Hitoshi Shiraki

Trunk Muscle Activity During Lumbar Stabilization Exercises on Both a Stable and Unstable Surface

STUDY DESIGN Controlled laboratory study. OBJECTIVES To clarify whether differences in surface stability influence trunk muscle activity. BACKGROUND Lumbar stabilization exercises on unstable surfaces are performed widely. One perceived advantage in performing stabilization exercises on unstable surfaces is the potential for increased muscular demand. However, there is little evidence in the literature to help establish whether this assumption is correct. METHODS Nine healthy male subjects performed lumbar stabilization exercises. Pairs of intramuscular fine-wire or surface electrodes were used to record the electromyographic signal amplitude of the rectus abdominis, the external obliques, the transversus abdominis, the erector spinae, and lumbar multifidus. Five exercises were performed on the floor and on an unstable surface: elbow-toe, hand-knee, curl-up, side bridge, and back bridge. The EMG data were normalized as the percentage of the maximum voluntary contraction, and data between doing each exercise on the stable versus unstable surface were compared using a Wilcoxon signed-rank test. RESULTS With the elbow-toe exercise, the activity level for all muscles was enhanced when performed on the unstable surface. When performing the hand-knee and side bridge exercises, activity level of the more global muscles was enhanced when performed on an unstable surface. Performing the curl-up exercise on an unstable surface, increased the activity of the external obliques but reduced transversus abdominis activation. CONCLUSION This study indicates that lumbar stabilization exercises on an unstable surface enhanced the activities of trunk muscles, except for the back bridge exercise.

Differences in EMG Activity in Scapular Plane Abduction under Variable Arm Positions and Loading Conditions

PURPOSE The present study was performed to investigate the activities of four shoulder muscles-the supraspinatus, the middle deltoid, the infraspinatus, and the upper trapezius-in scapular plane abduction in various exercise conditions. METHODS Eight male subjects (mean +/- SD: 23.4 +/- 1.3 yr) with an asymptomatic nondominant left shoulder participated in this study. Each subject performed scapular plane abduction with humeral external rotation (full can position) and with humeral internal rotation (empty can position), producing constant target torques of 4 and 12 N.m, respectively. In addition, the subjects performed each exercise in the supine position with the limb supported by straps. Electromyogram (EMG) was recorded with intramuscular electrodes at the supraspinatus and infraspinatus, and with surface electrodes placed at the middle deltoid and upper trapezius. The EMG activity (RMS) of each muscle was normalized according to the highest EMG activity (100% MVC) during a maximum manual muscle test for the corresponding muscle (% MVC). RESULTS EMG activity of the supraspinatus was significantly greater than those of the other shoulder muscles in the full can position from 10-20 degrees to 50-60 degrees arcs with a target torque of 4 N.m (P < 0.05). In contrast, the supraspinatus and middle deltoid showed similar EMG activities under other exercise conditions. CONCLUSIONS These results suggest that there is an exercise condition that induces greater activity of the supraspinatus in scapular plane abduction.

Acute Effect of High-Intensity Eccentric Exercise on Vascular Endothelial Function in Young Men.

Abstract Choi, Y, Akazawa, N, Zempo-Miyaki, A, Ra, S-G, Shiraki, H, Ajisaka, R, and Maeda, S. Acute effect of high-intensity eccentric exercise on vascular endothelial function in young men. J Strength Cond Res 30(8): 2279–2285, 2016—Increased central arterial stiffness is as an independent risk factor for cardiovascular disease. Evidence regarding the effects of high-intensity resistance exercise on vascular endothelial function and central arterial stiffness is conflicting. The purpose of this study was to examine the effects of acute high-intensity eccentric exercise on vascular endothelial function and central arterial stiffness. We evaluated the acute changes in endothelium-dependent flow-mediated dilation (FMD), low-flow–mediated constriction (L-FMC), and arterial stiffness after high-intensity eccentric exercise. Seven healthy, sedentary men (age, 24 ± 1 year) performed maximal eccentric elbow flexor exercise using their nondominant arm. Before and 45 minutes after eccentric exercise, carotid arterial compliance and brachial artery FMD and L-FMC in the nonexercised arm were measured. Carotid arterial compliance was significantly decreased, and &bgr;-stiffness index significantly increased after eccentric exercise. Brachial FMD was significantly reduced after eccentric exercise, whereas there was no significant difference in brachial L-FMC before and after eccentric exercise. A positive correlation was detected between change in arterial compliance and change in FMD (r = 0.779; p ⩽ 0.05), and a negative correlation was detected between change in &bgr;-stiffness index and change in FMD (r = −0.891; p < 0.01) with eccentric exercise. In this study, acute high-intensity eccentric exercise increased central arterial stiffness; this increase was accompanied by a decrease in endothelial function caused by reduced endothelium-dependent vasodilation but not by a change in endothelium-dependent vasoconstriction.

Immediate Effects of Different Trunk Exercise Programs on Jump Performance

The aim of this study was to investigate the immediate effects of trunk stabilization exercise (SE) and conventional trunk exercise (CE) programs on jump performance. 13 adolescent male soccer players performed 2 kinds of jump testing before and immediate after 3 experimental conditions: SE, CE, and non-exercise (NE). The SE program consisted of the elbow-toe, hand-knee, and back bridge, and the CE program consisted of the sit-up, sit-up with trunk rotation and back extension. Testing of a countermovement jump (CMJ) and rebound jump (RJ) were performed to assess jump performance. Jump height of the CMJ and RJ-index, contact time, and jump height of the RJ were analyzed. The RJ index was improved significantly only after SE (p=0.017). However, contact time and jump height did not improve significantly in the SE condition. Moreover, no significant interaction or main effects of time or group were observed in the CMJ. Consequently, this study showed the different immediate effect on the RJ between the SE and CE, and suggested the possibility that the SE used in this study is useful as a warm-up program to improve the explosive movements.

Relationships between clubshaft motions and clubface orientation during the golf swing

Abstract Since clubface orientation at impact affects ball direction and ball spin, the ability to control clubface orientation is one of the most important skills for golfers. This study presents a new method to describe clubface orientation as a function of the clubshaft motions (i.e., swing plane orientation, clubshaft angle in the swing plane, and clubshaft rolling angle) during a golf swing and investigates the relationships between the clubshaft motions and clubface orientation at impact. The club motion data of driver shots were collected from eight skilled golfers using a three-dimensional motion capture system. The degrees of influence of the clubshaft motions on the clubface orientation were investigated using sensitivity analysis. The sensitivity analysis revealed that the swing plane horizontal angle affected the clubface horizontal angle to an extent of 100%, that the clubshaft angle in the swing plane affected both the clubface vertical and horizontal angles to extents of 74 and 68%, respectively, and that the clubshaft rolling angle affected both the clubface vertical and horizontal angles to extents of -67 and 75%, respectively. Since the method presented here relates clubface orientation to clubshaft motions, it is useful for understanding the clubface control of a golfer.

Perception and Preference for Location in Golf Practice

Many studies of the psychological effects of physical location in small discussion groups and classrooms have indicated that seating positions in groups or classrooms are related to participation, personality, or perception. In this preliminary study, environmental perception of several positions occupied by Japanese participants and preference for location in a golf-practice situation were investigated. Analyses indicated that different positions in a group were differently perceived and that certain positions were preferred over others and the main reason for the preference was related to visibility. Such information could be useful for instructors in making a psychologically comfortable environment during golf practice.

A revised equation for estimating thigh muscle and bone area from anthropometric dimensions

The accuracy of an anthropometric equation for estimating thigh muscle and bone area (MBA) and fat area (FA) was examined in two groups of Japanese male university students, an athletic group (n = 31) and a non‐athletic group (n = 18). The anthropometric equation examined included the anterior thigh skinfold (SFT) and thigh circumference (CF): (CF – π × SFT)2/4π. Actual MBA and FA were calculated by means of a computed tomography (CT) scan. The anthropometric equation overestimated MBA and underestimated FA, although the estimated values were strongly correlated with actual values. In addition, total thigh area was also overestimated by using thigh circumference. As MBA increased, the difference between estimated and actual MBA increased. Regression analysis using estimated MBA through an anthropometric equation was also done. The resulting equation was as follows: MBA = c1 × (CF – π × SFT)2/4π + c2, where the value of (CF – π × SFT)2/4π was the estimated MBA through the first anthropometric equation. The mean ratio of the residual to actual MBA was very small, 2.8% in the athletic group and 3.3% in the non‐athletic group. When a non‐linear model (MBA = (k1 × CF – k2 × π × SFT)2/4π + k3) was applied, the ratio was almost the same, 2.7 and 3.2% in the athletic and non‐athletic groups, respectively. The equation for all subjects in this study was as follows: thigh MBA = 0.706 × (CF – π × SFT)2/4π + 27.94.

MRI reveals menstrually-related muscle edema that negatively affects athletic agility in young women

Context About 10% of Japanese female athletes are afflicted by menstrually-related edema, mainly in the lower limbs, and, with few studies on this problem, the effect on performance remains unclear. Objective To quantitatively evaluate fluid retention in the calf in female students over their menstrual cycle using magnetic resonance imaging (MRI) and to determine the relationship of MRI changes and athletic performance. Design The menstrual cycle was divided into 5 phases: menstrual, follicular, ovulatory, early luteal, and late luteal with sampling done in either morning (AM) or afternoon (PM) sessions. At each phase, MRI of the calf (7:00–8:00, 14:00–16:00), body composition and hormones (7:00–8:00), and athletic performance (14:00–16:00) were evaluated. Participants 13 adult healthy Japanese female students with eumenorrhea. Results Estradiol levels decreased significantly in the menstrual phase and the follicular phase compared to the early luteal phase (P = 0.001, P = 0.024 respectively). Menstrual phase estradiol levels were significantly lower compared to the ovulatory phase (P = 0.015), and the late luteal phase (P = 0.003). Progesterone levels decreased significantly in the menstrual phase and the follicular phase compared to the ovulatory phase (P = 0.012, P = 0.009 respectively), the early luteal phase (both P = 0.007), and the late luteal phase (P = 0.028, P = 0.029 respectively), and it along with a significant decrease in the ovulatory phase compared to the early luteal phase (P = 0.010). AM T2 signals were significantly lower in the menstrual phase compared to the ovulatory phase (P = 0.043) but not other phases. PM T2 signals increased significantly in the menstrual phase compared to the follicular phase (P = 0.003), ovulatory phase (P = 0.009), and the late luteal phase (P = 0.032), and the difference between the AM and PM values increased significantly in the menstrual phase compared to the other 4 phases (P<0.01). A negative correlation between fluid retention and agility was observed. Conclusion In female students fluid retention during the menstrual phase could be a factor that influences athletic agility.

High circulating levels of oxidized LDL in strength-trained athletes

Oxidized low-density lipoprotein (oxLDL) has been shown to play a major role in the progression of atherosclerosis and cardiovascular disease. Aerobic exercise training has been reported to decrease plasma oxLDL levels. However, until now, there have been no studies regarding the effect of strength exercise training on plasma oxLDL levels. The purpose of this study was to investigate the plasma oxLDL. concentration and antioxidant capacity of plasma in strength-trained athletes. We specifically assessed the total scavenging activity against plasma hydroxyl radical (HO,) and alkoxyl radical (RO,) by using the electron spin resonance (ESR) technique, as both radicals are involved in oxLDL production. The subjects included young strength-trained athletes (SA group; shot put, hammer, javelin throwers, or power lifters; n=9) and sedentary individuals (control group; n=9). We measured plasma oxLDL concentrations and total scavenging activity against HO, and RO. Maximal muscle strength, as assessed by isokinetic tests of the knee and elbow joints and maximal handgrip strength, was significantly greater in the SA group than in the control group. Plasma oxl.DL concentrations were found to be significantly higher in the SA group than in the control group. The total scavenging activity of plasma against HO, and RO. did not differ between the two groups. These results suggest that high-intensity strength training increases plasma oxLDL concentration without upregulating the total scavenging activity against plasma HO, and RO.