The purpose of this study was to investigate the relationships between force fluctuation during isometric plantar flexion and the sustainable time for single-leg standing. Fourteen healthy males (21±1 years) performed unilateral (preferred leg) force matching tasks and single-leg quiet standing. Force matching tasks were performed to maintain isometric plantar flexion for 15 s at levels corresponding to 10% and 20% maximal voluntary contraction (MVC) with the visual feedback of force. Force fluctuation during force matching tasks was quantified as the standard deviation of force. Sustainable time for single-leg quiet standing was performed to maintain a single-leg quiet standing barefoot on a platform using the preferred leg with their eyes closed. Force fluctuation was significantly greater in 20% MVC task compared to 10% MVC task. The sustainable time for single-leg quiet standing was strongly correlated with force fluctuation in 20% MVC task (r=−0.56, p=0.04). However, it was not related to force fluctuation in 10% MVC task (r=0.19, p=0.52) or MVC value (r=0.13, p=0.65). These results suggest that a specificity of contraction intensity is observed between force steadiness and the posture stability during single-leg quiet standing; force steadiness during 20% MVC plantar flexion is one of the important components for posture stability during single-leg quiet standing.
Strength training has been reported as a potentially useful exercise to improve psychological aspects in the elderly, but its effects remain controversial. This study investigated the effectiveness of strength training conducted twice a week for 12 weeks for improving health-related quality of life (HRQOL) and executive cognitive function. The study was a single-blind randomized controlled trial with assessments before and after intervention. HRQOL and executive function were assessed using the SF-36 Health Status Survey and a computerized neuro-cognitive assessment using task-switch reaction time trials, respectively. Subjects comprised 119 participants ≥65 years old, randomized to either strength training (n=65) or health education classes (controls, n=54). The strength training program was designed to strengthen the large muscle groups most important for functional activities and to improve balance. The effects of the intervention on the eight dimensions of the SF-36 in the control and training groups were analyzed. Only the mental health scale of the SF-36 was significantly improved for the training group compared with controls after 12 weeks. Task-switch reaction time and correct response rate remained unchanged. Short-term strength training might have modest positive effects on HRQOL, although this training period may not be sufficient to affect executive function in relatively healthy older people.
This study examined the influences of the oral ingestion of casein hydrolysate from bovine milk at rest physiologically and psychologically. Eleven male university students were given a casein hydrolysate drink (H) or a maltitol drink as a control (C) in a crossover study. Just before and one hour after ingestion of each drink, the total-hemoglobin (tHb) concentrations at ten points of the prefrontal cortex to evaluate cerebral activity, and heart rate variability (HRV) to evaluate autonomic nerve activity through spectral analysis were measured as physiological indicators. The Japanese version of the State—Trait Anxiety Inventory—state anxiety (STAI-s) score was also used, as a psychological indicator. In comparison between H and C ingestion, a significant difference is observed only in tHb concentrations at one of ten points. At this point, the change in tHb concentration was lower after H ingestion compared to C ingestion. And in comparison between before and after ingestion of each drink, a significant increase in tHb concentration at two points after C ingestion, a significant increase in parasympathetic activity and decrease in sympathetic activity after H ingestion, and a significant decrease in STAI-s score in H ingestion were observed. These results suggest that ingestion of the casein hydrolysate may keep prefrontal cortex activity stable while maltitol ingestion partially increases the activity. Moreover, there is a possibility that casein hydrolysate might decrease sympathetic activity, increase parasympathetic activity, and lower anxiety. We conclude that the bovine milk casein hydrolysate may have more relaxing effects than maltitol.
To express intensity of physical activity, energy expenditure is often divided by either body weight, resting metabolic rate, or fat-free mass. These calculations are used widely as the physical activity index. However, it is unclear how body size influences the valid estimation of intensity of various kinds of activities. In the present study, we investigated whether these indices are able to adjust for body size when calculating energy expenditure in various kinds of activities. In addition, we examined to what extent the error of index is introduced by differences in body size. Resting metabolic rates and energy expenditure during sitting light work, 4 lifestyle and 7 ambulant activities were measured in the postabsorptive state using indirect calorimetry in 71 healthy Japanese adults. We regarded an index as an inappropriate adjustment for body size when there was a significant correlation between it and body weight. Energy expenditure normalized by body weight correlated with body weight in all sedentary states; when normalized by lying resting metabolic rate it correlated with body weight in 3 ambulant activities; when normalized by sitting resting metabolic rate it correlated with body weight in 2 lifestyle and 5 ambulant activities; and when normalized by fat-free mass it correlated with only 1 ambulant activity. The indices caused errors in estimates of activity intensity of less than ±10% when body weight was more than 10 kg above average. In conclusion, the body weight-normalized index was inappropriate for sedentary activities and the other three indices were inappropriate for ambulant activities. However, the use of any of these indices introduces an error in the estimate of total energy expenditure of considerably less than ±10% for body weights within the normal range.
To test the hypothesis that pupil diameter, which is innervated by the autonomic nervous system, increases with exercise intensity, we determined pupil diameter during incremental exercise in eight healthy subjects. The subjects performed an incremental ergometer exercise in a room illuminated at 90–100 lx. We continuously measured pupil diameter and heart rate before, during, and after the exercise. Pupil diameter increased significantly with exercise intensity (except at the lowest intensity), peaking at 113±3% (mean±SE) of the diameter during the resting baseline period. The diameter did not differ significantly between the resting baseline and recovery periods. These findings suggest that exercise enlarges pupil diameter and that the magnitude of dilation is related to exercise intensity.