Kazushige Oshita

Asymmetry of Force Fluctuation in Knee Extension

The purpose of this study was to investigate the asymmetry of force fluctuation and mechanomyogram (MMG) signal during low intensity isometric knee extension. Twelve healthy males (21+/-1 years) performed unilateral force matching tasks; sustained isometric knee extension for 15 s at levels corresponding to 10% and 20% maximal voluntary contraction (MVC) with the visual feedback of force. During the force matching tasks, MMG was detected by an accelerometer arrangement placed on the vastus lateralis. Power spectrum density of the MMG was obtained by the fast Fourier transformation method, and mean power frequency (MPF) was calculated. Force fluctuation, amplitude of MMG and MPF of MMG were significantly increased in 20% MVC task compared to the 10% MVC task in both limbs. Significant differences between stronger MVC limb and weaker MVC limb were not observed in force fluctuation, amplitude of MMG and MPF of MMG during 10% and 20% MVC tasks. These results suggest that the asymmetry of force steadiness during low intensity isometric knee extension was not observed because there was no difference regarding mechanical characteristics in active muscle between stronger and weaker limbs.

Effects of light finger touch to the upper legs on postural sway and muscle activity during quiet standing

The purpose of the present study was to investigate the effects of light finger touch (LT) to ones own body on postural sway and ankle muscle activity during quiet standing. In the first part of the present study, 24 healthy men (19±1 years) stood upright with their eyes closed on a pneumatic balance disk under 3 different conditions. In the first condition, the participants kept their hands in loose fists, and contact between the fingers/palms and the legs was avoided. In the second condition, the participants touched the lateral sides of upper legs lightly (without applying force for mechanical support) with all fingers. In the third condition, the participants again held their hands in loose fists. Postural sway was significantly decreased during second condition compared to first condition. Further, it also tended to decrease in third condition (P = 0.08). The second part of the present study was designed to investigate the mechanisms underlying the association between postural sway and LT by analyzing electromyographic data. Data were obtained from 12 healthy men (20±1 years). During quiet stance on the stable surface, soleus activity did not significantly change by LT. However, tibialis-anterior activity significantly decreased with LT. These results suggest that LT to the upper part of ones own legs decreases postural sway (during and after touching) during a still stance by decreasing co-activation of the ankle muscles.

Asymmetry of Force Fluctuation during Low and Moderate Intensity Isometric Knee Extensions

The purpose of this study was to investigate the asymmetry of force fluctuation during isometric knee extension at low and moderate intensities. 11 healthy men (M age = 21 yr., SD = 1) performed unilateral force matching tasks; sustained isometric knee extension at 20% and 30% maximal voluntary contraction (MVC). During the tasks, a mechanomyogram was measured by an accelerometer arrangement placed on the vastus lateralis. Although force fluctuation was not significantly different between the two legs at 20% MVC, it was higher in the left (weaker) leg than in the right (stronger) leg at 30% MVC. A significant difference in mean power frequency of the mechanomyographic signal between the two legs was also observed only at 30% MVC. These results suggest that the asymmetry of force fluctuation during isometric knee extension was not statistically significant at low intensity; however, it was significant at moderate intensity. These differences in force fluctuation between intensities might be influenced by different motor-unit firing rates in active muscle.

The Critical Velocity and 1 500-m Surface Performances in Finswimming

The purpose of this investigation was to determine whether the concepts of critical velocity (CV) and anaerobic swimming capacity (ASC) could be used by coaches as a reliable index in order to monitor 1500-m Surface (SF) performances in Finswimming. Thirteen Finswimmers (6 males and 7 females, 24+/-6 years), members of the Japanese national team, were instructed to swim three different swimming distances (400-, 800-, and 1500-m) at maximal effort in a 50m long course swimming pool. CV and the ASC were calculated using 400-m and 800-m swim times. Mean height and body mass were 170.2 cm and 69.7 kg in male and 160.5 and 61.0 kg in female. A highly positive correlation was found between the CV and the mean velocity of 1500-m SF (V1500) (r=0.91, P<0.01), but no correlation was found between the ASC and V1500. (r=0.46, P=0.11). However, a high correlation was found between the ASC and the residual error of V1500, calculated from the relationship between V1500 and the CV (r=0.89, P<0.01). These results suggest that the CV is a useful method for evaluating 1500-m SF performance and an aerobic performance expressed as the CV contributes to 1500-m SF performance.

Association of force steadiness of plantar flexor muscles and postural sway during quiet standing by young adults.

This study was conducted to assess the relations of force fluctuations during isometric plantar-flexion and postural sway during quiet standing. Twelve healthy men (M age = 21 yr., SD = 1) performed unilateral plantar flexion measured by a strain gauge force transducer. Participants performed force-matching tasks; sustained plantar flexion for 20 sec. at levels corresponding to 10% and 20% of maximum voluntary contraction with the visual feedback. Also, participants were asked to stand quietly with their eyes open, and then the center of mass displacement and velocity in the anteroposterior were measured. In analysis, postural sway was associated with force fluctuation at only 10% of maximum voluntary contraction. The statistically significant correlation between variables was found only at corresponding contraction intensities for plantar-flexor muscles. From this one may infer neural strategies in plantar-flexor muscles during quiet standing may be characteristics similar to those controlling the plantar-flexion force in young adults.

The Effect of Lightly Gripping a Cane on the Dynamic Balance Control.

The purpose of the current study was to investigate the effect of lightly gripping a cane on the Functional Reach Test (FRT) to evaluate dynamic balance. 21 healthy men (19±1 years) were asked to perform the FRT three times. The standard FRT was performed in the first and third trials. In the second trial, participants in a light-grip group (n = 11) were told to lightly grip (but to not apply force for mechanical support) the cane during the FRT. Participants in a depend-on-cane group (n = 10) were told to perform the FRT while supporting their weight with the cane. FRT is improved by not only supporting a person’s own weight with a cane but also just lightly gripping the cane. These findings would be helpful in the development of a useful application to improve the human movement using a haptic sensory supplementation for activities of daily living.

Development and initial validation of the Morningness-Eveningness Exercise Preference Questionnaire (MEEPQ) in Japanese university students

The aim of this study was to develop a questionnaire to conveniently assess the diurnal preferences of physical activity (PA) in Japanese university students. A total of 219 subjects completed our novel Morningness-eveningness Exercise Preference Questionnaire (MEEPQ). The MEEPQ consisted of 30 items (15 items for the morning and the same 15 items for the evening) rated on a 5-point Likert scale concerning their preference for participating in PA in the morning and evening. The morning score (MS) and evening score (ES) were determined by summing each of the respective 15 items. The internal consistency and construct validity were assessed, and a factor analysis was conducted. To examine the external validity of the MEEPQ, participants wore an accelerometer for seven consecutive days to measure their PA levels objectively. Finally, the test-retest reliability was evaluated at a one-month interval. The MEEPQ showed excellent internal consistency (Cronbachs alpha = 0.896) and construct validity (morning KMO = 0.913, evening KMO = 0.875). A factor analysis showed a three-factor structure involving Physical Wellness (MEEPQ-W), Psychological Well-Being (MEEPQ-P) and Exercise Barrier (MEEPQ-B). The percent of variance was largest for MEEPQ-W in the morning (45.2%) and MEEPQ-P in the evening (40.8%). Test-retest showed that MEEPQ scores had fair repeatability. Significant and positive associations between scores and objectively measured PA levels were found in the MS and 6–9 AM PA and in the ES and 6–9 PM and 9 PM– 0 AM PA (all p<0.05). In summary, the novel MEEPQ showed relatively good agreement and thus can be used for Japanese university student samples. In the MEEPQ, three factors (the physical wellness, psychological well-being and exercise barrier) contributed to a morning or evening PA preference. The summed scores were significantly associated with the objectively measured PA levels in both the morning and evening. Therefore the MEEPQ appears to be a suitable tool for assessing diurnal PA preferences.

Effects of Haptic Sensory Input of a Fluttering Cloth on Static and Dynamic Postural Control

This study investigated the effect of haptic sensory input provided by a fluttering cloth (FC) on postural control. Twenty-one healthy men were randomly assigned to a static or dynamic balance task group. Participants in the static task group performed a single-leg stance for 30s, while those in the dynamic task group performed a functional reach test under three different conditions, with their eyes closed. In the first condition, participants wore only half- or short-tights (HT) during each task. In the second and third conditions, they wore HT and a cloth wrapped snugly around the waist, or HT and an FC wrapped around the waist extending to the lower leg, respectively. Both balance test results were significantly improved in the FC-condition than in the HT-condition. The effect size of improvement was large in the dynamic task, but small in the static task. Therefore, the effect of clothing on balance control was more pronounced in the dynamic than in the static task. These results suggest that postural control might be enhanced by a garment’s shape or material.

Functional Significance of Force Fluctuation During Voluntary Muscle Contraction

Human movement is the result of the joint torque or muscle force generated by the contraction of multiple muscles. The force generated during voluntary muscle contraction is not constant, but fluctuates as observed through the variability in movement. The normalised force fluctuation (measured according to the standard deviation (SD) of force) during isometric contractions is referred to as ‘steadiness’, which influences functional human movement (Carville et al., 2007; Kornatz et al., 2005; Marmon et al., 2011; Salonikidis et al., 2009). For example, Salonikidis et al. (2009) and Kornatz et al. (2005) report that greater fluctuation during voluntary muscle contraction can influence functional human movement in the upper limbs. With regard to the lower limbs, Carville et al. (2007) report that the elderly who tend to fall exhibit less steady knee extension than do both the young and the elderly who do not tend to fall. However, the relationship between force fluctuations in lower limb muscles and human movements for daily activities remains unclear. The ability to control posture during quiet standing is one of the fundamental activities of daily living. Furthermore, the muscle activities of lower limb muscles are important for postural stability during quiet standing. Therefore, this chapter focuses on the relationship between force steadiness in lower limb muscles and postural stability during quiet standing.

Force Steadiness Training Reduces Force Fluctuations during Isometric Plantar Flexion in Young Adults

The purpose of this study was to investigate the effects of low frequency force steadiness training on force fluctuations during isometric plantar flexion in young adults. Sixteen young healthy males (21±1 yrs) were randomly assigned to two training groups or a non-exercising control group (n=5). Training groups were divided by the frequency of training; six subjects trained once a week (1TR) and five subjects trained twice a week (2TR) for 4 wk. Subjects performed unilateral (non-preferred leg) force matching tasks and strength test in plantar flexor before and after 4 wk training. Strength was assessed with a maximal voluntary contraction (MVC). Force matching tasks were performed to maintain isometric plantar flexion for 15s at levels corresponding to 10% and 20% MVC with the visual feedback of force. Force fluctuation during force matching tasks was quantified as the standard deviation of force and the coefficient of variability. Force fluctuation was reduced by the force steadiness training in training groups. Further, force fluctuation was greater in 20% MVC than in 10% MVC. Relative change in force fluctuation was greater in the TR2 than in the TR1. Further, it was greater in 20% MVC than in 10% MVC. However, the interaction between training frequency and contraction intensity was not found to be statistically significant. Force fluctuation of < 4 Hz power (contribution of afferent input from Ia circuit) was reduced by force steadiness training. However, force fluctuation of 8-12 Hz power (contribution of physiological tremor) was not changed by force steadiness training. These results suggest that (1) force steadiness training reduces force fluctuation in plantar flexor, (2) the effects of low frequency training on fluctuation are affected by training frequency, and (3) reduction of fluctuation might be influenced by the afferent input from Ia circuit.