Obesity and aging reduce skeletal muscle contractile function, which represents a reduction in muscle quality. Dysfunction of muscle contraction may contribute to a greater risk for diabetes, cardiovascular diseases, and cancer; therefore, the synergistic effects of obesity and aging on muscle function may exacerbate morbidity and mortality. However, evidence directly examining the synergistic effects of obesity and aging on muscle contractile function is lacking and controversial. We recently demonstrated that diet-induced obesity significantly exacerbates contractile dysfunction in aged skeletal muscle. The focus of this review is the effects of obesity on muscle contractile dysfunction in skeletal muscle, particularly during aging.

The aim of this study was to examine the effects of voluntary exercise on plasma and urinary metabolites and the changes in gut microbiota in mice fed with a high-fat-diet. Healthy male C57BL/6J mice (four-week-old, n = 27) were fed a normal controlled diet (CD) and a high-fat-diet (HFD) for 10 weeks under two conditions: voluntary wheel running (W) and sedentary controlled condition (C). The metabolites in the collected plasma and urine were detected using ¹H-NMR spectroscopy techniques. Also, 16S-rRNA gene next-generation sequencing was carried out on the collected feces. Wheel running activity in HFDW mice was slightly higher than that in CDW mice (p = 0.075). Exercise and diet significantly altered body weight, fat accumulation, and glucose tolerance tests. In plasma, amino acids such as Leu, Ile, Ala and Tyr, were increased by exercise. Diet influenced the metabolites in both the plasma and urine of mice and showed significant differences; in plasma, Leu, Ile, Glu, 3-HB, lactate and acetate, whereas in urine, citrate, trimethylamine (TMA), trimethylamine-N-oxide (TMAO), taurine, hippurate and allantoin. With regard to beta diversity, unweighted UniFrac analysis (principal coordinate analysis: PCoA) showed the difference between CD and HFD mice could be observed under PC1 (22.61%). Although there was substantial overlap between two conditions (C vs. W), HFD groups were positioned in a slightly different area when compared to the C and W conditions. Firmicutes/Bacteroidetes ratio, which might be associated with obesity, in HFD mice was significantly higher than that in CD mice, but not affected by wheel running. Our results suggest that testing in both plasma and urinary metabolites may prove to be a more reliable approach to quantitative metabolite analysis on the effects of exercise-dependent hosts or as an independent alteration of gut microbiota on the hosts.

Stretching exercises conducted by oneself, herein referred to as self-stretching exercises, improve arterial stiffness in healthy people. Such exercises include voluntary contraction of peripheral muscles in addition to stretching of target muscles. However, the effects of static passive stretching without voluntary contraction of skeletal muscles on arterial stiffness remain unknown. In addition, it is important to verify the effects of stretching in the elderly lacking exercise habits with advanced arterial stiffness. Therefore, the purpose of the present study was to verify the acute effects of static passive stretching, without voluntary contraction of skeletal muscles, on the cardio-ankle vascular index (CAVI) in elderly individuals lacking exercise habits. The present study followed a pretest-posttest design without a control group. Twenty-nine elderly individuals (mean age, 77.8 ± 7.0 years; 24 female) recruited at an orthopedic clinic participated in the present study. The participants were subjected to static passive stretching of the neck, trunk, and extremities for 40 min by the same physical therapist. Stretching involved the shoulder flexors/extensors, elbow flexors/extensors, wrist palmar flexors/dorsal flexors, hip flexors/extensors/adductors, knee flexors/extensors, ankle plantar flexors/dorsal flexors, neck muscles, and trunk muscles. The CAVI (Rt, Lt, Ave), ankle-brachial index (ABI), blood pressure, and pulse rate were assessed before and after stretching. After stretching, both CAVI (Lt, Ave) and pulse rate were significantly decreased. In contrast, no significant changes in CAVI (Rt), ABI, or blood pressure were observed. The key new finding of the present study was that static passive stretching without voluntary contraction of skeletal muscles acutely improved the CAVI in elderly individuals lacking exercise habits.

To the best of our knowledge, most previous studies regarding the epidemiology of injuries in rugby union (rugby) players have focused on professional players. Therefore, data on injuries in collegiate rugby players in Japan is limited. The purpose of this study was to conduct a prospective injury survey of Japanese male collegiate rugby players over several years and to analyze the injuries that occurred during matches and training according to field position, type of injury, and mechanism of injury. This prospective study initially registered 128 rugby players from one university club. The occurrence of injuries was recorded by athletic trainers during the rugby seasons between 2017 and 2019. The total injury rate (IR) was 7.26 injuries/1000 player-hours (1000 PHs). The match IR (122.73 injuries/1000 PHs) was almost 31.9 times higher than the training IR (3.84 injuries/1000 PHs). Ankle sprains/ligament injuries (17.7%; 1.28 injuries/1000 PHs) were the most common injuries, in addition to acromioclavicular joint injuries in forwards and hamstring strain injuries in backs. The most common injury mechanism was tackling (16.4%). Injury characteristics differed according to field position; therefore, preventive measures according to field position are necessary. Moreover, the high number of tackle injuries suggests that improved tackle skills would help reduce injuries. The IR among Japanese collegiate rugby players was higher than that reported previously. Injury prevention training for collegiate players is necessary to reduce the number of injuries.

Our previous studies used type-2 diabetic model Otsuka Long-Evans Tokushima fatty (OLETF) rats, and showed that both exercise and diet regimen decreased body weight (BW) and improved glucose intolerance (GI), and dyslipidemia. However, exercise regimenwas also associated with increased blood pressure (BP), diabetic nephropathy (DN) progression characterized by an increase in urinary albumin excretion (U_Alb), and morphological abnormalities of the kidneys. This study examined the effects of an exercise regimen alone and the combined treatment of exercise and an antihypertensive medication, captopril (Capt), on systemic BP, DN progression, BW, GI, and dyslipidemia in OLETF rats. Twenty-four male OLETF rats were divided into the following groups: voluntary exercise alone (OLETF-Ex), Capt administration alone (OLETF-Capt), Capt and exercise (OLETF-Capt & Ex), and sedentary control (OLETF-Sed) groups. Six male Long-Evans Tokushima Otsuka (LETO) rats were used as a normal sedentary control (LETO-Sed). These treatments were conducted from 21 to 30 weeks of age. Approximately 20 mg/kg/day of Capt was administered daily. After the treatment, the OLETF-Ex group experienced decreased BW and improved GI and dyslipidemia; however, it was associated with diastolic BP elevation and DN progression. The OLETF-Capt group experienced decreased BP and serum TG concentration and inhibited DN progression. The OLETF-Capt & Ex group experienced decreased BW and BP, and improved GI and dyslipidemia without the progression of DN. This study demonstrated that a combined treatment of exercise and antihypertensive agents, such as Capt, is recommended as an ideal regimen for hypertensive diabetic patients in the pre-nephropathy stage to avoid DN progression induced by an exercise regimen alone.

Although static stretching is commonly performed to improve flexibility, it has been reported to have detrimental effects on muscle force and performance. Previous studies have reported that low-intensity and short-duration isometric contraction after static stretching inhibits stretch-induced force loss. However, the detailed effects of low-intensity short-duration isometric contraction after static stretching on flexibility, such as passive torque and stiffness, are currently unclear. Therefore, the current study sought to reveal the effects of low-intensity and short-duration isometric contraction after static stretching on flexibility and muscle force. Sixteen healthy participants (eight men, eight women) performed 300-s static stretching (SS), 300-s static stretching followed by 6-s 30% maximum isometric voluntary contraction (MIVC) (SS-30% MIVC), and 6-s 30% MIVC (30% MIVC) of the right hamstring on three separate days, in random order. Range of motion (ROM) and passive stiffness during knee extension, peak passive torque, and MIVC torque were obtained before and after exercise. ROM and peak passive torque were significantly increased after all exercises, whereas passive stiffness and MIVC torque were significantly decreased after SS only. Moreover, ROM after SS and SS-30% MIVC were significantly greater than that of 30% MIVC, and peak passive torque after SS-30% MIVC was significantly greater than that of SS, while passive stiffness after SS was significantly lower than that of 30% MIVC. These results indicate that low-intensity and short-duration isometric contraction after static stretching is effective for inhibiting stretch-induced force loss while also inhibiting the effects of static stretching on passive stiffness.