The effect of various degrees of foot posture on standing balance in a healthy adult population

Abstract

Purpose: Foot biomechanics plays a significant role in the quality of standing and walking. It has been believed that even minor biomechanical alterations in the foot support surface may influence strategies to maintain body standing balance. Hence, the aim of this study was to investigate the role of various degrees of foot posture on static and dynamic standing balance components in a healthy adult population.

Subjects and methods: A convenience sample of 41 healthy adult subjects with a mean age of 24.3?±?6.4 years and a body mass index (BMI) of 29?kg/m² participated in this study. On the basis of foot posture index (FPI), the participants were allocated into either group A or B. Group A included 16 subjects with an FPI range of 6–11 whereas group B included 25 subjects with an FPI range of 0–5. Standing balance components were analyzed using computerized dynamic posturography (CDP) by the Modified Clinical Test of Sensory Interaction on Balance (mCTSIB) and the limit of stability (LOS).

Results: Spearman’s correlation coefficient showed a significant correlation between the standing dynamic balance and FPI in group B but not in group A. Moreover, it also showed no significant correlation between the standing static balance component and FPI in either group A or B.

Conclusion: This study concluded that higher degrees of FPI might have an effect on standing dynamic balance in healthy subjects. These components may require extra attention during the preventive aspects of rehabilitation.     

Parametric study of orthopedic insole of valgus foot on partial foot amputation

Orthopedic insole was important for partial foot amputation (PFA) to achieve foot balance and avoid foot deformity. The inapposite insole orthosis was thought to be one of the risk factors of reamputation for foot valgus patient, but biomechanical effects of internal tissues on valgus foot had not been clearly addressed. In this study, plantar pressure on heel and metatarsal regions of PFA was measured using F-Scan. The three-dimensional finite element (FE) model of partial foot evaluated different medial wedge angles (MWAs) (0.0°–10.0°) of orthopedic insole on valgus foot. The effect of orthopedic insole on the internal bone stress, the medial ligament tension of ankle, plantar fascia tension, and plantar pressure was investigated. Plantar pressure on medial heel region was about 2.5 times higher than that of lateral region based on the F-Scan measurements. FE-predicted results showed that the tension of medial ankle ligaments was the lowest, and the plantar pressure was redistributed around the heel, the first metatarsal, and the lateral longitudinal arch regions when MWA of orthopedic insole ranged from 7.5° to 8.0°. The plantar fascias maintained about 3.5% of the total load bearing on foot. However, the internal stresses from foot bones increased. The simulation in this study would provide the suggestion of guiding optimal design of orthopedic insole and therapeutic planning to pedorthist.     

Biomechanical analysis of foot with different foot arch heights: a finite element analysis

Clinically, different foot arch heights are associated with different tissue injuries to the foot. To investigate the possible factors contributing to the difference in foot arch heights, previous studies have mostly measured foot pressure in either low-arched or high-arched feet. However, little information exists on stress variation inside the foot with different arch heights. Therefore, this study aimed to implement the finite element (FE) method to analyse the influence of different foot arches. This study established a 3D foot FE model using software ANSYS 11.0. After validating the FE model, this study created low-arched, high-arched and normal-arched foot FE models. The FE analysis found that both the stress and strain on the plantar fascia and metatarsal were higher in the high-arched foot, whereas the stress and strain on the calcaneous, navicular and cuboid were higher in low-arched foot. Additionally, forefoot pressure was increased with an increase in arch height.     

Human esophageal pressures and chest wall configuration in upright and head-down posture

Pressures were measured at two levels in the esophagus in 14 young healthy subjects performing slow inspiratory and expiratory vital capacity (VC) maneuvers in upright and head-down posture (180 degrees body tilt). In both postures, a gravitational pressure gradient was found, which increased very slightly with decreasing lung volumes (0.006 cmH2O X % VC-1 X cm descent-1) except for upright expiratory curves above 60% VC. The expiratory pressure gradient tended to be larger in head-down than in upright posture; however, during inspiration the opposite was true. In both postures the pressure change between 100 and 20% VC was smaller in the uppermost zone, which is consistent with the smaller changes in alveolar expansion in this zone. Also, in seven of the subjects, changes in cross-sectional area of the middle and lower part of the rib cage (HRC and LRC) and of the abdomen (ABD) were measured by respiratory inductive plethysmography in upright and head-down posture. The ratio of HRC motion to LRC motion was constant throughout the VC and did not change with posture, yet the ratio of ABD motion to mean RC motion changed with overall volume and was also larger in head-down than in upright posture. In conclusion, the changes in esophageal pressure gradient during slow VC maneuvers in head-down vs. upright posture were not related to (and thus not caused by) changes in chest wall configuration.     

Measurement of capillary pressure in humans using a venous occlusion method

The venous occlusion technique was used to measure capillary pressure in the forearm and foot of man over a wide range of venous pressures. In six recumbent subjects venous pressure (Pv) in the forearm (mean +/- SE) was 9.3 +/- 1.4 mmHg and the venous occlusion estimate of capillary pressure (Pc) was 17.0 +/- 1.6 mmHg, whereas in another six subjects Pv in the foot was 17.1 +/- 1.2 mmHg and Pc was 23.4 +/- 2.5 mmHg. Venous pressure in the limbs was increased either by changes in posture or by venous congestion with a sphygmomanometer cuff. On standing Pv in the foot increased to 95.2 +/- 1.5 mmHg and Pc rose to 112.8 +/- 3.1 mmHg. The relationship established between venous pressure and capillary pressure in the forearm is Pc = 1.16 Pv + 8.1, whereas in the foot the relationship is Pc = 1.2 Pv + 1.6. The magnitude and duration of the changes in capillary pressure were also recorded during reactive hyperemia. The venous occlusion method of measuring capillary pressure is simple and easily applied to studies in humans.     

Differences in foot contact times between obese and non-obese postmenopausal women when crossing obstacles

Abstract

Objective: This study aimed to investigate the foot contact time differences between obese and non-obese subjects during walking when crossing obstacles.

Methods: Ninety-eight postmenopausal women were assigned to four groups, and their plantar pressure temporal data were collected using a two-step protocol during walking when crossing an obstacle set at 30% height of lower limb length of each subject. The initial, final, and duration of contact of 10?foot areas were measured.

Results: Leading limb: (1) the heel groups initiated foot contact using the heel, and the non-heel groups initiated contact using the metatarsals; (2) heel obese subjects showed an earlier initial contact and a longer contact duration of metatarsals 2–3; (3) non-heel obese subjects showed an earlier midfoot initial contact. Regarding the trailing limb: (4) heel obese subjects showed an earlier midfoot initial contact and a longer contact duration of metatarsal 5; (5) non-heel obese subjects showed an earlier initial contact and a longer contact duration of metatarsals 4–5.

Conclusions: (1) The non-heel groups’ foot rollover pattern may result from an attempt of rapidly restoring stability; (2) the heel obese subjects seem to regulate their plantar foot muscles to overcome their overweight; (3) the overweight of the non-heel obese subjects leads to a quicker backward foot roll-over from the metatarsals to the heel; (4) the overweight of the heel obese subjects can distort their footprints and/or their higher inertia may precipitate an anticipation of the midfoot contact, which can also explain the result observed for 5.     

Effects of excessive body weight on postural control

Research that evaluated both static and dynamic stability was performed, to clarify the impact of excessive body weight on postural control. The spontaneous center of foot pressure (CP) motion during quiet stance and a range of forward voluntary CP displacements were studied in 100 obese, and 33 lean women. Characteristics of postural sway were acquired while the subjects were standing quiet on a force plate with eyes open (EO) and with eyes closed (EC). Their anterior range of CP voluntary displacements was assessed upon a range of maximal whole body leanings which were directed forward. A substantial reduction of postural sway was observed in all patients which had increased body weight. Main postural sway parameters i.e., the total path length as well as its directional components were negatively correlated with the body mass and body mass index (BMI). The range of a whole body voluntary forward leaning, did not exhibit any significant change in patients with an obesity grade of I and II. Such a deficit was, however, found in subjects with a body mass index above 40. In conclusion, the increased body weight imposed new biomechanical constraints, that resulted in functional adaptation of the control of the erect posture. This functional adaptation was characterized by a reduced postural sway associated with a substantial reduction of the dynamic stability range in subjects with BMI>40.     

Differential effects of mental concentration and acute psychosocial stress on cervical muscle activity and posture

Physical and psychosocial stressors in the workplace have been independently associated with the development of neck pain, yet interactions among these risk factors remain unclear. The purpose of this study was to compare the effects of mentally challenging computer work performed with and without exposure to a psychosocial stressor on cervical muscle activity and posture. Changes in cervical posture and electromyography of upper trapezius, cervical extensor, and sternocleidomastoid muscles were compared between a resting seated posture at baseline, a low stress condition with mental concentration, and a high stress condition with mental concentration and psychosocial stress in sixty healthy office workers. Forward head posture significantly increased with mental concentration compared to baseline, but did not change with further introduction of the stressor. Muscle activity significantly increased from the low stress to high stress condition for both the dominant and non-dominant upper trapezius, with no corresponding change in activity of the cervical extensors or flexors between stress conditions. These findings suggest that upper trapezius muscles are selectively activated by psychosocial stress independent of changes in concentration or posture, which may have implications for the prevention of stress-related trapezius myalgia in the workplace.     

Postural changes associated with public speech tests lead to mild and selective activation of stress hormone release.

We tested whether simulation of postural changes, which occur during public speech test procedures, activates cardiovascular system and stress hormone release that could interfere with the effect of psychosocial stress load. Young healthy male volunteers (n=8) underwent procedure imitating exactly all postural changes present in the psychosocial stress model based on public speech used in this laboratory (namely changes from sitting to standing and repeated sitting). Postural changes were associated with increases in heart rate, blood pressure, plasma concentrations of noradrenaline and aldosterone and elevation in plasma renin activity. In contrast to cardiovascular parameters, adrenocorticotropic hormone, cortisol and adrenaline, the main characteristics of hormonal response during mental stress, were not significantly influenced. The overall magnitude of all observed alterations was much smaller than that seen following mental stress procedures in our previous studies. This study provides evidence that changes in body posture during public speech test procedure influence hemodynamics and endocrine responses in a mild manner. Though this influence may represent a source of unspecific variance, substantial confounding effects on responses to the psychosocial component of the procedure are unlikely. In any case, models combining mental stressors and changes in body posture must be interpreted as complex stress stimuli.     

Effects of mental stress on insulin-mediated glucose metabolism and energy expenditure in lean and obese women

The effects of the sympathetic activation elicited by a mental stress on insulin sensitivity and energy expenditure (VO(2)) were studied in 11 lean and 8 obese women during a hyperinsulinemic-euglycemic clamp. Six lean women were restudied under nonselective beta-adrenergic blockade with propranolol to determine the role of beta-adrenoceptors in the metabolic response to mental stress. In lean women, mental stress increased VO(2) by 20%, whole body glucose utilization ([6,6-(2)H(2)]glucose) by 34%, and cardiac index (thoracic bioimpedance) by 25%, whereas systemic vascular resistance decreased by 24%. In obese women, mental stress increased energy expenditure as in lean subjects, but it neither stimulated glucose uptake nor decreased systemic vascular resistance. In the six lean women who were restudied under propranolol, the rise in VO(2), glucose uptake, and cardiac output and the decrease in systemic vascular resistance during mental stress were all abolished. It is concluded that 1) in lean subjects, mental stress stimulates glucose uptake and energy expenditure and produces vasodilation; activation of beta-adrenoceptors is involved in these responses; and 2) in obese patients, the effects of mental stress on glucose uptake and systemic vascular resistance, but not on energy expenditure, are blunted.     

Scintigraphic evaluation of shape of lung and chest in upright and head-down posture

We determined the configuration of lungs and chest in six healthy young subjects using anteroposterior and lateral technetium-99m-labeled scintigraphic images obtained in upright and in 90 degree head-down posture at 0, 25, 50, 75, and 100% vital capacity (VC). The lung shape was evaluated from curves relating vertical height vs. cumulative volume of 20 apicodiaphragmatic lung zones of equal height. S-shaped curves were obtained, which, after size normalization, were largely independent of volume or posture (P greater than 0.1). However, the apical zones tended to become relatively wider and the diaphragmatic zones relatively smaller with increasing volume, especially between 0 and 25% VC in upright posture and 0-50% VC in head-down posture. Changing posture from upright to head-down also tended to slightly widen the apical zones and to narrow the diaphragmatic zones, which is in line with a greater intrathoracic penetration of the diaphragm/abdomen. The shape of the chest was evaluated from the ratio of the transverse-thoracic and anteroposterior distances over height. These ratios did not clearly change with posture (P greater than or equal to 0.05) but increased by approximately 30% with decreasing volume (P less than 0.01). The fact that these shape changes of the chest were not accompanied by similar changes in lung shape can be explained mainly by widening of the mediastinum when volume decreases. In conclusion, the shape of the lung and chest are similar in head-down and upright humans, in contrast to the reversal of the apicodiaphragmatic differences in alveolar expansion and in transpulmonary pressure.     

Effect of load position on muscle forces, internal loads and stability of the human spine in upright postures

A novel kinematics-based approach coupled with a non-linear finite element model was used to investigate the effect of changes in the load position and posture on muscle activity, internal loads and stability margin of the human spine in upright standing postures. In addition to 397 N gravity, external loads of 195 and 380 N were considered at different lever arms and heights. Muscle forces, internal loads and stability margin substantially increased as loads displaced anteriorly away from the body. Under same load magnitude and location, adopting a kyphotic posture as compared with a lordotic one increased muscle forces, internal loads and stability margin. An increase in the height of a load held at a fixed lever arm substantially diminished system stability thus requiring additional muscle activations to maintain the same margin of stability. Results suggest the importance of the load position and lumbar posture in spinal biomechanics during various manual material handling operations.     

Variations in blood supply allocations for quadrupedal and for bipedal posture and locomotion

Hemodynamics and orthodynamics were investigated in quadrupeds (dogs) and in bipeds (humans). The subjects were investigated at rest in supine or lateral posture, in quadrupedal and then in bipedal posture, and during locomotion. Quadrupedalism in humans was with subjects on their hands and knees. Bipedalism in dogs was on hindlimbs with the forelimbs held by a technician. Blood flow in the main arteries of the body (aorta, external and internal carotid, subclavian, and femoral) was measured by sonography. Positional variations between the main bones of the body were determined from X-rays. This study investigated the reallocation of blood supply to different regions of the body when it switches from quadrupedal to bipedal posture and locomotion. Compared with resting posture, the principal findings are 1) cardiac output shows a minimal increase for humans in bipedal stance and a noticeable increase for dogs as well as humans in quadrupedal stance; 2) quadrupedal stance in humans and dogs and bipedal stance in dogs require increased blood supply to the muscles of the neck, back, and limbs, while human bipedal stance requires none of these; 3) cerebral blood flow (internal carotid) in humans did not change as a result of bipedal posture or locomotion, but showed a noticeable drop in quadrupedal posture and an even further drop in quadrupedal locomotion. The conclusion is that erect posture and encephalization produced a noticeable readjustment and reallocation of blood flow among the different regions of the body: This consisted in shifting a large volume of blood supply from the musculature to the human brain.     

Development of a patient-specific anatomical foot model from structured light scan data

The use of anatomically accurate finite element (FE) models of the human foot in research studies has increased rapidly in recent years. Uses for FE foot models include advancing knowledge of orthotic design, shoe design, ankle–foot orthoses, pathomechanics, locomotion, plantar pressure, tissue mechanics, plantar fasciitis, joint stress and surgical interventions. Similar applications but for clinical use on a per-patient basis would also be on the rise if it were not for the high costs associated with developing patient-specific anatomical foot models. High costs arise primarily from the expense and challenges of acquiring anatomical data via magnetic resonance imaging (MRI) or computed tomography (CT) and reconstructing the three-dimensional models. The proposed solution morphs detailed anatomy from skin surface geometry and anatomical landmarks of a generic foot model (developed from CT or MRI) to surface geometry and anatomical landmarks acquired from an inexpensive structured light scan of a foot. The method yields a patient-specific anatomical foot model at a fraction of the cost of standard methods. Average error for bone surfaces was 2.53 mm for the six experiments completed. Highest accuracy occurred in the mid-foot and lowest in the forefoot due to the small, irregular bones of the toes. The method must be validated in the intended application to determine if the resulting errors are acceptable.     

Muscle force and power in obese and overweight children

The study investigated differences in skeletal muscle function between obese and non-obese children using a force platform. Forty obese children and adolescents (age range 8 to 18 years; 21 girls) and 40 age- and sex-matched controls performed two tests: (1) single two-legged jump, a countermovement jump for maximal height; (2) multiple one-legged hopping on the forefoot, a test of maximal force. In the single two-legged jump, obese subjects had higher absolute peak force (1.62 kN vs 1.09 kN) and peak power (2.46 kW vs 2.06 kW), but lower body weight-related peak force (2.10 vs 2.33) and lower peak power per body mass (30.9 W/kg vs 41.6 W/kg). Jump height (29.3 cm vs 37.5 cm) and maximal vertical velocity (1.92 ms(-1) vs 2.31 ms(-1)) were reduced in obese children. In multiple one-legged hopping, obese subjects had 72% and 84% higher absolute peak force on the left and right foot, respectively. However, forces relative to body weight were 24% and 23% lower in the obese group than in the control group. In conclusion, obese children and adolescents have increased muscle force and power. This partly compensates for the effect of high body weight on muscle performance.     

Posture effects on timing of abdominal muscle activity during stimulated ventilation.

In humans during stimulated ventilation, substantial abdominal muscle activity extends into the following inspiration as postexpiratory expiratory activity (PEEA) and commences again during late inspiration as preexpiratory expiratory activity (PREA). We hypothesized that the timing of PEEA and PREA would be changed systematically by posture. Fine-wire electrodes were inserted into the rectus abdominis, external oblique, internal oblique, and transversus abdominis in nine awake subjects. Airflow, end-tidal CO2, and moving average electromyogram (EMG) signals were recorded during resting and CO2-stimulated ventilation in both supine and standing postures. Phasic expiratory EMG activity (tidal EMG) of the four abdominal muscles at any level of CO2 stimulation was greater while standing. Abdominal muscle activities during inspiration, PEEA, and PREA, were observed with CO2 stimulation, both supine and standing. Change in posture had a significant effect on intrabreath timing of expiratory muscle activation at any level of CO2 stimulation. The transversus abdominis showed a significant increase in PEEA and a significant decrease in PREA while subjects were standing; similar changes were seen in the internal oblique. We conclude that changes in posture are associated with significant changes in phasic expiratory activity of the four abdominal muscles, with systematic changes in the timing of abdominal muscle activity during early and late inspiration.     

秦岭川金丝猴的一种自发性双足姿势的脚偏好

与手偏好相比较,脚偏好被认为是研究大脑半球中语言功能偏侧性调控表达的一种更佳的行为预测指标。当前国际科学界对于人类大脑半球功能不对称性和肢体偏好进化起源的关注,有力地推动了非人灵长类物种肢体偏好行为学研究,其中关于树栖灵长类物种的相关研究,对身体姿势在灵长类肢体偏好表达的理解有十分关键作用。川金丝猴(Rhinopithecus roxellana)是我特有濒危灵长类物种,主要营树栖生活。本研究首次关注秦岭川金丝猴自发性非移动双足姿势(双足叠放)的脚偏好。研究发现在个体水平上每个焦点动物均表现出明显的脚偏好,在群组水平上表现出显著的右脚偏好,脚偏好表达无显著性别差异,其研究结果支持“姿势起源理论”。本文首次呈现野生旧大陆猴物种群组水平脚偏好的研究证据。     

Effects of oral and intravenous fat load on blood pressure, endothelial function, sympathetic activity, and oxidative stress in obese healthy subjects

We compared the effects of high and low oral and intravenous (iv) fat load on blood pressure (BP), endothelial function, autonomic nervous system, and oxidative stress in obese healthy subjects. Thirteen obese subjects randomly received five 8-h infusions of iv saline, 20 (32 g, low iv fat) or 40 ml/h intralipid (64 g, high iv fat), and oral fat load at 32 (low oral) or 64 g (high oral). Systolic BP increased by 14 ± 10 (P = 0.007) and 12 ± 9 mmHg (P = 0.007) after low and high iv lipid infusions and by 13 ± 17 (P = 0.045) and 11 ± 11 mmHg (P = 0.040) after low and high oral fat loads, respectively. The baseline flow-mediated dilation was 9.4%, and it decreased by 3.8 ± 2.1 (P = 0.002) and 4.1 ± 3.1% (P < 0.001) after low and high iv lipid infusion and by 3.8 ± 1.8 (P = 0.002) and 5.0 ± 2.5% (P < 0.001) after low and high oral fat load, respectively. Oral and iv fat load stimulated oxidative stress, increased heart rate, and decreased R-R interval variability. Acute iv fat load decreased blood glucose by 6-10 mg/dl (P < 0.05) without changes in insulin concentration, whereas oral fat increased plasma insulin by 3.7-4.0 μU/ml (P < 0.01) without glycemic variations. Intravenous saline and both oral and iv fat load reduced leptin concentration from baseline (P < 0.01). In conclusion, acute fat load administered orally or intravenously significantly increased blood pressure, altered endothelial function, and activated sympathetic nervous system by mechanisms not likely depending on changes in leptin, glucose, and insulin levels in obese healthy subjects. Thus, fat load, independent of its source, has deleterious hemodynamic effects in obese subjects.     

Effect of load position on muscle forces,internal loads and stability of the human spine in upright postures

A novel kinematics-based approach coupled with a non-linear finite element model was used to investigate the effect of changes in the load position and posture on muscle activity, internal loads and stability margin of the human spine in upright standing postures. In addition to 397 N gravity, external loads of 195 and 380 N were considered at different lever arms and heights. Muscle forces, internal loads and stability margin substantially increased as loads displaced anteriorly away from the body. Under same load magnitude and location, adopting a kyphotic posture as compared with a lordotic one increased muscle forces, internal loads and stability margin. An increase in the height of a load held at a fixed lever arm substantially diminished system stability thus requiring additional muscle activations to maintain the same margin of stability. Results suggest the importance of the load position and lumbar posture in spinal biomechanics during various manual material handling operations.