A model for differential leg joint function during human running

Lower Limb Joint Functions during Single-Leg Hopping in-Place in Children and Adults

Children often display different whole-body dynamics compared to adults during locomotion such as walking and hopping. However, it is unknown whether these differences result in diverging functional usage of the lower limb joints. This study aimed to compare the mechanical functions of the ankle, knee, and hip joints between children and adults during single-leg hopping in-place at different frequencies. Children aged 5-11 years and adults aged 18-35 years performed hopping at their preferred frequency and slower and faster frequencies. Function of the joint was modeled as a combination of a strut, spring, motor, and damper. At the preferred frequency, children hopped equally with strut and spring functions at the ankle and knee joints while adults primarily used the spring function. When increasing frequency, both children and adults decreased the spring index and increased the strut index at the ankle and knee joints. Across all conditions, both children and adults used the strut function primarily at the hip joint. Results suggest that preadolescent children are still developing the adult-like spring function of their ankle and knee joints during hopping in-place. Quantification of spring function during hopping in-place may present an innovative approach to understand the maturation of the stretch-shortening cycle in children.

Postural Control, Dual Task Performance and Executive Function Following an Ultramarathon

As research into the postural and cognitive effects of ultramarathon running is sparse and still needed, we investigated the effect of ultramarathon running on runners' postural control, dual task postural control and a measure of executive function-the flanker test, expecting fatigue-related deterioration on each measure. We used a pre- and post-test research design with 14 runners who completed (a) postural assessment with eyes open and closed, on a flat surface and on foam during (b) a two-choice reaction time dual task postural assessment, and (c) an executive function modified flanker task. With regard to postural stability, we observed, after running, increased anterior-posterior (AP) path length and AP root mean square (RMS) and reductions in both mediolateral (ML) RMS and ML median frequency. Dual task analysis showed reduced ML RMS prior to the race, whereas the effect was absent afterwards. Reaction times were not significantly altered between pre-post or surface conditions assessments. There were no statistically significant differences in mean modified flanker scores before and after the race. These data demonstrated that, following an endurance run, there were plane specific movement adaptations in postural sway that may have resulted from neuroprotective changes under extreme fatigue.

Leg Joint Mechanics When Hopping at Different Frequencies

Although the dynamics of center of mass can be accounted for by a spring-mass model during hopping, less is known about how each leg joint (ie, hip, knee, and ankle) contributes to center of mass dynamics. This work investigated the function of individual leg joints when hopping unilaterally and vertically at 4 frequencies (ie, 1.6, 2.0, 2.4, and 2.8 Hz). The hypotheses are (1) all leg joints maintain the function as torsional springs and increase their stiffness when hopping faster and (2) leg joints are controlled to maintain the mechanical load in the joints or vertical peak accelerations at different body locations when hopping at different frequencies. Results showed that all leg joints behaved as torsional springs during low-frequency hopping (ie, 1.6 Hz). As hopping frequency increased, leg joints changed their functions differently; that is, the hip and knee shifted to strut, and the ankle remained as spring. When hopping fast, the body's total mechanical energy decreased, and the ankle increased the amount of energy storage and return from 50% to 62%. Leg joints did not maintain a constant load at the joints or vertical peak accelerations at different body locations when hopping at different frequencies.

Leg Joint Stiffness Affects Dynamics of Backward Falling From Standing Height: A Simulation Work

Falling backward can lead to injuries including hip fracture, back injury, and traumatic brain impact among older adults. A loss of consciousness is associated with falling backward and accounts for about 13% of all falls among older adults. Little is known about the dynamics of backward falls, such as the falling duration, the impact severity, and how the fall dynamics are affected by the biomechanical properties of the lower limb joints, particularly the rotational stiffness. The purpose of this study was to investigate the influence of the stiffness of individual leg joints on the dynamics of backward falls after losing consciousness in terms of the falling duration and impact velocities. Based on a 15-segment human model, we simulated the process of falling backward by sweeping the parameter space of ankle, knee, and hip's stiffnesses varying from 0 to 8.73 N·m·deg-1 (or 500 N·m·rad-1). The results revealed that the falling duration and impact speeds of the head and hip ranged from 0.27 to 0.63 s, 2.65 to 7.88 m·s-1, and 0.35 to 3.36 m·s-1, respectively, when the stiffness of the leg joints changed within their limits. Overall, the influence of the joint stiffness on the falling dynamics (falling duration and impact speed) is comparable between hip and knee joints, whereas ankle stiffness showed little influence on the backward falling dynamics. Our findings could provide references for designing protective devices to prevent impact-induced injuries after a backward fall.

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

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).

Bio-inspired upper limb soft exoskeleton to reduce stroke-induced complications

Stroke has become the leading cause of disability and the second-leading cause of mortality worldwide. Dyskinesia complications are the major reason of these high death and disability rates. As a tool for rapid motion function recovery in stroke patients, exoskeleton robots can reduce complications and thereby decrease stroke mortality rates. However, existing exoskeleton robots interfere with the wearer's natural motion and damage joints and muscles due to poor human-machine coupling. In this paper, a novel ergonomic soft bionic exoskeleton robot with 7 degrees of freedom was proposed to address these problems based on the principles of functional anatomy and sports biomechanics. First, the human motion system was analysed according to the functional anatomy, and the muscles were modelled as tension lines. Second, a soft bionic robot was established based on the musculoskeletal tension line model. Third, a robot control method mimicking human muscle control principles was proposed and optimized on a humanoid platform manufactured using 3D printing. After the control method was optimized, the motion trajectory similarities between humans and the platform exceeded 87%. Fourth, the force-assisted effect was tested based on electromyogram signals, and the results showed that muscle signals decreased by 58.17% after robot assistance. Finally, motion-assistance experiments were performed with stroke patients. The joint movement level increased by 174% with assistance, which allowed patients to engage in activities of daily living. With this robot, stroke patients could recover their motion functions, preventing complications and decreasing fatality and disability rates.