Tzyy Yuang Shiang

The effect of insoles in therapeutic footwear—A finite element approach

Current practice in the prevention of recurrence of neuropathic foot ulcers is to prescribe accommodative in-shoe orthoses or insoles which reduce plantar pressure levels at locations of bony prominences, particularly under the metatarsal heads. To date, design of these orthoses has largely been a trial and error process. There is little quantitative information available regarding the effects of thickness and the influence of soft tissue characteristics on the cushioning effect of such interventions. The current paper investigated alterations in pressure under the second metatarsal head as a function of insole thickness and tissue thickness. Both experimental and quasi-static plane strain finite element approaches were employed. The orthoses chosen reduced plantar pressure by a maximum of approximately 30% and were more effective (on a percentage basis) in the setting of reduced sub-metatarsal tissue thickness. Peak normal stresses predicted by the FE models were, on average, within 5.9% of experimentally measured values for the normal tissue case and 8.1% for the reduced tissue case. The techniques presented represent a promising approach to understanding plantar cushioning and the principles involved in the design of therapeutic footwear for insensate feet.

Is the foot striking pattern more important than barefoot or shod conditions in running

People have advocated barefoot running, claiming that it is better suited to human nature. Humans usually run barefoot using a forefoot strike and run shod using a heel strike. The striking pattern was thought to be a key factor that contributes to the benefit of barefoot running. The purpose of this study is to use scientific data to prove that the striking pattern is more important than barefoot or shod conditions for runners on running injuries prevention. Twelve habitually male shod runners were recruited to run under four varying conditions: barefoot running with a forefoot strike, barefoot running with a heel strike, shod running with a forefoot strike, and shod running with a heel strike. Kinetic and kinematic data and electromyography signals were recorded during the experiments. The results showed that the lower extremity can gain more compliance when running with a forefoot strike. Habitually shod runners can gain more shock absorption by changing the striking pattern to a forefoot strike when running with shoes and barefoot conditions. Habitually shod runners may be subject to injuries more easily when they run barefoot while maintaining their heel strike pattern. Higher muscle activity in the gastrocnemius was observed when running with a forefoot strike, which may imply a greater training load on the muscle and a tendency for injury.

Comparison of shock transmission and forearm electromyography between experienced and recreational tennis players during backhand strokes.

ObjectiveTo test the hypothesis that recreational tennis players transmit more shock impact from the racket to the elbow joint than experienced tennis players during the backhand stroke. Also, to test whether recreational tennis players used higher electromyographic (EMG) activities in common wrist extensor and flexor around epicondylar region at follow-through phase. DesignA repeated-measure, cross-sectional study. SettingNational College of Physical Education and Sports at Taipei, Taiwan. ParticipantsTwenty-four male tennis players with no abnormal forearm musculoskeletal injury participated in the study. According to performance level, subjects were categorized into 2 groups: experienced and recreational. Main Outcome MeasurementsImpact transmission and wrist extensor-flexor EMG for backhand acceleration, impact, and follow-through phases were recorded for each player. An independent t test with a significance level of 0.05 was used to examine mean differences of shock impact and EMG between the 2 test groups. One-way ANOVA associated with Tukey multiple comparisons was used to identify differences among different impact locations and EMG phases. ResultsExperienced athletes reduced the racket impact to the elbow joint by 89.2%, but recreational players reduced it by only 61.8%. The largest EMG differences were found in the follow-through phase (P<0.05). Experienced athletes showed that their extensor and flexor EMGs were at submaximal level for follow-through phase, whereas recreational players maintained their flexor and extensor EMGs at either supramaximal or maximal level. ConclusionsOur results support the hypothesis that recreational players transmit more shock impact from the racket to the elbow joint and use larger wrist flexor and extensor EMG activities at follow-through phase of the backhand stroke. Follow-through control is proposed as a critical factor for reduction of shock transmission. Clinicians or trainers should instruct beginners to quickly release their grip tightness after ball-to-racket impact to reduce shock impact transmission to the wrist and elbow.

Assessment of walking, running, and jumping movement features by using the inertial measurement unit

PURPOSE To observe various modes of lower limb locomotion, an inertial measurement unit (IMU) was used. Digital signals were used to identify signal characteristics that help to distinguish among locomotion modes and intensity levels. METHODS A wireless IMU was installed on the outside of shoes and three forms of locomotion (walking, running, and jumping) were assessed at two intensity levels (low and high) to observe the acceleration, foot angular velocity variations, and characteristics of the curve variations in the anteroposterior, mediolateral, and superior-inferior directions. RESULTS Most interactions between intensity and locomotion were statistically significant, except for the acceleration in the anteroposterior direction and on the horizontal plane. In addition, as the intensity increased, the values of all the parameters increased. Thus, both the acceleration values and range of angular velocity variation can be used to distinguish the intensity levels. Moreover, the results indicated that the angular velocity in the frontal axis, which is the sequence of the plantar/dorsiflexion movements, can also be used to identify different locomotion. CONCLUSIONS Uniaxial acceleration or the range of angular velocity variation could be used to identify locomotion intensities, whereas the characteristics of the uniaxial angular velocity curve could be used to identify the locomotion modes.

Whole-body vibration combined with extra-load training for enhancing the strength and speed of track and field athletes.

Abstract Wang, H-H, Chen, W-H, Liu, C, Yang, W-W, Huang, M-Y, and Shiang, T-Y. Whole-body vibration combined with extra-load training for enhancing the strength and speed of track and field athletes. J Strength Cond Res 28(9): 2470–2477, 2014—The purpose of this study was to investigate whether whole-body vibration (WBV) combined with extra-load training can enhance the strength and speed of trained athletes compared with isolated WBV training or loaded training (LT) only. Twenty-one elite male track and field athletes were randomly assigned to a loaded vibration (LV) training group (n = 7), an unloaded vibration (ULV) training group (n = 7), and a LT group (n = 7). During 4 weeks of training, the LV group received the vibration stimulus (30 Hz and 4 mm) accompanied by a load comprising 75% of the maximum voluntary contraction (MVC), the ULV group received the same vibration stimulus without any load, and the LT group received only a load of 75% MVC without any vibration stimulus. The knee extensor isometric strength, and the concentric and eccentric strength were measured using an isokinetic dynamometer at 300°·s−1 at a 30-m sprint speed before and after the training period. A 2-way mixed analysis of variance (time × group) was used to analyze the differences. Significant time × group interactions were observed for all the dependent variables (p ⩽ 0.05). Regarding the post hoc analysis results, the LV group exhibited significant improvements for all the dependent variables after training (p ⩽ 0.05), whereas the ULV group exhibited significantly reduced sprint speeds (p ⩽ 0.05). The LV group demonstrated significantly superior eccentric strength compared with the ULV and LT groups after training (p ⩽ 0.05), and the LV group also produced significantly superior sprint speeds compared with the ULV group after training (p ⩽ 0.05). Vibration combined with extra-load training for 4 weeks significantly increased the muscle strength and speed of the elite male track and field athletes.

Noninvasive analysis of fascicle curvature and mechanical hardness in calf muscle during contraction and relaxation.

The purpose of this study was to investigate whether changes of fascicle curvature and muscle hardness of the gastrocnemius muscle during relaxation and isometric contraction could be measured using a noninvasive approach. Seventeen male college students (age 21.0+/-1.5 years) participated in this study. Measurements were made during the resting state and maximal isometric plantarflexion. Fascicle curvature (m(-1)) of the gastrocnemius medialis was measured by ultrasonography. Muscle hardness (kg/mm) was measured with a myotonometer. Angle of ankle joint (degrees), amplitude of electromyographic activities (mV), and plantarflexion force (kg) were simultaneously recorded using an electrogoniometer, surface electromyography (EMG), and a load cell, respectively. Results demonstrated that the joint angle, electromyographic activities, and force at muscle contraction for the myotonometer and ultrasound conditions were not significantly different (all p>0.05). Hardness and fascicle curvature during maximal isometric plantarflexion were significantly greater than those at rest (p=0.002 and p<0.001, respectively). Correlations between changes in fascicle curvature and changes of muscle hardness that took place between muscle relaxation and maximal contraction were significant (r=0.832, p=0.011). This study demonstrates that ultrasonographic and myotonometric measurements are useful to quantify changes in muscle geometry and mechanical properties for muscles during isometric contraction.

Chronic effects of whole-body vibration on jumping performance and body balance using different frequencies and amplitudes with identical acceleration load

UNLABELLED Previous studies on vibration training have all been based on protocols at different combinations of frequencies and amplitudes without controlling the loading intensity. OBJECTIVES This study investigated the effect of an 8-week vibration training program, under identical acceleration loads with various frequencies and amplitudes, on jumping performance, muscle activation and body balance. DESIGN Fifty young adults were randomly assigned to an high-frequency (32 Hz, 1mm, and 4 g), low-frequency (18 Hz, 3 mm, and 4 g), or a control group. The high-frequency and low-frequency groups underwent 60 s of squats exercise on the specific vibration platform three times a week, whereas the control group was trained without vibration. METHODS A force platform was used to measure the center of pressure of a static single leg stance, and the heights and impulse of two consecutive countermovement jumps before and after intervention. The activation of the rectus femoris and biceps femoris were also measured synchronously by surface electromyography. RESULTS The heights and impulse of both the first and second countermovement jumps were significantly increased and the area of center of pressure was significantly decreased after training in both the high-frequency and low-frequency groups (P<.05). Consequently, activation of the rectus femoris during the first countermovement jump was significantly lower than the pre-training value in the HF group but increased in the low-frequency group after training (P<.05). CONCLUSIONS An 8-week identical acceleration vibration training regimen with various frequencies and amplitudes can significantly improve jumping performance and body balance, but the specific neuromuscular adaptation is possibly induced by different training settings.

Effect of Passive Repetitive Isokinetic Training on Cytokines and Hormonal Changes

It is well known that muscle strength and power are important factors in exercise. Plyometrics is designed to gain muscle strength and power in a shock method. The passive repetitive isokinetic (PRI) machine is developed for plyometrics. The present study aims to understand the effect of ten-week PRI training in different intensities on human plasma concentration cytokines as well as hormonal changes. Thirty young male subjects were enrolled into the ten-week PRI training program and were divided randomly into traditional, low- and high-intensity PRI training groups. Blood samples were obtained before, during, after and 1-, 2-, 3-, 5- and 7-day (D) post-training. The plasma concentrations of cytokines and hormones were measured by an enzyme-linked immunosorbent assay (ELISA). Elevated plasma IL-2 was found in the subjects in all the training programs. Significant increases of proinflammatory cytokines IL-1beta and TNF-alpha were observed at post 7 D in the high-intensity PRI training (29.5 +/- 4.4 and 515.8 +/- 127.1 pg/ml, respectively). No significance in differences in the plasma concentration of IL-6 was observed in the traditional and low-intensity PRI training. Significant elevation of IL-6 was found at post 5 D in high-intensity PRI training. Higher plasma IL-6 concentration was observed at post 3 and 5 D in high-intensity PRI training compared to low-intensity PRI training (P < 0.05). Significant elevation of plasma IL-15 during (week 6) and after (post 0 D) was observed in low-intensity PRI training. Also, there were differences between low-intensity PRI training and traditional training at post 0, 2, 3, and 5 D. The plasma concentration of cortisol was decreased to the lowest value (118.0 +/- 17.3 ng/ml) at post 0 D in traditional training, then returned to the baseline (220.5 +/- 19.1 ng/ml). In the high-intensity PRI training, but not in the low-intensity PRI training, the cortisol level dropped from 224.9 +/- 25.8 ng/ml at post 0 D down to the 123.2 +/- 22.6 ng/ml at post 1 D. Significant differences were found at post 1 and 5 D between low- and high-intensity PRI training, and post 0, 1, 2, and 3 D between traditional and high-intensity PRI training. Significant increased testosterone was found post 0, 1, 2, and 3 D in traditional training. Higher plasma testosterone was observed during and the recovery period in low-intensity, but not in high-intensity, PRI training. In conclusion, high-intensity PRI training could induce the proinflammatory cytokines, i.e., IL-1beta and TNF-alpha, and decrease plasma cortisol in the recovery period.

Measuring kinematic changes of the foot using a gyro sensor during intense running

Abstract Gyro sensor has been used to measure foot pronation during running with reliable results in previous studies, and the signals were not affected by the vibration of heel strikes. The purpose of this study was to observe the kinematic changes of the foot during intense running using a 3-axis gyro sensor. Fifteen male participants (average age: 24.5 ± 1.7 years; mean height: 174.1 ± 3.3 cm; mean body weight: 71.0 ± 5.5 kg) were recruited in this study. Foot kinematic changes were observed in 30-min intense running protocols. The comparisons of the signals from gyro and motion analysis system were also performed to determine the accuracy of the gyro and showed positive results. In the main experiment, the ankle range of motion (ROM) in the frontal plane, measured using a motion system, showed a significant increase over time. Accordingly, peak angular velocity in the frontal plane also showed a significant increase. The correlation between ankle ROM and peak angular velocity in the frontal plane is significantly high (r = 0.975). Moreover, peak angular velocity in the frontal plane is also significantly correlated with both rate of perceived exertion (RPE) (r = 0.911) and heart rate (r = 0.960). This study concluded that an alarm system for foot kinematic changes related to running injuries can be built based on the peak angular velocity of the foot in the frontal plane.

Walking beyond preferred transition speed increases muscle activations with a shift from inverted pendulum to spring mass model in lower extremity

BACKGROUND The triggers for the transition of gait from walking to running during increasing speed locomotion have been attributed to an energy conservation strategy or a relief of excessive muscle activation. Walking beyond the preferred transition speed (PTS) has been proposed as an exercise protocol for boosting energy consumption. However, the biomechanical factors involved while this protocol is used have not been investigated. Thus, this study investigated the difference between walking and running below, during, and beyond the PTS from a biomechanical perspective. METHODS Sixteen healthy male participants were recruited. After determination of their PTS, five speeds of walking and running were defined. Kinematic data, including center-of-mass (COM) displacement, COM acceleration, and electromyography (EMG) data of rectus femoris (RF), biceps femoris, gastrocnemius (GAS), and tibialis anterior were collected at the five speeds for both walking and running. RESULT The vertical COM displacement and acceleration in running were significantly larger than those in walking at all five speeds (p<0.05). EMG signals of the two antigravity muscles, RF and GAS, demonstrated a significant higher activation in walking than that in running at the speed beyond PTS (p<0.05). CONCLUSION The larger energy consumption in walking than that in running beyond the PTS may be attributed to the high activation of lower-extremity muscles. The smaller vertical COM displacements and accelerations exhibited when participants walked beyond the PTS rather than ran did not indicate adverse effects of using walking beyond the PTS as an exercise prescription for boosting energy consumption.