Increased toe flexor strength does not relate to altered postural sway during static upright standing after 12 weeks of multicomponent exercise training.

This study investigated whether an increase in toe flexor strength influenced postural control during static upright standing after 12 weeks of multicomponent exercise training in healthy young men. Twelve men (18-23 yrs) performed multicomponent exercise 3 days per week for 12 weeks. Twelve additional age-matched men were recruited for the untrained control group. The multicomponent exercise training consisted of strengthening and balance exercises for the foot and leg muscles. Toe flexor strength, foot arch height and postural control were assessed before, during, and after exercise training. Postural control was evaluated using the path of the centre of pressure, which was obtained with a force plate under three standing conditions: double-leg standing with eyes open, double-leg standing with eyes closed, and single-leg standing with eyes open. The dominant leg was used for single-leg standing. After exercise training, toe flexor strength increased by approximately 32% (p < 0.01), whereas the foot arch height did not change. The centre of pressure variables during double-leg standing did not change after exercise training; however, these variables decreased during single-leg standing. None of the variables in the control group changed after exercise training. The relative increase in toe flexor strength was not correlated with the relative improvement in the centre of pressure variables during single-leg standing after 12 weeks of exercise training (total length, r = 0.1734; mean velocity, r = 0.1734; sway area, r = -0.1372). These findings suggest that increased toe flexor strength has no significant effect on static postural control ability after exercise training in young men.HighlightsTwelve weeks of multicomponent exercise training aimed at strengthening foot and leg muscles increased toe flexor strength.Multicomponent exercise training did not alter postural stability during double-leg standing, but improved postural stability during single-leg standing.Increased toe flexor strength did not relate to altered postural stability during static upright standings after 12 weeks of exercise training.

The mechanical role of the metatarsophalangeal joint in human jumping.

This study investigated the mechanical role of metatarsophalangeal (MTP) joints in human jumping. Eighteen healthy young men performed three types of single-leg jumps (SJ: squat jump; CMJ: countermovement jump; HJ: standing horizontal jump) on a force plate under barefoot (BARE) and forefoot immobilisation (FFIM) conditions. For FFIM, the forefoot was immobilised around the MTP joints of the dominant leg by a custom-made splint. Force-time components and the centre of pressure (COP) trajectory were measured from the ground reaction force (GRF) in the take-off phase of jumping. The vertical jump heights calculated from the net vertical impulse were lower under FFIM than under BARE during the CMJ (p < 0.05). The HJ distance under FFIM was significantly shorter than that under BARE (p < 0.01). The relative net vertical impulse was lower under FFIM than under BARE during the CMJ (p < 0.05). During the HJ, all the horizontal GRF variables were significantly lower under FFIM than under BARE (p < 0.01), but none of the vertical GRF variables differed between the two conditions. The horizontal relative GRF in the 90-95% of the final take-off phase during the HJ was significantly lower under FFIM than under BARE (p < 0.01). Under FFIM, the COP range in the antero-posterior direction in the take-off phase of the HJ decreased (p < 0.05), whereas its range in the anterior direction for the SJ and CMJ increased (p < 0.05). The results of this study indicate that MTP joint motion can play an important role in regulating force-generating capacities of toe flexor muscles in the take-off phase of human jumping, especially in the horizontal direction of horizontal jumping.

Importance of toe flexor strength in vertical jump performance.

This study investigated whether toe flexor strength and foot arch height were related to force components during the ground contact phase in vertical jump performance. The toe flexor strength, foot arch height and vertical jump performance were studied in 31 healthy young men. For the measurement of toe flexor strength, participants explosively exerted maximum force on a toe grip dynamometer. The maximum isometric force (Fmax) and the rate of force development (RFD) of the toe flexor strength were evaluated. Foot arch height was assessed as the distance between the navicular tuberosity and the floor. Fmax and foot arch height were normalized by body mass (rFmax) and height, respectively. Three types of vertical jumps without arm swing were performed on a force plate: a squat jump (SJ), a countermovement jump (CMJ), and a rebound jump (RJ). Fmax, rFmax and RFD of the toe flexor strength were positively correlated with the vertical jump height in the SJ (r = 0.408, r = 0.452, r = 0.514) and CMJ (r = 0.377, r = 0.444, r = 0.548) and the rebound jump index in the RJ (r = 0.549, r = 0.582, r = 0.575); however, foot arch height was not correlated with the vertical jump performance, and it was only significantly correlated with the minimum ground reaction force relative to body weight during the unloading phase of the CMJ (r = -0.366). These results suggest that the toe flexor strength is an important parametre for enhancing the jump performance.

Toe flexor strength is not related to postural stability during static upright standing in healthy young individuals.

BACKGROUND: The human foot has adapted specifically to support body weight when standing upright. At the base of the postural control system, the unique arch structure of the foot still has an uncertain role in human upright standing. Because the toe flexor muscles help to support the foot arches, they might be an important contributor to postural stability. However, no research has identified the influence of the toe flexor strength or the foot arch height on postural stability in static upright standing. RESEARCH QUESTION: The aim of this study was to examine whether the toe flexor strength and the foot arch height were related to postural stability in static standing in healthy young individuals. METHODS: Fifty healthy young individuals were recruited into this cross-sectional study. Toe flexor strength was measured using a toe grip dynamometer, and it was normalised by body mass (rTFS). Foot arch height was assessed as the distance between the navicular tuberosity of the foot and the floor, and it was normalised by height (rFAH). Postural stability was evaluated using the path of the centre of pressure (COP) during double-leg standing with eyes open and single-leg standing with eyes open. RESULTS: rTFS and rFAH were 2.6 ±â€¯0.8 N/kg and 2.8 ±â€¯0.4%, respectively, and they were not significantly correlated (r = 0.094), indicating that they were independent variables. The results of Pearson's correlation analysis revealed that any body size related variables (height, body mass, BMI) were not significantly correlated with COP variables under either double-leg or single-leg standing, rTFS was not significantly correlated with COP variables under either double-leg or single-leg standing and rFAH was not significantly correlated with COP variables under double-leg standing. SIGNIFICANCE: Toe flexor strength has no significant role in maintaining postural stability during static upright standing.

Toe Flexor Muscle Strength and Morphological Characteristics of the Foot in Judo Athletes.

Whether practicing in judo influences the muscle strength and morphological characteristics of the foot is unknown. The purpose of this study was to determine the toe flexor muscle strength and morphological characteristics of the foot in judo athletes. Judo athletes (JUDO, men=24) and age-, gender- and body mass-matched physically active healthy subjects (CON, men=24) were recruited, and their toe flexor strength and morphological characteristics of the foot were compared. The maximum isometric toe flexor strength and foot intrinsic muscle thicknesses were measured using a toe grip dynamometer and a B-mode ultrasound, respectively. Foot arch height was assessed as the distance between the navicular tuberosity of the foot and the floor in the sitting and standing positions. JUDO showed a significantly lower foot arch height and smaller foot arch index than CON, whereas foot length and muscle thickness did not significantly differ between groups. The toe flexor strength relative to total muscle thickness was significantly larger in JUDO than CON. The foot arch dynamics was significantly larger in JUDO than CON. This study suggests that exercise training specific to judo may affect the force-generating capacity, morphological structure and arch function of the foot.

Relation between the ankle joint angle and the maximum isometric force of the toe flexor muscles.

The purpose of this study was to investigate the relationships between the ankle joint angle and maximum isometric force of the toe flexor muscles. Toe flexor strength and electromyography activity of the foot muscles were measured in 12 healthy men at 6 different ankle joint angles with the knee joint at 90 deg in the sitting position. To measure the maximum isometric force of the toe flexor muscles, subjects exerted maximum force on a toe grip dynamometer while the activity levels of the intrinsic and extrinsic plantar muscles were measured. The relation between ankle joint angle and maximum isometric force of the toe flexor muscles was determined, and the isometric force exhibited a peak when the ankle joint was at 70-90 deg on average. From this optimal neutral position, the isometric force gradually decreased and reached its nadir in the plantar flexion position (i.e., 120 deg). The EMG activity of the abductor hallucis (intrinsic plantar muscle) and peroneus longus (extrinsic plantar muscle) did not differ at any ankle joint angles. The results of this study suggest that the force generation of toe flexor muscles is regulated at the ankle joint and that changes in the length-tension relations of the extrinsic plantar muscle could be a reason for the force-generating capacity at the metatarsophalangeal joint when the ankle joint angle is changed.

Force-generating capacity of the toe flexor muscles and dynamic function of the foot arch in upright standing.

The muscle and tendon complex of the foot helps to support the foot arch and generates the muscle force of the foot. The present study investigated the force-generating capacity of the toe flexor muscles and the dynamic function of the foot arch when standing upright, and the relationships between these indices. The maximum toe flexor force and foot arch height in the sitting and standing positions were studied in the left and right feet of 224 healthy young individuals. To measure the maximum isometric force of the toe flexor muscles, the subjects exerted maximum force on a toe grip dynamometer. Measurements were repeated three times with at least a 1-min rest period between bouts, and the maximum value among the measurements for each foot was used for further analysis. The absolute value of the toe flexor strength was normalised by body mass. The foot arch height was measured the distance between the tuberosity of the navicular bone and the floor, and normalised by height. The relative foot arch height difference between the sitting and standing positions was evaluated as the foot arch dynamics. The maximum isometric toe flexor strength was 42% higher in the standing position than in the sitting position. There was no relationship between the relative toe flexor strength and the relative foot arch height in either the sitting or standing positions; however, the relative increase in toe flexor strength from sitting to standing (the force amplification factor) was related to the foot arch dynamics, and the flexible foot arch showed a greater increase in the toe flexor strength from sitting to standing compared with the strength in the stiff foot arch. The results of this study suggest that the force-generating capacity of the toe flexor muscles is augmented by bodyweight bearing in upright standing. Additionally, the force amplification mechanism is mechanically regulated by the dynamic function of the foot arch in conjunction with the stretching of the muscle-tendon complex of the foot.

Comparison of lower limb kinetics, kinematics and muscle activation during drop jumping under shod and barefoot conditions.

This study was to investigate the acute effects of wearing shoes on lower limb kinetics, kinematics and muscle activation during a drop jump. Eighteen healthy men performed a drop jump under barefoot and shod conditions. Vertical ground reaction force (GRF) was measured on a force plate during the contact phase of a drop jump, and GRF valuables were calculated for each condition. The angles of the knee and ankle joints, and the foot strike angle (the angle between the plantar surface of the foot and the ground during ground contact) as well as the electromyography of 7 muscles were measured. The shod condition showed a significant larger first peak GRF, longer time to first peak GRF from the initial ground contact and lower initial loading rate than the barefoot condition. The shod condition showed a significant larger ankle joint angle at initial ground contact, smaller knee joint angle between the second peak GRF and take-off as well as smaller foot strike angle at both initial ground contact and take-off than the barefoot condition. There were significant correlations between relative differences in ankle joint at the initial ground contact and relative differences in the initial loading rate. The muscle activity of all muscles during foot ground contact did not differ between two conditions; however, in the shod condition, muscle activation of 150 ms before foot ground contact was significantly higher in the rectus femoris, whereas it was lower in the biceps femoris and tibialis anterior muscles than the barefoot condition. These results indicate that wearing shoes alternates the GRF variables at initial ground contact, joint kinematics at the ground contact and muscle activation before foot ground contact during a drop jump, suggesting that the effects of wearing shoes on drop jump training differ from being barefoot.

Altered postural sway following fatiguing foot muscle exercises.

This study investigated the acute effects of fatiguing foot muscle exercises on the maximum muscle strength of the foot and postural control ability. Eighteen healthy young individuals performed fatiguing foot muscle strength exercises, and their toe flexor and ankle plantar flexor strength and postural control ability were measured before and after the exercises. Postural control ability was evaluated using the path of the center of pressure (COP) during three balance tasks: double-leg standing with eyes open; double-leg standing with eyes closed; and single-leg standing with eyes open. After the exercises, the muscle strength of both the toe and ankle plantar flexor significantly decreased. Under all of the conditions, most COP variables did not significantly differ before and after the exercises; however, the total length and mean velocity in the single-leg standing with eyes open significantly decreased after the exercises. Postural sway velocities in the anteroposterior direction of double-leg standing with eyes closed and in both anteroposterior and mediolateral directions of single-leg standing with eyes open significantly decreased after the exercises. The associations between relative changes in muscle strength after the exercise and relative changes in COP variables after the exercise were not found. These results indicate that postural control while standing could be maintained even though foot muscle strength is decreased after fatiguing foot muscle exercises.

The effect of ankle taping on the ground reaction force in vertical jump performance.

The purpose of this study was to investigate the effects of closed basket weave (CBW) ankle taping on the vertical ground reaction force during the contact phase before the take-off in vertical jump performance. We hypothesized that ankle taping would limit the capability for explosive force generation during the contact phase before the take-off in jump performance. Twelve healthy young men (age, 20.2 ± 1.3 years; height, 1.76 ± 0.05 m; body mass, 66.1 ± 6.1 kg; mean ± SD) performed a vertical jump performance on a force plate without (CON) or with ankle taping (CBW technique) of the right ankle joint. Vertical jump ability was assessed using 2 styles of vertical jump with no arm swing: a countermovement jump (CMJ) and squat jump (SJ). From the vertical ground reaction force (GRF), maximum jump height, vertical impulse (VI), rate of force development, maximum GRF (GRFmax), and time-series GRF (GRFts) during the contact phase before the take-off in jump performance were determined. Jump height was significantly lower for CBW (36.6 ± 6.6 cm) than CON (38.1 ± 6.7 cm) in CMJ, but not in SJ. Rate of force development and GRFts at 35, 40, 45, 50, 55, 60, and 65% of total time of the contact phase in jumping performance were also significantly smaller for CBW than CON in CMJ, but not in SJ. Conversely, VI and GRFmax were not significantly different between the groups in either jump condition. These results suggest that ankle taping impairs CMJ performance, because of a decreased ability to develop large force rapidly on the ground before the take-off.

Effects of unstable shoes on energy cost during treadmill walking at various speeds.

In recent years, shoes having rounded soles in the anterior-posterior direction have been commercially introduced, which are commonly known as unstable shoes (US). However, physiological responses during walking in US, particularly at various speeds, have not been extensively studied to date. The purpose of this study was to investigate the effect of wearing unstable shoes while walking at low to high speeds on the rate of perceived exertion (RPE), muscle activation, oxygen consumption (VO2), and optimum speed. Healthy male adults wore US or normal walking shoes (WS), and walked at various speeds on a treadmill with no inclination. In experiment 1, subjects walked at 3, 4, 5, 6, and 7 km·h(-1) (duration, 3 min for all speeds) and were recorded on video from the right sagittal plane to calculate the step length and cadence. Simultaneously, electromyogram (EMG) was recorded from six different thigh and calf muscles, and the integrated EMG (iEMG) was calculated. In experiment 2, RPE, heart rate and VO2 were measured with the walking speed being increased from 3.6 to 7.2 km·h(-1) incrementally by 0.9 km·h(-1) every 6 min. The optimum speed, defined by the least oxygen cost, was calculated from the fitted quadratic relationship between walking speed and oxygen cost. Wearing US resulted in significantly longer step length and lower cadence compared with WS condition at any given speed. For all speeds, iEMG in the medial gastrocnemius and soleus muscles, heart rate, and VO2 were significantly higher in US than WS. However, RPE and optimum speed (US, 4.75 ± 0.32 km·h(-1); WS, 4. 79 ± 0.18 km·h(-1)) did not differ significantly between the two conditions. These results suggest that unstable shoes can increase muscle activity of lower legs and energy cost without influencing RPE and optimum speed during walking at various speeds.