Posture Changes with a Seat Insert: Changes in Strength and Not EMG

Body posture affects how we perceive ourselves and how others perceive us. It also has an impact on our physiology and emotions. Adapting an expanded 'power posture,' we experience a change in memory, subjective perception of strength and energy. The purpose of this research is to explore the impact the BackJoy[R] Sitsmart Posture Plus (BSPP) seat insert on muscle tension and perceived strength. Seven college students between the ages of 19-41 volunteered to participate. Surface electromyography was recorded from the participants' medial deltoid and the upper trapezius of the dominant arm while the participant underwent two muscle resistance tests, one while seated in their normal (self-determined) 'comfortable' upright position and the other while sitting on a BSPP, which shifts the pelvis from a posterior to anterior tilt and allows the person sit more upright. The measurements showed that six of seven participants rated their own strength and ability to resist the downward pressure applied to the wrist was significantly higher while seated on the BSPP seat insert compared to sitting normally. There was a high degree of correlation between the participant and the tester in terms of perceived resistance to downward pressure, Kendall's [tau] = .88, p (one-tailed) = .004. There were no significant difference between average SEMG measures of the trapezius and deltoid muscles when resisting the downward pressure while sitting on the BSPP (W/BackJoy) or sitting on the chair compared to (W/O Backjoy) [M = 129.8 mV vs. 128.0 mV, t(6) = 0.11, p = n.s., r = .73 and, M = 227.1 mV vs. 222.4 mV, t(6) = 1.35, p = n.s., r = .98, respectively]. This pilot study supports the concept that posture affects a sense of personal power. Using the seat insert increased the subjective sense of strength. This observation is similar to previous findings that subjects perceive strength and resist downward pressure on their wrists while in erect versus collapsed postures. This pilot study demonstrated that the BSPP seat insert increased subjective experience of strength however the SEMG recordings did not confirm this subjective experience. Further research is needed to understand the mechanisms of perceived versus measured strength. Nonetheless, more upright postures seem to result in increased strength as compared to less upright postures. Furthermore, if postural adjustments can have such an impact on our perception of strength, they also can have impacts on other aspects of our s