PF
P.A. Forbes
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1
Maintaining standing balance requires continuous sensorimotor control and is associated with a measurable metabolic cost. While minimization of energy usage is thought to influence human movements, it remains unclear how this applies to standing balance and how postural variability contributes to metabolic cost, because previous studies could not separate the effects of biomechanics from those of variability. This study aimed to quantify the metabolic cost of standing balance and to determine how this cost relates to postural variability independently of biomechanical alterations.
Twenty healthy participants performed seven standing conditions in which postural variability was manipulated using electrical vestibular stimulation (EVS) with varying frequencies and amplitudes. With EVS, postural responses were evoked without mechanically destabilizing the body. Metabolic cost was measured using indirect calorimetry, while postural variability was quantified using center of pressure (CoP) velocity and upper-body kinematics.
Free-standing resulted in an approximately 8% higher metabolic cost compared to externally supported standing, indicating the energetic cost of active balance control. Increasing postural variability through low-frequency EVS significantly elevated metabolic cost and revealed a positive relationship between variability and metabolic cost. In addition, vestibular stimulation and its reflexive muscle activity did not increase metabolic cost when postural variability remained unchanged. Furthermore, movements with comparable variability resulted in similar metabolic costs, regardless of whether they were reflexively induced or self-initiated.
These findings demonstrate that the metabolic cost of standing is primarily determined by postural variability rather than by vestibular input or reflexive muscle activity alone. The results support the hypothesis that humans adopt a preferred level of postural variability that is close to the metabolic minimum, consistent with principles of optimal control.
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Twenty healthy participants performed seven standing conditions in which postural variability was manipulated using electrical vestibular stimulation (EVS) with varying frequencies and amplitudes. With EVS, postural responses were evoked without mechanically destabilizing the body. Metabolic cost was measured using indirect calorimetry, while postural variability was quantified using center of pressure (CoP) velocity and upper-body kinematics.
Free-standing resulted in an approximately 8% higher metabolic cost compared to externally supported standing, indicating the energetic cost of active balance control. Increasing postural variability through low-frequency EVS significantly elevated metabolic cost and revealed a positive relationship between variability and metabolic cost. In addition, vestibular stimulation and its reflexive muscle activity did not increase metabolic cost when postural variability remained unchanged. Furthermore, movements with comparable variability resulted in similar metabolic costs, regardless of whether they were reflexively induced or self-initiated.
These findings demonstrate that the metabolic cost of standing is primarily determined by postural variability rather than by vestibular input or reflexive muscle activity alone. The results support the hypothesis that humans adopt a preferred level of postural variability that is close to the metabolic minimum, consistent with principles of optimal control.
...
Maintaining standing balance requires continuous sensorimotor control and is associated with a measurable metabolic cost. While minimization of energy usage is thought to influence human movements, it remains unclear how this applies to standing balance and how postural variability contributes to metabolic cost, because previous studies could not separate the effects of biomechanics from those of variability. This study aimed to quantify the metabolic cost of standing balance and to determine how this cost relates to postural variability independently of biomechanical alterations.
Twenty healthy participants performed seven standing conditions in which postural variability was manipulated using electrical vestibular stimulation (EVS) with varying frequencies and amplitudes. With EVS, postural responses were evoked without mechanically destabilizing the body. Metabolic cost was measured using indirect calorimetry, while postural variability was quantified using center of pressure (CoP) velocity and upper-body kinematics.
Free-standing resulted in an approximately 8% higher metabolic cost compared to externally supported standing, indicating the energetic cost of active balance control. Increasing postural variability through low-frequency EVS significantly elevated metabolic cost and revealed a positive relationship between variability and metabolic cost. In addition, vestibular stimulation and its reflexive muscle activity did not increase metabolic cost when postural variability remained unchanged. Furthermore, movements with comparable variability resulted in similar metabolic costs, regardless of whether they were reflexively induced or self-initiated.
These findings demonstrate that the metabolic cost of standing is primarily determined by postural variability rather than by vestibular input or reflexive muscle activity alone. The results support the hypothesis that humans adopt a preferred level of postural variability that is close to the metabolic minimum, consistent with principles of optimal control.
Twenty healthy participants performed seven standing conditions in which postural variability was manipulated using electrical vestibular stimulation (EVS) with varying frequencies and amplitudes. With EVS, postural responses were evoked without mechanically destabilizing the body. Metabolic cost was measured using indirect calorimetry, while postural variability was quantified using center of pressure (CoP) velocity and upper-body kinematics.
Free-standing resulted in an approximately 8% higher metabolic cost compared to externally supported standing, indicating the energetic cost of active balance control. Increasing postural variability through low-frequency EVS significantly elevated metabolic cost and revealed a positive relationship between variability and metabolic cost. In addition, vestibular stimulation and its reflexive muscle activity did not increase metabolic cost when postural variability remained unchanged. Furthermore, movements with comparable variability resulted in similar metabolic costs, regardless of whether they were reflexively induced or self-initiated.
These findings demonstrate that the metabolic cost of standing is primarily determined by postural variability rather than by vestibular input or reflexive muscle activity alone. The results support the hypothesis that humans adopt a preferred level of postural variability that is close to the metabolic minimum, consistent with principles of optimal control.
Reaction-time paradigms are widely used to investigate multisensory processing and sensorimotor integration, yet their application to postural control has been limited. This may stem from the view that most self-generated balance-correcting motor actions occur without conscious awareness. However, this contrasts with evidence that reaction times to external stimuli can still be modulated during balance tasks (e.g., sitting, standing, walking), suggesting that even automatic balance control can interact with higher-level cognitive processing. Yet the temporal dynamics distinguishing automatic postural from consciously mediated responses to balance perturbations remain underexplored. In this study, we used a robotic balance simulator to impose disruptions to ongoing balance and dissociate balance-correcting and perceptual mechanisms of standing balance control. Participants stood on a robotic simulator that applied 200 ms torque perturbations of varying amplitudes. Additional ankle torque perturbations mimicking natural balance-control statistics were delivered to artificially increase ongoing motor noise. We recorded both EMG-based corrective muscle responses and perceptual reaction times via button presses, enabling direct comparison of automatic and conscious responses. Both response types decreased with increasing perturbation amplitude, consistent with findings from other sensory domains. Crucially, perceptual reaction times increased with higher noise amplitudes, whereas automatic postural responses did not. This dissociation highlights distinct neural mechanisms underlying conscious perception and postural control based on the functional purposes these processes fulfill.
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Reaction-time paradigms are widely used to investigate multisensory processing and sensorimotor integration, yet their application to postural control has been limited. This may stem from the view that most self-generated balance-correcting motor actions occur without conscious awareness. However, this contrasts with evidence that reaction times to external stimuli can still be modulated during balance tasks (e.g., sitting, standing, walking), suggesting that even automatic balance control can interact with higher-level cognitive processing. Yet the temporal dynamics distinguishing automatic postural from consciously mediated responses to balance perturbations remain underexplored. In this study, we used a robotic balance simulator to impose disruptions to ongoing balance and dissociate balance-correcting and perceptual mechanisms of standing balance control. Participants stood on a robotic simulator that applied 200 ms torque perturbations of varying amplitudes. Additional ankle torque perturbations mimicking natural balance-control statistics were delivered to artificially increase ongoing motor noise. We recorded both EMG-based corrective muscle responses and perceptual reaction times via button presses, enabling direct comparison of automatic and conscious responses. Both response types decreased with increasing perturbation amplitude, consistent with findings from other sensory domains. Crucially, perceptual reaction times increased with higher noise amplitudes, whereas automatic postural responses did not. This dissociation highlights distinct neural mechanisms underlying conscious perception and postural control based on the functional purposes these processes fulfill.
The metabolic cost of walking reflects gait efficiency and is influenced by biomechanical factors as walking speed. While most walking research uses treadmills, older adults are found to exhibit a greater elevation in the cost of walking on the treadmill compared to overground walking than younger adults. A possible cause for this elevation could be the higher stability demands in older adults during treadmill walking, possibly influenced by a higher vestibular contribution. This study investigated whether increased vestibular demands for balance control contribute to this elevated cost in older adults. Ten younger (mean age 26.4 years) and ten older adults (mean age 68.6 years) completed 5-minute treadmill and overground walking trials at preferred and slow fixed speeds. Metabolic cost was measured, and vestibular contributions to balance were assessed via electrical vestibular stimulation, which induced virtual movements and evoked balance correcting responses measured by inertial sensors on the back and ankles. Treadmill walking increased the cost of walking significantly by 15-23% compared to overground walking, with no significant age effect. Vestibular stimulation increased metabolic cost significantly in both overground and treadmill walking and age groups. Assessment of the vestibular contributions to kinematic measures revealed a significant increase in vestibular contribution to balance at slower walking speeds, but no significant effect of age and no large effect of treadmill or overground. Indicating that the measured participants cannot conclude that the elevation of cost in treadmill walking in older adults is due to the vestibular contribution to balance.
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The metabolic cost of walking reflects gait efficiency and is influenced by biomechanical factors as walking speed. While most walking research uses treadmills, older adults are found to exhibit a greater elevation in the cost of walking on the treadmill compared to overground walking than younger adults. A possible cause for this elevation could be the higher stability demands in older adults during treadmill walking, possibly influenced by a higher vestibular contribution. This study investigated whether increased vestibular demands for balance control contribute to this elevated cost in older adults. Ten younger (mean age 26.4 years) and ten older adults (mean age 68.6 years) completed 5-minute treadmill and overground walking trials at preferred and slow fixed speeds. Metabolic cost was measured, and vestibular contributions to balance were assessed via electrical vestibular stimulation, which induced virtual movements and evoked balance correcting responses measured by inertial sensors on the back and ankles. Treadmill walking increased the cost of walking significantly by 15-23% compared to overground walking, with no significant age effect. Vestibular stimulation increased metabolic cost significantly in both overground and treadmill walking and age groups. Assessment of the vestibular contributions to kinematic measures revealed a significant increase in vestibular contribution to balance at slower walking speeds, but no significant effect of age and no large effect of treadmill or overground. Indicating that the measured participants cannot conclude that the elevation of cost in treadmill walking in older adults is due to the vestibular contribution to balance.
Predictive simulation is a powerful tool that can be used to examine the impacts of aging on complex movement behaviors. These models rely on neuromuscular controllers that modulate sensory feedback, including vestibular feedback, in order to transition between different movement phases. Current models, however, define the phase transitions based on the kinematics of movement without consideration for the underlying neurophysiological feedback mechanisms driving actual behavior. Here, we studied sit-to-walk movements, a challenging task commonly faced by aging populations, and examined how vestibular feedback is modulated for the control of balance. We estimated the coupling between an electrical vestibular stimulus and ground reaction forces in healthy participants (N = 16) while they performed a sit-to-walk task. Because sit-to-walk transitions are thought to be comprised of simultaneous transitions of standing up and walking, we also compared the sit-to-walk (STW) task to sit-to-stand (STS) (N= 8) and gait-initiation (GI) tasks (N = 8). Four main phases of vestibular control were identified for STW: quiet sitting, flexion, transition, and gait. Similarly, four main phases were identified for STS, though they differed after the first two: quiet sitting, flexion, rising/stabilizing, and quiet standing. In contrast, five main phases were identified for GI: quiet standing, adjustment I, adjustment II, transition, and gait. Importantly, the timings of the identified phases differed from the timings of the events used to define kinematic phases, and the magnitude of the vestibular responses was modulated gradually between phases. We also found that the vestibular modulation observed in STW could be explained as a sharp shift from an STS task just after flexion, around seat-off, into a GI task starting at transition. These results demonstrate that defining the timing of neuromuscular controllers in predictive simulation based on neurophysiological events may be better suited to improving their accuracy.
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Predictive simulation is a powerful tool that can be used to examine the impacts of aging on complex movement behaviors. These models rely on neuromuscular controllers that modulate sensory feedback, including vestibular feedback, in order to transition between different movement phases. Current models, however, define the phase transitions based on the kinematics of movement without consideration for the underlying neurophysiological feedback mechanisms driving actual behavior. Here, we studied sit-to-walk movements, a challenging task commonly faced by aging populations, and examined how vestibular feedback is modulated for the control of balance. We estimated the coupling between an electrical vestibular stimulus and ground reaction forces in healthy participants (N = 16) while they performed a sit-to-walk task. Because sit-to-walk transitions are thought to be comprised of simultaneous transitions of standing up and walking, we also compared the sit-to-walk (STW) task to sit-to-stand (STS) (N= 8) and gait-initiation (GI) tasks (N = 8). Four main phases of vestibular control were identified for STW: quiet sitting, flexion, transition, and gait. Similarly, four main phases were identified for STS, though they differed after the first two: quiet sitting, flexion, rising/stabilizing, and quiet standing. In contrast, five main phases were identified for GI: quiet standing, adjustment I, adjustment II, transition, and gait. Importantly, the timings of the identified phases differed from the timings of the events used to define kinematic phases, and the magnitude of the vestibular responses was modulated gradually between phases. We also found that the vestibular modulation observed in STW could be explained as a sharp shift from an STS task just after flexion, around seat-off, into a GI task starting at transition. These results demonstrate that defining the timing of neuromuscular controllers in predictive simulation based on neurophysiological events may be better suited to improving their accuracy.
By monitoring head movement and orientation in space, the vestibular system can evoke appropriate muscle responses in order to maintain standing balance. The present study investigates whether vestibular-evoked muscle responses are dependent on sensory cues of gravity by examining these responses across varying load and gravity conditions. Standing subjects were exposed to a stochastic electrical vestibular stimulus (EVS, ±5 mA, 0-25 Hz) that induced a vestibular error signal, while vertical loading forces or vestibular signals of gravity were independently modified. A backboard structure limited subjects’ whole-body rotation to the sagittal plane which corresponded with the EVS-evoked sway responses in anteroposterior direction, as the subject’s head was rotated in yaw. Vestibular-evoked muscle responses were greatest when sensory cues of gravity matched the expected terrestrial force of gravity, and decreased when these cues were modified. The reduction was largest when both load- and vestibular-related cues of gravity were different from normal. Our results indicate that the vestibular drive for standing balance control is attenuated when sensory cues of gravity are not congruent to normal (i.e. terrestrial) expectations of standing balance and that the degree of attenuation is dependent upon the cumulative incongruency that arises from multiple sensory cues.
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By monitoring head movement and orientation in space, the vestibular system can evoke appropriate muscle responses in order to maintain standing balance. The present study investigates whether vestibular-evoked muscle responses are dependent on sensory cues of gravity by examining these responses across varying load and gravity conditions. Standing subjects were exposed to a stochastic electrical vestibular stimulus (EVS, ±5 mA, 0-25 Hz) that induced a vestibular error signal, while vertical loading forces or vestibular signals of gravity were independently modified. A backboard structure limited subjects’ whole-body rotation to the sagittal plane which corresponded with the EVS-evoked sway responses in anteroposterior direction, as the subject’s head was rotated in yaw. Vestibular-evoked muscle responses were greatest when sensory cues of gravity matched the expected terrestrial force of gravity, and decreased when these cues were modified. The reduction was largest when both load- and vestibular-related cues of gravity were different from normal. Our results indicate that the vestibular drive for standing balance control is attenuated when sensory cues of gravity are not congruent to normal (i.e. terrestrial) expectations of standing balance and that the degree of attenuation is dependent upon the cumulative incongruency that arises from multiple sensory cues.