Kinematic and electromyographic analyses of normal and device-assisted sit-to-stand transfers

Abstract

Mechanical sit-to-stand devices assist patient transfers and help protect against work-related injuries in rehabilitation environments. However, observational differences between patient's movements within devices compared to normal sit-to-stand transfers deter clinician use. This study compared kinematics and muscle demands during sit-to-stand transfers with no device (ND), and device-assisted during which participants exerted no effort (DA-NE) and best effort (DA-BE). Coefficient of multiple correlations (CMCs) compared kinematic profiles during each device-assisted condition to ND. Compared to DA-NE, CMCs were higher during DA-BE at the hip, knee, and ankle. However, DA-BE values were lower than DA-NE at the trunk and pelvis due to the device's mechanical constraints. In general, all joints’ final DA-NE postures were more flexed than other conditions. Electromyographic was significantly lower during DA-NE compared to ND for all muscles except lateral hamstring, and during DA-BE compared to ND for gluteus maximus, gastrocnemius, and soleus. Verbal encouragement (DA-BE) significantly increased medial hamstring, vastus lateralis, gastrocnemius, soleus and tibialis anterior activation compared to DA-NE. In conclusion, device-assisted sit-to-stand movements differed from normal sit-to-stand patterns. Verbally encouraging best effort during device-assisted transfers elevated select lower extremity muscle activation and led to greater similarity in hip, knee and ankle movement profiles. However, trunk and pelvis profiles declined.

Introduction

Workplace injuries are prevalent in healthcare [1], [2], [3], [4], [5], [6], [7], [8], [9], [10]. Among nursing home employees, incidence rates for back injuries resulting in lost work days are more than twice construction workers’ rates and over three times agricultural workers’ rates [1], [2], [3], [4], [5], [6]. A significant number of clinicians’ injuries result from lifting and transferring patients [11]. Physical therapists performing 6–10 patient transfers a day are 2.4 times more likely to experience low back injuries than therapists not performing transfers [12].

The nursing profession's implementation of safe patient handling and movement policies [13] has dramatically reduced work-related injuries [14], chronic pain (23%) [15], medical expenses (74%), worker compensation payments (50%), and estimated restricted duty costs (95%) [16]. One tool emerging from these initiatives is the battery-powered sit-to-stand transfer device. It safely lifts and lowers patients between seated and standing positions, while reducing the risk of caregiver injury [17], [18].

Given notable reductions in injuries that have arisen from implementing safe lifting policies in nursing, it is reasonable to expect that therapists would readily incorporate lifting equipment into their routines to reduce injuries. However, therapists have been reluctant to adopt device usage due to concerns regarding therapeutic value [19]. Movement patterns displayed by patients when performing device-assisted transfers observationally differ from normal sit-to-stand transfers. Additionally, traditional approaches to using automated devices often do not encourage patients to try to stand-up, thus may discourage active muscle engagement compared to clinician-assisted transfers. Clinicians’ concerns regarding mechanical sit-to-stand devices arise in part from current practice paradigms that emphasize intensive, task-specific training for promoting recovery of function and cortical reorganization following neurologic injury [20], [21].

Given the importance of task specificity to rehabilitation, this study's primary aim was to explore whether kinematic and electromyographic patterns during device-assisted sit-to-stand transfers were similar to unassisted transfers. Individuals without known pathology were specifically recruited to isolate the effects of the device's mechanical design from the confounding influence of weakness, balance impairments, and movement control deficits on transfers. Participants were assessed while exerting no purposeful effort to simulate traditional device-assisted sit-to-stand transfers performed by patients. Participants also were assessed while attempting to offer their best effort to stand within the device to explore the mechanical constraints imposed by the device. It was hypothesized that compared to sit-to-stand transfers without a device, during device-assisted conditions forward trunk lean would be restricted due to the device's mechanical constraints. Additionally, it was hypothesized that the ankle would show minimal motion during device-assisted sit-to-stands because ankle stabilizing mechanisms would constrain dorsiflexion. Finally, it was hypothesized that muscle activity would be greater in key lower extremity extensors when participants were encouraged to use their legs to help stand within the device.