Propulsive Work Research Articles

Propulsive fractions of joint work during maximal sprint running

PurposeThe purpose of the study was to determine which of the ankle, knee or hip joint is the most important contributor to horizontal velocity during maximal sprint running. Furthermore, it was undertaken to quantify the fraction of propulsive power and work produced at each of the three joints.MethodsSeven athletes of national class served as subjects for the study. One running cycle of each subject was recorded by four video cameras (240 f/s) and a recessed force platform. Inverse dynamics in 3D was calculated as well as an angle between joint moment and angular velocity to express propulsive power and propulsive joint work.ResultsPrevious studies indicating the hip joint being the most important joint could not be confirmed by the present results due to large inter-individual differences for the hip joint. Averaged across all subjects, 64% of the normalized positive ankle joint work and 71% of the knee joint work were propulsive, while for the hip joint, four athletes showed 0%, one athlete 8%, and two athletes 96% and 97% propulsive work, respectively. For the whole leg, the propulsive fraction was 70% of the total positive work (range 40–87%). Normalized propulsive work was significantly correlated with maximal running velocity.ConclusionThe whole leg should be considered as one functional unit in which one or more of the joints may dominate generation of propulsive joint work.

The effect of existing and novel walker boot designs on offloading and gait mechanics.

Orthopedic walker boots are often used to treat foot ulcers and other wounds with the goal of offloading plantar pressure. However, poor ulcer healing outcomes and high recurrence rates show a need for additional solutions in the growing diabetes epidemic. We compared a novel spring-loaded walker boot to a traditional rigid ankle boot and a hinged ankle boot as well as a control shoe. Our aim was to better understand how boot design affects offloading mechanisms. We hypothesized that all boots would offload force from the foot to the shank, but that the hinged boot would have fewer gait alterations and the spring boot would further reduce pressure in early and late stance. Ten healthy participants tested each of the four conditions in static stance and walking gait. Offloading was quantified by the difference between pressure insole and platform forces, while joint mechanics changes were calculated from instrumented gait analysis and inverse dynamics. Minimal offloading was found in the rigid and hinged boots compared to athletic shoes. In contrast, the spring boot offloaded nearly 50% of total load in static stance, with similarly large reductions in peak pressures during gait, particularly under the hindfoot during early stance. All boots resulted in some ankle joint mechanics compensations, with the rigid and spring boots showing similar restrictions in ankle motion and propulsive work. While the hinged boot resulted in ankle mechanics more like the shoe condition, it increased dorsiflexion and negative work, suggesting energetic inefficiency. The novel spring boot shows promise for more effective offloading that could lead to improved healing outcomes.

Comparison of Existing Methods for Characterizing Bi-Linear Natural Ankle Quasi-Stiffness.

Natural ankle quasi-stiffness (NAS) is a mechanical property of the ankle joint during dynamic motion. NAS has been historically calculated as the average slope (linear regression) of the net ankle moment versus ankle angle during discrete phases of stance. However, recent work has shown that NAS is nonlinear during the stance phase. Specifically, during the loading phase of stance (∼10 to 60% of total stance), plantarflexion moment increases at an accelerating rate compared to dorsiflexion angle. Updated models have been developed to better capture this inherent nonlinearity. One type of model called bi-linear NAS (BL-NAS) divides the loading phase of stance into two subphases, called early loading (EL) and late loading (LL) NAS. Two papers, written by Crenna and Frigo (2011, "Dynamics of the Ankle Joint Analyzed Through Moment-Angle Loops During Human Walking: Gender and Age Effects," Hum. Mov. Sci., 30(6), pp. 1185-1198) and Shamaei et al. (2013, "Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking," PLoS One, 8(3), p. e59935), outline different BL-NAS models. Both models fit measured data better (lower root-mean-squared error (RMSE)) than standard single linear NAS (SL-NAS) models but have not been widely adopted, possibly because of methodological discrepancies and lack of applicability to physical devices at the time. This paper compares and contrasts these existing BL-NAS models and translates those findings to possible orthotic device designs. Results showed that both BL-NAS models had lower RMSE than SL-NAS, EL-NAS was not significantly different across walking speeds, and LL-NAS increased significantly at faster walking speeds. These improved models of NAS much better approximate natural human movement than commonly used SL-NAS models, and thus provide a basis to design ankle-foot devices with multiple stiffness properties to emulate and facilitate natural human motion.

Biomechanical Impacts of Toe Joint With Transfemoral Amputee Using a Powered Knee-Ankle Prosthesis.

Transfemoral amputees are currently forced to utilize energetically passive prostheses that provide little to no propulsive work. Among the several joints and muscles required for healthy walking, the ones most vital for push-off assistance include the knee, ankle, and metatarsophalangeal (MTP) joints. There are only a handful of powered knee-ankle prostheses (also called powered transfemoral prostheses) in literature and few of them comprise a toe-joint. However, no one has researched the impact of toe-joint stiffness on walking with a power transfemoral prosthesis. This study is aimed at filling this gap in knowledge. We conducted a study with an amputee and a powered transfemoral prosthesis consisting of a spring loaded toe-joint. The prosthesis's toe-joint stiffness was varied between three values: 0.83 Nm/deg, 1.25 Nm/deg, and infinite (rigid). This study found that 0.83 Nm/deg stiffness reduced push-off assistance and resulted in compensatory movements that could lead to issues over time. While the joint angles and moments did not considerably vary across 1.25 Nm/deg and rigid stiffness, the latter led to greater power generation on the prosthesis side. However, the 1.25 Nm/deg joint stiffness resulted in the least power production from the intact side. We, thus, concluded that the use of a stiff toe-joint with a powered transfemoral prosthesis can reduce the cost of transport of the intact limb.

388 Haemodynamic arterial changes in heart failure: a proposed new paradigm of heart and vessels failure. The Copernican revolution?

Abstract Aims Although heart failure (HF) is one of the most common conditions affecting the heart, little attention has been placed on the role of arteries in contributing to the progression of this disease. We sought to determine the haemodynamic change of arteries in HF patients subdivided according to left ventricular ejection fraction. The major goal was to establish the active compensatory role of arteries in HF. Methods and results Using sphygmography, we systematically studied a cohort of 228 HF patients and 52 healthy controls. We focused on the common carotid as the main elastic artery and the posterior tibial as the main muscular artery (Figure 1). Moreover, we categorized the three HF groups, HFrEF, HFmrEF, HFpEF, into two subgroups (A and B) according to the presence or absence of HF signs at baseline. We discovered that all the parameters of measured arterial kinetics, i.e. work, power, acceleration, and speed, were significantly increased (P < 0.001 by one-way ANOVA) in the groups without HF signs. In contrast, all the arterial kinetics parameters were significantly reduced (P < 0.001) in the groups exhibiting HF signs. Similar results were obtained in both types of arteries and were consistently observed across all the three different types of HF, although with some differences in magnitude. Finally, we discovered that HFpEF patients exhibited more compromised arterial function vis-à-vis HFrEF patients [Figure 2: Patients disposition (Top) and quantification of arterial kinetics and haemodynamic parameters (Down) from the common carotid artery (A) and the posterior tibial artery (B)]. Conclusions We provide the first documentation of an active compensatory role of arteries during HF. Mechanistically, we explain these findings by a dual activity of large arteries accomplished via an active propulsive work and a concurrent haemodynamic suction. These underestimated arterial functions partially compensate for the heart dysfunction in HF, underlining a key interplay between the heart and the vessels. We propose a new paradigm that we define as ‘heart and vessels failure’ that explicitly focuses on both heart and vessels’ interaction during the progression of HF.

Hemodynamic arterial changes in heart failure. a proposed new paradigm of heart and vessels failure. The Copernican revolution?

Abstract Background Although heart failure (HF) is one of the most common conditions affecting the heart, little attention has been placed on the role of arteries in contributing to the progression of this disease. Purpose We sought to determine the hemodynamic change of arteries in HF patients subdivided according to left ventricular ejection fraction. The major goal was to establish the active compensatory role of arteries in HF Methods Using sphygmography, we systematically studied a cohort of 228 HF patients and 52 healthy controls. We focused on the common carotid as the main elastic artery and the posterior tibial as the main muscular artery (Figure 1). Moreover, we categorized the three HF groups, HFrEF, HFmrEF, HFpEF, into two subgroups (A and B) according to the presence or absence of HF signs at baseline. Results We discovered that all the parameters of measured arterial kinetics, i.e., work, power, acceleration, and speed, were significantly increased (p<0.001 by one-way ANOVA) in the groups without HF signs. In contrast, all the arterial kinetics parameters were significantly reduced (p<0.001) in the groups exhibiting HF signs. Similar results were obtained in both types of arteries and were consistently observed across all the three different types of HF, although with some differences in magnitude. Finally, we discovered that HFpEF patients exhibited more compromised arterial function vis-à-vis HFrEF patients (Figure 2: Patients Disposition (Top) and Quantification of arterial kinetics and hemodynamic parameters (Down) from the common carotid artery [A] and the posterior tibial artery [B]). Conclusions We provide the first documentation of an active compensatory role of arteries during HF. Mechanistically, we explain these findings by a dual activity of large arteries accomplished via an active propulsive work and a concurrent hemodynamic suction. These underestimated arterial functions partially compensate for the heart dysfunction in HF, underlining a key interplay between the heart and the vessels. We propose a new paradigm that we define as “heart and vessels failure” that explicitly focuses on both heart and vessels' interaction during the progression of HF. Funding Acknowledgement Type of funding sources: None. Figure 1. Sphygmograms of CCA and PTAFigure 2. Patients disposition & Results

Hemodynamic arterial changes in heart failure: a proposed new paradigm of "heart and vessels failure".

Although heart failure (HF) is one of the most common conditions affecting the heart, little attention has been placed on the role of arteries in contributing to the progression of this disease. We sought to determine the hemodynamic change of arteries in HF patients subdivided according to left ventricular ejection fraction. The major goal was to establish the active compensatory role of arteries in HF. Using sphygmography, we systematically studied a cohort of 228 HF patients and 52 healthy controls. We focused on the common carotid as the main elastic artery and the posterior tibial as the main muscular artery. Moreover, we categorized the three HF groups, HFrEF, HFmrEF, HFpEF, into two subgroups (A and B) according to the presence or absence of HF signs at baseline. We discovered that all the parameters of measured arterial kinetics, i.e., work, power, acceleration, and speed, were significantly increased (P<0.001 by one-way ANOVA) in the groups without HF signs. In contrast, all the arterial kinetics parameters were significantly reduced (P<0.001) in the groups exhibiting HF signs. Similar results were obtained in both types of arteries and were consistently observed across all the three different types of HF, although with some differences in magnitude. Finally, we discovered that HFpEF patients exhibited more compromised arterial function vis-à-vis HFrEF patients. We provide the first documentation of an active compensatory role of arteries during HF. Mechanistically, we explain these findings by a dual activity of large arteries accomplished via an active propulsive work and a concurrent hemodynamic suction. These underestimated arterial functions partially compensate for the heart dysfunction in HF, underlining a key interplay between the heart and the vessels. We propose a new paradigm that we define as "heart and vessels failure" that explicitly focuses on both heart and vessels' interaction during the progression of HF.

Heart failure: the influence of different types on the main arteries kinetics

Abstract Funding Acknowledgements Type of funding sources: None. Nowadays the term "heart-vessels failure" does not exist. Aim To study the kinetics and hemodynamics of arteries in the patients with heart failure with different ejection fraction. Materials and methods In our investigation we included 74 patients with heart failure with preserved ejection fraction more than 55% (44 were men and 30 women). Mediana age – 71,3 years old. In the control group we included 52 practically healthy people without cardiac and vessels pathologies. We divided patients into two groups (I and II) in accordance to the presence of clinical manifestations of heart failure in them. Group I - with clinical symptoms of heart failure (32), group II –without heart failure symptoms (42). We paid attention to the symptoms of heart failure, myocardial infarction, cardiomyopathies, valves defects, operations on heart in anamnesis. We performed 24-hours ECG monitoring, general blood analysis, biochemical blood analysis (lipids, electrolytes, urine, creatinine, bilirubin, potassium, glucose, NT-proBNP), transthoracic echocardiography, ultrasound doppler of brachiocephalic arteries, abdominal aorta branches, lower extremities arteries, renal arteries, chest radiography, ultrasound investigation of B-lines. If prescribed we performed stress echocardiography, transesophageal echocardiography, coronary angiography, renal arteries angiography, pancerebral angiography, magnet tomography of heart. All patients were registered sphygmography of main arteries: a.carotis communis, ulnaris, radialis, a.tibialis posterior. We analyzed the regular contractions in each type of arteries. The main parameters main arteries kinetics using sphygmography we calculated in automatic mode: speed, acceleration, power, work in period of prevalence of inflow over outflow and in period of prevalence of outflow over inflow. Results We analysed the main parameters of arteries kinetics and hemodynamics in each group of patients as well as in control group. We observed the effects: 1)In group II the parameters of arteries kinetics were higher than in group I. It indicates the active propulsive work of arteries in spreading the stroke volume of the heart. 2)In group I the parameters of arteries kinetics were lower than in control group. It indicates that propulsive function of the arteries is reduced in patients with heart failure. Conclusion Arterial vessels are active, full-fledged participant in cardiovascular system. Vessels make an active work in blood movement from the heart to the distal parts and tissues. The clinical manifestations of heart failure are determined not only the heart function but also the function of arteries that is needed to be examined. In patients with preserved ejection fraction we can observe the symptoms of heart failure, the function abilities of arteries are reduced. The term "heart-vessels failure" should be used and applied not only to the heart but also to the arteries function in their coupling with heart. Abstract Figure.

Slow walking synergies reveal a functional role for arm swing asymmetry in healthy adults: A principal component analysis with relation to mechanical work

IntroductionThe purpose of this study was to reveal a functional role for arm-swing asymmetry during gait in healthy adults. To this end, the primary aim was to investigate the role of neuromuscular control on the asymmetry of propulsive and collision joint work at either end of the double-support phase (WDS) in the context of sidedness. The secondary aim was to investigate the effect of neuromuscular control on propulsive and collision joint work at either end of the single-support phase (WSS) in the context of arm-swing asymmetry. MethodsSlow -walking trials of 25 participants were analysed using principal component analysis to generate movement synergies (PMk). Independent variables included the tightness of neuromuscular control (N1) formulated from the first PMk and the directional Arm-swing asymmetry index (dASI). Dependent variables included the difference between double-support collision and propulsive joint work (WDS) and a ratio consisting of the difference between single-support collision and propulsive work of both sides (WSS). A linear mixed-effects model was utilized for aim 1 while a multiple linear regression analysis was undertaken for aim 2. ResultsHealthy adult gait was accompanied by a left-side dominant arm-swing on average. For aim 1, N1 demonstrated a significant negative effect on WDS while sidedness had a negative direct effect and positive indirect effect through N1 on WDS. The most notable finding was the interaction between dASI and N1 which demonstrated a highly significant positive effect on WSS. InterpretationEvidence was put forward that arm-swing asymmetry during gait is related to footedness among healthy adults. Future studies should look to formally confirm this finding.

Measurement of push-rim forces during racing wheelchair propulsion using a novel attachable force sensor system

To improve competitive skills, it is important to clarify the relationship between the propulsion motion (the propulsive force in the use of racing wheelchairs optimized for athletes) and aerodynamic drag, which can change during propulsive motion. Therefore, the purpose of this research was to construct a novel force sensor system that is attachable to racing wheelchairs for individual athletes and usable in a wind tunnel facility to examine differences in the push-rim force characteristics of athletes based on the measured results. The system was composed of four two-dimensional component force sensors, batteries, and radio transmitters. From the output of the four two-dimensional component sensors, tangential and radial components of the push-rim force were measured. Three top-class long-distance wheelchair athletes participated in this study, which required each athlete to push a racing wheelchair at 5.56 m/s on a wheelchair roller system in a wind tunnel facility. The force sensor system was mounted on the participants’ individual racing wheelchairs. The measured tangential force waveforms were classified as either bimodal or unimodal depending on the athletes’ propulsion styles. Although two athletes showed similar propulsion style characteristics, the athlete with more years of experience showed better propulsive work efficiency and repeatability. Therefore, a difference in skill for applying propulsive force during the push phase, which is difficult to estimate by kinematic analysis, could be estimated by using the force sensor system.

Kinematics and pushrim kinetics in adolescents propelling high-strength lightweight and ultra-lightweight manual wheelchairs

Purpose: The purpose of this study is to describe and compare pushrim forces, propulsive work cost, and upper body kinematics in adolescents propelling (1) a standard high strength lightweight wheelchair, and (2) an ultra-lightweight wheelchair with adjustable main axle positioning, on a level tiled floor (“Tile”), ascending a ramp (“Ramp”), and across a foam mat (“Mat”).Methods: A within-subjects repeated measures study design was used. Eight adolescent manual wheelchair users propelled the standard and ultra-lightweight wheelchairs across the three conditions. Average pushrim tangential force, propulsive power and work per unit distance travelled, as well as upper body kinematic angles, were analyzed.Results: Average pushrim tangential force (1.80 ± 0.7 N, p = .042) and propulsive work per unit distance travelled (8.3 ± 1.7 J·m− 1, p = .002) were higher for the standard lightweight wheelchair, whereas average speed was lower (0.12 ± 0.03 m/s, p = .006). Maximum shoulder (9.2 ± 2.0°, p = .003) and elbow flexion (8.0 ± 2.2°, p = .009) were higher for the ultra-lightweight wheelchair. Compared with Tile, propulsion on Mat and Ramp was associated with higher average tangential force, work per unit distance, power, and maximum flexion of the neck and trunk, whereas shoulder extension and average speed were lower for Mat and Ramp.Conclusions: Compared with the standard lightweight wheelchair, ultra-lightweight wheelchair propulsion was associated with lower pushrim forces, lower energy costs, higher self-selected speeds, and increased shoulder and elbow flexion. These variables have been linked to injury risk and mobility efficiency, and the results provided evidence that differences in weight and configuration options are both contributors. Findings can inform decision-making in the prescription of manual wheelchairs for pre-adult populations.Implications for RehabilitationA significant proportion of manual wheelchair users are children and adolescents, and due to the early onset of use they may be especially predisposed to the development of chronic overuse injuries.The study reports differences in energy costs, pushrim forces, and upper body kinematics measured when adolescents propelled standard and ultra-lightweight wheelchairs across three trial conditions.In the ultra-lightweight wheelchair, reduced energy cost is linked to more efficient mobility, and lower forces may be linked to lower risk of chronic injury.Significant differences in elbow and shoulder kinematics are also reported, and the findings support the importance of both weight and setup options in the selection of manual wheelchairs.

A Comparison of Different Methods for Assessing Plyometric Ability During Jumps

PURPOSE: To compare different methods for assessing plyometric ability during countermovement (CMJ) and drop jumps (DJ) from different heights. METHODS: Twelve resistance-trained men (age: 21.8 ± 1.7 years; height: 1.81 ± 0.06 m; mass: 85.1 ± 8.6 kg) performed CMJ and DJ from heights of 0.40 m, 0.60 m, and 0.80 m. Force plates recorded the ground reaction force from which the descent (absorption phase) and ascent (propulsive phase) of the center of mass during ground contact was determined. Jump height (JH), vertical stiffness (VSTIFF) and normalized work (WNORM), power output (PONORM), and impulse (INORM) during the absorption and propulsion phases were calculated. Plyometric ability was assessed using the modified reactive strength index (RSIMOD) and four indices using propulsion time (PTI), propulsive work (PWI), propulsive power (PPI), and propulsive impulse (PII). Analysis of variance was used to assess the differences in the mechanical variables and the plyometric indices across the four jump conditions. Correlations were used to assess the relationships between the plyometric indices and JH. RESULTS: JH (mean differences: 0.03 – 0.06 m; p=0.007) and VSTIFF (mean differences: 0.69 – 0.93 kN/m, p<0.001) were greater during CMJ compared to the DJ conditions. The mechanical variables during the absorption phase were greatest during the highest DJ (WNORM mean differences: 1.6 – 10.0 J/kg, p<0.001; PONORM mean differences: 4.9 – 31.3 W/kg, p<0.001; INORM mean differences: 0.36 – 2.52 m/s, p<0.001), while WNORM and INORM during the propulsive phase were greatest during the CMJ (WNORM mean differences: 0.2 – 1.1 J/kg, p=0.020; INORM mean differences: 0.09 – 0.21 m/s, p<0.001) with no differences in PONORM (p>0.05). RSIMOD increased across the four jumps and was greatest at the highest DJ condition (mean differences: 0.003 – 0.150, p<0.001). The greatest values for the other indices were reported for the CMJ (p<0.001). The largest correlations with JH were found for PII (r = 0.958 – 0.993). CONCLUSION: RSIMOD does not reflect the changes in mechanical variables during the propulsion phases of CMJ and DJ and may not therefore provide an accurate assessment of the ability to utilize the stretch-shortening cycle during different jumps. Practitioners should consider using PII as a measure of plyometric ability.

Two biomechanical strategies for locomotor adaptation to split-belt treadmill walking in subjects with and without transtibial amputation

Locomotor adaptation is commonly studied using split-belt treadmill walking, in which each foot is placed on a belt moving at a different speed. As subjects adapt to split-belt walking, they reduce metabolic power, but the biomechanical mechanism behind this improved efficiency is unknown. Analyzing mechanical work performed by the legs and joints during split-belt adaptation could reveal this mechanism. Because ankle work in the step-to-step transition is more efficient than hip work, we hypothesized that control subjects would reduce hip work on the fast belt and increase ankle work during the step-to-step transition as they adapted. We further hypothesized that subjects with unilateral, trans-tibial amputation would instead increase propulsive work from their intact leg on the slow belt. Control subjects reduced hip work and shifted more ankle work to the step-to-step transition, supporting our hypothesis. Contrary to our second hypothesis, intact leg work, ankle work and hip work in amputees were unchanged during adaptation. Furthermore, all subjects increased collisional energy loss on the fast belt, but did not increase propulsive work. This was possible because subjects moved further backward during fast leg single support in late adaptation than in early adaptation, compensating by reducing backward movement in slow leg single support. In summary, subjects used two strategies to improve mechanical efficiency in split-belt walking adaptation: a CoM displacement strategy that allows for less forward propulsion on the fast belt; and, an ankle timing strategy that allows efficient ankle work in the step-to-step transition to increase while reducing inefficient hip work.

Performance and physiological effects of different descending strategies for cross-country mountain biking

This study investigated the performance-related feasibility and physiological benefits of purposefully eliminating propulsive work while descending in mountain biking and compared values to those measured during road descending. Participants cycled uphill on a road at race pace before descending over three conditions (off-road pedalling; off-road coasting; road coasting). Relatively low power output during off-road pedalling was associated with a greater oxygen uptake (p < .01) when compared with off-road coasting despite no difference in vibration exposure (p > .05). Importantly, pedalling did not invoke a performance benefit (p > .05) on the descent used in this study. Significantly greater heart rate and oxygen uptake (both p < .01) were observed between road and off-road descending, likely caused by the increase in terrain-induced vibrations (p < .01) experienced between the bicycle and rider. Results indicate that reducing propulsive work during descending can improve recovery without being disadvantageous to performance. Similarly, the vibrations experienced during road descending are relatively low, and further reduce oxygen cost. In an effort to increase efficiency, it is recommended that mountain bike athletes focus on skills to increase descending speed without the addition of pedalling, and that equipment be used to decrease vibrations nearer to those seen on the road.

Biomechanics of Step Initiation After Balance Recovery With Implications for Humanoid Robot Locomotion.

Balance-recovery stepping is often necessary for both a human and humanoid robot to avoid a fall by taking a single step or multiple steps after an external perturbation. The determination of where to step to come to a complete stop has been studied, but little is known about the strategy for initiation of forward motion from the static position following such a step. The goal of this study was to examine the human strategy for stepping by moving the back foot forward from a static, double-support position, comparing parameters from normal step length (SL) to those from increasing SLs to the point of step failure, to provide inspiration for a humanoid control strategy. Healthy young adults instrumented with joint reflective markers executed a prescribed-length step from rest while marker positions and ground reaction forces (GRFs) were measured. The participants were scaled to the Gait2354 model in opensim software to calculate body kinematic and joint kinetic parameters, with further post-processing in matlab. With increasing SL, participants reduced both static and push-off back-foot GRF. Body center of mass (CoM) lowered and moved forward, with additional lowering at the longer steps, and followed a path centered within the initial base of support (BoS). Step execution was successful if participants gained enough forward momentum at toe-off to move the instantaneous capture point (ICP) to within the BoS defined by the final position of both feet on the front force plate. All lower extremity joint torques increased with SL except ankle joint. Front knee work increased dramatically with SL, accompanied by decrease in back-ankle work. As SL increased, the human strategy changed, with participants shifting their CoM forward and downward before toe-off, thus gaining forward momentum, while using less propulsive work from the back ankle and engaging the front knee to straighten the body. The results have significance for human motion, suggesting the upper limit of the SL that can be completed with back-ankle push-off before additional knee flexion and torque is needed. For biped control, the results support stability based on capture-point dynamics and suggest strategy for center-of-mass trajectory and distribution of ground force reactions that can be compared with robot controllers for initiation of gait after recovery steps.

Ankle work and dynamic joint stiffness in high- compared to low-arched athletes during a barefoot running task

High- (HA) and low-arched (LA) athletes have an exaggerated risk of injury. Ankle joint stiffness is a potential underlying mechanism for the greater rate of injury within these two functionally different groups. An alternative candidate mechanism of injury in HA and LA athletes pertains to the efficacy of the foot as a rigid lever during propulsion. The purpose of this study was to quantify the differences in ankle dynamic joint stiffness, and ankle braking work and ankle propulsive work during stance phase of running. MethodsTen HA and ten LA athletes performed five barefoot running trials while ground reaction forces and three-dimensional kinematics were recorded. Ankle dynamic joint stiffness was calculated as the slope of the ankle joint moment–ankle joint angle plot during load attenuation. Ankle braking and propulsive work values were calculated for the stance phase. ResultsHA athletes had significantly greater ankle dynamic joint stiffness and significantly smaller ankle net and propulsive work than LA athletes. ConclusionsThese data demonstrate that HA and LA athletes exhibit unique biomechanical patterns during running. These patterns may be related to lower extremity injury.

Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking

Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as prostheses and orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for 216 gait trials across 26 subjects (speeds from 0.75–2.63 m/s) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R2 of 75% to 81% in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of 13% to 30%. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking.

Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking

Estimation of Quasi-Stiffness and Propulsive Work of the Human Ankle in the Stance Phase of Walking

Powered ankle-foot prosthesis to assist level-ground and stair-descent gaits

The human ankle varies impedance and delivers net positive work during the stance period of walking. In contrast, commercially available ankle-foot prostheses are passive during stance, causing many clinical problems for transtibial amputees, including non-symmetric gait patterns, higher gait metabolism, and poorer shock absorption. In this investigation, we develop and evaluate a myoelectric-driven, finite state controller for a powered ankle-foot prosthesis that modulates both impedance and power output during stance. The system employs both sensory inputs measured local to the external prosthesis, and myoelectric inputs measured from residual limb muscles. Using local prosthetic sensing, we first develop two finite state controllers to produce biomimetic movement patterns for level-ground and stair-descent gaits. We then employ myoelectric signals as control commands to manage the transition between these finite state controllers. To transition from level-ground to stairs, the amputee flexes the gastrocnemius muscle, triggering the prosthetic ankle to plantar flex at terminal swing, and initiating the stair-descent state machine algorithm. To transition back to level-ground walking, the amputee flexes the tibialis anterior muscle, triggering the ankle to remain dorsiflexed at terminal swing, and initiating the level-ground state machine algorithm. As a preliminary evaluation of clinical efficacy, we test the device on a transtibial amputee with both the proposed controller and a conventional passive-elastic control. We find that the amputee can robustly transition between the finite state controllers through direct muscle activation, allowing rapid transitioning from level-ground to stair walking patterns. Additionally, we find that the proposed finite state controllers result in a more biomimetic ankle response, producing net propulsive work during level-ground walking and greater shock absorption during stair descent. The results of this study highlight the potential of prosthetic leg controllers that exploit neural signals to trigger terrain-appropriate, local prosthetic leg behaviors.

Vehicle Speed Profiles to Minimize Work and Fuel Consumption

This paper addresses the question of what speed profile will minimize fuel consumption of a land transport vehicle (road or rail) in traversing a path or route. Numerous previous studies, using a control theory approach applied to specific profiles, have suggested that fuel consumption is approximately minimized by operation at constant speed. This result is derived much more directly here, along with boundaries on the conditions under which this result holds. The derivation relies on: (1) the approximate proportionality between fuel consumption and propulsive work; (2) the inherent resistance of a vehicle having the usual quadratic form (of road and rail vehicles); (3) the energy conversion characteristics of on-board gasoline or diesel (or diesel–electric) propulsion systems; and (4) relatively long distances between stops. Tests, using a train performance simulator, confirm the theoretical results. The results are discussed from the standpoint of basic principles in transportation engineering, and as g...