Postural role for intrinsic muscles

NewsBot · Mar 11, 2018

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Vestibular-evoked responses indicate a functional role for intrinsic foot muscles during standing balance.
Wallace JW et al
Neuroscience. 2018 Mar 7. pii: S0306-4522(18)30161-1. doi: 10.1016/j.neuroscience.2018.02.036.

Maintaining standing balance involves multisensory processing and integration to produce dynamic motor responses. Electrical vestibular stimulation (EVS) delivered over the mastoid processes can be used to explore the vestibular control of balance. The purpose of this study was to determine whether intrinsic foot muscles exhibit vestibular-evoked balance responses and to characterize the traits associated with these responses. Electromyography (EMG) of the abductor hallucis, abductor digiti minimi and medial gastrocnemius and anterior-posterior (AP) forces were sampled while quietly standing participants were subjected to a random continuous EVS signal (peak-to-peak amplitude = ±3 mA). The relationship between EVS input and motor output was characterized in both the frequency (coherence) and time (cumulant density) domains. When head orientation was rotated in yaw from left to right, the biphasic cumulant density function was inverted for all muscle (EVS-EMG) and wholse-body (EVS-AP forces) balance responses. When vision was occluded, the EVS-EMG and EVS-AP forces coherence function amplitude increased at low frequencies (<2 Hz) and was accompanied by a heightened medium-latency peak amplitude for all muscles as well as the whole-body balance response (AP forces) compared to when static visual cues were present. The enhanced coherence amplitudes at lower frequencies may highlight a mechanism for the increase in postural sway from vision to occluded vision. The current findings indicate that the vestibular control of standing balance can be represented by the intrinsic foot muscles and implicate a postural role for these muscles in modulating quiet standing.
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Admin2 · Mar 11, 2018

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NewsBot · Jul 14, 2022

Intrinsic foot muscle hardness is related to dynamic postural stability after landing in healthy young men
NoriakiMaeda et al
Gait & Posture
Volume 86, May 2021, Pages 192-198

Background
The human foot has competent mechanisms for supporting weight and adapting movement to various surfaces; in particular, the toe flexor muscles aid in supporting the foot arches and may be important contributors to postural stability. However, the role of intrinsic foot muscle morphology and structure in the postural control system remains unclear, and the relationship between them is not well known.

Research question
Are intrinsic foot muscle morphology and toe flexor strength related to static and dynamic postural stability in healthy young men?.

Methods
A total of 27 healthy men aged 19–27 years participated in this study. intrinsic foot muscle morphology included muscle hardness and thickness. Cross-sectional area was measured by ultrasonography at an ankle dorsiflexion angle of 0°. The hardness of the abductor hallucis (AbH), flexor hallucis brevis, and flexor digitorum brevis (FDB) muscles was measured using ultrasound real-time tissue elastography. Static postural stability during single-leg standing on a single force platform with closed eyes was assessed for the right leg. In the assessment of dynamic postural stability, the subjects jumped and landed on single-leg onto a force platform and the dynamic postural stability index (DPSI) was measured.

Results
FDB muscle thickness showed a positive correlation with anteroposterior stability index (APSI) (r = 0.398, p = 0.040). AbH muscle hardness was negatively correlated with APSI (r = −0.407, p = 0.035); whereas FDB muscle hardness was positively correlated with DPSI (r = 0.534, p = 0.004), vertical stability index (r = 0.545, p = 0.003), and maximum vertical ground reaction force (r = 0.447, p = 0.020). Multiple regression with forced entry revealed that only DPSI was significantly correlated with FDB muscle hardness (p = 0.003).

Significance
The results indicated that intrinsic foot muscle hardness plays an important role in dynamic postural control among healthy young men, which may enable a more rapid muscular response to changes in condition during jump landing and better performance in balance tasks.
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NewsBot · Sep 25, 2023

The Relationship between Features of Foot Posture, Thickness of Intrinsic Foot Muscles and Dynamic Postural Stability
Gyucheol Shin et al
Exercise Science 2023;32(3): 275-285. doi: https://doi.org/10.15857/ksep.2023.00108

PURPOSE:
This study aimed to determine the correlations between foot posture features, intrinsic foot muscles (IFMs) thickness, and dynamic postural stability.
METHODS:
Forty-one male participants were divided into two groups according to quantified foot postures using the Foot Posture Index (FPI-6) scores: the neutral foot group (FPI-6 score: 0 to +5) and the pronated foot group (FPI-6 score: >+6). The IFMs thickness was measured using ultrasound images of the flexor digitorum brevis (FDB), flexor hallucis brevis (FHB), and abductor hallucis muscles. To investigate the association between IFMs thickness and dynamic postural stability, the Biodex Balance System (BBS) was used in a single-leg stance position with both the eyes open and closed.
RESULTS:
In the BBS tests, the pronated foot group demonstrated significant results in the eyes-closed condition (p<.05). In particular, the differences between the eyes open and closed conditions in postural stability indices were significantly greater in the pronated foot group than in the neutral foot group (p<.05). No significant differences in IFMs thickness between the two groups were observed; however, some subdomains of the FPI-6 demonstrated significant positive correlations with postural stability indices and significant negative correlations with IFMs thickness (p<.05). The talonavicular joint was associated with FDB thickness (R=-0.311). Moreover, the forefoot was correlated with FHB thickness (R=-0.327).
CONCLUSIONS:
The aforementioned results suggest that dynamic postural stability and IFMs thickness are affected by the foot type. Although no significant differences in IFMs thickness were observed, dynamic postural stability and IFMs thickness reduced as the foot displayed features of pronation. This indicates that postural control ability and IFMs are vulnerable to changes in foot posture.
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NewsBot · Nov 28, 2023

Neuromechanical characterization of the abductor hallucis and its potential role in upright postural control
Tushar Sharma et al
Source

There is growing evidence to support a role for the abductor hallucis (AH) in standing balance control, however functional properties of the muscle that may provide more insight into AH’s specific contribution to upright posture have yet to be characterized. This study was conducted to quantify functional neuromechanical properties of the AH and correlate the measures with standing balance variables. We quantified strength and voluntary activation during maximal voluntary isometric contractions of the great toe abductor in nine (3 females, 6 males) healthy, young participants. During electrically-evoked twitch and tetanic contractions we measured great toe abduction peak force and constructed a force-frequency curve. We also evaluated peak abduction force, contraction time (CT), half-relaxation time (HRT), rate of force development (RFD) and relaxation rate (RR) from twitch contractions evoked using doublet stimuli. Strength, VA, CT, HRT, RFD and RR were correlated to centre of pressure standard deviation (COP SD) and velocity (COP VEL) variables of the traditional COP trace and its rambling and trembling components during single-legged stance. AH twitch properties (e.g., CT: 169.8 ± 32.3 ms; HRT: 124.1 ± 29.2 ms) and force-frequency curve were similar to other slow contractile muscles. Contractile speed related negatively with COP VEL, suggesting AH may be appropriate for slow, prolonged tasks such as ongoing postural balance control. Correlation coefficient outcomes for all variables were similar between rambling and trembling components. Our results provide further evidence for the importance of AH neuromechanical function for standing balance control, at least during a challenging single-legged posture.
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