Abstract
Recent studies suggest that in addition to movements between ankle and hip joints, movements of the upper body, in particular of the arms, also significantly contribute to postural control. In line with these suggestions, we analyzed regulatory movements of upper and lower body joints supporting dynamic balance regulation during challenged locomotion. The participants walked over three beams of varying width and under three different verbally conveyed restrictions of arm posture, to control the potential influence of arm movements on the performance: The participants walked (1) with their arms stretched out perpendicularly in the frontal plane, (2) spontaneously, i.e., without restrictions to the arm movements, and (3) with their hands on their thighs. After applying an inverse-dynamics analysis to the measured joint kinematics, we investigated the contribution of upper and lower body joints to balance regulation in terms of torque amplitude and variation. On the condition with the hands on the thighs, the contribution of the upper body remains significantly lower than the contribution of the lower body irrespective of beam widths. For spontaneous arm movements and for outstretched arms we find that the upper body (including the arms) contributes to the balancing to a similar extent as the lower body. Moreover, when the task becomes more difficult, i.e., for narrower beam widths, the contribution of the upper body increases, while the contribution of the lower body remains nearly constant. These findings lend further support to the hypothetical existence of an “upper body strategy” complementing the ankle and hip strategies especially during challenging dynamic balance tasks.
Highlights
When humans try to maintain their equilibrium in a challenging balancing task, they unwittingly engage upper body parts including their trunk, arms, and head (Otten, 1999; Milosevic et al, 2011; Schärli et al, 2013)
When balancing across a wire or a narrow beam, they intuitively stretch out and move their arms (Honegger et al, 2013; Patel et al, 2014). Such dynamic movements are possible because the many interconnected body parts are regulated by a powerful postural control system that allows for maintaining balance even when highly challenging external
A widespread and frequently cited concept of postural control dates back to Nashner and McCollum (1985), who postulated the existence of two distinct postural control mechanisms termed the ankle strategy and the hip strategy, which are engaged by the nervous system either separately or in combination to reposition the body’s center of mass over the base of support and maintain equilibrium
Summary
When humans try to maintain their equilibrium in a challenging balancing task, they unwittingly engage upper body parts including their trunk, arms, and head (Otten, 1999; Milosevic et al, 2011; Schärli et al, 2013). For dynamic balance tasks it appears reasonable to assume that there are several strategies simultaneously engaged for the same task, since individually different, multi-joint coordination patterns occur (Bernstein, 1967; Alexandrov et al, 2005; Wang et al, 2014) To address these issues, we applied an inverse-dynamics analysis to kinematic and force plate data recorded during a dynamic balance task involving challenged locomotion, to gain information about the extent to which the multiple joints of the entire body, and in particular of the upper body as compared to the lower body, contribute to postural control under such circumstances. As an extension of Nashner and McCollum’s concept of ankle and hip strategies, we hypothesize that in a dynamic balance task during challenged locomotion, (1) a multijoint coordination pattern with a significant contribution of upper body movements shows up, and (2) the contribution of upper body movements to balance regulation increases with task difficulty
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