Acute changes in passive stiffness of the individual hamstring muscles induced by resistance exercise: effects of muscle length and exercise duration.

PURPOSE: A previous study revealed that resistance exercise with eccentric contraction and a wide range of motion (ROM) can acutely decrease muscle stiffness of a specific muscle. To explore further approaches to decrease the stiffness, we examined the acute changes in passive stiffness of the individual hamstring muscles after eccentric-only resistance exercise with different combinations of muscle lengths and exercise durations. METHODS: Thirteen healthy young male participants performed three sessions of eccentric-only exercises that comprised stiff-leg deadlift with different muscle lengths and exercise durations (duration per repetition × the total number of repetitions) on separate days as follows: (1) short muscle lengths with a short duration (SS); (2) long muscle lengths with a short duration (LS); and (3) long muscle lengths with a long duration (LL). Maximal joint ROM, passive torque, shear modulus of each hamstring muscle, and maximal isometric torque of knee flexion were measured before, and at 3, 30, and 60 min after each session. RESULTS: The shear modulus of the semimembranosus was significantly lower at 3 min post-exercise (129.8 ± 22.7 kPa) than at pre-exercise (140.5 ± 19.1 kPa, p < 0.01) in LL, but not in SS or LS. No significant differences were observed in the shear moduli of the biceps femoris long head or semitendinosus between pre-exercise and 3 min post-exercise in any session. CONCLUSION: The combination of long muscle lengths and a long duration during eccentric-only resistance exercise is important to immediately decrease the stiffness (shear modulus) of a specific muscle.

Synergistic Dominance Induced by Hip Extension Exercise Alters Biomechanics and Muscular Activity During Sprinting and Suggests a Potential Link to Hamstring Strain.

ABSTRACT: Iguchi, J, Hojo, T, Fujisawa, Y, Kuzuhara, K, Yanase, K, Hirono, T, Koyama, Y, Tateuchi, H, and Ichihashi, N. Synergistic dominance induced by hip extension exercise alters biomechanics and muscular activity during sprinting and suggests a potential link to hamstring strain. J Strength Cond Res 37(9): 1770-1776, 2023-Hamstring strain is likely to occur during the late swing phase or the first half of the stance phase in sprinting. During the late swing phase, the hamstrings and gluteus maximus (Gmax) contract eccentrically to decelerate the lower limb. We hypothesized that, when the Gmax becomes dysfunctional because of delayed onset muscle soreness (DOMS), the hamstring workload is increased (i.e., there is synergetic dominance), which could lead to an increased risk of strain. A total of healthy 15 male undergraduate or graduate students (age 23.1 ± 1.28 years) were recruited to perform exercises and maximal sprints. On day 1, before subjects performing DOMS-causing exercises, and on day 3, while subjects were experiencing DOMS in the Gmax, lower-limb biomechanical and muscle activity data were recorded using a motion analysis system and electromyography (EMG), respectively. Data were analyzed and compared between day 1 and day 3. Hip flexion angle on day 3 was significantly lower than that on day 1, but the opposite was true for the knee flexion angle (P < 0.05). Vastus medialis (VM), biceps femoris (BF), and Gmax muscle activities on day 3 were significantly higher than those on day 1 (P < 0.05). Peak propulsive forces on day 3 were significantly higher than those on day 1 (P < 0.05). Kinematic changes such as decreased hip flexion angle and EMG changes such as increased BF EMG activity on day 3 to compensate for the loss of function of the Gmax may potentially increase the risk of hamstring strain.

The field study about the effects of artificial CO2-rich cool-water immersion after outdoor sports activity in a hot environment.

Background/objective: In our previous laboratory experiment (room temperature of 25 °C), CO2-rich cool-water immersion (CCWI) suppressed subjects' core body temperature even during repeated exercise. It is unclear whether the suppression of body temperature elevation would also continue after CCWI in a hot outdoor environment. Herein we investigated the thermal effects of CCWI after regular exercise training in heat on subjects' core temperature (Tcore), three skin temperatures (Tskin), heart rate (HR), and the rate of perceived ice (RPI). Methods: Thirty-six subjects (25 males, 11 females) were randomly allocated into three groups (CCWI, CWI, and control). After training at their competitive clubs, each subject was immersed up to the chest in CCWI or CWI at 20 °C for 20 min, followed by a 60-min recovery period. Tcore, Tskin, HR, and RPI were measured at the initial rest, the end of immersion, and every 10 min during the recovery period. Results: Compared to the control, the CCWI subjects' Tcore was significantly lower at 50-60 min after the end of immersion (p < 0.05). Tskin at abdominal and lower-leg regions during the recovery period was maintained at significantly lower values in the CWI and CCWI groups versus control (p < 0.05). The CCWI subjects maintained lower Tskin for a longer time than the CWI subjects. Conclusions: These findings indicate that CCWI suppresses the rise in body temperatures more than CWI, even in a hot environment, suggesting that CCWI may be a more effective countermeasure against increasing body temperature in a hot outdoor environment.

Acute changes in passive stiffness of the individual hamstring muscles induced by resistance exercise: effects of contraction mode and range of motion.

PURPOSE: Recent studies raise an interesting possibility that resistance exercise also decreases passive muscle stiffness, as does stretching exercise. However, little is known about how program variables of resistance exercise acutely influence muscle stiffness. We aimed to examine the acute changes in passive stiffness of the individual hamstring muscles after resistance exercises using different combinations of contraction modes and ranges of motion (ROMs). METHODS: Thirteen healthy young male participants performed three sessions of resistance exercises that comprised stiff-leg deadlift with different contraction modes and exercise ROMs on separate days as follows: (1) eccentric contractions with a wide exercise ROM (EW); (2) eccentric contractions with a narrow exercise ROM (EN); and (3) concentric contractions with a wide exercise ROM (CW). Maximal joint ROM, passive torque, shear modulus of the individual hamstring muscles, and maximal isometric torque of knee flexion were measured before and 3 min, 30 min, and 60 min after completing each session. RESULTS: The shear modulus of the semimembranosus was significantly lower at 3 min post-exercise (121.8 ± 16.0 kPa) than at pre-exercise (129.0 ± 18.9 kPa, p = 0.021, r = 0.45) in EW, but not in EN or CW. There were no significant changes in the shear moduli of the biceps femoris long head or the semitendinosus at any timepoint in any exercise protocols. CONCLUSIONS: The present results suggest that the combination of eccentric contraction and wide ROM during resistance exercise has the potential to acutely decrease passive stiffness (shear modulus) of a specific muscle.

Anaerobic performance after 3-day consecutive CO2-rich cold-water immersion in physically active males.

Background Objective: We investigated the effects of a 3-day consecutive CO2-rich cold (20 °C) water immersion (CCWI) following a high-intensity intermittent test (HIIT) on subjects' sublingual temperature (Tsub), blood lactate ([La]b), and heart rate (HR) compared to cold (20 °C) tap-water immersion (CWI) or passive recovery (PAS). Methods: Thirty-two subjects were randomly allocated into three groups (CCWI, CWI, and PAS), each of which completed 4 consecutive days of cycling experiments. HR, Tsub, and [La]b were recorded on each day of exercise testing (immersion from Day 1 to Day 3 and Day 4). HIIT consisted of 8 sets of 20-sec maximum exercise at an intensity of 120% of VO2max with 10-sec passive rest. The mean and peak power, and peak pedal repetitions (PPR) within HIIT were averaged and the decline in PPR (ΔPPR) from Day 1 to Day 4 was measured. Results: In CCWI and CWI, HR declined significantly following each immersion, with CCWI showing the larger reduction (p < 0.001). At Day 2, CCWI showed a significantly lower [La]b compared to PAS (p < 0.01). The changes in mean and peak power from Day 1 to Day 4 did not differ among the groups (p = 0.302). ΔPPR of HIIT was significantly correlated with the HR and [La]b values after immersions (ΔPPR-HR: r2 = 0.938, p < 0.001, ΔPPR-[La]b: r2 = 0.999, p < 0.001). Conclusions: These findings indicate that CCWI is a promising intervention for maintaining peak performance in high-intensity intermittent exercise, which is associated with a reduction in [La]b and HR.

Effects of artificial CO2-rich cold-water immersion on repeated-cycling work efficiency.

We investigated the acute effects of cold-water immersion (20°C) with higher CO2 concentration (CCWI) following a high-intensity Wingate anaerobic exercise test (WAnT) on subjects' sublingual temperature (Tsub), blood lactate ([La]b), heart rate (HR), and aerobic cycling work efficiency (WE) compared to cold tap-water immersion (20°C; CWI) and passive recovery (PAS). Fifteen subjects completed three testing sessions at 1-week intervals. Each trial consisted of a first WE and WAnT, and a 20-min recovery intervention (randomized: CCWI, CWI, and PAS) before repeating a second WE and WAnT. The WE was measured by the metabolic demand during 50% V.O2max exercise. HR, Tsub, and [La]b were recorded throughout the testing sessions. There was a significant decline in the WE from 1st bout to 2nd bout at each recovery intervention. The WAnT was also significantly reduced at 2nd bout. Significantly reduced [La]b was achieved at CCWI compared to PAS, but not to the CWI. Likewise, the reduction in HR following immersion was the largest at CCWI compared to the other conditions. These findings indicate that CCWI is an effective intervention for maintaining repeated cycling work efficiency, which might be associated with reduced [La]b and HR.

Side-To-Side Difference in Electromyographic Activity of Abdominal Muscles during Asymmetric Exercises.

A side-to-side difference in the muscle size of the rectus abdominis has been suggested to increase the strain injury risk. Attenuating the difference in size of the rectus abdominis may decrease the injury risk. To explore ways to highly activate one side of the rectus abdominis, we aimed to clarify the activity levels of both sides of the muscle during asymmetric abdominal exercises. Fifteen male sprinters performed the following five asymmetric exercises for the right and left sides: (i) sit-up twist, (ii) oblique leg raise, (iii) side bridge, (iv) side bridge roll out with the elbow, and (v) side bridge roll out with the foot. Side bridge roll out with the elbow and that with the foot were performed using a wheeled platform. During the exercises, electromyographic signals were recorded bilaterally from the upper, central, and lower portions of the rectus abdominis. We calculated the root mean square of electromyograms during the concentric and eccentric phases of the exercises and normalized to that during maximal voluntary contractions. In all portions of the rectus abdominis, the root mean squares of electromyograms were significantly higher in the moving side than in the non-moving side during the concentric and eccentric phases of the side bridge, the side bridge roll out with the elbow and that with the foot (all p < 0.01), but not in sit-up twist or oblique leg raise. The root mean squares of electromyograms of all portions of the rectus abdominis in the moving side were significantly higher in the side bridge roll out with the elbow and that with the foot than in the side bridge during both phases (all p < 0.01). The results suggest that the application of the wheeled platform to side bridge is useful to highly activate one side of the rectus abdominis.

Seasonal Changes in Anthropometric, Physiological, Nutritional, and Performance Factors in Collegiate Rowers.

Iguchi J, Kuzuhara, K, Katai, K, Hojo, T, Fujisawa, Y, Kimura, M, Yanagida, Y, and Yamada, Y. Seasonal changes in anthropometric, physiological, nutritional, and performance factors in collegiate rowers. J Strength Cond Res 34(11): 3225-3231, 2020-Well-controlled seasonal distribution of training intensity seems to be an important variable for endurance athletes' success as competitors and for avoidance of overtraining. The aim of this study was to examine the interrelationships of training distribution, body composition, energy intake/expenditure, and rowing ergometer performance throughout the 2012-2013 season. In this study of 15 collegiate male rowers, most of whom started rowing during their time at the university, we divided the 2012-2013 season (total 37 weeks) into 3 phases (off-season, December to mid-March, 16 weeks; pre-season, late March-April, 5 weeks; and in-season, May-August, 16 weeks) and analyzed the transition of 2,000-m rowing ergometer time, training intensity/volume, body composition (body mass and body fat), and energy intake/expenditure in each phase. There were significant main effects of the training time by the intensities; 2,000-m rowing ergometer time; energy expenditure; and protein, fat, and carbohydrate intake across the seasons (p < 0.05). Two findings were particularly important. First, on-water high-intensity training, especially for inexperienced rowers, may contribute to improvement of 2,000-m rowing ergometer performance. Second, higher intake of carbohydrate, and to a lesser degree, protein, is necessary for optimal training adaptation (e.g., increase of muscle glycogen content), and results in better 2,000-m performance on the rowing ergometer. Also, those findings may be beneficial to the coaches who are interested in designing the well-controlled seasonal training program, which is especially intended to improve the 2,000-m rowing ergometer performance as well as avoidance of overtraining.

Prevalence of posterior elbow problems in Japanese high school baseball players.

BACKGROUND: Various posterior elbow problems cause posterior elbow pain among baseball players. We aimed to determine the prevalence and diagnoses associated with posterior elbow problems and post-treatment recovery time for returning to sports in Japanese high school baseball players when treated in the off-season. METHODS: A total of 576 Japanese high school baseball players who participated in baseball skill training camp during the off-season were enrolled in the study. The elbow of each player's throwing arm was assessed by use of a questionnaire and physical examination. Players with abnormal results were advised to visit the hospital. Players who visited the hospital were initially treated conservatively and underwent surgery if necessary. Retrospectively, players with positive physical examination results associated with posterior elbow pain, defined as olecranon tenderness and/or a positive elbow extension impingement test, were selected. Information about their position, elbow pain, physical examination results, diagnosis, treatment, and recovery time before returning to playing sports was assessed. RESULTS: Olecranon tenderness and/or positive elbow extension impingement test results were found in 76 players (13.2%). Of these, 33 agreed to visit the hospital for further diagnostic imaging and 25 players (75.8%) were diagnosed with posteromedial elbow impingement. By the next spring, 87.9% of players returned to sport, and 100% of players returned to sport before the next summer. The average recovery period was 77 ± 47 days. CONCLUSION: Physical examinations related to posterior elbow injuries were positive in 13.2% of high school baseball players. The most common diagnosis for posterior elbow pain was posteromedial elbow impingement. All players returned to competitive sports activity levels within 77 ± 47 days.

Risk Factors for Injury Among Japanese Collegiate Players of American Football Based on Performance Test Results.

Iguchi, J, Watanabe, Y, Kimura, M, Fujisawa, Y, Hojo, T, Yuasa, Y, Higashi, S, and Kuzuhara, K. Risk factors for injury among Japanese collegiate players of American football based on performance test results. J Strength Cond Res 30(12): 3405-3411, 2016-The purpose of this study was to identify how risk factors for injury during American football are related to players' physical strength as determined using typical performance tests. One hundred 53 Japanese collegiate players of American football were recruited for this study. Eight potential risk factors were evaluated: position (skill vs. lineman), body mass index, back squat one-repetition maximum, vertical jump height, power, height, body weight, and previous injury. Using multivariate Cox regression, we examined how these factors were associated with knee sprain, ankle sprain, and hamstring strain. We recorded 63 injuries (17 knee sprains, 23 ankle sprains, and 23 hamstring strains). Players with higher power were at significantly greater risk for knee sprains (p = 0.04), those with low power had a significantly higher incidence of ankle sprain (p = 0.01), and vertical jump height was a significant predictor of hamstring strain (p = 0.02). We identified several independent predictors of injuries associated with American football. Our findings may contribute to the development of effective screening tests and prevention exercises.

Muscle morphological changes and enhanced sprint running performance: A 1-year observational study of well-trained sprinters.

Numerous cross-sectional studies have attempted to identify the muscle morphology required to achieve high sprint velocity. Our longitudinal study addressed an unanswered question of cross-sectional studies: whether hypertrophy of the individual trunk and thigh muscles induced by daily training (e.g., sprint, jump, and resistance training) is linked to an improvement in sprint performance within well-trained sprinters. Twenty-three collegiate male sprinters (100-m best time of 11.36 ± 0.44 s) completed their daily training for 1 year without our intervention. Before and after the observation period, the sprint velocities at 0-100 m, 0-10 m, and 50-60 m intervals were measured using timing gates. The volumes of 14 trunk and thigh muscles were measured using magnetic resonance imaging. Muscle volumes were normalized to the participants' body mass at each time point. Sprint velocities increased at the 0-100 m (p < 0.001), 0-10 m (p = 0.019), and 50-60 m (p = 0.018) intervals after the observation period. The relative volumes of the tensor fasciae latae, sartorius, biceps femoris long head, biceps femoris short head, semitendinosus, and iliacus were increased (all p < 0.050). Among the hypertrophied muscles, only the change in the relative volume of the semitendinosus was positively correlated with the change in sprint velocity at the 50-60 m interval (p = 0.018 and ρ = 0.591). These findings suggest that semitendinosus hypertrophy seems to be associated with sprint performance improvement within well-trained sprinters during the maximal velocity phase.

Can Eccentric-only Resistance Training Decrease Passive Muscle Stiffness while Increasing Size and Strength of Hamstrings?

PURPOSE: Resistance training may be empirically believed to increase passive muscle stiffness. Meanwhile, a recent study showed that the passive stiffness of a specific hamstring muscle acutely decreased after eccentric-only resistance exercise at long muscle lengths with a long contraction duration (LL). To extend this finding, the present study investigated the chronic effects of eccentric-only resistance training with LL at different weekly frequencies on the passive stiffness of the biarticular hamstring muscles. METHODS: Thirty-six healthy young males were assigned into two training groups with two and three weekly sessions (W2 and W3, n = 12, respectively) and a control group (CON, n = 12). The participants in both training groups performed eccentric-only stiff-leg deadlift at 50-100% of exercise range of motion (0% = upright position) with 5 s per repetition for 10 weeks. Before and after the intervention period, the shear moduli of the biarticular hamstring muscles, maximal voluntary isometric torque of knee flexion, and volumes of the individual hamstring muscles were measured. RESULTS: In W3, the shear modulus of the semimembranosus (-11.4%) significantly decreased, whereas those of the other biarticular muscles did not change. There were no significant changes in the shear moduli of the biarticular hamstring muscles in W2 or CON. The isometric torque (20.3 and 26.2%, respectively) and semimembranosus volume (5.7% and 7.4%, respectively) were significantly increased in W2 and W3. CONCLUSIONS: Passive stiffness of a specific muscle could be chronically decreased when eccentric-only resistance training with LL is performed at a relatively high weekly frequency with a high total training volume. Our training modality may be a promising strategy for decreasing passive muscle stiffness while increasing muscular strength and size.

Effect of CO2 and H2 gas mixture in cold water immersion on recovery after eccentric loading.

Background: The findings of previous studies support the efficacy of cold water immersion (CWI) with carbon dioxide (CO2) in enhancing muscle blood flow and maintaining aerobic performance efficiency. We hypothesize that the addition of hydrogen gas (H2), known for its antioxidant properties and role in inflammation regulation, to C-CWI can enhance recovery after eccentric exercise. Subjects: and Methods: Thirty-four healthy subjects performed a knee-extensor eccentric exercise. They were randomly allocated into four groups: control, CWI, CO2-rich CWI (C-CWI), and CO2 + H2 gas mixture CWI (CH-CWI). In the three CWI groups, all subjects were immersed in the appropriate bath at 20 °C for 20 min immediately after 60 repetitions of eccentric exercise. Before exercise and after 48 h of recovery, the subjects' maximal voluntary isometric contraction torque (MVC-ISO), maximal voluntary concentric (MVC-CON) contraction torque, countermovement jump (CMJ) height, knee flexion range of motion (ROM), muscle soreness, and muscle thickness were measured. Results: In the CH-CWI group only, the MVC-ISO, CMJ height, and ROM did not decrease significantly post-exercise, whereas all of these decreased in the other three groups. Muscle soreness at palpation, contraction, and stretching significantly increased post-exercise in all groups. Echo intensity and tissue hardness did not increase significantly in the CH-CWI group. Conclusions: CH-CWI stimulated recovery from impairments in MVC-ISO torque, CMJ height, knee-flexion ROM, tissue hardness, and echo intensity. These findings indicate that CH-CWI can promote recovery after eccentric exercise.

The Acute Effects of a Single Dose of Molecular Hydrogen Supplements on Responses to Ergogenic Adjustments during High-Intensity Intermittent Exercise in Humans.

This research examined the effects of single-dose molecular hydrogen (H2) supplements on acid-base status and local muscle deoxygenation during rest, high-intensity intermittent training (HIIT) performance, and recovery. Ten healthy, trained subjects in a randomized, double-blind, crossover design received H2-rich calcium powder (HCP) (1500 mg, containing 2.544 µg of H2) or H2-depleted placebo (1500 mg) supplements 1 h pre-exercise. They performed six bouts of 7 s all-out pedaling (HIIT) at 7.5% of body weight separated by 40 s pedaling intervals, followed by a recovery period. Blood gases' pH, PCO2, and HCO3- concentrations were measured at rest. Muscle deoxygenation (deoxy[Hb + Mb]) and tissue O2 saturation (StO2) were determined via time-resolved near-infrared spectroscopy in the vastus lateralis (VL) and rectus femoris (RF) muscles from rest to recovery. At rest, the HCP group had significantly higher PCO2 and HCO3- concentrations and a slight tendency toward acidosis. During exercise, the first HIIT bout's peak power was significantly higher in HCP (839 ± 112 W) vs. Placebo (816 ± 108 W, p = 0.001), and HCP had a notable effect on significantly increased deoxy[Hb + Mb] concentration during HIIT exercise, despite no differences in heart rate response. The HCP group showed significantly greater O2 extraction in VL and microvascular (Hb) volume in RF during HIIT exercise. The HIIT exercise provided significantly improved blood flow and muscle reoxygenation rates in both the RF and VL during passive recovery compared to rest in all groups. The HCP supplement might exert ergogenic effects on high-intensity exercise and prove advantageous for improving anaerobic HIIT exercise performance.

Physical and performance characteristics of Japanese division 1 collegiate football players.

Iguchi, J, Yamada, Y, Ando, S, Fujisawa, Y, Hojo, T, Nishimura, K, Kuzuhara, K, Yuasa, Y, and Ichihashi, N. Physical and performance characteristics of Japanese division 1 collegiate football players. J Strength Cond Res 25(12): 3368-3377, 2011-This study aimed to establish the physical and performance characteristics of football players in the Japanese Division 1 collegiate football program and perform a comparison of these characteristics between Japanese (n = 208) and US Division 1 football players (n = 797). The following comparisons were made: (a) between a higher-ranked university team vs. a lower-ranked university team in Japan, (b) between different playing positions in Japan, (c) between starters and nonstarters in Japan, and (d) between playing positions in Japan vs. those in the United States. The results of this study suggest that players in the higher-ranked university team were heavier, stronger in back squat, jumped higher, and had greater power than those on the lower-ranked team. Furthermore, linemen were generally characterized by larger size, greater strength, and more fat as compared with backs. On the other hand, backs tended to be faster, smaller in physical size, have higher vertical jump height, and show greater relative strength than linemen did. Starters were taller, heavier, stronger, had more powerful, and more fat-free mass than nonstarters. Finally, our results revealed that players in the United States were superior to players in Japan in all body status comparisons (p < 0.01). This study revealed that performance and superior body composition are essential for the success of a football player. Power and strength seem to be key factors in defining good football performance.

Application of Molecular Hydrogen as an Antioxidant in Responses to Ventilatory and Ergogenic Adjustments during Incremental Exercise in Humans.

We investigated effects of molecular hydrogen (H2) supplementation on acid-base status, pulmonary gas exchange responses, and local muscle oxygenation during incremental exercise. Eighteen healthy, trained subjects in a randomized, double-blind, crossover design received H2-rich calcium powder (HCP) (1500 mg/day, containing 2.544 µg/day of H2) or H2-depleted placebo (1500 mg/day) for three consecutive days. They performed cycling incremental exercise starting at 20-watt work rate, increasing by 20 watts/2 min until exhaustion. Breath-by-breath pulmonary ventilation (V˙E) and CO2 output (V˙CO2) were measured and muscle deoxygenation (deoxy[Hb + Mb]) was determined via time-resolved near-infrared spectroscopy in the vastus lateralis (VL) and rectus femoris (RF). Blood gases' pH, lactate, and bicarbonate (HCO3-) concentrations were measured at rest and 120-, 200-, and 240-watt work rates. At rest, the HCP group had significantly lower V˙E, V˙CO2, and higher HCO3-, partial pressures of CO2 (PCO2) versus placebo. During exercise, a significant pH decrease and greater HCO3- continued until 240-watt workload in HCP. The V˙E was significantly lower in HCP versus placebo, but HCP did not affect the gas exchange status of V˙CO2 or oxygen uptake (V˙O2). HCP increased absolute values of deoxy[Hb + Mb] at the RF but not VL. Thus, HCP-induced hypoventilation would lead to lower pH and secondarily impaired balance between O2 delivery and utilization in the local RF during exercise, suggesting that HCP supplementation, which increases the at-rest antioxidant potential, affects the lower ventilation and pH status during incremental exercise. HPC induced a significantly lower O2 delivery/utilization ratio in the RF but not the VL, which may be because these regions possess inherently different vascular/metabolic control properties, perhaps related to fiber-type composition.

Effect of electroacupuncture on the healing process of tibia fracture in a rat model: a randomised controlled trial.

BACKGROUND: Electrical stimulation is used to promote bone reunion, and is most effective when applied directly to the fracture site. OBJECTIVE: To examine the effects of electroacupuncture (EA) on the healing process of tibia fracture in a rat model. METHODS: Thirty 12-week-old male Wistar rats underwent unilateral open osteotomies of the tibiae. The rats were then assigned randomly to three groups: EA group (n=10), sham group (n=10) and control group (n=10). In the EA group, a cathodal electrode was connected to an acupuncture needle percutaneously penetrated directly at the surgery site, while an acupuncture needle inserted at 15 mm proximal to the surgery site was used as an anodal electrode. EA (50 Hz, 20 µA, 20 min) was performed daily for 3 weeks. In the sham group the acupuncture needles were inserted at the same sites but no electrical stimulation was given and in the control group, no treatment was given. The response was evaluated at 1, 3, 4 and 6 weeks after surgery by radiographic, macroscopic and mechanical examinations. RESULTS: The EA group showed accelerated bone healing (EA group 29.92+/-4.55 mm², sham group 26.46+/-5.21 mm², control group 26.19+/-2.81 mm², p<0.05 at 3 weeks) and accretion of the callus (radiographic evaluation: EA group 35.66+/-4.37 mm², sham group 32.60+/-5.73 mm², control group 29.72+/-6.39 mm², p<0.05 at 6 weeks) compared with the other groups. Mechanical testing also showed an excellent result (EA group 16.54+/-9.92 N, sham group 7.13+/-3.57 N, control group 6.67+/-3.12 N, p<0.05) at 6 weeks in the EA group compared with the other groups. There was no difference between the sham and control groups in any evaluation. CONCLUSION: The use of EA enhanced callus development and bone mineralisation during the bone healing process.

In-match physical demands on elite Japanese rugby union players using a global positioning system.

OBJECTIVES: Our aim of this study was to quantify the physical demands of elite rugby union players by each position as a step towards designing position-specific training programme using a Global Positioning System/accelerometer system. METHODS: This study was performed as a retrospective observational study. Data were obtained from 45 official matches. The sample size used for the analysis was 298. The per-match total distances, accelerations and impacts were calculated and statistically compared for the forwards and backs and for individual positions. RESULTS: Total distances for the forwards and backs were 5731.1±507.8 and 6392.1±646.8 m, respectively. The high-velocity running distances (>18.0 km/hour) covered by the forwards and backs were 317.4±136.9 and 715.0±242.9 m, respectively. The number of accelerations (>1.5 m/s2) for the forwards and backs were 76.3±18.9 and 100.8±19.6 times, respectively, and the number of high impacts (>10 g) were 48.0±46.9 and 35.6±28.3 times for the forwards and backs, respectively. All characteristics were significantly different between the forwards and backs (p<0.05). The per-position characteristics were also calculated. Within the backs, scrum half (SH) and wingers (WTBs) covered high-velocity running significantly higher distance than fly-half (SH d=2.571, WTBs d=1.556) and centres (SH d=1.299, WTBs d=0.685) (p<0.05). CONCLUSION: By clarifying the physical demands according to the positions, it will be possible to create optimised position-specific training programmes.

Application of carbon dioxide to the skin and muscle oxygenation of human lower-limb muscle sites during cold water immersion.

BACKGROUND: Cold therapy has the disadvantage of inducing vasoconstriction in arterial and venous capillaries. The effects of carbon dioxide (CO2) hot water depend mainly on not only cutaneous vasodilation but also muscle vasodilation. We examined the effects of artificial CO2 cold water immersion (CCWI) on skin oxygenation and muscle oxygenation and the immersed skin temperature. SUBJECTS AND METHODS: Fifteen healthy young males participated. CO2-rich water containing CO2 >1,150 ppm was prepared using a micro-bubble device. Each subject's single leg was immersed up to the knee in the CO2-rich water (20 °C) for 15 min, followed by a 20-min recovery period. As a control study, a leg of the subject was immersed in cold tap-water at 20 °C (CWI). The skin temperature at the lower leg under water immersion (Tsk-WI) and the subject's thermal sensation at the immersed and non-immersed lower legs were measured throughout the experiment. We simultaneously measured the relative changes of local muscle oxygenation/deoxygenation compared to the basal values (Δoxy[Hb+Mb], Δdeoxy[Hb+Mb], and Δtotal[Hb+Mb]) at rest, which reflected the blood flow in the muscle, and we measured the tissue O2 saturation (StO2) by near-infrared spectroscopy on two regions of the tibialis anterior (TA) and gastrocnemius (GAS) muscles. RESULTS: Compared to the CWI results, the Δoxy[Hb+Mb] and Δtotal[Hb+Mb] in the TA muscle at CCWI were increased and continued at a steady state during the recovery period. In GAS muscle, the Δtotal[Hb+Mb] and Δdeoxy[Hb+Mb] were increased during CCWI compared to CWI. Notably, StO2values in both TA and GAS muscles were significantly increased during CCWI compared to CWI. In addition, compared to the CWI, a significant decrease in Tsk at the immersed leg after the CCWI was maintained until the end of the 20-min recovery, and the significant reduction continued. DISCUSSION: The combination of CO2 and cold water can induce both more increased blood inflow into muscles and volume-related (total heme concentration) changes in deoxy[Hb+Mb] during the recovery period. The Tsk-WI stayed lower with the CCWI compared to the CWI, as it is associated with vasodilation by CO2.