Elsevier

Gait & Posture

Volume 36, Issue 3, July 2012, Pages 614-618
Gait & Posture

Patterns of inter-joint coordination during a single-limb standing

https://doi.org/10.1016/j.gaitpost.2012.06.005Get rights and content

Abstract

Past studies have documented contributions of multiple joints in maintaining a single-limb standing, but no reports on patterns of inter-joint coordination. It is also unknown whether such inter-joint coordination, if exists, depends on visual feedback. Eight health young volunteers took part in this study. The inter-joint coordination during a single-limb standing were examined using 3D joint kinematics. There were five testing trials with eyes open (EO) and five trials with eyes close (EC) conditions. During each trial the subject stood on the right leg on an even platform for 20 s while 3D kinematic data was recorded. Recorded data was processed for an “adjusted coefficient of multiple determinations (ACMD)” to evaluate the inter-joint similarities in joint motions. Under both EO and EC conditions moderate to good similarities were found in axial rotation between the ankle and hip joints, and between ankle inversion/eversion and hip axial rotation. This pattern of the inter-joint coordination might be a unique feature of biomechanical configuration of the lower extremity. The significant increases in joint rotations but maintained inter-joint coordination from EO to EC condition may indicate a minimal influence of vision on the inter-joint coordination. Future studies to test patients with pathological conditions in single-limb stance need to examine any alternation/impairment of the inter-joint coordination pattern.

Highlights

► We examined the pattern of joint-coordination in the lower limb during single-leg standing. ► We examined the effect of vision to the pattern of joint-coordination during single-leg standing. ► The axial rotation of the ankle was synchronized with the axial rotation of the hip during single-leg standing. ► The ankle inversion/eversion was synchronized with hip axial rotation too. ► Those patterns remained the same with or without visual input.

Introduction

The ability to maintain a controlled upright posture is essential for daily activities and is made possible through limited number of control strategies that have evolved over time. Although redundancies exist among various musculature and kinematical combinations, the central nervous system may simplify the control task with a limited number of muscular strategies/movement patterns to be chosen from [1]. For instance, ankle and hip strategies have been observed in a double-limb standing perturbed along the anterior–posterior axis [2], [3], [4], [5]. When an ankle synergy is evoked the torso and legs move in the same direction about the ankle joint. When a hip strategy is evoked, the torso and legs move in the opposite direction about the hip joint. Muscles involved are not activated in response to a stretch of each individual joint, rather according to a muscular synergy leading to a synergistic movement pattern [2], [6]. Control of a double-limb standing under a perturbation along the medio-lateral axis showed the coordination primarily in motions at the hip and trunk [7], [8]. Studies of muscular synergies/movement patterns can help us to better understand human postural control [9].

Movement patterns during a single-limb standing has not been studied extensively. Biomechanically when compared to double-limb standing, the base of support against lateral bending and/or axial rotation in single-limb standing significantly decreases from the distance between two feet to the width of the supporting foot. The control strategies in maintaining upright single-limb standing, presented as movement patterns, are therefore expected to be different from that in double-limb standing. Single-limb stance always presents with large multi-joint movements in the lower extremity that limits the use of posturographic analysis of center of pressure trajectory because it provides no information on movement pattern or joint-coordination. Some investigators examined movement patterns during a single-limb standing in studies of functional ankle instability [10], [11], low back pain, or knee osteoarthritis [12], [13]. Tropp and Odenrick [14] observed a central role of the ankle joint in postural corrections during a single-limb standing. Hoogvliet et al. [15] suggested that lateral foot tilting strategy (ankle supination/pronation) might be an important corrective movement for postural control during a single-limb standing. Riemann et al., [16] compared corrective actions of the trunk, ankle, knee and hip joints during a single-limb standing on different surfaces. They concluded that corrective actions on either firm or soft surfaces occurred in multiple body segments rather than a single segment. It is commonly accepted that proprioceptive deficit after an ankle sprain is an important factor in functional ankle instability. However, studies of the effect of lateral ankle ligament anesthesia on body movement during a single-leg standing have reported inconsistent findings [17], [18]. The contradictory findings may be a result of differences in assessment techniques and instrumentation used. There is a need to identify key movement patterns for balance control during a single-limb standing in order to develop a standardized assessment tool. No past studies have systematically investigated the patterns of inter-joint coordination in the lower limb during a single-limb standing. We speculate that there may exit some forms of inter-joint coordination in the lower extremity during a sing-limb standing, like in a double-limb standing. We further speculate that the inter-joint coordination, if exits, may not depend on visual feedback.

The purpose of this study was to examine movement patterns of inter-joint coordination in the lower extremity during a single-limb standing and whether such patterns remain without visual input. Three-dimensional kinematics of lower extremity was quantitatively measured in a group of healthy young adults during a single-limb standing with or without vision. An “adjusted coefficient of multiple determination (ACMD)” [19] was used to examine potential patterns of inter-joint coordination in the motions of lower extremity. ACMD analysis provides us a tool to examine continuous waveforms of the recorded kinematic data which is crucial in identifying possible movement patterns.

Section snippets

Methods

A total of eight healthy young volunteers (three males, five females, mean age of 26.4 years, mean height 1.68 m, mean body weight 69.3 kg) took part in this study after they signed the informed consent approved by the Institutional Review Board of the University of Kansas Medical Center. None of the subjects had history of severe ankle, knee, and/or hip injury, vestibular lesions or any other pathology that would impair their motor performance.

Results

Fig. 2 shows an example of recorded joint angular motion curves from one trial presented in a pair of hip IER and ankle IER (Fig. 2). A clear similarity between the two curves was visible when one of the curves was flipped. In other words, the internal rotation of the hip showed similar pattern as external rotation of the ankle, or the external rotation of the hip was similar to internal rotation of the ankle.

In EO condition moderate to good similarities were found in joint angular motions

Discussion

Unlike double-limb stance during which small body sway is found primarily in the sagittal plane, single limb stance showed the inter-joint coordination mainly in the transverse plane (e.g. ankle and hip internal/external rotations) and frontal plane (e.g. ankle inversion/eversion) in the current study. The patterns of inter-joint coordination during single limb standing, presented as synchronized motions between ankle inversion/eversion and hip axial rotation and between ankle axial rotation

Conflict of interest statement

The authors have no conflicts of interest that are directly relevant to the content of this report.

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