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Neuromuscular electrical stimulation (NMES) induces involuntary muscle contraction, preferentially promotes anaerobic metabolism, and is applicable for increasing exercise intensity. This study aimed to assess whether superimposing NMES onto moderate-intensity voluntary exercise imitates physiological adaptations that occur in response to vigorous voluntary exercise.Eight participants trained with a cycling ergometer at 100% of the ventilatory threshold (VT) (73.3% of peak oxygen consumption) (VOL), and another nine participants trained with the cycling ergometer at 75% of VT (56.2% of peak oxygen consumption) with subtetanic NMES applied to the gluteus and thigh muscles (VOLES), matched to VOL training sessions, for nine weeks.Rating of perceived exertion (RPE) in VOLES (12.00 ± 1.50) was significantly lower than in VOL (14.88 ± 1.81) (p 0.05) during training sessions. Peak power output during the exercise tolerance test was increased in VOL and VOLES following interventions. Oxygen consumption and heart rate (HR) at VT and blood lactate concentration (BLC) at VT were decreased from before (PRE) to after (POST) training interventions for both VOL and VOLES. There were no significant differences in absolute changes from PRE to POST for peak power output and oxygen consumption, HR, and BLC at a submaximal intensity between VOL and VOLES.Our results suggest that both superimposing subtetanic NMES onto moderate-intensity voluntary exercise and vigorous voluntary intensity exercise induce the improvement in cardiovascular and metabolic systems, but the adaptation of former method is provided without perceived strenuous exertion.

We aimed to test the effect of additional electrical muscle stimulation (EMS) during moderate-intensity voluntary pedaling exercise on metabolic and cardiovascular responses. Eleven healthy male subjects performed moderate-intensity pedaling exercise at a constant workload (80 % of ventilatory threshold) for 20 min while EMS was applied to thigh muscles from 5 to 10 min and from 15 to 20 min during the exercise. A significantly higher oxygen uptake (VO2), heart rate, and respiratory gas exchange ratio were observed during the exercise periods with EMS despite the constant workload. These changes were accompanied by an elevated blood lactate concentration, suggesting the existence of additional fast-twitch motor unit (MU) recruitment during the exercise with EMS. Our data suggest that the use of intermittent EMS during a constant load exercise mimics the high-intensity interval training, possibly due to additional fast-twitch MU recruitment and co-contractions of the quadriceps and hamstrings muscles, leading to higher anaerobic metabolism and a lower mechanical efficiency.

The aims of this study were (1) to evaluate changes in muscle activity associated with physiological fatigue and decreased swimming velocity (SV) during 200 m of front crawl swimming, and (2) to examine the relationship between the decreased SV and changes in kinematic or electromyogram parameters. Twenty swimmers participated in a 4 × 50-m swim test. The surface EMG of 11 muscles (7 in the upper limbs and 4 in the lower limbs) was measured and the mean amplitude value (MAV) for one stroke cycle was obtained. The SV and arm angular velocity (AAV) of shoulder flexion during the first (early stroke) and second (late stroke) half of the underwater arm stroke were analyzed using an underwater camera. The AAV, the MAV of flexor carpi ulnaris (FCU), biceps brachii (BB), and triceps brachii during the early stroke, and the MAV of rectus femoris decreased along with a decrease in SV. In contrast, the MAV of the pectoralis major (PM) increased significantly in the final 50 m. The rate of change in MAVs (ΔMAVs) of FCU, BB and latissimus dorsi during the early stroke, and ΔMAV of biceps femoris were significantly correlated with ΔSV and/or ΔAAV. Positive correlations were identified between ΔMAVs of several muscles. However, no negative correlations were observed between ΔMAVs. These results suggest that the decrease in SV was related to decreases in the activities of several muscles that coordinated with each other, and that a compensating strategy occurred between PM and other muscles in the final 50 m.

Tremendous numbers of heart rate variability studies have aimed to elucidate age-associated alterations of autonomic function in the past decades. However, the studies, far from clarifying ageing mechanisms, fell into confusion by a lack of common scales. The purpose of this study is to show a possibility to establish a comparative scale of autonomic function through a method, tone-entropy (T-E) analysis on heart period variation, whose validity has been already examined on typical physiological cases (Oida et al. in J Appl Physiol 82:1794-1801, 1997; Oida et al. in J Gerontol 54A:M219-M224, 1999a; Oida et al. in Acta Physiol Scand 165:129-134, 1999b; Oida et al. in Acta Physiol Scand 165:421-422, 1999c; Amano et al. in Eur J Appl Physiol 94:602-610, 2005). In this study, 276 subjects from teens to seventies were examined at rest by T-E analysis together with conventional time and frequency domain analyses. The tone (negativity represents vagal predominance) became significantly high [-0.174 +/- 0.026 (teens) to -0.024 +/- 0.004 (seventies), P0.05 for one-way ANOVA], and the entropy (total autonomic activity), significantly low [4.40 +/- 0.12 (teens) to 2.90 +/- 0.09 bit (seventies), P0.05] with advancing age. The result, plotted in 2-D T-E space, showed that the ageing traced a curvi-linear relation from right-bottom to left-top, and was consistent with previously studied typical physiological cases. The conventional analyses showed almost the same autonomic reduction as T-E did, but failed in detecting delicate alteration of autonomic balance. The results, showing that autonomic activity reduced in both pathways impairing vagal predominance significantly with ageing, suggested a possibility to assess autonomic function in 2-D T-E space in a comparative way.

Reductions in tonic vagal controls of the heart and depressed baroreflex sensitivity (BRS) have been associated with a postural fall in blood pressure (BP) and the incidence of cardiac events among older people. We examined the hypothesis that BP regulation during orthostatic challenge as well as heart rate variability (HRV) at rest can be better maintained in long-term exercise-trained, healthy, older men (aged 60-70 years). Subjects were classified into two groups; long-term exercise-trained (LTET, n=14) and sedentary (SED, n=10) according to their history of physical activity. Prior to the dynamic BRS assessment, supine resting autonomic cardiac modulation was assessed by means of time domain HRV [standard deviation of ECG R-R interval (RRISD) and the coefficient of variation (CV)]. The BRS was assessed during 60 degrees head-up tilting by simultaneously measuring beat-by-beat systolic blood pressure (SBP) and ECG R-R interval changes. The BRS gain was determined by the regression slope coefficient based on the extent of the SBP fall and the corresponding ECG R-R shortening during the orthostatic challenge. The results indicated that the LTET group manifested greater ECG R-R interval fluctuations with significantly higher resting RRISD and CV, compared with the SED group [59.5 (10.4) versus 27.7 (7.8) ms, p0.05; 5.5 (0.8) versus 2.8 (0.7)%, p0.05], respectively. Using dynamic BRS testing during the acute orthostatic challenge, the LTET group showed a significantly higher BRS gain than the SED [6.4 (0.8) versus 3.8 (0.6) ms x mmHg(-1), p0.017] group. These results indicate that CV and BRS are well maintained in healthy, LTET older individuals when compared with their sedentary peers. Our data suggest that this augmented autonomic cardiac modulation reflects better parasympathetic responsiveness in LTET individuals. Data provide further support for long-term exercise training as another possible cardioprotective factor that might decrease susceptibility to ventricular fibrillation as well as assist arterial BP at the onset of an orthostatic challenge in older men.

The effects of caffeine ingestion on the activities of the autonomic nervous system (ANS) during endurance exercise at low intensity were investigated using a power spectrum analysis of heart rate variability. Placebo or caffeine (300 mg) capsules were randomly administered to the subjects. Each subject ingested the samples 2 h before cycling on an ergometer for 30 min at an intensity corresponding to 40%-50% of his ventilatory threshold. The electrocardiogram, blood pressure (BP) and gas exchange parameters were monitored during rest and exercise. The results indicated that there were no significant differences in heart rate and systolic blood pressure between the trials. The spectrum integrated values of the low frequency power and total power components in the caffeine trial were significantly greater than in the placebo trial during exercise, which implied that activities of the ANS were augmented by caffeine. Caffeine also induced enhanced lipid oxidation as shown by the significantly lower respiratory gas exchange ratio and increases in diastolic blood pressure during exercise. The results shed some light upon the relationship between the activity of the ANS, energy metabolism and BP. In conclusion, the results suggest that caffeinated beverages have a potential to be useful supplements to the prescription of exercise for individuals who experience a depressed activity of the ANS. The results also suggest that the experiment protocol used in this study is a sensitive and noninvasive method for evaluating the effects of various foods and nutrients on the activity of the ANS.

To elucidate whether combined adrenergic and parasympathetic blockade would affect the ventilatory response to exercise, especially at the initial stage (phase I), six healthy subjects performed a brief and light voluntary bilateral leg extension exercise and passive movements under the conditions of control (before the blockade) and after intravenous administration of combined beta-adrenergic (propranolol, 0.2 mg.kg-1) and muscarinic (atropine, 0.04 mg.kg-1) receptor antagonists. The movements were continued only within two breaths after the onset of the motion. Ventilation increased immediately and significantly (P < 0.05) within the first breath at the onset of voluntary exercise in all conditions as compared with at rest. However, the magnitude of increase in mean ventilation within two breaths at the start of exercise as against the resting value (delta ventilation) was significantly less (P < 0.05) after the combined blockades (2.5 l.min-1) than in the control condition (3.7 l.min-1). Passive movements showed a similar but smaller change as compared with voluntary exercise. The heart rate response to exercise was attenuated by the combined blockade while cardiac output showed a slight change at the onset of exercise. It is concluded that phase I should occur despite the inhibited activity of the beta-adrenergic and the cholinergic systems; nevertheless, the response was attenuated by the combined blockade. These results suggest a possible role of the beta-adrenergic and/or cholinergic systems in the rapid increase in ventilation that occurs at the start of exercise.

The purpose of this study was to determine the walking speed which has the greatest influence on neural relaxation in healthy elderly women as determined by electromyogram (EMG) and electroencephalogram (EEG) analyses. Seven elderly female volunteers [mean age 68.5 (SD 3.95) years] served as subjects for this study. The EMG signals were recorded from the gastrocnemius (MG), soleus (SL) and tibialis anterior (TA) muscles while walking on a treadmill, starting at 40␣m · min−1 and increasing 6 m · min−1 incrementally for 10␣min. The turning point of muscle activities (by integrated EMG, iEMGtp) was determined as the walking speed at the point at which the mean rate of change of iEMG (MG + SL + TA) abruptly increased. After the determination of iEMGtp, the treadmill was set at three constant speeds, one corresponding to the speed for the iEMGtp and two others 20% higher or lower than that for the iEMGtp. The subjects then walked for 20 min at each of these speeds on 3 separate days and their EEG power spectrum data were obtained for frequencies from the 8 to 13 Hz (α-wave component, AWC). The mean of iEMGtp for our subjects was at a mean walking speed of 64.7 (SD 7.9) m · min−1. Considering the subjects' age and height, iEMGtp was somewhat faster than their expected self-paced normal walking speed. There were no differences between the mean AWC values of the subjects prior to exercising at each of the three speeds. The mean AWC values after exercise were significantly (P

The present study examined whether the mechanomyogram (MMG) could assess the fatigue-related changes in muscle mechanical properties during cycle exercise. In eight male subjects, the MMG signals were measured in vastus lateralis and rectus femoris by electret condenser microphones. It was found that the integrated MMG (iMMG) showed non linear increase against workload during continuous, incremental cycle exercise and the onset of abrupt changes in iMMG coincided with the ventilatory threshold (VT). Specifically, iMMG in vastus lateralis showed a significant decrement in the rate of increase against workload above VT, reflecting the fatigue-induced impairment of contractile properties of the fibers of active motor units. These results suggest that the MMG measured by electret condenser microphone could be practically used to retrieve the fatigue-related changes in muscle mechanical properties during cycle exercise.

To examine the orthostatic influence on heart rate and blood pressure variability in persons with tetraplegia playing wheelchair basketball, ten trained persons with tetraplegia, ten untrained persons with tetraplegia, and ten able-bodied participated in this study. Spectrum analysis of the ECG R-R interval and blood-pressure on a beat-by-beat basis during head-up tilt 60 degrees sitting were performed. The ratio of the high frequency to total frequency (HF/TF) in the R-R interval decreased from supine (0.5 +/- 0.2) to sitting (0.3 +/- 0.2), and the low frequency (LF) power in systolic blood pressure increased from 4.7 +/- 9.1 to 15.0 +/- 13.1 mmHg(2) only in the untrained persons with tetraplegia (P0.01). The decrease in the HF/TF ratio in the untrained persons with tetraplegia indicates attenuated parasympathetic activity to the orthostatic challenge and the similar increase in LF power indicate that parasympathetic activity was reduced and sympathetic activity increased only in these persons. These results suggest that training enhances cardiovascular stability in tetraplegic subjects.

The present study investigated the activity of the autonomic nervous system (ANS), a major influence in normal physiological function, and its association with unfavorable postmenopausal states in body composition, lipid and/or glucose metabolism, or cardiovascular profiles. Body composition, blood pressure, and blood profiles of lipid and glucose of 175 postmenopausal women were measured. Resting ANS activity was assessed by heart rate variability (HRV) power spectral analysis. To scrutinize the influence of ANS activity levels on postmenopausal obesity-related factors, we divided the subjects into a low group ( 220 ms(2)), based on the total power of HRV. Low-frequency (P < 0.01) and high-frequency power (P < 0.01) were both significantly lower in the low group. No significant difference was found in age, age at menopause, or years after menopause between the two groups. In contrast, body mass index (P < 0.05), percentages of body fat (P < 0.01), and systolic (P < 0.01) and diastolic (P < 0.01) blood pressure were significantly greater in the low group. As to blood lipid profiles, triglycerides (P < 0.05), total cholesterol (P < 0.05), and low-density lipoprotein cholesterol (P < 0.05) were significantly higher in the low group. Our findings indicate that reduced sympatho-vagal activity is associated with higher postmenopausal body fat content, blood pressure, and blood lipid concentrations. This study further implies that such autonomic depression could be a crucial risk factor in undermining the health and, ultimately, the quality of life, of postmenopausal women.

Through our recent studies on heart rate variability (Oida et al. J Appl Physiol 82:1794-1801, 1997; J Gerontol 54A:M219-M224, 1999a; Acta Physiol Scand 165:129-134, 1999b; Acta Physiol Scand 165:421-422, 1999c), we discover that autonomic functions could be assessed quantitatively in time domain by the tone-entropy (T-E) methodology, where the tone represents sympatho-vagal balance, and the entropy, autonomic regulatory activity. The purpose of this study was then to elucidate an age-associated alteration of sympatho-vagal balance in a female population through this T-E method. ECG R-R time intervals at rest were acquired on 10 min for 73 female subjects. Ageing influence was examined by comparisons between two groups: middle-aged group (40-50), (51.5 +/- 0.7 year, n = 28) and old-aged (60-70), (69.5 +/- 0.8 year, n = 45)]. Evaluated tone: [-0.058 +/- 0.011 (40-50), and 0.027 +/- 0.003 (60-70) (P < 0.01)], and entropy: [3.46 +/- 0.11 (40-50), and 3.06 +/- 0.08 bit (60-70) (P

The purpose of the present study was to determine whether reaction time (RT) for the peripheral visual field increases at exercise intensity above the ventilatory threshold (VT) during incremental exercise and to examine the relationship between aerobic capacity and the extent of increase in the RT. Nine healthy subjects performed a simple manual RT task for the peripheral visual field at rest, during exercise on a cycle ergometer, and immediately after exercise. After warm-up exercise, the subjects cycled at 40 W for 3 min, increasing by 40 W every 3 min until 240 W in a step-wise manner. During incremental exercise, RT measurements were performed 1 min and 30 s after the start of every increase in workload. The RT for the peripheral visual field significantly increased at exercise intensity above VT, as compared with at rest. The increase in the RT, which was calculated by subtracting the RT at rest from the RT at 240 W, negatively correlated with maximal oxygen uptake $$\left( {\dot V{\text{O}_{2 \max}}} \right)$$ for each subject (r=−0.73, P

The purpose of this study was to elucidate the responses of the mechanomyogram (MMG) from two apparently different muscles (biceps brachii and soleus) during a sustained voluntary contraction at 50% maximum voluntary contraction. The MMG and surface electromyogram (EMG) were recorded from human biceps brachii and soleus during sustained elbow flexion and plantar flexion, respectively. Results indicated that the slope coefficient of rise in EMG amplitude as a function of time for the biceps was significantly greater than that for the soleus (P

We have investigated the etiology of lower-back muscle fatigue using simultaneous recordings of electromyography (EMG), mechanomyography (MMG), and near-infrared spectroscopy (NIRS) in an attempt to shed some light on the electrophysiological, mechanical, and metabolic characteristics, respectively. Eight male subjects performed isometric back extensions at an angle of 15 degrees with reference to the horizontal plane, for a period of 60 s. Surface EMG, MMG and NIRS signals were recorded simultaneously from the center of the erector spinae at the level of L3. NIRS was measured to determine the level of muscle blood volume (BV) and oxygenation (Oxy-Hb). The root mean square amplitude value (RMS) of the EMG signal was significantly increased at the initial phase of contraction and then fell significantly, while mean power frequency (MPF) of the EMG signal decreased significantly and progressively as a function of time. There were also significant initial increases in RMS-MMG that were followed by progressive decreases at the end of fatiguing contractions. MPF-MMG remained unchanged. Muscle BV and Oxy-Hb decreased dramatically at the onset of the contraction and then remained almost constant throughout the rest of the contraction. These results, obtained by simultaneous recordings of EMG, MMG, and NIRS, demonstrate that the restriction of blood flow due to high intramuscular mechanical pressure is one of the most important factors in muscle fatigue in the lower-back muscles. In addition, the simultaneous recording system described here can be used to obtain more reliable information regarding the mechanism(s) of lower-back muscle fatigue.

Non-invasive measurement of arterial pulse wave velocity (PWV) is used to diagnose peripheral vascular disease. We examined the relationship between PWV and risk factors related to peripheral vascular disease [body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), serum total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-C), atherogenic index (AI) and blood glucose (GLU)] in 45 healthy male volunteers, aged 25-85 years. The correlation coefficient of PWV with age was r = 0.46, and the correlation coefficients of PWV with DBP, AI and GLU were r = 0.71, 0.56, and 0.22, respectively (P < 0.05). Multiple linear regression analysis revealed that 67% of the variance in PWV could be accounted for by these three variables. The relative contributions of DBP, AI and GLU to PWV were 66%, 26% and 8%, respectively. To test the applicability of PWV for clinical use, a multiple regression equation of PWV derived from these three variables was then applied to male patients with hypertension (n = 53), hyperlipidaemia (n = 35) or hyperglycaemia (n = 39). The results suggest that the multiple regression equation of PWV is an indicator that discriminates between these patient categories and healthy men.