Oxygen uptake kinetics during treadmill running across exercise intensity domains

The purpose of the present study was to examine comprehensively the kinetics of oxygen uptake ( ) during treadmill running across the moderate, heavy and severe exercise intensity domains. Nine subjects [mean (SD age, 27 (7) years; mass, 69.8 (9.0) kg; maximum , , 4,137 (697) ml·min^–1] performed a series of "square-wave" rest-to-exercise transitions of 6 min duration at running speeds equivalent to 80% and 100% of the at lactate threshold (LT; moderate exercise); and at 20%, 40%, 60%, 80% and 100% of the difference between the at LT and (Δ, heavy and severe exercise). Critical velocity (CV) was also determined using four maximal treadmill runs designed to result in exhaustion in 2–15 min. The response was modelled using non-linear regression techniques. As expected, the amplitude of the primary component increased with exercise intensity [from 1,868 (136) ml·min^–1 at 80% LT to 3,296 (218) ml·min^–1 at 100% Δ, P<0.05]. However, there was a non-significant trend for the "gain" of the primary component to decrease as exercise intensity increased [181 (7) ml·kg^–1·km^–1 at 80% LT to 160 (6) ml·kg^–1·km^–1 at 100% Δ]. The time constant of the primary component was not different between supra-LT running speeds (mean value range = 17.9–19.1 s), but was significantly shorter during the 80% LT trial [12.7 (1.4) s, P<0.05]. The slow component increased with exercise intensity from 139 (39) ml·min^–1 at 20% Δ to 487 (57) ml·min^–1 at 80% Δ (P<0.05), but decreased to 317 (84) ml·min^–1 during the 100% Δ trial (P<0.05). During both the 80% Δ and 100% Δ trials, the at the end of exercise reached [4,152 (242) ml·min^–1 and 4,154 (114) ml·min^–1, respectively]. Our results suggest that the "gain" of the primary component is not constant as exercise intensity increases across the moderate, heavy and severe domains of treadmill running. These intensity-dependent changes in the amplitudes and kinetics of the response profiles may be associated with the changing patterns of muscle fibre recruitment that occur as exercise intensity increases. Electronic Publication     

The effect of prolonged submaximal exercise on gas exchange kinetics and ventilation during heavy exercise in humans

This study compared ventilation, gas exchange (oxygen uptake, V̇O₂) and the surface electromyogram (EMG) activity of four major lower limb muscles during heavy exercise before (Pre-Ex) and after (Post-Ex) a sustained 90-min cycling exercise at 60% V̇O_2peak. The 90-min exercise was incorporated under the hypothesis that sustained exercise would alter substrate availability in the second exercise bout causing differences in fibre recruitment patterns, gas exchange and ventilation. Nine trained male subjects [V̇O_2peak=60.2 (1.7) ml·kg⁻¹·min⁻¹] completed two identical 6-min bouts of cycling performed at high intensity [~90% V̇O_2peak; 307 (6) W, mean (SE)]. Ventilation and gas exchange were measured breath-by-breath and the EMG was recorded during the last 12 s of each minute of the two 6-min bouts. EMG signals were analysed to determine integrated EMG (iEMG) and mean power frequency (MPF). V̇O₂ at min 3 and min 6 in Post-Ex were significantly higher (i.e., +201 and 141 ml·min⁻¹, respectively, P<0.05) than in Pre-Ex but there was a ~25% decrease of the slow component, taken as the difference between min 6 and min 3 [187 (27) vs 249 (35) ml·min⁻¹, respectively, P<0.05]. The greater whole-body V̇O₂ after 3 min of exercise in Post-Ex was not accompanied by clear alterations in the iEMG and MPF of the examined leg muscles. Ventilation and heart rate were elevated (~12–16 l·min⁻¹ and ~10 beats·min⁻¹, respectively, P<0.05) as were the ratios V̇ _E/O₂ and V̇ _E/V̇CO₂ in the Post-Ex tests. It was concluded that the V̇O₂ and ventilation responses to high-intensity exercise can be altered following prolonged moderate intensity exercise in terms of increased amplitude without associated major changes in either iEMG or MPF values among conditions.     

Heart rate is lower during ergometer rowing than during treadmill running

This study evaluated whether the heart rate (HR) response to exercise depends on body position and on the active muscle mass. The HR response to ergometer rowing (sitting and using both arms and legs) was compared to treadmill running (upright exercise involving mainly the legs) using a progressive exercise intensity protocol in 55 healthy men [mean (SD) height 176 (5) cm, body mass 71 (6) kg, age 21 (3) years]. During rowing HR was lower than during running at a blood lactate concentration of 2 mmol·l^–1 [145 (13) compared to 150 (11) beat·min^–1, P<0.05], 4 mmol·l^–1 [170 (10) compared to 177 (13) beat·min^–1, P<0.05], and 6 mmol·l^–1 [182 (10) compared to 188 (10) beat·min^–1, P<0.05]. Also during maximal intensity rowing, HR was lower than during maximal intensity running [194 (9) compared to 198 (11) beat·min^–1, P<0.05]. These results were accompanied by a higher maximal oxygen uptake during rowing than during running [rowing compared to running, 4.50 (0.5) and 4.35 (0.4) l·min^–1, respectively, P<0.01]. Thus, the oxygen pulse, as an index of the stroke volume of the heart, was higher during rowing than during running at any given intensity. The results suggest that compared to running, the seated position and/or the involvement of more muscles during rowing facilitate venous return and elicit a smaller HR response for the same relative exercise intensity. Electronic Publication     

Muscle blood flow and flow heterogeneity during exercise studied with positron emission tomography in humans

Blood flow is the main regulator of skeletal muscle's oxygen supply, and several studies have shown heterogeneous blood flow among and within muscles. However, it remains unclear whether exercise changes the heterogeneity of flow in exercising human skeletal muscle. Muscle blood flow and spatial flow heterogeneity were measured simultaneously in exercising and in the contralateral resting quadriceps femoris (QF) muscle in eight healthy men using H¹⁵ ₂O and positron emission tomography. The relative dispersion (standard deviation/mean) of blood flow was calculated as an index of spatial flow heterogeneity. Average muscle blood flow in QF was 29 (10) ml · (kg muscle)⁻¹ · min⁻¹ at rest and 146 (54) ml · (kg muscle)⁻¹ · min⁻¹ during exercise (P=0.008 for the difference). Blood flow was significantly (P < 0.001) higher in the vastus medialis and the vastus intermedius than in the vastus lateralis and the rectus femoris, both in the resting and the exercising legs. Flow was more homogeneous in the exercising vastus medialis and more heterogeneous (P < 0.001) in the exercising vastus lateralis (P=0.01) than in the resting contralateral muscle. Flow was more homogeneous (P < 0.001) in those exercising muscles in which flow was highest (vastus intermedius and vastus medialis) as compared to muscles with the lowest flow (vastus lateralis and the rectus femoris). These data demonstrate that muscle blood flow varies among different muscles in humans both at rest and during exercise. Muscle perfusion is spatially heterogeneous at rest and during exercise, but responses to exercise are different depending on the muscle. Accepted: 16 June 2000     

Effects of inducing physiological hyperglucagonemia on metabolic responses to exercise

The purpose of the present study was to assess the effects of exogenously increasing the circulating levels of glucagon on the metabolic responses to exercise in rats. A total of six groups of rats were infused (iv) either with glucagon (20 or 50 ng·kg⁻¹·min⁻¹) or saline (0.9% NaCl), either in the resting state or during a bout of running exercise (45 min, 26 m·min⁻¹, 0% grade). Blood samples were taken at the end of the 45-min experiment. Animals infused with glucagon at 50 ng·kg⁻¹·min⁻¹ showed significantly (P<0.01) higher mean plasma glucagon concentrations than animals infused with saline or glucagon at 20 ng·kg⁻¹·min⁻¹. In addition, exercise resulted in significantly (P<0.05) higher mean plasma glucagon concentrations, compared to rest, in all groups. In spite of these differences in glucagon concentrations, there were no significant (P>0.05) effects of exercise and glucagon infusion on mean hepatic glycogen, plasma glucose, insulin, C-peptide, β-hydroxybutyrate, or catecholamine concentrations. Although exercise resulted in a significant (P<0.01) increase in plasma glycerol and free fatty acid concentrations and a significant (P<0.05) decrease in glycogen in the soleus muscle, these responses were not affected by the glucagon infusion. These results suggest that the liver is non-responsive to physiological hyperglucagonemia in a short-term (45 min) exercise situation. Electronic Publication     

Thermoregulatory responses to exercise at low ambient temperature performed after precooling or preheating procedures

Summary Seven male skiers exercised for 30 min on a cycle ergometer at 50% of maximal oxygen uptake and an ambient temperature of 5° C. The exercise was preceded either by cold exposure (PREC) or active warming-up (PREH). The data were compared with control exercise (CONT) performed immediately after entering the thermal chamber from a thermoneutral environment. Cold exposure resulted in negative heat storage (96.1 kJ·m⁻², SE 5.9) leading to significantly lower rectal, mean body and mean skin temperatures at the onset of exercise in PREC, as compared to PREH and CONT. The PREC-PREH temperature differences were still significant at the end of the exercise period. During exercise in the PREC test, oxygen uptake was higher than in PREH test (32.8 ml·kg⁻¹·min⁻¹, SE 1.5 vs 30.5 ml·kg⁻¹·min⁻¹, SE 1.3, respectively). Heart rate showed only a tendency to be higher in PREC than in PREH and CONT tests. In the PREH test skin and body temperatures as well as sweat rate were already elevated at the beginning of exercise. Exercise-induced changes in these variables were minimal. Heat storage decreased with the duration of the exercise. Exercise at low ambient temperature preceded by a 30-min rest in a cold environment requires more energy than the same exercise performed after PREH. This work was partly supported by the Polish Central Programme of Basic Research 06-02.III.2.1.     

Cardiorespiratory responses to exercise in acute hypoxia, hyperoxia and normoxia

There is a prevailing hypothesis that an acute change in the fraction of oxygen in inspired air (F _IO₂) has no effect on maximal cardiac output ( ), although maximal oxygen uptake ( ) and exercise performance do vary along with F _IO₂. We tested this hypothesis in six endurance athletes during progressive cycle ergometer exercise in conditions of hypoxia (F _IO₂=0.150), normoxia (F _IO₂=0.209) and hyperoxia (F _IO₂=0.320). As expected, decreased in hypoxia [mean (SD) 3.58 (0.45) l·min^–1, P<0.05] and increased in hyperoxia [5.17 (0.34) l·min^–1, P<0.05] in comparison with normoxia [4.55 (0.32) l·min^–1]. Similarly, maximal power ( ) decreased in hypoxia [334 (41) W, P<0.05] and tended to increase in hyperoxia [404 (58) W] in comparison with normoxia [383 (46) W]. Contrary to the hypothesis, was 25.99 (3.37) l·min^–1 in hypoxia (P<0.05 compared to normoxia and hyperoxia), 28.51 (2.36) l·min^–1 in normoxia and 30.13 (2.06) l·min^–1 in hyperoxia. Our results can be interpreted to indicate that (1) the reduction in in acute hypoxia is explained both by the narrowing of the arterio-venous oxygen difference and reduced , (2) reduced in acute hypoxia may be beneficial by preventing a further decrease in pulmonary and peripheral oxygen diffusion, and (3) reduced and in acute hypoxia may be the result rather than the cause of the reduced and skeletal muscle recruitment, thus supporting the existence of a central governor. Electronic Publication     

Energy cost of treadmill and floor walking at self-selected paces

Summary Oxygen uptake-velocity regression equations were developed for floor and level treadmill walking by having two groups of men, aged 19–29 years (n=20) and 55–66 years (n=22), walk at four self-selected paces, from “rather slowly” to “as fast as possible”. A two-variable quadratric model relating VO₂ (ml·kg⁻¹·min⁻¹) to velocity (m·s⁻¹) was adopted for prediction purposes. However, age and fatness significantly (p<0.05) interacted with treadmill walking speed, while age alone significantly interacted with floor speed. In addition, a significant difference was found between the energy cost of floor and treadmill walking. For example at the normal walking speed of 1.33 m·s⁻¹, the energy cost for the treadmill (age 55–66 years) was 10.58 ml·kg⁻¹·min⁻¹ and for the floor, 11.04 ml·kg⁻¹·min⁻¹ (p<0.05). Four quadratic equations are therefore presented, one each for floor and treadmill in each of the two age-groups. The percent variance explained was between 87 and 95% for each of these equations. Supported by a grant from the Ontario Ministry of Health (DM449)     

Carbohydrate feeding and exercise: effect of beverage carbohydrate content

Summary The purpose of this study was to determine the effect of ingesting fluids of varying carbohydrate content upon sensory response, physiologic function, and exercise performance during 1.25 h of intermittent cycling in a warm environment (T _db=33.4°C). Twelve subjects (7 male, 5 female) completed four separate exercise sessions; each session consisted of three 20 min bouts of cycling at 65% , with each bout followed by 5 min rest. A timed cycling task (1200 pedal revolutions) completed each exercise session. Immediately prior to the first 20 min cycling bout and during each rest period, subjects consumed 2.5 ml·kg BW⁻¹ of water placebo (WP), or solutions of 6%, 8%, or 10% sucrose with electrolytes (20 mmol·l⁻¹ Na⁺, 3.2 mmol·l⁻¹ K⁺). Beverages were administered in double blind, counterbalanced order. Mean (±SE) times for the 1200 cycling task differed significantly: WP=13.62±0.33 min, *6%=13.03±0.24 min, 8%=13.30±0.25 min, 10%=13.57±0.22 min (*=different from WP and 10%,P<0.05). Compared to WP, ingestion of the CHO beverages resulted in higher plasma glucose and insulin concentrations, and higher RER values during the final 20 min of exercise (P<0.05). Markers of physiologic function and sensory perception changed similarly throughout exercise; no differences were observed among subjects in response to beverage treatments for changes in plasma concentrations of lactate, sodium, potassium, for changes in plasma volume, plasma osmolality, rectal temperature, heart rate, oxygen uptake, rating of perceived exertion, or for indices of gastrointestinal distress, perceived thirst, and overall beverage acceptance. Compared to ingestion of a water placebo, consumption of beverages containing 6% to 10% sucrose resulted in similar physiologic and sensory response, while ingestion of the 6% sucrose beverage resulted in significantly improved end-exercise performance following only 60 min of intermittent cycling exercise.     

Blood metabolite and catecholamine responses to prolonged exercise following either acute plasma volume expansion or short-term training

 To determine the effect of acute plasma volume (PV) expansion on substrate utilization, blood metabolites and catecholamines to prolonged, moderate intensity cycle exercise, eight untrained men mean maximal oxygen uptake,O_2max 4.10 (SEM 0.32) l · min⁻¹ were infused (10 ml·kg⁻¹) with a 6% dextran (DEX) solution. These responses were also compared to those elicited using a short-term training (TR) protocol involving cycling for 90 to 120 min · day⁻¹ at 60% O_2max for 3 consecutive days. In general DEX, which resulted in a calculated expansion of PV by 23.9%, was without effect in modifying exercise oxygen uptake or the reduction in the respiratory exchange ratio (R) observed during prolonged exercise. In addition, the concentrations of blood glucose, glycerol, alanine and serum free fatty acids, although altered (P < 0.05) by exercise, were not altered by DEX. Blood lactate concentration was only higher (P < 0.05) at 30 min of exercise during DEX compared to the control. With the exception of blood lactate concentration, which was reduced (P < 0.05), TR did not change R or the concentrations of other blood metabolites. The concentrations of nonadrenaline and adrenaline, were depressed (P < 0.05) by DEX and TR at 60 and 90 min of exercise. These results would suggest that mechanisms as yet undefined can compensate for the estimated 10% reduction in arterial oxygen content mediated by acute PV expansion and enable prolonged exercise to be performed without adjustments in substrate selection and substrate mobilization. Accepted: 23 August 1996     

Effect of a 1 year combined aerobic- and weight-training exercise programme on aerobic capacity and ventilatory threshold in patients suffering from coronary artery disease

Weight-training is recommended as a complement to conventional aerobic-training for most low to moderate risk patients suffering from coronary artery disease (CAD). The purpose of this study was to evaluate the effect of a 1 year exercise programme combining weight- and aerobic-training on peak oxygen uptake (VO_2,peak) and ventilatory threshold (VT). We studied 40 men suffering CAD who were divided into three groups: 14 subjects to weight-training plus aerobic-training [mean (SD] [combined exercise group, age 55 (10) years], 14 to aerobic-training only [aerobic-training group, age 57 (11) years], and 12 to a control group [standard care, age 57 (11) years]. A symptom-limited graded exercise test using the standard Bruce protocol was performed using a 12-lead electrocardiogram, and gas analysis techniques. Muscle strength was determined only in the combined exercise group using the one-repetition maximum method on each of eight weight exercises. Arm and leg strength increased by 21.9% and 27.8% respectively (P<0.0001) from pre to post-tests. The VO_2,peak did not differ between the combined and aerobic-training groups but their adjusted means were greater than those of the control group [39 (1.8) and 35.3 (1.8) compared to 26.2 (2.7) ml·kg^–1·min^–1 (P<0.001)]. The oxygen uptake at VT was higher in the combined group [24.7 (1.4) ml·kg^–1·min^–1] compared to aerobic [18.7 (1.4) ml·kg^–1·min^–1] and control [13.6 (1.7) ml·kg^–1min^–1] groups (P<0.001). Similar results were found for exercise tolerance (treadmill time to peak and at VT). Combined exercise training increased the VT more than aerobic-training alone. Combined exercise training did not improve the VO_2,peak or the functional capacity more than aerobic-training alone. Electronic Publication     

Effect of water ingestion on cardiovascular and thermal responses to prolonged cycling and running in humans: a comparison

The aim of this investigation was to examine the effect of water ingestion on physiological responses to prolonged cycling (CYC) and running (RUN). A group of 11 men with mean (SEM) maximal oxygen uptake (V˙O_2max) 48.5 (1.8) ml·kg^–1·min^–1 on a cycle-ergometer and 52.1 (2.2) ml·kg^–1·min^–1 on a treadmill (P<0.01) exercised for 90 min on four occasions, twice on each ergometer, at 60% of mode specific V˙O_2max. No fluid was taken (D) in one trial on each ergometer, whereas 60% of fluid losses were replaced by drinking water in the other trial (W). In CYC, water ingestion attenuated the change in cardiac output ( ) and the reduction in stroke volume (ΔSV) [ΔSV: –22.7 (3.8) in D, –10.7 (2.9) ml·beat^–1 in W, P<0.01; : –1.9 (0.5) in D, –0.2 (0.4) l·min^–1 in W at 85 min, P<0.01], but did not affect rectal temperature [T _re at 90 min: 38.8 (0.1)°C in D, 38.7 (0.1)°C in W]. In contrast, fluid replacement reduced hyperthermia in RUN [T _re at 90 min: 39.6 (0.2) in D, 39.1 (0.2)°C in W, P<0.01], and this was linked with a higher skin blood flow [RUN-W 88.9 (8.5), RUN-D 70.7 (8.4)%, P<0.05]. The and ΔSV were also attenuated with water ingestion in this mode of exercise (P<0.05). It is concluded that water ingestion improves physiological function in both cycling and running, but that the underlying mechanism is different in the two modes of exercise. Electronic Publication     

Local and systemic effects on blood lactate concentration during exercise with small and large muscle groups

To evaluate the relationship between lactate release and [lac]_art and to investigate the influence of the catecholamines on the lactate release, 14 healthy men [age 25±3 (SE) year] were studied by superimposing cycle on forearm exercise, both at 65% of their maximal power reached in respective incremental tests. Handgrip exercise was performed for 30 min at 65% of peak power. In addition, between the tenth and the 22nd minute, cycling with the same intensity was superimposed. The increase in venous lactate concentration ([lac]_ven) (rest: 1.3±0.4 mmol·l⁻¹; 3rd min: 3.9±0.8 mmol·l⁻¹) begins with the forearm exercise, whereas arterial lactate concentration ([lac]_art) remains almost unchanged. Once cycling has been added to forearm exercise (COMB), [lac]_art increases with a concomitant increase in [lac]_ven (12th min: [lac]_art, 3.2±1.3 mmol·l⁻¹; [lac]_ven, 5.7±2.2 mmol·l⁻¹). A correlation between oxygen tension (P_vO₂) and [lac]_ven cannot be detected. There is a significant correlation between [lac]_art and norepinephrine ([NE]) (y=0.25x+1.2; r=0.815; p<0.01) but no correlation between lactate release and epinephrine ([EPI]) at moderate intensity. Our main conclusion is that lactate release from exercising muscles at moderate intensities is neither dependent on P_vO₂ nor on [EPI] in the blood.     

Blood flow to the brown adipose tissue of conscious young rabbits during hypoxia in cold and warm conditions

 Brown adipose tissue (BAT) non-shivering thermogenesis is stimulated by cold temperature and depressed by hypoxia. We investigated the extent to which changes in metabolic rate during cold and hypoxia, singly or combined, were accompanied by changes in BAT perfusion. One-month-old rabbits were instrumented for measurements of regional blood flow by the coloured microsphere technique. One group of rabbits was tested in warm (24 °C, n=17), and the other in cold (13 °C, n=9) conditions, first in normoxia (inspired oxygen concentration FIO₂ about 21%, arterial oxygen saturation S _aO₂ approximately 88%) followed by hypoxia (FIO₂ approximately 10%, S _aO₂ approximately 54%). In warm conditions, oxygen consumption (V·O₂, measured by an open-flow method) averaged 22 ml·kg^–1·min^–1 (STPD), and BAT blood flow 98 ml·100g^–1·min^–1. In hypoxia, V·O₂ dropped on average to 87%, whereas BAT flow dropped to 43% of the normoxic values. In the cold during normoxia, V·O₂ averaged 31 ml·kg^–1·min^–1 (STPD), and BAT blood flow was 155 ml·100g^–1·min^–1. In cold and hypoxia V·O₂ dropped to 19 ml·kg^–1·min^–1 (STPD) (i.e. 60% of the normoxic value), whereas BAT blood flow was not altered significantly (148 ml·100g^–1·min^–1). Hence, BAT blood flow decreased in hypoxia in absence of cold stimuli, whereas it remained high when hypoxia occurred during cold, despite the major drop in V·O₂. We conclude that cold is more important than hypoxia in determining BAT perfusion, and that changes in BAT blood flow are not a mechanism for the hypoxic control of V·O₂. Received: 24 June 1998 / Received after revision: 21 September 1998 / Accepted: 29 September 1998     

Sympathetic control of the forearm blood flow in man during brief isometric contractions

Summary Experiments were performed to assess the possible neurally mediated constriction in active skeletal muscle during isometric hand-grip contractions. Forearm blood flow was measured by venous occlusion plethysmography on 5 volunteers who exerted a series of repeated contractions of 4 s duration every 12 s at 60% of their maximum strength of fatigue. The blood flows increased initially, but then remained constant at 20–24 ml·min⁻¹·100 ml⁻¹ throughout the exercise even though mean arterial blood pressure reached 21–23 kPa (160–170 mm Hg). When the same exercise was performed after arterial infusion of phentolamine, forearm blood flow increased steadily to near maximal levels of 38.7±1.4 ml·min⁻¹·100 ml⁻¹. Venous catecholamines, principally norepinephrine, increased throughout exercise, reaching peak values of 983±258 pg·ml⁻¹ at fatigue. Of the vasoactive substances measured, the concentration of K⁺ and osmolarity in venous plasma also increased initially and reached a steady-state during the exercise but ATP increased steadily throughout the exercise. These data indicate a continually increasing α-adrenergic constriction to the vascular beds in active muscles in the human forearm during isometric exercise, that is only partially counteracted by vasoactive metabolites.     

Changes in blood lactate and respiratory gas exchange measures in sports with discontinuous load profiles

This study compares two different sport events (orienteering = OTC; tennis = TEC) with discontinuous load profiles and different activity/recovery patterns by means of blood lactate (LA), heart rate (HR), and respiratory gas exchange measures (RGME) determined via a portable respiratory system. During the TEC, 20 tennis-ranked male subjects [age: 26.0 (3.7) years; height: 181.0 (5.7) cm; weight: 73.2 (6.8) kg; maximal oxygen consumption (V˙O₂max): 57.3 (5.1) ml·kg⁻¹·min⁻¹] played ten matches of 50 min. During the OTC, 11 male members of the Austrian National Team [age: 23.5 (3.9) years; height: 183.6 (6.8) cm; weight: 72.4 (3.9) kg; V˙O₂max: 67.9 (3.8) ml·kg⁻¹·min⁻¹] performed a simulated OTC (six sections; average length: 10.090 m). In both studies data from the maximal treadmill tests (TT) were used as reference values for the comparison of energy expenditure of OTC and TEC. During TEC, the average V˙O₂ was considerably lower [29.1 (5.6) ml^·kg^−1·min⁻¹] or 51.1 (10.9)% of VO₂max and 64.8.0 (13.3)% of V˙O₂ determined at the individual anaerobic threshold (IAT) on the TT. The short high-intensity periods (activity/recovery = 1/6) did not result in higher LA levels [average LA of games: 2.07 (0.9) mmol·l⁻¹]. The highest average V˙O₂ value for a whole game was 47.8 ml·kg^−1·min⁻¹ and may provide a reference for energy demands required to sustain high-intensity periods of tennis predominately via aerobic mechanism of energy delivery. During OTC, we found an average V˙O₂ of 56.4 (4.5) ml·kg⁻¹·min⁻¹ or 83.0 (3.8)% of V˙O₂max and 94.6 (5.2)% of V˙O₂ at IAT. In contrast to TEC, LA were relatively high [5.16 (1.5) mmol·l⁻¹) although the average V˙O₂ was significantly lower than V˙O₂ at IAT. Our data suggest that portable RGEM provides valuable information concerning the energy expenditure in sports that cannot be interpreted from LA or HR measures alone. Portable RGEM systems provide valuable assessment of under- or over-estimation of requirements of sports and assist in the optimization and interpretation of training in athletes. Electronic Publication     

Thermoregulatory responses of paraplegic and able-bodied athletes at rest and during prolonged upper body exercise and passive recovery

The thermoregulatory responses of ten paraplegic (PA; T3/4-L4) and nine able-bodied (AB) upper body trained athletes were examined at rest and during prolonged arm-cranking exercise and passive recovery. Exercise was performed for 90 min at 80% peak heart rate, and at 21.5 (1.7)°C and 47.0 (7.8)% relative humidity on a Monark cycle ergometer (Ergomedic 814E) adapted for arm exercise. Mean peak oxygen uptake values for the PA and AB athlete groups were 2.12 (0.41) min⁻¹ and 3.19 (0.38) l · min⁻¹, respectively (P<0.05). At rest, there was no difference in aural temperature between groups [36.2 (0.4)°C for both groups]. However, upper body skin temperatures for the PA athletes were approximately 1.0 °C warmer than for the AB athletes, whereas lower body skin temperatures were cooler than those for the AB athletes (1.3 °C and 2.7 °C for the thigh and calf, respectively). Upper and lower body skin temperatures for the AB athletes were similar. During exercise, blood lactate peaked after 15 min of exercise for both groups [3.33 (1.26) mmol · l⁻¹ and 4.30 (1.03) mmol · l⁻¹ for the PA and AB athletes, respectively, P<0.05] and decreased throughout the remainder of the exercise period. Aural temperature increased by 0.7 (0.5)°C and 0.6 (0.4)°C for the AB and PA athletes, respectively. Calf skin temperature for the PA athletes increased during exercise by 1.4 (2.8)°C (P<0.05), whereas a decrease of 0.8 (2.0)°C (P<0.05) was observed for the AB athletes. During the first 20 min of recovery from exercise, the calf skin temperature of the AB athletes decreased further [−2.6 (1.3)°C; P<0.05]. Weight losses and changes in plasma volume were similar for both groups [0.7 (0.5) kg and 0.7 (0.4) kg; 5.4 (4.9)% and 9.7 (6.2)% for the PA and AB athletes, respectively]. In conclusion, the results of this study suggest that the PA athletes exhibit different thermoregulatory responses at rest and during exercise and passive recovery to those of upper body trained AB athletes. Despite this, during 90 min of arm-crank exercise in a cool environment, the PA athletes appeared to be at no greater thermal risk than the AB athletes. Accepted: 7 May 1997     

Oxygen uptake kinetics during severe intensity running and cycling

The purpose of this study was to investigate the effect of exercise mode on the characteristics of the oxygen uptake ( V̇O₂) response to exercise within the severe intensity domain. Twelve participants each performed a treadmill running test and a cycle ergometer test to fatigue at intensities selected to elicit a mode-specific V̇O₂max and to cause fatigue in ~5 min. The tests were at 234 (30) m·min⁻¹ and 251 (59) W, and times to fatigue were 297 (15) s and 298 (14) s, respectively. The overall rapidity of the V̇O₂response was influenced by exercise mode [ V̇O₂max was achieved after 115 (20) s in running versus 207 (36) s in cycling; p<0.01]. V̇O₂ responses were fit to a three-phase exponential model. The time constant of the primary phase was faster in treadmill tests than in cycle ergometer tests [14 (6) s versus 25 (4) s; p<0.01], and the amplitude of the primary phase was greater in running than in cycling when it was expressed in absolute terms [2327 (393) ml·min⁻¹ versus 2036 (301) ml·min⁻¹; p=0.02] but not when it was expressed as a percentage of the total increase in V̇O₂ [86 (6)% versus 82 (6)%; p=0.09]. When quantified as the difference between the end-exercise V̇O₂ and the V̇O₂ at 2 min, the amplitude of the slow component was ~40% smaller in running [177 (92) ml·min⁻¹ versus 299 (153) ml min⁻¹; p=0.03]. It is concluded that exercise modality affects the characteristics of the V̇O₂ response at equivalent intensities in the severe domain.     

Mobilization and oxidative burst of neutrophils are influenced by carbohydrate supplementation during prolonged cycling in humans

Prolonged, strenuous exercise may lead to suppressive effects on the immune system, which might be responsible for a greater susceptibility to opportunistic infections. The aim of this study was to examine the influence of carbohydrate substitution (CHS) during prolonged, strenuous exercise on neutrophil granulocytes and their oxidative burst (intracellular oxidation of dihydrorhodamine₁₂₃ to rhodamine₁₂₃ after induction by formylized 1-methionyl-1-leucyl-1-phenylalanin) using flow cytometry. In three trials different concentrations of CHS (placebo compared to 6% and 12% CHS; 50 ml·kg^–1) were given randomly to 14 endurance trained cyclists [mean (SD) age 25 (5) years, maximal oxygen uptake 67 (6) ml·min^–1·kg^–1] cycling for 4 h in a steady state at 70% of their individual anaerobic threshold. Blood samples were taken before, immediately after cessation, 1 h and 19 h after exercise. A significant rise in neutrophil counts was observed immediately after cessation and 1 h after exercise with a return to normal rest values 19 h after exercise for all three conditions (P<0.001). The relative proportions of rhodamine₁₂₃+ neutrophils were significantly diminished in all three conditions 1 h after exercise (P<0.01), while the mean fluorescence intensity was lowest in the placebo trial and differed significantly to the 12% CHS trial (P=0.024) and almost significantly to the 6% CHS trial (P=0.052). In conclusion, these data suggest a beneficial effect of CHS on the neutrophil oxidative burst and a possible attenuation of the susceptibility to infections, presumably due to the reduction of metabolic stress in prolonged, strenuous exercise. Electronic Publication     

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