Ankle Angular Velocity Research Articles

How boots affect the kinematics and kinetics of lower limb joints during walking compared to casual footwear

Boots are widely used by many people for various purposes, but their impact on gait biomechanics and injury risk is not well understood. This study investigated the effects of boots on walking biomechanics, compared to casual footwear. The lower limb joint kinematics and kinetics of 20 healthy male participants aged 20 to 30 years old were compared during self-paced walking with boots and shoes. The results showed that walking with boots is associated with greater hip extensor (P = 0.009) and ankle dorsiflexor (P < 0.001) moments in early stance, hip power generation (P < 0.001) and knee power absorption (P < 0.001) in early swing phase, hip abductor (P < 0.001) and knee adduction (P < 0.001) moments in the entire stance, net concentric work for the hip joint in sagittal (13.9%, P = 0.001) and frontal (21.7%, P = 0.002) planes. In contrast, the subtalar supinator moment in the entire stance (P < 0.001), ankle angular velocity in late stance (P < 0.001), and net concentric (− 42.7%, P < 0.001) and eccentric (− 44.6%, P = 0.004) works of subtalar joint were significantly lower in the boot condition. The compensatory adjustments in the hip and knee joints may result from ankle restrictions. While boots may aid those with ankle disorders, lower limb loading and the risk of musculoskeletal injuries and osteoarthritis could be increased. This study offers new perspectives on the biomechanical impact of boots on gait, potential prevention and treatment strategies of related injuries, and advancing footwear design.

A novel biomechanical indicator for impaired ankle dorsiflexion function during walking in individuals with chronic stroke

BackgroundAnkle dorsiflexion function during swing phase contributes to foot clearance and plays an important role in walking ability post-stroke. Commonly used biomechanical measures such as foot clearance and ankle joint excursion have limited ability to accurately evaluate impaired dorsiflexor function. Research questionCan ankle angular velocity and acceleration be used as reliable measurers of dorsiflexion function in post-stroke gait? MethodsUsing linear regression and Pearson’s correlation we retrospectively compared peak ankle angular velocity (AωP), peak ankle angular acceleration (AαP), peak dorsiflexion angle (DFAP) and peak foot clearance (FCLP) as direct measures for swing phase dorsiflexor function in 60 chronic stroke survivors. Intraclass correlation coefficient (ICC) analysis was used for test-retest reliability of AωP and AαP. ResultsLinear regression models revealed that AωP, AαP, DFAP, FCLP had a significant relationship (p < 0.05) with impaired dorsiflexion function. AαP and DFAP accounted for the most variance of dorsiflexion function. AωP, AαP, FCLP, correlated significantly with all clinical outcome measures of walking ability. DFAP had a positive correlation only with FMA-LE. Post-hoc William’s t-tests, used to compare the magnitude of difference between two non-independent correlations, revealed that the correlation between all clinical measures and DFAP were significantly weaker than with AωP and AαP. Correlation between FMA-LE and FCLP was weaker than with AωP and AαP. Excellent test-retest reliability for both AωP (ICC = 0.968) and AαP (ICC = 0.947) was observed. SignificanceThese results suggest that DFAP may only be associated with dorsiflexion function during non-task specific isolated movements, but not during walking. FCLP is associated with dorsiflexion function and walking ability measures but not as strongly as AωP and AαP possibly because FCLP is influenced by contribution from hip and knee joint movements. Therefore, AωP and AαP are reliable measures and represent dorsiflexion function more accurately than DFAP, and FCLP.

Acute Neuromuscular Alterations of Ankle Evertors Induced by Short Trail Running: Sex-Related Considerations.

Abstract Ravier, G, Dury, J, Grevillot, J, Girard, B, Bouzigon, R, and Michel, F. Acute neuromuscular alterations of ankle evertors induced by short trail running: sex-related considerations. J Strength Cond Res 37(10): 2008–2015, 2023—This study investigated the exercise-induced effects on the neuromuscular function of ankle evertors, balance control associated with trail running, and sex-related interactions. Fourteen male and 14 female medium-level runners completed a 16-km (400 D+) course. At rest and immediately after running, maximal voluntary isometric contraction (MVC) and rate of force development (RFD) for knee extension and ankle eversion, electromyographic (EMG) activity of peroneus muscles during MVC plateau (EMG) and the first 200 ms (EMG200), ankle angular velocity ( INV) during 20 weight-bearing inversion movements, and balance control during destabilizing single-leg task were evaluated. Repeated measures ANOVA-revealed changes in knee and ankle MVC (ankle: P = 0.0004, −12%) and RFD (ankle: P &lt; 0.0001, −19%), EMG (P &lt; 0.0001, −17%), EMG200 (P &lt; 0.0001, −19%), and ankle INV (P &lt; 0.0001, +35%) in response to trail running. Single-leg balance was not impaired. Sex-related differences were observed in EMG and EMG200 with higher values in men than in women. MVC and RFD were greater in men when expressed in absolute values, but not different relative to body mass. Single-leg balance and ankle INV did not differ between men and women. Finally, none of these variables showed any sex-related difference when considering pre-exercise to postexercise changes. This study demonstrated impairment in neuromuscular function of evertor muscles and ability in braking inversion in response to trail running. Sex-related differences were observed in neuromuscular activity but not in fatigability. These data suggest that coaches might implement strength exercises specifically designed for ankle lateral stability into their training program.

드롭 랜딩 시 팔의 위치에 따른 발레 무용수들의 하지분절 충격흡수 전략 차이

Purpose: The purpose of this study is to investigate the difference rthough analysis of kinematic and kinetics variables to determine how ballet dancers absorb the impact on the human body during drop landing to minimize injury.BR Method: Twelve female ballerinas in their twenties (age: 21.83±1.85 years, height: 161.82±4.86㎝, weight: 51.47±6.55㎏, experience: 9.67±2.77 years old) who were familiar with jumping and landing movements were studied. To analyze the motion of the lower extremity for the drop landing motion, a 3D motion analysis was performed using 18 infrared cameras (Qualasiys7+, SWE), and the ground reaction force was obtained using a ground reaction force measuring device (Kistler 9287BA).BR Results: The results of this study are as follows. 1) There was a stisatically significant difference in the maximum and minimum angles of the hip joint during single-leg rdop landing according to the position of the arm (p＜.05). 2) There was a statistically significant difference in the range of motion of the hip joint during single-leg drop landing according to the position of th earm (p＜.05). 3) There was a statistically significant difference in ankle angular velocity during single-leg drop landing according to the position of the arm (p＜.05). 4) There was no statistically significant difference in the amount of change in the moment of the lower extremity joint during single-leg drop landing according to the position of the arm (p＞.05). 5) There was no statistically significant difference in the maximum ground reaction force value during singleleg drop landing according to the position of the arm (p＞.05).BR Conclusion: Therefore, as a result of this study, there was no differenc ein both feet during one drop landing depending on the position of the arm, and it seems that the ballet dancer makes a stable landing by increasing the flexion movement of the hip joint.

Faster triceps surae muscle cyclic contractions alter muscle activity and whole body metabolic rate.

Hundred years ago, Fenn demonstrated that when a muscle shortens faster, its energy liberation increases. Fenn's results were the first of many that led to the general understanding that isometric muscle contractions are energetically cheaper than concentric contractions. However, this evidence is still primarily based on single fiber or isolated (ex vivo) muscle studies and it remains unknown whether this translates to whole body metabolic rate. In this study, we specifically changed the contraction velocity of the ankle plantar flexors and quantified the effects on triceps surae muscle activity and whole body metabolic rate during cyclic plantar flexion (PF) contractions. Fifteen participants performed submaximal ankle plantar flexions (∼1/3 s activation and ∼2/3 s relaxation) on a dynamometer at three different ankle angular velocities: isometric (10° PF), isokinetic at 30°/s (5-15° PF), and isokinetic at 60°/s (0-20° PF) while target torque (25% MVC) and cycle frequency were kept constant. In addition, to directly determine the effect of ankle angular velocity on muscle kinematics we collected gastrocnemius medialis muscle fascicle ultrasound data. As expected, increasing ankle angular velocity increased gastrocnemius medialis muscle fascicle contraction velocity and positive mechanical work (P < 0.01), increased mean and peak triceps surae muscle activity (P < 0.01), and considerably increased net whole body metabolic rate (P < 0.01). Interestingly, the increase in triceps surae muscle activity with fast ankle angular velocities was most pronounced in the gastrocnemius lateralis (P < 0.05). Overall, our results support the original findings from Fenn in 1923 and we demonstrated that greater triceps surae muscle contraction velocities translate to increased whole body metabolic rate.NEW & NOTEWORTHY Single muscle fiber studies or research on isolated (ex vivo) muscles demonstrated that faster concentric muscle contractions yield increased energy consumption. Here we translated this knowledge to muscle activation and whole body metabolic rate. Increasing ankle angular velocity increased triceps surae contraction velocity and mechanical work, increasing triceps surae muscle activity and substantially elevating whole body metabolic rate. Additionally, we demonstrated that triceps surae muscle activation strategy depends on the mechanical demands of the task.

Gait-related Factors That Explain Power Production In Patients Before And After Total Ankle Arthroplasty

Total ankle arthroplasty (TAA) reduces pain and improves joint function, including power production at the ankle. Patients can ambulate at higher velocities and generate greater joint power after TAA. To date, little is known about which factors – angular velocity (AV), ground reaction force (GRF), or range of motion (ROM) – most influence power production before and after TAA. Identifying the factors that affect power production and their relative contribution can provide rehabilitation targets. PURPOSE: To examine the role of ankle kinematics and kinetics in generating power in the last third of the stance phase and to evaluate which factors play the most important role in generating increased power after surgery. It is hypothesized that reduction in pain will primarily increase GRF and AV to a greater degree than ankle ROM. METHODS: Two hundred and eighteen patients (101 male and 117 female; age = 63.1 + 9.4) with requiring TAA were studied using a motion analysis system and force plates before and after TAA. Peak ankle power and associated vertical GRF (vGRF), center of pressure (COP) position, ankle angle, moment and AV were compared before and after surgery using Wilcoxon signed rank tests. Predictive models for pre and post surgical power generation were created using AIC multiple stepwise regression. RESULTS: Following TAA, ankle plantarflexion power increased on both the surgical and nonsurgical limbs (0.83 to 1.1, p < 0.001; 0.97 to 1.4, p < 0.001 respectively). To increase power, patients increased surgical and non-surgical side vGRF (0.51 to 0.58, p < 0.001; 0.51 to 0.57, p = 0.002 respectively) and AR (1.1 to 1.7, p < 0.001; 1.1 to 1.8, p < 0.001 respectively). Ankle ROM did not change significantly on either limb following surgery. Ankle AV and vGRF are the best predictors of peak plantar flexion power across all models, with AV being the strongest single predictor. CONCLUSIONS: TAA improves power production at the ankle by allowing patients to generate a greater force at a higher rate. Increased power production relates to faster and more efficient gait, relieving other joints of the need to generate compensatory power. Pre and post-TAA treatment strategies should focus on helping patients increase vGRF and plantarflexion angular velocity during terminal stance to improve physical functional before and after TAA.

Inertia Sensors for Measuring Spasticity of the Ankle Plantarflexors Using the Modified Tardieu Scale-A Proof of Concept Study.

Ankle spasticity is clinically assessed using goniometry to measure the angle of muscle reaction during the Modified Tardieu Scale (MTS). The precision of the goniometric method is questionable as the measured angle may not represent when the spastic muscle reaction occurred. This work proposes a method to accurately determine the angle of muscle reaction during the MTS assessment by measuring the maximum angular velocity and the corresponding ankle joint angle, using two affordable inertial sensors. Initially we identified the association between muscle onset and peak joint angular velocity using surface electromyography and an inertial sensor. The maximum foot angular velocity occurred 0.049 and 0.032 s following the spastic muscle reaction for Gastrocnemius and Soleus, respectively. Next, we explored the use of two affordable inertial sensors to identify the angle of muscle reaction using the peak ankle angular velocity. The angle of muscle reaction and the maximum dorsiflexion angle were significantly different for both Gastrocnemius and Soleus MTS tests (p = 0.028 and p = 0.009, respectively), indicating that the system is able to accurately detect a spastic muscle response before the end of the movement. This work successfully demonstrates how wearable technology can be used in a clinical setting to identify the onset of muscle spasticity and proposes a more accurate method that clinicians can use to measure the angle of muscle reaction during the MTS assessment. Furthermore, the proposed method may provide an opportunity to monitor the degree of spasticity where the direct help of experienced therapists is inaccessible, e.g., in rural or remote areas.

Soft robotic exosuit augmented high intensity gait training on stroke survivors: a pilot study

BackgroundStroke is a leading cause of serious gait impairments and restoring walking ability is a major goal of physical therapy interventions. Soft robotic exosuits are portable, lightweight, and unobtrusive assistive devices designed to improve the mobility of post-stroke individuals through facilitation of more natural paretic limb function during walking training. However, it is unknown whether long-term gait training using soft robotic exosuits will clinically impact gait function and quality of movement post-stroke.ObjectiveThe objective of this pilot study was to examine the therapeutic effects of soft robotic exosuit-augmented gait training on clinical and biomechanical gait outcomes in chronic post-stroke individuals.MethodsFive post-stroke individuals received high intensity gait training augmented with a soft robotic exosuit, delivered in 18 sessions over 6–8 weeks. Performance based clinical outcomes and biomechanical gait quality parameters were measured at baseline, midpoint, and completion.ResultsClinically meaningful improvements were observed in walking speed (p < 0.05) and endurance (p < 0.01) together with other traditional gait related outcomes. The gait quality measures including hip (p < 0.01) and knee (p < 0.05) flexion/extension exhibited an increase in range of motion in a symmetric manner (p < 0.05). We also observed an increase in bilateral ankle angular velocities (p < 0.05), suggesting biomechanical improvements in walking function.ConclusionsThe results in this study offer preliminary evidence that a soft robotic exosuit can be a useful tool to augment high intensity gait training in a clinical setting. This study justifies more expanded research on soft exosuit technology with a larger post-stroke population for more reliable generalization.Trial registration This study is registered with ClinicalTrials.gov (ID: NCT04251091)

Plantar flexor muscles of kangaroo rats (Dipodomys deserti) shorten at a velocity to produce optimal power during jumping.

The musculotendon work contributions across all joints during jumping by kangaroo rats are not well understood. Namely, measures of external joint work do not provide information on the contributions from individual muscles or in-series elastic structures. In this study, we examined the functional roles of a major ankle extensor muscle, the lateral gastrocnemius (LG), and a major knee extensor muscle, the vastus lateralis (VL), through in vivo sonomicrometry and electromyography techniques, during vertical jumping by kangaroo rats. Our data showed that both muscles increased shortening and activity with higher jumps. We found that knee angular velocity and VL muscle shortening velocity were coupled in time. In contrast, the ankle angular velocity and LG muscle shortening velocity were decoupled, and rapid joint extension near the end of the jump produced high power outputs at the ankle joint. Further, the decoupling of muscle and joint kinematics allowed the LG muscle to prolong the period of shortening velocity near optimal velocity, which likely enabled the muscle to sustain maximal power generation. These observations were consistent with an LG tendon that is much more compliant than that of the VL.

Effect of Kinesio Taping on Ankle Joint Kinematics During Landing on Stable and Unstable Surfaces in Ankle Sprain and Health Persons

Background and Aims: Landing is a typical sports motion that can create impact force 2-12 times of body weight, and finally, it’s one of the main reasons for non-contact injuries in ankle ligaments. Specialized. The usual effects of Kinesio tape include increasing proprioception, health direction of joints, reducing pain, and raising pressure on nervous tissue. The study aimed to investigate the effect of Kinesio taping on ankle joint kinematics during landing on stiff and soft surfaces in ankle sprain and healthy persons. Methods: The method of the present study was quasi-experimental with a two-group design in control groups (without ankle sprain) and experimental (with an ankle sprain). A total of 30 male students of the Shahid Bahonar University of Kerman were purposefully and accessibly selected and divided into two groups with (15 students) and without ankle sprains (15 students). Then, they performed both landing operations on stable and unstable surfaces, with and without Kinesio tape. Maximum dorsi and plantar flexion, supination, pronation and maximum ankle angular velocity parameters were recorded by a three-dimensional motion analysis system. Statistical analysis was performed using independent t-test and repeated measures analysis of variance at the significant level of 0.05. Results: There was no significant reduction in plantar flexion of the ankle in healthy and twisted individuals while landing on stable and unstable surfaces with and without Kinesio tape (P≤0.07), but there was a significant reduction in the dorsiflexion in both groups(P≤0.001). On the other hand, there was no significant decrease in pronation (P≤0.66), but there was a significant decrease in foot supination (P≤0.001). Conclusion: Generally, Kinesio tape in recovery ankle movement is offered to persons for ankle sprain. Thus recommendation landing exercises fare with more flexion angle and less knee joint valgus and more dorsiflexion angle at ankle joint and preferable on the unstable surfaces.

MO614A PRACTICAL SOLUTION TO SCREEN COGNITIVE FRAILTY AMONG HEMODIALYSIS PATIENTS USING A GAME-BASED INTRADIALYTIC EXERCISE WITH WEARABLE SENSORS

Abstract Background and Aims Assessing and monitoring cognitive frailty (CF; coexistence of physical frailty and cognitive impairment) are critical for hemodialysis patients. For administering physical frailty and cognitive assessments, however, clinical settings need to address challenges (e.g., cost, human and technical resources, patient’s fatigue, etc.). This study aims to investigate the feasibility and accuracy of a novel intradialytic cognitive-demanding exercise program based on wearables, called, intradialytic-exergame for screening CF in hemodialysis patients. Method Individuals diagnosed with diabetes and end-stage renal disease requiring hemodialysis (n=28, age: 61.36 ± 6.85 years, 54% female) participated. All participants were assessed for physical frailty using the Fried frailty phenotype method and cognitive impairment using the Mini-Mental State Examination (MMSE). The Fried frailty phenotype method assesses physical frailty, which ranges between 0 and 5 based on five criteria (unintentional weight loss, weakness, slowness, exhaustion, and low physical activity). CF was determined with a frailty phenotype greater than or equal to 1 and a MMSE score less than or equal to 24. The intradialytic-exergame system consists of an inertial wearable sensor and an interactive software installed on a standard laptop. A clinician attaches one wearable sensor to each foot after the participant sits or lies down on a bed (Figure A). While undergoing hemodialysis treatment, the participant performs 15 non-weight-bearing cognitively-demanding dorsiflexion and plantarflexion exercises for each foot. For each exercise, the laptop’s screen displays a target (solid yellow circle) and a cursor (solid red square), which the participant points down for a dorsiflexion motion or up for a plantarflexion motion (Figure B). When the participant successfully puts the cursor in the target, the target disappears, and a new target appears in a different location on the screen (dashed yellow circle shown in Figure B). If the participant moves the cursor to a target in less than 2s, the custom software provides both visual (the target explodes) and auditory (positive sound) feedback as a reward (success). The three outcome measures (Exergame-slowness, frailty, and cognitive performance) were analyzed. Exergame-slowness was computed as an average of the ranges of ankle angular velocity measured by wearable sensors. Linear regression analysis was conducted for the three outcome measures to examine correlations between each outcome measure. Binary logistic regression model was conducted, and its area-under-curve (AUC) was calculated to determine the ability of Exergame-slowness to identify CF. An independent t-test was conducted to compare the differences of Exergame-slowness for CF and non-CF conditions. Significance was defined at the 2-sided p &amp;lt; 0.05 level. Results Five out of 28 participants were identified with CF. Significant correlations were observed between Exergame-slowness and frailty (p = 0.004, R = -0.531), Exergame-slowness and cognitive performance (p = 0.023, R = 0.437), and frailty and cognitive performance (p = 0.015, R = -0.463). The model was significantly reliable (p = 0.012) and its AUC was 0.90. Results indicated that Exergame-slowness was significantly higher (lower velocity) for participants with CF than for those with non-CF (CF: 27.41 ± 3.58 degree/s, non-CF: 34.25 ± 5.24 degree/s, p = 0.010). Conclusion To our knowledge, this is the first study to investigate the feasibility and accuracy of intradialytic-exergame with wearable sensors, as a practical tool for routine screening CF assessment in hemodialysis patients. The results of this study indicate that speed of ankle rotation, measurable using a wearable sensor during a simple intradialytic cognitive-demanding exercise, can be used as a practical digital biomarker for screening CF in hemodialysis patients.

Modified Ankle Joint Neuromechanics during One-Legged Heel Raise Test after an Achilles Rupture and Its Associations with Jumping

This study had two purposes. The first purpose of the study was to compare the electromyographic(EMG) and dynamic characteristics in injured and non-injured legs during the one-legged heel-raise test after a unilateral Achilles repair. The second purpose was to determine the correlations between the EMG results and the dynamic characteristics and between the characteristics in the eccentric phase and jumping distance. Twenty-six participants who underwent an Achilles repair between 4 and 12 months prior to the measurement were recruited to perform the following bilateral tests: (1) one-legged heel-raise test with measurements of muscle activation, kinematics, and kinetics and (2) one-legged forward jumping. During the heel-raise exercise, there were increases of the EMG amplitudes in the soleus and tibialis anterior muscles, lower ankle joint angle and angular velocity, lower normalized ground reaction force, and mechanical work in the repaired legs in comparison to the non-injured legs. The EMG results of the medial gastrocnemius and soleus muscles correlated with the dynamic results (rs = 0.467 and −0.537). Furthermore, the dynamic data in the eccentric phase were correlated with the jumping performance (rs = 0.575 and −0.471). It is concluded the soleus muscle undergoes neuromechanical changes, including changes in EMG and dynamic characteristics, and changes affecting jumping performance.

The efficiency of mirror therapy on drop foot in Multiple Sclerosis Patients.

Although the effectiveness of mirror therapy (MT) has been proved in stroke persons, there is no scientific evidence about the results in people with multiple sclerosis. The aim was to investigate whether adding MT to exercise training and neuromuscular electrical stimulation (NMES) has any effect on clinical measurements, mobility, and functionality in people with multiple sclerosis (MS). Ambulatory people with MS, with unilateral drop foot, were included. MT group (n=13) applied bilateral ankle exercise program with mirror following NMES for 3days a week at hospital and exercise program for 2days a week at home. Control group (n=13) performed same treatment without mirror box (6weeks). The later 6weeks both groups performed only exercise program. Clinical measurements included proprioception, muscle tone of plantar flexor muscles (MAS), muscle strength of dorsiflexor, ankle angular velocity, and range of motion (ROM) of ankle. Functionality (Functional Independence Measurement-FIM), mobility (Rivermead Mobility Index-RMI), ambulation (Functional Ambulation Scale-FAS), duration of stair climb test, and 25-foot walking velocity were assessed at the beginning, in 6th and 12th weeks. More positive improvements were obtained in MT group than control group in terms of range of motion (0.012), muscle strength (0.008), proprioception (0.001), 25 feet walking duration (0.015), step test duration (0.001), FAS (0.005), RMI (0.001), and FIM (0.001) after 6weeks treatment. It was seen that this improvement maintained to 12th week on all clinical and functional measurements (p<.05). The trial revealed that adding MT to exercise training and NMES has more beneficial effects on clinical measurements, mobility, and functionality in people with multiple sclerosis with unilateral drop foot.

Ankle-knee coupling responses to ankle Kinesio™ taping during single-leg drop landings in collegiate athletes with chronic ankle instability.

Ankle Kinesio-taping (KT) is being globally used an intervention to provide the ankle joint complex with sufficient support against sudden excessive mechanical stress during various activities. However, its effects on proximal joints are unclear. This study investigated the impact of ankle KT on ankle-knee joint coupling in sagittal, frontal and transverse planes. Adopting a pretest post-test study design, 30 collegiate athletes with chronic ankle instability performed 3 single-leg drop landings in each non-taped and Kinesio-taped conditions and their movement kinematics were recorded using 6 optoelectronic cameras. The ankle angular velocities in sagittal (P=0.038, d=0.64) and transverse planes (P=0.001, d=0.95) decreased after KT application, while the knee internal rotation velocities increased (P=0.020, d=0.51). The coupling angles revealed that the ankle movement ratios significantly decreased in 3 planes in comparison with knee movement ratios. Outcomes of this study illustrated that application of ankle KT leaves the individuals with a stiffer ankle joint, which increases the mechanical stresses to this joint and decreases its stiffness in absorbing the applied shocks. Further, ankle KT application resulted in more knee internal rotation moments and may increase the risk of knee injuries during landing after a long-term usage in patients with instability ankle sprain.

Closing the Loop on Exoskeleton Motor Controllers: Benefits of Regression-Based Open-Loop Control.

Lower-limb exoskeletons are widely researched to improve walking performance and mobility. Low-level sensor-less exoskeleton motor control is attractive for consumer applications due to reduced device complexity and cost, but complex and variable transmission system configurations make the development of effective open-loop motor controllers that are responsive to user input challenging. The objective of this study was to develop and validate an open-loop motor control framework resulting in similar or greater performance vs. closed-loop torque control. We used generalized linear regression to develop two open-loop controllers by modeling motor current during exoskeleton-assisted walking; a "complex" model used desired torque and estimated ankle angular velocity as inputs, while a "simple" model used desired torque alone. Five participants walked at 1.0-1.3 m/s on a treadmill with closed-loop and both open-loop controllers providing ankle exoskeleton assistance. Both open-loop current controllers had similar root-mean-squared torque tracking error (p=0.23) compared to the closed-loop torque-feedback controller. Both open-loop controllers had improved relative average torque production (p<0.001 complex, p=0.022 simple), lower power consumption (p<0.001 for both), and reduced operating noise (p=0.002 complex, p<0.001 simple) over the closed-loop controller. New control models developed for a different ankle exoskeleton configuration showed similar improvements (lower torque error, greater average and peak torque production, lower power consumption) over closed-loop control during over-ground walking. These results demonstrate that our framework can produce open-loop motor controllers that match closed-loop control performance during exoskeleton operation.

Aquatic and terrestrial takeoffs require different hindlimb kinematics and muscle function in mallard ducks.

Mallard ducks are capable of performing a wide range of behaviors including nearly vertical takeoffs from both terrestrial and aquatic habitats. The hindlimb plays a key role during takeoffs from both media. However, because force generation differs in water versus on land, hindlimb kinematics and muscle function are likely modulated between these environments. Specifically, we hypothesize that hindlimb joint motion and muscle shortening are faster during aquatic takeoffs, but greater hindlimb muscle forces are generated during terrestrial takeoffs. In this study, we examined the hindlimb kinematics and in vivo contractile function of the lateral gastrocnemius (LG), a major ankle extensor and knee flexor, during takeoffs from water versus land in mallard ducks. In contrast to our hypothesis, we observed no change in ankle angular velocity between media. However, the hip and metatarsophalangeal joints underwent large excursions during terrestrial takeoffs but exhibited almost no motion during aquatic takeoffs. The knee extended during terrestrial takeoffs but flexed during aquatic takeoffs. Correspondingly, LG fascicle shortening strain, shortening velocity and pennation angle change were greater during aquatic takeoffs than during terrestrial takeoffs because of the differences in knee motion. Nevertheless, we observed no significant differences in LG stress or work, but did see an increase in muscle power output during aquatic takeoffs. Because differences in the physical properties of aquatic and terrestrial media require differing hindlimb kinematics and muscle function, animals such as mallards may be challenged to tune their muscle properties for movement across differing environments.

Control Reference Parameter for Stance Assistance Using a Passive Controlled Ankle Foot Orthosis—A Preliminary Study

This paper aims to present a preliminary study of control reference parameters for stance assistance among different subjects and walking speeds using a passive-controlled ankle foot orthosis. Four young male able-bodied subjects with varying body mass indexes (23.842 ± 4.827) walked in three walking speeds of 1, 3, and 5 km/h. Two control references, average ankle torque (aMa), and ankle angular velocity (aω), which can be implemented using a magnetorheological brake, were measured. Regression analysis was conducted to identify suitable control references in the three different phases of the stance. The results showed that aω has greater correlation (p) with body mass index and walking speed compared to aMa in the whole stance phase (p1(aω) = 0.666 &gt; p1(aMa) = 0.560, p2(aω) = 0.837 &gt; p2(aMa) = 0.277, and p3(aω) = 0.839 &gt; p3(aMa) = 0.369). The estimation standard error (Se) of the aMa was found to be generally higher than of aω (Se1(aMa) = 2.251 &gt; Se1(aω) = 0.786, Se2(aMa) = 1.236 &gt; Se2(aω) = 0.231, Se3(aMa) = 0.696 &lt; Se3(aω) = 0.755). Future studies should perform aω estimation based on body mass index and walking speed, as suggested by the higher correlation and lower standard error as compared to aMa. The number of subjects and walking speed scenarios should also be increased to reduce the standard error of control reference parameters estimation.

Ankle power biofeedback attenuates the distal-to-proximal redistribution in older adults

BackgroundCompared to young adults, older adults walk slower, with shorter strides, and with a characteristic decrease in ankle power output. Seemingly in response, older adults rely more than young on hip power output, a phenomenon known as a distal-to-proximal redistribution. Nevertheless, older adults can increase ankle power to walk faster or uphill, revealing a translationally important gap in our understanding. Research questionOur purpose was to implement a novel ankle power biofeedback paradigm to encourage favorable biomechanical adaptations (i.e. reverse the distal-redistribution) during habitual speed walking in older adults. Methods10 healthy older adults walked at their preferred speeds while real-time visual biofeedback provided target increases and decreases of 10 and 20% different from preferred ankle power. We evaluated the effect of changes in ankle power on joint kinetics, kinematics, and propulsive ground reaction forces. Pre and post overground walking speed assessments evaluated the effect of increased ankle power recall on walking speed. ResultsBiofeedback systematically elicited changes in ankle power; increasing and decreasing ankle power by 14% and 17% when targeting ±20% different from preferred, respectively. We observed a significant negative correlation between ankle power and hip extensor work. Older adults relied more heavily on changes in ankle angular velocity than ankle moment to modulate ankle power. Lastly, older adults walked almost 11% faster when recalling increased ankle power overground. SignificanceOlder adults are capable of increasing ankle power through targeted ankle power biofeedback – effects that are accompanied by diminished hip power output and attenuation of the distal-to-proximal redistribution. The associated increase in preferred walking speed during recall suggests a functional benefit to increased ankle power output via transfer to overground walking. Further, our mechanistic insights allude to translational success using ankle angular velocity as a surrogate to modulate ankle power through biofeedback.

On the measurement of ski boot viscoelasticity

ObjectivesSince the polymeric materials commonly used for ski boots feature viscoelastic properties, the results of ski boot flexion tests are expected to be influenced by flexion velocity. Devices testing at all skiing specific ankle angular velocities are currently not available. Therefore, the aims of this study were to (i) develop a system allowing the testing of ski boots at high ankle angular velocities, (ii) quantify the effect of ankle angular velocity on viscoelasticity and (iii) determine the repeatability of the system. Design and MethodA test bench and a lower limb prosthesis were developed to determine tibia angle and applied torque. To assess the effect of angular velocity, two pairs of ski boots were tested at 5°/s, 50°/s, 75°/s and 100°/s. To assess stiffness variation and measurement repeatability, ten different used ski boots of different manufacturers were tested twice. ResultsFour ski boot flexion stiffness parameters and two energy dissipation factors were reported. The repeatability of the stiffness and the energy dissipation parameters was better than 4% and 3%, respectively. Stiffnesses and dissipation factors increased with increasing angular velocity. ConclusionIn the present study a reliable system facilitating the testing of ski boots at velocities of up to 100°/s was developed. To comprehensively characterise the viscoelastic properties of ski boots, we propose to report four ski boot stiffness parameters and two energy dissipation factors. An ankle angular velocity above 50°/s was recommended to perform mechanical tests of ski boots if employed in slalom-like skiing.

The Relationship Between Medial Gastrocnemius Lengthening Properties and Stretch Reflexes in Cerebral Palsy.

Stretch reflex hyperactivity in the gastrocnemius of children with spastic cerebral palsy (CP) is commonly evaluated by passively rotating the ankle joint into dorsiflexion at different velocities, such as applied in conventional clinical spasticity assessments. However, surface electromyography (sEMG) collected from the medial gastrocnemius (MG) during such examination reveals unexplained heterogeneity in muscle activation between patients. Recent literature also highlights altered muscle tensile behavior in children with spastic CP. We aimed to document MG muscle and tendon lengthening during passive ankle motion at slow and fast velocity and explore its interdependence with the elicited hyperactive stretch reflex. The ankle of 15 children with CP (11 ± 3 years, GMFCS 9I 6II, 8 bilateral, 7 unilateral) and 16 typically developing children (TDC) was passively rotated over its full range of motion at slow and fast velocity. Ultrasound, synchronized with motion-analysis, was used to track the movement of the MG muscle-tendon junction and extract the relative lengthening of muscle and tendon during joint rotation. Simultaneously, MG sEMG was measured. Outcome parameters included the angular and muscle lengthening velocities 30 ms before EMG onset and the gain in root mean square EMG during stretch, as a measure of stretch reflex activity. Compared to slow rotation, the muscle lengthened less and stretch reflex activity was higher during fast rotation. These velocity-induced changes were more marked in CP compared to TDC. In the CP group, muscle-lengthening velocity had higher correlation coefficients with stretch reflex hyperactivity than joint angular velocity. Muscles with greater relative muscle lengthening during slow rotation had earlier and stronger stretch reflexes during fast rotation. These initial results suggest that ankle angular velocity is not representative of MG muscle lengthening velocity and is less related to stretch reflex hyperactivity than MG muscle lengthening. In addition, muscles that lengthened more during slow joint rotation were more likely to show a velocity-dependent stretch reflex. This interdependence of muscle lengthening and stretch reflexes may be important to consider when administering treatment. However, muscle and tendon lengthening properties alone could not fully explain the variability in stretch reflexes, indicating that other factors should also be investigated.