further exponential increase in COM excursion, from approximately four times that of bipedal stance with the most stable pad, to nine times that of bipedal stance with the least stable pad. Interestingly, although balance performance on the two  
Figure 3: Mean normalized center of mass (COM) displacement for all balance conditions in females and males. Error bars represent standard error. Note that there were no significant differences between males and females. Mean (\(\pm\) standard error) normalized COM displacement values are shown for each balance condition. * Balance condition significantly different from all other conditions (\(p<0.05\)). + Balance condition significantly different from all other conditions except PM and PM-ST1 (\(p<0.05\)). + Balance condition significantly different from all other conditions except PM, PM-ST1 and PM-ST2 (\(p<0.05\)). + Balance condition significantly different from all other conditions except PM-ST1 (\(p<0.05\)). + Balance condition significantly different from all other conditions except ST2, ST3 and PM-ST2 (\(p<0.05\)). + Balance condition significantly different from all other conditions except ST3 and PM-ST1 (\(p<0.05\)). most stable pads (ST1 and 2) was moderately correlated, performance on the least stable, air-filled balance pad (ST3) was unrelated to performance on either of the foam pads (ST1 and 2). Hence, while instability pads appear to provide a progressive stimulus for sensorimotor coordination in healthy young athletes, coaches and sports trainers should be aware that the stimulus across the three graded balance pads is not linear. It was also hypothesized that an oscillating platform would induce greater COM displacement than instability pads. In partial support of this hypothesis, significantly greater COM displacement was observed during stance on the oscillating platform (PM) than on the most stable balance pad (ST1). However, contrary to our hypothesis, no statistically significant difference in COM displacement was observed between the oscillating platform and the intermediate (ST2) or the least stable balance pad (ST3). Hence, the oscillating platform provided no greater perturbation to balance in healthy young adults, on average, than either the intermediate or the least stable balance pad (ST2 and ST3); even when used in combination with ST1. The variability between participants, however, was greatest for the oscillatory platform when used either in isolation (PM) or in combination with balance pads (PM-ST1, PM-ST2). The between-subject variance in COM displacement was approximately seven times greater during stance on the oscillatory platform (PM) than on a stable hard, flat surface (Floor) and was approximately 12-fold greater during combined conditions (PM-ST1, PM-ST2).