Determining the centre of pressure during walking and running using an instrumented treadmill

In this paper, a new method of determining spatial and temporal gait parameters by using centre of pressure (CoP) data is presented. A treadmill is used which was developed to overcome limitations of regular methods for the analysis of spatio-temporal gait parameters and ground reaction forces during walking and running. The design of the treadmill is based on the use of force transducers underneath a separate left and right plate, which together form the treadmill walking surface. The results of test procedures and measurements show that accurate recordings of vertical ground reaction force can be obtained. These recordings enable a separate analysis of vertical ground reaction forces during double support phases in walking, and the analysis of changes in the centre of pressure (CoP) position during subsequent foot placements. From the CoP data, temporal gait parameters (e.g. duration of left/right support and swing phases) and spatial gait parameters (i.e. left/right step lengths and widths) can be derived.     

A cycle ergometer mounted on a standard force platform for three-dimensional pedal forces measurement during cycling

This report describes a new method allowing to measure the three-dimensional forces applied on right and left pedals during cycling. This method is based on a cycle ergometer mounted on a force platform. By recording the forces applied on the force platform and applying the fundamental mechanical equations, it was possible to calculate the instantaneous three-dimensional forces applied on pedals. It was validated by static and dynamic tests. The accuracy of the present system was -7.61 N, -3.37 N and -2.81 N, respectively, for the vertical, the horizontal and the lateral direction when applying a mono-directional force and -4.52 N when applying combined forces. In pedaling condition, the orientation and magnitude of the pedal forces were comparable to the literature. Moreover, this method did not modify the mechanical properties of the pedals and offered the possibility for pedal force measurement with materials often accessible in laboratories. Measurements obtained showed that this method has an interesting potential for biomechanical analyses in cycling.     

A comparison of the oxygen consumption/body weight relationship obtained during submaximal exercise on a bicycle ergometer and on a treadmill.

It is widely accepted that the relationship between oxygen consumption and body weight obtained during exercise on a bicycle ergometer differs from that obtained during treadmill walking. Experimental evidence to support this claim is lacking. To examine this difference a group of subjects (body weight 41--81 kg) undertook a predetermined level of submaximal exercise on a bicycle ergometer and a treadmill. Oxygen consumption was measured in a steady state at rest (i.e. sitting on the bicycle ergometer and standing on the treadmill) and during the two modes of exercise. A significant positive correlation between oxygen consumption and body weight was obtained under all four conditions of measurement. At rest the two regression lines did not differ in slope or elevation. During exercise the slope and the elevation of the line obtain from treadmill walking were significantly greater than from bicycle ergometer exercise. The 'metabolic cost' of bicycle ergometer exercise, (Vo2 during exercise--V02 at rest), showed no significant correlation with body weight. In contrast, there was a significant positive correlation during walking. It is suggested that these differences have arisen due to a different proportion of the total body weight supported by the subject in the two forms of exercise.     

Human-Robot Interaction: Does Robotic Guidance Force Affect Gait-Related Brain Dynamics during Robot-Assisted Treadmill Walking?

In order to determine optimal training parameters for robot-assisted treadmill walking, it is essential to understand how a robotic device interacts with its wearer, and thus, how parameter settings of the device affect locomotor control. The aim of this study was to assess the effect of different levels of guidance force during robot-assisted treadmill walking on cortical activity. Eighteen healthy subjects walked at 2 km.h^-1 on a treadmill with and without assistance of the Lokomat robotic gait orthosis. Event-related spectral perturbations and changes in power spectral density were investigated during unassisted treadmill walking as well as during robot-assisted treadmill walking at 30%, 60% and 100% guidance force (with 0% body weight support). Clustering of independent components revealed three clusters of activity in the sensorimotor cortex during treadmill walking and robot-assisted treadmill walking in healthy subjects. These clusters demonstrated gait-related spectral modulations in the mu, beta and low gamma bands over the sensorimotor cortex related to specific phases of the gait cycle. Moreover, mu and beta rhythms were suppressed in the right primary sensory cortex during treadmill walking compared to robot-assisted treadmill walking with 100% guidance force, indicating significantly larger involvement of the sensorimotor area during treadmill walking compared to robot-assisted treadmill walking. Only marginal differences in the spectral power of the mu, beta and low gamma bands could be identified between robot-assisted treadmill walking with different levels of guidance force. From these results it can be concluded that a high level of guidance force (i.e., 100% guidance force) and thus a less active participation during locomotion should be avoided during robot-assisted treadmill walking. This will optimize the involvement of the sensorimotor cortex which is known to be crucial for motor learning.     

Responses of the lower limb to load carrying in walking man

Muscle activity patterns of several lower limb muscles were examined in the left leg of normal human subjects walking at comfortable speed on a treadmill. In addition knee angular changes and the durations of the swing and stance phases of the step cycle were recorded. Data were collected during a period of normal control walking and when the subject carried a load, either in his right or left hand or on his back. Load (up to 20% of body weight) carried in either hand caused minimal changes in the kinematic parameters investigated but evoked significant prolongation of the normal ongoing electromyographic activity in the contralateral Gluteus medius and in the ipsilateral Gastrocnemius, Vastus lateralis and Semimembranosus. Load (up to 50% of body weight) carried on the back significantly shortened the swing phase and prolonged the ongoing electromyographic activity of the Vastus lateralis. These findings would seem to indicate that the activity of the leg musculature during walking is so tightly controlled that deviation from the normal kinematic pattern of the legs is largely prevented even when body posture and balance are disturbed by carrying substantial additional load.     

Repeatability of 3D gait kinematics obtained from an electromagnetic tracking system during treadmill locomotion

The purpose of this paper was to describe a technique that enables three-dimensional (3D) gait kinematics to be obtained using an electromagnetic tracking system, and to report the intra-trial, intra-day/inter-tester and inter-day/intra-tester repeatability of kinematic gait data obtained using this technique. Ten able-bodied adults underwent four gait assessments; the same two testers tested each subject independently on two different days. Gait assessments were conducted on a custom-built long-bed treadmill with no metal components between the rollers. Each gait assessment involved familiarisation to treadmill walking, subject anatomical and functional calibration, and a period of steady-state treadmill walking at a self-selected speed. Following data collection, 3D joint kinematics were calculated using the joint coordinate system approach. 3D joint angle waveforms for 10 left and right strides were extracted and temporally normalised for each trial. Intra-trial, intra-day/inter-tester and inter-day/intra-tester repeatability of the temporally normalised kinematic waveforms were quantified using the coefficient of multiple determination (CMD). CMDs for joint kinematics averaged 0.942 intra-trial, 0.849 intra-day/inter-tester and 0.773 inter-day/intra-tester. In general, sagittal plane kinematics were more repeatable than frontal or transverse plane kinematics, and kinematics at the hip were more repeatable than at the knee or ankle. The level of repeatability of kinematic gait data obtained during treadmill walking using this protocol was equal or superior to that reported previously for overground walking using image-based protocols.     

Characteristics of the maintenance of the vertical posture during standing with an asymmetrical load on the legs

Movements of the common center of pressure (CP) and the CPs of the right and left legs separately were studied during the maintenance of the vertical posture by subjects standing with symmetrical load on their legs or with the shift of the load to the right or left leg. It was shown that standing with a symmetrical load on the legs was accompanied by the movement of the CP of an individual leg along the straight line with small deviations aside, whereas movement of the common CP represented the curve with frequent changes in direction and filling up some space. The shift of the load to one leg resulted in the movement of the CP of the loaded leg that was similar to that observed during a symmetrical load on the legs. The movement of the CP of the unloaded leg was chaotic. The shift of the load to one leg decreased the correlation between the movements of the CPs of the left and right legs compared to standing with a symmetrical load on the legs. The velocity of movement of the CP of the leg loaded increased in the sagittal direction but remained stable in the frontal direction. The velocity of movement of the CP of the unloaded leg remained stable in the sagittal direction but increased in the frontal direction. We suppose that during standing with an asymmetrical load on the legs the role of the single in the maintenance of the vertical posture depend on the load on the leg.     

Comparison of forces developed by the leg of the rock lobster when walking free or on a treadmill

Summary In the free walking rock lobster the forces developed by legs 4 and 5 were investigated during the power stroke. Two orthogonal force components lying in the horizontal plane were measured. Based on these results the diffent tasks of the two legs during walking are discussed. The forces developed by leg 4 were compared when the animal walked freely and on a treadmill. In these two situations the results differ qualitatively as in driven walking the forces are nearly identical in a long series of consecutive steps whereas in free walking the forces can vary greatly from step to step. However, similar mean values of force were measured with those on the treadmill being somewhat higher. This shows that, although the treadmill is driven by a motor, the animal does perform active walking movements. In the treadmill situation the forces increase as the speed of treadmill motor is decreased.Supported by DAAD and DFG (Cr 58) for H. Cruse and by ATP (80 119.112) INSERM for F. Clarac     

Energy cost and muscular activity required for leg swing during walking.

To investigate the metabolic cost and muscular actions required for the initiation and propagation of leg swing, we applied a novel combination of external forces to subjects walking on a treadmill. We applied a forward pulling force at each foot to assist leg swing, a constant forward pulling force at the waist to provide center of mass propulsion, and a combination of these foot and waist forces to evaluate leg swing. When the metabolic cost and muscle actions were at a minimum, the condition was considered optimal. We reasoned that the difference in energy consumption between the optimal combined waist and foot force trial and the optimal waist force-only trial would reflect the metabolic cost of initiating and propagating leg swing during normal walking. We also reasoned that a lower muscle activity with these assisting forces would indicate which muscles are normally responsible for initiating and propagating leg swing. With a propulsive force at the waist of 10% body weight (BW), the net metabolic cost of walking decreased to 58% of normal walking. With the optimal combination, a propulsive force at the waist of 10% BW plus a pulling force at the feet of 3% BW the net metabolic cost of walking further decreased to 48% of normal walking. With the same combination, the muscle activity of the iliopsoas and rectus femoris muscles during the swing phase was 27 and 60% lower, respectively, but the activity of the medial gastrocnemius and soleus before swing did not change. Thus our data indicate that approximately 10% of the net metabolic cost of walking is required to initiate and propagate leg swing. Additionally, the hip flexor muscles contribute to the initiation and propagation leg swing.     

Ground reaction force estimation using an insole-type pressure mat and joint kinematics during walking

Kinetic analysis of walking requires joint kinematics and ground reaction force (GRF) measurement, which are typically obtained from a force plate. GRF is difficult to measure in certain cases such as slope walking, stair climbing, and track running. Nevertheless, estimating GRF continues to be of great interest for simulating human walking. The purpose of the study was to develop reaction force models placed on the sole of the foot to estimate full GRF when only joint kinematics are provided (Type-I), and to estimate ground contact shear forces when both joint kinematics and foot pressure are provided (Type-II and Type-II-val). The GRF estimation models were attached to a commercial full body skeletal model using the AnyBody Modeling System, which has an inverse dynamics-based optimization solver. The anterior–posterior shear force and medial–lateral shear force could be estimated with approximate accuracies of 6% BW and 2% BW in all three methods, respectively. Vertical force could be estimated in the Type-I model with an accuracy of 13.75% BW. The accuracy of the force estimation was the highest during the mid-single-stance period with an average RMS for errors of 3.10% BW, 1.48% BW, and 7.48% BW for anterior–posterior force, medial–lateral force, and vertical force, respectively. The proposed GRF estimation models could predict full and partial GRF with high accuracy. The design of the contact elements of the proposed model should make it applicable to various activities where installation of a force measurement system is difficult, including track running and treadmill walking.     

IMU-based ambulatory walking speed estimation in constrained treadmill and overground walking

This study evaluated the performance of a walking speed estimation system based on using an inertial measurement unit (IMU), a combination of accelerometers and gyroscopes. The walking speed estimation algorithm segments the walking sequence into individual stride cycles (two steps) based on the inverted pendulum-like behaviour of the stance leg during walking and it integrates the angular velocity and linear accelerations of the shank to determine the displacement of each stride. The evaluation was performed in both treadmill and overground walking experiments with various constraints on walking speed, step length and step frequency to provide a relatively comprehensive assessment of the system. Promising results were obtained in providing accurate and consistent walking speed/step length estimation in different walking conditions. An overall percentage root mean squared error (%RMSE) of 4.2 and 4.0% was achieved in treadmill and overground walking experiments, respectively. With an increasing interest in understanding human walking biomechanics, the IMU-based ambulatory system could provide a useful walking speed/step length measurement/control tool for constrained walking studies.     

IMU-based ambulatory walking speed estimation in constrained treadmill and overground walking

This study evaluated the performance of a walking speed estimation system based on using an inertial measurement unit (IMU), a combination of accelerometers and gyroscopes. The walking speed estimation algorithm segments the walking sequence into individual stride cycles (two steps) based on the inverted pendulum-like behaviour of the stance leg during walking and it integrates the angular velocity and linear accelerations of the shank to determine the displacement of each stride. The evaluation was performed in both treadmill and overground walking experiments with various constraints on walking speed, step length and step frequency to provide a relatively comprehensive assessment of the system. Promising results were obtained in providing accurate and consistent walking speed/step length estimation in different walking conditions. An overall percentage root mean squared error (%RMSE) of 4.2 and 4.0% was achieved in treadmill and overground walking experiments, respectively. With an increasing interest in understanding human walking biomechanics, the IMU-based ambulatory system could provide a useful walking speed/step length measurement/control tool for constrained walking studies.     

Cycling as a novel approach to resistance training increases muscle strength, power, and selected functional abilities in healthy older women.

Cycling on a mechanically braked cycle ergometer was used as a novel approach to compare the effects of three different 16-wk resistance-training programs on isometric force, power output, and selected functional abilities in 31 healthy 65- to 74-yr-old women. Training was conducted three times per week. During each session, individuals of the speed group performed 8 sets of 16 pedal revolutions at 40% of the maximal resistance to complete two revolutions (2 RM); strength group performed 8 sets of 8 revolutions at 80% of 2 RM; and combination group performed 4 sets of 16 revolutions at 40% and 4 sets of 8 revolutions at 80% of 2 RM. During each set, all participants were required to pedal as fast as possible with a 2-min interval between sets. All training groups significantly increased force, power, and functional abilities (maximal treadmill walking speed, vertical jumping, and box stepping) at week 8 (in the range from 6.5 to 20.8%) with no further improvement at week 16 (except maximal treadmill walking speed), but no significant differences were observed between the three groups. The novel approach to performing both low- and high-resistance training, based on the use of a cycle ergometer, has been shown to be effective in improving strength, power, and functional abilities in a group of healthy women. Even fit older women can still improve in functional abilities. Interestingly, the "high-speed" and "low-speed" programs induced an increase in both power and strength of similar magnitude.     

Comparative Study on Biomechanics of Two Legs in the Action of Single-Leg Landing in Men’s Badminton

This study aims to analyze the biomechanical difference between the two legs of male badminton players when they land on one leg, thereby providing some guidance for preventing sports injury. Ten male badminton players were selected as the subjects. They did the single-leg landing movement successfully three times. The kinematic data were obtained by the Vicon infrared high-speed motion capture system. The kinetic data were obtained by the KISTLER three-dimensional forcing measuring platform. The data were processed and analyzed. The center of gravity of the right leg on the X and Y axes were 0.25 ± 0.05 and 0.21 ± 0.04 m, respectively, which were lower than that of the left leg (p < 0.05). At the moment of landing by a single leg, the hip angle of the left and right legs was 164.78 ± 6.12° and 156.29 ± 6.89°, respectively (p < 0.05), the hip joint speed of the left and right legs was 2.21 ± 0.32 and 1.98 ± 0.31 m/s, respectively (p < 0.05), the knee joint speed of the left and right legs was 2.51 ± 0.21 and 2.21 ± 0.21 m/s, respectively (p < 0.05). Although there was no significant difference in the range of joint motion, the motion range of the right leg was larger than that of the left leg, and the buffering time of the knee joint of the right leg was also significantly less than that of the left leg. The comparison of the kinetic data demonstrated that the ground reaction force (GRF), peak vertical ground reaction force (PVGRF), and lower limb stiffness of the right leg were significantly smaller than those of the left leg, and the time to peak force was greater than that of the left leg (p < 0.05). The injury risk of the left leg is greater than that of the right leg when the athlete land on a single leg. In the process of training, the athlete should strengthen the stability training of two legs, especially the left leg, in order to reduce sports injury.     

Intracellular recordings from nonspiking interneurons in a semiintact, tethered walking insect.

Nonspiking interneurons were investigated in a tethered, walking insect, Carausius morosus, that was able to freely perform walking movements. Experiments were carried out with animals walking on a lightweight, double-wheel treadmill. Although the animal was opened dorsally, the walking system was left intact. Intracellular recordings were obtained from the dorsal posterior neuropil of the mesothoracic ganglion. Nonspiking interneurons, in which modulations of the membrane potential were correlated with the walking rhythm, were described physiologically and stained with Lucifer Yellow. Interneurons are demonstrated in which membrane potential oscillations mirror the leg position or show correlation with the motoneuronal activity of the protractor and retractor coxae muscles during walking. Other interneurons showed distinct hyperpolarizations at certain important trigger points in the step cycle, for example, at the extreme posterior position. Through electrical stimulation of single, nonspiking interneurons during walking, the motoneuronal activity in two antagonistic muscles--protractor and retractor coxae--could be reversed and even the movement of the ipsilateral leg could be influenced. The nonspiking interneurons described appear to be important premotor elements involved in walking. They receive, integrate, and process information from different leg proprioceptors and drive groups of leg motoneurons during walking.     

Can treadmill walking be used to assess propulsion generation?

Instrumented treadmills offer significant advantages for analysis of human locomotion, including recording consecutive steady-state gait cycles, precisely controlling walking speed, and avoiding force plate targeting. However, some studies of hemiparetic walking on a treadmill have suggested that the moving treadmill belt may fundamentally alter propulsion mechanics. Any differences in propulsion mechanics during treadmill walking would be problematic since recent studies assessing propulsion have provided fundamental insight into hemiparetic walking. The purpose of this study was to test the hypothesis that there would be no difference in the generation of anterior/posterior (A/P) propulsion by performing a carefully controlled comparison of the A/P ground reaction forces (GRFs) and impulses in healthy adults during treadmill and overground walking. Gait data were collected from eight subjects walking overground and on a treadmill with speed and cadence controlled. Peak negative and positive horizontal GRFs in early and late stance, respectively, were reduced by less than 5% of body weight (p<0.05) during treadmill walking compared to overground walking. The magnitude of the braking impulse was similarly lower (p<0.05) during treadmill walking, but no significant difference was found between propulsion impulses. While there were some subtle differences in A/P GRFs between overground and treadmill walking, these results suggest there is no fundamental difference in propulsion mechanics. We conclude that treadmill walking can be used to investigate propulsion generation in healthy and by implication clinical populations.     

Effects of asymmetric load carrying on the biomechanics of walking

The purpose of the study was to investigate the effects of an asymmetric sidepack carrying system on frontal plane joint moments of force in both lower extremities and in the L5/S1 joint during level walking. Ground reaction force data and frontal plane film records were obtained from five males performing three walking conditions: 0, 10 and 20% bodyweight loads in a sidepack supported by the left shoulder. Inverse dynamics were used to calculate the lower extremity moments during stance and a static model of the pelvis was used to calculate the L5/S1 moments during single support for each limb. Normal walking was characterized by symmetric kinetics between left and right limbs and around the L5/S1 joint. The asymmetric loads produced unbalanced lateral trunk muscle dominance between left and right limb stance phases, increased right hip and knee moments and decreased left hip and knee moments. During normal walking, the L5/S1 moment was dominant on the contralateral trunk side for both limbs. The asymmetric loads applied to the left side caused a shift in L5/S1 moment dominance to the right side during left and right single support phases.     

Effect of surgery to implant motion and force sensors on vertical ground reaction forces in the ovine model

Activities of daily living (ADLs) generate complex, multidirectional forces in the anterior cruciate ligament (ACL). While calibration problems preclude direct measurement in patients, ACL forces can conceivably be measured in animals after technical challenges are overcome. For example, motion and force sensors can be implanted in the animal but investigators must determine the extent to which these sensors and surgery affect normal gait. Our objectives in this study were to determine (1) if surgically implanting knee motion sensors and an ACL force sensor significantly alter normal ovine gait and (2) how increasing gait speed and grade on a treadmill affect ovine gait before and after surgery. Ten skeletally mature, female sheep were used to test four hypotheses: (1) surgical implantation of sensors would significantly decrease average and peak vertical ground reaction forces (VGRFs) in the operated limb, (2) surgical implantation would significantly decrease single limb stance duration for the operated limb, (3) increasing treadmill speed would increase VGRFs pre- and post operatively, and (4) increasing treadmill grade would increase the hind limb VGRFs pre- and post operatively. An instrumented treadmill with two force plates was used to record fore and hind limb VGRFs during four combinations of two speeds (1.0 m/s and 1.3 m/s) and two grades (0 deg and 6 deg). Sensor implantation decreased average and peak VGRFs less than 10% and 20%, respectively, across all combinations of speed and grade. Sensor implantation significantly decreased the single limb stance duration in the operated hind limb during inclined walking at 1.3 m/s but had no effect on single limb stance duration in the operated limb during other activities. Increasing treadmill speed increased hind limb peak (but not average) VGRFs before surgery and peak VGRF only in the unoperated hind limb during level walking after surgery. Increasing treadmill grade (at 1 m/s) significantly increased hind limb average and peak VGRFs before surgery but increasing treadmill grade post op did not significantly affect any response measure. Since VGRF values exceeded 80% of presurgery levels, we conclude that animal gait post op is near normal. Thus, we can assume normal gait when conducting experiments following sensor implantation. Ultimately, we seek to measure ACL forces for ADLs to provide design criteria and evaluation benchmarks for traditional and tissue engineered ACL repairs and reconstructions.     

Intracellular recordings from nonspiking interneurons in a semiintact,tethered walking insect

Nonspiking interneurons were investigated in a tethered, walking insect, Carausius morosus, that was able to freely perform walking movements. Experiments were carried out with animals walking on a lightweight, double-wheel treadmill. Although the animal was opened dorsally, the walking system was left intact. Intracellular recordings were obtained from the dorsal posterior neuropil of the mesothoracic ganglion. Nonspiking inter-neurons, in which modulations of the membrane potential were correlated with the walking rhythm, were described physiologically and stained with Lucifer Yellow. Interneurons are demonstrated in which membrane potential oscillations mirror the leg position or show correlation with the motoneuronal activity of the protractor and retractor coxae muscles during walking. Other interneurons showed distinct hyperpolarizations at certain important trigger points in the step cycle, for example, at the extreme posterior position. Through electrical stimulation of single, nonspiking interneurons during walking, the motoneuronal activity in two antagonistic muscles—protractor and retractor coxae—could be reversed and even the movement of the ipsilateral leg could be influenced. The nonspiking interneurons described appear to be important premotor elements involved in walking. They receive, integrate, and process information from different leg proprioceptors and drive groups of leg motoneurons during walking.     

Mechanics of running under simulated low gravity.

Using a linear mass-spring model of the body and leg (T. A. McMahon and G. C. Cheng. J. Biomech. 23: 65-78, 1990), we present experimental observations of human running under simulated low gravity and an analysis of these experiments. The purpose of the study was to investigate how the spring properties of the leg are adjusted to different levels of gravity. We hypothesized that leg spring stiffness would not change under simulated low-gravity conditions. To simulate low gravity, a nearly constant vertical force was applied to human subjects via a bicycle seat. The force was obtained by stretching long steel springs via a hand-operated winch. Subjects ran on a motorized treadmill that had been modified to include a force platform under the tread. Four subjects ran at one speed (3.0 m/s) under conditions of normal gravity and six simulated fractions of normal gravity from 0.2 to 0.7 G. For comparison, subjects also ran under normal gravity at five speeds from 2.0 to 6.0 m/s. Two basic principles emerged from all comparisons: both the stiffness of the leg, considered as a linear spring, and the vertical excursion of the center of mass during the flight phase did not change with forward speed or gravity. With these results as inputs, the mathematical model is able to account correctly for many of the changes in dynamic parameters that do take place, including the increasing vertical stiffness with speed at normal gravity and the decreasing peak force observed under conditions simulating low gravity.