Shank Segments Research Articles

Effects of running skill and speed on limb coordination during submaximal and maximal sprinting

In locomotion, the relative phasing of the limbs changes with speed and provides valuable insight to neuromuscular control of gait. At present, it is unknown if individuals trained in sprinting coordinate their limbs differently than runners from other athletic backgrounds. Therefore, we aimed to characterize the effects of speed and skill on lower limb coordination. Twenty-five physically active (PA) and fifteen track and field (TF) athletes performed 40 m running trials at self-selected speeds, from jogging to maximal sprinting. We measured lower limb kinematics during steady-speed running, and quantified coordination using continuous relative phase (CRP) methods for interlimb pairs (Thigh-Thigh, Shank-Shank) and intralimb pairs (Shank-Thigh). Regression techniques showed between-group differences in scaling of coordination with speed during the stance phase, such that coordination was significantly more antiphase during jogging and running speeds in TF. During flight the scaling between groups was similar, but there were persistent and significant differences in coordination across all speeds. Comparing only the maximal speed trials, we found interlimb coordination was significantly more antiphase for TF in both stance and flight. In all cases, Shank-Shank coordination showed the largest between-group differences. Our results demonstrate the importance of interlimb coordination at maximal sprint speed, particularly during the flight phase and between shank segments. Between-group differences in coordination at slower speeds suggest a selective tuning of coordination in trained runners. We speculate differences in limb coordination are due to acquired motor patterns from optimizing forward velocity and its mechanical determinants, which differ particularly during flight/swing and between shank segments.

Sex differences in pelvis, thigh, and shank coordination during walking

Differences in lower limb kinematics between males and females during functional activities may be attributed to sex differences in the incidence of patellofemoral pain, which is more common in females. To better comprehend the knee joint motion, it is necessary to understand both inter-segmental coordination patterns and angular amplitude. This exploratory study aimed to assess sex differences in pelvis–thigh and thigh–shank coordination patterns in the frontal and horizontal planes during walking. Data regarding the kinematic characteristics of the pelvis, thigh, and shank segments were collected from 26 males and 26 females performing walking at self-selected speeds using a 3D motion capture system. Furthermore, we compared the kinematics of the pelvis, thigh, and shank during walking as well as the pelvis–thigh and thigh–shank coordination patterns in the frontal and horizontal planes during the stance phase between males and females. Compared to males, females had greater thigh adduction (p < 0.001) and internal rotation (p < 0.001) throughout the stance phase; significantly greater frequency of the pelvis–thigh anti-phase pattern in the frontal plane in the early (p = 0.002) and mid-stance (p = 0.003); and significantly greater thigh–shank anti-phase pattern in the frontal plane in the early (p = 0.001) and mid-stance (p = 0.015). These results suggest the presence of sex differences in the inter-segmental coordination of the pelvis and lower limb during walking. However, as this study could not determine a causal relationship between female sex and knee joint injury, further longitudinal studies are needed to determine the effects of differences in coordination patterns on the pathophysiology of the injury and pain generation.

Metabolic power response to added mass on the lower extremities during running

BackgroundWearable exoskeletal devices can enhance locomotor performance, but their mass results in a metabolic penalty. Previous studies have quantified the metabolic cost of running with added mass on the feet, but less is known about the effects of adding mass to the thigh and shank segments. AimTo quantify the metabolic cost of running with additional leg mass. Methods15 participants (7 F, 8 M) completed treadmill running trials (3 m/s) normally and with lead mass (300–1350 g) attached to either the thigh, shank, or foot, bilaterally. We measured metabolic power using expired gas analysis. ResultsPer 1000 g of added mass per leg, gross metabolic power increased by approximately 16% (foot) and 11% (shank) for females which was slightly greater than the 11% and 8% increases for males, respectively. For thigh loading, metabolic power increased by just 4% per 1000 g in both sexes. ConclusionAdding mass more distally on the leg increases the metabolic cost of running to a greater extent. For the same absolute added mass on the foot or shank, metabolic power increases more in females.

A Novel Classification of Coronal Plane Knee Joint Instability Using Nine-Axis Inertial Measurement Units in Patients with Medial Knee Osteoarthritis

The purpose of this study was to propose a novel classification of varus thrust based on gait analysis with inertial motion sensor units (IMUs) in patients with medial knee osteoarthritis (MKOA). We investigated thigh and shank acceleration using a nine-axis IMU in 69 knees with MKOA and 24 (control) knees. We classified varus thrust into four phenotypes according to the relative medial-lateral acceleration vector patterns of the thigh and shank segments: pattern A (thigh medial, shank medial), pattern B (medial, lateral), pattern C (lateral, medial), and pattern D (lateral, lateral). Quantitative varus thrust was calculated using an extended Kalman filter-based algorithm. We compared the differences between our proposed IMU classification and the Kellgren-Lawrence (KL) grades for quantitative varus thrust and visible varus thrust. Most of the varus thrust was not visually perceptible in early-stage OA. In advanced MKOA, increased proportions of patterns C and D with lateral thigh acceleration were observed. Quantitative varus thrust was significantly increased stepwise from patterns A to D. This novel IMU classification has better clinical utility due to its ability to detect subtle kinematic changes that cannot be captured with conventional motion analysis even in the early stage of MKOA.

Wand-mounted lateral markers are less prone to misplacement and soft-tissue artefacts than skin-mounted markers when using the conventional gait model

BackgroundThe conventional gait model (CGM1) is extensively used for 3D clinical gait analysis. It uses lateral wand-mounted markers for the thigh and shank segments to avoid colinearity of the tracking markers. However, gait analysts may be tempted to use skin-mounted markers instead. Research question:Does it matter if the lateral markers for the thigh and shank segments are mounted on wands or directly taped to the skin when using the CGM1? MethodsGait sessions from 147 and 73 patients equipped with wand-mounted and skin-mounted markers, respectively, were extracted from the database of a single clinical gait laboratory. The marker trajectories were reprocessed with the CGM1. The risk of marker colinearity was assessed from the planar angle constructed from the proximal joint center, the lateral joint marker and the lateral segmental marker (i.e. skin or wand). We assessed the effect of marker misplacement and soft-tissue artefact on kinematics. Results:The averaged planar angles calculated from static ranged from 10° to 30° and 7° to 21° for the skin-mounted thigh and shank markers respectively, while planar angles were always larger than 25° with wand-mounted markers. One cm misplacement of the thigh marker altered hip rotation by 10° if skin-mounted against 5° if wand-mounted. Soft tissue artefact led to 7.6° or 4.3° depending if it was skin- or wand-mounted, respectively. Significance:Our analysis showed moderate risk of collinearity, increased effect of STA, and larger potential effect of marker misplacement with the use of skin- rather than wand-mounted markers.

Relationships between kinematic characteristics and ratio of forces during initial sprint acceleration

ABSTRACT In track sprinting, acceleration performance is largely determined by the ability to generate a high ratio of forces (RF), but the technical features associated with this remain unknown. This study therefore investigated the relationships between selected kinematic characteristics and RF during the initial acceleration phase. Fourteen male sprinters completed two maximal 60 m sprints from a block start. Full-body kinematic and external kinetic data were obtained from the first four steps, and the relationships between selected kinematic characteristics and mean RF over the first four steps were determined. Placing the stance foot further behind (or less far in front of) the whole-body centre of mass at touchdown was significantly related to greater RF (r = −0.672), and more anterior orientation of the proximal end of the foot (r = −0.724) and shank (r = −0.764) segments at touchdown were also significantly related to greater RF. Following touchdown, greater ankle dorsiflexion range of motion during early stance was significantly related to greater RF (r = 0.728). When aiming to enhance RF during initial acceleration, practitioners should be encouraged to focus on lower leg configurations when manipulating touchdown distance, and the role of dorsiflexion during early stance is also an important consideration.

Thigh and Shank, Kinetic and Potential Energies during Gait Swing Phase in Healthy Adults and Stroke Survivors.

Background/Problem. Given the treatment-resistant gait deficits after stroke and known elevated energy cost of gait after stroke, it is important to study the patterns of mechanical energies of the lower limb segments. There is a dearth of information regarding mechanical energies specifically for the thigh and shank across the gait cycle. Therefore, the purpose of the current work was to characterize the following: (1) relative patterns of oscillation kinetic energy (KE) and potential energy (PE) within lower limb segments and across lower limb segments in healthy adults during the swing phase at chosen and slow gait speeds; (2) KE and PE swing phase patterns and values for stroke survivors versus healthy adults walking at slow speed; and (3) KE and PE patterns during the swing phase for two different compensatory gait strategies after stroke,. Methods. This was a gait characterization study, a two-group, parallel-cohort study of fourteen stroke survivors with gait deficits, walking at <0.4 m/s and eight adults with no gait deficits. For testing, the eight healthy adults walked at their chosen speed, and then at the imposed slow speed of <0.04 m/s. We used a standard motion capture system and calculation methods to acquire, calculate, and characterize oscillation patterns of KE and PE of the limb segments (thigh and shank) across the gait cycle. Results. In healthy adults, we identified key energy conservation mechanisms inherent in the interactions of KE and PE, both within the thigh and shank segments and across those limb segments, partially explaining the low cost of energy of the normal adult chosen speed gait pattern, and the underlying mechanism affording the known minimal set of activated muscles during walking, especially during the early swing phase. In contrast, KE was effectively absent for both healthy adults at imposed slow walking speed and stroke survivors at their very slow chosen speed, eliminating the normal conservation of energy between KE and PE within the thigh and across the thigh and shank. Moreover, and in comparison to healthy adult slow speed, stroke survivors exhibited greater abnormalities in mechanical energies patterns, reflected in either a compensatory stepping strategy (over-flexing the hip) or circumducting strategy (stiff-legged gait, with knee extended throughout the swing phase). Conclusions and contribution to the field. Taken together, these findings support targeted training to restore normal balance control and normal activation and de-activation coordination of hip, knee, and ankle muscles, respectively (agonist/antagonist at each joint), so as to eliminate the known post-stroke abnormal co-contractions; this motor training is critical in order to release the limb to swing normally in response to mechanical energies and afford the use of conservation of KE and PE energies within the thigh and across thigh and shank.

Lower extremity coordination and joint kinetic distribution during gait in adults with and without Prader-Willi Syndrome

Individuals with Prader-Willi Syndrome (PWS) have reduced mobility, which may be due to altered gait biomechanics. This study compared lower extremity intersegmental coordination and joint kinetics in adults with and without PWS. Walking biomechanics were evaluated in 10 adults with PWS and 10 controls without and 10 with obesity. The foot-shank and shank-thigh coordination was evaluated using modified vector coding and compared between groups using Kruskal-Wallis and Mann-Whitney U tests. The total support moment was summed from the ankle, knee, and hip extensor moments; and relative joint contributions were expressed as a percentage and compared between groups using one-way MANOVA. The group with PWS had greater exclusive shank segment rotation during later stance compared with controls with (p < 0.001) and without obesity (p < 0.001). The group with PWS also had a smaller absolute total support moment than controls with obesity during early and late stance (both p < 0.001), and lower normalized total support moment compared to controls without obesity during early stance (p = 0.019) and compared to controls with obesity during late stance (p = 0.004). Extensor moment contributions was similar between groups during early and late stance (all p > 0.05). Findings suggest a flat-footed gait pattern in PWS during late stance, which may negatively influence propulsion and speed. Moreover, those with PWS had lower total support moments than controls during early and late stance, but similar relative extensor contributions when walking at self-selected speeds. As such, improving overall torque generation in the lower extremity may be useful to improve stability and mobility during gait in PWS.

Passive double pendulum in the wake of a cylinder forced to rotate emulates a cyclic human walking gait

The goal of this work is to present a method based on fluid–structure interactions to enforce a desired trajectory on a passive double pendulum. In our experiments, the passive double pendulum represents human thigh and shank segments, and the interaction between the fluid and the structure comes from a hydrofoil attached to the double pendulum and interacting with the vortices that are shed from a cylinder placed upstream. When a cylinder is placed in flow, vortices are shed in the wake of the cylinder. When the cylinder is forced to rotate periodically, the frequency of the vortices that are shed in its wake can be controlled by controlling the frequency of cylinder’s rotation. These vortices exert periodic forces on any structure placed in the wake of this cylinder. In our system, we place a double pendulum fitted with a hydrofoil at its distal end in the wake of a rotating cylinder. The vortices exert periodic forces on this hydrofoil which then forces the double pendulum to oscillate. We control the cylinder to rotate periodically, and measure the displacement of the double pendulum. By comparing the joint positions of the double pendulum with those of human hip, knee and ankle joint positions during walking, we show how the system is able to generate a human walking gait cycle on the double pendulum only using the interactions between the vortices and the hydrofoil.

Effect of the foot-strike pattern on the sagittal plane knee kinetics and kinematics during the early phase of cutting movements

Anterior cruciate ligament (ACL) injury occurs soon after foot-strike. Cutting with a shallow flexed knee is considered a risk factor for ACL injury; however, how foot-strike patterns (forefoot strike [FFS] vs. rearfoot strike [RFS]) affect sagittal plane knee kinetics and kinematics after a foot-strike, is unknown. This study aimed to investigate the effect of foot-strike patterns on the sagittal plane knee kinetics and kinematics during cutting. Twenty-three males performed 45° cutting under RFS and FFS conditions. The marker position data on the lower limb, and the ground reaction force (GRF) data were collected and time-normalized (0–100%) during the stance phase. The knee flexion angle, shank and GRF vector inclination angle relative to the global vertical axis, knee flexion/extension moment, and anterior/posterior component of GRF relative to the shank segment were calculated and compared between foot-strike patterns using statistical parametric mapping paired t-test (p < 0.0071). The knee flexion angle was smaller in RFS than in FFS in the initial 40% of the stance phase. In the RFS condition, the GRF vector was directed anteriorly to the shank segment, and the knee extension moment was produced by GRF in 0–7% of the stance phase, while these results were not observed in the FFS condition. These results suggest that compared to FFS, RFS induces a shallow flexed knee with an anterior-directed GRF component in the early stance phase and might potentially provoke a risk of ACL injury.

Wearables-Only Analysis of Muscle and Joint Mechanics: An EMG-Driven Approach.

Complex sensor arrays prohibit practical deployment of existing wearables-based algorithms for free-living analysis of muscle and joint mechanics. Machine learning techniques have been proposed as a potential solution, however, they are less interpretable and generalizable when compared to physics-based techniques. Herein, we propose a hybrid method utilizing inertial sensor- and electromyography (EMG)-driven simulation of muscle contraction to characterize knee joint and muscle mechanics during walking gait. Machine learning is used only to map a subset of measured muscle excitations to a full set thereby reducing the number of required sensors. We demonstrate the utility of the approach for estimating net knee flexion moment (KFM) as well as individual muscle moment and work during the stance phase of gait across nine unimpaired subjects. Across all subjects, KFM was estimated with 0.91%BW•H RMSE and strong correlations (r = 0.87) compared to ground truth inverse dynamics analysis. Estimates of individual muscle moments were strongly correlated (r = 0.81-0.99) with a reference EMG-driven technique using optical motion capture and a full set of electrodes as were estimates of muscle work (r = 0.88-0.99). Implementation of the proposed technique in the current work included instrumenting only three muscles with surface electrodes (lateral and medial gastrocnemius and vastus medialis) and both the thigh and shank segments with inertial sensors. These sensor locations permit instrumentation of a knee brace/sleeve facilitating a practically deployable mechanism for monitoring muscle and joint mechanics with performance comparable to the current state-of-the-art.

Reliability of Measuring Leg Segments and Joint Angles Using Smartphones during Aquatic Exercise.

ObjectivesAquatic therapy is a significant intervention method for both patients and healthy individuals. However, in clinical practice, quantitative measurements are rarely applied in aquatic therapy due to the disadvantages of submerging expensive instruments in water. In this study, we used readily available smartphones and armbands to measure leg segments and joint angles during aquatic gait and evaluated the reliability of these measurements.MethodsWaterproof smartphones were strapped to the trunk, thighs, and shanks of 19 healthy young adults using armbands. The angles of the trunk, thigh, and shank segments were measured during aquatic gait. The measurements were repeated 1 day later. The data were analyzed to obtain the angles of the hip and knee joints.ResultsMeasurement repeatability, calculated using the intraclass correlation coefficient (ICC), was the highest for the shank segment range of motion (ROM) (first 46.79° ± 5.50°, second 50.12° ± 9.98°, ICC = 0.78). There was high agreement in trunk segment ROM (first 6.36° ± 1.42°, second 4.29° ± 1.83°, ICC = 0.73), thigh segment ROM (first 33.49° ± 5.18°, second 37.31° ± 8.70°, ICC = 0.62), and knee joint ROM (first 52.43° ± 11.26°, second 62.19° ± 16.65°, ICC = 0.68) and fair agreement in hip joint ROM (first 34.60°±4.71°, second 37.80° ± 7.84°, ICC = 0.59).ConclusionsSmartphones can be used to reliably measure leg segments and joint angles during aquatic gait, providing a simpler method for obtaining these measurements and enabling the wider use of aquatic motion analysis in clinical practice and research.

Calculated functional joint center positions are highly variable in individuals with unilateral transtibial amputation walking with identical prosthetic ankle-foot devices.

Biomechanical modeling of the lower limbs, including prosthetic componentry, makes a number of assumptions that influence the data obtained and their subsequent interpretation. Calculated prosthetic ankle functional joint center (FJC) positions vary between devices and have been suggested as a possible method of comparing device function. The study aimed to assess the variability of joint center position estimates, calculated using an FJC methodology, in all three planes. This was assessed in participants with unilateral transtibial amputation using an identical prosthetic ankle-foot device during walking on a flat surface. Case series. Three-dimensional motion capture recorded the position of markers placed on the shank and ankle-foot device of five individuals with unilateral transtibial amputation, as they completed 10 trials of level walking using the same ankle-foot device. The FJC between the prosthetic foot and shank segments were calculated for each trial. The calculated FJC positions were highly variable across individual participants and within each individual. This variability was observed across all three planes of movement and resulted in calculated joint center positions created beyond the physical boundaries of the prosthetic device. Biomechanical data are affected by lower limb and prosthetic device modeling assumptions. Definition of a prosthetic "ankle" joint using an FJC method results in highly variable "ankle" joint center positions when applied to a prosthetic ankle-foot device. Their use should be discouraged to avoid misleading interpretations of data.

Impact of scaling errors of the thigh and shank segments on musculoskeletal simulation results

Musculoskeletal simulations are widely used in the research community. The locations of surface markers are mostly used to scale a generic model to the participant's anthropometry. Marker-based scaling approaches include errors due to inaccuracies in marker placements. How do scaling errors of the thigh and shank segments influence simulation results? Motion capture data and magnetic resonance images from a child with cerebral palsy and a typically developing child were used to create a subject-specific reference model for each child. These reference models were modified to mimic scaling errors due to inaccurately placed lateral epicondyle markers, which are frequently used to scale the thigh and shank segments. The thigh length was altered in 1 % steps from the original length and the shank length was accordingly adjusted to keep the total leg length constant. Thirty additional models were created, which included models with an altered thigh length of ±15 %. Subsequently, musculoskeletal simulations with OpenSim were performed with all models. Joint kinematics, joint kinetics, muscle forces and joint contact forces (JCF) were compared between the reference and altered models. The investigated scaling error influenced joint kinematics and joint kinetics by up to 9.4° (hip flexion angle) and 0.15 Nm/kg (knee flexion moment), respectively. Maximum muscle and JCF differences of 46 % (medial gastrocnemius) and 72 % (hip JCF) bodyweight, respectively, were observed between the reference and altered models. Scaling errors mainly changed the magnitude but not the shape of most analyzed parameters. The influence of scaling errors on simulation results were similar in both participants. Scaling errors of the thigh segment influence simulation results at all joints due to the global optimization approach used in musculoskeletal simulations. Our findings can be used to estimate potential errors due to marker-based scaling approaches in previous and future studies.

Effect of Functional Electrical Stimulation of the Gluteus Medius during Gait in Patients following a Stroke.

Many stroke patients rely on cane or ankle-foot orthosis during gait rehabilitation. The purpose of this study was to investigate the immediate effect of functional electrical stimulation (FES) to the gluteus medius (GMed) and tibialis anterior (TA) on gait performance in stroke patients, including those who needed assistive devices. Fourteen stroke patients were enrolled in this study (mean poststroke duration: 194.9 ± 189.6 d; mean age: 72.8 ± 10.7 y). Participants walked 14 m at a comfortable velocity with and without FES to the GMed and TA. After an adaptation period, lower-limb motion was measured using magnetic inertial measurement units attached to the pelvis and the lower limb of the affected side. Motion range of angle of the affected thigh and shank segments in the sagittal plane, motion range of the affected hip and knee extension-flexion angle, step time, and stride time were calculated from inertial measurement units during the middle ten walking strides. Gait velocity, cadence, and stride length were also calculated. These gait indicators, both with and without FES, were compared. Gait velocity was significantly faster with FES (p = 0.035). Similarly, stride length and motion range of the shank of the affected side were significantly greater with FES (stride length: p = 0.018; motion range of the shank: p = 0.026). Meanwhile, cadence showed no significant difference (p = 0.238) in gait with or without FES. Similarly, range of motion of the affected hip joint, knee joint, and thigh did not differ significantly depending on FES condition (p = 0.115‐0.529). FES to the GMed and TA during gait produced an improvement in gait velocity, stride length, and motion range of the shank. Our results will allow therapists to use FES on stroke patients with varying conditions.

골볼 터닝 드로우 동작의 운동역학적 분석

The purpose of this study is to analyze the kinematics of the goal ball turning throwing motion, and the conclusions are as follows. First, the total time for goal ball turning and throwing motion was 1.82 s, 76.95 % in P1 and 23.02 % in P2. Second, it was found that the COM (center of mass) left and right displacement of the goalball turning throwing motion moved leftward from P1 (E1~E2) and moved to the right from P2 (E2~E3). COM forward and backwark displacement Moved to the forward according to the progress of the event. COM vertical displacement moved downward according to the progress of the event. Third, the COM left and right velocities of the goal ball turning throwing motion showed the fastest velocity from E3 to the right, and the COM forward and backward velocities showed the fastest speed from E2 to the forward. COM vertical velocity showed the fastest downward velocity at E2. Fourth, when the goal ball turning throwing motion was released, the velocity of the ball was 12.00±0.88 ㎧, and the stride width was 1.09±0.12 m. Fifth, the body segment’s angular momentum at the time of release of the goal ball turning throwing motion was found to be the largest in the trunk. And the upper arm, forearm, and hand segment of the upper limb all showed greater angular momentum than the left. In the case of the lower extremities, the right thigh and foot segments showed greater angular momentum than the left, but the left shank segment showed greater angular momentum than the right. Sixth, when the goal ball turning throwing motion was released, the ground reaction force of the forefoot showed the force in the right direction, the rear direction, and the vertical upward direction, and at this time, the large force was in the order of Fz, Fy, and Fx.

Classification Of Lower Limb Frontal Plane Excursion During Single-legged Landing Using Principal Component Analysis Of Inertia Sensor Data

PURPOSE: This study aimed to evaluate the temporal pattern of the frontal-plane lower limb translation during single-legged landing using the principal component analysis (PCA) of the inertial sensor data. METHODS: Eighteen legs from nine healthy women were tested. Participants performed a total of six single-legged landings for each leg. The wearable inertial sensor was fixed at the participant’s tibial tuberosity. The x-axis of the inertia sensor was aligned to the transverse axis of the shank segment, and the mediolateral acceleration of the proximal end of the shank segment was measured at 200Hz. The time window of interest was 0 to 75 ms after foot contact (15 data points). The acceleration data matrix (108 trials * 15 data point) from all trials of all participants was constructed for PCA. Eigenvalues and eigenvectors of the covariance matrix of the acceleration data matrix were calculated to identify the principal components (PC). RESULTS: The first two PCs explained more than 90% of total data variation (1st PC 69.7%, and 2nd PC 21.7%). The 1st PC represented the medially directed abrupt acceleration of the proximal shank, and the 2nd PC showed the slow but oscillated knee motion. The athlete of the highest PC score of the 1st PC showed a rapid medial knee motion just after foot impact, whereas the lowest one showed a stable knee motion after landing. CONCLUSIONS: PCA using acceleration signals successfully classified the degree of the medial knee translation after single-legged landing and screened the athletes who had a rapid medial knee translation. The abrupt increase of the medial knee translation has reported being a risk of non-contact anterior cruciate ligament (ACL) injury; therefore, the PCA based evaluation would be a useful technology for risk prediction of the non-contact ACL injury.

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.

Characteristics of Postural Muscle Activity in Response to A Motor-Motor Task in Elderly

The purpose of the current study was to evaluate postural muscle performance of older adults in response to a combination of two motor tasks perturbations. Fifteen older participants were instructed to perform a pushing task as an upper limb perturbation while standing on a fixed or sliding board as a lower limb perturbation. Postural responses were characterized by onsets and magnitudes of muscle activities as well as onsets of segment movements. The sliding board did not affect the onset timing and sequence of muscle initiations and segment movements. However, significant large muscle activities of tibialis anterior and erector spinae were observed in the sliding condition (p &lt; 0.05). The co-contraction values of the trunk and shank segments were significantly larger in the sliding condition through the studied periods (p &lt; 0.05). Lastly, heavy pushing weight did not change the timing, magnitude, sequence of all studied parameters. Older adults enhanced postural stability by increasing the segment stiffness then started to handle two perturbations. In conclusion, they were able to deal with a dual motor-motor task after having secured their balance but could not make corresponding adjustments to the level of the perturbation difficulty.

Stance and Swing Detection Based on the Angular Velocity of Lower Limb Segments During Walking

Lower limb exoskeletons require the correct support magnitude and timing to achieve user assistance. This study evaluated whether the sign of the angular velocity of lower limb segments can be used to determine the timing of the stance and the swing phase during walking. We assumed that stance phase is characterized by a positive, swing phase by a negative angular velocity. Thus, the transitions can be used to also identify heel-strike and toe-off. Thirteen subjects without gait impairments walked on a treadmill at speeds between 0.5 and 2.1 m/s on level ground and inclinations between −10 and +10°. Kinematic and kinetic data was measured simultaneously from an optical motion capture system, force plates, and five inertial measurement units (IMUs). These recordings were used to compute the angular velocities of four lower limb segments: two biological (thigh, shank) and two virtual that were geometrical projections of the biological segments (virtual leg, virtual extended leg). We analyzed the reliability (two sign changes of the angular velocity per stride) and the accuracy (offset in timing between sign change and ground reaction force based timing) of the virtual and biological segments for detecting the gait phases stance and swing. The motion capture data revealed that virtual limb segments seem superior to the biological limb segments in the reliability of stance and swing detection. However, increased signal noise when using the IMUs required additional rule sets for reliable stance and swing detection. With IMUs, the biological shank segment had the least variability in accuracy. The IMU-based heel-strike events of the shank and both virtual segment were slightly early (3.3–4.8% of the gait cycle) compared to the ground reaction force-based timing. Toe-off event timing showed more variability (9.0% too early to 7.3% too late) between the segments and changed with walking speed. The results show that the detection of the heel-strike, and thus stance phase, based on IMU angular velocity is possible for different segments when additional rule sets are included. Further work is required to improve the timing accuracy for the toe-off detection (swing).