Kinematic and electromyographic analyses of normal and device-assisted sit-to-stand transfers
Highlights
► Kinematics and muscle demands of sit-to-stand transfers without a device (ND) and device-assisted (DA) were compared. ► Mechanical DA movements differed from normal ND sit-to-stand patterns. ► During DA transfers, verbally encouraging best effort (DA-BE) elevated muscle activity. ► DA-BE hip, knee, and ankle motion profiles more closely simulated normal ND than DA transfers without effort (DA-NE). ► DA-BE trunk and pelvis motion profiles were less similar to normal than DA-NE.
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.
Section snippets
Participants
Ten adults (5 males), free from musculoskeletal and neurological impairment, were recruited from the local community [mean (SD) age: 21.0 (2.4) years; body mass: 71.9 kg (10.7); height: 178.2 cm (12.2)].
Instrumentation
The Qualisys Motion Analysis System and Qualisys Track Manager software (Gothenburg, Sweden) defined three-dimensional motion (12 Oqus Series-3 cameras, sampling rate 120 Hz). The MA-300-10 EMG system and MA-411 surface electrodes (Motion Lab Systems, Inc., Baton Rouge, LA) recorded muscle
Kinematics
Compared to ND, device-assisted conditions (i.e., feet supported on platform) resulted in significantly narrower heel-to-heel (ND = 24 cm vs. DA-BE = 18 cm, DA-NE = 17 cm; p < 0.001) and toe-to-toe (ND = 35 cm vs. DA-BE = 26 cm, DA-NE = 27 cm; p < 0.001) distances.
Compared to DA-NE, CMC values were higher during DA-BE at the hip (0.87 vs. 0.77), knee (0.95 vs. 0.86), and ankle (0.69 vs. 0.58; Fig. 2). In contrast, DA-BE values were substantially lower than DA-NE at the trunk (0.49 vs. 0.56) and pelvis (0.35 vs.
Discussion
Relearning to transfer is a key rehabilitation goal for many individuals. When profound weakness and balance deficits prevent patients from safely performing the task, external human and/or device assistance is often required. Device-assisted movement patterns that simulate normal transfers could enable patients to transfer safely while also practicing an activity they seek to relearn.
In the current study, the lift device transferred participants to a standing position with only negligible
Conflict of interest statement
No conflicts of interest existed for any authors.
Acknowledgements
This work was supported, in part, by Undergraduate Creative Activities and Research Experiences Program and Agricultural Research Division grants from the University of Nebraska-Lincoln.
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