Estimating highest capacity propulsion performance using backward-directed force during walking evaluation for individuals with acquired brain injury

NOTHING HERE gets survivors recovered! Useless. It is just measurements. NO PROTOCOLS!

Estimating highest capacity propulsion performance using backward-directed force during walking evaluation for individuals with acquired brain injury

• Kelli LaCroix,
• Lauren Horelka,
• Clif Hung &
• David A. Brown 

Journal of NeuroEngineering and Rehabilitation volume 21, Article number: 134 (2024) Cite this article

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Abstract

There are over 5.3 million Americans who face acquired brain injury (ABI)-related disability as well as almost 800,000 who suffer from stroke each year. To improve mobility and quality of life, rehabilitation professionals often focus on walking recovery soon after hospital discharge for ABI. Reduced propulsion capacity (force output of the lower limbs to counteract ground reaction forces) negatively impacts walking ability and complicates recovery during rehabilitation for brain injured people. We describe a method, using backward-directed resistance (BDR) in a robotic-based treadmill device, to allow measurement of maximum walking propulsion force (MWPF) that is not otherwise possible during overground walking assessment. Our objective was to test the construct validity of a maximum walking propulsion force (MWPF) measure that reflects a person’s propulsive strength against applied BDR, while walking on a robotic treadmill-based device for participants with acquired brain injury (ABI). Our study enrolled 14 participants with ABI at an in inpatient rehabilitation in Galveston, TX from 8/1/21 − 4/31/22. The range of weight-adjusted MWPF was 2.6–27.1% body weight (%BW), mean 16.5 ± 8.4%BW, reflecting a wide range of propulsive force capability. The strongest correlation with overground tests was between the 6-minute walk test (6-MWT) distance and the MWPF values (r = 0.83, p < 0.001) with moderate correlations between the 10-meter walk tests at comfortable (CWS) and fast speeds (FWS). The Five Times Sit-to-Stand (used as a standard clinical measure of functional lower extremity strength) and MWPF tests were poorly correlated (r = 0.26, p = 0.4). Forward model selection included 6-MWT distance, age, and overground CWS as significant partial predictors of MWPF. We conclude that this novel MWPF measure is a valid representation of maximum propulsive force effort during walking for people post-ABI. Additional research could help determine the impact of interventions designed to increase propulsive force generation during rehabilitation training to improve overground walking performance.

Introduction

There are over 5.3 million Americans who face brain injury-related disability [1] as well as almost 800,000 who suffer from stroke each year [2]. To improve mobility and quality of life, rehabilitation professionals often focus on walking recovery soon after hospital discharge for such acquired brain injuries (ABI). One goal of physical rehabilitation is to attain optimal functional outcomes such as independent community walking, but therapists are tasked with determining how challenging a training environment should be to match therapy goals with the person’s capacity to realistically achieve them, a concept that been explored by the challenge point framework in research [3, 4]. Intensive mobility training, specifically in adults who have had a brain injury, can significantly improve gait speed, balance, and mobility [5], but diminished walking strength due to reduced lower limb power generation and/or poor distribution of lower limb power [6] is a barrier to attaining faster, more appropriate walking speeds. ABI is also associated with hemiparesis and abnormal muscle pattern activation [7] muscle weakness due to gross muscle atrophy, particularly of hip extensors and plantar flexors [8], and neural changes of the motor cortex that result in reduced motor neuron recruitment and rate coding [9]. These factors all contribute to propulsive deficits that are essential to address during rehabilitation.

Studies commonly use the FXSTS as a measure of functional lower extremity strength [10, 11], but biomechanical factors are unique in those who have experienced a head injury. Slower FXSTS times are associated with lower peak whole-body center of mass velocity in a vertical direction, which reflects a decreased ability to perform functional transitional movements and activities such as stair ambulation [12]. However, this ability may not reflect the capability to generate horizontal forward propulsive force during walking. In fact, no studies to date have validated the FXSTS test in people with ABI as a measure of forward propulsion force generation. Overground walking tests such as the 10-Meter Walk Test (comfortable and fast 10MWT) [13] and 6-Minute Walk Test (6-MWT) [14] are the gold standard for measuring walking impairments. These tests provide insight into an individual’s capacity for improvement during rehabilitation and help clinicians set realistic patient goals, track progress, and assess outcomes.

Modern robotic-based treadmills allow the clinician to manipulate the walking force requirements of their clients, which provides a way to analyze forward propulsion force generation in a way that is not feasible in the standard overground environment. Previous research demonstrated a walking assessment based on overcoming horizontal force resistance generated by a robotic assistance treadmill belt in the post-stroke population [15]. This test was performed by applying increased magnitudes of backward horizontal resistance to the treadmill belt while instructing individuals to walk comfortably until they reached a level of resistance that prevented them from moving the treadmill belt forward [15, 16]. This test could be further applied to examine upper limits of force generation as an estimate of propulsive force. The KineAssist-MX used in this study can apply backward-directed force to create a precise amount of resistance against forward walking while the participant is walking in the device. A precise amount of resistance can be applied in the opposite direction of walking; when incrementally increased, it is possible to determine a propulsion threshold, referred to as the maximum walking propulsion force (MWPF), for each user.

We developed a MWPF test to examine the forward propulsion generation capability of individuals post-ABI. Our approach was to provide a walking environment with progressive levels of backward-directed resistance (BDR) until the person was no longer able to overcome the forces; this threshold measurement can be used to estimate the potential MWPF that a person could theoretically move at if they were to utilize the propulsive forces during normal (unresisted) walking conditions.

We used the robotic treadmill to explore the use of BDR to determine a MWPF value for participants with ABI. To validate the MWPF measure, we assessed the validity between overground walking tests and MWPF values. We hypothesized the MWPF measure would be positively correlated with overground FWS and the 6-MWT distance. We also hypothesized that MWPF could be used to predict CWS, FWS, and 6-MWT distance overground to potentially explain why some people post-ABI have less endurance compared to others post-ABI. Finally, since we propose that MWPF would be more strongly correlated than the FXSTS with walking performance (e.g., endurance, comfortable walking speed, fast walking speed), we hypothesized there would be a poor correlation between the FXSTS and MWPF measure, reflecting divergent construct validity. Support of these hypotheses would demonstrate that measuring propulsive forces capability can provide useful information about the role of propulsive force generation in walking performance.