Biology subjects

Lemaire, K. K.

Publications and source records attributed to Lemaire, K. K..

4 recordsLinked to original sources

bioRxiv2025

Simultaneous stabilizing feedback control of linear and angular momentum in human walking

Stabilizing bipedal gait is mechanically challenging. To analyze how gait is stabilized, previous studies have focused on the control of the body center of mass (CoM). These studies often linked deviations in linear momentum of the CoM to subsequent shifts in position of the center of pressure (CoP), or of the foot, relative to the COM, and interpreted these as stabilizing responses to correct linear CoM momentum. Mechanically, however, CoP shifts do not cause changes of linear CoM momentum, whereas they do cause changes in whole-body angular momentum. We hypothesized that experimentally observed correlations between CoP to CoM distance and horizontal ground reaction forces are related to the need to control both linear and whole-body angular momentum. We show that, in human walking, linear and angular momentum follow quasi-periodic functions with similar periodicity and phase. Combining the equations of linear and rotational motion for a system of linked rigid segments shows that, in this case, the horizontal distance between CoP and CoM should be correlated to horizontal force in the corresponding direction. This suggests that linear and angular momentum are simultaneously controlled and may explain the success of preceding studies that correlated CoM states to CoP or foot locations. Regression models fitted to experimental data of participants walking at normal and slow speeds showed that deviations in horizontal ground reaction forces and in moments of the ground reaction force about the sagittal and transverse axes could be predicted from deviations in the preceding linear and angular momentum respectively. Our analyses support that linear and angular momentum are indeed controlled simultaneously in human walking.

biophysics↗

bioRxiv2024

Milliseconds matter: Biomechanical inverse dynamics analysis is highly sensitive to imperfect data synchronization

Inverse dynamics analysis is the primary means of quantifying joint moments and powers from biomechanical data. The data are often combined from force plates, motion capture cameras, and perhaps body-worn inertial sensors, and must be temporally synchronized to avoid potentially large inverse dynamics errors. The principles behind the errors, and the sensitivities for movements such as human walking, have yet to be demonstrated. Here we quantify how inverse dynamics computations of joint moments, powers, and work are highly sensitive to temporal mis-synchronization. We do this with (1) a theoretical examination of inverse dynamics, supported by (2) a simulated multi-body jumping movement, and (3) experimental human walking data. The theoretical analysis shows that root-mean-square errors in joint powers increase linearly with temporal mis-synchronization, and increase more for faster movements. With the other analyses we quantify the specific amount. For example, for human walking at 1.25 m/s, an artificially induced 5 ms lag of force relative to motion resulted in a 29% root-mean-square error of the ankle joint moment. The corresponding error in ankle joint power was 58%, and five times as much for walking at 2.2 m/s. The residual force, a measure of internal inconsistency in the data, increased by almost 1% body weight for each millisecond of mis-synchronization for walking. These sensitivities are relevant because standard experimental equipment usually synchronizes only the recording of data, but not processing latencies internal to equipment, which can and do cause mis-synchronization on the order of ten milliseconds. Biomechanical data should be synchronized to within a few milliseconds, and with respect to physical stimulus, to yield accurate inverse dynamics analysis.

biophysics↗

bioRxiv2024

The effect of head orientation on vestibular signal-based modulation of paraspinal muscle activity during walking

Vestibulospinal reflexes play a role in maintaining the upright posture of the trunk. Head orientation has been shown to modify the vestibulospinal reflexes during standing. This study investigated how vestibular signals affect paraspinal muscle activity during walking, and whether head orientation changes these effects. Sixteen participants were instructed to walk on a treadmill for 8 min at 78 steps/min and 2.8 km/h in four conditions defined by the presence of electrical vestibular stimulation (EVS) and by head orientation (facing forward and facing leftward), while bipolar electromyography (EMG) was recorded bilaterally from the paraspinal muscles from cervical to lumbar levels. In both head orientations, significant phasic EVS-EMG coherence (p < 0.01) in the paraspinal muscles was observed at ipsilateral and/or contralateral heel strikes. Compared to walking with the head forward, a significant decrease (p < 0.05) was found in EVS evoked responses (i.e., EVS-EMG coherence and gain) when participants walked with the leftward head orientation, with which EVS induced disturbance in the sagittal plane. This overall decrease may be explained by less need of feedback control for walking stabilization in the sagittal plane compared to in the frontal plane. The decrease in coherence was only significant at the left lower vertebral levels and at the right upper vertebral levels around left heel strikes (p < 0.05). Together, these findings confirm the contribution of the vestibular afferent signals to the control of paraspinal muscle activity during walking and indicate that this control is changed in response to different head orientations. Key Point SummaryO_LIVestibulospinal reflexes simultaneously contribute to stabilizing the centre of mass trajectory and to maintaining an upright posture of the trunk. C_LIO_LIHead orientation, which challenges stability via altered visual, vestibular and proprioceptive signals, modifies vestibulospinal reflexes during standing. C_LIO_LITo explore the impact of head orientation during walking, we recorded bilateral surface EMG of cervical to lumbar paraspinal muscles, and characterized coherence, gain and delay between EMG and electrical vestibular stimulation, during walking with head facing forward and leftward. C_LIO_LIWhen walking with head facing leftward, vestibular stimulation caused disturbance in sagittal plane. Phasic response in paraspinal muscles with a significant smaller magnitude was found compared to facing forward. C_LIO_LIOur results agree with the idea that less feedback control is required for walking stabilization in the sagittal plane and confirm that vestibular afference modulates paraspinal muscle activity for trunk control during walking, and this modulation is changed in response to head orientation. C_LI

physiology↗

bioRxiv2023

Vertebral level specific modulation of paraspinal muscle activity based on vestibular signals during walking.

Evoking muscle responses by electrical vestibular stimulation (EVS) may help to understand the contribution of the vestibular system to postural control. Although paraspinal muscles play a role in postural stability, the vestibulo-muscular coupling of these muscles during walking has rarely been studied. This study aimed to investigate how vestibular signals affect paraspinal muscle activity at different vertebral levels during walking with preferred and narrow step width. Sixteen healthy participants were recruited. Participants walked on a treadmill for 8 minutes at 78 steps/min and 2.8 km/h, at two different step width, either with or without EVS. Bipolar electromyography was recorded bilaterally from the paraspinal muscles at eight vertebral levels from cervical to lumbar. Coherence, gain, and delay of EVS and EMG responses were determined. Significant EVS-EMG coupling (p<0.01) was found at ipsilateral and/or contralateral heel strikes. This coupling was mirrored between left and right relative to the midline of the trunk and between the higher and lower vertebral levels, i.e., a peak occurred at ipsilateral heel strike at lower levels, whereas it occurred at contralateral heel strike at higher levels. EVS-EMG coupling only partially coincided with peak muscle activity. EVS-EMG coherence slightly, but not significantly, increased when walking with narrow steps. No significant differences were found in gain and phase between the vertebral levels or step width conditions. In summary, vertebral level specific modulation of paraspinal muscle activity based on vestibular signals might allow a fast, synchronized, and spatially co-ordinated response along the trunk during walking. Key Points SummaryO_LIMediolateral stabilization of gait requires an estimate of the state of the body, which is affected by vestibular afference. C_LIO_LIDuring gait, the heavy trunk segment is controlled by phasic paraspinal muscle activity and in rodents the medial and lateral vestibulospinal tracts activate these muscles. C_LIO_LITo gain insight in vestibulospinal connections in humans and their role in gait, we recorded paraspinal surface EMG of cervical to lumbar paraspinal muscles, and characterized coherence, gain and delay between EMG and electrical vestibular stimulation, during slow walking. C_LIO_LIVestibular stimulation caused phasic, vertebral level specific modulation of paraspinal muscle activity at delays of around 40 milliseconds, which was mirrored between left, lower and right, upper vertebral levels. C_LIO_LIOur results indicate that vestibular afference causes fast, synchronized, and spatially co-ordinated responses of the paraspinal muscles along the trunk, that simultaneously contribute to stabilizing the centre of mass trajectory and to keeping the head upright. C_LI

physiology↗