Anticipatory postural adjustments while sitting: The effects of different leg supports

Abstract

The aim of this study was twofold, to analyze the effects of changes in body position and changes in the location of body supports on anticipatory postural adjustments (APAs). Eight healthy subjects were studied while sitting and standing. Subjects exerted upward or downward vertical force against an object attached to a rigid frame and released the object with a fast bilateral shoulder abduction movement. While sitting, four support conditions were studied: with and without feet support, and with anterior or posterior lower-leg supports. The electromyographic activity of leg and trunk muscles was recorded and quantified for APA activity. APAs in sitting with feet support were attenuated in the leg muscles (tibialis anterior, soleus, rectus femoris, and biceps femoris) but not in trunk muscles (erector spinae, rectus abdominis) when compared with standing. In the sitting task, series with and without feet support showed no difference in APAs. Anterior or posterior supports to the lower legs while sitting were associated with enhanced anticipatory activity in biceps femoris and rectus femoris muscles, respectively. However, trunk muscles showed similar anticipatory patterns across all the support conditions. We conclude that the central nervous system uses flexible, adaptive control strategies to adjust APAs to particular mechanical conditions induced by modification of a leg support.

Activation timing of soleus and tibialis anterior muscles during sit-to-stand and stand-to-sit in post-stroke vs. healthy subjects

“…In SitTS and StandTS, the forward movement of the trunk over the lower limbs justifies the need of TA activation timing prior to the movement. This is based on the fact that the central nervous system can previously adjust anticipatory activity of muscles in response to perturbations/changes in the direction of the movement (Aruin & Shiratori, 2003).…”

“…An voluntary movement requires an adequate postural control (PC) to the desired action under a particular environment (Bigongiari et al, 2011;MacKinnon et al, 2007), being generally preceded and accompanied by postural adjustments, which have been previously described as anticipatory postural adjustments (APAs) (Aruin, 2002;Aruin & Shiratori, 2003;Ruget et al, 2008). Therefore, the muscles responsible for postural adjustments are activated before those acting as prime movers (Ruget et al, 2008).…”

“…There is some evidence that suggests that APAs are strongly dependent on the afferent input from the initial biomechanical conditions (Aruin & Shiratori, 2003). A study performed by Galli et al (2008), which aimed to test this hypothesis, found that the APAs in the frontal plane when producing a step are under proprioception-based online control.…”

“…It remains unknown if in the presence of a dysfunction of this modulation process, due to inappropriate inputs, it is possible to observe changes in APAs' behavior in different initial conditions, like sitting and standing position. Aruin et al (2003) reported that changes in the organization of APAs' due to differences in body positions in sitting vs standing could be expected.…”

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“…The redistribution of weight using the legs is further complicated by their use in applying independent pressure to the hi-hat and bass drum pedals. Consequently, upper body stabilization is carried out by the trunk, specifically the erector spinae (ES) and rectus abdominis (RA), irrespective of the types levels of support in the legs (Aruin & Shiratori, 2003). These findings were supported by Santos and Aruin (2008), who also found that the lateral muscles contributed to upright posture control in feed-forward movements (i.e., movements relying on anticipatory correction), akin to feedforward movements in drumming and where the level of muscle activation being is directionally specific.…”