Carnitine is well recognized for transporting fatty acids across the mitochondrial membrane; however, studies conducted in the last decade have highlighted another role of carnitine in buffering the excess of mitochondrial acetyl-CoA, an intermediate metabolite of beta-oxidation and glycolytic metabolism. Although acetyl-CoA is an essential metabolite, excess accumulation of acetyl-CoA inhibits pyruvate dehydrogenase, resulting in negative regulation of glucose uptake. In this situation, carnitine binds to acetyl-CoA and is converted to acetylcarnitine, resulting in a decrease in acetyl-CoA levels. It has been demonstrated that carnitine acetylation is essential for glucose homeostasis, and that its dysfunction, caused by aging and high-fat feeding, induces metabolic failure. To analyze carnitine dynamics in skeletal muscle, we have used imaging mass spectrometry to visualize the distribution of acetylcarnitine in rodent skeletal muscle and performed tracing experiments using isotopic labeled carnitine. It was shown that carnitine uptake and acetylation were elevated in oxidative muscles, and that they were dynamically controlled by muscle contraction. Recent studies using cell culture experiments demonstrated that acetylcarnitine is exported from skeletal muscle cells. It is hypothesized that muscle carnitine acetylation in skeletal muscle is not only beneficial for buffering the excess acetyl-CoA, but also plays in the endocrine system. In fact, previous work has shown that plasma acetylcarnitine concentration increases during exercise in humans, suggesting that the acetylcarnitine produced during muscle contraction may be released from muscle cells to serve different functions. In this article, we reviewed the novel roles of carnitine in skeletal muscle by analyzing carnitine dynamics.

Marathon running performance closely related to the several physiological and performance variables such as maximal oxygen uptake, running economy, and peak velocity. It is well known that muscle damage has a negative impact on the physiological and performance variables. Thus, restarting training or participating in the race in a state where recovery is inadequate may cause injury and loss of race performance. The aims of this review article are to (1) summarize the previous studies that investigated effects of a marathon race on muscle damage and physiological and performance variables, (2) discuss the middle and long term effects of marathon races on physical condition, (3) suggest the practical strategy for some runners that participate in consecutive races within a short period.

This study examined the effects of a 6-month circuit gym workout on muscle and fat cross-sectional area (CSA) and muscle strength in middle-aged and older women. The participants were 49 women without severe metabolic disease, exercise limitation, or exercise habits. They were randomly assigned to two groups, circuit gym using group (CRT: n = 25) and walking group (WALK: n = 24). Both groups followed the exercise program for 6 months. Thigh and abdominal CSA before and after the program were measured using magnetic resonance imaging. Moreover, knee extensor/flexor and hip flexor strength were measured using a dynamometer. After completion of the exercise program, CSA of the psoas major muscle and isokinetic knee and hip flexion strength significantly increased in the CRT group compared with the WALK group (CSA: 7.1% vs 1.4% respectively; isokinetic strength: 7.5% vs −4.3% (knee), 23.6% vs 2.2% (hip), respectively). In addition, subcutaneous adipose tissue of the thigh in the CRT group significantly decreased compared with that in the WALK group (−6.5% vs −1.8%, respectively). These results imply that in middle-aged and older women, the use of circuit gym leads to a more effective increase in CSA of the psoas major muscle, decrease in thigh subcutaneous adipose tissue, and increase in knee and hip flexor strength compared with brisk walking.

This study aimed to examine the association of practice hour, frequency, and amount with self-rated health (SRH) and outpatient visits (OV) among senior soccer players in Japan. This cross-sectional study included a total of 995 players who participated in the 5th Senior Soccer Festival in Shizuoka in May 2016. We conducted a self-administered questionnaire (response rate, 43.7%). Information on practice hour and frequency in the past 3 months was obtained. Practice amount was calculated by multiplying them. Information on SRH and OV were obtained using the same items of Health questionnaire on Comprehensive Survey of Living Conditions 2013. Practice hour, frequency, and amount were divided into the following tertiles: low, moderate, and high. The SRH and OV for 16 diseases were categorized into 2 groups, respectively. Prevalence ratios (PRs) were calculated using Poisson regression analysis with SRH or OV as objective variables, and practice hour, frequency, and amount as explanatory variables in separate models. The mean age was 67.2 years; all subjects were men. Overall, 196 (44.9%) subjects had good SRH, and 211 (48.3%) had OV for 16 diseases. PRs for good SRH on practice frequency and amount was 2.34 (95% confidence interval, 1.34-4.09) with high group (reference was low group) and 1.58 (1.18-2.11) with high group. The trend test was also significant. PRs for OV for the endocrine metabolic system on practice frequency was 0.39 (0.16-0.98) with high group. The trend test was also significant. This study suggested that higher practice frequency lead to maintain or improve health status.

The aim of this study was to investigate the effects of the difference in the ways to carry a baby using a baby carrier on the respiratory response during upslope walking. Fourteen healthy adults participated in this study. We set the individualized walking speed at 30% of the maximum oxygen uptake at 0% grade. The test began at 0% grade walking on the treadmill and increased by 2% every 5 min until 8%. The test was performed randomly in these two conditions: holding an infant model weighing approximately 15% of body weight in front of the subject with a baby carrier (F) and backpack with a baby carrier (B). Heart rate (HR), oxygen uptake (VO₂), minute ventilation (VE), tidal volume (TV), respiratory exchange ratio (R), and respiratory rate (RR) were measured and the values from the last 1 min of each grade were averaged. HR, VO₂, VE, TV, R, and RR significantly increased with increasing grade in each condition. There were no significant differences in interaction effects in HR, VO₂, VE, TV, R, and RR. This study suggests that the difference in the ways to carry a baby using a baby carrier has no effects on the respiratory response during upslope walking at a speed corresponding to 30% of the maximum oxygen uptake at 0% grade until 8% grade.