The purpose of the present study was to examine the associations of replacing accelerometer-measured sedentary behavior (SB) with physical activity (PA) and depression in a sample of Japanese frail older adults using an Isotemporal Substitution (IS) model. Among 139 frail older adults, accelerometer was utilized to identify the daily average time spent in SB, light-intensity PA (LPA), and moderate- to vigorous-intensity PA (MVPA). Depression was assessed using the Geriatric Depression Scale-Short Version-Japanese (GDS-S-J). The relationship between SB, LPA, and MVPA with depression was examined with three models of multiple regression analysis: single factor model, partition model, and IS model. As results, LPA times was negatively associated with GDS-S-J scores in the single factor model (B = -0.09, p = 0.007) and the partition model (B = -0.13, p < 0.001). In the IS model, replacement of 10 minutes of SB with an equal amount of LPA time showed a significant negative association with GDS-S-J scores (B = -0.09, p=0.003). These results suggest that replacing a small amount of SB with LPA may be associated with an improvement in depression in frail older adults.

Prolonged exercise in a hot environment increases the minute ventilation (VE) and respiratory rate (RR) with an increase in core temperature. This hyperthermia-induced hyperventilation decreases the partial pressure of arterial blood carbon dioxide (PaCO₂). Conversely, nasal breathing during exercise has been reported to produce low VE and RR values and high PaCO₂ values; however, no studies have investigated this in hot environments. Therefore, the purpose of this study was to clarify the effect of nasal breathing on estimated partial pressure of carbon dioxide in arterial blood (PaCO_2,estimate) during prolonged exercise in a hot environment. Twelve university endurance athletes participated in the study and performed a 40-minutes steady-state cycling exercise at an intensity of 55% of peak oxygen uptake in a hot environment (room temperature 35℃, relative humidity 40%). Using randomized crossover design, two experiments were performed—nasal breathing condition (NB) and mouth breathing condition (MB). Moreover, physiological indices were measured during the exercise. Rectal temperature increased in both conditions, but there was no significant difference between these conditions. PaCO_2,estimate values were significantly higher in NB between 10 minutes and 40 minutes of exercise (p < 0.05) compared to MB, and decreased with time in MB. Compared to MB, the VE was significantly lower in NB between 30 minutes and 40 minutes (p < 0.05), while the RR was significantly lower in NB between 25 minutes and 40 minutes of exercise (p < 0.05). Therefore, nasal breathing during a prolonged moderate-intensity exercise in a hot environment prevented the decrease in PaCO_2,estimate due to hyperthermia-induced hyperventilation.

Since the rectus femoris muscle is associated with trauma and disorders such as muscle strain, it is often a target for evaluation and treatment. However, in many studies, measurement results were obtained from only a part of the rectus femoris muscle and used as a representative value without considering the differences across the muscle. The rectus femoris muscle may change shape with knee flexion because the structure is complicated; it has an intramuscular tendon. The purpose of this study was to assess the changes in shape of the rectus femoris muscle during flexion of the knee joint in different directions. Twelve lower limbs of 12 male university students were analyzed. The rectus femoris muscle was divided into eight parts, and short-axis images were taken with an ultrasonic diagnostic imaging device at the knee joint; in extension; flexion at 30 °, 60 °, 90 °, and 120 °; muscle thickness; muscle width; and cross-sectional area. It was suggested that the thickness of the rectus femoris muscle increased from “A” to “F” due to knee flexion, and that this increase occurred because of stretching at the same site. In “G,” there was no difference between the angle conditions; conversely, in “H,” the muscle thickness decreased due to knee flexion. It should also be noted that D and E have the greatest muscle thickness when measuring in the knee flexion position.

This study aimed to examine whether a single ingestion of arginine activates the mammalian target of rapamycin complex 1 (mTORC1) in rat fast- and slow-twitch skeletal muscles. In the first experiment, the rats were orally administered arginine (3 or 10 mmol/kg body weight) in water. The plantaris, gastrocnemius, and soleus muscles were excised 1 h after the administration. Immunoblot analysis showed that the administration with a higher dose (10 mmol/kg) resulted in increased phosphorylation of ribosomal S6 kinase (S6K) and ribosomal protein S6 only in the soleus muscles. The amounts of cellular arginine sensor for mTORC1 subunit 1 (CASTOR1) expressed were similar in these three muscles. In the second experiment, the plantaris and soleus muscles were excised 1 h after the administration of 10 mmol/kg of arginine. The binding of CASTOR1 to the GATOR2 complex was not detected in either muscle in co-immunoprecipitation and immunoblot analyses, irrespective of arginine administration. In the third experiment, a role of nitric oxide (NO) was elucidated. Treatment with an inhibitor of NO synthase blocked the arginine-induced increase in S6K phosphorylation. These results indicate that a single ingestion of arginine is capable of activating mTORC1 only in slow-twitch muscles and suggest that the activation may be mediated via NO, but not via the CASTOR1-GATOR2 complex pathway.

To create a safe and effective aerobic dance exercise (ADE) program, the intensity, and difficulty level of each step, and muscle activation during the program must be considered. This study evaluated the muscle activity levels of the lower extremities when major ADE movements were repeated at a fixed speed. The subjects were seven females 21-22 years old who were familiar with the ADE movements. Eleven low impact steps and nine high impact steps representative of the ADE movements were selected, and while the movements were performed, the surface electromyograms (EMG) of six muscles in the lower extremities were measured using a telemeter electromyograph. The EMG data for 10 cycles of each step were full wave rectified and integrated. Then, the average value per unit time was calculated, and normalized (%EMGmax) by the EMG integral value during isometric maximum voluntary contraction (EMGmax). The EMGmax was measured for each of the six muscles to evaluate the muscle activity level, and determine which muscles were activated at higher or lower levels in response to the specific steps. The highest levels of total muscle activity detected in the six muscles were for: double hop, jumping jack, and pendulum. The results of this study may help create ADE programs that consider the differences in muscle activation in the lower extremities.

We investigated the effect of anodal transcranial direct current stimulation (anodal tDCS) on the performance of full-effort box stepping exercises in athletes and non-athletes. Twenty-one subjects (athletes: five men and six women, non-athletes: four men and six women) participated in this study. tDCS was applied through two electrodes placed on the vertex (anode) and the forehead (cathode). A 2-mA anodal stimulation was applied for 15 minutes, while sham stimulation was applied on different days with similar electrodes. Participants were asked to apply a maximal effort while stepping up and down a 10-cm tall box for 20 s following termination of the tDCS. The 20 s box stepping was repeated three times with 15 s of rest. The number of total steps was significantly increased following anodal tDCS compared to sham tDCS. The degree of increase in performance was more prominent in non-athletes than in athletes. In non-athletes, a differential pattern of fatigue in performance between stimulus conditions was observed. In contrast, this significant performance modulation between stimulus conditions was not detected in athletes. Our findings of improved stepping performance following anodal tDCS depended on the training level of the subject group; this implies modulation of descending command from CNS to active muscles by tDCS. It is suggested that the degree of neural modulation for controlling complex and full-effort leg movements due to tDCS is higher in non-athletes than in athletes.