Mechanics of walking and running up and downhill: A joint-level perspective to guide design of lower-limb exoskeletons

• Published in: PloS one Vol. 15; no. 8; p. e0231996
• Main Authors: Nuckols, Richard W., Takahashi, Kota Z., Farris, Dominic J., Mizrachi, Sarai, Riemer, Raziel, Sawicki, Gregory S.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 28.08.2020; Public Library of Science (PLoS)
• Subjects: Adult; Ankle; Ankle - physiology; Ankle Joint - physiology; Artificial legs; Biology and Life Sciences; Biomechanical Phenomena; Biomechanics; Braking; Clinical trials; Electric power generation; Energy; Energy transfer; Exoskeleton; Exoskeleton Device - trends; Exoskeletons; Female; Fitness equipment; Gait; Gait - physiology; Gait Analysis - methods; Health aspects; Hip; Hip - physiology; Hip Joint - physiology; Humans; Industrial engineering; Joints (anatomy); Kinematics; Knee; Knee - physiology; Knee Joint - physiology; Laboratories; Locomotion; Lower Extremity - physiology; Male; Mechanical properties; Mechanics; Mechanics (physics); Medicine and Health Sciences; Metabolism; Muscle, Skeletal - physiology; Physiological aspects; Physiological research; Physiology; Regenerative braking; Robotics; Robotics - instrumentation; Running; Running - physiology; Treadmills; Velocity; Walking; Walking - physiology; Wearable technology; United States; Israel; Georgia; United Kingdom > UK; United States > US
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0231996

Lower-limb wearable robotic devices can improve clinical gait and reduce energetic demand in healthy populations. To help enable real-world use, we sought to examine how assistance should be applied in variable gait conditions and suggest an approach derived from knowledge of human locomotion mechanics to establish a 'roadmap' for wearable robot design. We characterized the changes in joint mechanics during walking and running across a range of incline/decline grades and then provide an analysis that informs the development of lower-limb exoskeletons capable of operating across a range of mechanical demands. We hypothesized that the distribution of limb-joint positive mechanical power would shift to the hip for incline walking and running and that the distribution of limb-joint negative mechanical power would shift to the knee for decline walking and running. Eight subjects (6M,2F) completed five walking (1.25 m s-1) trials at -8.53°, -5.71°, 0°, 5.71°, and 8.53° grade and five running (2.25 m s-1) trials at -5.71°, -2.86°, 0°, 2.86°, and 5.71° grade on a treadmill. We calculated time-varying joint moment and power output for the ankle, knee, and hip. For each gait, we examined how individual limb-joints contributed to total limb positive, negative and net power across grades. For both walking and running, changes in grade caused a redistribution of joint mechanical power generation and absorption. From level to incline walking, the ankle's contribution to limb positive power decreased from 44% on the level to 28% at 8.53° uphill grade (p < 0.0001) while the hip's contribution increased from 27% to 52% (p < 0.0001). In running, regardless of the surface gradient, the ankle was consistently the dominant source of lower-limb positive mechanical power (47-55%). In the context of our results, we outline three distinct use-modes that could be emphasized in future lower-limb exoskeleton designs 1) Energy injection: adding positive work into the gait cycle, 2) Energy extraction: removing negative work from the gait cycle, and 3) Energy transfer: extracting energy in one gait phase and then injecting it in another phase (i.e., regenerative braking).