Haemodynamic and baroreflex responses to whole-body tilting in exercising men before and after 6 weeks of bedrest

We sought to determine whether the cardiovascular deconditioning that occurs in exercising men after prolonged (42 days) bedrest in the head-down tilt (HDT) position is primarily related to mechanical changes in the heart or to an impaired arterial-cardiac-chronotropic baroreflex. Seven subjects were studied before (C, control) and repeatedly after HDT with rapid tilting between the upright and supine positions during steady-state 50-W dynamic leg exercise. Ventricular interdependence was assumed to be an index of cardiac size; it was assessed on the basis of the initial dip of arterial pulse pressure (PP) induced by a sudden tilt from the upright to the supine position (down-tilt). Arterial-cardiac-chronotropic baroreflex sensitivity (ABS) was assessed as the ratio between tilt-induced heart rate transients and the preceding (and reciprocal) transient in arterial pressure. On the first day of recovery, the initial PP dip was −4 (2) mmHg (where 1 mmHg is 0.13 kPa), less than half of the control value; on subsequent recovery days, the initial PP dip was not significantly different from the control value. When tilting from the upright to the supine position, mean ABS ranged from 1.02 to 1.06 bpm/mmHg during three separate control sessions. Tilts in the opposite direction gave lower ABS values because of the more sluggish HR response and ranged from 0.43 to 0.45 bpm/mmHg in the control situations. ABS did not change after HDT. Our results indicate that impairments of the cardiovascular system after long-term bedrest are of haemodynamic rather than baroreflex origin. Accepted: 8 March 2000     

Baroreflex impairment during rapid posture changes at rest and exercise after 120 days of bed rest

Orthostatic intolerance is common after space flight and head-down tilt (HDT) bed rest. We hypothesized that HDT-induced impairments of arterial blood pressure (AP) control would be more marked during exercise and that recovery of baroreflex function after very long-term HDT would be delayed. Six subjects were studied before (BDC) during (day 60, D60; D113) and after (recovery day 0, R0; R3; R15) 120 days of HDT. Supine resting subjects were exposed to repeated 1 min passive tilts to upright at 3-min interval. During 50 W steady-state exercise corresponding tilt had a 2-min duration at 4-min interval. The amplitudes of the tilt-induced transient beat-by-beat deviations in AP and rate (HR) were determined during the gravity transients. At rest these deviations did not change over time, but during exercise the total peak-to-nadir range of deviations in systolic AP (SAP) at up-tilt and down-tilt increased to 168±16% (mean±SEM) of BDC at D113 with no clear recovery upto and including R15. Counter-regulatory HR responses were not increased proportionally and especially not tachycardic responses to up-tilt, resulting in a reduction of baroreflex sensitivity (ΔRR-interval/ΔSAP) by 55±9% of BDC at D113 with no recovery upto and including R15. We conclude that prolonged bed rest cause long-lasting impairments in AP control and baroreflex function in exercising humans.     

Sinusoidal galvanic vestibular stimulation (sGVS) induces a vasovagal response in the rat

Blood pressure (BP) and heart rate (HR) were studied in isoflurane-anesthetized Long-Evans rats during sinusoidal galvanic vestibular stimulation (sGVS) and sinusoidal oscillation in pitch to characterize vestibular influences on autonomic control of BP and HR. sGVS was delivered binaurally via Ag/AgCl needle electrodes inserted over the mastoids at stimulus frequencies 0.008–0.4 Hz. Two processes affecting BP and HR were induced by sGVS: 1) a transient drop in BP (≈15–20 mmHg) and HR (≈3 beat*s⁻¹), followed by a slow recovery over 1–6 min; and 2) inhibitory modulations in BP (≈4.5 mmHg/g) and HR (≈0.15 beats*s⁻¹/g) twice in each stimulus cycle. The BP and HR modulations were approximately in-phase with each other and were best evoked by low stimulus frequencies. A wavelet analysis indicated significant energies in BP and HR at scales related to twice and four times the stimulus frequency bands. BP and HR were also modulated by oscillation in pitch at frequencies 0.025–0.5 Hz. Sensitivities at 0.025 Hz were ≈4.5 mmHg/g (BP) and ≈0.17 beat*s⁻¹/g (HR) for pitches of 20–90°. The tilt-induced BP and HR modulations were out-of-phase, but the frequencies at which responses were elicited by tilt and sGVS were the same. The results show that the sGVS-induced responses, which likely originate in the otolith organs, can exert a powerful inhibitory effect on both BP and HR at low frequencies. These responses have a striking resemblance to human vasovagal responses. Thus, sGVS-activated rats can potentially serve as a useful experimental model of the vasovagal response in humans.     

Cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise

In occupational work, continuous repetitive and isometric actions performed with the upper extremity primarily cause local muscle strain and musculoskeletal disorders. They may also have some adverse effects on the cardiorespiratory system, particularly, through the elevation of blood pressure. The aim of the present study was to compare peak cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise. The subjects were 21 untrained healthy men aged 24–45 years. The dynamic hand-grip exercise (DHGE) was performed using the left hand-grip muscles at the 57 (SD 4)% level of each individual's maximal voluntary contraction (MVC) with a frequency of 51 (SD 4) grips · min^−l. The isometric hand-grip exercise (IHGE) was done using the right hand at 46 (SD 3)% of the MVC. The endurance time, ventilatory gas exchange, heart rate (HR) and blood pressure were mea- sured during both kinds of exercise. The mean endurance times for DHGE and IHGE were different, 170 (SD 62) and 99 (SD 27) s, respectively (P < 0.001). During DHGE the mean peak values of the breathing frequency [20 (SD 6) breaths · min⁻¹] and tidal volume [0.89 (SD 0.34) l] differed significantly (P < 0.01) from peak values obtained during IHGE [15 (SD 5) breaths · min⁻¹, and 1.14 (SD 0.32) l, respectively]. The corresponding peak oxygen consumptions, pulmonary ventilations, HR and systolic blood pressures did not differ, and were 0.51 (SD 0.06) and 0.46 (SD 0.11) l · min⁻¹, 17.1 (SD 3.0) and 16.7 (SD 4.7) l · min⁻¹, 103 (SD 18) and 102 (SD 17) beats · min⁻¹, and 156 (SD 17) and 161 (SD 17) mmHg, respectively. The endurance times of both DHGE and IHGE were short (<240 s). The results indicate that the peak responses for the ventilatory gas exchange, HR and blood pressure were similar during fatiguing DHGE and IHGE, whereas the breathing patterns differed significantly between the two types of exercise. The present findings emphasize the importance of following ergonomic design principles in occupational settings which aim to reduce the output of force, particularly in tasks requiring isometric and/or one-sided repetitive muscle actions. Accepted: 16 February 2000     

Cardiovascular responses to upright and supine exercise in humans after 6 weeks of head-down tilt (−6°)

Seven healthy men performed steady-state dynamic leg exercise at 50 W in supine and upright postures, before (control) and repeatedly after 42 days of strict head-down tilt (HDT) (−6°) bedrest. Steady-state heart rate (f _c), mean arterial blood pressure, cardiac output (Q˙ _c), and stroke volume (SV) were recorded. The following data changed significantly from control values. The f _c was elevated in both postures at least until 12 days, but not at 32 days after bedrest. Immediately after HDT, SV and Q˙ _c were decreased by 25 (SEM 3)% and 19 (SEM 3)% in supine, and by 33 (SEM 5)% and 20 (SEM 3)% in upright postures, respectively. Within 2 days there was a partial recovery of SV in the upright but not in the supine posture. The SV and Q˙ _c during supine exercise remained significantly decreased for at least a month. Submaximal oxygen uptake did not change after HDT. We concluded that the cardiovascular response to exercise after prolonged bedrest was impaired for so long that it suggested that structural cardiac changes had developed during the HDT period. Accepted: 6 June 2000     

Intra- and extracranial artery blood velocity during a sudden blood pressure decrease in humans

The intra- and extracerebral Doppler artery blood velocity responses to a 10-mmHg abrupt blood pressure (BP) decrease in ten healthy men were studied. This decrease was obtained using two cuffs placed over both thighs. First, cuffs were inflated to pressures greater than the arterial BP for 5 min. Next, they were deflated to 60 mmHg in order to prevent venous return from the legs. We obtained a decrease in mean arterial BP of from 101 (10) to 90 (10) mmHg [mean (SD), P < 0.01] without modifications in the heart rate [HR, 88 (14) beats min⁻¹]. Middle cerebral artery mean blood velocity (MCAmv) decreased immediately from 50 (10) to 42 (12) cm s⁻¹ (P < 0.05). Simultaneously, temporal superficial artery mean blood velocity (TSAmv) decreased from 11 (3) to 7 (2) cm s⁻¹ (P < 0.05) and common carotid artery blood flow (CCAbf ) decreased from 305 (23) to 233 (33) ml min⁻¹ (P < 0.05). After 5 s, MCAmv and CCAbf returned to baseline values, whereas TSAmv [8 (2) cm s⁻¹], mean arterial BP [86 (10) mmHg] remained low and HR increased [92 (12) beats min⁻¹]. TSAmv, BP and HR returned to baseline values in 1 min. These data confirm that cerebral blood flow (CBF) is very rapidly regulated but that blood flow in extracranial territories is not and that it follows the arterial BP changes. Accepted: 8 April 1997     

Effect of body tilt angle on fatigue and EMG activities in lower limbs during cycling

This study compared the rate of fatigue and lower limb EMG activities during high-intensity constant-load cycling in upright and supine postures. Eleven active males performed seven cycling exercise tests: one upright graded test, four fatigue tests (two upright, two supine) and two EMG tests (one upright, one supine). During the fatigue tests participants initially performed a 10 s all-out effort followed by a constant-load test with 10 s all-out bouts interspersed every minute. The load for the initial two fatigue tests was 80% of the peak power (PP) achieved during the graded test and these continued until failure. The remaining two fatigue tests were performed at 20% PP and were limited to the times achieved during the 80% PP tests. During the EMG tests subjects performed a 10 s all-out effort followed by a constant-load test to failure at 80% PP. Normalised EMG activities (% maximum, NEMG) were assessed in five lower limb muscles. Maximum power and maximum EMG activity prior to each fatigue and EMG test were unaffected by posture. The rate of fatigue at 80% PP was significantly higher during supine compared with upright posture (−68 ± 14 vs. −26 ± 6 W min⁻¹, respectively, P < 0.05) and the divergence of the fatigue responses occurred by the second minute of exercise. NEMG responses were significantly higher in the supine posture by 1–4 min of exercise. Results show that fatigue is significantly greater during supine compared with upright high-intensity cycling and this effect is accompanied by a reduced activation of musculature that is active during cycling.     

Effect of co-contractions on the cardiovascular response to submaximal static handgrip

The aim of this study was to investigate the influence of concomitant involuntary contractions of different muscles on heart rate (HR) and blood pressure (BP) during a sustained, submaximal handgrip. Nine male subjects [23.6 (0.4) years, 177.0 (1.5) cm, and 73.0 (2.7) kg, means (SE)] participated in the experiment. The maximal integrated electromyographic activity (IEMG_max) of four ipsilateral muscles, flexor digitorum (FD), biceps brachii (BB), rectus abdominalis (RA) and vastus lateralis (VA), was recorded. Then, after 30 min of rest, the subjects maintained a submaximal isometric handgrip for 2 min. Heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure and surface electromyography (EMG) of the four muscles were recorded. The amplitude and power spectrum of the EMG were analysed. During the handgrip the force was kept constant at 43 (1)% of the maximum voluntary contraction (MVC) only for 90 (12) s. After that time, the subjects were unable to maintain the target force which decreased continuously up to the end of the contraction (P < 0.01) with a residual force of 27 (3)% MVC at t=120 s. HR increased from 75 (3) beats · min⁻¹ at rest to 109 (6) beats · min⁻¹ at t=120 s (P < 0.01). SBP and DBP also increased from 112 (5) and 81 (2) mmHg to 176 (5) and 133 (7) mmHg, respectively (P < 0.01). The EMG activity rose significantly for both FD and BB with a moderate increase for RA and VL. In fact, the individual contributions of FD and BB to the EMG activity of the four muscles were 52 (2)% and 37 (2)%, respectively, whereas the RA and VL contributed only 9 (1)% and 1.4 (0.1)%. The amplitude ratio of FD's EMG to the total EMG activity of the four muscles from which recordings were made decreased with time from 72% to 33% (P < 0.01). The central command's level of activation, as reflected by the increased EMG activity of the four recorded muscles, was probably high enough to stimulate the cardiovascular centres through cortical spread (sometimes known as cortical irradiation). On the other hand, maintaining an isometric handgrip at 43% MVC reduced local muscle blood flow and metabolites known to stimulate type III and IV afferents then accumulated, which in turn induced a reflex-mediated elevation of blood pressure. However, the relative forces developed by the co-contracting muscles were of low intensity (less than 20% MVC) and short duration compared to those of the muscle group under study. These results suggest that the mass of the muscle groups recruited during a fatiguing submaximal handgrip contributes little to the cardiovascular response. Accepted: 20 July 2000     

Ultra short-term heart rate recovery after maximal exercise in continuous versus intermittent endurance athletes

This study tested the hypothesis that athletes participating in intermittent sports would exhibit a faster heart rate recovery (HRR) during the initial phase (<30 s) following maximal exercise than athletes participating in continuous endurance sports. Forty-six male athletes were allocated into continuous (CNT, n = 24) or intermittent groups (INT, n = 22), matched for age and aerobic fitness. Athletes performed maximal exercise on a treadmill using the ramp protocol. Immediately upon exercise cessation, subjects were placed supine with continuous measurement of HR during the first minute of recovery. Data were analyzed in 10-s intervals and compared between the groups. Repeated measures ANOVA showed a group × time interaction effects (p ≤ 0.01) for HRR expressed in both beats min⁻¹ and in percentage of peak post-exercise HR (% HR_peak). The INT group had lower HR than CNT group at 10 s (189 vs. 192 beats min⁻¹, p = 0.04; and 96.3 vs. 97.9% HR_peak, p = 0.009) and 20 s (184 vs. 188 beats min⁻¹, p = 0.049; and 93.6 vs. 95.7% HR_peak, p = 0.021) intervals of recovery. The results suggest that athletes engaged in intermittent sports are likely to have faster HRR during the first 20 s after maximal exercise than their counterparts trained for continuous performance.     

Energy expenditure of horse riding

Oxygen consumption (VO₂), ventilation (V _E) and heart rate (HR) were studied in five recreational riders with a portable oxygen analyser (K2 Cosmed, Rome) telemetric system, during two different experimental riding sessions. The first one was a dressage session in which the rider successively rode four different horses at a walk, trot and canter. The second one was a jumping training session. Each rider rode two horses, one known and one unknown. The physiological parameters were measured during warm up at a canter in suspension and when jumping an isolated obstacle at a trot and canter. This session was concluded by a jumping course with 12 obstacles. The data show a progressive increase in VO₂ during the dressage session from a mean value of 0.70 (0.18) l · min⁻¹ [mean (SD)] at a walk, to 1.47 (0.28) l · min⁻¹ at a trot, and 1.9 (0.3) l · min⁻¹ at a canter. During the jumping session, rider VO₂ was 2 (0.33) l · min⁻¹ with a mean HR of 155 beats · min⁻¹ during canter in suspension, obstacle trot and obstacle canter. The jumping course significantly enhanced VO₂ and HR up to mean values of 2.40 (0.35) l · min⁻¹ and 176 beats · min⁻¹, respectively. The comparison among horses and riders during the dressage session shows differences in energy expenditure according to the horse for the same rider and between riders. During the jumping session, there was no statistical difference between riders riding known and unknown horses. In conclusion these data confirm that riding induces a significant increase in energy expenditure. During jumping, a mean value of 75% VO_2max was reached. Therefore, a good aerobic capacity seems to be a factor determining riding performance in competitions. Regular riding practice and additional physical training are recommended to enhance the physical fitness of competitive riders. Accepted: 3 March 2000     

Continuous heart rate monitoring over 1 week in teenagers aged 11–16 years

Heart rate (HR) was monitored in 66 French pubertal boys (B, n=28) and girls (G, n=38) aged 11–16 years to evaluate habitual physical activity (HPA) over a 1-week period in the winter. The HR and the percentage of heart rate reserve (%HRR) were taken to be indexes of the metabolic activity for the whole day and for the different parts of the day. The HPA was evaluated from the time spent each day below 50%HRR, between 50%–70%HRR and above 70%HRR, which related to the time spent in no or low physical activity (NLPA), moderate physical activity (MPA) and vigorous physical activity (VPA), respectively. No sex differences were observed in the average %HRR each day {%HRR_mean, [B 30 (SD 4)%; G 32 (SD 4)%]} or in NLPA [B 715 (SD 61) min, G 711 (SD 81) min] and VPA [B 19 (SD 16) min, G 21 (SD 21) min] throughout the week. During school days, daily %HRR_mean was 7% smaller in 14–16 year olds compared to 11–13 year olds. This was linked to a decrease in MPA and a concomitant increase in NLPA (P<0.05). Daily %HRR_mean varied significantly during the week (range: 28–34% HRR). There were significant differences among the periods of the day (P<0.05). The HR was the greatest during physical education lessons [128 (SD 11) beats · min⁻¹], recreation [113 (SD 15) beats · min⁻¹] and lunch break [108 (SD 12) beats · min⁻¹] and the lowest during the evening [94 (SD 10) beats · min⁻¹]. It was only during the lunch breaks that %HRR_mean was greater (P<0.05) on school days than on free days. Of all the teenagers studied 32% were considered active during the week. Accepted: 9 June 1997     

A new impedance cardiograph device for the non-invasive evaluation of cardiac output at rest and during exercise: comparison with the “direct” Fick method

The objectives of this study were to evaluate the reliability and accuracy of a new impedance cardiograph device, the Physio Flow, at rest and during a steady-state dynamic leg exercise (work intensity ranging from 10 to 50 W) performed in the supine position. We compared cardiac output determined simultaneously by two methods, the Physio Flow (Q˙ _cPF) and the direct Fick (Q˙ _cFick) methods. Forty patients referred for right cardiac catheterisation, 14 with sleep apnoea syndrome and 26 with chronic obstructive pulmonary disease, took part in this study. The subjects' oxygen consumption values ranged from 0.14 to 1.19 l · min⁻¹. The mean difference between the two methods (Q˙ _cFick−Q˙ _cPF) was 0.04 l · min⁻¹ at rest and 0.29 l · min⁻¹ during exercise. The limits of agreement, defined as mean difference ± 2SD, were −1.34, +1.41 l · min⁻¹ at rest and −2.34, +2.92 l · min⁻¹ during exercise. The difference between the two methods exceeded 20% in only 2.5% of the cases at rest, and 9.3% of the cases during exercise. Thoracic hyperinflation did not alter Q˙ _cPF. We conclude that the Physio Flow provides a clinically acceptable and non-invasive evaluation of cardiac output under these conditions. This new impedance cardiograph device deserves further study using other populations and situations. Accepted: 3 April 2000     

Dose-related elevations in venous pH with citrate ingestion do not alter 40-km cycling time-trial performance

The purpose of the current investigation was to determine whether sodium citrate enhances endurance cycling performance and, if so, what dosage(s) produces this effect. Eight trained [peak power output: 362 (48) W; power:weight: 5.1 (0.4) W · kg⁻¹, mean (SD)] male cyclists were requested to complete four, 40-km time-trials, each separated by 3–7 days, on their own bicycles, mounted on a Kingcycle ergometer. To mimic the stochastic nature of cycle road races, the time-trials included four 500-m, four 1-km and two 2-km sprints. The experimental conditions involved the ingestion of three dosages of sodium citrate dissolved in 400 ml water: 0.2 g · kg⁻¹, 0.4 g · kg⁻¹ and 0.6 g · kg⁻¹ body mass (b.m.) and a placebo (calcium carbonate, 0.1 g · kg⁻¹ b.m.). Subjects were asked to complete both the sprints and total distance in the fastest time possible. Venous blood samples were collected before, as well as at 10-km intervals during the trials for the analysis of plasma lactate and glucose concentrations and for the measurement of blood pH and PCO₂ levels. Immediately before, as well as during exercise, pH was significantly higher in the group ingesting the highest citrate dose (range 7.36–7.45) compared to the placebo (range 7.31–7.39) and the two lower citrate dosages. Despite this, no significant differences in power output (P=0.886) or time taken to complete the 40 km (P=0.754) were measured between the four trials. The average performance times (in min:s, with SD in parentheses) and average power output (in W) for the 40-km time-trials were: 58:46 (5:06) [265 (62) W], 60:24 (6:07) [251 (59) W], 61:47 (5:07) [243 (44) W] and 60:02 (5.05) [255 (55) W] for the 0.2, 0.4, 0.6 g · kg⁻¹ b.m. sodium citrate and placebo trials, respectively. There were also no significant differences measured between treatments in terms of time, power output, speed or heart rate during the 500-m, 1-km and 2-km sprints. The ingestion of increasing sodium citrate dosages before exercise produced dose-dependent changes in pH, base excess and HCO⁻ ₃ concentrations before and during the 40-km time-trial. However, these changes influenced neither the time-trial time nor the sprinting performance times. Accepted: 7 June 2000     

Difference in human cardiovascular response between upright and supine recovery from upright cycle exercise

Cardiovascular responses were examined in seven healthy male subjects during 10 min of recovery in the upright or supine position following 5 min of upright cycle exercise at 80% peak oxygen uptake. An initial rapid decrease in heart rate (f _c) during the early phase of recovery followed by much slower decrease was observed for both the upright and supine positions. The average f _c at the 10th min of recovery was significantly lower (P < 0.05) in the supine position than in the upright position, while they were both significantly greater than the corresponding pre-exercise levels (each P < 0.05). Accordingly, the amplitude of the high frequency (HF) component of R-R interval variability (by spectrum analysis) in both positions was reduced with a decrease in mean R-R interval, the relationship being expressed by a regression line – mean R-R interval = 0.006 × HF amplitude + 0.570 (r = 0.905, n = 28, P < 0.001). These results would suggest that the slower reduction in f _c following the initial rapid reduction in both positions is partly attributable to a retardation in the restoration of the activity of the cardiac parasympathetic nervous system. Post-exercise upright stroke volume (SV, by impedance cardiography) decreased gradually to just below the pre-exercise level, whereas post-exercise supine SV increased markedly to a level similar to that at rest before exercise. The resultant cardiac output (Q˙ _c) and the total peripheral vascular resistance (TPR) in the upright and supine positions returned gradually to their respective pre-exercise levels in the corresponding positions. At the 10th min of recovery, both average SV and Q˙ _c were significantly greater (each P < 0.005) in the supine than in the upright position, while average TPR was significantly lower (P < 0.05) in the supine than in the upright position. In contrast, immediately after exercise, mean blood pressure dropped markedly in both the supine and upright positions, and their levels at the 10th min of recovery were similar. Therefore we concluded that arterial blood pressure is maintained relatively constant through various compensatory mechanisms associated with f _c, SV, Q˙ _c, and TPR during rest and recovery in different body positions. Accepted: 4 September 1999     

The effect of endurance training on the ventilatory response to exercise in elite cyclists

The purpose of this study was to investigate the effects of endurance training on the ventilatory response to acute incremental exercise in elite cyclists. Fifteen male elite cyclists [mean (SD) age 24.3 (3.3) years, height 179 (6) cm, body mass 71.1 (7.6) kg, maximal oxygen consumption (V˙O_2max) 69 (7) ml · min⁻¹ · kg⁻¹] underwent two exercise tests on a cycle ergometer. The first test was assessed in December, 6 weeks before the beginning of the cycling season. The second test was performed in June, in the middle of the season. During this period the subjects were expected to be in a highly endurance-trained state. The ventilatory response was assessed during an incremental exercise test (20 W · min⁻¹). Oxygen consumption (V˙O₂), carbon dioxide production (V˙CO₂), minute ventilation (V˙ _E), and heart rate (HR) were assessed at the following points during the test: at workloads of 200 W, 250 W, 300 W, 350 W, 400 W and at the subject's maximal workload, at a respiratory exchange ratio (R) of 1, and at the ventilatory threshold (Th_vent) determined using the V-slope-method. Post-training, the mean (SD) V˙O_2max was increased from the pre-training level of 69 (7) ml · min⁻¹ · kg⁻¹ (range 61.4–78.6) to 78 (6) ml · min⁻¹ · kg⁻¹ (range 70.5–86.3). The mean post-training V˙O₂ was significantly higher than the pre training value (P < 0.01) at all work rates, at Th_vent and at R=1. V˙O₂ was also higher at all work rates except for 200 W and 250 W. V˙ _E was significantly higher at Th_vent and R=1. Training had no effect on HR at all workloads examined. An explanation for the higher V˙O₂ cost for the same work rate may be that in the endurance-trained state, the adaptation to an exercise stimulus with higher intensity is faster than for the less-trained state. Another explanation may be that at the same work rate, in the less-endurance-trained state power is generated using a significantly higher anaerobic input. The results of this study suggest the following practical recommendations for training management in elite cyclists: (1) the V˙O₂ for a subject at the same work rate may be an indicator of the endurance-trained state (i.e., the higher the V˙O₂, the higher the endurance-trained capacity), and (2) the need for multiple exercise tests for determining the HR at Th_vent during a cycling season is doubtful since at Th_vent this parameter does not differ much following endurance training. Accepted: 19 October 1999     

Effect of posture on body temperature of young men in cold air

We studied eight young adult men to see whether a supine posture caused a fall in body core temperature in the cold, as it does in thermoneutral conditions. In air at 31°C (thermoneutral), a supine posture for 3 h reduced mean aural, gastric, oesophageal and rectal temperatures by 0.2–0.4°C, compared to upright and increased femoral artery blood flow from 278 (SEM 42) ml · min⁻¹ whilst upright to 437 (SEM 42) ml·min⁻¹ whilst supine. In cold air (8°C) the supine posture failed to reduce these temperature differences significantly, or to increase femoral blood flow; it reduced heart rate, and increased arterial systolic and pulse pressures adjusted to carotid sinus level, less than in thermoneutral conditions. However, the behaviour of core temperature at the four sites was significantly nonuniform between the two postures in the cold, mainly because the supine posture tended to reduce rectal temperature. It may have done so by reducing heat production in the muscles of the pelvis, since it reduced overall metabolic rate from 105 (SEM 8) to 87 (SEM 4) W · m⁻² in the cold. In other respects the results indicated that posture ceased to have an important effect on body core temperatures during cold stress.     

Face temperature and cardiorespiratory responses to wind in thermoneutral and cool subjects exposed to −10 °C

The effects of the thermal state of the body (slightly cool and neutral) and moderate wind speeds on face temperature, blood pressure, respiratory function and pain sensation during cold exposure were studied on eight healthy male subjects. They were dressed in cold-protective clothing and preconditioned at +20 °C (TN) and −5 °C (CO) for 60 min, then exposed to −10 °C and 0 m · s⁻¹ (NoW), 1 (W1) and 5 (W5) m · s⁻¹ wind for 30 min. Thus, each individual was exposed six times. The exposure to wind entailed a combination of strong cooling of the bare face and mild body cooling. The forehead, cheek and nose temperatures decreased during cold exposure, and the decrease was greater at higher air velocities (P < 0.0001). All subjects reported pain sensations at 5 m · s⁻¹. At the end of exposure only the nose temperature was significantly lower in CO than in TN subjects; it was about 2 °C and reached 0 °C in two experiments. The systolic and diastolic blood pressure (SBP and DBP, respectively) increased significantly by 7.7 and 5.9 mmHg, respectively, during preconditioning at −5 °C, but did not change at +20 °C. SBP and DBP increased during exposure to −10 °C in TN by approximately 9 mmHg. However, the total average increase of blood pressure (1–90 min) was similar in TN and CO (SBP 15 mmHg and DBP 13 mmHg). SBP and DBP increased more during exposure to 5 m · s⁻¹ at −10 °C than NoW. Blood pressure responses as observed in this study (SBP and DBP up to 51 and 45 mmHg, respectively) are potential health risks for hypertensive individuals and angina patients. Respiratory functions (FVC, FEV₁) were reduced by about 3% by the cold (−5 and −10 °C) compared to pre-experiment values. Furthermore, the Wind Chill Index seems to underestimate the cooling power of 5 m · s⁻¹ at −10 °C of bare skin (e.g. face). Therefore it needs to be revised and we suggest that it is expanded to include risk levels for pain sensation. Accepted: 29 May 2000     

Psychomotor performance during prolonged exercise above and below the blood lactate threshold

Previous investigations from this laboratory have demonstrated that during graded exercise with exercise intensities increasing every 3 min until exhaustion the multiple choice reaction time (RT) decreased until the intensity exceeded the lactate threshold (LT) by approximately 25%, and then rapidly increased. The aim of this study was to follow up changes in RT during prolonged exercise at constant intensities above and below LT and to relate these changes to changes in venous blood lactate [La⁻]_b, and plasma catecholamine [CA]_pl concentration responses to the exercise. For this purpose eight young soccer players exercised for 20-min on a cycle ergometer at 10% above LT, and nine exercised for 60 min at an intensity 30% below LT. During both tests RT, heart rate (HR), as well as [La⁻]_b, and [CA]_pl were measured. Above LT, RT decreased from the 5th min until the end of exercise, whilst HR, [La⁻]_b, and [CA]_pl increased progressively. Significant inverse correlations were ascertained between RT and plasma adrenaline (r = − 0.651) and noradrenaline concentrations (r = − 0.678). During exercise below LT, RT decreased up to approximately 40 min, then it reached a nadir, and stabilized at this level. This was accompanied by only small changes in [La⁻]_b and [CA]_pl. The present findings would indicate that young athletes are able to maintain for a relatively long time, or even increase, their psychomotor performance during endurance exercise both below and above the LT. Accepted: 23 June 1997     

Substrate utilisation during exercise and shivering

It is generally assumed that exercise and shivering are analogous processes with regard to substrate utilisation and that, as a consequence, exercise can be used as a model for shivering. In the present study, substrate utilisation during exercise and shivering at the same oxygen consumption (V˙O₂) were compared. Following an overnight fast, eight male subjects undertook a 2-h immersion in cold water, designed to evoke three different intensities of shivering. At least 1 week later they undertook a 2-h period of bicycle ergometry during which the exercise intensity was varied to match the V˙O₂ recorded during shivering. During both activities hepatic glucose output (HGO), the rate of glucose utilisation (Rd), blood glucose, plasma insulin, free fatty acid (FFA) and beta-hydroxybutyrate (B-HBA) concentrations were measured. The V˙O₂ measured during the different levels of shivering averaged 0.49 l · min⁻¹ (level 1: low), 0.6 l · min⁻¹ (level 2: low-moderate), and 0.9 l · min⁻¹ (level 3: moderate), and corresponded closely to the levels measured during exercise. HGO and Rd were greater (P < 0.05) during exercise than during shivering at the same V˙O₂ (9.5% and 14.7%, respectively). The average (SD) HGO during level 3 exercise was 3.0 (0.91) mg · kg⁻¹ . min⁻¹ compared to 2.76 (1.0) mg · kg⁻¹ . min⁻¹ during shivering. The values for Rd were 3.06 (0.98) mg · kg⁻¹ · min⁻¹ during level 3 exercise and 2.68 (0.82) mg · kg⁻¹ · min⁻¹ during shivering. Blood glucose levels did not differ between conditions, averaging 5.4 (0.3) mmol . l⁻¹ over all levels of shivering and 5.2 (0.3) mmol · l⁻¹ during exercise. Plasma FFA and B-HBA were higher (P < 0.01) during shivering than during corresponding exercise (12.3% and 33.3%, respectively). FFA averaged 0.61 (0.2) mmol · l⁻¹ over all levels of shivering and 0.47 (0.16) mmol · l⁻¹ during exercise. The figures for B-HBA were 0.44 (0.13) mmol · l⁻¹ during all levels of shivering and 0.32 (0.1) mmol · l⁻¹ during exercise. Plasma insulin was higher (P < 0.05) during level 2 and 3 shivering compared to corresponding exercise; at these levels the average value for plasma insulin was 95.9 (21.9) pmol · l⁻¹ during shivering and 80.6 (16.1) pmol · l⁻¹ during exercise. On the basis of the present findings it is concluded that, with regard to substrate utilisation, shivering and exercise of up to 2 h duration should not be regarded as analogous processes. Accepted: 12 February 1997     

Effect of a pulsating anti-gravity suit on peak exercise performance in individual with spinal cord injuries

The aim of this study was to examine effects of a pulsating pressure anti-gravity suit on the peak values of oxygen uptake (V˙O₂) and power during maximal arm exercise in spinal-cord-injured (SCI) individuals. Five well-trained SCI men (with lesions at levels between T6 and L1) and seven well-trained able-bodied men (ABC) performed two incremental (10 W · min⁻¹) arm-cranking tests. During one test the pressure in the anti-G suit pulsated between 4.7 kPa (35 mmHg) and 9.3 kPa (70 mmHg) every 2 s (PPG+), during the other test (PPG−) all the subjects wore the anti-G suit in a deflated state. Tests were performed in a counter-balanced order. Peak V˙O₂ in SCI was 1 ml · kg⁻¹ · min⁻¹ lower during PPG+ compared to PPG− (P = 0.05). Peak power and peak heart rate were not significantly different during PPG+ compared to PPG−. These results would suggest that no increase in work capacity can be obtained with a pulsating pressure anti-gravity suit in either SCI or ABC. Accepted: 1 September 1998