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Recruitment of the plantar intrinsic foot muscles with increasing postural demand

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... Among the intrinsic foot muscles, the abductor hallucis (AH), which abducts and flexes the great toe, is thought to be particularly involved in postural tasks. The AH is active during quiet bipedal standing and adapts to an increased postural challenge (double support to single-legged stance) by increasing its activity (Kelly et al. 2012). Additionally, during single-legged stance, Kelly et al. (2012) reported a positive relationship between AH electromyography (EMG) activity and mediolateral (ML) centre of pressure (COP) displacement. ...
... The AH is active during quiet bipedal standing and adapts to an increased postural challenge (double support to single-legged stance) by increasing its activity (Kelly et al. 2012). Additionally, during single-legged stance, Kelly et al. (2012) reported a positive relationship between AH electromyography (EMG) activity and mediolateral (ML) centre of pressure (COP) displacement. Further, when standing, the AH is responsive to vestibular-driven signals, similar to other postural muscles, and, as such, is likely involved in actively contributing to upright balance control (Wallace et al. 2018). ...
... Given the evidence for the role of AH in standing balance (Kelly et al. 2012;Zhang et al. 2017;Wallace et al. 2018;Taş et al. 2020), a secondary aim was to determine if contractile speed, strength, and VA were related to standing balance performance. In AH, strength has been inferred to be a factor that influences postural control based on findings that greater AH muscle volume (Zhang et al. 2017) and total pressure under the great toe (Tanaka et al. 1996a) correlate with postural sway measures. ...
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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 and 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.
... Simpler tasks elicited lower postural sway, thereby reducing the LoA (see Figure 1B). 8 More complex tasks elicit higher movement variability from the smaller base of support, requiring more effort to maintain balance and increasing the LoA (see Figure 1C). 8 For simpler tasks (ie, BS) COP moves stochastically compared with complex tasks (ie, NDS), 9 requiring greater precision testing to determine whether subtle errors were committed. ...
... 8 More complex tasks elicit higher movement variability from the smaller base of support, requiring more effort to maintain balance and increasing the LoA (see Figure 1C). 8 For simpler tasks (ie, BS) COP moves stochastically compared with complex tasks (ie, NDS), 9 requiring greater precision testing to determine whether subtle errors were committed. Minute variations in COP might not be detectable during manual scoring, even for trained investigators. ...
Article
Context: The Balance Error Scoring System (BESS) is a commonly used clinical tool to evaluate postural control that is traditionally performed through visual assessment and subjective evaluation of balance errors. The purpose of this study was to evaluate an automated computer-based scoring system using an instrumented pressure mat compared to the traditional human-based manual assessment. Design: A descriptive cross-sectional study design was used to evaluate the performance of the automated versus human BESS scoring methodology in healthy individuals. Methods: Fifty-one healthy active participants performed BESS trials following standard BESS procedures on an instrumented pressure mat (MobileMat, Tekscan Inc). Trained evaluators manually scored balance errors from frontal and sagittal plane video recordings for comparison to errors scored using center of force measurements and an automated scoring software (SportsAT, version 2.0.2, Tekscan Inc). A linear mixed model was used to determine measurement discrepancies across the 2 methods. Bland-Altman analyses were conducted to determine limit of agreement for the automated and manual scoring methods. Results: Significant differences between the automated and manual errors scored were observed across all conditions (P < .05), excluding bilateral firm stance. The greatest discrepancy between scoring methods was during the tandem foam stance, while the smallest discrepancy was during the tandem firm stance. Conclusion: The 2 methods of BESS scoring are different with wide limits of agreement. The benefits and risks of each approach to error scoring should be considered when selecting the most appropriate metric for clinical use or research studies.
... Kelly et al. [14] compared the activation patterns of plantar intrinsic foot muscles between double-and single-leg stances. The single-leg stance results in greater electromyographic activity in the abductor hallucis, FDB, and QP. ...
... Concerning toe flexion strength, we did not observe a significant correlation between the strength of the lesser toes and balance ability. Previous studies have identified toe flexion strength as a crucial factor in determining balance ability [3,14,20]. This discrepancy may arise from variations in the measurement methods of toe flexion strength. ...
Article
Background: Toe function is characterised by the strength and dexterity of toe motion. However, previous studies have mostly focused on the importance of toe strength. Objective: This study aimed to investigate the relationships between flexion strength and dexterity of the toes and physical performance. Methods: Twenty healthy participants were included in this study. The flexion force of each toe was measured using a digital force gauge, and the toe dexterity was evaluated using the marble pick-up and rock-paper-scissors tests. These parameters were statistically analysed in relation to physical performance, including repeated side step and balance ability, which was evaluated using centre of pressure (COP) data during single-leg standing, tiptoe standing, and single-leg drop-jumping. Results: A significant correlation was found between the first toe flexion force and the total trajectory length of the COP during one-leg standing and between the time required for marble pick-up and the rock-paper-scissors score and the COP during single-leg drop-jumping. Conclusion: The results underscore the importance of flexion strength and dexterity of the toes in human physical performance and the necessity for the evaluation and improvement of both functions.
... However, the PIFMs have complex features (e.g., four-layered structure and/or small cross-sections), which make it challenging to quantify their activity using only standard surface electromyography (EMG) techniques with a pair of electrodes. Limited intramuscular EMG studies suggest that PIFM activity is dependent on foot loading and postural demands, and has been shown to be minimal in sitting and bipedal standing, but increases markedly when transitioning from bipedal to single-legged or tiptoe standing [11][12][13]. However, these studies only examined and compared PIFM activity between different postural demands, and focused only on non-dancers. ...
... This may be due to the much lower values of both COP variables and PIFM activity levels and lower inter-individual variability in dancers than non-dancers. Intramuscular EMG studies have reported that PIFM activity level respond synchronously to postural sway in single-legged standing, but not in bipedal standing, and increase markedly when transitioning from bipedal to single-legged or tiptoe standing [11,13]. Thus, this study generally supports previous findings that the increase in PIFM activity level in the standing position is dependent on postural demands. ...
... According to muscle synergy theory, the central nervous system (CNS) controls specific muscle groups rather than a single muscle to perform motor tasks. 10 Although intrinsic foot muscles are also activated and associated with the center of pressure (COP) sway during single-leg standing (SLS), 3,14 they have yet to be included in muscle synergy analysis studies. To quantify the simultaneous activity of antagonist muscle pairs crossing the same joint, the cocontraction index (CI) is often calculated. ...
... Compared to DLS, SLS is a challenging balance task, which is highly integrative and demanding. 3,29 In the current study, only 56% of older adults accomplished 30s SLS, which agreed with a previous study on 1827 older adults. 30 The reduced ability to stand on one leg has been suggested as a particularly strong predictor of injurious falls. ...
Article
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The foot core system is essential for upright stability. However, aging‐induced changes in the foot core function remain poorly understood. The present study aimed to examine age‐related differences in postural stability from the perspective of foot core capacity and neuromuscular control during quiet standing. Thirty‐six older and 25 young adults completed foot core capacity tests including toe flexion strength, muscle ultrasonography, and plantar cutaneous sensitivity. The center of pressure (COP) and electromyography (EMG) of abductor hallucis (ABH), peroneus longus (PL), tibialis anterior (TA) and medial gastrocnemius (GM) were simultaneously recorded during double‐leg and single‐leg standing (SLS). EMG data were used to calculate muscle synergy and intermuscular coherence across three frequency bands. Compared to young adults, older adults exhibited thinner hallucis flexors, weaker toe strength, and lower plantar cutaneous sensitivity. The ABH thickness and plantar cutaneous sensitivity were negatively associated with the COP mean peak velocity in older adults, but not in young adults. Besides, older adults had higher cocontraction of muscles spanning the arch (ABH‐PL) and ankle (TA‐GM), and had lower beta‐ and gamma‐band coherence of the ABH‐PL and TA‐PL during SLS. Foot core capacities became compromised with advancing age, and the balance control of older adults was susceptible to foot core than young adults in balance tasks. To compensate for the weakened foot core, older adults may adopt arch and ankle stiffening strategies via increasing muscle cocontraction. Furthermore, coherence analysis indicated that aging may increase the demand for cortical brain resources during SLS.
... However, the PIFMs have complex features (e.g., four-layered structure and/or small cross-sections), which make it challenging to quantify their activity using only standard surface electromyography (EMG) techniques with a pair of electrodes. Limited intramuscular EMG studies suggest that PIFM activity is dependent on foot loading and postural demands, and has been shown to be minimal in sitting and bipedal standing, but increases markedly when transitioning from bipedal to single-legged or tiptoe standing [11][12][13]. However, these studies only examined and compared PIFM activity between different postural demands, and focused only on non-dancers. ...
... This may be due to the much lower values of both COP variables and PIFM activity levels and lower inter-individual variability in dancers than non-dancers. Intramuscular EMG studies have reported that PIFM activity level respond synchronously to postural sway in single-legged standing, but not in bipedal standing, and increase markedly when transitioning from bipedal to single-legged or tiptoe standing [11,13]. Thus, this study generally supports previous findings that the increase in PIFM activity level in the standing position is dependent on postural demands. ...
... Single-leg standing is a more challenging task than bipedal standing [1] and has been used to evaluate Parkinson's disease [2,3], anterior cruciate ligament reconstruction [4], fall risk [5], the impact of a history of sprain [6], and left-right asymmetry [7][8][9]. A subject is generally evaluated based on how long they can remain standing on a single leg [2,5,10]; however, the balance mechanism has not been discussed. ...
Article
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Single-leg standing is a conventional balance evaluation method used in medicine. Although the center of mass (COM) displacement should be evaluated to determine balance quality, no practical COM estimation methods have been developed for single-leg standing. This study aimed to estimate the COM displacement in the anteroposterior and mediolateral directions during single-leg standing using practical measurements. We used a force platform and three inertial measurement units to estimate the COM displacement based on rigid-link models in the sagittal and frontal planes. The rigid-link models were composed of the stance leg, upper body, and non-stance leg. Seven healthy male subjects participated in the experiment to validate the estimation accuracy. The COM estimation accuracy was verified by comparison with measurements obtained using an optical motion capture system. The root mean square error of this method was 1.18 mm in the sagittal plane and 1.26 mm in the frontal plane. This technique will contribute to the detailed evaluation of individual balance abilities in the medical and sports fields.
... [15] In addition, when postural control is required more frequently, as in single-leg stance and walking, the intrinsic toe flexors contract harder. [16] Perhaps unsurprisingly, research on young adults' toe flexor muscle strength has shown that it improves performance outcomes that depend on dynamic balance, such walking speed. [17] , such as quicker 50meter sprints, greater jump distances, longer single-leg jumps, and higher vertical jumps. ...
Article
Background: Lateral ankle sprain stands out as a prevalent injury in both competitive sports and recreational pursuits. Athletes reported residual ankle pain, instability, and weakness. People who have Chronic ankle instability frequently have mechanical deficits, sensorimotor deficits, or a combination of both. Flexor hallucis weakness and decreased toe-flexion strength have been observed in these patients, in order to maintain balance, the extrinsic toe flexors at the ankle joint and all of the toe flexors against the supporting surface through the pads of the planted foot's toes must provide the maximum amount of plantar flexor force. Therefore, the aim of this study is to correlate between hallux flexor strength and dynamic balance in chronic ankle sprains individuals Methods: The study included 20 individuals with Chronic ankle sprain. Each participant’s great toe flexor strength was measured by pinch gauge dynamometer and dynamic balance was assessed using star excursion balance test. Data was analysed using SPSS version 20.0 and p value less than 0.05 was considered statistically significant. Findings: The correlation analysis between the Star Excursion Balance Test scores and hallux flexor strength (lbs) yielded a correlation coefficient (r value) of -0.122 and a corresponding p-value of 0.562. p value >0.05 shows correlation is not statistically significant. Therefore, there is insufficient evidence to conclude a significant correlation between Star Excursion Balance Test scores and hallux flexor strength based on the provided data. Conclusion: According to the study’s findings, the hallux flexor strength does not influence dynamic balance in chronic ankle sprain individuals Key words: Chronic ankle sprain, Chronic ankle instability, Hallux flexor strength, Flexor hallucis longus, Dynamic balance, Star excursion balance test
... Functional exercise programs, including fall preventive exercise interventions, are established without noticeable understanding of the plantar intrinsic foot muscles (PIFMs), while there are indications that these muscles have a role in fall related aspects of mobility. The PIFMs stabilize and stiffen the foot [8,9] and consequently contribute to balance and propulsive gait [10,11]. These mobility aspects are reflected in maximum gait speed, which has been associated with falling [12,13] and toe flexor strength [14]. ...
Article
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Background Falling is highly prevalent among older adults and has serious impact. Age-induced mobility impairments, such as gait modifications, are strongly associated with increased fall risk. Among fall prevention interventions, those including exercises are most effective. However, there is an urgent need to further improve these kinds of interventions. Strengthening the plantar intrinsic foot muscles might benefit mobility in older adults, which may contribute to the reduction of fall risk. The aim of this paper is to provide a protocol to investigate the effect of a plantar intrinsic foot muscle strengthening training versus no training on gait and intrinsic foot muscle function in older adults who are involved in a functional exercise program. Methods For this assessor-blinded RCT, older adults (> 65 years) are recruited who are involved in a group-based functional exercise program. Eligibility criteria include: being able to ambulate 10 m barefoot without using a walking aid and reporting to have either fear of falling or experienced a fall in the previous 12 months or have difficulties with mobility, gait, or balance in daily life. Participants are randomly assigned to an intervention and a control group. The intervention group follows a 12-week plantar intrinsic foot muscle strengthening training. The training consists of isolated and functional foot exercises to be performed 5 times a week, each session lasting approximately 20 min. The training is supervised once a week and the intensity gradually increases based on the participant’s progression. Both groups keep a diary to report physical activities, fall incidents and movement related discomfort. The control condition is limited to keeping this diary. Data are collected at baseline and post-intervention. The trial outcomes are the between group differences in the mean change from baseline in maximum gait speed (primary outcome measure), capacity and strength of the plantar intrinsic foot muscles, foot and ankle biomechanics during gait, and various other fall risk-related variables. ANCOVA’s are used to analyze the trial outcomes. Discussion The results of this RCT will offer recommendations, related to plantar intrinsic foot muscle strengthening, to existing fall preventive exercise programs. Trial registration The trial is registered in the United States National Library of Medicine through ClinicalTrials.gov (NCT05531136, 07/26/2022).
... EMG signals of ABH during standing, squatting and heel raise were found to be greater during single-limb positions than during double limb positions [20]. In addition, mean ABH EMG amplitude was greater in single leg stance than in double leg stance, with EMG amplitude waveforms correlated to of pressure [23]. Another study showed that functional exercises such as toe stance, toe walking, and hopping provoked comparable or more activation of the plantar intrinsic foot muscles than isolated foot exercises and suggested the usefulness of the functional exercises. ...
... The abductor hallucis muscle is also involved in the windlass mechanism along with central band (Farris et al., 2020). It is fundamental to acceleration during walking (Riddick et al., 2019) and in regulating foot balance (Kelly et al., 2012). In Grant's Method of Anatomy (Grant et al., 1989) and the abductor hallucis muscle is described as originating from the central band and medial calcaneal tuberosity. ...
Article
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The plantar aponeurosis comprises medial, central, and lateral bands, which arise from the calcaneal tuberosity. Descriptions of the origin of the abductor hallucis vary among different textbooks. The central band and abductor hallucis muscles are related to the windlass mechanism. Given the uncertainties regarding the details of the origins of the central band and the abductor hallucis muscle, we examined those origins in 100 feet of 50 cadavers (25 males and 25 females) by dissection. There were three central band patterns, depending on the attachment sites of the origins of the central and lateral bands: Pattern Ia, the central band covers the lateral band completely; Pattern Ib, the central band covers part of the lateral band; Pattern II, the lateral band covers part of the central band. The origin of the abductor hallucis muscle was confirmed. It showed two types of variation: attachment type, originating from the central band; non‐attachment type, not originating from the central band. Central band Patterns Ia, Ib, and II were found in 23 feet (17 males, 6 females), 24 feet (25 males, 28 females), and 24 feet (eight males, 16 females), respectively. Pattern Ia predominated in males and Pattern II in females. The attachment and non‐attachment types of abductor hallucis muscle were observed in 28 feet (28%) and 72 feet (72%), respectively. The attachment type with Patterns Ia, Ib, and II was shown in 17 feet, 10 feet, and one foot, respectively. Thus, we revealed variation and sex differences in the central band, which could affect foot morphology and the efficacy of the windlass mechanism.
... 12,13 The IFM are activated in response to increased postural demands, such as transitioning from a double to a single limb stance. 14 According to Tanaka et al. (2019), although elite sprinters have thicker foot muscles than non-sprinters, their Abductor Hallucis (AbH) thickness positively correlates with their 100-m personal best. 15 On the contrary, Yuasa et al. (2018) demonstrated a strong link between the ability to change direction in the pro-agility and 3-cone tests and maximal toe flexor strength with a dorsiflexed MTP in collegiate American football players. ...
Article
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Purpose: The intrinsic foot muscles (IFM) are crucial to the passive, active, and neurological subsystems that compose the foot core, and their weakness may predispose to various foot pathologies, systemic diseases and musculoskeletal conditions. Strengthening of IFM is an effective intervention in clinical conditions, but its role in sports and clinical rehabilitation is still inconclusive. Thus, this review aims to evaluate the effects of IFM strengthening exercises in athletes with normal feet. Methods: An electronic database search was conducted using Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science (WoS), Scopus, MEDLINE, PubMed, and the Physiotherapy Evidence Database (PEDro). The Cochrane risk of bias tool was used for assessing bias in the included studies. Results: Four studies were included for qualitative review. The meta-analysis was not possible due to the het-erogeneity of measuring units of outcome measures in the included studies. All the studies showed an improvement in intrinsic foot muscle strength, though the training protocols used by them were only roughly equivalent. One study reported no significant differences in MLA stiffness after 8 weeks of intervention. The clinician assessed motor performance and morphological assessments showed considerable improvements. Improved vertical running propulsive forces were reported, though the running economy showed no changes. Conclusion: Findings suggest that IFM exercises effectively improve outcomes such as foot morphology and function, strength, running mechanics and subjective function in athletes and may be incorporated in sports rehabilitation. These conclusions should be considered with caution due to bias in included studies.
... Plantar foot intrinsic muscle activation was strongly correlated mediolateral postural sway in single leg stance, with increased activity observed in abductor hallucis, flexor digitorum brevis and quadratus plantae during medial lateral sway. (24) These compensatory changes in the foot intrinsic muscles with respect to pronated and supinated foot can be the possible reason that our study failed to find significant correlation of supinated, neutral and pronated foot postures with dynamic balance. ...
Article
Background: Nursing is a healthcare profession involving prolonged standing and heavy lifting of patients. Working in awkward positions for longer durations may lead to musculoskeletal problems in weight bearing joints like knee and ankle/foot. Abnormal knee or ankle/foot biomechanics can affect balance by changing somatosensory afferents which can affect their job and quality of life. This study aims to understand the relationship of dynamic balance with foot posture index and Q angle in premenopausal nursing population. Materials and Methods: Materials required for this study included pen and paper, a measuring tape, a weighing machine, a marker, adhesive tape, and a full-circle goniometer. The study design employed a cross-sectional analytical approach, and convenience sampling was utilized as the sampling method. The study included 175 premenopausal nursing professionals aged between 25 to 45 years with a minimum of 5 years of work experience. Foot posture was evaluated using the Foot Posture Index, and the Q angle was measured using a full-scale goniometer. Dynamic balance was assessed through the Star Excursion Balance Test (Y balance test). Data collection was done, and appropriate statistical analyses were conducted for the obtained data. Results: Correlation analyses were performed, but no significant (p value > 0.05) correlations were found between foot posture (FPI), Q angle, and dynamic balance (CRDS) for both the right and left sides. Conclusion: Our study concluded that there is no significant correlation of dynamic balance with foot posture index and Q angle in premenopausal nursing population. Key words: Foot Posture Index, Composite Reach Distance Score, Star Excursion Balance Test
... 발 내재근은 발의 안정화 및 보행 시 신체 균형에 영 향을 주는 기능적 근육으로서 [15][16], 발내재근 중 엄지 벌림근은 체중지지 시에 안쪽 세로아치의 안정성에 관 여하고 보행 시 발가락 떼기 및 목말밑관절의 엎침을 조절하는데 중요한 역할을 하며, 엄지벌림근의 약화 및 기능장애는 신체 균형 조절에 영향을 줄 수 있다 [17][18]. 이러한 발 내재근을 강화하고 엄지벌림근을 활 성화하며, 발의 고유수용성 감각 및 자세 안정성을 향상 시키기 위한 효과적인 방법이 SFE이다 [19][20][21][22]. ...
... It also enables the maintenance of proper movement patterns. The relationship between the distal segments of the body and core muscles is well-established, as the core's stability influences mobility and energy transmission from proximal to distal segments [8,9]. Dysfunctions in the plantar region of the foot can manifest as issues in the upper aspects of the anatomy trains. ...
Article
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Background The hamstring muscle is related to the lumbar spine, pelvic, and lower limb movement dysfunction, as well as low back pain and abnormal gait. The kinematic chain's distal elements dysfunctions may affect the body's proximal segments. There is a biomechanical connection between the foot and proximal segments of the body and its effect on the body's functional status, but there is a lack of research that focuses on the correlation between foot posture and hamstring muscle tightness. The study aimed to find the correlation between hamstring muscle tightness and foot posture using the foot posture index (FPI). Methods After obtaining ethical committee approval, necessary authorization was obtained from relevant authorities to proceed with participant screening. Informed consent was obtained from every participant, accompanied by a comprehensive explanation of the study. Screening of participants was conducted based on specific inclusion and exclusion criteria. These criteria were crucial for selecting a homogeneous sample and ensuring the study's objectives were met. The assessment of foot posture was carried out using FPI, and hamstring tightness was examined using an active knee extension test. Result and discussion In our study, which included 188 participants aged between 18 and 25 (mean age: 21.91±1.97), we examined the correlation between FPI and active knee extension (AKE) test results. Using Pearson's correlation coefficient, we found a statistically significant correlation between the FPI and AKE test results. For the right side, the r-value was 0.678 (p-value = 0.0001); for the left side, the r-value was 0.653 (p-value = 0.0001); and for the total, the r-value was 0.663 (p-value = 0.0001). These findings indicate a significant relationship between the FPI and AKE test results. Conclusion The findings of our study revealed a significant relationship between hamstring tightness and pronation of the foot, as measured by the FPI. Understanding this relationship is crucial as it sheds light on the potential impact of hamstring tightness on foot biomechanics. By establishing this link, our study contributes to the body of knowledge surrounding the prevention of alterations in foot biomechanics. It highlights the importance of addressing hamstring tightness to mitigate potential foot pronation issues. Moreover, the study serves as a stepping stone for future research endeavors. It lays the groundwork for further large-scale investigations that encompass a broader range of age groups.
... In addition, the posterior tibialis muscle is the most critical dynamic factor for supporting and maintaining the longitudinal arch of the foot [69]. Changes in the muscular system involved in flexible flatfoot deformity (joint dynamic stabilizers) are believed to affect positional fluctuations (static and dynamic balance) [70]; therefore, this change in the pattern of muscle activity potentially leads to a lack of balance in people with flexible flatfoot. However, the present study's results were inconsistent with the study of Cote et al. (2005) [16]. ...
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Background & purpose Afferent input from the sole affects postural stability. Cutaneous reflexes from the foot are important to posture and gait. Lower-limb afferents alone provide enough information to maintain upright stance and are critical in perceiving postural sway. Altered feedback from propreoceptive receptors alters gait and patterns of muscle activation. The position and posture of the foot and ankle may also play an important role in proprioceptive input.Therefore, the current research aims to compare static balance and ankle and knee proprioception in people with and without flexible flatfeet. Methodology 91 female students between the ages of 18 and 25 voluntarily participated in this study, of which 24 were in the flexible flatfoot group and 67 were in the regular foot group after evaluating the longitudinal arch of the foot. The position sense of ankle and knee joints were measured using the active reconstruction test of the ankle and knee angle; Static balance was measured using the Sharpened Romberg test. Data were non-normally distributed. Accordingly, non-parametric tests were applied. The Kruskal-Wallis test was applied to compare differences between groups in variables. Result Kruskal-Wallis test showed a significant difference between two groups of flat feet and normal feet in the variables of static balance and position sense of ankle plantarflexion, ankle dorsiflexion, and knee flexion (p ≤ 0.05). A significant correlation was found between static balance and sense of ankle and knee position in the group with normal feet. The analysis of the regression line also showed that ankle and knee position sense could predict the static balance score in the regular foot group (ankle dorsiflexion position sense 17% (R² = 0.17), ankle plantarflexion position sense 17% (R² = 0.17) and knee flexion position sense 46% (R² = 0.46) explain of changes in static balance). Discussion & conclusion Flexible flatfoot soles can cause loss of balance and sense of joint position; therefore, according to this preliminary study, clinicians must be aware and should take into account this possible deficit in the management of these patients.
... Although not always explicitly, it has often been considered that a compliant support was simply a way to make standing critical or to mimic a sensory deficit, especially by making proprioceptive feedback less pertinent, mostly at the ankle [52][53][54]. However, increasing postural demand leads to an increase in activity of many muscles, including the intrinsic foot muscles [55]. On the other hand, recent data show that proprioception is not significantly associated with body sway while standing on foam with eyes closed [56,57]. ...
Article
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The ground reaction force (GRF) recorded by a platform when a person stands upright lies at the interface between the neural networks controlling stance and the body sway deduced from centre of pressure (CoP) displacement. It can be decomposed into vertical (VGRF) and horizontal (HGRF) vectors. Few studies have addressed the modulation of the GRFs by the sensory conditions and their relationship with body sway. We reconsidered the features of the GRFs oscillations in healthy young subjects (n = 24) standing for 90 s, with the aim of characterising the possible effects of vision, support surface and adaptation to repeated trials, and the correspondence between HGRF and CoP time-series. We compared the frequency spectra of these variables with eyes open or closed on solid support surface (EOS, ECS) and on foam (EOF, ECF). All stance trials were repeated in a sequence of eight. Conditions were randomised across different days. The oscillations of the VGRF, HGRF and CoP differed between each other, as per the dominant frequency of their spectra (around 4 Hz, 0.8 Hz and ECS ≈ EOS. Adaptation had no effect except in ECF condition. Specific rhythms of the GRFs do not transfer to the CoP frequency, whereas the magnitude of the forces acting on the ground ultimately determines body sway. The discrepancies in the time-series of the HGRF and CoP oscillations confirm that the body’s oscillation mode cannot be dictated by the inverted pendulum model in any experimental conditions. The findings emphasise the robustness of the VGRF “postural rhythm” and its correspondence with the cortical theta rhythm, shed new insight on current principles of balance control and on understanding of upright stance in healthy and elderly people as well as on injury prevention and rehabilitation.
... IFM has an essential dynamic function during gait and running (Cheung et al., 2016;Farris et al., 2019Farris et al., , 2020Kelly et al., 2012;Mckeon et al., 2014;Okamura et al., 2018) as part of the foot's dynamic system (Mckeon et al., 2014). During gait, the IFM activation can increase in propulsion phase, acting as a rigid lever for impulse and stabilizing the MLA (Kelly et al., 2014). ...
... Jacob et al [38] combined anthropometrical and plantar pressure data and revealed that FDB muscles can exert a force approximately 13% of body weight during the propulsive phase of walking. A similar EMG study has reported a small amount of activity in abductor hallucis and FDB during relaxed standing and significant increase in activity at increased postural demands [39]. Mann et al [40] demonstrated that the abductor hallucis and FDB are active during the stance phase of gait and continued until toe off. ...
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This study aimed to compare the intrinsic foot muscle (IFM) morphology and isometric strength among runners with habitual rearfoot strike (RFS) and non-rearfoot strike (NRFS) patterns. A total of 70 recreational male runners were included in this study (32 RFS and 38 NRFS), an ultrasound device and hand-held dynamometry were used to measure IFM morphology and isometric strength. Results indicated that the RFS runners had significantly thicker tibialis anterior (P = 0.01, ES = 0.64, 95% CI [0.01–0.07]) in IFMs morphology and higher Toe2345 flexion strength in IFMs strength (P = 0.04, ES = 0.50, 95% CI [0.01–0.27]) than NRFS runners, the cross-sectional area of flexor digitorum brevis was positively correlated with T2345 flexion strength (r = 0.33, p = 0.04), T12345 (r = 0.37, p = 0.02) and Doming (r = 0.36, p = 0.03) for runners with NRFS. IFMs morphology and isometric strength were associated with foot strike pattern, preliminary findings provide new perspectives for NRFS runners through the simple measurement of IFMs morphological characteristics predicting IFMs strength, future studies could adopt IFMs training to compensate the muscle strength defects and prevent foot-related injuries.
... Foot muscles play an important role to maintain balance [22]. Due to temporary disuse, foot muscle volume diminishes after ankle inversion trauma and unfortunately does not recover in chronic ankle instability [23]. ...
... However, standing in critical conditions, such as in tandem stance or on foam, is an attention-demanding task, where the cognitive task may affect the level of instability (Boisgontier et al., 2013;Honeine et al., 2017). Further, maintaining the equilibrium in critical conditions requires continuous activity in several muscles (Schieppati et al., 1995;Tokuno et al., 2007;Kelly et al., 2012;Sozzi et al., 2013), implying a considerable effort. When standing on foam, muscle activity and metabolic cost increases Mohapatra et al., 2014;Mademli et al., 2021) and body sway increases concurrently (Teasdale et al., 1991;Patel et al., 2011;Anson et al., 2019;Hsiao et al., 2020). ...
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This special issue adresses acute and chronic changes in postural control in response to different physiological states and external environmental conditions.
... This method differs from all the previous studies using a bipedal standing position (50% of BW). Since the IFM shows little to no activity during double-limb upright standing (Basmajian & Stecko, 1963;Mann & Inman, 1964) but are active during single-limb upright standing (Kelly et al., 2012;Ridge et al., 2022) using a 'quasi' single leg stance position in the loading condition allows a greater activity of the IFM, which increases their contribution in controlling foot arches deformation. ...
Article
Background Standing toe curl (STC) has an immediate effect on muscle activity, but the kinematics of the exercise and its effect on the medial longitudinal arch of the foot are unknown. Objective The purpose of this study was to examine the differences in kinematic and kinetic changes during toe flexion while performing towel curl (TC) in a standing position and STC. Methods Ten healthy adults with normal feet (18 limbs) participated in this study. Using a three-dimensional motion analysis system, we calculated the toe flexion angle, medial longitudinal arch (MLA) angle, MLA height, MLA length, ankle joint angle, center of foot pressure, and center position of the hip joint during toe flexion using TC and STC exercises. Results The TC exercise resulted in a decrease in the MLA due to the backward shift in the center of pressure and ankle dorsiflexion. On the other hand, STC did not demonstrate any significant difference in the position of the center of pressure or ankle joint angle, allowing the toes to flex while maintaining a standing posture and resulting in an increase in the MLA. Conclusions STC was suggested to be effective in maintaining MLA for weight support.
Article
Background: Sports injuries often occur during landing, necessitating postural stability for injury prevention. Electrical stimulation of the plantar foot induces activities of the intrinsic foot muscles and improves somatosensory and postural stability during landing. However, this effect remains unclear. Therefore, the aim of this study was to investigate the immediate effects of electrical stimulation on the activities of the intrinsic foot muscles, plantar somatosensory system, and postural stability during landing. Methods: Twenty-two college athletes were divided into an electrical stimulation group and a control group. Electrical stimulation was applied to the plantar foot using a commercial device. The toe function and plantar tactile sensations were evaluated. The activities of the intrinsic muscles and the parameters of the ground reaction force were measured and calculated. We compared pre- and postintervention outcomes. Results: In the electrical stimulation group, two subjects showed improvement in toe function, and plantar tactile sensation improved significantly postintervention. The control group exhibited no significant change in plantar tactile sensation. A significant interaction was observed in anteroposterior postural stability during landing, notably improving in the electrical stimulation group. Conclusions: Electrical stimulation of the plantar foot immediately improved toe function, plantar tactile sensation, and postural stability during landing. Such stimulation would be beneficial in preventing sports injuries.
Chapter
In this book titled Current Exercise Approaches in Orthopedic Disorders: A handbook for rehabilitation professionals, it is aimed to compile the exercise approaches currently used in orthopedic pathologies. A physiotherapist or a health professional interested in rehabilitation processes who reads this book will have access to a world of up-to-date exercise approaches that include all anatomical joint areas of the body. The current exercise approaches explained throughout the book have been tried to be presented in a high-quality manner, supported by visuals. In addition, those who read the book will be able to access important clues about the anatomy and kinesiology of many body joints and important issues regarding possible orthopedic pathologies of the relevant joints. We hope that our book will contribute to the _eld of orthopedic rehabilitation.
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During tiptoe standing, especially with the single-legged support, the foot joints in ballet dancers are heavily loaded. Thus, the activity of the plantar intrinsic foot muscles (PIFMs), which stabilize the foot joints, may be important in reducing postural sway during tiptoe standing. We compared PIFM activity during single-legged and bipedal tiptoe standing and examined its relationship to postural sway in dancers. In 11 female ballet dancers, the electromyography (EMG) amplitudes of PIFMs and the center of pressure (COP) data were recorded during single-legged and bipedal tiptoe standing tasks. The EMG amplitudes were normalized to those during the maximal voluntary contraction, and PIFM activity level and its coefficient of variation over time (EMG-CVtime) during the task were assessed. From the COP data, standard deviations in the anteroposterior (COP-SDAP) and mediolateral (COP-SDML) direction, velocity, and area were calculated. PIFM activity level and COP velocity were 2–2.5-fold higher in the single-legged than bipedal task (p≤0.003). Significant correlations were found between PIFM activity level and COP velocity (r=0.666, p=0.025) and between EMG-CVtime and COP-SDAP or COP-SDML (r≥0.738, p≤0.010) only in the single-legged task. These results suggest that PIFM activity is associated with postural sway, especially during single-legged tiptoe standing in dancers.
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Prevalence of impaired foot function among baseball players with and without a disabled throwing shoulder/elbow was investigated. The study included 138 male players. Players who had previously complained of shoulder/elbow pain during throwing motion were defined as the players with a history, and those who experienced shoulder/elbow pain during the examination were defined as having the injury. Foot function was evaluated by foot “rock paper scissors” movements and floating toes. Their prevalence was assessed and the relationships between players with and without the injuries were statistically analyzed. The prevalence of players with a history and injury was 27% and 7%, respectively. The prevalence of impaired foot function on the non-throwing side among players with injury was significantly higher than those without (60% vs. 28%, P < 0.001) and higher tendency on the throwing side than those without (60% vs. 32%). Regarding floating toes, players with a relevant history showed a significantly higher prevalence on the throwing side than those without (49% vs 28%, P < 0.001) and higher tendency on the non-throwing side than those without (49% vs 32%). Players with disabled throwing shoulder/elbow have a significantly higher prevalence of impaired foot function and floating toes than players without it.
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Purpose] The immediate effects of the towel-gathering exercise (conventional method) and a devised intrinsic foot muscles exercise (yubidashi method) in the standing position on the muscle activities of the intrinsic and extrinsic foot muscles during flexion of the toes were examined by foot morphology. [Participants and Methods] Thirty-five limbs of healthy adults were divided into normal and pronated foot groups, and the muscle activities and toe grasping forces of the intrinsic and extrinsic foot muscles were compared before and after the two toe flexion exercises. [Results] The conventional method increased the muscle activity of the extrinsic foot muscles in the normal foot, decreased the muscle activity of the intrinsic foot muscles, and increased the toe grasp strength. The yubidashi method increased the muscle activity of the extrinsic and intrinsic foot muscles of the pronated foot. [Conclusion] The results suggest that the conventional method is effective for normal feet while the yubidashi method is effective for pronated feet.
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Background: Intrinsic foot muscle (IFM) weakness can result in reduced foot function, making it crucial for clinicians to track IFM strength changes accurately. However, assessing IFM strength can be challenging for clinicians, as there is no clinically applicable direct measure of IFM strength that has been shown to be reliable and valid with the foot on the ground. Purpose: The purpose was to investigate the intra-rater and inter-rater reliability of a novel, budget-friendly IFM dynamometer and determine its agreement with a handheld dynamometer (HHD). The researchers also examined correlations of foot morphology and activity level to IFM strength. Methods: Two assessors measured IFM strength of 34 healthy volunteers (4 male, 30 female; age=21.14±2.57, height=164.66 ±7.62 cm, mass=64.45±11.93 kg) on two occasions 6.62±0.78 days apart with the novel dynamometer to assess intra-and inter-rater reliability. The HHD was used to measure IFM in the first session in order to assess validity. Results: For the novel dynamometer, intra-and inter-rater reliability was moderate-to-excellent (ICC = 0.73-0.95), and the majority of the strength tests were within the 95% limits of agreement with the HHD. Wider foot morphology and a higher number of days walking over the prior seven days had small but significant correlations with IFM strength (dominant foot r = 0.34, non-dominant foot r = 0.39; r =-0.33,-0.39 respectively). Conclusion: This novel IFM dynamometer is a budget-friendly ($75) tool that was shown to be reliable and valid in a healthy population.
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Background The effect of foot, especially intrinsic muscles, on postural control and its related mechanisms remain unclear due to the complex structure. Therefore, this study aims to investigate the activation of intrinsic foot muscles in the elderly under static and dynamic postural tasks. Methods Twenty-one elderly participants were included to perform different postural tests (sensory organization test (SOT), motor control test (MCT), limit of stability test (LOS), and unilateral stance test) by a NeuroCom Balance Manager System. The participants were instructed to maintain postural stability under conditions with combined different sensory inputs (vision, vestibular, and proprioception) in SOT as well as conditions with translation disturbance in MCT, and to perform an active weight-shifting tasks in LOS. During these tasks, muscle activation were simultaneously acquired from intrinsic foot muscles (abductor halluces (AbH) and flexor digitorum brevis (FDB)) and ankle muscles (anterior tibialis, medial head of gastrocnemius, lateral head of gastrocnemius, and peroneus longus). The root-mean-square amplitude of these muscles in postural tasks was calculated and normalized with the EMG activity in unilateral stance task. Results The activation of intrinsic foot muscles significantly differed among different SOT tasks ( p < 0.001). Post-hoc tests showed that compared with that under normal condition 1 without sensory interference, EMGs increased significantly under sensory disturbance (conditions 2–6). By contrast, compared with that under the single-sensory disturbed conditions (conditions 2–4; 2 for disturbed vision, 3 for disturbed vestibular sensation, 4 for disturbed proprioception), activation was significantly greater under the dual-sensory disturbed postural tasks (conditions 5 and 6; 5 for disturbed vision and proprioception, 6 for disturbed vestibular sensation and proprioception). In MCT, EMGs of foot muscles increased significantly under different translation speeds ( p < 0.001). In LOS, moderate and significant correlations were found between muscle activations and postural stability parameters (AbH, r = 0. 355–0.636, p < 0.05; FDB, r = 0.336–0.622, p < 0.05). Conclusion Intrinsic foot muscles play a complementary role to regulate postural stability when disturbances occur. In addition, the recruitment magnitude of intrinsic foot muscles is positively correlated with the limit of stability, indicating their contribution to increasing the limits of stability in the elderly.
Article
Zur Therapie und Prophylaxe von Sprunggelenkdistorsionen wird meist die extrinsische Fußmuskulatur trainiert. Ein spezielles Training der intrinsischen Fußmuskeln findet kaum statt. Wie wichtig „Short-Foot Exercises“ oder ein Zehentraining nach einem Supinationstrauma sind, zeigt ein Review der Hochschule Furtwangen. Die Kernaussage: Das Trainieren der kurzen Fußmuskeln kann die subjektive Instabilität, Balance, Somatosensibilität und Funktionalität signifikant verbessern. Für Praxistipps ist die Qualität der Evidenz jedoch noch zu gering.
Article
Background: Foot-related complications including impaired peripheral circulation and lower limb ulceration are severe consequences for those with diabetes mellitus. This study aimed to assess differences in tissue oxygenation and oxygen utilization of the plantar surface intrinsic foot muscles between diabetic participants and healthy comparisons following short foot exercise and a standard walking protocol. Methods: Eighteen participants, 9 with diabetes and 9 healthy age- and sex-matched comparisons, completed two interventions in a randomized order. For the short foot exercise intervention, participants completed 5 sets of 15 intrinsic foot muscle contractions. For the walking intervention, participants completed a modified six-minute walk test. Tissue oxygenation variables including oxygenated hemoglobin, deoxygenated hemoglobin, and tissue saturation index were measured using near-infrared spectroscopy in quiet stance and during intrinsic foot muscle contraction cycles following each intervention. Means, standard deviations, 95 % confidence intervals, mean differences, and Cohen's d effect sizes were calculated for each tissue oxygenation variable. Results: The results of this study indicated no significant group differences in quiet standing tissue oxygenation measures at baseline and following each intervention. Participants in the diabetic group had significantly less change in tissue saturation index during intrinsic foot muscle contractions compared to healthy participants after the short foot exercise intervention (ES= 4.00, P = .0002) and walking intervention (ES= 1.33, P = .015). Conclusions: By utilizing wireless NIRS and novel research methodology, this study was able to explore changes in plantar surface tissue oxygenation of the intrinsic foot muscles following a targeted short foot exercise intervention as well as a standard walking protocol in patients diagnosed with diabetes compared to age- and sex- matched individuals without diabetes. We identified that diabetic participants presented with less oxygen utilization during intrinsic foot muscle contractions performed following both exercise interventions compared to their healthy age- and sex- matched comparisons.
Article
Background Training the plantar intrinsic foot muscles (PIFMs) has the potential to benefit patients with lower extremity musculoskeletal conditions as well as the aged population. Isolated foot exercises, often standard in clinical practice, are difficult to perform, whereas functional exercises are much easier to accomplish. However, it is unclear whether functional exercises are comparable to isolated foot exercises in activating the PIFMs. Objective This study aims to compare the activation of PIFMs between functional exercises versus isolated foot exercises. Methods Using surface electromyography (EMG), muscle activation of three PIFMs was measured in four functional exercises (i.e. normal/unstable toe stance, toe walking, and hopping) versus a muscle-specific isolated foot exercise in 29 younger adults, resulting in 12 comparisons. Results Functional exercises showed larger mean EMG amplitudes than the isolated foot exercises in 25% of the 12 comparisons, while there was no difference in the remaining 75%. Conclusion Functional exercises provoked comparable or even more activation of the PIFMs than isolated foot exercises. Given that functional exercises are easier to perform, this finding indicates the need to further investigate the effectiveness of functional exercises in physical therapy to improve muscle function and functional task performance in populations that suffer from PIFM weakness or dysfunction.
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Much of the work describing support of the medial longitudinal arch has focused on the plantar fascia and the extrinsic muscles. There is little research concerning the function of intrinsic muscles in the maintenance of the medial longitudinal arch. Ten healthy volunteer adults served as subjects for this study, which was approved by the University Investigational Review Board. The height of the navicular tubercle above the floor was measured in both feet while subjects were seated with the foot in a subtalar neutral position and then when standing in a relaxed calcaneal stance. Subtalar neutral was found by palpating for talar congruency. Recordings of muscle activity from the abductor hallucis muscle were performed while the subjects maintained a maximal voluntary contraction in a supine position by plantarflexing their great toes. An injection of lidocaine (1% with epinephrine) was then administered by a Board-certified orthopedic surgeon in the region of the tibial nerve, posterior and inferior to the medial malleolus. Measurements were repeated and compared by using a paired t test. After the nerve block, the muscle activity was 26.8% of the control condition (P =.011). This corresponded with an increase in navicular drop of 3.8 mm. (P =.022). The observation that navicular drop increased when the activity of the intrinsic muscles decreased indicates that the intrinsic pedal muscles play an important role in support of the medial longitudinal arch.
Article
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Ageing is associated with changes to the structure and function of the foot and ankle, and there is preliminary evidence that foot problems impair balance and increase the risk of falls. To explore this in more detail, we conducted a study to determine the relative contribution of several foot and ankle characteristics to performance on a range of balance and functional tests. One hundred seventy-six people (56 men and 120 women, mean age 80.1 years, standard deviation 6.4 years) residing in a retirement village underwent tests of foot and ankle characteristics (including foot posture, range of motion, strength, and deformity), sensorimotor function (including vision, sensation, strength, and reaction time), and balance and functional ability (including tests of standing balance, leaning balance, stepping, sit-to-stand, and walking speed). Many foot and ankle characteristics and sensorimotor measures were associated with performance on the balance and functional tests in univariate analyses. Multiple regression analysis consistently revealed that ankle flexibility, plantar tactile sensitivity, and toe plantarflexor strength were significant and independent predictors of balance and functional test performance, explaining up to 59% of the variance in these test scores. Foot and ankle characteristics, particularly ankle flexibility, plantar tactile sensation, and strength of toe plantarflexor muscles, are significant independent predictors of balance and functional ability in older people. Programs to improve the strength and flexibility of the foot and interventions to augment plantar sensation may be beneficial in improving mobility and reducing the risk of falls.
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Previous research has shown that changes in spinal excitability occur during the postural sway of quiet standing. In the present study, it was of interest to examine the independent effects of sway position and sway direction on the efficacy of the triceps surae Ia pathway, as reflected by the Hoffman (H)-reflex amplitude, during standing. Eighteen participants, tested under two different experimental protocols, stood quietly on a force platform. Percutaneous electrical stimulation was applied to the posterior tibial nerve when the position and direction of anteroposterior (A-P) center of pressure (COP) signal satisfied the criteria for the various experimental conditions. It was found that, regardless of sway position, a larger amplitude of the triceps surae H-reflex (difference of 9-14%; P = 0.005) occurred when subjects were swaying in the forward compared with the backward direction. The effects of sway position, independent of the sway direction, on spinal excitability exhibited a trend (P = 0.075), with an 8.9 +/- 3.7% increase in the H-reflex amplitude occurring when subjects were in a more forward position. The observed changes to the efficacy of the Ia pathway cannot be attributed to changes in stimulus intensity, as indicated by a constant M-wave amplitude, or to the small changes in the level of background electromyographic activity. One explanation for the changes in reflex excitability with respect to the postural sway of standing is that the neural modulation may be related to the small lengthening and shortening contractions occurring in the muscles of the triceps surae.
Article
The common denominator in the assessment of human balance and posture is the inverted pendulum model. If we focus on appropriate versions of the model we can use it to identify the gravitational and acceleration perturbations and pinpoint the motor mechanisms that can defend against any perturbation.We saw that in quiet standing an ankle strategy applies only in the AP direction and that a separate hip load/unload strategy by the hip abd/adductors is the totally dominant defence in the ML direction when standing with feet side by side. In other standing positions (tandem, or intermediate) the two mechanisms still work separately, but their roles reverse. In the tandem position ML balance is an ankle mechanism (invertors/evertors) while in the AP direction a hip load/unloading mechanism dominates.During initiation and termination of gait these two separate mechanisms control the trajectory of the COP to ensure the desired acceleration and deceleration of the COM. During initiation the initial acceleration of the COM forward towards the stance limb is achieved by a posterior and lateral movement of the COP towards the swing limb. After this release phase there is a sudden loading of the stance limb which shifts the COP to the stance limb. The COM is now accelerated forward and laterally towards the future position of the swinging foot. Also ML shifts of the COP were controlled by the hip abductors/adductors and all AP shifts were under the control of the ankle plantar/dorsiflexors. During termination the trajectory of both COM and COP reverse. As the final weight-bearing on the stance foot takes place the COM is passing forward along the medial border of that foot. Hyperactivity of that foot's plantarflexors takes the COP forward and when the final foot begins to bear weight the COP moves rapidly across and suddenly stops at a position ahead of the future position of the COM. Then the plantarflexors of both feet release and allow the COP to move posteriorly and approach the COM and meet it as quiet stance is achieved. The inverted pendulum model permitted us to understand the separate roles of the two mechanisms during these critical unbalancing and rebalancing periods.During walking the inverted pendulum model explained the dynamics of the balance of HAT in both the AP and ML directions. Here the model includes the couple due to the acceleration of the weight-bearing hip as well as gravitational perturbations. The exclusive control of AP balance and posture are the hip extensors and flexors, while in the ML direction the dominant control is with the hip abductors with very minor adductor involvement. At the ankle the inverted pendulum model sees the COM passing forward along the medial border to the weight-bearing foot. The model predicts that during single support the body is falling forward and being accelerated medially towards the future position of the swing foot. The model predicts an insignificant role of the ankle invertors/evertors in the ML control. Rather, the future position of the swing foot is the critical variable or more specifically the lateral displacement from the COM at the start of single support. The position is actually under the control of the hip abd/adductors during the previous early swing phase.The critical importance of the hip abductors/adductors in balance during all phases of standing and walking is now evident. This separate mechanism is important from a neural control perspective and clinically it focuses major attention on therapy and potential problems with some surgical procedures. On the other hand the minuscule role of the ankle invertors/evertors is important to note. Except for the tandem standing position these muscles have negligible involvement in balance control.
Article
• We studied quiet stance investigating strategies for maintaining balance. Normal subjects stood with natural stance and with feet together, with eyes open or closed. Kinematic, kinetic and EMG data were evaluated and cross-correlated. • Cross-correlation analysis revealed a high, positive, zero-phased correlation between anteroposterior motions of the centre of gravity (COG) and centre of pressure (COP), head and COG, and between linear motions of the shoulder and knee in both sagittal and frontal planes. There was a moderate, negative, zero-phased correlation between the anteroposterior motion of COP and ankle angular motion. • Narrow stance width increased ankle angular motion, hip angular motion, mediolateral sway of the COG, and the correlation between linear motions of the shoulder and knee in the frontal plane. Correlations between COG and COP and linear motions of the shoulder and knee in the sagittal plane were decreased. The correlation between the hip angular sway in the sagittal and frontal planes was dependent on interaction between support and vision. • Low, significant positive correlations with time lags of the maximum of cross-correlation of 250-300 ms were found between the EMG activity of the lateral gastrocnemius muscle and anteroposterior motions of the COG and COP during normal stance. Narrow stance width decreased both correlations whereas absence of vision increased the correlation with COP. • Ankle mechanisms dominate during normal stance especially in the sagittal plane. Narrow stance width decreased the role of the ankle and increased the role of hip mechanisms in the sagittal plane, while in the frontal plane both increased. • The modulation pattern of the lateral gastrocnemius muscle suggests a central program of control of the ankle joint stiffness working to predict the loading pattern.
Article
Aim: The study examined the role of the motor cortex in the control of human standing. Methods: Subjects (n = 15) stood quietly with or without body support. The supported standing condition enabled subjects to stand with a reduced amount of postural sway. Peripheral electrical stimulation, transcranial magnetic stimulation (TMS) or transcranial electrical stimulation (TES) was applied to elicit a soleus (SOL) H-reflex, or motor-evoked potentials (MEPs) in the SOL and the tibialis anterior (TA). Trials were grouped based on the standing condition (i.e. supported vs. normal) as well as sway direction (i.e. forward and backward) while subjects were standing normally. Results: During normal when compared to supported standing, the SOL H-reflex was depressed (−11 ± 4%), while the TMS-evoked MEPs from the SOL and TA were facilitated (35 ± 11% for the SOL, 51 ± 15% for the TA). TES-evoked SOL and TA MEPs were, however, not different between the normal and supported standing conditions. The data based on sway direction indicated that the SOL H-reflex, as well as the SOL TMS- and TES-evoked MEPs were all greater during forward when compared to backward sway. In contrast, the TMS- and TES-evoked MEPs from the TA were smaller when swaying forward as compared to backward. Conclusions: The results indicated the presence of an enhanced cortical excitability because of the need to control for postural sway during normal standing. The increased cortical excitability was, however, unlikely to be involved in an on-going control of postural sway, suggesting that postural sway is controlled at the spinal and/or subcortical levels.
Article
Electromyography with fine‐wire electrodes and special equipment for synchronized motion pictures were used to study six muscles of the leg and foot during walking in five different ways in ten “normal” and ten flatfooted subjects. Detailed analyses and comparisons of the two groups are described and discussed. Tibialis Anterior has two peaks of activity at heel‐strike and toe‐off of the stance phase; is inactive during mid‐swing and middle of the stance phase; is active at full‐foot in flatfooted subjects, and generally more active during toe‐out and toe‐in walking. Tibialis posterior is inactive through the swing phase. In flatfooted persons it becomes activated at heel‐strike and more active at full‐foot during level walking. The toe‐out position reduces its activity. Flexor hallucis longus is most active in mid‐stance; during toe‐out walking, activity increases in both phases, generally being more active in “normal” persons. Peroneus longus is most active at mid‐stance and heel‐off and generally more active in flatfooted persons. Abductor hallucis and Flexor digitorum brevis are generally more active in flatfooted persons. An important regular pattern of inversion and eversion during the walking cycle is described. Contingent arch support by muscles rather than continuous support is the rule, muscles being recruited to compensate for lax ligaments and special stresses during the walking cycle.
Article
Non‐technical summary Homeostasis, the physiological control of variables such as body position, is founded on negative feedback mechanisms. The default understanding, consistent with a wealth of knowledge related to peripheral reflexes, is that feedback mechanisms controlling body position act continuously. For more than fifty years, it has been assumed that sustained control of position is best interpreted using continuous paradigms from engineering control theory such as those which regulate speed in a vehicle ‘cruise control’ system. Using a joystick to control an unstable load that falls over like a person fainting, we show that control using intermittent gentle taps is natural, more effective and robust to unexpected changes than continuous hand contact, works best with two taps per second, and can explain the upper frequency limit of control by both methods. Serial ballistic control, limited to an optimum rate, provides a new physiological paradigm for interpreting sustained control of posture and movement.
Article
Surface and wire myoelectric activity of the medial gastrocnemius (MG), lateral gastrocnemius (LG) and tibialis anterior (TA) of the cat were recorded during supramaximal stimulation applied via their nerves before and after the muscle nerve to the LG and TA were cut in order to determine the amount of EMG crosstalk amongst neighbouring muscles. It was shown that the peak-to-peak (p-p) amplitude and mean absolute value (MAV) of crosstalk M waves recorded from the LG and TA after their nerve was cut did not exceed 5% of their maximal value for surface electrodes and 2.5% of their maximal value for wire electrodes. EMG crosstalk values were similar in terms of peak to peak and MAV. Surface EMG crosstalk values were significantly higher in preparations in which a substantial amount of subcutaneous fat covered the muscles, being 20 (± 16.6) % MAV and 16 (± 12) % p-p. During increasing force contraction (accomplished by orderly recruitment of motor units) from 10-100% of the maximal force of the MG the corresponding crosstalk in the LG and TA increased linearly with the EMG of the MG. It is concluded that the crosstalk problem in surface recording is negligible for most biomechanical studies in which standard EMG recording protocol is employed, yet a warning is issued against the indiscriminate recording of surface EMG from muscles covered by adipose tissue.
Article
Hallux valgus and lesser toe deformities are highly prevalent foot problems in older people. One factor contributing to the development of these toe deformities is reduced toe flexor strength. As adequate toe flexor strength is also crucial in maintaining balance, it was hypothesised that poor toe flexor strength and toe deformities would increase the risk of falls in community-dwelling older people. The feet of 312 men and women aged 60-90 years were assessed for the presence of lesser toe deformities and hallux valgus. Hallux and lesser toe flexor strength were assessed using an emed AT-4 pressure platform and novel test protocol. Participants were then followed prospectively to determine their falls incidence over 12 months. During the 12 month follow-up, 107 (35%) participants experienced a fall. Compared to non-fallers, fallers displayed significantly less strength of the hallux (11.6 (SD 6.9) versus 14.8 (SD 7.8)% BW, P<0.01) and lesser toes (8.7 (SD 4.7) versus 10.8 (SD 4.5)% BW, P<0.01), and were more likely to have hallux valgus (relative risk [RR]=2.36; 95% CI=1.03-5.45; P<0.01) and lesser toe deformity (RR=1.32; 95% CI=1.04-1.69; P<0.01). Reduced toe flexor strength and the presence of toe deformities increase the risk of falling in older people. To reduce this risk, interventions designed to increase strength of the toe flexor muscles combined with treatment of those older individuals with toe deformities may be beneficial.
Article
Technical note. To provide background theory and information and to describe relevant applications of autocorrelation and cross-correlation methodology as they apply to the field of motor control in human movement and rehabilitation research. Commonly used methodologies for pattern and event recognition, determination of muscle activation timing for investigation of movement coordination, and motor control are generally difficult to implement, particularly with large datasets. A brief description of the underlying mathematical theory of correlation analyses is given, followed by 4 different examples of how this methodology is useful for research in the movement sciences. Examples demonstrating the utility of correlation analyses are presented from several different studies conducted at the University of Waterloo. Autocorrelation was used to demonstrate the presence of 60-Hz noise in an electromyography signal that was not visible in the raw data. A "top-down" paraspinal muscle activation pattern was demonstrated for healthy adults during gait, with the use of cross-correlation. Cross-correlation was also used to quantify coactivation of bilateral gluteus medius muscles during standing in individuals who developed low-back pain. Gender differences in gluteus medius control of mediolateral center of pressure were seen with the use of cross-correlation. Autocorrelation and crosscorrelation have been shown to be an effective tool for several different applications in the movement sciences. Examples of the method's utility include noise detection within a signal, determination of relative muscle activation onsets for postural control, objective quantification of muscle coactivation, and relating muscle activations with mechanical events.
Article
Understanding muscle architecture of the foot may assist in the design of surgical procedures such as tendon transfer, biomechanical modeling of the foot, prosthesis design, and analysis of foot function. There is limited published information regarding foot intrinsic muscle architecture. Eleven fresh-frozen cadaveric feet were studied from eight males and three females. Twenty-eight intrinsic muscles were dissected in each foot, and measurements of fiber length, muscle length, and muscle volume obtained using calipers and water displacement technique. The physiologic cross-sectional area, fiber/muscle length ratio, muscle mass fraction, and tension fraction were then calculated. Intrinsic muscle length was related to foot size. The mean fiber length ranged from 13.6 mm (first plantar interosseous) to 28.0 mm (second extensor digitorum brevis). The mean muscle length ranged from 24.8 mm (adductor hallucis transverse) to 115.8 mm (abductor hallucis). The mean muscle volume ranged from 0.4 cc (fifth lumbrical) to 15.2 cc (abductor hallucis). The physiologic cross-sectional area ranged from 0.28 cm2 (second and third lumbrical) to 6.68 cm2 (abductor hallucis). The fiber/ muscle ratio ranged from 0.20 (abductor hallucis) to 0.82 (adductor hallucis transverse). The mass fraction ranged from 0.33% (fifth lumbrical) to 16.59% (abductor hallucis). The tension fraction ranged from 0.34% (fifth lumbrical) to 15.37% (abductor hallucis). The abductor hallucis and adductor hallucis oblique had much greater physiologic cross-sectional areas compared to those of the other intrinsic muscles. The lumbrical muscles had relatively low physiologic cross-sectional areas. These observations illustrate the underlying structural basis for the functional capacities of the intrinsic muscles of the foot.
Article
The aim of this study was to investigate the relationship between the strength of the foot muscles that control the toes and disorders such as shin splint. In order to this, we designed and built a toe dynamometer to compare the muscle power exerted through the toes in top female marathon runners and age-matched women not involved in sports. The subjects were 12 top-level female marathon runners (Group A) and 37 student nurses who were not involved in sports (Group B). We devised a dynamometer to measure the total power exerted by the flexor muscles of the 5 toes of a single foot (total flexor power) and the combined power of the abductors of the big (1st) and little (5th) toes (abductor power). In Group A, the total flexor power was 14.3 +/- 5.3 kg in the right foot and 15.4 +/- 4.7 kg in the left foot. The abductor power was 1.9 +/- 1.8 kg in the right foot and 2.2 +/- 1.9 kg in the left foot. In Group B, total flexor power was 18.3 +/- 6.7 kg in the right foot, while the abductor power was 1.9 +/- 1.7 kg. The subjects from Group A with an arch index < 1.0 (n = 8) or > 1.0 (n = 4) were respectively classified as Group I and Group II. In Group I, total flexor power was 14.9 +/- 5.3 kg (right) and 15.5 +/- 5.2 kg (left), while the abductor power was 2.6 +/- 1.9 kg (right), and 3.1 +/- 1.7 kg (left). In Group II, the total flexor power was 13.2 +/- 5.8 kg (right) and 15.1 +/- 4.2 kg (left), while the abductor power was 0.7 +/- 0.6 kg (right) and 0.3 +/- 0.2 kg (left). The abductor power of toes was significantly lower in Group II than in Group I. The incidence of posteromedial shin pain was higher in Group II (75.0%) than in Group I (12.5%).
Article
As mathematical models of the musculoskeletal system become increasingly detailed and precise, they require more accurate information about the architectural parameters of the individual muscles. These muscles are typically represented as Hill-type models, which require data on fiber length, physiological cross-sectional area (PCSA) and pennation angle. Most of this information for lower limb muscles has been published, except for data on the pennation angle of the intrinsic muscles of the foot. Each (n=20) intrinsic muscle of three human feet was dissected free. The dorsal and plantar surfaces were photographed and a digitized color image was imported into Abobe Photoshop. The muscles were divided into "anatomical units". For each anatomical unit (n=26), a line was drawn along the tendon axis and a number of other lines were drawn along individual muscle fibers. The angle between the tendon line and each fiber line was defined as the pennation angle of that fiber. By visual inspection, an effort was made to take measurements such that they represented the distribution of fibers in various parts of the muscle. Although some individual muscles had higher or lower pennation angles, when averaged for all specimens, the second dorsal interosseous had the smallest pennation angle (6.7+/-6.81 degrees) while the abductor digiti minimi had the largest (19.1+/-11.19 degrees). Since the cosines of the angles range from 0.9932 to 0.9449, the effect of the pennation angle on the force generated by the muscle was not great.
Article
Investigation into the effects of foot structure on foot function, and the risks of injury, has been at the core of many studies, sometimes with conflicting results. Often different methods of foot type classification have been used, making comparison of the results and drawing sound conclusions impossible. This article aims to critically review current methods of foot type classification. It is concluded that if a classification method combines data on structure with information on foot function in dynamic loading situations, it should relate more closely to the functional behaviour of the foot during locomotion.
Article
Hallux valgus is a very common foot deformity in modern societies. Muscle imbalance in abductor and adductor muscles was cited as a major factor in the production of hallux valgus. Our aim in this study was to evaluate the role of certain muscles in this deformity. Twenty hallux valgus patients and 20 healthy volunteers participated in the study. After thorough physical, neurologic, and radiographic investigations, we performed an electromyographic study to observe the relationship of hallux valgus deformity with the muscles coordinating first metatarsophalangeal joint movements. Voluntary extension, flexion, abduction, and adduction at the hallux with maximum resistance were performed. Firing rates and amplitudes of motor unit potentials of four muscles: musculus abductor hallucis, musculus adductor hallucis, musculus extensor hallucis longus, and musculus flexor hallucis brevis were recorded. Statistical analysis, including Spearman's correlation analysis and Mann-Whitney U tests were performed with SPSS 8.0 for Windows. We observed that in the hallux valgus group, abduction activity of musculus abductor hallucis was markedly decreased when compared with adduction of musculus adductor hallucis. Motor unit potential amplitude of abductor activity recorded from musculus abductor hallucis was slightly more than half of the activity in flexion. Muscle imbalance in abductor and adductor muscles is apparent in hallux valgus deformity, and this imbalance may be the reason or the result of joint deformity.
Article
The maintenance of quiet stance requires the activation of muscles bilaterally. The soleus muscles in each leg share a common function in standing; that is, each muscle acts to control antero-posterior (AP) sway on its own side. We sought to determine the extent to which oscillations in motor unit discharge were related in motor unit pairs of the soleus muscles during postural and voluntary isometric tasks, both within and between legs. Subjects stood quietly for 5 min or performed a voluntary isometric plantarflexion contraction in a seated position. During the postural tasks, the excursions of AP sway between legs were highly correlated (rho = 0.86 +/- 0.06). The strength of common modulation of motor unit discharge rates was assessed using time- and frequency-domain analyses. The time-domain common drive analysis revealed that the strongest correlation in motor unit discharge modulation occurred in the postural task with unilateral pairs (rho = 0.71 +/- 0.13) being more strongly correlated than bilateral pairs (rho = 0.50 +/- 0.16). Common modulation of motor unit discharge was lowest for the voluntary tasks, with rho = 0.38 +/- 0.11 and 0.16 +/- 0.08 for unilateral and bilateral pairs, respectively. Similarly, the frequency-domain coherence analysis demonstrated an identical ordering effect, with the largest maximum pooled coherence occurring during standing posture in unilateral (0.070 at 1.6 Hz) and bilateral (0.055 at 1.6 Hz) recordings, whereas minimal coherence was observed in the voluntary task in both unilateral and bilateral recordings within the 0-5 Hz range. These results indicate that in the soleus muscle, common modulation of motor unit discharge is greater during postural tasks than during voluntary isometric tasks and can be observed in both bilateral and unilateral motor unit pairs. Differences in the extent of co-modulation of motor unit discharge between tasks may be attributed to either differences in the descending control or differences in the proprioceptive input between postural and isometric tasks.
Article
Plantar fasciitis is a musculoskeletal disorder primarily affecting the fascial enthesis. Although poorly understood, the development of plantar fasciitis is thought to have a mechanical origin. In particular, pes planus foot types and lower-limb biomechanics that result in a lowered medial longitudinal arch are thought to create excessive tensile strain within the fascia, producing microscopic tears and chronic inflammation. However, contrary to clinical doctrine, histological evidence does not support this concept, with inflammation rarely observed in chronic plantar fasciitis. Similarly, scientific support for the role of arch mechanics in the development of plantar fasciitis is equivocal, despite an abundance of anecdotal evidence indicating a causal link between arch function and heel pain. This may, in part, reflect the difficulty in measuring arch mechanics in vivo. However, it may also indicate that tensile failure is not a predominant feature in the pathomechanics of plantar fasciitis. Alternative mechanisms including 'stress-shielding', vascular and metabolic disturbances, the formation of free radicals, hyperthermia and genetic factors have also been linked to degenerative change in connective tissues. Further research is needed to ascertain the importance of such factors in the development of plantar fasciitis.
Article
Matched group comparison of 3 subject groups with 3 different foot structures for force plate and clinical measures of postural control. To determine if subjects with different weight-bearing foot structure would demonstrate differences in static standing postural control, and to determine the reliability of study procedures. Weight-bearing foot structure may influence postural control either because of a decreased base of support (supinated foot structure) or because of passive instability of the joints of the foot (pronated foot structure). Young adults were categorized based on weight-bearing foot structure into neutral, pronated, or supinated groups (15 subjects per group). Postural control in single-limb stance with eyes closed was assessed using force plate measures and by measuring duration of single-limb stance on a firm floor and on a balance pad. Force plate measures were normalized center-of-pressure average speed; and standard deviation and maximum displacement in the anterior-posterior and medial-lateral directions. Individuals in the supinated group had significantly greater center-of-pressure average speed, greater maximum displacement in the anterior-posterior direction, and greater SD and maximum displacement in the medial-lateral direction than individuals in the neutral group. The individuals in the pronated group had significantly greater SD and maximum displacement in the anterior-posterior direction, used more trials to complete force plate testing, and had shorter single-limb stance duration than those in the neutral group. Individuals with pronated feet or supinated feet have poorer postural control than individuals with neutral feet, but perhaps through different mechanisms.
Article
Our purpose was to assess the effect of foot intrinsic muscle fatigue on pronation, as assessed with navicular drop, during static stance. Twenty-one healthy young adults participated. Navicular drop was measured before and after fatiguing exercise of the plantar foot intrinsic muscles. Surface electromyography of the abductor hallucis muscle was recorded during maximum voluntary isometric contractions (MVIC) in order to find the baseline median frequency (MedF). Subjects then performed sets of 75 repetitions of isotonic flexion contractions of the intrinsic foot muscles against a 4.55 kg weight on a custom pulley system. After each set an MVIC was performed to track shifts in MedF. After a MedF shift of at least 10%, navicular drop measurements were repeated. Subjects exhibited 10.0+/-3.8mm of navicular drop at baseline and 11.8+/-3.8mm after fatigue (p<0.0005). The change in navicular drop was significantly correlated with change in MedF (r=.47, p=.03). The intrinsic foot muscles play a role in support of the medial longitudinal arch in static stance. Disrupting the function of these muscles through fatigue resulted in an increase in pronation as assessed by navicular drop.
Article
The present study investigated how the triceps surae are controlled at the spinal level during the naturally occurring postural sway of quiet standing. Subjects stood on a force platform as electrical stimuli were applied to the posterior tibial nerve when the center of pressure (COP) was either 1.6 standard deviations anterior (COP(ant)) or posterior (COP(post)) to the mean baseline COP signal. Peak-to-peak amplitudes of the H-reflex and M-wave from the soleus (SOL) and medial gastrocnemius (MG) muscles were recorded to assess the efficacy of the Ia pathway. A significant increase in the H(max) : M(max) ratio for both the SOL (12 +/- 6%) and MG (23 +/- 6%) was observed during the COP(ant) as compared to the COP(post) condition. The source of the modulation between COP conditions cannot be determined from this study. However, the observed changes in the synaptic efficacy of the Ia pathway are unlikely to be simply a result of an altered level of background electromyographic activity in the triceps surae. This was indicated by the lack of differences observed in the H(max) : M(max) ratio when subjects stood without postural sway (via the use of a tilt table) at two levels of background activity. It is suggested that the phase-dependent modulation of the triceps surae H-reflexes during the postural sway of quiet standing functions to maintain upright stance and may explain the results from previous studies, which, until now, had not taken the influence of postural sway on the H-reflex into consideration.
Article
The current study aimed to understand how deep and superficial abdominal muscles are coordinated with respect to activation onset times and amplitudes in response to unpredictable support-surface translations delivered in multiple directions. Electromyographic (EMG) data were recorded intra-muscularly using fine-wire electrodes inserted into the right rectus abdominis (RA), obliquus externus (OE), obliquus internus (OI) and transversus abdominis (TrA) muscles. Twelve young healthy male subjects were instructed to maintain their standing balance during 40 support surface translations (peak acceleration 1.3 m s(-2); total displacement 0.6 m) that were counter-balanced between four different directions (forward, backward, leftward, rightward). Differences between abdominal muscles in EMG onset times were found for specific translation directions. The more superficial RA (backward translations) and OE (forward and leftward translations) muscles had significantly earlier EMG onsets compared to TrA. EMG onset latencies were dependent on translation direction in RA, OE and OI, but independent of direction in TrA. EMG amplitudes in RA and OE were dependent on translation direction within the first 100 ms of activity, whereas responses from the two deeper muscles (TrA and OI) were independent of translation direction during this interval. The current results provide new insights into how abdominal muscles contribute to postural reactions during human stance. Response patterns of deep and superficial abdominal muscles during support surface translations are unlike those previously described during upper-body perturbations or voluntary arm movements, indicating that the neural mechanisms controlling individual abdominal muscles are task-specific to different postural demands.
Muscle imbalance in hallux valgus: an electromyographic study.
  • Arinci-Incel N.
  • Genc H.
  • Erdem H.R.
  • Yorgancioglu Z.R.
Arinci-Incel, N., Genc, H., Erdem, H.R., Yorgancioglu, Z.R., 2003. Muscle imbalance in hallux valgus: an electromyographic study. Am. J. Phys. Med. Rehabil. 82, 345-349.
Quantitative analysis of the intrinsic muscles of the foot.
  • Kura H.
  • Luo Z.P.
  • Kitoaka H.B.
  • An K.N.
Kura, H., Luo, Z.P., Kitoaka, H.B., An, K.N., 1997. Quantitative analysis of the intrinsic muscles of the foot. Anat. Rec. 249, 143-151.
Human control of an inverted pendulum: is continuous control necessary? Is intermittent control effective? Is intermittent control physiological?.
  • Loram I.D.
  • Gollee H.
  • Lakie M.
  • Gawthorpe P.J.
Loram, I.D., Gollee, H., Lakie, M., Gawthorpe, P.J., 2011. Human control of an inverted pendulum: is continuous control necessary? Is intermittent control effective? Is intermittent control physiological? J. Physiol. 589, 307-324.