Recent field studies have reported the effects of exercise on the cortisol awakening response (CAR); however, no study has experimentally examined the effects. The purpose of this study was to investigate the effect of exercise intensity on CAR among 14 healthy male university students. Participants rested for 20 min (control condition) and exercised on a cycle ergometer for 20 min at 40% (low), 60% (moderate), and 80% (high) intensity of VO₂max on separate days. Saliva samples were collected 10 times as follows: 1) before and 2) immediately after the experimental session, 3) 10 min, 4) 20 min, and 5) 30 min into the recovery period, 6) 9 PM and 7) 11 PM in the evening following the session, 8) immediately after awakening, 9) 15 min, and 10) 30 min post-awakening the day after the session. Cortisol concentration increased after the high-intensity exercise and recovered in the evening following the session. The 30 min post-awakening sampling point the day after the session of high-intensity exercise was higher than the control condition (p = .039). In addition, the higher intensity exercise condition led to the magnitude of change in CAR (CAR_c) (p = .006) and the area of cortisol increased under the curve (AUC_i) (p = .034), making it higher than the control condition. There were no significant differences in other confounders. These results suggest that CAR showed a higher value in healthy male university students the day after performing high-intensity exercise.

The aim of the present study was to examine the effect of an amino acid (AA) mixture of arginine, valine, and serine on exercise performance after prolonged exercise in humans. In a randomized, double-blinded, placebo-controlled crossover trial, nineteen recreationally active healthy males ingested an AA mixture of 1.8 g of arginine, 1.1 g of valine, and 0.1 g of serine or a placebo twice a day for 3 days and carried out a cycling exercise at 50% VO₂max for 90 min with a 15-min rest at the midpoint. After the exercise, subjects performed a 30-s Wingate test. Their leg and grip strength, rating scale of perceived exertion (RPE), and blood biochemical parameters were also evaluated. There were no significant differences between the two conditions in the Wingate test performance (peak power: AA 650.9 ± 80.8 vs placebo 644.7 ± 78.0, p = 0.585; mean power: AA 491.6 ± 58.8 vs placebo 490.8 ± 63.7, p = 0.907), leg and grip strength, or RPE score during exercise. The plasma noradrenaline concentrations in the AA condition were significantly higher than those in the placebo condition during exercise (p < 0.05). Moreover, strong correlations were found between the Wingate test performance and level of plasma noradrenaline (p < 0.001). These results indicated that the AA mixture supplement significantly elevated the plasma noradrenaline level during exercise, while sprint performance after prolonged exercise was not improved by the AA mixture supplement in the study.

Injury can possibly change an athlete’s career. To date, few epidemiological studies have been made of amateur soccer players. More data is needed to allow medical professionals to develop realistic injury prevention and conditioning programs for the amateur level. The purpose of this study was to determine injury incidence, common injury types and body regions, and pain in amateur soccer players. Soccer-related injury and pain data were collected daily in June 2016 thorough October 2017 involving 76 amateur soccer players from two teams. Overall injury incidence was 69 injuries and 2.72/1000 player hours. Acute injuries were 52 (2.05/1000 player hours) and chronic injuries were 17 (0.67/1000 player hours). Most acute injuries occurred during a game (1.99/1000 player hours). In terms of body regions, ankle injury (27.5%) was the most common, followed by knee (15.9%), and thigh (9.0%). Pain incidence was reported 1042 (41.10/1000 player hours). The highest pain incidence was reported during a game (36.9/1000 player hours). The most common location of pain was foot/toe (5.80/1000 player hours), followed by lateral ankle (5.21/1000 player hours), anterior thigh (3.98/1000 player hours), and groin (3.27/1000 player hours). Type of injury, location of injury, and the higher incidence of injury during a game, as opposed to training, were the same as other studies. The pain incidence rate was higher than injury incidence. More epidemiological studies are needed in amateur sports to better understand athletes’ injuries and pain and be able to develop an appropriate injury prevention strategy.

Hindlimb immobilization (IM) produces a decrease in functional oxidative capacity as well as morphological changes in muscles. However, the effect of IM on the mechanism of O₂ supply to mitochondria in muscle tissue during muscle contraction is unknown, especially the contribution of myoglobin (Mb) to mitochondrial respiration. This study investigated whether IM causes a delayed response of intracellular Mb saturation (S_mbO₂) and decreased muscle oxygen uptake (mVO₂) due to elevated intracellular oxygen tension (P_mbO₂) in contracting muscles using a rat hindlimb perfusion model. Three-week IM decreased the O₂ release rate from Mb at the onset of muscle contraction (IM: 3.2 ± 0.9 vs. control (Con): 7.5 ± 2.9 10^-2 µmol g^-1 min^-1; p < 0.05) and state 3 of mitochondrial respiration in muscle tissue (IM: 0.021 ± 0.006 vs. Con: 0.030 ± 0.009 10^-3 µM g^-1 sec^-1; p < 0.05). Despite the increase in mVO₂, the steady-state level of S_mbO₂ was higher during muscle contraction in the IM group, resulting in elevated P_mbO₂ (IM: 4.2 ± 1.0 vs. Con: 2.1 ± 1.0 mmHg; p < 0.05). In conclusion, IM decreased the O₂ release rate from Mb; this alteration could be associated with mitochondrial dysfunction. These changes within muscle cells may be related to the delayed tissue response seen with near-infrared spectroscopy at the onset of muscle contraction.

This study aimed to investigate motor control characteristics of the upper limbs through bilateral simultaneous grading tasks. The participants included 18 healthy right-handed women. They were instructed to perform isometric elbow flexion tasks under unilateral and bilateral conditions. The grading tasks were aimed at increasing the maximum voluntary force (MVF) from 10% to 30% or 50%. In the unilateral condition, participants performed tasks with the right or left upper limb. In the bilateral condition, participants increased their force level to 30% MVF with the right limb and then to 50% MVF with the left limb, or they increased their force level to 50% MVF with the right limb and then to 30% MVF with the left limb. Participants were asked to perform tasks as rapidly and accurately as possible. We evaluated the rapidity, accuracy, and reproducibility. Regarding the rapidity, the reaction time at 30% MVF was longer than that at 50% MVF, while the adjustment time at 50% MVF was longer than that at 30% MVF. Regarding the total adjustment time, there was no difference between both limbs in both bilateral conditions. Accuracy and reproducibility were higher when the task was performed at 30% MVF. These results suggest that when different levels of force are exerted by both upper limbs, the movement time is drawn to the side that exerts larger force, and the accuracy of force exertion increases on the limb that exerts less force.

The purpose of this study was to examine whether the bone parameters and food groups consumed differ according to the energy availability (EA) status in Japanese female athletes, and to determine the relationship between calcium intake and other food groups consumption among these athletes. We investigated EA status, nutritional and food group intake, bone metabolism using biochemical analysis, and evaluated body composition and bone parameters using dual-energy X-ray absorptiometry. Fifty-two Japanese female athletes (Age: 20.0 ± 1.2 years) were enrolled in this study. Group differences between the low EA (EA < 30 kcal/kg FFM/d, n = 22) and moderate EA (EA ≥ 30 kcal/kg FFM/d, n = 30) groups were examined. Compared to the moderate EA group, the low EA group exhibited a lower daily intake of protein (g/kg BW), carbohydrate (g/kg BW), calcium (mg), grains (g), meats (g), milk and dairy products (g). Moreover, the bone resorption marker was significantly higher in the low-EA group. The daily intake of soybean products (g), vegetables (g), fish and shellfish (g) and milk and dairy products (g) correlated positively with daily calcium intake (mg). Female athletes with low EA and insufficient intake of milk and dairy products exhibited increased serum tartrate-resistant acid phosphatase 5b levels. As with milk and dairy products intake, consumption of various food groups was also significantly positively correlated with calcium intake. These findings suggest that a diet with sufficient energy and multiple food groups to provide adequate calcium may benefit bone health among Japanese female athletes.

This study investigated the relationships between subjective and objective indicators of training load in female handball players. Twelve female handball players (age: 20.1 ± 1.2 years, height: 164.3 ± 4.2 cm, and weight: 61.8 ± 4.1 kg) belonging to the first division of a university league were included in the study. The training load was investigated over a nine-week period of the competition phase. The subjective load indicator was the session rating of perceived exertion (sRPE), and the objective load indicators were total distance, Player Load™, and heart rate-based training load (HRTL). We observed 20.5 ± 2.3 sessions for each player. The sRPE demonstrated significant relationships (p < 0.05) with all objective load indicators, with correlation coefficients r = 0.73 ± 0.09, 0.73 ± 0.08, and 0.75 ± 0.10 for total distance, Player Load™, and HRTL, respectively. All the relationships were very strong (0.7 < r < 0.9). These results reveal the potential validity of sRPE use in handball and suggest that the sRPE is an indicator that reflects the characteristics of both biomechanical and physiological load indicators.