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     

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     

Saliva flow and composition in humans exposed to acute altitude hypoxia

Summary The effects of acute hypoxia (2 days at 4350 m) on whole saliva flow and composition were studied on 12 sea-level natives, at rest and following a maximal exercise. Exercise, performed in normoxia and hypoxia, did not induce variations in saliva flow rate, saliva potassium or α-amylase concentrations. In contrast, acute hypoxia did lead to an increase in mean saliva flow rate both at rest (0.63 ml·min⁻¹ to 0.93 ml·min⁻¹,P<0.01) and after exercise (0.56 ml·min⁻¹ to 1.06 ml·min⁻¹,P<0.05) and a decrease in mean saliva potassium concentration at rest (20.8 mmol·1⁻¹ to 14.7 mmol·1⁻¹,P<0.01) as well as after exercise (21.7 mmol·1⁻¹ to 16.5 mmol·1⁻¹,P<0.05). This effect might be the consequence of a hypoxia-induced stimulation of the parasympathetic nervous system.     

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     

Relationship of exercise test variables to cycling performance in an Ironman triathlon

The purpose of this study was, firstly, to investigate the intensity of exercise performanceof highly trained ultra-endurance triathletes during the cycling portion of an Ironman triathlon, and, secondly, to examine the anaerobic threshold and its relationship to this performance. Following a peak oxygen consumption (VO_2peak) test on a cycle ergometer to determine the heart rate (HR_Th,vent) and power output (PO_Th,vent) at the ventilatory threshold (Th_vent), 11 highly trained male triathletes [mean (SEM) age 35.8 (1.6) years, body fat 11.7 (1.2)%. VO_2peak 67.5 (1.0) ml·kg^–1·min^–1] who were participating in an Ironman triathlon, in random order: (1) cycled at their PO_Th,vent (Bi_Th,vent) until they were exhausted, and (2) cycled for 5 h at a self-selected intensity (Bi_SSI). Cycling power output (PO), oxygen uptake (VO₂), heart rate (HR) and blood lactate concentration ([La^–]_b) were recorded at regular intervals during these trials, while performance HR was recorded during the cycling phase of the Ironman triathlon. Significantly greater (P<0.05) values were attained during Bi_Th,vent than during Bi_SSI for PO [274 (9) compared to 188 (9) W], VO₂ [3.61 (0.15) compared to 2.64 (0.09) l·min^–1], and [La^–]_b [6.7 (0.8) compared to 2.8 (0.4) mmol·l^–1]. Moreover, mean HR during the Ironman triathlon cycle phase [146.3 (2.4) beats·min^–1; n=7] was significantly greater than mean HR during Bi_SSI [130 (4) beats·min^–1], and significantly less than mean HR during Bi_Th,vent [159 (3) beats·min^–1; all P<0.05]. However, HR during the cycle portion of the Ironman triathlon was highly related to (r=0.873; P<0.05) and not significantly different to HR_Th,vent [150 (4) beats·min^–1]. These data suggest that ultra-endurance triathletes cycle during the Ironman triathlon at a HR intensity that approximates to HR_Th,vent, but at a PO that is significantly below PO_Th,vent. 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.     

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)     

Maximal oxygen uptake during field running does not exceed that measured during treadmill exercise

Modern ergometric equipment enables the simulation of laboratory maximal oxygen uptake (V˙O_2max) testing in the field. Therefore, it was investigated whether the improved event specificity on the track might lead to higher V˙O_2max measurements in running. Identical protocols were used on the treadmill and on the track (speed was indicated by a computer-driven flashing light system). Ambulatory measurements of gas exchange were carried out throughout both tests, which were executed in randomized order. There were no significant differences (P=0.71) in V˙O_2max between treadmill [4.65 (0.51) ml·min^–1] and field tests [4.63 (0.55) ml·min^–1]. However, the test duration differed significantly (P<0.001) by approximately 5%: treadmill 691 (39) s; field test 727 (42) s. With the exception of maximum heart rate (HR_max; significantly higher in the field with P=0.02) all criteria for the degree of effort were similar between the two tests. However, the difference in HR_max at less than 2 beats·min^–1, was practically negligible. Submaximal measurements of oxygen uptake and minute ventilation were significantly higher on the treadmill (P<0.001 for both parameters). In summary, field tests with incremental running protocols do not result in higher V˙O_2max measurements compared to laboratory treadmill exercise. A better running economy on the track results in higher maximal velocities and longer exercise durations being sustained. The determination of V˙O_2max is not a reasonable application for ambulatory gas exchange measurements because laboratory values are not surpassed. Electronic Publication     

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     

Metabolic profile of 4 h cycling in the field with varying amounts of carbohydrate supply

Several laboratory studies have demonstrated a performance-enhancing effect of carbohydrate (CHO) supplementations during endurance sessions of long duration. However, the transferability of these results to real training and competition circumstances has not been conclusively shown. Therefore, we tried to test the influence of graded CHO substitution on substrate utilization and selected physiological parameters under standardized but practically orientated field conditions. Fourteen endurance-trained male subjects [mean (SD): 25 (5) years, 72 (9) kg, V˙O_2max 67 (6) ml·min^–1·kg^–1, individual anaerobic threshold (IAT) 269 (30) W] after a stepwise increasing pre-test had to perform three 4-h endurance rides on their own bicycles with simultaneous spiroergometry: constant workload 70% IAT (monitoring by SRM-System). Before and during exercise, solutions without (0%), with 6% or 12% CHO were administered double-blindly and in randomized order (total volume: 50 ml·kg^–1). After cessation of exercise, significant differences between 0% and both CHO concentrations were detected for blood glucose (GLU; 75 mg dl^–1 for 0% vs 101 mg dl^–1 for 6% vs 115 mg dl^–1 for 12%; P<0.001) and respiratory exchange ratio (0.84 vs 0.88 vs 0.90; P<0.01; correlation to GLU: r=0.46, P<0.05). Free fatty acids (0.19 vs 0.16 vs 0.10 mmol l^–1) and glycerol (0.41 vs 0.22 vs 0.12 mmol l^–1) were significantly different between the endurance trials in a dose-dependent manner (both P<0.001). Lactate concentration (P=0.42) and heart rate (P=0.12) had no significant influence from CHO substitution. We conclude that CHO substitution during 4-h endurance training inhibits lipolysis in a dose-dependent manner and enhances aerobic glycolysis. This proves that earlier laboratory findings can be replicated under field conditions using modern portable equipment. Electronic Publication     

Breath-by-breath fluctuations of pulmonary gas exchange and ventilation in COPD patients

The purpose of the study was to characterise statistically the inherent fluctuations in breath-by-breath measurements of pulmonary gas exchange (oxygen uptake and carbon dioxide output, VO₂ and VCO₂, respectively) and pulmonary ventilation (V_E) in patients with chronic obstructive pulmonary disease (COPD) and to compare them with those of healthy control subjects. Thirty subjects with COPD [mean (SD): 67 (6) years old; forced expiratory volume in 1 min, FEV₁ 1.25( 0.18) l; 42 (6)% predicted FEV₁] and 12 healthy subjects [31 (3) years old; FEV₁ 3.62 (0.54) l; 99 (8)% predicted FEV₁] performed exercise tests on a cycle ergometer at a constant work rate of moderate intensity. Steady-state exercise values for VO₂, VCO₂ and V_E were 905 (96) ml·min^–1, 847(90) ml·min^–1 and 23 (3) l·min^–1, respectively for the COPD patients and 1239(89) ml·min^–1, 1191(84) ml·min^–1 and 37(3) l·min^–1, respectively, for the healthy controls. The breath-by-breath fluctuations were well characterised by a Gaussian density-probability function with breath-to-breath autocorrelations that were not significantly different from 0, up to four subsequent breaths. Its magnitude varied among variables, but was independent of the signal amplitude for the same subject and variable. With ratios of amplitude of fluctuation:signal of around 10%, typical of the patients studied, the resolution of time constants and amplitude were ≅9 s and ≅100 ml·min^–1, respectively for VO₂ or VCO₂ with one repetition. Electronic Publication     

Substrate utilization in boys during exercise with [13C]-glucose ingestion

The influence of glucose ingestion on substrate utilization during prolonged exercise in children and adolescents is currently unknown. In the present study we determined the effect of intermittent exogenous glucose (GLU_exo) ingestion on substrate utilization during prolonged exercise, in adolescent boys ages 13–17 years. Healthy untrained volunteers performed four 30-min exercise bouts on a cycle ergometer, separated by 5-min rest periods (≅60% maximum O₂ consumption), on two occasions spaced 1–4 weeks apart. Two trials were performed, a control trial (CT), in which subjects ingested water intermittently during the exercise, and a glucose trial (GT), in which subjects ingested a ¹³C-enriched GLU_exo drink (≅3 g glucose · kg body mass⁻¹), also intermittently during the exercise. Total free fatty acids (FAT_total), glucose (GLU_total) and carbohydrate (CHO_total) oxidation was determined from indirect calorimetry, while GLU_exo oxidation was calculated from the ¹³C/¹²C ratio in expired air after 5–10 min and 25–30 min of exercise in each bout. Heart rate and rating of perceived exertion (RPE) were determined at the same time intervals. The oxidation of CHO_total was 169.1 (12.9) g · 120 min⁻¹ and 203.1 (15.9) g · 120 min⁻¹ (P < 0.01) and that of FAT_total was 31.0 (4.2) g · 120 min⁻¹ and 17.1 (2.5) g · 120 min⁻¹ (P < 0.01) in CT and GT, respectively. GLU_exo oxidation in GT was 57.8 (4.3) g · 120 min⁻¹, or 34.2 (2.2)% of that ingested. Endogenous glucose oxidation was 169.1 (12.9) g · 120 min⁻¹ and 145.3 (11.9) g · 120 min⁻¹ (P < 0.01) in CT and GT, respectively. Insulin and glucose concentrations were higher in GT than in CT by 226% and 37%, respectively (both P < 0.05). Free fatty acids and glycerol concentrations were lower in GT than in CT, by 27% and 79%, respectively (both P < 0.05). Heart rate was similar between trials, but RPE was lower in GT vs CT at both 115 and 135 min. Thus, under these experimental conditions, GLU_exo intake spares endogenous carbohydrate and fat by 16% and 45%, respectively, contributes to approximately 25% of the total energy demand of exercise, and lowers the RPE. Accepted: 21 May 2000     

Vastus medialis muscle oxygenation trends during a simulated 20-km cycle time trial

In this study we examined the oxygenation trend of the vastus medialis muscle during sustained high-intensity exercise. Ten cyclists performed an incremental cycle ergometer test to voluntary exhaustion [mean (SD) maximum oxygen uptake 4.29 (0.63) l·min^–1; relative to body mass 60.8 (2.4) ml·kg^–1·min^–1] and a simulated 20-km time trial (20TT) on a wind-loaded roller system using their own bicycle (group time = 23–31 min) in two separate sessions. Cardiorespiratory responses were monitored using an automated metabolic cart and a wireless heart rate monitor. Tissue absorbency, which was used as an index of muscle oxygenation, was recorded simultaneously from the vastus medialis using near-infrared spectroscopy. Group mean values for oxygen uptake, ventilation, heart rate, respiratory exchange ratio, power output, and rating of perceived exhaustion were significantly (P≤0.05) higher during the incremental test compared to the 20TT [4.29 (0.63) l·min^–1 vs 4.01 (0.55) l·min^–1, 120.4 (26) l·min^–1 vs 97.6 (16.1) l·min^–1, 195 (8) beats·min^–1 vs 177 (9) beats·min^–1, 1.15 (0.06) vs 0.93 (0.06), 330.1 (31) W vs 307.2 (24.5) W, and 19 (1.5) vs 16 (1.7), respectively]. Oxygen uptake and heart rate during the 20TT corresponded to 93.5% and 90.7%, respectively, of the maximal values observed during the incremental test. Comparison of the muscle oxygenation trends between the two tests indicated a significantly greater degree of deoxygenation during the 20TT [–699 (250) mV vs –439 (273) mV; P≤0.05] and a significant delay in the recovery oxygenation from the 20TT. The mismatching of whole-body oxygen uptake and localised tissue oxygenation between the two tests could be due to differences in muscle temperature, pH, localised blood flow and motor unit recruitment patterns between the two tests. Electronic Publication     

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     

The effect of selective beta1-blockade on EMG signal characteristics during progressive endurance exercise

This study analysed the effect of selective β₁-blockade on neuromuscular recruitment characteristics during progressive endurance exercise. Ten healthy subjects ingested a selective β₁-blocker, acebutolol (200 mg b.d.), for 7 days (for one of two cycling trials), with a 10-day wash-out period between trials. On the last day of acebutolol ingestion subjects performed three successive 15-min rides at 30%, 50% and 70% of their peak power output and then cycled at increasing (15 W min^–1) work rates to exhaustion. Force output, heart rate, submaximal V˙O₂, rate of perceived exertion (RPE), electromyographic (EMG) data and blood lactate were captured during the cycling activity. Peak work rate [270 (111) W vs 197 (75) W, CON vs BETA, P <0.01], time to exhaustion [49.7 (23.2) min vs 40.3 (23.7) min, CON vs BETA, P <0.05] and heart rate [mean, for the full ride 135.5 (38.3) beats min^–1 vs 111.5 (30.0) beats min^–1 CON vs BETA, P <0.05] were significantly lower for the group who ingested β₁-blockade (BETA) compared to the control group (CON). Although not significant, submaximal V˙O₂ was reduced in BETA during the ride, while RPE was significantly higher during the ride for BETA (P <0.01). Mean integrated electromyography was higher in the BETA group although these differences were not significant. Mean power frequency values of the BETA group showed a significant (P <0.05) shift to the upper end of the spectrum in comparison to the control group. Lactate values [11.7 (3.5) mmol.l^–1 vs 7.1 (4.1) mmol.l^–1 CON vs BETA] were significantly lower (P <0.05) at exhaustion in BETA. Significant reductions in cycling performance were found when subjects ingested β₁-blockers. This study has shown significant shifts to the upper end of the EMG frequency spectrum after β₁-blocker ingestion, which could be caused by a change in neuromuscular recruitment strategy to compensate for the impaired submaximal exercise performance. Electronic Publication     

Meropenem Alone and in Combination with Vancomycin in Experimental Meningitis Caused by a Penicillin-Resistant Pneumococcal Strain

 In a rabbit model of meningitis caused by a pneumococcus highly resistant to penicillin (MIC, 4 μg/ml), meropenem, a broad-spectrum carbapenem, was bactericidal (–0.48±0.14 Δlog₁₀ cfu/ml·h) and slightly superior to ceftriaxone (–0.34±0.23 Δlog₁₀ cfu/ml·h) and vancomycin (–0.39±0.19 Δlog₁₀ cfu/ml·h). Although the combination of vancomycin with ceftriaxone was significantly more active than ceftriaxone alone (–0.55±0.19 Δlog₁₀ cfu/ml·h), only an insignificant gain was observed by the addition of vancomycin to meropenem (–0.55±0.28 Δlog₁₀ cfu/ml·h).     

The effect of training in male prepubertal and pubertal monozygotic twins

Nine male pairs of monozygotic twins aged 11–14 years, height 147 (7.6) cm and body mass 39.7 (9.6) kg, participated in this study. Twin zygocity was tested using morphological, dermatoglyphic and hematologic methods, and Tanner's five stages were used for the evaluation of biological maturation. One twin from each pair undertook training for 6 months, three times a week, with running at 85–120% of the lactate anaerobic threshold (LT). Anthropometrics, determination of maximum O₂ uptake (V˙O_2max), LT and maximal blood lactate concentration ([La]_max) was carried out before, during and after training. No significant difference existed between the trained twins and their untrained brothers before training. After training, the trained twins increased their V˙O_2max (per kg body mass) by 10.6% and their LT by 18.2% (P<0.01), reaching values that differed significantly from those of their untrained brothers [57.5 (3.6) ml·kg⁻¹·min⁻¹ vs 55.4 (3.3) ml·kg⁻¹·min⁻¹ and 13.4 (1.1) km·h⁻¹ vs 12.7 (1.1) km·h⁻¹, respectively]. In addition, in the trained twins relative body fat was reduced (P<0.05) from 17.8 to 16.2% and their somatotype altered significantly (decrease of endomorphy and mesomorphy and increase of ectomorphy), while in the untrained twins there was no change in these parameters. Both groups of twins significantly increased their absolute V˙O_2max after the 6 months of training, the trained by 14,9% [from 2.08 (0.43) to 2.37 (0.45) l·min⁻¹] and the untrained by 10.5% [from 2.10 (0.41) to 2.32 (0.47) l·min⁻¹], but no difference was registered between them. A comparison of the intrapair changes in V˙O_2max of prepubertal and pubertal twins showed an influence of training in the prepubertal (19.3% vs 5.2%) but not in the pubertal twins (12.7% vs 13.1%). Using analysis of variance, the relative importance of training, heredity and their interaction was evaluated to be 20%, 70% and 10%, respectively, for the change in body fat, 35%, 45% and 20%, respectively, for the change in relative V˙O_2max and 25–30%, 50–60% and 15–20%, respectively, for the change in LT. In conclusion, training during pubertal growth can favour aerobic power (depending on body composition) as well as aerobic capacity, but it has no effect on absolute V˙O_2max. Genetic control seems to have a strong effect on the extent of adaptations, and the genotype—training interaction explains a small, but prominent part of them. Electronic Publication     

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.     

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     

Effects of prior heavy exercise,prior sprint exercise and passive warming on oxygen uptake kinetics during heavy exercise in humans

Prior heavy exercise (above the lactate threshold, Th_la) increases the amplitude of the primary oxygen uptake (VO₂) response and reduces the amplitude of the VO₂ slow component during subsequent heavy exercise. The purpose of this study was to determine whether these effects required the prior performance of an identical bout of heavy exercise, or if prior short-duration sprint exercise could cause similar effects. A secondary purpose of this study was to determine the effect of elevating muscle temperature (through passive warming) on VO₂ kinetics during heavy exercise. Nine male subjects performed a 6-min bout of heavy exercise on a cycle ergometer 6 min after: (1) an identical bout of heavy exercise; (2) a 30-s bout of maximal sprint cycling; (3) a 40-min period of leg warming in a hot water bath at 42°C. Prior sprint exercise elevated blood [lactate] prior to the onset of heavy exercise (by ≅5.6 mM) with only a minor increase in muscle temperature (of ≅0.7°C). In contrast, prior warming had no effect on baseline blood lactate concentration, but elevated muscle temperature by ≅2.6°C. Both prior heavy exercise and prior sprint exercise significantly increased the absolute primary VO₂ amplitude (by ≅230 ml·min^–1 and 260 ml·min^–1, respectively) and reduced the amplitude of the VO₂ slow component (by ≅280 ml·min^–1 and 200 ml·min^–1, respectively) during heavy exercise, whereas prior warming had no significant effect on the VO₂ response. We conclude that the VO₂ response to heavy exercise can be markedly altered by both sustained heavy-intensity submaximal exercise and by short-duration sprint exercise that induces a residual acidosis. In contrast, passive warming elevated muscle temperature but had no effect on the VO₂ response. Electronic Publication