This study determined the phase response and amplitude response (delta) of esophageal temperature (T(es)), mean skin temperature (Tsk), and forearm sweating rate (Msw) to sinusoidal work. Six healthy male subjects exercised on a cycle ergometer with a constant load (approximately 35% maximal O2 uptake) for a 30-min period; for the next 40 min they exercised with a sinusoidal load at 25 degrees C at 35% relative humidity. The sinusoidal load varied between approximately 10 and 60% maximal O2 uptake, and three different time periods (1.3, 4, and 8 min) were selected. Each subject performed three experiments that differed only in the timing of sinusoidal work. During the 4- and 8-min periods, T(es), Tsk, and Msw changed almost sinusoidally. The phase of Msw change significantly preceded those of T(es) and Tsk changes (P < 0.05). During the 1.3-min period, the level of T(es) and Tsk remained almost constant (delta T(es) 0.01 +/- 0.00 degrees C, delta Tsk 0.03 +/- 0.01 degrees C), whereas Msw showed a clear sinusoidal pattern. We conclude that the sweating response during sinusoidal work depends on both thermal and nonthermal factors, the latter being emotional, mental, or sensory stimulation. The contribution of the nonthermal factors to the general sweating response during exercise can be separated from that of the thermal factors by using sinusoidal work during a short period (e.g., 1.3 min).

To evaluate the mechanism of potentiation of sweating after long-term physical training, we compared sweating function in trained and untrained subjects using the frequency of sweat expulsion (fsw) as an indicator of central sudomotor activity. Nine trained male subjects (trained group) and eight untrained male subjects (untrained group) performed 30-min cycle exercise at 35% maximal oxygen uptake at 25 degrees C ambient temperature and 35% relative humidity. Oesophageal temperature (T(oes)), mean body temperature (Tb), chest sweating rate (msw,chest), forearm sweating rate (msw,forearm), and fsw were measured. The slopes of the msw,chest versus body temperature (T(oes) and Tb) and versus fsw relationships in the trained group were significantly greater than those in the untrained group (both, P < 0.05), while there was no difference between the groups in the slopes of the msw,forearm versus body temperature or versus fsw relationships. Neither the body temperature threshold for initiation of chest or forearm sweating nor the slope of the fsw-Tb relationship differed between groups. We concluded that, during light exercise at moderate ambient temperature, the msw,chest in the subjects who had undergone long-term physical training was greater than that in the untrained subjects while the msw,forearm was not changed. The greater msw,chest in the trained subjects was concluded to be due to an increase of sensitivity of peripheral mechanisms.

The purpose of this study was to evaluate the specificity of maximal oxygen uptake (VO2max) and the dynamic response of oxygen uptake (VO2) to sinusoidal work load in distance runners and in American-football players. Sinusoidal work load during ergometer cycling was carried from 30 W to 60% to VO2max (60% VO2max) for a 2 min period. VO2 was measured by the breath-by-breath method. The subjects were 10 distance runners (DRs), 10 American-football players (AFPs), and 11 untrained men (UTM). Mean VO2max was 64.4 mL kg-1 min-1 in the DRs, 53.1 mL kg-1 min-1 in the AFPs and 47.3 mL kg-1 min-1 in the UTM. The fundamental amplitudes of the VO2 response, normalized by dividing by steady state VO2 at 60% VO2max, were similar in the AFPs (20.3%) and the UTM (19.5%), and both were significantly less than in the DRs (25.5%). Phase shift to work load expressed in degrees was similar in the AFPs (87.7 degrees) and UTM (88.0 degrees), but significantly greater than in the DRs (80.4 degrees). HR dynamics in all three groups were similar to a dynamic VO2 response. These findings suggest that development of the dynamic VO2 response and higher VO2max is achieved in the DRs. They also suggest that despite the higher VO2max in the AFPs there is no improvement in the dynamic VO2 response. The results of the present study demonstrate that athletes participating in different sports have characteristic dynamic VO2 responses during cycling exercise.

The present study was undertaken to investigate possible distortion in responses of respiratory variables including O2 uptake (VO2), CO2 output (VCO2), and ventilation (VE) to sinusoidal work load, and to find out whether the conventional transfer models were applicable to analyze the dynamics of these variables. Six healthy subjects performed exercise for 32 min on a bicycle ergometer with electro-magnetic braking. The work load was varied sinusoidally between 30 W and 60% of maximum O2 uptake (VO2max) during periods from 1 to 16 min. The respiratory variables were measured on a breath-by-breath basis with a mass spectrometer and a computer system. The responses of VO2, VCO2, and VE to sinusoidal work load were not completely sinusoidal in form but were somewhat distorted, forming saw-tooth waves with steeper down-slopes during periods of 4-16 min, but this distortion was not observed at 1 min or 2 min periods. However, the results could be approximately described by a first-order model without or with time delay. Time constants of the first-order model without time delay were 46 sec for VO2, 62 sec for VCO2, and 73 sec for VE, respectively. We also found a close relationship between the time constants of VO2 and VCO2 and VO2max. These results suggested that exponential functions may be applied and are expected to yield valid results in assessing physical fitness, although the control of ventilatory and gas exchange in exercise does show non-linear characteristics.

During the application of a wide range of graded lower body pressures (LBP) (-50 to 50 mmHg), we examined how (1) the tissue oxygenation in the lower and upper parts of the body changes at rest, and (2) how tissue oxygenation changes in the lower extremities during dynamical leg exercise. We used near-infrared spectroscopy (NIRS) to measure the changes induced by LBP in total Hb content and Hb oxygenation in seven subjects. At rest, total Hb increased and Hb oxygenation decreased in the thigh muscles during -25 and -50 mmHg LBP, while both decreased during +25 and +50 mmHg LBP. However, in the forearm muscles during graded LBP, the pattern of change in total Hb was the reverse of that in the thigh. Measurements from the forehead showed changes only during +50 mmHg LBP. These results demonstrated that the pattern of change in total Hb and Hb oxygenation differed between upper and lower parts with graded LBP at rest. During dynamical leg exercise, total Hb and Hb oxygenation in the thigh muscles decreased during stepwise increases in LBP above -25 mmHg, Hb oxygenation decreasing markedly during +50 mmHg LBP. These results suggest that during dynamical exercise (i) LBP at +25 mmHg or more causes a graded decline in blood volume and/or flow in the thigh muscles, and (ii) especially at +50 mmHg LBP, the O2 content may decrease markedly in active muscles. Our results suggest that NIRS can be used to monitor in a non-invasive and continuous fashion the changes in oxygenation occurring in human skeletal muscles and head during the graded changes in blood flow and/or volume caused by changes in external pressure and secondary reflexes both at rest and during dynamical exercise.