Foot muscle morphology is related to center of pressure sway and control mechanisms during single-leg standing

Mechanical drivers of intrinsic foot muscle for maximum toe flexor strength in upright standing across different body size

This study aimed to evaluate maximum toe flexor strength, foot arch height, intrinsic toe flexor muscle size and foot arch stiffness among individuals with different body sizes, and to compare these variables between sitting and standing positions. Maximum toe flexor strength in sitting and standing, and intrinsic foot muscle thicknesses (flexor hallucis brevis: FHB, flexor digitorum brevis: FDB, abductor hallucis: AH and quadratus plantae: QP), were measured using a toe grip dynamometer and a B-mode ultrasound in healthy young men. FHB was thicker than AH, FDB and QP, AH was thicker than FDB and QP, and no significant difference was found between FDB and QP. Toe flexor strength was correlated with FHB and AH, and foot arch height was correlated with FHB. Toe flexor strength was greater in standing than in sitting. Stepwise multiple regression analysis identified FHB and AH as determinants of toe flexor strength in standing, and the relative muscle strength values per body weight in standing were determined by QP, foot arch index and foot arch stiffness. Overweight individuals had a decreased rate of increase in relative toe flexor strength compared to normal individuals. These results suggest that a large muscle thickness of intrinsic foot muscle a key contributor to toe flexor strength. Moreover, toe flexor muscle in upright standing could have the potential to generate force independently of intrinsic foot muscle size, but obese individuals who chronically put weight on their feet might impair the force amplification mechanism in upright standing.

Effects of a 12-week intrinsic foot muscle strengthening training (STIFF) on gait in older adults: a parallel randomized controlled trial protocol

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).

Minimalist school shoes improve intrinsic foot muscle size, strength, and arch integrity among primary school students

Minimalist walking shoes have been shown to improve foot muscle size and strength in active adults, but not in our previous study involving children, which could relate to the more structured footwear used in our study. Hence, this study examined the effects of true minimalists on intrinsic foot muscle size and strength, foot arch integrity, and physical function among primary school children. After a baseline assessment, 30 primary school students aged between 9 and 12 were given a pair of minimalist shoes (minimalist index = 92%) as their regular school shoes for two school terms, followed by a re-assessment. Seventeen of the 30 participants in the minimalist group completed the study. Compared to the control group, the minimalist group showed significantly increased cross-sectional area of abductor hallucis (p = 0.047, Cohen's d = 0.57) and flexor digitorum brevis (p = 0.037, Cohen's d = 0.80), increased strength of the hallux (p = 0.015, Cohen's d = 0.76) and lesser toes (p = 0.014, Cohen's d = 0.66), greater arch height (p = 0.020, Cohen's d = 0.52) and standing long jump distance (p = 0.001, Cohen's d = 9.79). The control group exhibited improved standing long jump performance only (p = 0.020, Cohen's d = 10.70). Minimalist shoes worn daily to school promote intrinsic foot muscle size and strength, and improve foot arch integrity among primary school students.

Neuromechanical characterization of the abductor hallucis and its potential role in upright postural control

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.

Age-related differences in the capacity and neuromuscular control of the foot core system during quiet standing

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.

Immediate effects of local muscle vibration on static and dynamic balance control in individuals with chronic ankle instability

OBJECTIVES

To investigate the immediate effects of local muscle vibration (LMV) on static and dynamic balance control in individuals with and without chronic ankle instability (CAI).

DESIGN

Quasi-experimental study.

SETTING

Research laboratory.

PARTICIPANTS

Twenty-six individuals with CAI and 26 healthy controls.

MAIN OUTCOME MEASURES

Center of pressure variables (mean total velocity and displacement in anteroposterior (AP) and mediolateral (ML) directions) during single-leg standing with eyes open and eyes closed and also reach distances in anterior (ANT), posteromedial (PM), and posterolateral (PL) directions of the modified star excursion balance test (MSEBT) were assessed before and after LMV.

RESULTS

Statistical analyses showed a significant decrease in mean total velocity and displacement in AP direction from before to after LMV in eyes open condition for both individuals with CAI (p = 0.025, p = 0.041, respectively) and healthy controls (p = 0.001, p = 0.003, respectively). Similar results were observed in eyes closed condition for both individuals with CAI (p < 0.001, p < 0.001, respectively) and healthy controls (p = 0.040, p = 0.014, respectively). The results also showed increased reach distances in ANT (p < 0.001), PM (p < 0.001), and PL directions (p < 0.001) in all participants after LMV.

CONCLUSION

Our results suggest that LMV may be a useful tool in rehabilitation of static and dynamic balance deficits in individuals with CAI.

Current evidence regarding 2D ultrasonography monitoring of intrinsic foot muscle properties: A systematic review

Background

Ultrasonography can discriminate between intrinsic and extrinsic foot muscle properties and has therefore gained considerable popularity as an indirect strength evaluation. However, an overview on the use of ultrasound for assessing intrinsic foot musculature (IFM) is currently lacking.

Research question

What is the current evidence regarding (1) 2D ultrasonography protocols and its reliability? (2) Reference values for cross-sectional area and dorso-plantar thickness evaluation in asymptomatic and symptomatic persons?

Methods

The PRISMA guidelines were used to conduct this systematic review. Eight databases (PubMed, Embase, Web of Science, Cochrane Library, Scopus, CINAHL, SPORTDiscus and EuropePMC) were searched up to November 1, 2021. Studies reporting quantitative 2D ultrasound findings of the intrinsic foot muscles with no limitation to sex, BMI, ethnicity or physical activity were included. Studies were assessed for methodological quality using the Downs and Black checklist.

Results

Fifty-three studies were retained. Protocols showed an overall good to great reliability, suggesting limits of agreement between 8 and 30% of relative muscle size with minimal detectable changes varying from 0.10 to 0.29 cm² for cross-sectional area and 0.03-0.23 cm for thickness. Reference values are proposed for both cross-sectional area and thickness measurements of the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis and quadratus plantae in asymptomatic persons. This could not be performed in the symptomatic studies due to a limited number of relevant studies addressing the symptomatic population, therefore a clinical overview is outlined. Clinically, IFM properties have been studied in ten distinct pathological conditions, predominantly pointing towards decreased muscle properties of the abductor hallucis.

Significance

We provide a clear and comprehensive overview of the literature regarding 2D ultrasonography of the IFM, making the available evidence more accessible to decision makers and researchers.

Effects of Rearfoot Eversion on Foot Plantar Pressure and Spatiotemporal Gait Parameters in Adolescent Athletes

BACKGROUND

Foot malalignment can augment the risk of lower-extremity injuries and lead to musculoskeletal disorders. This study aimed to clarify the contribution of rearfoot alignment to plantar pressure distribution and spatiotemporal parameters during gait in healthy adolescent athletes.

METHODS

This retrospective study included 39 adolescent athletes who were divided into the rearfoot eversion and control groups according to a leg heel angle of 7°. A total of 78 legs were analyzed (45 and 33 legs in the rearfoot eversion [women, 53.3%] and control groups [women, 48.5%], respectively). Gait was assessed using an in-shoe plantar pressure measuring system and a wearable inertial sensor.

RESULTS

The foot plantar pressure distribution in the hallux was higher in the rearfoot eversion group than that in the control group (p = 0.034). Spatiotemporal parameters showed that the foot pitch angle at heel strike was significantly larger in the rearfoot eversion group than that in the control group (24.5° vs. 21.7°; p = 0.015). Total sagittal range of motion of the ankle during the stance phase of gait was significantly larger in the rearfoot eversion group than that in the control group (102.5 ± 7.1° vs. 95.6 ± 15.8°; p = 0.020). Logistic regression analysis revealed that plantar pressure at the hallux and medial heel and foot pitch angle at heel strike were significantly associated with rearfoot eversion.

CONCLUSIONS

Our findings suggest that rearfoot eversion affects the gait patterns of adolescent athletes. Notably, leg heel angle assessment, which is a simple and quick procedure, should be considered as an alternative screening tool for estimating plantar pressure and spatiotemporal gait parameters to prevent sports-related and overuse injuries in adolescent athletes.

The Rehabilitation Program Improves Balance Control in Children with Excessive Body Weight and Flat Feet by Activating the Intrinsic Muscles of the Foot: A Preliminary Study

BACKGROUND

determining the appropriate rehabilitation protocol is essential to influence the correction of flat feet, e.g., by activating the intrinsic muscles of the foot. Therefore, this study aimed to determine the impact of the exercises activating the intrinsic foot muscles for postural control in children with flat feet, with normal and excessive body weight.

METHODS

Fifty-four children aged 7 to 12 were enrolled in the research. Forty-five children were qualified for the final evaluation. Each child in the experimental group was demonstrated an appropriate technique for performing a short foot exercise without compensation by extrinsic muscle. The participants then performed a supervised short foot training session once a week and on other days of the week under the supervision of caregivers for 6 weeks. Flat feet were scored on the foot posture index scale. A postural test was evaluated with a Biodex balance system SD. Statistical significance in the foot posture index scale and postural test were evaluated using an analysis of variance (ANOVA) with Tukey's post-hoc test.

RESULTS

according to the six indices of the foot posture index scale, five indicators showed statistically significant improvement after rehabilitation. At the 8-12 platform mobility level, it was revealed that the excessive body weight group had significant improvements in the overall stability index and medio-lateral stability index, with eyes closed.

CONCLUSION

our results indicate that a 6-week rehabilitation program based on the activation of the intrinsic muscles of the foot resulted in an improvement in the foot position. This, in turn, affected balance control, especially in children with excess body weight in conditions of closed eyes.

Intrinsic Foot Muscle Exercises With and Without Electric Stimulation

CONTEXT

Exercising intrinsic foot muscles (IFMs) can improve dynamic balance and foot posture. The exercises are not intuitive and electrotherapy (neuromuscular electrical stimulation [NMES]) has been suggested to help individuals execute the exercises. The aim of this study was to evaluate the effects of training IFM program on dynamic balance and foot posture and compare traditional training methods (TRAIN) with traditional training plus NMES on the perceived workload of the exercises, balance, and foot posture.

DESIGN

Randomized controlled trial.

METHODS

Thirty-nine participants were randomized to control, TRAIN, or NMES. TRAIN and NMES performed IFM exercises daily for 4 weeks; NMES received electrotherapy during the first 2 weeks of training. The Y-Balance test and arch height index were measured in all participants at baseline. The training groups were measured again at 2 weeks; all participants were measured at 4 weeks and 8 weeks, after 4 weeks of no training. Perceived workload (National Aeronautics and Space Administration Task Load Index) of exercises was assessed throughout the first 2 weeks and at 4 weeks.

RESULTS

A 4-week IFM training program demonstrated increases in Y-Balance (P = .01) for TRAIN and in arch height index (seated P = .03; standing P = .02) for NMES, relative to baseline. NMES demonstrated improvement in Y-Balance (P = .02) and arch height index standing (P = .01) at 2 weeks. There were no significant differences between the training groups. Groups were similar in the number responding to exercises in excess of minimal detectable change on all clinical measures. Perceived workload of the exercises decreased during the first 2 weeks of training (P = .02), and more notably at 4 weeks (P < .001). The groups did not differ in how they perceived the workload.

CONCLUSIONS

A 4-week IFM training program improved dynamic balance and foot posture. Adding NMES in early phases of training provided early improvement in dynamic balance and foot posture, but did not affect perceived workload.

Contributions of Intrinsic and Extrinsic Foot Muscles during Functional Standing Postures

Purpose. Maintaining balance during static standing postures requires the coordination of many neuromuscular mechanisms. The role of the intrinsic and extrinsic foot muscles in this paradigm has yet to be clearly defined. The purpose of this study was to explore foot muscle activation during static phases on common weight-bearing tasks of varying loads and balance demands. Methods. Twenty healthy young adults performed 6 standing postures (single-limb and double-limb stand, squat, and heel raise) with one foot on a force plate. Muscle activity was recorded from the abductor hallucis, flexor hallucis longus and brevis, and tibialis posterior using intramuscular electrodes; surface electrodes were used to record activity from the peroneus longus and tibialis anterior. Two-way repeated measures ANOVA (2 loading conditions × 3 postures) were run to compare muscle activation and center of pressure velocity. Results. Intrinsic foot muscle activity increased as loading and postural demand increased; however, the specific effects varied for each of the extrinsic foot muscles. Conclusions. These results suggest that the intrinsic foot muscles play an important role in maintaining static balance. Strengthening intrinsic and extrinsic foot muscles may help increase stability in people who have weak toe flexors or who suffer from a variety of foot pathologies.

Muscle Quality Assessment by Ultrasound Imaging of the Intrinsic Foot Muscles in Individuals with and without Plantar Fasciitis: A Case-Control Study

Objective: The primary aim of the present study was to compare the echo intensity (EI) and echovariation (EV) of the intrinsic foot muscles (IFMs) between individuals with and without plantar fasciitis (PF), using ultrasound imaging. The secondary objective was to study the intra-rater reliability of the echotexture variables. Methods: A case−control study was conducted with 64 participants, who were divided into the following two groups: A, the PF group (n = 32); B, the healthy group (n = 32). Results: The comparison between the two groups did not identify significant differences (p > 0.05) between the flexor hallucis brevis (FHB), flexor digitorum brevis (FDB), quadratus plantae (QP) and abductor hallucis brevis (AHB) variables for the EI and EV. Moreover, excellent intra-rater reliability was reported for the following ultrasound imaging EI variables: ABH (ICC = 0.951), FHB (ICC = 0.949), FDB (ICC = 0.981) and QP (ICC = 0.984). Conclusions: The muscle quality assessment using the EI and EV variables did not identify differences in the FHB, FDB, AHB and QP muscles between individuals with and without PF through USI evaluation. The reliability of all the IFM measurements was reported to be excellent.

The effect of interventions anticipated to improve plantar intrinsic foot muscle strength on fall-related dynamic function in adults: a systematic review

Background

The plantar intrinsic foot muscles (PIFMs) have a role in dynamic functions, such as balance and propulsion, which are vital to walking. These muscles atrophy in older adults and therefore this population, which is at high risk to falling, may benefit from strengthening these muscles in order to improve or retain their gait performance. Therefore, the aim was to provide insight in the evidence for the effect of interventions anticipated to improve PIFM strength on dynamic balance control and foot function during gait in adults.

Methods

A systematic literature search was performed in five electronic databases. The eligibility of peer-reviewed papers, published between January 1, 2010 and July 8, 2020, reporting controlled trials and pre-post interventional studies was assessed by two reviewers independently. Results from moderate- and high-quality studies were extracted for data synthesis by summarizing the standardized mean differences (SMD). The GRADE approach was used to assess the certainty of evidence.

Results

Screening of 9199 records resulted in the inclusion of 11 articles of which five were included for data synthesis. Included studies were mainly performed in younger populations. Low-certainty evidence revealed the beneficial effect of PIFM strengthening exercises on vertical ground reaction force (SMD: − 0.31-0.37). Very low-certainty evidence showed that PIFM strength training improved the performance on dynamic balance testing (SMD: 0.41–1.43). There was no evidence for the effect of PIFM strengthening exercises on medial longitudinal foot arch kinematics.

Conclusions

This review revealed at best low-certainty evidence that PIFM strengthening exercises improve foot function during gait and very low-certainty evidence for its favorable effect on dynamic balance control. There is a need for high-quality studies that aim to investigate the effect of functional PIFM strengthening exercises in large samples of older adults. The outcome measures should be related to both fall risk and the role of the PIFMs such as propulsive forces and balance during locomotion in addition to PIFM strength measures.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13047-021-00509-0.

Adaptations in Reactive Balance Strategies in Healthy Older Adults After a 3-Week Perturbation Training Program and After a 12-Week Resistance Training Program

Both resistance training (RT) and perturbation-based training (PBT) have been proposed and applied as interventions to improve reactive balance performance in older adults. PBT is a promising approach but the adaptations in underlying balance-correcting mechanisms through which PBT improves reactive balance performance are not well-understood. Besides it is unclear whether PBT induces adaptations that generalize to movement tasks that were not part of the training and whether those potential improvements would be larger than improvements induced by RT. We performed two training interventions with two groups of healthy older adults: a traditional 12-week RT program and a 3-week PBT program consisting of support-surface perturbations of standing balance. Reactive balance performance during standing and walking as well as a set of neuro-muscular properties to quantify muscle strength, sensory and motor acuity, were assessed pre- and post-intervention. We found that both PBT and RT induced training specific improvements, i.e., standing PBT improved reactive balance during perturbed standing and RT increased strength, but neither intervention affected reactive balance performance during perturbed treadmill walking. Analysis of the reliance on different balance-correcting strategies indicated that specific improvements in the PBT group during reactive standing balance were due to adaptations in the stepping threshold. Our findings indicate that the strong specificity of PBT can present a challenge to transfer improvements to fall prevention and should be considered in the design of an intervention. Next, we found that lack of improvement in muscle strength did not limit improving reactive balance in healthy older adults. For improving our understanding of generalizability of specific PBT in future research, we suggest performing an analysis of the reliance on the different balance-correcting strategies during both the training and assessment tasks.

Functional Electrical Stimulation of Peroneal Muscles on Balance in Healthy Females

Balance improvement could contribute to ankle stability for the prevention of ankle sprains. Functional electrical stimulation (FES) is an effective way of augmenting muscle activity and improving balance. This study investigated the effect of FES of peroneal muscles on single-and double-leg balance. Fifteen healthy females (age = 23.1 ± 1.6 years, height = 1.63 ± 0.07 m, and weight = 63.7 ± 9.9 kg) performed single- and double-leg standing balance tests with eyes open and closed before and after 15-minute FES intervention during treadmill running at a comfortable, self-selected pace. FES of peroneal muscles was provided bilaterally, using an Odstock Dropped Foot Stimulator. The total excursion of the centre of pressure (COP) was calculated to assess the standing balance control ability. The total excursion of COP in single- and double-leg stance with eyes open reduced significantly after FES intervention by 14.7% (p < 0.001) and 5.9% (p = 0.031), respectively. The eyes-closed condition exhibited a 12.7% (p = 0.002) reduction in single-leg stance but did not significantly change in double-leg stance (p > 0.05). Limb preference did not account for balance postintervention. No significant difference in total excursion of COP was found between preferred and less preferred limbs with both visual conditions (p > 0.05). FES of peroneal muscles improved standing balance control with eyes open in double-leg and single-leg stance and with eyes closed in double-leg stance. The improvements in balance control with FES treatment did not vary concerning limb preference.

Intrinsic foot muscle hardness is related to dynamic postural stability after landing in healthy young men

BACKGROUND

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

RESEARCH QUESTION

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

METHODS

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

RESULTS

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

SIGNIFICANCE

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

Contribution of Plantar Fascia and Intrinsic Foot Muscles in a Single-Leg Drop Landing and Repetitive Rebound Jumps: An Ultrasound-Based Study

The plantar fascia and intrinsic foot muscles (IFM) modulate foot stiffness. However, it is unclear whether the corresponding ultrasonography findings reflect it. This study aimed to examine the effect of the plantar fascia and IFM morphologies on force attenuation during landing and reactivity when jumping in healthy adults (n = 21; age, 21-27 years). Thickness, cross-sectional area (CSA), and hardness of the plantar fascia, abductor hallucis (AbH), and flexor hallucis brevis (FHB) muscles were measured using ultrasonography. Single-leg drop landing and repetitive rebound jumping tests assessed the ground reaction force (GRF) and reactive jump index (RJI), respectively. The CSA of FHB was negatively correlated with maximum vertical GRF (r = -0.472, p = 0.031) in the single-leg drop landing test. The CSA of AbH was negatively correlated with contact time (r = -0.478, p = 0.028), and the plantar fascia thickness was positively correlated with jump height (r = 0.615, p = 0.003) and RJI (r = 0.645, p = 0.002) in the repetitive bound jump test. In multivariate regression analysis, only the plantar fascia thickness was associated with RJI (β = 0.152, 95% confidence interval: 7.219-38.743, p = 0.007). The CSA of FHB may contribute to force attenuation during landing. The thickness of the plantar fascia and CSA of AbH may facilitate jumping high with minimal contact time.

Proximal and distal muscle thickness is different in women with patellofemoral pain but is not associated with knee frontal plane projection angle

OBJECTIVE

The aim of this study was to compare proximal and distal muscle thickness between patellofemoral pain (PFP) and asymptomatic women (CG) and to verify the possible association between morphology and lower limb alignment during single leg-squat.

METHODS

Thirty women (PFP, n = 15 and CG, n = 15) performed the following evaluations: (i) muscle thickness of external oblique (EO), gluteus medius (GMed), tensor fascia latae (TFL), peroneus (PER) and tibialis anterior (TA); (ii) knee frontal plane projection angle (FPPA) during single-leg squat.

RESULTS

Compared with the CG, PFP showed: (1) smaller GMed (-10.02%; p = 0.04; effect size = 0.82), greater TFL (+18.44%; p = 0.02; effect size = 0.92) and PER (+14.23%; p = 0.02; effect size = 0.87) muscle thickness and greater knee FPPA during single-leg squat (+31.8%; p = 0.04; effect size = 1.12). No differences were observed in EO (+7.17%; p = 0.37; effect size = 0.34) and TA (-1.35%; p = 0.81; effect size = 0.12) muscle thickness. Additionally, we failed to observe significant associations between muscle morphology and knee FPPA in both groups.

CONCLUSION

PFP patients showed alterations in proximal and distal muscle thickness, despite the lack of association with poor lower limb alignment. Prospective studies are necessary to determine if differences in muscle morphology are the cause or the consequence of PFP and to confirm the absence of relationship with lower limb alignment.

Core muscles thickness is not associated with knee frontal plane projection angle during single-leg squat in healthy people

BACKGROUND

Core muscles play an important role in lower limb stability and alignment, with their weakness being associated with poor alignment and, consequently, with injuries. Despite muscle structure being critical to muscle strength production, we did not find studies associating the morphology of the core muscles and lower limb alignment during functional tasks.

RESEARCH QUESTION

Is there association between thickness of core muscles (external oblique - EO, internal oblique - IO, transversus abdominis - TrA and gluteus medius - GMed) and lower limb alignment during the single-leg squat in healthy subjects?

METHODS

Forty-six healthy participants (27 male and 19 female) performed the following evaluations: (i) measurements of muscle thickness of the EO, IO, TrA and GMed using ultrasound and (ii) measurements of lower limb alignment using the knee frontal plane projection angle (FPPA) during the single-leg squat. A Spearman rank correlation coefficient (r_s) was performed between the thickness of selected core muscles (OE, OI, TrA and GMed) and the knee FPPA. In addition, a partial correlation (r) was performed, using sex, physical activity level and body mass index as control variables.

RESULTS

We did not observe significant correlations between the knee FPPA and the thickness of the EO (r_s = 0.194; p = 0.197), IO (r_s = 0.182; p = 0.225), TrA (r_s = 0.073; p = 0.627) and GMed (r_s = -0.092; p = 0.542). When controlling for sex, physical activity level and body mass index, similar results were observed [EO (r = 0.157; p = 0.316), IO (r = 0.261; p = 0.092), TrA (r = 0.030; p = 0.850) and GMed (r = -0.144; p = 0.356)] SIGNIFICANCE: Our results demonstrated that core muscles' thickness is not associated with lower limb alignment during the single-leg squat in healthy people.

Intrinsic foot muscles act to stabilise the foot when greater fluctuations in centre of pressure movement result from increased postural balance challenge

BACKGROUND

Increased postural balance challenge is associated with more fluctuations in centre of pressure movement, indicating increased interference from the postural control system. The role of intrinsic foot muscles in balance control is relatively understudied and whether such control system interference occurs at the level of these muscles is unknown.

RESEARCH QUESTION

Do fewer fluctuations in intrinsic foot muscle excitation occur in response to increased postural balance challenge?

METHODS

Surface EMGs were recorded using a grid of 13 × 5 channels from the plantar surface of the foot of 17 participants, who completed three balance tasks: bipedal stance; single leg stance and bipedal tip-toe. Centre of pressure (CoP) movement was calculated from simultaneously recorded force plate signals. Fluctuations in CoP and EMGs for each task were quantified using a sample entropy based metric, Entropy Halflife (EnHL). Longer EnHL indicates fewer signal fluctuations.

RESULTS

The shortest EMG EnHL, 9.27 ± 3.34 ms (median ± interquartile range), occurred during bipedal stance and the longest during bipedal tip-toe 15.46 ± 11.16 ms, with 18.80 ± 8.00 ms recorded for single leg stance. Differences were statistically significant between bipedal stance and both bipedal tip-toe (p < 0.001) and single leg stance (p < 0.001). CoP EnHL for both anterior-posterior and medial-lateral movements also differed significantly between tasks (p < 0.001, both cases). However, anterior-posterior CoP EnHL was longest for bipedal stance 259.84±230.22 ms and shortest for bipedal tip-toe 146.25±73.35 ms. Medial-lateral CoP EnHL was also longest during bipedal stance 215.73±187.58 ms, but shortest for single leg stance 113.48±83.01 ms.

SIGNIFICANCE

Fewer fluctuations in intrinsic foot muscle excitation occur in response to increased postural balance challenge. Fluctuations in CoP movement during balance must be predominantly driven by excitation of muscles extrinsic to the foot. Intrinsic foot muscles therefore likely play a greater role in stabilisation of the foot than balance control during the postural tasks studied.

Ultrasound examination of intrinsic foot muscles in patients with 1st metatarsophalangeal joint arthrodesis

1st MTP arthrodesis often alleviates pain in osteoarthritis of hallux, long term outcomes vary, yet there is little known about potentially modifiable changes in the small muscles of the foot and hallux. This study was performed to determine the changes in the size of the Intrinsic Foot Muscles (IFMs) after the arthrodesis of the 1st metatarsophalangeal (MTP) joint by comparing the cross-sectional area (CSA) and muscle thickness (MT) of Abductor Hallucis (AbH), Flexor Digitorum Brevis (FDB) and Flexor Hallucis Brevis (FHB) between surgical and non-surgical feet. A convenience sample of 18 feet of 9 subjects (age: 57.56±9.07, weight: 81.33±1.32kg, height: 163.26±11.03cm) with a unilateral history of 1st MTP arthrodesis was recruited. B-mode ultrasound images were collected during sitting and standing positions with a wireless 8-MHz transducer. Hand-held dynamometer was used to measure toe flexion strength. CSA and MT of the surgical feet were significantly lower (P<0.05) for AbH and FHB in both positions. For FDB, the significant difference (P<0.05) was smaller MT in standing. Significantly lower (P<0.05) toe strength was observed in involved toe compared to uninvolved. Greater correlations were seen between toe strength and CSA of FHB and AbH in uninvolved toes compared with involved toes. IFMs in the surgical foot exhibited reduced CSA and MT. Weak core muscles of the foot may result in transmission of shock and forces to the foot skeleton which can lead to skeletal problems such as metatarsalgia, IP joint arthritis etc. that are seen as post-surgical complications. There is nothing in literature that delineates the rehabilitation of foot in this group of patients after surgery. This directs surgeons and clinicians to integrate IFM training in the rehabilitation programs after surgery. Developing appropriate rehabilitation protocols for these patients may help in preventions of post-surgical complications.

Thickness, cross-sectional area, and stiffness of intrinsic foot muscles affect performance in single-leg stance balance tests in healthy sedentary young females

The purpose of this study was to investigate the effect of thickness, cross-sectional area and stiffness of intrinsic foot muscles on performance in single-leg stance balance tasks in healthy sedentary young females. This study included a total of 40 healthy sedentary young females between the ages of 19 and 35 years. Single-leg stance balance assessments were carried out using Biodex Balance Systems (Biodex Medical Systems, Shirley, NY, USA). Performance in the single-leg stance balance tests was assessed using the overall stability index (OSI), mediolateral stability index (MLSI) and the anteroposterior stability index (APSI). Lower scores indicated better postural stability. Stiffness, thickness and cross-sectional area measurements of the abductor hallucis (AbH), flexor digitorum brevis (FDB) and flexor hallucis brevis (FHB) muscles were performed using an ultrasonography device. Larger AbH and FHB muscles were correlated with higher OSI, APSI, and MLSI (r = 0.31-0.46, p < 0.05), whereas larger FDB muscle was correlated with higher OSI and MLSI (r = 0.28-0.38, p < 0.05). Higher stiffness of the AbH and FHB muscles were correlated with lower OSI, APSI, and MLSI (r = -0.32 to 0.58, p < 0.05), but stiffness of the FDB muscle was not significantly correlated with OSI, APSI, and MLSI (r = 0.03-0.22, p ˃ 0.05). These results suggest that larger AbH, FDB and FHB muscles are related to reduced performance in single-leg stance balance tests, whereas higher AbH and FHB stiffness are related to better performance in single-leg stance balance tests in healthy sedentary young females.

H-reflex in abductor hallucis and postural performance between flexible flatfoot and normal foot

OBJECTIVE

Morphological changes of the abductor hallucis muscle (AbH) in flexible flatfoot (FF) individuals influence regulations of the medial longitudinal arch (MLA). Prolonged and repeated stretching of AbH in flexible flatfoot may cause changes in muscle reflex properties and further influence postural performance. However, AbH muscle reflex under different postural conditions have never been examined. The purpose of this study was to investigate differences in AbH H-reflex and postural performance between individuals with normal foot (NF) alignment and FF under prone, double-leg stance (DLS), and single-leg stance (SLS) conditions.

DESIGN

Cross-sectional study.

SETTING

University laboratory.

PARTICIPANTS

Individuals with FF (n = 12) and NF (n = 12).

MAIN OUTCOME MEASURES

AbH H-reflex, AbH EMG and center of pressure (CoP) displacement.

RESULTS

Under all postural conditions, AbH H-reflex was significantly lower in the FF group (P < .05). Under the SLS condition, AbH EMG was significantly higher in the FF group (P < .05), and CoP displacement for the medial-lateral and anterior-posterior directions were significantly higher in the FF group (P < .05).

CONCLUSIONS

With increased postural demand, FF individuals maintained their postural stability by recruiting greater AbH activities than through automatic stretch reflex, but FF individuals still showed inferior posture stability.

Effects of morphological and mechanical properties of plantar fascia and heel pad on balance performance in asymptomatic females

INTRODUCTION

Personal differences in morphological and mechanical properties of plantar fascia and heel fat pad may be an important parameter regarding an individual's balance performance. The purpose of this study was to investigate the effect of thickness and stiffness of heel fat pad and plantar fascia on balance performance in asymptomatic sedentary females.

MATERIALS AND METHODS

This study was carried out on 37 asymptomatic sedentary females between the ages of 19 and 35 years. Balance assessments during single-leg standing were carried out using Biodex Balance Systems (Biodex Medical Systems, Shirley, NY, USA). In this study, the individuals' balance performance was assessed using the center of balance (COB) parameters, which were the standard deviation of the COB amplitude in the anterior-posterior (AP_SD) and medial-lateral (ML_SD) directions. Stiffness and thickness measurements of heel fat pad and plantar fascia were performed using an ACUSON S3000 Ultrasound System and a 9L4 probe (4-9MHz) (Siemens Medical Solution, Mountain View, CA, USA).

RESULTS

AP_SD during single-leg standing tests had a moderate correlation with heel pad thickness (r=0.46, p=0.004) and heel pad stiffness (r=0.41, p=0.011), and a fair correlation with plantar fascia thickness (r=0.34, p=0.038) and plantar fascia stiffness (r=0.38, p=0.021). ML_SD during single-leg standing tests had a moderate correlation with heel pad thickness (r=0.41, p=0.013) and heel pad stiffness (r=0.53, p=0.001), and a fair correlation with plantar fascia thickness (r=0.40, p=0.015).

CONCLUSION

It was found that higher plantar fascia and heel fat pad stiffness and thickness are related to higher postural sway in anterior-posterior and medial-lateral directions based on the single-leg balance tests. These results suggest that the morphological and mechanical properties of plantar fascia and heel fat pad play an important role in balance performance.