Relationship of Clubhead Speed With Explosive Power and Muscle Strength of the Hip and Trunk Joints of Elite Golfers.

ABSTRACT: Suhara, H, Nariai, M, Takagi, T, Akiyama, K, Nagashima, J, and Shiraki, H. Relationship of clubhead speed with explosive power and muscle strength of the hip and trunk joints of elite golfers. J Strength Cond Res 37(4): 859-865, 2023-In golf, the driving distance of the ball is affected by the clubhead speed (CHS) on impact. We aimed to clarify the relationship between CHS and explosive power and muscle strength of the hip and trunk muscles in elite golfers (male age: 19.6 ± 1.9 years, male handicap: 4.4 ± 0.9, female age: 17.7 ± 1.4 years, and female handicap: 6.2 ± 0.7). A correlational design was used to assess the relationships between CHS and strength (hip extension-flexion and trunk rotation of peak torque at an isokinetic 60 and 180°·s -1 angular velocity) and CHS and power (countermovement jump [CMJ]; peak power and jump height; backward overhead medicine ball [BOMB] throw). Fourteen each of male and female elite golfers were included. The CHS during the golf swing was measured using a Doppler radar measurement device (Trackman). A correlation analysis between each measurement and CHS ( p ≤ 0.05) was conducted. We found that the peak torque of right hip extension at an angular velocity of 180°/s (male, r = 0.67; female, r = 0.61), peak CMJ power (male: r = 0.63, female: r = 0.75), and BOMB throw distance (male, r = 0.6; female, 0.6) were positively correlated with CHS in both male and female golfers. These results suggest that the extensor strength of the lower extremities and trunk, centered on the hip joint in the sagittal plane, is important for physical fitness and muscle strength measurement related to CHS. Conversely, concentric trunk rotator strength and CHS were not correlated, suggesting that concentric trunk rotator strength may not be actively involved in CHS.

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

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 ß-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 ß-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.

Factors Associated with the Prevalence and Severity of Menstrual-Related Symptoms: A Systematic Review and Meta-Analysis.

This study aimed to identify factors associated with the prevalence and severity of menstrual-related symptoms. The protocol was registered in PROSPERO (CRD42021208432). We conducted literature searches of PubMed and Ichushi-Web and used the Jonna Briggs Institute critical appraisal checklist to assess the quality. Of the 77 studies included in the meta-analysis, significant odds ratios (ORs) were obtained for eight factors associated with primary dysmenorrhea (PD): age ≥ 20 years (OR: 1.18; 95% confidence interval [CI]: 1.04−1.34), body mass index (BMI) < 18.5 kg/m2 (OR: 1.51; 95% CI: 1.01−2.26), longer menstrual periods (OR: 0.16; 95% CI: 0.04−0.28), irregular menstrual cycle (OR: 1.28; 95% CI: 1.13−1.45), family history of PD (OR: 3.80; 95% CI: 2.18−6.61), stress (OR: 1.88; 95% CI: 1.30−2.72), sleeping hours < 7 h (OR: 1.19; 95% CI: 1.04−1.35), and bedtime after 23:01 (OR: 1.30; 95% CI: 1.16−1.45). Two factors were associated with severity of PD (moderate vs. severe): BMI < 18.5 kg/m2 (OR: 1.89; 95% CI: 1.01−3.54) and smoking (OR: 1.94; 95% CI: 1.08−3.47). PD severity (mild vs. severe) and prevalence of premenstrual syndrome were associated with BMI < 18.5 kg/m2 (OR: 1.91; 95% CI: 1.04−3.50) and smoking (OR: 1.86; 95% CI: 1.31−2.66), respectively. The identified risk factors could be utilized to construct an appropriate strategy to improve menstrual symptoms and support women's health.

Dynamics of pelvis rotation about its longitudinal axis during the golf swing.

The purpose of this study was to identify the dynamic factors contributing to pelvis angular velocity about its longitudinal axis (pelvis axial angular velocity) during the golf swing. Thirty-one right-handed skilled golfers (handicap, 3.5 ± 1.8) performed swings with a driver. The kinematic and kinetic data were collected using an optical motion analysis system and two force platforms. The dynamic factors (i.e., joint torque, gravitational force, motion-dependent forces and inertia forces) contributing to pelvis axial angular acceleration were calculated. The present study revealed that the left (lead) hip flexor and adductor torques as well as the right (trail) hip extensor and abductor torques were identified as the main contributors to pelvis axial angular velocity. These hip joint torques contributed not synchronously but sequentially to the pelvis. Although the knee joint torques contributed little to pelvis axial angular velocity directly, the knee joint torques might support the generation of large hip joint torques by regulating joint postures. These findings indicate that the functional coordination of the lower limb segments as well as the magnitude of the joint torques play an important role in rotating the pelvis.

Effect of temporary school closure due to COVID-19 on musculoskeletal function in elementary school children.

Objective: In 2020, coronavirus disease-2019 (COVID-19) became the cause of a pandemic. In response, the Japan Sports Agency issued warnings about secondary damage to health, such as the threat to physical and mental well-being due to the lack of exercise in this situation. In this study, we report on cross-sectional and longitudinal examinations of standing trunk flexion to evaluate how temporary long-term school closures affected musculoskeletal function in elementary school students. Patients and Methods: All children in one public elementary school in T-city during the school years 2019 and 2020 were included in this study. A digital forward flexion meter was used to measure standing trunk flexion. Results: In this study, 284 (284/289: 98.3%) and 266 (266/274: 97.1%) children in school years 2020 and 2019, respectively, were found to have valid data for cross-sectional analysis. The standing trunk flexion did not show significant differences between grades or sexes. In the longitudinal analysis, the results of the comparison of standing trunk flexion in children for two consecutive years revealed significant differences only between grades 3 and 4 (P<0.05) and between girls in grades 3 and 4 (P<0.01), but no significant differences in other grades or among boys or girls were observed. Conclusion: Initially, we expected that there would be a difference in the results of functional assessment using standing trunk flexion depending on the period of absence from school. However, the results of this study showed no significant changes in standing trunk flexion. Moreover, since children's musculoskeletal functions may be affected by various factors during the COVID-19 pandemic, they should be carefully monitored in the future.

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.

Risk of female athlete triad development in Japanese collegiate athletes is related to sport type and competitive level.

INTRODUCTION: Menstrual dysfunction, musculoskeletal injury, and poor nutrition combine to form the female athlete triad (FAT), which results in serious health consequences for affected athletes. To this point, the risk factors of this phenomenon have not been fully explored in Japanese female college athletes. Additionally, the effect of competitive level on FAT risk factors has also not been reported. Therefore, we aimed to examine FAT risk factors in Japanese female athletes of various sports as well as examine the impact of competitive level on FAT. METHODS: A Japanese-language survey was completed by 531 athletes and 20 nonathletes at two Japanese universities and answers with regard to menstrual status, musculoskeletal injury, nutrition, and other variables were analyzed based on classification of the sports into nine distinct groups based on activity type. Sport intensity, training volume, and competitive levels were used to further classify each sport. One-way ANOVA and the Bonferroni post hoc test using SPSS were carried out to analyze significance for relationships between sport intensity and FAT risk factors. Additionally, the relationship between competitive level and FAT risk factors was analyzed by ANOVA and Bonferroni post hoc tests. RESULTS: Sport intensity was positively correlated with a delay in menarche as well as dysmenorrhea and poor nutrition while musculoskeletal injury was correlated with repetitive, high-training volume sports. Lower competitive levels increased dysmenorrhea but did not impact injury status or nutrition. CONCLUSION: Sport intensity and training volume, but not competitive level, are the critical factors affecting FAT risk in Japanese female college athletes.

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.

Relationships between clubshaft motions and clubface orientation during the golf swing.

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.

A Biomechanical Comparison Among Three Kinds of Rebound-Type Jumps in Female Collegiate Athletes.

BACKGROUND: Single-legged drop jumps (SDJ), single-legged repetitive jumps (SRJ), and single-legged side hops (SSH) are often used as plyometric training and functional performance tests. Differences in the kinetics and kinematic characteristics of lower extremity joints during these jumps are unclear. HYPOTHESIS/PURPOSE: The purpose of this study was to investigate the joint motion and mechanical work of the takeoff leg from foot contact to foot-off during SDJ, SRJ, and SSH in the sagittal and frontal planes in female athletes. It was hypothesized that the joint motion and mechanical work of the lower extremity joints during the SDJ and SRJ would be larger than the SSH in the sagittal plane, those during the SSH would be larger than the SDJ and SRJ in the frontal plane, and during SRJ would be larger than SDJ. STUDY DESIGN: Cross-sectional study. METHODS: Seventeen female collegiate athletes participated and performed the SDJ (0.15-m box height), and SRJ and SSH (by crossing two lines 0.3 m apart). Three-dimensional coordinate data and ground reaction forces were collected. Contact time, jump height, jump index (i.e., the jump height divided by the contact time) of the SDJ and SRJ, and the total times of the SSH were calculated. Range of motion (ROM) from touchdown to the lowest center of mass, and the positive and negative (mechanical) work from touchdown to foot-off were analyzed. RESULTS: There were no significant differences in jump performance variables. Compared to the SSH, the SDJ and SRJ had significantly larger ankle and knee ROM and positive and negative work at the lower extremity joints, except for positive work at the hip joint, in the sagittal plane (p < 0.05). Compared to the SDJ and SRJ, the SSH had a significantly larger ankle ROM and positive work at the knee joint in the frontal plane (p < 0.05). Compared to the SDJ, the SRJ had a significantly larger ROM and negative work at each lower extremity joint in the frontal plane (p < 0.05). CONCLUSION: Although there were no significant differences in the jump performance variables, different characteristics of the takeoff leg ROM and mechanical work were found between three kinds of rebound-type jump tests. These findings may help clinicians choose jump methods to assess lower extremity function and to design plyometric training programs in sports and clinical fields. LEVEL OF EVIDENCE: 3b.

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. © 1992 Wiley-Liss, Inc.

Effects of two types of trunk exercises on balance and athletic performance in youth soccer players.

PURPOSE/BACKGROUND: Many athletes perform trunk stabilization exercises (SE) and conventional trunk exercises (CE) to enhance trunk stability and strength. However, evidence regarding the specific training effects of SE and CE is lacking and there have been no studies for youth athletes. Therefore, the purpose of this study was to investigate the training effects of SE and CE on balance and athletic performance in youth soccer players. METHODS: Twenty-seven male youth soccer players were assigned randomly to either an SE group (n = 13) or CE group (n = 14). Data from nineteen players who completed all training sessions were used for statistical analyses (SE, n = 10; CE, n = 9). Before and after the 12-week intervention program, pre- and post-testing comprised of a static balance test, Star Excursion Balance Test (SEBT), Cooper's test, sprint, the Step 50, vertical jump, and rebound jump were performed. After pre-testing, players performed the SE or CE program three times per week for 12 weeks. A two-way repeated-measures ANOVA was used to assess the changes over time, and differences between the groups. Within-group changes from pre-testing to post-testing were determined using paired t-tests. Statistical significance was inferred from p < 0.05. RESULTS: There were significant group-by-time interactions for posterolateral (p = 0.022) and posteromedial (p < 0.001) directions of the SEBT. Paired t-tests revealed significant improvements of the posterolateral and posteromedial directions in the SE group. Although other measurements did not find group-by-time interactions, within-group changes were detected indicating significant improvements in the static balance test, Cooper's test, and rebound jump in the only SE group (p < 0.05). Vertical jump and sprint were improved significantly in both groups (p < 0.05), but the Step 50 was not improved in either group (p > 0.05). CONCLUSIONS: Results suggested that the SE has specific training effects that enhance static and dynamic balance, Cooper's test, and rebound jump. LEVEL OF EVIDENCE: 3b.

Comparison of the immediate effect of different types of trunk exercise on the star excursion balance test in male adolescent soccer players.

PURPOSE/BACKGROUND: Trunk exercises, such as trunk stabilization exercises (SE) and conventional trunk exercises (CE), are performed to improve static or dynamic balance. Recently, trunk exercises have also been often used as part of warm-up programs. A few studies have demonstrated the immediate effects of SE and CE on static balance. However, immediate effects on dynamic balance are not yet known. Therefore, the purpose of this study was to compare the immediate effect of SE with that of CE on the Star Excursion Balance Test (SEBT). METHODS: Eleven adolescent male soccer players (17.9 ± 0.3 years, 168.5 ± 5.4 cm, and 60.1 ± 5.1 kg) participated in this study. A crossover design was used, and each participant completed three kinds of testing sessions: SE, CE, and non-exercise (NE). Experiments took place for three weeks with three testing sessions, and a 1-week interval was provided between different conditions. Each testing session consisted of three steps: pretest, intervention, and posttest. To assess dynamic balance, the SEBT score in the anterior, posteromedial, and posterolateral directions was measured before and 5 minutes after each intervention program. The data of reach distance were normalized with the leg length to exclude the influence of the leg length on the analysis. RESULTS: The SEBT composite score was significantly improved after the SE (p < 0.05) but did not change after the CE and NE (p > 0.05). Furthermore, in the SE condition, SEBT scores of the posterolateral and posteromedial directions were significantly improved at the posttest, compared with those at the pretest (p < 0.05). CONCLUSIONS: This study demonstrated the immediate improvements in the posteromedial and posterolateral directions of the SEBT only after the SE. This result suggests that the SE used in this study is effective in immediately improving dynamic balance. LEVELS OF EVIDENCE: 3b.