Ryanodine receptors (RyRs) are tetrameric Ca2+ release channels of sarcoplasmic reticulum (SR). This review attempts to detail the key mechanism of RyR channel gating and to discuss the hypothesis that skeletal muscle fatigue, defined as reduced force production, would result from functional changes in both individual RyR channel opening and coupling among RyR channels. Previous studies have shown that RyR channels in skeletal muscle open simultaneously, called coupled gating, because of physical interaction among channels. In this review, mechanisms underlying muscle fatigue are discussed with consideration of the coupling effect. Fatigue mechanisms are thought to be different between acute exercise and long-term exercise training. The impairments in individual channel opening and coupling between RyR channels can occur after acute exercise, leading to decreased SR Ca2+ release and force depression. On the contrary, during long-term exercise training, individual channel opening would be enhanced but coupling between channels would be impaired. If this were to continue for long periods, SR Ca2+ content would reduce, leading to less Ca2+ release and lower force production.
The aim of this study was to evaluate the transition of the tensor fasciae latae (TFL) and the iliotibial band (ITB) hardness after repetitive hip abduction exercise (RE) and the effect of vibration stimulation immediately after RE. Nine healthy man performed the RE (20 reps×5 sets) and the TFL and the ITB hardness were measured before and after RE. Participants were performed RE by 2 conditions(i.e. with and without vibration stimulation after RE). The results showed that with no vibration condition, hardness of the TFL significantly increased immediately, 15 min, 30 min, and 24 hours and the ITB significantly increased immediately, and 24 hours after RE compared with before RE, respectively. With vibration condition, vibration after RE, both of the TFL and the ITB hardness significantly increased only immediately after compared with before RE. On the other hand, TFL and ITB hardness significantly decreased 15 min, 30 min, and 24 hours compared with immediately after RE. In addition, with vibration condition, TFL and ITB hardness significantly decreased 15 min, 30 min, 24 hours compared with no vibration condition, respectively. This study indicated that the ITB hardness might be increased with excessive activity of TFL, and the vibration stimulation immediately after exercise is effective for decreasing the hardness.
The purpose of this study is to considerate the prediction formula for marathon time based on 20-m shuttle run test and training indexes in recreational runners. 100 male and 111 female recreational runners who have experienced one or more marathon races were measured. Each participant was measured with regard to physical characteristics, 20-m shuttle run test, and answered questionnaires about his/her training (monthly running distance, frequency of training, and years of experience of running training). Moreover, participants self-reported their best marathon time. Additionally, to examine the validity of the prediction formula, 14 male and 13 female recreational runners were measured using the 20-m shuttle run test and they answered the questionnaires about his/her training. The marathon time was significantly correlated with the participant’s BMI, the times of 20-m shuttle run test, the monthly running distance, the frequency of training and the years of experience of running training for both male and female runners. Subsequently, multiple regression analysis generated the prediction model for marathon time by the measurement items. Furthermore, in the examination of the validity of the prediction formula, predicted marathon time was significantly highly correlated with measured marathon time. This study suggested that the marathon time can be predicted by the 20-m shuttle run test, the monthly running distance, and the years of experience of running training and the predicted marathon time may be useful for the marathon race and training in recreational runners.
This retrospective observational study aimed to examine the effects of playing Pokémon GO on daily steps of male college students. Twenty-five Japanese male college students (20 ± 1 years) were assigned to Control group (C, n = 11) or Pokémon GO group (P, n = 14) based on their playing Pokémon GO or not. Daily step levels were obtained from the health care app of Apple iPhone from September 2016 to October 2016. In P group, the data for the 4 weeks to determine baseline values and for the 4 weeks of playing Pokémon GO were analyzed. The steps data of C group were also analyzed in the same period of the total 8 weeks. There were no significant differences in steps at baseline level between both groups. In addition, no significant time-course changes in steps were observed in C group. In contrast, steps in P group significantly increased from baseline 8,368 ± 544 steps/day to week 1 10,028 ± 617 steps/day (P < 0.01). The changes in steps from baseline to week 1 were significantly greater in P group than in C group (1,671 ± 345 vs. -81 ± 582, P < 0.01). However, the increased steps returned to baseline level by week 2, and the values did not increase again. Therefore, our findings indicate that playing Pokémon GO increases daily steps only during one week in Japanese male college students.
Cancer, congestive heart failure, chronic obstructive pulmonary disease, type 2 diabetes and aging induce skeletal muscle atrophy. These diseases and aging promote the formation of reactive oxygen species (ROS), which in turn regulate catabolic pathways involved in muscle atrophy. The first line of antioxidant defense system from ROS is comprised of superoxide dismutase (SOD), which scavenges superoxide (O2•−) to produce the less reactive hydrogen peroxide (H2O2). Mammalian skeletal muscle expresses cytosolic copper/zinc-containing SOD (CuZnSOD or SOD1), manganese SOD (MnSOD or SOD2), and extracellular SOD (EcSOD or SOD3). In this review, we provide an overview of 1) oxidative stress and antioxidants, 2) EcSOD ameliorates skeletal muscle abnormalities, cachexia, and exercise intolerance, 3) muscle-derived EcSOD protects against organ dysfunction, and 4) role of the Keap1-Nrf2 signaling pathway in the regulation of antioxidant defense system.