Compensatory strategies during walking in response to excessive muscle co-contraction at the ankle joint

Policy Design for an Ankle-Foot Orthosis Using Simulated Physical Human-Robot Interaction via Deep Reinforcement Learning

This paper presents a novel approach for designing a robotic orthosis controller considering physical human-robot interaction (pHRI). Computer simulation for this human-robot system can be advantageous in terms of time and cost due to the laborious nature of designing a robot controller that effectively assists humans with the appropriate magnitude and phase. Therefore, we propose a two-stage policy training framework based on deep reinforcement learning (deep RL) to design a robot controller using human-robot dynamic simulation. In Stage 1, the optimal policy of generating human gaits is obtained from deep RL-based imitation learning on a healthy subject model using the musculoskeletal simulation in OpenSim-RL. In Stage 2, human models in which the right soleus muscle is weakened to a certain severity are created by modifying the human model obtained from Stage 1. A robotic orthosis is then attached to the right ankle of these models. The orthosis policy that assists walking with optimal torque is then trained on these models. Here, the elastic foundation model is used to predict the pHRI in the coupling part between the human and robotic orthosis. Comparative analysis of kinematic and kinetic simulation results with the experimental data shows that the derived human musculoskeletal model imitates a human walking. It also shows that the robotic orthosis policy obtained from two-stage policy training can assist the weakened soleus muscle. The proposed approach was validated by applying the learned policy to ankle orthosis, conducting a gait experiment, and comparing it with the simulation results.

Coactivation pattern in leg muscles during treadmill walking in patients suffering from intermittent claudication

BACKGROUND

In patients with peripheral arterial disease and presenting intermittent claudication (PAD-IC), the pain due to ischemia impacts gait parameters, particularly in cases of unilateral disease. Deterioration of gait parameters in a pathological context is frequently associated with increased coactivation (simultaneous activation of agonist and antagonist muscles around a joint).

RESEARCH QUESTION

Does unilateral PAD-IC affect the coactivation pattern during walking? Does the coactivation pattern change with increasing pain intensity?

METHOD

We evaluated symptomatic and asymptomatic legs in 17 subjects with unilateral PAD-IC and 16 without PAD-IC (control group), during walking. Tibialis anterior (TA) and gastrocnemius medialis (GM) electromyographic activity, and peaks of vertical ground reaction force were recorded in this prospective study. We analyzed the coactivation index (CI_(GM/TA)) during three periods (pain-free, pain and maximum pain) and phases of the gait cycle. Statistical analysis was carried out using the ANOVA procedure.

RESULTS

During single support, CI_(GM/TA) increases in the symptomatic leg during the pain period (+28 %) and in the asymptomatic leg during the maximum pain period (+29 %). During second double support, CI_(GM/TA) increases in the symptomatic leg only (+49 %). In these gait phases, pain elicits differences in CI_(GM/TA) between legs (p < 0.05). Second peak force decreases in the symptomatic leg only (-9%) and is negatively correlated with CI_(GM/TA) during the three periods (r = -0.57; -0.76 and -0.78 respectively, p < 0.05). No difference is found in the control group.

SIGNIFICANCE

The appearance and development of pain in the lower limbs is associated with a higher level of CI_(GM/TA), revealing a compensatory gait pattern in PAD-IC patients. Optimal prevention, rehabilitation and re-training strategies for PAD-IC patients should take into consideration neuromuscular compensatory mechanisms between asymptomatic and symptomatic legs.

Loss of Mechanical Ankle Function Is Not Compensated by the Distal Foot Joints in Patients with Ankle Osteoarthritis

BACKGROUND

Patients with isolated ankle osteoarthritis (OA) often demonstrate disturbed ankle biomechanics during walking. Clinicians often believe that this triggers the distal foot joints to compensate these altered ankle biomechanics and that these foot joints are consequently subjected to degenerative joint diseases due to overuse.

QUESTIONS/PURPOSES

Do patients with isolated ankle OA differ from those without ankle OA in terms of (1) ankle and foot joint kinematics and (2) ankle and foot joint kinetics as measured using three-dimensional (3-D) gait analysis? (3) Do these patients demonstrate compensatory strategies in their Chopart, Lisfranc, or first metatarsophalangeal joints in terms of increased joint kinematic and kinetic outputs?

METHODS

Between 2015 and 2018, we treated 110 patients with unilateral ankle OA, and invited all of them to participate in the gait analysis laboratory. Of those, 47% (52) of patients did so, and of these, 16 patients met the inclusion criteria for this study, which were (1) diagnosis of unilateral ankle OA; (2) absence of radiographical signs of OA in the contralateral foot or lower limbs; (3) ability to walk at least 100 m without rest; and (4) being older than 18 years of age. A control group (n = 25) was recruited through intranet advertisements at the University Hospitals of Leuven. Participants were included if their age matched the age-range of the patient group and if they had no history of OA in any of the lower limb joints. Patients were slightly older (55.9 ± 11.2 years), with a slightly higher BMI (28 ± 6 kg/m2) than the control group participants (47.2 ± 4.4 years; p = 0.01 and 25 ± 3 kg/m2; p = 0.05). All participants underwent a 3-D gait analysis, during which a multisegment foot model was used to quantify the kinematic parameters (joint angles and ROM) and the kinetic parameters (rotational forces or moments), as well as power generation and absorption in the ankle, Chopart, Lisfranc, and first metatarsophalangeal joints during the stance phase of walking. Peak values were the maximum and minimum values of waveforms and the latter were time-normalized to 100% of the stance phase.

RESULTS

Regarding joint kinematics, patients demonstrated a sagittal plane ankle, Chopart, Lisfranc, and first metatarsophalangeal joint ROM of 11.4 ± 3.1°, 9.7 ± 2.7°, 8.6 ± 2.3° and 34.6 ± 8.1°, respectively, compared with 18.0 ± 2.7° (p < 0.001), 13.9 ± 3.2° (p < 0.001), 7.1 ± 2.0° (p = 0.046) and 38.1 ± 6.5° (p = 0.15), respectively, in the control group during the stance phase of walking. With regard to joint kinetics in the patient group, we found a mean decrease of 1.3 W/kg (95% CI confidence interval 1.0 to 1.6) (control group mean: 2.4 ± 0.4 W/kg, patient group mean: 1.1 ± 0.5 W/kg) and 0.8 W/kg (95% CI 0.4 to 1.0) (control group mean: 1.5 ± 0.3 W/kg, patient group mean: 0.7 ± 0.5 W/kg) of ankle (p < 0.001) and Chopart (p < 0.001) joint peak power generation. No changes in kinetic parameters (joint moment or power) were observed in any of the distal foot joints.

CONCLUSION

The findings of this study showed a decrease in ankle kinematics and kinetics of patients with isolated ankle OA during walking, whereas no change in kinematic or kinetic functions were observed in the distal foot joints, demonstrating that these do not compensate for the mechanical dysfunction of the ankle.

CLINICAL RELEVANCE

The current findings suggest that future experimental laboratory studies should look at whether tibiotalar joint fusion or total ankle replacement influence the biomechanical functioning of these distal joints.

Neuromuscular control of the ankle during pre-landing in athletes with chronic ankle instability: Insights from statistical parametric mapping and muscle co-contraction analysis

OBJECTIVE

The present study aimed to compare the neuromuscular control of the muscles around the ankle between athletes with CAI and without history of any ankle sprain (Non-CAI) by using statistic parametric mapping (SPM) and co-contraction analyses.

DESIGN

Cross-sectional study; Setting: Laboratory; Participants: 40 athletes (20 CAI, 20 Non-CAI) were pair-matched for age and gender.

MAIN OUTCOME MEASURES

Neuromuscular control was examined using surface electromyography (EMG) amplitude and muscle co-contraction 200 ms before foot-contact with the ground during a jump-landing task.

RESULTS

The EMG amplitude of tibialis anterior, peroneus longus, and gastrocnemius medialis were analyzed using statistic parametric mapping. The CAI group exhibited decreased EMG amplitude of peroneus longus during preparation for foot-contact. There were no significant co-contraction differences between groups.

CONCLUSIONS

Our findings demonstrate that SPM combined with the co-contraction provides a comprehensive EMG analysis to detect the differences of neuromuscular control between athletes with and without chronic ankle instability. Additionally, this finding indicates that CAI contributed to altered neuromuscular control during the pre-landing phase, which may contribute to re-injury mechanisms.

Walking characteristics including mild motor paralysis and slow walking speed in post-stroke patients

Walking speed is strongly influenced by the severity of motor paralysis in post-stroke patients. Nevertheless, some patients with mild motor paralysis still walk slowly. Factors associated with this difference in walking speed have not been elucidated. To confirm walking characteristics of patients with mild motor paralysis and slow walking speed, this study identified patient subgroups based on the association between the severity of motor paralysis and walking speed. Fugl-Meyer assessment synergy score (FMS) and the walking speed were measured (n = 42), and cluster analysis was performed based on the association between FMS and walking speed to identify the subgroups. FMS and walking speed were associated (ρ = 0.50); however, some patients walked slowly despite only mild motor paralysis. Cluster analysis using FMS and walking speed as the main variables classified patients into subgroups. Patients with mild motor paralysis (FMS: 18.4 ± 2.09 points) and slow walking speed (0.28 ± 0.14 m/s) exhibited poorer trunk stability, increased co-contraction of the shank muscle, and increased intramuscular coherence in walking compared to other clusters. This group was identified by their inability to fully utilize the residual potential of motor function. In walking training, intervention in instability and excessive cortical control may be effective.

Neural and non-neural related properties in the spastic wrist flexors: An optimization study

Quantifying neural and non-neural contributions to increased joint resistance in spasticity is essential for a better understanding of its pathophysiological mechanisms and evaluating different intervention strategies. However, direct measurement of spasticity-related manifestations, e.g., motoneuron and biophysical properties in humans, is extremely challenging. In this vein, we developed a forward neuromusculoskeletal model that accounts for dynamics of muscle spindles, motoneuron pools, muscle activation and musculotendon of wrist flexors and relies on the joint angle and resistant torque as the only input measurement variables. By modeling the stretch reflex pathway, neural and non-neural related properties of the spastic wrist flexors were estimated during the wrist extension test. Joint angle and resistant torque were collected from 17 persons with chronic stroke and healthy controls using NeuroFlexor, a motorized force measurement device during the passive wrist extension test. The model was optimized by tuning the passive and stretch reflex-related parameters to fit the measured torque in each participant. We found that persons with moderate and severe spasticity had significantly higher stiffness than controls. Among subgroups of stroke survivors, the increased neural component was mainly due to a lower muscle spindle rate at 50% of the motoneuron recruitment. The motoneuron pool threshold was highly correlated to the motoneuron pool gain in all subgroups. The model can describe the overall resistant behavior of the wrist joint during the test. Compared to controls, increased resistance was predominantly due to higher elasticity and neural components. We concluded that in combination with the NeuroFlexor measurement, the proposed neuromusculoskeletal model and optimization scheme served as suitable tools for investigating potential parameter changes along the stretch-reflex pathway in persons with spasticity.

Functional implications of muscle co-contraction during gait in advanced age

Older adults often exhibit high levels of lower extremity muscle co-contraction, which may be the cause or effect of age-related impairments in gait and associated falls. Normal gait requires intact executive function and thus can be slowed by challenging executive resources available to the neuromuscular system through the performance of a dual task. We therefore investigated associations between lower limb co-contraction and gait characteristics under normal and dual task conditions in healthy older adults (85.4±5.9years). We hypothesized that greater co-contraction is associated with slower gait speed during dual task conditions that stress executive and attentional abilities. Co-contraction was quantified during different phases of the gait cycle using surface electromyography (EMG) signals obtained from the anterior tibialis and lateral gastrocnemius while walking at preferred speed during normal and dual task conditions. Variables included the time difference to complete the Trail Making Test A and B (ΔTMT) and gait measures during normal or dual task walking. Higher co-contraction levels during the swing phase of both normal and dual task walking were associated with longer ΔTMT (normal: R²=0.25, p=0.02; dual task: R²=0.27, p=0.01). Co-contraction was associated with gait measures during dual task walking only; greater co-contraction levels during stride and stance were associated with slower gait speed (stride: R²=0.38, p=0.04; stance: R²=0.38, p=0.04), and greater co-contraction during stride was associated with longer stride time (R²=0.16, p=0.03). Our results suggest that relatively high lower limb co-contraction may explain some of the mobility impairments associated with the conduct of executive tasks in older adults.

Assessment of lower leg muscle force distribution during isometric ankle dorsi and plantar flexion in patients with diabetes: a preliminary study

AIM

The aim of this study was to evaluate the differences in ankle muscle strength using hand-held dynamometry and to assess difference in the isometric muscle force distribution between the people with diabetes and control participants.

METHODS

The maximal muscle strength of ankle plantarflexion, dorsiflexion, eversion, inversion, lesser toes flexors and extensors, hallux flexors, and extensors was assessed in 20 people with diabetes and 20 healthy participants using hand-held dynamometry. The maximal isometric ankle plantarflexion and dorsiflexion were imported to OpenSim software to calculate 12 individual muscle (8 plantarflexors and 4 dorsiflexors) forces acting on ankle joint.

RESULTS

A significant reduction in ankle strength for all measured actions and a significant decrease in muscle force for each of the 12 muscles during dorsi and plantar flexion were observed. Furthermore, the ratios of agonist to antagonist muscle force for 6 of the muscles were significantly different between the control group and the group with diabetes.

CONCLUSIONS

It is likely that the muscles for which the agonist/antagonist muscle force ratio was significantly different for the healthy people and the people with diabetes could be more affected by diabetes.