Amplitude and phase response of ventilation (V_E), carbon dioxide output (VCO₂) and oxygen uptake (VO₂) during sinusoidally varying work load for periods (T) of 1-16 min were studied in six healthy men. The relationships between these parameters and aerobic capacity (VO₂max, ATVO₂) were also examined. The results and conclusions obtained were as follows:
(1) The relationship between the period (T) of exercise and amplitude response of VO₂, VCO₂ and V_E was well described by first-order exponential models. However, the relationship between the period of exercise and the phase shift (phase responses of VO₂, VCO₂, and V_E) was better described by complex models comprising a first-order exponential function and a linear equation. This can be explained by Karpman's threshold theory.
(2) High negative correlations were observed between the steady-state amplitude (A) of phase response or the time constants (r) of amplitude response and VO₂max, and ATVO₂. Significantly high negative correlations for all gas exchange parameters may be more rapid in individuals with greater aerobic capacity.
(3) A close relationship between the response of VCO₂ and V_E was demonstrated by a higher correlation coefficient than that between VO₂ and VCO₂ or between VO₂ and V_E. This can be partly, but not completely, explained by the cardiodynamic theory.

A study was conducted for further investigation of the mechanism of notch formation of heart rate (HR) in sudden strenuous exercise (SSE), and rapid increase in stroke volume (SV) right after SSE which were the questions arised in the prior experiment.
Six healthy male students volunteered for the study. A bicycle ergometer was prepared for SSE. The intensity and duration of SSE were 100%VO₂max and 1 min, respectively. Warming-up consisting of 80%VO₂max for 5 min, preceeded SSE. The interval between SSE and warming-up varied from 5 to 30 min. A control experiment was also conducted without warming-up.
The main results obtained were as follows :
1) Diastolic time (DT) temporarily elongated when a notch of HR was formed at the early stage of SSE. Warming-up prevented this formation. No notch was observed throughout total electromechanical systolic time (QS₂), left ventricular ejection time (LVET) or preejection time (PEP) .
2) DT was prolonged immediately after SSE, while LVET, PEPi (PEP index, Weissler's equation) were shortened. PEP/LVET did not change in the initial stage of the recovery period, while electrical systolic time (QT) and QS₂ shortend and QT/QS₂ increased temporarily.
These results suggest the following conclusions :
1) Notch formation observed in heart rate is due to the temporary extension of DT at the early stage of SSE.
2) Decrease in afterload may be the main cause for the rapid increase in stroke volume after SSE, though other factors such as increase in preload, myocardial contractility and sympathetic tone should also be considered.

This study was undertaken to clarify the influence of respiratory blood pressure variability upon the relationship between respiratory period and respiratory cardiac cycle variability. In 4 healthy male university students respiratory period was varied over the range of 6-20 sec while tidal volume was maintained constant (21) and in 5 other male students tidal volume was varied over the range of 1.0-2.5l while respiratory period was maintained constant (6 sec) . For cardiac cycle (RR) and systolic and diastolic blood pressure (SBP and DBP), amplitude of respiratory variability and phase difference between respiratory variability and respiration were measured.
1. Patterns of change of amplitude of RR and of SBP were similar when respiratory period was changed.
2. When respiratory period was short (6sec), RR was nearly in phase with SBP. However, as respiratory period increased, the phases of RR and SBP had a tendency to proceed, with the tendency being more pronounced in the latter. Thus, when respiratory period was prolonged (20 sec), SBP led RR.
3. Phase relationship between respiratory SBP variability and respiration did not change when tidal volume was changed.
4. Respiratory DBP variability became more marked as respiratory period increased, and showed more marked phase shift than did respiratory SBP variability. Therefore, of those parameters DBP occurred earlier.
Based on these results, it is concluded that respiratory RR variability is closely related to respiratory SBP variability when respiratory period is changed, but that the phase difference between RR and SBP reflects the effect of pulmonary stretch reflex which is dependent on respiratory period.

This study was designed to evaluate the effect of exercise duration on the relation between sympathetic and adrenomedullary activities. Six trained subjects completed the following two exercise protocols ; six 2-min exercise sessions at 100% maximal O₂uptake (VO₂max) interspersed with 10-min recovery periods, and three 10-min exercise sessions at 80%VO₂max interspersed with 10-min recovery periods. Plasma noradrenaline (NA), plasma adrenaline (A), NA/A ratio (NA/A), heart rate (HR), coefficient of variation of R-R intervals (CVRR) and blood lactate (La) were measured. With repetition of exercise sessions in both protocols, HR, NA and A gradually increased. CVRR rapidly decreased at the first exercise session and remained unchanged thereafter. NA/A increased by the first exercise session, but decreased by the following exercise sessions. NA in the second exercise session at 100%VO₂max was significantly lower than that in the first. We conclude that, at the beginning of exercise, the increase of sympathetic activity is more dominant than that of adrenomedullary activity, whereas, with prolongation of exercise duration, the increase of adrenomedullary activity becomes more dominant than that of sympathetic activity,

Using near-infrared spectroscopy, we monitored changes of oxygenated hemoglobin and myoglobin contents [oxy (Hb+Mb) ], deoxygenated hemoglobin and myoglobin contents [deoxy (Hb+Mb) ], and total hemoglobin and myoglobin contents [total (Hb+Mb) ] of the thigh muscle at rest and during incremental bicycle exercise and recovery in 10 healthy male volnuteers. Gas exchange parameters were also measured in breath-by-breath mode.
The following results were obtained :
1) During low-intensity exercise (216 kpm/min), oxy (Hb+Mb) increased, while deoxy (Hb+Mb) and total (Hb+Mb) decreased. These changes are thought to reflect an increase in arterial blood flow to the exercising muscle and an increase in venous return.
2) During high-intensity exercise (above 972 kpm/min), oxy (Hb+Mb) decreased, while deoxy (Hb+Mb) increased. These findings probably reflect increased O₂extraction.
3) Upon cessation of exercise, oxy (Hb+Mb) and total (Hb+Mb) increased, and deoxy (Hb+Mb) decreased abruptly. These changes probably reflect post-exercise hyperemia with decreased O₂extraction.
4) Oxy (Hb+Mb) level at ventilatory threshold (VT) was the same as or higher than that of resting condition, indicating that VT occurs when the level of O₂in the vessels of the thigh muscle is relatively high.
5) Spontaneous fluctuation of oxy (Hb+Mb) with frequency of 7-10 cycles/min was observed. This fluctuation was more marked during exercise than during rest or recovery.
These findings suggest that the influence of increased blood flow and venous return on oxy (Hb+Mb), deoxy (Hb+Mb) and total (Hb+Mb) are greater than that of O₂extraction during low intensity exercise, whereas the influence of O₂extraction increases with exercise intensity.
Near-infrared spectroscopy provides valuable information with regard to O₂transport and O₂extraction in the exercising muscle.

The expression levels of heat shock proteins after heat stress on rat slow soleus and fast plantaris muscles were examined and compared during a recovery period following 1 h of heat stress. The left hindlimbs of adult male Wistar rats (n=15) were carefully inserted into a stainless steel can and subjected to heat stress for 1 h by raising the air temperature inside the steel can to 54-58t with a flexible heater so as to bring the muscle temperature up to 42°C. The muscles of the contralateral right hindlimb served as the control. The expression levels of HSP 60, HSP 72, and HSC 73 were analyzed by Western blotting after 0, 2, and 4 h of recovery following 1 h of heat stress. In the soleus muscle, all of the HSP levels analyzed were significantly increased during 0-4 h of recovery. On the other hand, heat stress had no effect on the expression levels of HSPs, except HSP 60, in the plantaris muscle during recovery after 1 h of heat stress. These results suggest that the slow soleus muscle has a higher ablility to respond quickly to heat stress than the fast plantaris muscle.

BACKGROUND: Research has indicated that early postoperative step counts are below the recommended levels for health-enhancing physical activity after total knee arthroplasty (TKA). This study aimed to evaluate the effects of preoperative individual characteristics, pain, physical function, and psychological factors on early postoperative physical activity, as measured by step counts, in 137 patients scheduled for TKA. METHODS: Patients were preoperatively assessed for individual characteristics (age, sex, body mass index, employment status, smoking and drinking habits, long-term care insurance), pain, range of motion, muscle strength, timed 10-m walk test performance, pain catastrophizing scale (PCS) scores (rumination, helplessness, and magnification), and pain self-efficacy. The daily step count was analyzed 4 weeks postoperatively. Multivariate regression analysis was performed to analyze the relationships between postoperative step counts and individual characteristics, pain, physical function, and psychological factors. RESULTS: Step counts were significantly influenced by preoperative PCS magnification scores (β= -0.31, p= 0.01) and the category of long-term care insurance (β= -0.24, p= 0.02). CONCLUSIONS Preoperative evaluation of the long-term care insurance category and PCS magnification score may aid in predicting early postoperative step counts in patients receiving TKA, which may, in turn, improve clinical management during the early stages of treatment.

  Foot baths reportedly reduce pain and improve sleeplessness. In addition, foot baths may induce vasodilation, and thereby improve blood flow, reduce swelling, induce relaxation, and increase deep body temperature. However, the influence of foot baths on energy metabolism and physiological indices are unclear. Therefore, the present study aimed to clarify the effects of foot baths on energy consumption and physiological indices (e.g., heart rate, tympanic temperature, and blood pressure). Nine healthy males were included in this study (age, 23.0±1.0 years; body weight, 66.5±5.6 kg; body fat percentage, 15.1±4.3%). Expired gas composition (i.e., oxygen and carbon dioxide consumption) was analyzed using the Food method in an environmentally-controlled room (room temperature 25°Cand humidity 40%). Subjects were rested in the hood during the measurement. After 30 min rest in the sitting position, a 30 min foot bath was performed, after which the subjects sat for 60 min. Expired gas composition and heart rate were measured over time, and tympanic temperature and blood pressure were measured every 15 min. The foot bath involved immersion of the knees, and the temperature of the water was maintained at 41°C. There were no significant changes in energy consumption after the foot bath, and no significant changes in heart rate, tympanic temperature, and blood pressure. Therefore, our results suggested that there were no significant energy metabolism changes after 30 min of foot bathing at 41°C.