The independent effects of speed and propulsive force on joint power generation in walking

Gait signature changes with walking speed are similar among able-bodied young adults despite persistent individual-specific differences

Understanding individuals' distinct movement patterns is crucial for health, rehabilitation, and sports. Recently, we developed a machine learning-based framework to show that "gait signatures" describing the neuromechanical dynamics governing able-bodied and post-stroke gait kinematics remain individual-specific across speeds. However, we only evaluated gait signatures within a limited speed range and number of participants, using only sagittal plane (i.e., 2D) joint angles. Here we characterized changes in gait signatures across a wide range of speeds, from very slow (0.3 m/s) to exceptionally fast (above the walk-to-run transition speed) in 17 able-bodied young adults. We further assessed whether 3D kinematic and/or kinetic (ground reaction forces, joint moments, and powers) data would improve the discrimination of gait signatures. Our study showed that gait signatures remained individual-specific across walking speeds: Notably, 3D kinematic signatures achieved exceptional accuracy (99.8%, confidence interval (CI): 99.1-100%) in classifying individuals, surpassing both 2D kinematics and 3D kinetics. Moreover, participants exhibited consistent, predictable linear changes in their gait signatures across the entire speed range. These changes were associated with participants' preferred walking speeds, balance ability, cadence, and step length. These findings support gait signatures as a tool to characterize individual differences in gait and predict speed-induced changes in gait dynamics.

Acute biomechanical responses to wearing a controlled ankle motion (CAM) Walker boot during walking

BACKGROUND

Controlled ankle motion (CAM) boots are often prescribed during the rehabilitation of lower limb injuries and pathologies to reduce foot and ankle movement and loading whilst allowing the patient to maintain normal daily function.

RESEARCH QUESTION

The aim of this study was to quantify the compensatory biomechanical mechanisms undergone by the ipsilateral hip and knee joints during walking. In addition, the compensatory mechanisms displayed by the contralateral limb were also considered.

METHODS

Twelve healthy participants walked on an instrumented treadmill at their preferred walking speed. They underwent kinematic and kinetic analysis during four footwear conditions: normal shoes (NORM), a Malleo Immobil Air Walker on the right leg (OTTO), a Rebound® Air Walker on the right leg with (EVEN) and without (OSS) an Evenup Shoelift™ on the contralateral leg.

RESULTS

CAM boot wear increased the relative joint contribution to total mechanical work from the ipsilateral hip and knee joints (p < 0.05), which was characterised by increased hip and knee abduction during the swing phase of the gait cycle. EVEN increased the absolute work done and relative contribution of the contralateral limb. CAM boot wear reduced walking speed (p < 0.05), which was partially compensated for during EVEN.

SIGNIFICANCE

The increased hip abduction in the ipsilateral leg was likely caused by the increase in effective leg length and limb mass, which could lead to secondary site complications following prolonged CAM boot wear. Although prescribing an even-up walker partially mitigates these compensatory mechanisms, adverse effects to contralateral limb kinematics and kinetics (e.g., elevated knee joint work) should be considered.

Lower extremity joint power and work during recovery following trip-induced perturbations

BACKGROUND

Successful recovery following a perturbation during walking depends on a quick well-coordinated response from the body. As such, lower limb joint power and work provide critical information characterizing the success of the recovery after a perturbation. Therefore, this study aimed to investigate lower-limb joint power and the relative contribution of each joint to the total leg work during the recovery following a trip-induced perturbation.

METHODS

Twenty-four young male volunteers walked at 1.1 m/s for 2 min, followed by two unexpected perturbations induced by rapidly decelerating the right belt of the split-belt treadmill. Joint moments and powers were calculated using an inverse dynamic approach. Joint work was found as the integral of joint power with respect to time. Statistical parametric mapping (SPM) and paired-sample t-tests were used to compare joint power and work between recovery and unperturbed steps.

RESULTS

Compared to normal walking, recovery from the trip required a significant increase in both positive (+27 %, p < 0.05) and negative(+28 %,p < 0.05) leg work. During unperturbed walking, the ankle was the key contributor to both positive (ankle=50 %, hip=34 %, and knee=15 %) and negative (ankle=62 %, knee=32 %, and hip=6 %) leg work. During recovery, the knee eccentric work significantly increased (+83 %,p < 0.05) making it the main contributor to the negative leg work (knee=46 %, ankle=45 %, and hip=9 %). The hip positive work also increased during recovery (+62.7 %, p < 0.05), while ankle and the knee positive work remained unchanged.

SIGNIFICANCE

These findings highlight the importance of eccentric work of the knee, and concentric work of the hip joint during recovery from trip-induced perturbations. The additional mechanical demand of producing and absorbing more power during recovery is primarily imposed on the knee and hip, rather than the ankle. This new insight into the specific functions of lower-limb joints during recovery from trip-induced perturbations has important implications for the design of targeted fall prevention interventions.

Simulations suggest walking with reduced propulsive force would not mitigate the energetic consequences of lower tendon stiffness

Aging elicits numerous effects that impact both musculoskeletal structure and walking function. Tendon stiffness (kT) and push-off propulsive force (FP) both impact the metabolic cost of walking and are diminished by age, yet their interaction has not been studied. We combined experimental and computational approaches to investigate whether age-related changes in function (adopting smaller FP) may be adopted to mitigate the metabolic consequences arising from changes in structure (reduced kT). We recruited 12 young adults and asked them to walk on a force-sensing treadmill while prompting them to change FP (±20% & ±40% of typical) using targeted biofeedback. In models driven by experimental data from each of those conditions, we altered the kT of personalized musculoskeletal models across a physiological range (2-8% strain) and simulated individual-muscle metabolic costs for each kT and FP combination. We found that kT and FP independently affect walking metabolic cost, increasing with higher kT or as participants deviated from their typical FP. Our results show no evidence for an interaction between kT and FP in younger adults walking at fixed speeds. We also reveal complex individual muscle responses to the kT and FP landscape. For example, although total metabolic cost increased by 5% on average with combined reductions in kT and FP, the triceps surae muscles experienced a 7% local cost reduction on average. Our simulations suggest that reducing FP during walking would not mitigate the metabolic consequences of lower kT. Wearable devices and rehabilitative strategies can focus on either kT or FP to reduce age-related increases in walking metabolic cost.

Effects of induced motor fatigue on walking mechanics and energetics

Lower-body robotic exoskeletons can be used to reduce the energy demand of locomotion and increase the endurance of wearers. Understanding how motor fatigue affects walking performance may lead to better exoskeleton designs to support the changing physical capacity of an individual due to motor fatigue. The purpose of this study was to investigate the effects of motor fatigue on walking mechanics and energetics. Treadmill walking with progressively increased incline gradient was used to induce motor fatigue. Twenty healthy young participants walked on an instrumented treadmill at 1.25 m/s and 0° of incline for 5 min before (PRE) and after (POST) motor fatigue. We examined lower-limb joint mechanics, metabolic cost, and the efficiency of positive mechanical work (η+work). Compared to PRE, participants had increased net metabolic power by ∼14% (p < 0.001) during POST. Participants also had increased total-limb positive mechanical power (Total P+mech) by ∼4% during POST (p < 0.001), resulting in a reduced η+work by ∼8% (p < 0.001). In addition, the positive mechanical work contribution of the lower-limb joints during POST was shifted from the ankle to the knee while the negative mechanical work contribution was shifted from the knee to the ankle (all p < 0.017). Although greater knee positive mechanical power was generated to compensate for the reduction in ankle positive power after motor fatigue, the disproportionate increase in metabolic cost resulted in a reduced walking efficiency. The findings of this study suggest that powering the ankle joint may help delay the onset of the lower-limb joint work redistribution observed during motor fatigue.

The efficacy of gait rehabilitations for the treatment of incomplete spinal cord injury: a systematic review and network meta-analysis

BACKGROUND

Recent pieces of evidence about the efficacy of gait rehabilitation for incomplete spinal cord injury remain unclear. We aimed to estimate the treatment effect and find the best gait rehabilitation to regain velocity, distance, and Walking Index Spinal Cord Injury (WISCI) among incomplete spinal cord injury patients.

METHOD

PubMed and Scopus databases were searched from inception to October 2022. Randomized controlled trials (RCTs) were included in comparison with any of the following: conventional physical therapy, treadmill, functional electrical stimulation and robotic-assisted gait training, and reported at least one outcome. Two reviewers independently selected the studies and extracted the data. Meta-analysis was performed using random-effects or fixed-effect model according to the heterogeneity. Network meta-analysis (NMA) was indirectly compared with all interventions and reported as pooled unstandardized mean difference (USMD) and 95% confidence interval (CI). Surface under the cumulative ranking curve (SUCRA) was calculated to identify the best intervention.

RESULTS

We included 17 RCTs (709 participants) with the mean age of 43.9 years. Acute-phase robotic-assisted gait training significantly improved the velocity (USMD 0.1 m/s, 95% CI 0.05, 0.14), distance (USMD 64.75 m, 95% CI 27.24, 102.27), and WISCI (USMD 3.28, 95% CI 0.12, 6.45) compared to conventional physical therapy. In NMA, functional electrical stimulation had the highest probability of being the best intervention for velocity (66.6%, SUCRA 82.1) and distance (39.7%, SUCRA 67.4), followed by treadmill, functional electrical stimulation plus treadmill, robotic-assisted gait training, and conventional physical therapy, respectively.

CONCLUSION

Functional electrical stimulation seems to be the best treatment to improve walking velocity and distance for incomplete spinal cord injury patients. However, a large-scale RCT is required to study the adverse events of these interventions.

TRIAL REGISTRATION

PROSPERO number CRD42019145797.

The energetic effect of hip flexion and retraction in walking at different speeds: a modeling study

In human walking, power for propulsion is generated primarily via ankle and hip muscles. The addition of a 'passive' hip spring to simple bipedal models appears more efficient than using only push-off impulse, at least, when hip spring associated energetic costs are not considered. Hip flexion and retraction torques, however, are not 'free', as they are produced by muscles demanding metabolic energy. Studies evaluating the inclusion of hip actuation costs, especially during the swing phase, and the hip actuation's energetic benefits are few and far between. It is also unknown whether these possible benefits/effects may depend on speed. We simulated a planar flat-feet model walking stably over a range of speeds. We asked whether the addition of independent hip flexion and retraction remains energetically beneficial when considering work-based metabolic cost of transport (MCOT) with different efficiencies of doing positive and negative work. We found asymmetric hip actuation can reduce the estimated MCOT relative to ankle actuation by up to 6%, but only at medium speeds. The corresponding optimal strategy is zero hip flexion and some hip retraction actuation. The reason for this reduced MCOT is that the decrease in collision loss is larger than the associated increase in hip negative work. This leads to a reduction in total positive mechanical work, which results in an overall lower MCOT. Our study shows how ankle actuation, hip flexion, and retraction actuation can be coordinated to reduce MCOT.

Are Age, Self-Selected Walking Speed, or Propulsion Force Predictors of Gait-Related Changes in Older Adults?

There is limited research that directly compares the effect of reduced speed with reduced propulsive force production (PFP) on age-related gait changes. We aimed to determine how changes in the gait of older adults correlate with age, speed, or peak PFP over a 6-year span. We collected kinematics and kinetics of 17 older subjects at 2 time points. We determined which biomechanical variables changed significantly between visits and used linear regressions to determine whether combinations of self-selected walking speed, peak PFP, and age correlated to changes in these variables. We found a suite of gait-related changes that occurred in the 6-year period, in line with previous aging studies. Of the 10 significant changes, we found 2 with significant regressions. Self-selected walking speed was a significant indicator of step length, not peak PFP or age. Peak PFP was a significant indicator for knee flexion. None of the biomechanical changes were correlated to the chronological age of the subjects. Few gait parameters had a correlation to the independent variables, suggesting that changes in gait mechanics were not solely correlated to peak PFP, speed, and/or age. This study improves understanding of changes in ambulation that lead to age-related gait modifications.

Quantifying mechanical and metabolic interdependence between speed and propulsive force during walking

Walking speed is a useful surrogate for health status across the population. Walking speed appears to be governed in part by interlimb coordination between propulsive (F_P) and braking (F_B) forces generated during step-to-step transitions and is simultaneously optimized to minimize metabolic cost. Of those forces, F_P generated during push-off has received significantly more attention as a contributor to walking performance. Our goal was to first establish empirical relations between F_P and walking speed and then to quantify their effects on metabolic cost in young adults. To specifically address any link between F_P and walking speed, we used a self-paced treadmill controller and real-time biofeedback to independently prescribe walking speed or F_P across a range of condition intensities. Walking with larger and smaller F_P led to instinctively faster and slower walking speeds, respectively, with ~80% of variance in walking speed explained by F_P. We also found that comparable changes in either F_P or walking speed elicited predictable and relatively uniform changes in metabolic cost, together explaining ~53% of the variance in net metabolic power and ~14% of the variance in cost of transport. These results provide empirical data in support of an interdependent relation between F_P and walking speed, building confidence that interventions designed to increase F_P will translate to improved walking speed. Repeating this protocol in other populations may identify other relations that could inform the time course of gait decline due to age and disease.

Investigation of the relationship between steps required to stop and propulsive force using simple walking models

To prevent falls in the elderly, it is essential to evaluate their gait stability and identify factors that negatively affect it. Although one of the probable factors is a decrease in propulsive force of walking, the relationship between the force and the gait stability has not been fully clarified. To this end, two simple walking models were used to investigate the relationship between the propulsive force and the number of steps required to stop, denoted N. N was calculated as the number of steps required for the rimless wheel to stop and was treated as a variable which is an indirect indicator of stability. A lower N corresponds to the gait being closer to a stopped state. The propulsive force was calculated using the push-off impulse applied to the simplest walking model during the step-to-step transition. To account for the effects of the double support phase in human walking, the gravitational impulse, which is the integral of the body weight (gravitational force) over the double support time, was applied to the step-to-step transition equation of the models. The models revealed that the propulsive force is reduced by two factors: the reduction in step length and the reduction in walking speed. In the former, N increases; in the latter, N decreases. The former is consistent with previous experimental results on human gait, whereas the latter has not been experimentally investigated. These results may provide important insights in clarifying the relationship between the stability and the propulsive force in human gait.

Biomechanics Analysis of the Lower Limbs in 20 Male Sprinters Using the International Society of Biomechanics Six-Degrees-of-Freedom Model and the Conventional Gait Model

Background

This biomechanics study of the lower limbs aimed to compare the use of the International Society of Biomechanics Six-Degrees-of-Freedom (ISB-6DOF) model and the conventional gait model (CGM), formerly known as the Helen Hayes model, in 20 male sprinters who habitually used the forefoot (FF) or rearfoot (RF) strike modes.

Material/Methods

We used a motion capture system to compare the difference in lower-extremity joint mechanics between sprinters’ forefoot or rearfoot strike mode during unplanned sidestepping (UPSS). Twenty elite sprinters participated in a motion capture test under 2 models. Each of the 10 participants were classified as having a habitual forefoot strike mode or rearfoot strike mode during unplanned sidestepping. Joint mechanics and gait parameters were calculated according to the designed movement.

Results

Comparison of the 2 models showed that the knee joint angles were inconsistent (P<0.05), highlighting the difficulty of the Helen Hayes model in anatomical recognition. The results of the 2 models show that during the unplanned sidestepping, the sprinter using the habitual rearfoot strike mode had a greater load through the knee joint (P<0.05). Sprinters who used the habitual forefoot strike mode experienced greater load through their ankle joints (P<0.05).

Conclusions

The findings from this biomechanics study showed that when compared with the ISB-6DoF model, the findings from the CGM were more reproducible for the evaluation of FF and RF strike during unplanned sidestepping.

The metabolic and mechanical consequences of altered propulsive force generation in walking

Older adults walk with greater metabolic energy consumption than younger for reasons that are not well understood. We suspect that a distal-to-proximal redistribution of leg muscle demand, from muscles spanning the ankle to those spanning the hip, contributes to greater metabolic energy costs. Recently, we found that when younger adults using biofeedback target smaller than normal peak propulsive forces (F_P), they do so via a similar redistribution of leg muscle demand during walking. This alludes to an experimental paradigm that emulates characteristics of elderly gait independent of other age-related changes relevant to metabolic energy cost. Thus, our purpose was to quantify the metabolic and limb- and joint-level mechanical energy costs associated with modulating propulsive forces during walking in younger adults. Walking with larger F_P increased net metabolic power by 47% (main effect, p = 0.001), which was accompanied by small by relatively uniform increases in hip, knee, and ankle joint power and which correlated with total joint power (R² = 0.151, p = 0.019). Walking with smaller F_P increased net metabolic power by 58% (main effect, p < 0.001), which was accompanied by higher step frequencies and increased total joint power due to disproportionate increases in hip joint power. Increases in hip joint power when targeting smaller than normal F_P accounted for more than 65% of the variance in the measured changes in net metabolic power. Our findings suggest that walking with a diminished push-off exacts a metabolic penalty because of higher step frequencies and more total limb work due to an increased demand on proximal leg muscles.

Muscle metabolic energy costs while modifying propulsive force generation during walking

We pose that an age-related increase in the metabolic cost of walking arises in part from a redistribution of joint power where muscles spanning the hip compensate for insufficient ankle push-off and smaller peak propulsive forces (F_P). Young adults elicit a similar redistribution when walking with smaller F_P via biofeedback. We used targeted F_P biofeedback and musculoskeletal models to estimate the metabolic costs of operating lower limb muscles in young adults walking across a range of F_P. Our simulations support the theory of distal-to-proximal redistribution of joint power as a determinant of increased metabolic cost in older adults during walking.

Plantarflexor strength, gait speed, and step length change in individuals with Parkinson's disease

Parkinson's disease affects the ability to walk often resulting in decreased independence and low quality of life. The purpose of this study was to examine differences in plantarflexor strength (PFS), gait speed, and step length in persons with Parkinson's disease (PwP) and healthy peers using clinical measures. A secondary purpose was to examine the relationship between these gait components across disease severity. The study was a convenience sample of 71 PwP and 25 community healthy peers. Outcome measures included 10-Meter Walk, step length, and Calf-Raise Senior Test. PwP were separated into mild and moderate impairment groups using the Movement Disorders Society United Parkinson's Disease Rating Scale Motor Subscale. Between group differences for gait speed (F2,93 = 24.560, P = 0.000), step length (F2,93 = 21.93, P = 0.000) and PFS (F2,93 = 19.49, P < 0.000) were observed. Post hoc testing determined a difference (P < 0.00) in gait speed, step length, and PFS testing between moderate impairment versus healthy peers and mild impairment. A difference (P = 0.045) in step length and a trend towards significance (P = 0.064) for PFS was found between healthy peers and mild impairment group. This study revealed that PwP with mild impairment also have significant changes in step length and trends toward plantarflexor weakness without a significant difference in gait speed. These early changes may warrant early assessment and intervention to prevent decline. This study may bring clinical focus onto the plantarflexor and step length for early comprehensive assessment and treatment of gait and mobility for PwP.

Foot strike alters ground reaction force and knee load when stepping down during ongoing walking

BACKGROUND

When stepping down from a raised surface, either a toe or heel contact strategy is performed. Increased vertical momentum is likely to be experienced during a step descent, yet the extent to which these descent strategies influence the development of load at the ground and knee has not been examined.

RESEARCH QUESTION

Does descent strategy influence ground and knee joint loading? Does the contribution from leading and trailing limb joint mechanics differ between descent strategies?

METHODS

Twenty-two healthy male participants (age: 34.0 ± 6.5 years, height: 179 ± 6.3 cm, mass: 83.5 ± 13 kg) walked along a raised platform, stepped down from a 14 cm height utilising either a toe (n = 10) or heel (n = 12) initial contact, and continued walking. Vertical ground reaction forces and knee external adduction and flexor moments were extracted for the duration of the braking phase. Joint work was calculated for the ankle, knee, and hip in both the leading and trailing limbs.

RESULTS

Waveform analysis of the loading features indicated that a toe-contact strategy resulted in significantly reduced loading rates during early braking (1-32% of the braking phase) and significantly increased magnitude in late braking (55-96% of the braking phase). Individuals performing toe landings completed 33% greater overall work (p = 0.091) in the lead limb and utilised the lead limb ankle joint as the main shock absorber (79% of total lead limb work). Concurrently, the trailing limb performed 29% and 21% less work when lowering the centre of mass and propulsion, respectively, compared to a heel landing.

SIGNIFICANCE

A toe-contact strategy results in reduced limb and knee joint loading rates through greater utilisation of the lead limb ankle joint. A heel-contact strategy, however, can reduce loading during late braking by utilising the functionality of the trailing limb.

Validity of Measurement for Trailing Limb Angle and Propulsion Force during Gait Using a Magnetic Inertial Measurement Unit

Propulsion force and trailing limb angle (TLA) are meaningful indicators for evaluating quality of gait. This study examined the validity of measurement for TLA and propulsion force during various gait conditions using magnetic inertial measurement units (IMU), based on measurements using a three-dimensional motion analysis system and a force platform. Eighteen healthy males (mean age 25.2  ±  3.2 years, body height 1.70   ±  0.06 m) walked with and without trunk fluctuation at preferred, slow, and fast velocities. IMU were fixed on the thorax, lumbar spine, and right thigh and shank. IMU calculated the acceleration and tilt angles in a global coordinate system. TLA, consisting of a line connecting the hip joint with the ankle joint, and the laboratory's vertical axis at late stance in the sagittal plane, was calculated from thigh and shank segment angles obtained by IMU, and coordinate data from the motion analysis system. Propulsion force was estimated by the increment of velocity calculated from anterior acceleration measured by IMU fixed on the thorax and lumbar spine, and normalized impulse of the anterior component of ground reaction force (AGRF) during late stance. Similarity of TLA measured by IMU and the motion analysis system was tested by the coefficient of multiple correlation (CMC), intraclass correlation coefficient (ICC), and root mean square (RMS) of measurement error. Relationships between normalized impulse of AGRF and increments of velocity, as measured by IMU, were tested using correlation analysis. CMC of TLA was 0.956–0.959. ICC between peak TLAs was 0.831–0.876 (p < 0.001), and RMS of error was 1.42°–1.92°. Velocity increment calculated from acceleration on the lumbar region showed strong correlations with normalized impulse of AGRF (r = 0.755–0.892, p < 0.001). These results indicated a high validity of estimation of TLA and propulsion force by IMU during various gait conditions; these methods would be useful for best clinical practice.

Triceps surae muscle-subtendon interaction differs between young and older adults

Background: Mechanical power generated via triceps surae muscle-tendon interaction during walking is important for walking performance. This interaction is made complex by distinct "subtendons" arising from the lateral and medial gastrocnemius (GAS) and soleus (SOL) muscles. Comparative data and our own in vivo evidence allude to a reduced capacity for sliding between adjacent subtendons compromising the Achilles tendon in old age. However, its unclear if and how these changes affect muscle contractile behavior.Objective: We investigated aging effects on triceps surae muscle-subtendon interaction using dual-probe ultrasound imaging during isolated muscle contractions. We hypothesized that, compared to young adults, older adults would have more uniform subtendon tissue displacements that are accompanied by anatomically consistent differences in GAS versus SOL muscle length change behavior.Materials and Methods: 9 younger subjects (age: 25.1 ± 5.6 years) and 10 older adult subjects (age: 74.3 ± 3.4 years) completed a series of ramped maximum isometric voluntary contractions at ankle angles spanning 0° (neutral) to 30° plantarflexion. Two linear array ultrasound transducers simultaneously recorded GAS and SOL fascicle kinematics and tissue displacements in their associated tendinous structures.Results: We revealed that older adults have more uniform subtendon tissue displacements that extend to anatomically consistent and potentially unfavorable changes in muscle contractile behavior - evidenced by smaller differences between gastrocnemius and soleus peak shortening during isometric force generation.Conclusions: These findings provide an important biomechanical basis for previously reported correlations between more uniform Achilles subtendon behavior and reduced ankle moment generation during waking in older adults.

The timing of locomotor propulsion in healthy adults walking at multiple speeds

In computational models of human walking, both magnitude and timing of locomotor propulsion are important for mechanical and metabolic efficiency, suggesting that these are likely tightly controlled by the neuromuscular system. Studies of actual human walking have focused primarily on magnitude-related measures of propulsion, often ignoring its timing. The purpose of this study was to quantify the timing of onset and peak propulsion relative to contralateral heel strike (HS) in healthy, young adults walking at multiple speeds. Propulsion was quantified at the ground-level using the anterior component of the anteroposterior ground reaction force, the limb-level using individual limb power, and the joint-level using ankle power. Contrary to common computational models, most of our timing-related measures indicated that propulsion occurred after contralateral HS. Timing-related measures of propulsion also changed with walking speed - as speed increased, individuals initiated propulsion earlier in the support phase. Timing of locomotor propulsion is theoretically important for walking performance, especially metabolic efficiency, and could therefore provide important clinical information. This study provides a set of relatively simple metrics that can be used to quantify propulsion and benchmark data that can be used for future comparisons with individuals or populations with gait impairments.

Compensatory sagittal plane ankle gait mechanics: Are they present in patients with a weak or stiff hip?

INTRODUCTION

Simulations suggest that subjects with reduced hip range of motion (ROM) and/or weakness can achieve more normal walking mechanics through compensations at the ankle. The aims of this study were to assess whether subjects with reduced hip ROM (Stiff hip) or hip flexor weakness (Weak hip) exhibit ankle compensations during walking and investigate redistribution of power in the lower extremity joints.

METHODS

Retrospective gait data were reviewed (IRB-approved hip registry). Preoperative kinematic/kinetic walking data were collected in patients with: adolescent hip dysplasia (AHD), femoral acetabular impingement (FAI), and Legg-Calvé Perthes disease (Perthes). AHD patients with significantly weak hip flexors on their affected side were included (Weak hip group). The Gait Profile Score (GPS) was calculated on the affected side of the FAI and Perthes groups to identify patients who had a Stiff hip. Patients who had undergone a hip arthrodesis (Fusion) were also included (Stiff hip group). Ankle kinematics/kinetics were compared to healthy participants (Control). The total positive work of sagittal plane hip, knee and ankle power were compared along with the distribution of power.

RESULTS

Patients in the Weak/Stiff hip groups did not walk with greater ankle plantarflexion, peak push-off power or positive ankle work on their affected sides compared to Control. Ankle work contribution (percentage of total positive work) on the affected or unaffected sides was greater in the Perthes and Hip Fusion patients compared to Control. Significant gait abnormalities on the unaffected side were observed.

CONCLUSIONS

Patients with a weak or stiff hip did exhibit altered ankle mechanics during walking. Greater percent ankle work contribution appeared to correspond with hip stiffness. In patients with hip pathology the redistribution of power among the lower extremity joints can highlight the importance of preserving ankle function.

Fore-aft resistance applied at the center of mass using a novel robotic interface proportionately increases propulsive force generation in healthy nonimpaired individuals walking at a constant speed

Background

Past studies have utilized external interfaces like resistive bands and motor-generated pulling systems to increase limb propulsion during walking on a motorized treadmill. However, assessing changes in limb propulsion against increasing resistance demands during self-controlled walking has not been undertaken.

Purpose

We assessed limb propulsion against increasing fore-aft loading demands by applying graded fore-aft (FA) resistance at the center of mass during walking in a novel, intent-driven treadmill environment that allowed participants to control their walking speeds. We hypothesized that to maintain a target speed against progressively increasing resistance, participants would proportionately increase their limb propulsion without increasing vertical force production, with accompanying increases in trailing limb angle and positive joint work.

Methods

Seventeen healthy-nonimpaired participants (mean age 52 yrs., SD = 11) walked at a target, self-controlled speed of 1.0 m/s against 10, 15, 20, and 25% (% body weight) FA resistance levels. We primarily assessed linear slope values across FA resistance levels for mean propulsive force and impulse and vertical impulse of the dominant limb using one-sample t-tests. We further assessed changes in trailing and leading limb angles and joint work using one-way ANOVAs.

Results

Participants maintained their target velocity within an a priori defined acceptable range of 1.0 m/s ± 0.2. They significantly increased propulsion proportional to FA resistance (propulsive force mean slope = 2.45, SD = 0.7, t (16) =14.44, p < 0.01; and propulsive impulse mean slope = 0.7, SD = 0.25, t (16) = 11.84, p < 0.01), but had no changes in vertical impulse (mean slope = − 0.04, SD =0.17, p > 0.05) across FA resistance levels. Mean trailing limb angle increased from 24.3° at 10% resistance to 27.4° at 25% (p < 0.05); leading limb angle decreased from − 18.4° to − 12.6° (p < 0.05). We also observed increases in total positive limb work (F (1.7, 26) = 16.88, p ≤ 0.001, η² = 0.5), primarily attributed to the hip and ankle joints.

Conclusions

FA resistance applied during self-driven walking resulted in increased propulsive-force output of healthy-nonimpaired individuals with accompanying biomechanical changes that facilitated greater limb propulsion. Future rehabilitation interventions for neurological populations may be able to utilize this principle to design task-specific interventions like progressive strength training and workload manipulation during aerobic training for improving walking function.

Electronic supplementary material

The online version of this article (10.1186/s12984-019-0577-x) contains supplementary material, which is available to authorized users.

Comparison of lower extremity joint mechanics between healthy active young and middle age people in walking and running gait

Progression of age can influence gait characteristics. Previous research has investigated lower extremity joint mechanics between young and elderly people in locomotion, however little is known about whether differences exist between young and middle age people. Ten young healthy subjects (22.8 ± 5.3 years) and ten middle age healthy subjects (50.7 ± 6.0 years) engaged in treadmill walking (from 0.8 to 2.0 m/s) and running (from 1.8 to 3.8 m/s). The middle age group had higher ankle plantar flexor moment angular impulse (p = 0.002), total support moment impulse (p = 0.016), and hip stance positive work (p = 0.029) across walking speeds. Additionally, the middle age group had higher knee flexion angle at ground contact in walking (p = 0.005) and running (p = 0.037). These findings indicate that moderate age affects changes in ankle and hip kinetic characteristics in walking, and knee kinematic patterns in both walking and running.

Biomechanical effects of augmented ankle power output during human walking

The plantarflexor muscles are critical for forward propulsion and leg swing initiation during the push-off phase of walking, serving to modulate step length and walking speed. However, reduced ankle power output is common in aging and gait pathology, and is considered a root biomechanical cause of compensatory increases in hip power generation and increased metabolic energy cost. There is a critical need for mechanistic insight into the precise influence of ankle power output on patterns of mechanical power generation at the individual joint and limb levels during walking. We also posit that rehabilitative approaches to improve locomotor patterns should consider more direct means to elicit favorable changes in ankle power output. Thus, here we used real-time inverse dynamics in a visual biofeedback paradigm to test young adults' ability to modulate ankle power output during preferred speed treadmill walking, and the effects thereof on gait kinematics and kinetics. Subjects successfully modulated peak ankle power in response to biofeedback targets designed to elicit up to ±20% of normal walking values. Increasing ankle power output alleviated mechanical power demands at the hip and increased trailing limb positive work, propulsive ground reaction forces and step lengths. Decreasing ankle power had the opposite effects. We conclude that ankle power generation systematically influences the workload placed on more proximal leg muscles, trailing leg mechanical output and step length. Our findings also provide a promising benchmark for the application of biofeedback to restore ankle power in individuals with deficits thereof due to aging and gait pathology.

More push from your push-off: Joint-level modifications to modulate propulsive forces in old age

Introduction

Compared to young adults, older adults walk with smaller propulsive forces and a redistribution to more proximal leg muscles for power generation during push-off. Despite this deficit in propulsive function, older adults can increase push-off intensity when encouraged to via real-time biofeedback. However, the specific joint-level modifications used by older adults to enhance propulsive force generation has yet to be elucidated. The purpose of this study was to identify the joint-level modifications used by young and older adults to modulate propulsive forces when walking at their preferred speed.

Methods

9 young and 16 older adults walked at their preferred speed while visual biofeedback prompted them to modulate their propulsive forces using targets prescribed at ±10% and ±20% of their preferred value. Older adults were then divided into groups exhibiting relatively larger or smaller baseline redistribution to more proximal leg muscles for power generation.

Results

Neither young nor either older adult cohort modulated propulsive forces by altering their peak ankle power generation. Instead, subjects increased trailing limb extension and attenuated mechanical power demands at the hip during push-off. Older adults that had a larger baseline redistribution exhibited larger responses to enhanced push-off intensity than their peers–for example, walking with 11% less hip flexor power and 10% more trailing limb extension during push-off when exerting larger than preferred propulsive forces.

Conclusion

Propulsive force biofeedback that elicits larger than preferred propulsive forces also increases trailing limb extension and attenuates mechanical power demands at the hip in older adults most exhibiting a distal-to-proximal redistribution. Our results suggest that considering baseline redistribution may be important in the personalized prescription of interventions aimed at enhancing walking performance by improving push-off intensity.

Does dynamic stability govern propulsive force generation in human walking?

Before succumbing to slower speeds, older adults may walk with a diminished push-off to prioritize stability over mobility. However, direct evidence for trade-offs between push-off intensity and balance control in human walking, independent of changes in speed, has remained elusive. As a critical first step, we conducted two experiments to investigate: (i) the independent effects of walking speed and propulsive force (F_P) generation on dynamic stability in young adults, and (ii) the extent to which young adults prioritize dynamic stability in selecting their preferred combination of walking speed and F_P generation. Subjects walked on a force-measuring treadmill across a range of speeds as well as at constant speeds while modulating their F_P according to a visual biofeedback paradigm based on real-time force measurements. In contrast to improvements when walking slower, walking with a diminished push-off worsened dynamic stability by up to 32%. Rather, we find that young adults adopt an F_P at their preferred walking speed that maximizes dynamic stability. One implication of these findings is that the onset of a diminished push-off in old age may independently contribute to poorer balance control and precipitate slower walking speeds.