Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, C11
Human standing: is there a postural set? What are the functional implications?
I. Di Giulio1, C. N. Maganaris1, V. Baltzopoulos1, I. D. Loram1
1. Manchester Metropolitan University, Manchester, United Kingdom.
One hypothesis is that movement is controlled via a motor set consisting of a pre-programmed combination of set points, thresholds and feedback gains associated with maintaining or changing a configuration of the body (1). Here we use walking as a perturbation of standing and study the initiation of normal standing. Following termination of walking, we study the whole body configuration as participants adopt their normal standing pose. One hypothesis is that standing is merely the cessation of walking (1,2). An alternative hypothesis is that human standing requires a postural set distinct from the cessation of walking. We ask whether participants maintain the standing configuration reached at the end of walking, or whether during the early stages of standing they adopt a different configuration. We also consider the functional implications of the 3D leg and spine configuration for leg stiffness, balance, muscular economy, initiation of movement and mechanical wear and tear. 14 healthy participants, aged 47 ± 13 years (mean±s.d), walked onto a force plate and stood normally, in a self chosen configuration, for 10s. A 10-camera motion analysis system measured body kinematics. The quantities calculated were: sagittal centre of gravity (CoG); joint centres, flexion-extension angles and internal-external rotation angles of the hip, knee, ankle; distance between the 7th cervical vertebra and sacrum. Quantities were tested for significant difference between the initiation of standing (feet placed) and “steady state” standing (10s later) (Wilcoxon). At the termination of walking, torso speed was 28±18mm/s. Hip and knee joint centres were approximately aligned with the CoG, the ankle was slightly behind. During the 10s after initiation of standing, the CoG moved more in front of the ankle and knee joint centre (p<0.001 and p=0.056 respectively) and further behind the hip (p<0.001). The ankle dorsiflexed more than 1.8deg (p<0.001), the knee extended (p=0.1880) and externally rotated (p=0.0476), the hip extended (p<0.001) and internally rotated (p=0.0462). Spine length (C7-sacrum) decreased on average of 4±0.5mm (p=0.0016). On average, with variability between people, the CoG was in front of the ankle and knee joint centre and behind the hip joint, which is consistent with established facts (3). The most significant point is that individuals adopt a standing postural set which is distinct from the one of cessation of walking. Comparing steady state and initiation of standing, the CoG is more in front of the ankle and knee and more behind the hip and the spine is shortened: it is predicted that the leg is stiffer and more locked. Every subject was able to stand in a more aligned and less locked configuration at the initiation of standing rather than in steady state. These different configurations can be evaluated in terms of biomechanics, proprioception and control of movement.
Where applicable, experiments conform with Society ethical requirements