Muscle coactivation during obstacle crossing corresponding to increasing obstacle height in patients with hemiplegia after stroke

Abstract

Introduction and aim: Stroke patients often encounter difficulties when crossing obstacles, which contribute to a high rate of falls [1]. Previous studies indicated that patients after stroke excessively elevate their leading limbwhile crossing an obstacle to minimize their risk of falling [1]. This adaptive behaviour occurred even though it is difficult to maintain balance by prolonging the single stance time. However, previous studies generally focused on the leading limb in obstacle crossing tasks; therefore, there is little information regarding the trailing limb. More recently, muscle coactivation during gait was reported as a compensation strategy to enhance postural stability in individuals after stroke [2]. Thus, a change in muscle coactivation in the trailing limb corresponding to an increase in obstacle height may be an indicator of postural stability during obstacle crossing. The aim of this study was to investigate changes in muscle coactivation patterns in the trailing limb using electromyography (EMG); these changes corresponded to an increasing obstacle height in stroke patients with hemiplegia. Patients/materials and methods: Twelve sub-acute patients who suffered a stroke less than 6 months previously participated in this study. Each patient performed several trials in an obstacle crossing task. First, patients performed two self-paced normal walking trials on a 5-m walkway. Subsequently, an obstacle was placed 2–2.5m ahead of the start position at a height that was randomly selected from three heights (0 cm, 4 cm, or 8 cm). The patients were instructed to walk at a self-selected speed and step over the obstacle without stopping. In each condition, EMG activity was recorded in the trailing limb from the tibialis anterior and lateral gastrocnemius muscles. The coactivation index (CoI) was calculated for both the paretic and non-paretic limbs when the trailing limb was in the stance phase. The stance phase was further divided into the three following sub-phases: the first and second double stance (DS1 and DS2), and the single stance (SS). Using the Friedman and Wilcoxon signed-rank tests (with Bonferroni correction),weevaluated theCoI calculatedduring each stance sub-phase. Results: Patients tripped over the obstacle in 16.6% trials when the paretic limb trailed and in 3.7% when the non-paretic limb trailed. When the paretic limb trailed, the paretic limb CoI significantly increased only during DS2 corresponding to an increasing obstacle height (p<0.01). In contrast, when the non-paretic limb trailed, the non-paretic limb CoI significantly increased during both SS (p<0.01) and DS2 (p<0.01) corresponding to an increasing obstacle height. The results for the multiple comparisons are shown in Fig. 1. Discussion and conclusions:When the paretic limb trailed, the paretic limb CoI significantly increased only during DS2. However, muscle coactivation decreased during DS2 in normal gait because the postural stability was no longer mainly required in the trailing limb as the weight was shifted to the opposite limb during this phase [3]. Thus, increased muscle coactivation occurring only during DS2 in the paretic limb with an increasing obstacle height may beanunnecessary adaptation that caused thepatients to frequently trip in these trials. In contrast, the non-paretic limb CoI also significantly increased during SSwith increasing an obstacle heightwhen the non-paretic limb trailed. Thus, although instability increased in the SS phase during obstacle crossing, muscle coactivation in the non-paretic limb increased postural stability during this phase, which resulted in a lower rate of trip trials.