Dual-belt Instrumented Treadmill Research Articles

Poster 217: Changes in Dynamic Hip Muscle Moment Arms During Activities of Daily Living

Objectives: Hip muscle function is affected by surgical intervention and is of particular concern when considering post-operative rehabilitation of the joint1. However, little is known about the dynamic, in vivo function of the hip muscles during activities of daily living. Marker-based motion capture studies have associated dysplastic hip anatomy with shorter abductor moment arm lengths during walking2, but these measurements are complicated by soft tissue artifact3. Biplane radiography is a highly accurate technique for measuring in vivo bone motion of the hip4 and has recently been utilized to estimate dynamic muscle moment arms, which are important factors influencing force and torque capabilities. Previous research studies utilizing biplane radiography have identified shorter muscle lengths and moment arms in the implanted hip compared to the contralateral hip of individuals with total hip arthroplasty during the double support phase of gait2, but normative in vivo moment arms of the hip musculature in asymptomatic individuals have yet to be established. Further, it remains unknown how moment arms change between activities of daily living, particularly during deep flexion activities that challenge hip stability. Developing a normative dataset of dynamic in vivo moment arm lengths would provide a valuable reference for clinicians and physical therapists developing rehabilitation protocols to strengthen the hip musculature and increase stability. The objective of this study was to determine in vivo moment arms of the hip abductors, adductors, and external rotators during gait and squatting in a cohort of asymptomatic adults. We hypothesized that the maximum moment arm length during squatting would be longer than during walking and static standing. Methods: Young adults with no history of hip surgery, chronic hip pathology, or severe lower extremity musculoskeletal injury were recruited to participate in this IRB-approved study. Participants performed bodyweight squats and treadmill walking within a biplane radiography system while ground reaction forces were collected at 1000 Hz from a dual-belt instrumented treadmill. The support phase of gait was defined by vertical ground reaction forces over 50 N. Synchronized biplane radiographs were collected at 50 images per second to image three trials of each hip for each activity. Subject-specific bone models of the pelvis and proximal femur were created from computed tomography (CT) scans (average 0.37x0.3 mm in-plane resolution, 0.625mm slice thickness). Coordinate systems5 and muscle origin and insertion points for the gluteus medius (hip abductor), gluteus minimus (hip abductor), pectineus (hip adductor), and grouped external rotators1 were identified based upon bony landmarks on the 3D bone models (Figure 1). In-vivo bone motion during each activity was determined by matching digitally reconstructed radiographs, created from the CT-based bone models, to the biplane radiographs using a registration process with a validated accuracy4 of 0.3mm. The line of action for each muscle segment was determined for each frame of the biplane radiographs as the vector from the muscle origin to the insertion. Moment arm length (MAL) was calculated for each frame of the dynamic biplane radiographs as the perpendicular distance between the hip joint center (acetabulum center) and the line of action of each muscle1 and interpolated to gait cycle for walking or percent maximum hip flexion during squatting. Differences between the maximum MAL during static standing, walking, and squatting were assessed within each muscle group using ANOVA with post-hoc pairwise comparisons performed as necessary. Results: Data from 186 trials of 43 hips from 22 individuals were included in the analysis (9M, 13F; mean age 22.0±2.2years; BMI 21.3±5.2kg/m2). Average walking velocity was 1.0±0.2m/s and the average maximum hip flexion during squatting was 101.6±16.1°. Average static standing MAL was greatest in the gluteus medius and smallest in the pectineus (Table 1). Maximum MAL was significantly different between all activities for all muscle groups (all p<0.001) (Table 1, Figure 2). Contrary to our hypothesis, moment arms of the abductors were smaller during squatting compared to other motions. Conclusions: This study demonstrates the in vivo torque generating capabilities of muscles surrounding the hip (reflected by their moment arm) change considerably from the standing position to positions encountered during active functional motions. Muscles involved in hip abduction and stabilization have less mechanical advantage at greater hip flexion, highlighting the importance of strengthening these muscle groups during rehabilitation. Specifically, moment arms of the hip abductors and external rotators are shorter during walking and squatting compared to standing, while moment arms of the adductors are shorter during walking and greater during squatting and standing. Knowledge of these postural changes in mechanical advantage can be useful when designing targeted rehabilitation protocols to strengthen the hip musculature and improve stability. Further research into relationships between dynamic in vivo hip muscle moment arms and lengths will yield additional insight into force and torque generating capacity of muscles during activities of daily living. These results are limited to treadmill walking and bodyweight squatting in asymptomatic young adults.

6MWT on a new self-paced treadmill system compared with overground

The 6-min walk test (6MWT) is a useful tool for clinicians and researchers to estimate gait performance and fatigue affecting functional mobility. A modified 6MWT administered on a treadmill (TM) can be an efficient, space-saving alternative to perform the 6MWT. The aim of this study was to investigate if a 6MWT on a self-paced (SP) TM produced similar results compared to an overground (OG) 6MWT among healthy participants with the hypothesis that users would demonstrate similar gait parameters. The second aim was to assess the reliability of SP TM sessions with the hypothesis that gait parameters would be reliable. Twelve healthy young adults performed one OG 6MWT and two SP TM 6MWTs, with the TM tests performed on two different testing days. The OG 6MWTs were conducted along a 20 m corridor with a portable optometric system. The SP TM 6MWTs were performed using a dual-belt instrumented TM with speed controlled by feedback from a LIDAR sensor. In the OG condition, participants walked 664.8 m ± 48.9 m when the standard method was used to calculate distance and 721.3 m ± 56.2 m with an average-speed-based estimation of distance, which corrects for U-turns. For the SP TM 6MWT, they covered 729.4 m ± 45.8 m in the first session and 727.4 m ± 56.0 m in the second session. Gait parameters showed good to excellent within- and between-day reliability on the adaptive TM. Gait parameters were similar between modalities. A significant difference in the 6MWT distance was found between modalities. This is attributable to the U-turns, because a comparison between TM 6MWT distance and the average-speed-based estimation of the distance for the OG modality showed no significant difference. However, this system produced similar spatiotemporal gait parameters among participants compared to OG.

Using a simple rope-pulley system that mechanically couples the arms, legs, and treadmill reduces the metabolic cost of walking

BackgroundEmphasizing the active use of the arms and coordinating them with the stepping motion of the legs may promote walking recovery in patients with impaired lower limb function. Yet, most approaches use seated devices to allow coupled arm and leg movements. To provide an option during treadmill walking, we designed a rope-pulley system that physically links the arms and legs. This arm-leg pulley system was grounded to the floor and made of commercially available slotted square tubing, solid strut channels, and low-friction pulleys that allowed us to use a rope to connect the subject’s wrist to the ipsilateral foot. This set-up was based on our idea that during walking the arm could generate an assistive force during arm swing retraction and, therefore, aid in leg swing.MethodsTo test this idea, we compared the mechanical, muscular, and metabolic effects between normal walking and walking with the arm-leg pulley system. We measured rope and ground reaction forces, electromyographic signals of key arm and leg muscles, and rates of metabolic energy consumption while healthy, young subjects walked at 1.25 m/s on a dual-belt instrumented treadmill (n = 8).ResultsWith our arm-leg pulley system, we found that an assistive force could be generated, reaching peak values of 7% body weight on average. Contrary to our expectation, the force mainly coincided with the propulsive phase of walking and not leg swing. Our findings suggest that subjects actively used their arms to harness the energy from the moving treadmill belt, which helped to propel the whole body via the arm-leg rope linkage. This effectively decreased the muscular and mechanical demands placed on the legs, reducing the propulsive impulse by 43% (p < 0.001), which led to a 17% net reduction in the metabolic power required for walking (p = 0.001).ConclusionsThese findings provide the biomechanical and energetic basis for how we might reimagine the use of the arms in gait rehabilitation, opening the opportunity to explore if such a method could help patients regain their walking ability.Trial registration: Study registered on 09/29/2018 in ClinicalTrials.gov (ID—NCT03689647).

Isolating the energetic and mechanical consequences of imposed reductions in ankle and knee flexion during gait

BackgroundWeakness of ankle and knee musculature following injury or disorder results in reduced joint motion associated with metabolically expensive gait compensations to enable limb support and advancement. However, neuromechanical coupling between the ankle and knee make it difficult to discern independent roles of these restrictions in joint motion on compensatory mechanics and metabolic penalties.MethodsWe sought to determine relative impacts of ankle and knee impairment on compensatory gait strategies and energetic outcomes using an unimpaired cohort (N = 15) with imposed unilateral joint range of motion restrictions as a surrogate for reduced motion resulting from gait pathology. Participants walked on a dual-belt instrumented treadmill at 0.8 m s−1 using a 3D printed ankle stay and a knee brace to systematically limit ankle motion (restricted-ank), knee motion (restricted-knee), and ankle and knee motion (restricted-a + k) simultaneously. In addition, participants walked without any ankle or knee bracing (control) and with knee bracing worn but unrestricted (braced).ResultsWhen ankle motion was restricted (restricted-ank, restricted-a + k) we observed decreased peak propulsion relative to the braced condition on the restricted limb. Reduced knee motion (restricted-knee, restricted-a + k) increased restricted limb circumduction relative to the restricted-ank condition through ipsilateral hip hiking. Interestingly, restricted limb average positive hip power increased in the restricted-ank condition but decreased in the restricted-a + k and restricted-knee conditions, suggesting that locking the knee impeded hip compensation. As expected, reduced ankle motion, either without (restricted-ank) or in addition to knee restriction (restricted-a + k) yielded significant increase in net metabolic rate when compared with the braced condition. Furthermore, the relative increase in metabolic cost was significantly larger with restricted-a + k when compared to restricted-knee condition.ConclusionsOur methods allowed for the reproduction of asymmetric gait characteristics including reduced propulsive symmetry and increased circumduction. The metabolic consequences bolster the potential energetic benefit of targeting ankle function during rehabilitation.Trial registrationN/A.

High day-to-day repeatability of lower extremity muscle activation patterns and joint biomechanics of dual-belt treadmill gait: A reliability study in healthy young adults

PurposeThe reliability of lower extremity muscle activation patterns has not been clearly studied in a dual-belt instrumented treadmill environment. The primary study objective was to quantify the day-to-day reliability of quadriceps, hamstrings, gastrocnemius and gluteus medius activation patterns in healthy young adult gait. Secondarily, the reliability of spatiotemporal, and knee/hip motion and moment-based gait outcomes was assessed.Scope: 20 young adults were recruited and tested on two separate days. Using standardized procedures, participants were prepared for surface electromyography and lower extremity motion capture. All individuals walked on a dual-belt instrumented treadmill while muscle activation, segment motions and ground reaction forces were recorded. Sagittal plane motion and net external sagittal and frontal plane moments were calculated. Discrete biomechanical and muscle activation measures were calculated, and non-negative matrix factorization extracted amplitude and temporal muscle activation features. Intraclass Correlation Coefficients, Standard Error of Measurement and Minimum Detectable Change were calculated. ConclusionsHigh to excellent Intraclass correlation coefficients were found between visits for most primary and secondary outcomes. The absolute and relative reliability, including Minimum Detectable Change values, provided in this study support the use of dual-belt instrumented treadmill walking as an acceptable medium to collect biomechanical and lower extremity EMG outcomes for future studies.

Walking challenges in moderate knee osteoarthritis: A biomechanical and neuromuscular response to medial walkway surface translations

Sensations of knee instability are self-reported in 60–80% of individuals with knee osteoarthritis. These sensations are most often reported during walking; however, it remains unclear how they affect knee joint biomechanics and muscle activation patterns as indicators of joint function. Perturbation paradigms may provide insight into how the knee joint responds to walking challenges. Thus, the purpose of this study was to determine how individuals with moderate medial compartment knee osteoarthritis respond to unexpected, 3 cm medial walkway surface translations during gait compared to an asymptomatic control group. It is hypothesized that individuals with knee osteoarthritis will demonstrate altered biomechanics, and elevated and prolonged muscle activation compared to the asymptomatic group. Twenty asymptomatic individuals and 20 individuals with knee osteoarthritis walked on a dual-belt instrumented treadmill. Participants experienced 24 unexpected medial/lateral, 1 cm/3 cm walkway translations during mid-stance on each leg. Joint motions, moments and maximal voluntary isometric contraction amplitude normalized muscle activations were analyzed for the 3 cm walkway translations. Discrete measures were extracted from each biomechanical waveform and Principal Component Analysis (PCA) was used to determine knee joint muscle activation patterns. PCA is a factorization method to reduce dimensionality of EMG envelopes into linearly uncorrelated principal patterns (PP1, PP2, PP3) that explain the largest possible variance in the dataset. PP1 is often interpreted as a feature that explains the overall amplitude, while PP2 and PP3 are features that explain the variance in temporal activation patterns (i.e. how activation patterns change over the gait cycle). Statistical significance was determined using Analysis of Covariance models (alpha = 0.05). In response to the medial 3 cm walkway translation, increased activation amplitudes in the hamstring and gastrocnemius, captured by PP1 were found in both groups, as well as alterations in temporal activation patterns (captured by combinations of PP2 and PP3 patterns) across all muscle sites (p < 0.05). No group differences were demonstrated in joint motion and moment discrete metrics (p > 0.05) in response to the 3 cm translation. These findings suggest that the medial 3 cm walkway translation posed a challenged to knee function, however the biomechanical and neuromuscular response was similar between individuals with moderate knee osteoarthritis and asymptomatic individuals.

Gait in patients with symptomatic osteoporotic vertebral compression fractures over 6\xa0months of recovery

BackgroundOne factor related to disability in people with spinal deformity is decreased postural control and increased risk of falling. However, little is known about the effect of osteoporotic vertebral compression fractures (OVCFs) and their recovery on gait and stability. Walking characteristics of older adults with and without vertebral fractures have not yet been compared.AimsThe purpose of the current study was to examine the spatiotemporal gait parameters and their variability in patients with an OVCF and healthy participants during treadmill walking at baseline and after 6 months of recovery.MethodsTwelve female patients suffering a symptomatic OVCF were compared to 11 matched controls. Gait analysis was performed with a dual-belt instrumented treadmill with a 180° projection screen providing a virtual environment (computer-assisted rehabilitation environment). Results of patients with an OVCF and healthy participants were compared. Furthermore, spatiotemporal gait parameters were assessed over 6 months following the fracture.ResultsPatients suffering from an OVCF appeared to walk with significantly shorter, faster and wider strides compared to their healthy counterparts. Although stride time and length improved over time, the majority of the parameters analysed remained unchanged after 6 months of conservative treatment.DiscussionSince patients do not fully recover to their previous level of mobility after 6 months of conservative treatment for OVCF, it appears of high clinical importance to add balance and gait training to the treatment algorithm of OVCFs.ConclusionsPatients suffering from an OVCF walk with shorter, faster and wider strides compared to their healthy counterparts adopt a less stable body configuration in the anterior direction, potentially increasing their risk of forward falls if perturbed. Although stride time and stride length improve over time even reaching healthy levels again, patients significantly deviate from normal gait patterns (e.g. in stability and step width) after 6 months of conservative treatment.

Effect of a semirigid thoracolumbar orthosis on gait and sagittal alignment in patients with an osteoporotic vertebral compression fracture.

BackgroundAn important goal in the treatment of osteoporotic vertebral compression fractures (OVCFs) is the prevention of new vertebral fractures and the subsequent progression to global sagittal malalignment. Current conservative treatment is multimodal and comprises analgesics, medication for osteoporosis, and physical therapy. However, little is known about the value of orthoses in the treatment of OVCFs.AimsThe primary purpose of this study was to examine the direct effect of a semirigid thoracolumbar orthosis on gait in patients suffering from an OVCF. The secondary purpose was to evaluate changes in gait, radiographic sagittal alignment, pain, and quality of life over time.MethodsFifteen postmenopausal patients with an OVCF were treated with a semirigid thoracolumbar orthosis. At baseline, after 6 weeks, and after 6 months, gait analysis was performed with a dual belt–instrumented treadmill with a 180° projection screen providing a virtual environment (computer-assisted rehabilitation environment) combined with clinical and radiographic assessments.ResultsAt baseline, bracing caused a significantly more upright posture during walking and patients walked faster, with larger strides, longer stride times, and lower cadence compared to walking without orthosis. After 6 weeks, radiographic and dynamic sagittal alignment had improved compared to baseline. The observed effect was gone after 6 months, when the orthosis was not worn anymore.ConclusionA semirigid thoracolumbar orthosis seems to have a positive effect on gait and stability in patients suffering from an OVCF, as was shown by a more upright posture, which may result in decreased compressive loading of the vertebrae. For studying the true effectiveness of dynamic bracing in the treatment of OVCFs, a prospective, randomized controlled trial will be needed.

Differences in Hip Joint Biomechanics and Muscle Activation in Individuals With Femoroacetabular Impingement Compared With Healthy, Asymptomatic Individuals: Is Level-Ground Gait Analysis Enough?

Background:Femoroacetabular impingement (FAI) is a recognized cause of hip and groin pain and a significant factor in hip joint function during sport. Objective tests for understanding hip function are lacking in this population.Purpose:To determine whether biomechanical and electromyographic features of hip function during level-ground walking differ between a group diagnosed with FAI and those with no symptoms of FAI.Study Design:Controlled laboratory study.Methods:A total of 20 asymptomatic individuals and 20 individuals with FAI walked on a dual-belt instrumented treadmill at self-selected walking velocities. Sagittal and frontal plane joint motions, moments, and muscle activation for the gluteus medius, gluteus maximus, rectus femoris, and medial and lateral hamstrings were analyzed. Discrete measures were extracted from each biomechanical waveform, and principal component analysis was used to determine hip joint muscle activation and hip adduction moment patterns. Statistical significance was determined by use of Student t tests with Bonferroni adjustments for multiple comparisons (α = .05).Results:Individuals with FAI walked more slowly (P = .015) and had lower self-reported function (P < .001). No differences in muscle strength were found between the symptomatic and contralateral legs in the FAI group (P > .017), but those with FAI had lower strength in the knee extensors and flexors and the hip extensors, flexors, and adductors compared with the asymptomatic group (P < .017). Individuals with unilateral symptomatic FAI walked with similar biomechanical and hip muscle electromyographic results bilaterally. The only differences found were a greater amplitude of gluteus maximus activation in the FAI symptomatic leg compared with the asymptomatic group and greater medial hamstring activation than lateral hamstring activation in the FAI group in both limbs compared with the asymptomatic group.Conclusion:Individuals with FAI were generally deconditioned and reported significantly more functional limitations. No biomechanical differences existed between groups during level walking, yet hamstring and gluteus maximus activation differed when the symptomatic group was compared with the asymptomatic group.Clinical Relevance:The field lacks objective testing of hip joint function to understand implications of FAI for dynamic movements, particularly with applications to biomechanics and electromyography. Level walking was of limited value for understanding FAI hip function, and the development of a more challenging gait assessment is warranted.

The effect of knee joint effusion on gait mechanics and muscle activations in individuals with moderate knee osteoarthritis

Purpose: Knee osteoarthritis (OA) is the most common joint disease and is often characterized by pain, stiffness, swelling and limited tolerance to weight-bearing activities. It has been shown to be associated with biological inflammatory processes in the synovium, synovitis, and mechanical insults that lead to the deterioration of the joint structures. Synovitis is usually characterized by knee joint swelling and the mechanical knee joint environment during a loading stimulus can be studied in vivo using state-of-the-art gait analyses. The study objective is to compare knee mechanics and muscle activation patterns during gait in individuals with knee OA who have and do not have knee joint swelling. Methods: 45 patients diagnosed with moderate medial compartment knee OA were recruited. Knee swelling was measured at three locations (mid, medial, lateral) of the supra-patellar recess (SRD) using ultrasound imaging. A maximum depth, regardless of the location was determined. Effusion presence was defined as a SRD depth >4 mm. Knee joint motion was calculated from skin markers and net external moments calculated through inverse dynamics during walking on a dual-belt instrumented treadmill at self-selected speed. Electromyography (EMG) from vastus medialis (VM) and lateralis (VL), medial (MH) and lateral hamstrings (LH), medial (MG) and lateral gastrocnemius (LG) was recorded using standardized procedures. Two-sample unpaired t-tests were used to test for significant differences in sagittal plane knee joint angles, sagittal and frontal external moments, pain, Knee Osteoarthritis Outcome Scores, age, body mass index, stride characteristics, and knee extensor and flexor strength. Principal component analysis (PCA) was performed on the EMG waveforms to capture amplitude and temporal based features. Principal Pattern (PP)-scores were calculated from principal patterns that together explained >90% of the waveform variability. Two-way mixed-model Analysis of Variance models were performed on the PP-scores to identify muscle, group and interaction effects. Bonferroni corrected pairwise post-hoc comparisons were made. A P-value of 0.05 was used to determine statistical significance. Results: Of the 45 participants, 25 had effusion (SRD > 4mm). No significant differences were found between groups in subject demographic and anthropometrics, questionnaire outcomes, and knee strength (P > 0.05). Both groups had a similar radiographic grade distribution. No biomechanical differences existed between both groups, however the effusion group had greater overall amplitudes of VM and VL (PP1-scores) and greater early stance activation of the gastrocnemius muscles (PP2-scores). No other group differences or group by muscle interactions existed. Conclusions: These results, as shown in Figure 1, indicate that specific amplitude knee joint muscle activation patterns are altered in the presence of knee effusion during gait in individuals with knee OA. Greater stance phase amplitudes in the quadriceps and gastrocnemius muscles are consistent with responses aimed at providing neuromuscular knee joint support and increasing early stance active stiffness, respectively, in order to preserve knee function when effusion is present. These muscular adaptations have been previously reported with increased OA severity suggesting a possible link between gait mechanics and knee swelling as knee OA progresses. The 4 mm SRD threshold has previously been linked to a higher risk of knee OA progression, supporting findings of this study. Future studies can investigate different cut-off values for the detection of effusion sonographically to establish whether biomechanical subgroups may exist.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Technical Aspects and Validation of a New Biofeedback System for Measuring Lower Limb Loading in the Dynamic Situation.

Background: A variety of techniques for measuring lower limb loading exists, each with their own limitations. A new ambulatory biofeedback system was developed to overcome these limitations. In this study, we described the technical aspects and validated the accuracy of this system. Methods: A bench press was used to validate the system in the static situation. Ten healthy volunteers were measured by the new biofeedback system and a dual-belt instrumented treadmill to validate the system in the dynamic situation. Results: Bench press results showed that the sensor accurately measured peak loads up to 1000 N in the static situation. In the healthy volunteers, the load curves measured by the biofeedback system were similar to the treadmill. However, the peak loads and loading rates were lower in the biofeedback system in all participants at all speeds. Conclusions: Advanced sensor technologies used in the new biofeedback system resulted in highly accurate measurements in the static situation. The position of the sensor and the design of the biofeedback system should be optimized to improve results in the dynamic situation.

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

Walking speed is modulated using propulsive forces (FP) during push-off and both preferred speed and FP decrease with aging. However, even prior to walking slower, reduced FP may be accompanied by potentially unfavorable changes in joint power generation. For example, compared to young adults, older adults exhibit a redistribution of mechanical power generation from the propulsive plantarflexor muscles to more proximal muscles acting across the knee and hip. Here, we used visual biofeedback based on real-time FP measurements to decouple and investigate the interaction between joint-level coordination, whole-body FP, and walking speed. 12 healthy young subjects walked on a dual-belt instrumented treadmill at a range of speeds (0.9–1.3m/s). We immediately calculated the average FP from each speed. Subjects then walked at 1.3m/s while completing a series of biofeedback trials with instructions to match their instantaneous FP to their averaged FP from slower speeds. Walking slower decreased FP and total positive joint work with little effect on relative joint-level contributions. Conversely, subjects walked at a constant speed with reduced FP, not by reducing total positive joint work, but by redistributing the mechanical demands of each step from the plantarflexor muscles during push-off to more proximal leg muscles during single support. Interestingly, these naturally emergent joint- and limb-level biomechanical changes, in the absence of neuromuscular constraints, resemble those due to aging. Our findings provide important reference data to understand the presumably complex interactions between joint power generation, whole-body FP, and walking speed in our aging population.

Estimating pushrim temporal and kinetic measures using an instrumented treadmill during wheelchair propulsion: A concurrent validity study

Using ground reaction forces recorded while propelling a manual wheelchair on an instrumented treadmill may represent a valuable alternative to using an instrumented pushrim to calculate temporal and kinetic parameters during propulsion. Sixteen manual wheelchair users propelled their wheelchair equipped with instrumented pushrims (i.e., SMARTWheel) on an instrumented dual-belt treadmill set a 1m/s during a 1-minute period. Spatio-temporal (i.e., duration of the push and recovery phase) and kinetic measures (i.e. propulsive moments) were calculated for 20 consecutive strokes for each participant. Strong associations were confirmed between the treadmill and the instrumented pushrim for the mean duration of the push phase (r=0.98) and of the recovery phase (r=0.99). Good agreement between these two measurement instruments was also confirmed with mean differences of only 0.028s for the push phase and 0.012s for the recovery phase. Strong associations were confirmed between the instrumented wheelchair pushrim and treadmill for mean (r=0.97) and peak (r=0.96) propulsive moments. Good agreement between these two measurement instruments was also confirmed with mean differences of 0.50Nm (mean moment) and 0.71Nm (peak moment). The use of a dual-belt instrumented treadmill represents an alternative to characterizing temporal parameters and propulsive moments during manual wheelchair propulsion.

Biomechanical gait characteristics of naturally occurring unsuccessful foot clearance during swing in individuals with chronic stroke

BackgroundAltered gait mechanics are common following stroke and may increase the risk of falls. Paretic gait impairments have been previously compared to the non-paretic limb or control participants. Unfortunately, the biomechanical parameters underlying instances of naturally occurring unsuccessful foot clearance (trips) have yet to be examined in individuals with chronic stroke. MethodsGait data from 26 participants with chronic stroke were obtained on a dual-belt instrumented treadmill. Instances of successful and unsuccessful foot swing were identified. Temporal, kinematic, and kinetic measures of the paretic limb occurring during late stance, toe-off, and swing were compared between trip and non-trip steps using paired samples t-tests. An α=0.004 was used to adjust for multiple comparisons. FindingsIn the paretic limb, the ankle angle at toe off (P=0.003; d=0.64), knee flexion velocity at toe off (P<0.001; d=0.73), and peak knee extension moment during terminal stance (P<0.001; d=0.74) were significantly different between trips and non-trip steps. During trip steps, ankle plantarflexion at toe-off was 1.0° greater, knee flexion velocity was reduced by 17.6°/sec, and peak knee extension moment was increased by 0.011Nm/kg·m compared to non-trip steps. InterpretationIt appears to take only minor changes in the movement of the paretic limb to result in a trip in individuals with chronic stroke. Although small, the multi-joint biomechanical changes occurring in the paretic limb during unsuccessful foot clearance result in a functionally longer limb. Thus, interventions targeting multiple joints in the paretic limb may be needed to reduce the risk of trips following stroke.

Energy exchange between subject and belt during treadmill walking

Treadmill walking aims to simulate overground walking, but intra-stride belt speed variations of treadmills result in some interaction between treadmill and subject, possibly obstructing this aim. Especially in self-paced treadmill walking, in which the belt speed constantly adjusts to the subject, these interactions might affect the gait pattern significantly. The aim of this study was to quantify the energy exchange between subject and treadmill, during the fixed speed (FS) and self-paced (SP) modes of treadmill walking. Eighteen subjects walked on a dual-belt instrumented treadmill at both modes. The energy exchange was calculated as the integration of the product of the belt speed deviation and the fore-aft ground reaction force over the stride cycle. The total positive energy exchange was 0.44J/stride and the negative exchange was 0.11J/stride, which was both less than 1.6% of the performed work on the center of mass. Energy was mainly exchanged from subject to treadmill during both the braking and propulsive phase of gait. The two treadmill modes showed a similar pattern of energy exchange, with a slightly increased energy exchange during the braking phase of SP walking. It is concluded that treadmill walking is only mildly disturbed by subject-belt interactions when using instrumented treadmills with adequate belt control.

Effects of adding a virtual reality environment to different modes of treadmill walking

Differences in gait between overground and treadmill walking are suggested to result from imposed treadmill speed and lack of visual flow. To counteract this effect, feedback-controlled treadmills that allow the subject to control the belt speed along with an immersive virtual reality (VR) have recently been developed. We studied the effect of adding a VR during both fixed speed (FS) and self-paced (SP) treadmill walking. Nineteen subjects walked on a dual-belt instrumented treadmill with a simple endless road projected on a 180° circular screen. A main effect of VR was found for hip flexion offset, peak hip extension, peak knee extension moment, knee flexion moment gain and ankle power during push off. A consistent interaction effect between VR and treadmill mode was found for 12 out of 30 parameters, although the differences were small and did not exceed 50% of the within subject stride variance. At FS, the VR seemed to slightly improve the walking pattern towards overground walking, with for example a 6.5mm increase in stride length. At SP, gait became slightly more cautious by adding a VR, with a 9.1mm decrease in stride length. Irrespective of treadmill mode, subjects rated walking with the VR as more similar to overground walking. In the context of clinical gait analysis, the effects of VR are too small to be relevant and are outweighed by the gains of adding a VR, such as a more stimulating experience and possibility of augmenting it by real-time feedback.

A comparison of slow, uphill and fast, level walking on lower extremity biomechanics and tibiofemoral joint loading in obese and nonobese adults

We determined if slow, uphill walking (0.75 m/s, 6°) reduced tibiofemoral (TF) loading compared to faster, level walking (1.50 m/s) in obese and nonobese adults. We collected kinematic, kinetic, and electromyographic data as 9 moderately obese and 10 nonobese participants walked on a dual-belt instrumented treadmill. We used OpenSim to scale a musculoskeletal model and calculate joint kinematics, kinetics, muscle forces, and TF forces. Compressive TF forces were greater in the obese adults during both speed/grade combinations. During level walking, obese participants walked with a straighter leg than nonobese participants, resulting in early stance vasti muscle forces that were similar in the obese and nonobese participants. Early stance peak compressive TF forces were reduced by 23% in obese (2,352 to 1,811 N) and 35% in nonobese (1,994 to 1,303 N) individuals during slow, uphill walking compared to brisk level walking. Late stance peak TF forces were similar across speeds/grades, but were greater in obese (∼2,900 N) compared to nonobese (∼1,700 N) individuals. Smaller early stance TF loads and loading rates suggest that slow, uphill walking may be appropriate exercise for obese individuals at risk for musculoskeletal pathology or pain.

Self-paced versus fixed speed treadmill walking

Instrumented treadmills are increasingly used in gait research, although the imposed walking speed is suggested to affect gait performance. A feedback-controlled treadmill that allows subjects to walk at their preferred speed, i.e. functioning in a self-paced (SP) mode, might be an attractive alternative, but could disturb gait through accelerations of the belt. We compared SP with fixed speed (FS) treadmill walking, and also considered various feedback modes. Nineteen healthy subjects walked on a dual-belt instrumented treadmill. Spatio-temporal, kinematic and kinetic gait parameters were derived from both the average stride patterns and stride-to-stride variability. For 15 out of 70 parameters significant differences were found between SP and FS. These differences were smaller than 1cm, 1°, 0.2Nm and 0.2W/kg for respectively stride length and width, joint kinematics, moments and powers. Since this is well within the normal stride variability, these differences were not considered to be clinically relevant, indicating that SP walking is not notably affected by belt accelerations. The long-term components of walking speed variability increased during SP walking (43%, p<0.01), suggesting that SP allows for more natural stride variability. Differences between SP feedback modes were predominantly found in the timescales of walking speed variability, while the gait pattern was similar between modes. Overall, the lack of clinically significant differences in gait pattern suggests that SP walking is a suitable alternative to fixed speed treadmill walking in gait analysis.

The influence of a unilateral fixed ankle on metabolic and mechanical demands during walking in unimpaired young adults

The plantarflexors provide a major source of propulsion during walking. When mechanical power generation from the plantarflexor muscles is limited, other joints may compensate to maintain a consistent walking velocity, but likely at increased metabolic cost. The purpose of this study was to determine how a unilateral reduction in ankle plantarflexor power influences the redistribution of mechanical power generation within and across limbs and the associated change in the metabolic cost of walking. Twelve unimpaired young adults walked with an ankle brace on the dominant limb at 1.2m/s on a dual-belt instrumented treadmill. Lower extremity kinematics and kinetics as well as gas exchange data were collected in two conditions: (1) with the brace unlocked (FREE) and (2) with the brace locked (FIXED). The brace significantly reduced ankle plantarflexion excursion by 12.96±3.60° (p<0.001) and peak ankle mechanical power by 1.03±0.51W/kg (p<0.001) in the FIXED versus FREE condition. Consequently, metabolic power (W/kg) of walking in the FIXED condition increased by 7.4% compared to the FREE condition (p=0.03). Increased bilateral hip mechanical power generation was observed in the FIXED condition (p<0.001). These results suggest that walking with reduced ankle power increases metabolic demand due to the redistribution of mechanical power generation from highly efficient ankle muscle-tendons to less efficient hip muscle-tendons. A within and across limb redistribution of mechanical workload represents a potential mechanism for increased metabolic demand in pathological populations with plantarflexion deficits or those that walk with an ankle–foot orthosis that restricts range of motion.

Analysis of muscle activity during gait cycle using fuzzy rule-based reasoning

The purpose of this study was to determine the patterns of muscle activation as outcome measures of the ground reaction forces during normal walking tasks using optical motion analysis capture system, instrumented treadmill and electromyography (EMG), respectively. The recognition of the muscle patterns during gait dynamics offers insight into the control of skeletal position, joint stiffness, vibrations of the soft tissue packages, stability during ground contact, and propulsion for the movement task. Sixteen able-bodied participants were recruited to walk on a dual-belt instrumented treadmill with embedded force plates. A fuzzy rule-based reasoning algorithm for recognizing the activation patterns of the lower extremity muscles during normal walking maneuvers within the seven gait phases was developed. The resulting recognition will enable the determination of alterations in the locomotor control system, contribute to suggest symptoms of a neurological disease, disease severity, and also indications of improvements in response to therapeutic interventions.