Comparing thermoregulatory responses between short and long moderate intensity intermittent exercise protocols with the same duty cycle.

To date, the thermoregulatory response between continuous and intermittent exercises has been investigated whilst limited studies are available to examine the thermoregulatory responses between different modes of intermittent exercises. We sought to determine the effect of two patterns of short duration intermittent exercises (180:180 (3-min) and 30:30 s (30-s) work: rest) on thermoregulatory responses in a temperate environment (25 °C, 50% RH, vapor pressure: 1.6 kPa) with low airflow (0.2 m/s). Twelve male participants (Age:24.0(5.0) year; VO2max: 53(8) mL.kg-1.min-1; BSA:1.7(0.1) m2) cycled at 50% VO2max for 60 min in 3-min and 30-s intervals to result in the same 30-min net exercise duration. Core and skin temperatures, the percent increase of skin blood flow (forearm and chest) from baseline and local sweat rate (forearm and chest) were not different between 3-min and 30-s (all P > 0.35) from the onset of exercise to the end of the exercise. Similarly, the mean body temperature onsets of skin blood flow (forearm and chest) and local sweat rates (forearm and chest) were not different between different mode of intermittent exercises (all P > 0.1). Furthermore, thermal sensitivities of skin blood flow (forearm and chest) and local sweat rate (forearm and chest) with increasing mean body temperature were not different between different mode of intermittent exercises (all P > 0.1). We conclude that intermittent exercises with different work periods at moderate exercise intensity did not alter core temperature and thermoeffector responses in a temperate environment. (241/250).

Superficial venous vascular response of the resting limb during static exercise and postexercise muscle ischemia.

Superficial venous vascular response to exercise is mediated sympathetically, although the mechanism is not fully understood. We examined whether sympathetic activation via muscle metaboreflex plays a role in the control of a superficial vein in the contralateral resting limb during exercise. The experimental condition involved selective stimulation of muscle metaboreceptors: 12 subjects performed static handgrip exercises at 45% maximal voluntary contraction for 1.5 min followed by a recovery period with arterial occlusion of the exercise arm (OCCL). For the control condition (CONT), the same exercise protocol was performed except that the recovery period occurred without arterial occlusion. Heart rate (HR) and mean arterial blood pressure (MAP) were measured. The cross-sectional area of the basilic superficial vein (CSAvein) and blood velocity (Vvein) in the resting upper arm were measured by ultrasound while the cuff on resting upper arm was inflated constantly to a subdiastolic pressure of 50 mm Hg. Basilic vein blood flow (BFvein) was calculated as CSAvein × Vvein. During exercise under both OCCL and CONT, HR and MAP increased (p < 0.05), while CSAvein decreased (p < 0.05). During recovery under OCCL, HR returned to baseline, but the exercise-induced increase in MAP and decrease in CSAvein were maintained (p < 0.05). During recovery under CONT, HR, MAP, and CSAvein returned to baseline. BFvein did not change during exercise or recovery under either condition. These results suggest that sympathoexcitation via muscle metaboreflex may be one of the factors responsible for exercise-induced constriction of the superficial veins per se in the resting limb.

Tendon vibration attenuates superficial venous vessel response of the resting limb during static arm exercise.

BACKGROUND: The superficial vein of the resting limb constricts sympathetically during exercise. Central command is the one of the neural mechanisms that controls the cardiovascular response to exercise. However, it is not clear whether central command contributes to venous vessel response during exercise. Tendon vibration during static elbow flexion causes primary muscle spindle afferents, such that a lower central command is required to achieve a given force without altering muscle force. The purpose of this study was therefore to investigate whether a reduction in central command during static exercise with tendon vibration influences the superficial venous vessel response in the resting limb. METHODS: Eleven subjects performed static elbow flexion at 35% of maximal voluntary contraction with (EX + VIB) and without (EX) vibration of the biceps brachii tendon. The heart rate, mean arterial pressure, and rating of perceived exertion (RPE) in overall and exercising muscle were measured. The cross-sectional area (CSAvein) and blood velocity of the basilic vein in the resting upper arm were assessed by ultrasound, and blood flow (BFvein) was calculated using both variables. RESULTS: Muscle tension during exercise was similar between EX and EX + VIB. However, RPEs at EX + VIB were lower than those at EX (P <0.05). Increases in heart rate and mean arterial pressure during exercise at EX + VIB were also lower than those at EX (P <0.05). CSAvein in the resting limb at EX decreased during exercise from baseline (P <0.05), but CSAvein at EX + VIB did not change during exercise. CSAvein during exercise at EX was smaller than that at EX + VIB (P <0.05). However, BFvein did not change during the protocol under either condition. The decreases in circulatory response and RPEs during EX + VIB, despite identical muscle tension, showed that activation of central command was less during EX + VIB than during EX. Abolishment of the decrease in CSAvein during exercise at EX + VIB may thus have been caused by a lower level of central command at EX + VIB rather than EX. CONCLUSION: Diminished central command induced by tendon vibration may attenuate the superficial venous vessel response of the resting limb during sustained static arm exercise.

Active muscle oxygenation dynamics measured during high-intensity exercise by using two near-infrared spectroscopy methods.

Near-infrared spectroscopy is a noninvasive optical technique used to monitor tissue oxygenation. Generally, the modified Beer-Lambert's law (MBL) using continuous-wave light has been used to measure active muscle oxygenation during exercise; however, it cannot measure absolute changes in the oxy- (oxy-[Hb + Mb]), deoxy- (deoxy-[Hb + Mb]), and total hemoglobin/myoglobin concentrations (total-[Hb + Mb]) because the pathlength and scattering coefficient are not measured. In contrast, the time-resolved spectroscopy (TRS) using a ultra short pulsed laser can be used to determine absolute changes in the concentration, although the temporal resolution is inferior to that in MBL. This study evaluated the absolute changes in active muscle oxygenation and the optical mean pathlength and scattering and absorption coefficient during high-intensity exercise by using the TRS system. In addition, the difference between the changes determined using TRS and MBL measurements was assessed. When the TRS and MBL measurements obtained during high-intensity exercise were compared, the total-[Hb + Mb] and oxy-[Hb + Mb] dynamics differed markedly during high-intensity exercise, while the deoxy-[Hb + Mb] dynamics and kinetics did not differ.

Effects of prior heavy exercise on heterogeneity of muscle deoxygenation kinetics during subsequent heavy exercise.

We investigated the effects of prior heavy exercise on the spatial heterogeneity of muscle deoxygenation kinetics and the relationship to the pulmonary O(2) uptake (pVO(2)) kinetics during subsequent heavy exercise. Seven healthy men completed two 6-min bouts of heavy work rate cycling exercise, separated by 6 min of unloaded exercise. The changes in the concentration of deoxyhemoglobin/myoglobin (Delta deoxy-[Hb+Mb]) were assessed simultaneously at 10 different sites on the rectus femoris muscle using multichannel near-infrared spectroscopy. Prior exercise had no effect on either the time constant or the amplitude of the primary component pVO(2), whereas it reduced the amplitude of the slow component (SC). Delta deoxy-[Hb+Mb] across all 10 sites for bout 2 displayed a shorter time delay (mean and SD for subjects: 13.5 +/- 1.3 vs. 9.3 +/- 1.4 s; P < 0.01) and slower primary component time constant (tau: 9.3 +/- 1.3 vs. 17.8 +/- 1.0 s; P < 0.01) compared with bout 1. Prior exercise significantly reduced both the intersite coefficient of variation (CV) of the tau of Delta deoxy-[Hb+Mb] (26.6 +/- 11.8 vs. 13.7 +/- 5.6%; P < 0.01) and the point-by-point heterogeneity [root mean square error (RMSE)] during the primary component in the second bout. However, neither the change in the CV for tau nor RMSE of Delta deoxy-[Hb+Mb] correlated with the reduction in the SC in pVO(2) kinetics during subsequent heavy exercise. In conclusion, prior exercise reduced the spatial heterogeneity of the primary component of muscle deoxygenation kinetics. This effect was not correlated with alterations in the pVO(2) response during subsequent heavy exercise.

Changes in blood flow in conduit artery and veins of the upper arm during leg exercise in humans.

This study investigated changes in blood flow in the conduit artery, superficial vein, and deep vein of the upper arm during increase in internal temperature due to leg cycling. Additionally, we sought to demonstrate the contributions of blood velocity and vessel diameter on blood flow responses. Fourteen subjects performed supine cycling exercise at 60-69% maximal oxygen uptake for 30 min at an ambient temperature of 28 degrees C and relative humidity of 50%. Blood velocity and diameter in the brachial artery, basilic vein (superficial vein), and brachial vein (deep vein) were measured using ultrasound Doppler, and blood flow was calculated. Blood flow in the artery and superficial vein increased linearly with rising oesophageal temperature (DeltaT (oes)) after DeltaT (oes) was about 0.3 degrees C (within threshold), as well as cutaneous vascular conductance on the forearm. Changes in blood velocity in these vessels were similar to those in blood flow. Conversely, the brachial artery and superficial vein diameter did not affect the blood flow response. Blood flow variables in the deep vein did not change remarkably with rising DeltaT (oes). These results suggest that blood flow response, by an increase in velocity, in the conduit artery with rising DeltaT (oes) during exercise is similar to that in the superficial vein, but not deep vein. Also, it is indicated that these increases in blood flow relate to the increase in skin blood flow on the forearm with the rise in body temperature during exercise.

Changes in blood flow in a conduit artery and superficial vein of the upper arm during passive heating in humans.

The purposes of this study were (1) to evaluate changes in blood flow in the brachial artery and basilic vein of the upper arm with a rise in internal temperature during passive heating; and (2) to investigate the contributions of blood velocity and anteroposterior vessel diameter to these blood flow changes. Ten subjects rested in the supine position between a pair of tube-lined sheets. Thermoneutral water was circulated through the tubes to keep a mean skin temperature (Tsk) of 34-35 degrees C, and then hot water was circulated to maintain Tsk of 37-38 degrees C. The blood velocity and diameter in the brachial artery and basilic vein were continuously monitored by Doppler ultrasound technique and used to calculate blood flow. Blood flow in the brachial artery and basilic vein increased linearly as the oral temperature (T(or)) rose by < or =0.6 degrees C. The magnitude of the change in blood flow did not differ significantly between the two vessels. In addition, plots of DeltaT(or) versus blood flow yielded slopes that did not differ significantly between the brachial artery and the basilic vein. As T (or) increased, blood velocity, but not diameter, also increased. In conclusion, blood flow in the brachial artery and the basilic vein increased linearly as the internal temperature variable T (or) increased < or =0.6 degrees C. In both vessels, the passive heating-induced increases in blood flow resulted primarily from a change in blood velocity, rather than from a change in diameter.

Kinetics of pulmonary VO2 and femoral artery blood flow and their relationship during repeated bouts of heavy exercise.

The mechanism that alters the pulmonary VO2 response to heavy-intensity exercise following prior heavy exercise has been frequently ascribed to an improvement in pre-exercise blood flow (BF) or O(2) delivery. Interventions to improve O(2) delivery have rarely resulted in a similar enhancement of VO2. However, the actual limb blood flow and VO2 dynamics in the second bout of repeated exercise remain equivocal. Seven healthy female subjects (21-32 years) performed consecutive 6-min (separated by 6 min of 10 W exercise) bilateral knee extension (KE) exercise in a semisupine position at a work rate halfway between the lactate threshold (LT) and VO2peak. Femoral artery blood flow (FBF) was measured by Doppler ultrasound simultaneously with breath-by-breath VO2 each protocol being repeated at least four times for precise kinetic characterization. The effective time-constant (tau') of the VO2 response was reduced following prior exercise (bout 1: 61.0 +/-10.5 vs. bout 2: 51.6+/-9.0 s; mean +/- SD; P<0.05), which was a result of a reduced slow component (bout 1: 16.0+/-8.0 vs. bout 2: 12.5+/-6.7 %; P<0.05) and an unchanged 'primary' tau. FBF was consistently faster than VO2. However, there was no bout-effect on tau' FBF (bout 1: 28.2+/-12.0 vs. bout 2: 34.2+/-8.5 s). The relationship between the exercise-associated VO2 (i.e., deltaVO2) and Delta FBF was similar between bouts, with a tendency (N.S: P>0.05) for deltaVO2/deltaFBF to be increased during the transition to bout 2 rather than decreased, as hypothesized. The return of VO2 kinetics toward first order, therefore, was associated with an 'appropriate', not enhanced, BF to the working muscles. Whether a relative prior-hyperemia in bout 2 enables a more homogeneous intramuscular distribution of BF and/or metabolic response is unclear, however, these data are consistent with events more proximal to the exercise muscle in mediating the VO2 response during repeated heavy-intensity KE exercise.