Full length articleEffect of forward-directed aiding force on gait mechanics in healthy young adults while walking faster
Introduction
Treadmills are a common exercise system that can be used to provide interactive force environments to either provide greater walking challenge by increasing speed [1] and belt inclination or reduce the effort to walk at a particular speed by providing a downward inclination that allows gravity to aid with the required propulsive force generation [2,3]. Externally applied aiding forces may be used to make the functional task of walking easier to practice the motor pattern of stepping and act as an effective interventional tool to increase walking speed of individuals after they have experienced a stroke [4]. We recently described a new robotic treadmill system that can provide forward-directed aiding force at the individuals center of mass while they walk at a range of speeds [5]. These aiding forces have the potential to allow individuals with a limited range of walking speed or who are very deconditioned the ability to walk for longer periods of time and at faster walking speeds than could be achieved without them. Currently, little data exists describing changes to kinetics with aiding forces over different speeds. Characterizing how joint kinetics are modified with aiding forces can be used to better inform the development of intervention paradigms.
Previous investigations have used aiding forces to influence the walking speed of a patient population, as well as investigate the metabolic and neuromechanical cost of walking. Recently, an overground robotic system was used to apply a forward-directed aiding force to individuals post-stroke, while they walked, to investigate how these aiding forces influenced the maximum speed they could achieve. Persons post-stroke were able to walk faster without increasing propulsive forces [6]. Forward-directed aiding forces have been shown reduce the net metabolic rate about 47% [7]. It was also observed that the forward-directed aiding force (FAF) applied at the center of mass could reduce propulsive ground reaction forces, while also resulting in a decrease in medial gastrocnemius electromyographic (EMG) activity [8]. More recently Zirker et al. [3] observed a decrease in the oxygen consumption with aiding force, along with a decrease in hip extension and ankle plantar flexion, which suggests a decrease in the required force to propel the body forward at that speed.
These previous studies, apart from Capó-Lugo et al. [6], were performed at a single speed close to comfortable walking speed of healthy individuals (about 1.25 m/s). In addition, no investigation has reported lower limb joint kinetics with the use of an aiding force over different speeds. It is possible that forces applied at the center of mass may not only affect ankle kinetics but indeed power and work distribution across each joint of the lower limb could potentially be redistributed [9]. Further, investigations using aiding forces have shown, that while decreasing the need for propulsive force, such aiding forces also dramatically increased braking forces [3,7]. Thus, the effects of FAF on joint power and work during faster speed still need to be explored.
Here, we evaluated the net change in biomechanical parameters associated with walking at a faster speed: a) over a treadmill without robot system (no-FAF) and b) walking over a treadmill using a robot system applying FAF characterizing aiding mode. We hypothesized that, at faster speeds in both conditions, we would observe an increase in anterior-posterior force impulse, joint powers and net work. However, when comparing the change in measures associated with faster speed walking between the no-FAF and FAF conditions, we would observe reduced propulsive force, joint power, and net work during the FAF condition. It is important to understand changes in walking mechanics at faster speeds with forward-directed aiding conditions for eventual planning and application of gait training with impaired populations undergoing recovery of walking ability and restoration of functional walking speeds.
Section snippets
Participants
Twenty non-neurologically impaired physical active young adults (sex: 10 male; age: 23.8 ± 3.62 yr; height: 1.69 ± 0.09 m; and mass 69.99 ± 12.45 kg) participated in this study. The eligibility criteria for recruitment was no history of cardiac arrhythmia, hypertension, neurologic and/or musculoskeletal disorders, which can affect the lower limb, walking and/or balance. Informed consent was obtained from all participants with the approval of the University of Alabama at Birmingham Institutional
Results
One participant was removed from analysis due to an inability to maintain one foot on each belt for the duration of the data collection. The short version of IPAQ reveled that nine participants had a high level and ten had a moderate level of physical activity.
Spatiotemporal gait parameters were greater at the FAST speeds in both conditions. The cadence and step length were significantly larger at the FAST speed, and the change was not different between conditions (Table 1).
Propulsive force
Discussion
This study investigated the net change in biomechanical parameters associated with walking at a faster speed over a treadmill (regular treadmill walking – no-FAF) and walking over a treadmill using a robot system applying FAF. Our results confirmed our hypotheses that at faster speeds in both conditions, we observed an increase in anterior-posterior force impulse, joint powers and net work. However, when comparing the change in measures associated with SLOW versus FAST walking speed, we
Conclusion
In conclusion, forward-directed aiding forces applied at the hip through a robotic interface can reduce the necessary generation of ankle torque and propulsion required to walk at a faster speed. The future implications of these results are that people with reduced force generation capability, especially at the ankle, may benefit from training regimens where walking can be practiced at faster speeds.
Author contributions
The authors VCD, CPH and DAB conceived and designed the study. VCD participated in the data acquisition, performed the analysis and interpretation of the data and drafted the manuscript, and performed multiple critical reviews of the manuscript for intellectual content. CPH performed the analysis and interpretation of the data and drafted the manuscript and performed multiple critical reviews of the manuscript for intellectual content. DAB performed the analysis and interpretation of data and
Conflicts of interest statement
VCD none; CPH none; DAB participates as a scientific consultant with the company HDT Global, the company that markets and sells the KineAssist device. He is a co-inventor who will potentially receive royalty payments.
Acknowledgements
The authors thank for support by CNPq grant (201964/2014-7) and NIDLIRR grant (MARS – FI30305002) and also thank Ms. Camila Melo for help during data collection.
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