Muscle sympathetic nerve activity (MSNA) was measured directly along with blood pressure at rest in 69 healthy women (20–79 yr old) and 76 age-matched healthy men (16–80 yr old). All were nonobese and normotensive. In the women and men the MSNA was positively correlated with age (women: y = 0.788 x − 5.418, r = 0.846, P < 0.0001; men: y = 0.452 x + 12.565, r = 0.751, P < 0.0001). The regression intercept of y was significantly lower ( P < 0.0001) in the women than in the men, and the regression slope was significantly steeper ( P < 0.0001) in the women. The MSNA was lower in women than in men among those <30 ( P = 0.0012), 30–39 ( P = 0.0126), and 40–49 yr old ( P = 0.0462) but was similar in women and men among those 50–59 ( P = 0.1911, NS) and ≥60 yr old ( P = 0.1739, NS). The results suggest that MSNA increases with age in women and men and that the activity is markedly lower in young women than in men but is markedly accelerated with age.

We microneurographically recorded muscle sympathetic nerve activity (MSA) during sleep in 12 healthy volunteers while simultaneously recording EEG, EOG, ECG, respiration, and blood pressure and determined the number of pulse-synchronous MSA bursts per minute (burst rate) for non-rapid eye movement (nonREM) sleep and rapid eye movement (REM) sleep. MSA decreased during nonREM sleep with progressively deeper sleep stages. During REM sleep, the burst rate of MSA increased and was associated with marked fluctuations in arterial blood pressure. During sleep stage 2, MSA bursts occurred approximately 1 second after spontaneous K-complexes. We conclude that (1) the decreases in MSA during nonREM sleep stages may indicate sleep-stage dependent central suppression of MSA activity; (2) increases in MSA during REM sleep suggest instability of the autonomic nervous system; and (3) a common pathway may exist for MSA bursts and K-complexes.

Muscle sympathetic nerve activity (MSA) was recorded microneurographically from the tibial nerve in 40 healthy male subjects aged 18 to 75. Passive and graded head-up tiltings were loaded on the subjects. The effects of aging on the resting activity of muscle sympathetic nerve in supine position at rest (burst number per minute), increase in MSA from the resting level by orthostasis (slope of the regression line between sine of the tilt angle and MSA bursts per minute), and the MSA in upright standing position were analyzed. The resting MSA increased with age, and a significant positive correlation was observed between age and resting activity (Y = -6.83 +/- 0.876X, r = .882, p less than .001). The MSA was enhanced by head-up tilt linearly with the sine of the tilt angle, and a significant negative correlation was observed between age and the MSA increase by orthostasis (Y = 57.6 - 0.582X, r = . 843, p less than .001). Standing MSA increased significantly but less remarkably than resting MSA. It was concluded that aging increases the resting activity, but there is less increase in the standing activity of sympathetic outflow to muscles in humans.

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SR appears to represent muscle hardness changes in response to contraction intensity changes, in the assumption that the gastrocnemius muscle contraction intensity is proportional to the plantar flexion intensity. We concluded that gastrocnemius muscle hardness changes could be validly assessed by SR, and the force-hardness relationship was not linear.

In this study we attempted to determine the effects of exercise training at the intensity corresponding to lactate threshold (Thla-) on various health-related variables in sedentary but apparently healthy elderly subjects. Six men and five women volunteers [mean age 68.9 (SD 3.4) years] performed supervised endurance-type training on stationary cycle ergometers for 30 min and recreational activities for 30 min, 3 days a week for 12 weeks. Four men and four women served as the control group [68.8 (SD 4.4) years]. As a result of the training programme, statistically significant increases in maximal oxygen consumption (10%), oxygen consumption at Thla- (18%), distance covered in 12-min walk, side step, and leg extensor power were found in the training group, while no changes occurred in the control group. The changes in serum cholesterol and triglyceride concentrations from the pre- to post-training period were statistically significant. High-density lipoprotein cholesterol remained unchanged, and low-density lipoprotein cholesterol tended to decrease following the training programme. These data would indicate that exercise training at the intensity corresponding to Thla- may have favourable effects on overall physical fitness and some serum lipid variables in older individuals.