Oxygen uptake during moderate intensity running: response following a single bout of interval training

Eight male endurance runners [mean ± (SD): age 25 (6) years; height 1.79 (0.06) m; body mass 70.5 (6.0) kg; % body fat 12.5 (3.2); maximal oxygen consumption (V˙O_2max 62.9 (1.7) ml · kg⁻¹ · min⁻¹] performed an interval training session, preceded immediately by test 1, followed after 1 h by test 2, and after 72 h by test 3. The training session was six 800-m intervals at 1 km · h⁻¹ below the velocity achieved at V˙O_2max with 3 min of recovery between each interval. Tests 1, 2 and 3 were identical, and included collection of expired gas, measurement of ventilatory frequency (f _v ), heart rate (f _c), rate of perceived exertion (RPE), and blood lactate concentration ([La⁻]_B) during the final 5 min of 15 min of running at 50% of the velocity achieved at V˙O_2max (50% −V˙O_2max).␣Oxygen uptake (V˙O₂), ventilation (V˙ _E ), and respiratory exchange ratio (R) were subsequently determined from duplicate expired gas collections. Body mass and plasma volume changes were measured preceding and immediately following the training session, and before tests 1–3. Subjects ingested water immediately following the training session, the volume of which was determined from the loss of body mass during the session. Repeated measures analysis of variance with multiple comparison (Tukey) was used to test differences between results. No significant differences in body mass or plasma volume existed between the three test stages, indicating that the differences recorded for the measured parameters could not be attributed to changes in body mass or plasma volume between tests, and that rehydration after the interval training session was successful. A significant (P < 0.05) increase was found from test 1 to test 2 [mean (SD)] for V˙O₂ [2.128 (0.147) to 2.200 (0.140) 1 · min⁻¹], f _c [125 (17) to 132 (16) beats · min⁻¹], and RPE [9 (2) to 11 (2)]. A significant (P < 0.05) decrease was found for submaximal R [0.89 (0.03) to 0.85 (0.04)]. These results suggest that alterations in V˙O₂ during moderate-intensity, constant-velocity running do occur following heavy-intensity endurance running training, and that this is due to factors in addition to changed substrate metabolism towards greater fat utilisation, which could explain only 31% of the increase in V˙O₂. Accepted: 8 December 1997     

Detection of the change point in oxygen uptake during an incremental exercise test using recursive residuals: relationship to the plasma lactate accumulation and blood acid base balance

The purpose of this study was to develop a method to determine the power output at which oxygen uptake (V˙O₂) during an incremental exercise test begins to rise non-linearly. A group of 26 healthy non-smoking men [mean age 22.1 (SD 1.4) years, body mass 73.6 (SD 7.4) kg, height 179.4 (SD 7.5) cm, maximal oxygen uptake (V˙O_2max) 3.726 (SD 0.363) l · min⁻¹], experienced in laboratory tests, were the subjects in this study. They performed an incremental exercise test on a cycle ergometer at a pedalling rate of 70 rev · min⁻¹. The test started at a power output of 30 W, followed by increases amounting to 30 W every 3 min. At 5 min prior to the first exercise intensity, at the end of each stage of exercise protocol, blood samples (1 ml each) were taken from an antecubital vein. The samples were analysed for plasma lactate concentration [La]_pl, partial pressure of O₂ and CO₂ and hydrogen ion concentration [H⁺]_b. The lactate threshold (LT) in this study was defined as the highest power output above which [La⁻]_pl showed a sustained increase of more than 0.5 mmol · l⁻¹ · step⁻¹. The V˙O₂ was measured breath-by-breath. In the analysis of the change point (CP) of V˙O₂ during the incremental exercise test, a two-phase model was assumed for the 3rd-min-data of each step of the test: X _i =at _i +b+ɛ _i for i=1,2,…,T, and E(X _i )>at _i +b for i =T+1,…,n, where X ₁, … , X _n are independent and ɛ _i ∼N(0,σ²). In the first phase, a linear relationship between V˙O₂ and power output was assumed, whereas in the second phase an additional increase in V˙O₂ above the values expected from the linear model was allowed. The power output at which the first phase ended was called the change point in oxygen uptake (CP-V˙O₂). The identification of the model consisted of two steps: testing for the existence of CP and estimating its location. Both procedures were based on suitably normalised recursive residuals. We showed that in 25 out of 26 subjects it was possible to determine the CP-O₂ as described in our model. The power output at CP-V˙O₂ amounted to 136.8 (SD 31.3) W. It was only 11 W – non significantly – higher than the power output corresponding to LT. The V˙O₂ at CP-V˙O₂ amounted to 1.828 (SD 0.356) l · min⁻¹ was [48.9 (SD 7.9)% V˙O_{2 max} ]. The [La⁻]_pl at CP-V˙O₂, amounting to 2.57 (SD 0.69) mmol · l⁻¹ was significantly elevated (P<0.01) above the resting level [1.85 (SD 0.46) mmol · l⁻¹], however the [H⁺]_b at CP-V˙O₂ amounting to 45.1 (SD 3.0) nmol · l⁻¹, was not significantly different from the values at rest which amounted to 44.14 (SD 2.79) nmol · l⁻¹. An increase of power output of 30 W above CP-V˙O₂ was accompanied by a significant increase in [H⁺]_b above the resting level (P=0.03). Accepted: 25 March 1998     

Ventilatory efficiency and exercise tolerance in 101 healthy volunteers

The ventilatory equivalent for CO₂ defines ventilatory efficiency largely independent of metabolism. An impairment of ventilatory efficiency may be caused by an increase in either anatomical or physiological dead space, the latter being the most important mechanism in the hyperpnoea of heart failure, pulmonary embolism, pulmonary hypertension and the former in restrictive lung disease. However, normal values for ventilatory efficiency have not yet been established. We investigated 101 (56 men) healthy volunteers, aged 16–75 years, measuring ventilation and gas exchange at rest (n = 64) and on exercise (modified Naughton protocol, n = 101). Age and sex dependent normal values for ventilatory efficiency at rest defined as the ratio ventilation:carbon dioxide output (V˙ _E:V˙CO₂), exercise ventilatory efficiency during exercise, defined as the slope of the linear relationship between ventilation and carbon dioxide output (V˙ _E vs V˙CO₂ slope), oxygen uptake at the anaerobic threshold and at maximum (V˙O_2AT,V˙O_2max, respectively) and breathing reserve were established. Ventilatory efficiency at rest was largely independent of age, but was smaller in the men than in the women [V˙ _E:V˙CO₂ 50.5 (SD 8.8) vs 57.6 (SD 12.6) P<0.05]. Ventilatory efficiency during exercise declined significantly with age and was smaller in the men than in the women (men: (V˙ _E vs V˙CO₂ slope = 0.13 × age + 19.9; women: V˙ _E vs V˙CO₂ slope = 0.12 × age + 24.4). The V˙O_2AT and V˙O_2max were 23 (SD 5) and 39 (SD 7) ml O₂ · kg · min⁻¹ in the men and 18 (SD 4) and 32 (SD 7) in the women, respectively, and declined significantly with age. The V˙O_2AT was reached at 58 (SD 9)% V˙O_2max. Breathing reserve at the end of exercise was 41% and was independent of sex and age. It was concluded from this study that ventilatory efficiency as well as peak oxygen uptake are age and sex dependent in adults. Accepted: 11 June 1997     

The development of an isokinetic squat device: reliability and relationship to functional performance

The aims of the present study were: (1) to assess aerobic metabolism in paraplegic (P) athletes (spinal lesion level, T4–L3) by means of peak oxygen uptake (V˙O_2peak) and ventilatory threshold (VT), and (2) to determine the nature of exercise limitation in these athletes by means of cardioventilatory responses at peak exercise. Eight P athletes underwent conventional spirographic measurements and then performed an incremental wheelchair exercise on an adapted treadmill. Ventilatory data were collected every minute using an automated metabolic system: ventilation (l · min⁻¹), oxygen uptake (V˙O₂, l · min⁻¹, ml · min⁻¹ · kg⁻¹), carbon dioxide production (V˙CO₂, ml · min⁻¹), respiratory exchange ratio, breathing frequency and tidal volume. Heart rate (HR, beats · min⁻¹) was collected with the aid of a standard electrocardiogram. V˙O_2peak was determined using conventional criteria. VT was determined by the breakpoint in the V˙CO₂−V˙O₂ relationship, and is expressed as the absolute VT (V˙O₂, ml · min⁻¹ · kg⁻¹) and relative VT (percentage of V˙O_2peak). Spirometric values and cardioventilatory responses at rest and at peak exercise allowed the measurement of ventilatory reserve (VR), heart rate reserve (HRr), heart rate response (HRR), and O₂ pulse (O₂ P). Results showed a V˙O_2peak value of 40.6 (2.5) ml · min⁻¹ · kg⁻¹, an absolute VT detected at 23.1 (1.5) ml · min⁻¹ · kg⁻¹ V˙O₂ and a relative VT at 56.4 (2.2)% V˙O_2peak. HRr [15.8 (3.2) beats · min⁻¹], HRR [48.6 (4.3) beat · l⁻¹], and O₂ P [0.23 (0.02) ml · kg⁻¹ · beat⁻¹] were normal, whereas VR at peak exercise [42.7 (2.4)%] was increased. As wheelchair exercise excluded the use of an able-bodied (AB) control group, we compared our V˙O_2peak and VT results with those for other P subjects and AB controls reported in the literature, and we compared our cardioventilatory responses with those for respiratory and cardiac patients. The low V˙O_2peak values obtained compared with subject values obtained during an arm-crank exercise may be due to a reduced active muscle mass. Absolute VT was somewhat comparable to that of AB subjects, mainly due to the similar muscle mass involved in wheelchair and arm-crank exercise by P and AB subjects, respectively. The increased VR, as reported in patients with chronic heart failure, suggested that P athletes exhibited cardiac limitation at peak exercise, and this contributed to the lower V˙O_2peak measured in these subjects. Accepted: 22 April 1997     

Transient oxygen uptake response to exercise characterizes functional capacity of the cardiocirculatory system in patients with chronic heart failure: a random stimulus approach

The transient response of oxygen uptake (V˙O₂) to submaximal exercise, known to be abnormal in patients with cardiovascular disorders, can be useful in assessing the functional status of the cardiocirculatory system, however, a method for evaluating it accurately has not yet been established. As an alternative approach to the conventional test at constant exercise intensity, we applied a random stimulus technique that has been shown to provide relatively noise immune responses of system being investigated. In 27 patients with heart failure and 24 age-matched control subjects, we imposed cycle exercise at 50 W intermittently according to a pseudo-random binary (exercise-rest) sequence, while measuring breath-by-breath V˙O₂. After determining the transfer function relating exercise intensity (W˙) to V˙O₂ and attenuating the high frequency ranges (>6 exercise-rest cycles · min⁻¹), we computed the high resolution band-limited (0–6 cycles · min⁻¹) V˙O₂ response (0–120 s) to a hypothetical step exercise. The V˙O₂ response showed a longer time constant in the patients than in the control subjects [47 (SD 37) and 31 (SD 8) s, respectively, P < 0.05]. Furthermore, the amplitude of the V˙O₂ response after the initial response was shown to be significantly smaller in the patients than in the control subjects [176 (SD 50) and 267 (SD 54) ml · min⁻¹ at 120 s]. The average amplitude over 120 s correlated well with peak V˙O₂ (r = 0.73) and ΔV˙O₂/ΔW˙ (r = 0.70), both of which are well-established indexes of exercise tolerance. The data indicated that our band-limited V˙O₂ step response using random exercise was more markedly attenuated and delayed in the patients with heart failure than in the normal controls and that it could be useful in quantifying the overall functional status of the cardiocirculatory system. Accepted: 6 January 1998     

Anaerobic contribution to the time to exhaustion at the minimal exercise intensity at which maximal oxygen uptake occurs in elite cyclists, kayakists and swimmers

Using 23 elite male athletes (8 cyclists, 7 kayakists, and 8 swimmers), the contribution of the anaerobic energy system to the time to exhaustion (t _lim) at the minimal exercise intensity (speed or power) at which maximal oxygen uptake (V˙O_{2 max}) occurs (I _{V˙O2 max}) was assessed by analysing the relationship between the t _lim and the accumulated oxygen deficit (AOD). After 10-min warming up at 60% of V˙O_{2 max}, the exercise intensity was increased so that each subject reached his I _V˙O2max in 30 s and then continued at that level until he was exhausted. Pre-tests included a continuous incremental test with 2 min steps for determining the I _V˙O2max and a series of 5-min submaximal intensities to collect the data that would allow the estimation of the energy expenditure at I _V˙O2max . The AOD for the t _lim exercise was calculated as the difference between the above estimation and the accumulated oxygen uptake. The mean percentage value of energy expenditure covered by anaerobic metabolism was 15.2 [(SD 6)%, range 8.9–24.1] with significant differences between swimmers and kayakists (16.8% vs 11.5%, P≤0.05) and cyclists and kayakists (16.4% vs 11.5%, P≤0.05). Absolute AOD values ranged from 26.4 ml · kg⁻¹ to 83.6 ml · kg⁻¹ with a mean value of 45.9 (SD 18) ml · kg⁻¹. Considering all the subjects, the t _lim was found to have a positive and significant correlation with AOD (r = 0.62, P≤0.05), and a negative and significant correlation with V˙O_{2 max} (r = −0.46, P≤0.05). The data would suggest that the contribution of anaerobic processes during exercise performed at I _V˙O2max should not be ignored when t _lim is used as a supplementary parameter to evaluate specific adaptation of athletes. Accepted: 17 December 1996     

Oxygen uptake does not increase linearly at high power outputs during incremental exercise test in humans

A group of 12 healthy non-smoking men [mean age 22.3 (SD 1.1) years], performed an incremental exercise test. The test started at 30 W, followed by increases in power output (P) of 30 W every 3 min, until exhaustion. Blood samples were taken from an antecubital vein for determination of plasma concentration lactate [La⁻]_pl and acid-base balance variables. Below the lactate threshold (LT) defined in this study as the highest P above which a sustained increase in [La⁻]_pl was observed (at least 0.5 mmol · l⁻¹ within 3 min), the pulmonary oxygen uptake (V˙O₂) measured breath-by-breath, showed a linear relationship with P. However, at P above LT [in this study 135 (SD 30) W] there was an additional accumulating increase in V˙O₂ above that expected from the increase in P alone. The magnitude of this effect was illustrated by the difference in the final P observed at maximal oxygen uptake (V˙O_2max) during the incremental exercise test (P _max,obs at V˙O_2max) and the expected power output at V˙O_2max(P _max,exp at V˙O_2max) predicted from the linear V˙O₂-P relationship derived from the data collected below LT. The P _max,obs at V˙O_2max amounting to 270 (SD 19) W was 65.1 (SD 35) W (19%) lower (P<0.01) than the P _max,exp at V˙O_{2max .} The mean value of V˙O_2max reached at P _max,obs amounted to 3555 (SD 226) ml · min⁻¹ which was 572 (SD 269) ml · min⁻¹ higher (P<0.01) than the V˙O₂ expected at this P, calculated from the linear relationship between V˙O₂ and P derived from the data collected below LT. This fall in locomotory efficiency expressed by the additional increase in V˙O₂, amounting to 572 (SD 269) ml O₂ · min⁻¹, was accompanied by a significant increase in [La⁻]_pl amounting to 7.04 (SD 2.2) mmol · l⁻¹, a significant increase in blood hydrogen ion concentration ([H⁺]_b) to 7.4 (SD 3) nmol · l⁻¹ and a significant fall in blood bicarbonate concentration to 5.78 (SD 1.7) mmol · l⁻¹, in relation to the values measured at the P of the LT. We also correlated the individual values of the additional V˙O₂ with the increases (Δ) in variables [La⁻]_pl and Δ[H⁺]_b. The Δ values for [La⁻]_pl and Δ[H⁺]_b were expressed as the differences between values reached at the P _max,obs at V˙O_2max and the values at LT. No significant correlations between the additional V˙O₂ and Δ[La⁻]_pl on [H⁺]_b were found. In conclusion, when performing an incremental exercise test, exceeding P corresponding to LT was accompanied by a significant additional increase in V˙O₂ above that expected from the linear relationship between V˙O₂ and P occurring at lower P. However, the magnitude of the additional increase in V˙O₂ did not correlate with the magnitude of the increases in [La⁻]_pl and [H⁺]_b reached in the final stages of the incremental test. Accepted: 30 October 1997     

Muscle oxygenation during incremental arm and leg exercise in men and women

The purpose of this study was to compare the rates of muscle deoxygenation in the exercising muscles during incremental arm cranking and leg cycling exercise in healthy men and women. Fifteen men and 10 women completed arm cranking and leg cycling tests to exhaustion in separate sessions in a counterbalanced order. Cardiorespiratory measurements were monitored using an automated metabolic cart interfaced with an electrocardiogram. Tissue absorbency was recorded continuously at 760 nm and 850 nm during incremental exercise and 6 min of recovery, with a near infrared spectrometer interfaced with a computer. Muscle oxygenation was calculated from the tissue absorbency measurements at 30%, 45%, 60%, 75% and 90% of peak oxygen uptake (V˙O₂) during each exercise mode and is expressed as a percentage of the maximal range observed during exercise and recovery (%Mox). Exponential regression analysis indicated significant inverse relationships (P < 0.01) between %Mox and absolute V˙O₂ during arm cranking and leg cycling in men (multiple R = −0.96 and −0.99, respectively) and women (R =−0.94 and −0.99, respectively). No significant interaction was observed for the %Mox between the two exercise modes and between the two genders. The rate of muscle deoxygenation per litre of V˙O₂ was 31.1% and 26.4% during arm cranking and leg cycling, respectively, in men, and 26.3% and 37.4% respectively, in women. It was concluded that the rate of decline in %Mox for a given increase in V˙O₂ between 30% and 90% of the peak V˙O₂ was independent of exercise mode and gender. Accepted: 31 March 1998     

Influence of climate on heart rate in children: comparison between intermittent and continuous exercise

Heart rate (HR) monitoring is commonly used to assess 24-h energy expenditure (EE) in children but it has been found to overestimate the true values. One reason for this may be the effect of climatic heat stress on HR. An equation has been previously developed to adjust HR measured during continuous exercise for the influence of climate. Since play in children is rarely of a continuous pattern, one objective of this study was to compare the effects of climatic heat stress on the HR response to intermittent and to continuous exercise. A second objective was to determine whether the previously developed equation is suitable for intermittent exercise. A group of 12 boys and 8 girls (aged 8–11 years) cycled in a climatic chamber. The exercise consisted of continuous cycling for 5 min at 35%, 55%, and 75% of peak oxygen up take (random order) followed by alternating cycling at the same resistance and cadence (30 s) and rest (30 s) for 3 additional min. The oxygen uptake (V˙O₂) and HR were determined for 2 min at the end of continuous cycling and for 2 min during intermittent cycling. Climatic conditions (randomly assigned) were dry bulb temperature T _db 22°C, 50% relative humidity (rh); T _db 28°C, 55% rh; T _db 32°C, 52% rh; or T _db 35°C, 58% rh. The difference between HR measured at a given T _db (HR_meas) and HR at 22°C and at the same V˙O₂ was then calculated (ΔHR). The ΔHR increased linearly with increasing temperature but was not related to V˙O₂ or to exercise type. However, a small but significant difference was found if the published equation was used with data from intermittent exercise. The accuracy of the existing equation adjusting HR_meas for the influence of T _db (HR_corr) could be improved to HR_corr= HR_meas · (1.18308−(0.0083218 · T _db)). In conclusion, the effects of climatic heat stress on HR were similar in continuous and intermittent exercise, and HR can be adjusted for the influence of climate in groups of pre- and early pubertal children during rest, intermittent and continuous exercise at ambient temperatures between 22°C and 35°C, thereby reducing the error in predicting EE from HR. Accepted: 13 January 1998     

Ventilation response to CO2 and exercise-induced hypoxaemia in master athletes

Exercise-induced hypoxaemia (EIH) in master athletes may be related to a diminished exercise hyper- pnoea. The aim of this study was to determine whether EIH is associated with a change in the sensitivity of the ventilation response to activation of the central chemoreceptors. The ventilation response to CO₂ was measured in nine elderly untrained men (UT) [mean age 66.3 (SEM 3.1) years] and nine master athletes (MA) [mean age 62.7 (SEM 0.8) years] at rest, during moderate exercise (40% maximal oxygen uptake, V˙O_2max), and during strenuous exercise (70% V˙O_2max) using the rebreathing method. Our results showed that the ventilation response to CO₂ did not differ with endurance training and/or exercise, that the threshold of the CO₂ response (Th) increased with exercise (P < 0.001), that the increase in Th in MA was higher than in UT between rest and moderate exercise [ΔTh_0–40: 8.55 (SEM 1.8) vs 3.06 (SEM 1.72) mmHg, P < 0.05], and that ΔTh_0–40 and Th during moderate exercise were negatively correlated with arterial O₂ saturation during maximal exercise (r = 0.50, P<0.05). We concluded therefore that exercise-induced hypoxaemia in master athletes may not be due to a lower ventilation response to CO₂, but may be partly related to a greater increase in Th during moderate exercise. Accepted: 18 August 1997     

Relationship between maximal oxygen uptake on different ergometers, lean arm volume and strength in paraplegic subjects

The present experiment was designed to study the importance of strength and muscle mass as factors limiting maximal oxygen uptake (V˙O_{2 max} ) in wheelchair subjects. Thirteen paraplegic subjects [mean age 29.8 (8.7) years] were studied during continuous incremental exercises until exhaustion on an arm-cranking ergometer (AC), a wheelchair ergometer (WE) and motor-driven treadmill (TM). Lean arm volume (LAV) was estimated using an anthropometric method based upon the measurement of various circumferences of the arm and forearm. Maximal strength (MVF) was measured while pushing on the rim of the wheelchair for three positions of the hand on the rim (−30°, 0° and +30°). The results indicate that paraplegic subjects reached a similar V˙O_{2 max} [1.23 (0.34) l · min⁻¹, 1.25 (0.38) l · min⁻¹, 1.22 (0.18) l · min⁻¹ for AC, TM and WE, respectively] and V˙O_{2 max} /body mass [19.7 (5.2) ml · min⁻¹ · kg⁻¹, 19.5 (6.14) ml · min⁻¹ · kg⁻¹, 19.18 (4.27) ml · min⁻¹ · kg⁻¹ for AC, TM and WE, respectively on the three ergometers. Maximal heart rate f _{c max} during the last minute of AC (173 (17) beats · min⁻¹], TM [168 (14) beats · min⁻¹], and WE [165 (16) beats · min⁻¹], were correlated, but f _{c max} was significantly higher for AC than for TM (P<0.03). There were significant correlations between MVF and LAV (P<0.001) and between the MVF data obtained at different angles of the hand on the rim [311.9 (90.1) N, 313.2 (81.2) N, 257.1 (71) N, at −30°, 0° and +30°, respectively]. There was no correlation between V˙O_{2 max} and LAV or MVF. The relatively low values of f _{c max} suggest that V˙O_{2 max} was, at least in part, limited by local aerobic factors instead of central cardiovascular factors. On the other hand, the lack of a significant correlation between V˙O_{2 max} and MVF or muscle mass was not in favour of muscle strength being the main factor limiting V˙O_{2 max} in our subjects. Accepted: 31 January 1997     

Effects of artificially-induced anaemia on sudomotor and cutaneous blood flow responses to heat stress

The influence of artificially induced anaemia on thermal strain was evaluated in trained males. Heat stress trials (38.6°C, water vapour pressure 2.74 kPa) performed at the same absolute work rates [20 min of seated rest, 20 min of cycling at 30% peak aerobic power (V˙O_2peak), and 20 min cycling at 45% V˙O_2peak] were completed before (HST1) and 3–5 days after 3 units of whole blood were withdrawn (HST2). Mild anaemia did not elevate thermal strain between trials, with auditory canal temperatures terminating at 38.5°C [(0.16), HST1] and 38.6°C [(0.13), HST2; P > 0.05]. Given that blood withdrawal reduced aerobic power by 16%, this observation deviates from the close association often observed between core temperature and relative exercise intensity. During HST2, the absolute and integrated forearm sweat rate (m˙ _sw) exceeded control levels during exercise (P < 0.05), while a suppression of forehead m˙ _sw occurred (P < 0.05). These observations are consistent with a possible peripheral redistribution of sweat secretion. It was concluded that this level of artificially induced anaemia did not impact upon heat strain during a 60-min heat stress test. Accepted: 17 April 1997     

The influence of cold stress and a 36- h fast on the physiological responses to prolonged intermittent walking in man

In a previous study, rectal temperature (T _re) was found to be lower, and oxygen consumption (V˙O₂) and the respiratory exchange ratio (R) were higher in a cold (+5°C), wet and windy environment (COLD), compared with a thermoneutral environment during intermittent walking at ≈30% of peak V˙O₂ (Weller AS, Millard CE, Stroud MA et al. Am J Physiol 272:R226–R233, 1997). The aim of the present study was to establish whether these cold-induced responses are influenced by prior fasting, as impaired thermoregulation has been demonstrated in cold-exposed, resting men following a 48-h fast. To address this question, eight men attempted a 360-min intermittent (15 min rest, 45 min exercise) walking protocol under COLD conditions on two occasions. In one condition, the subjects started the exercise protocol ≈120 min after a standard meal (FED/COLD), whereas in the other the subjects had fasted for 36 h (FASTED/COLD). The first two exercise periods were conducted at a higher intensity (HIGHER, 6 km · h⁻¹ and 10% incline), than the four subsequent exercise periods (LOW, 5 km · h⁻¹ and 0% incline). There was no difference in the time endured in FED/COLD and FASTED/COLD. In FASTED/COLD com pared with FED/COLD, R was lower during HIGHER and LOW, and T _re was lower during LOW, whereas there was no difference in V˙O₂, mean skin temperature and heart rate. Therefore, although the 36-h fast impaired temperature regulation during intermittent low-intensity exercise in the cold, wet and windy environment, it was unlikely to have been the principal factor limiting exercise performance under these experimental conditions. Accepted: 26 August 1997     

Physiological and performance responses to supplementation with thiamin and pantothenic acid derivatives

The purpose of this study was to investigate the physiological and performance responses to supplementation with allithiamin and pantethine. On two separate occasions, six highly trained cyclists [maximum O₂ consumption or V˙O_2max 61.8 (2.1) ml · kg⁻¹ · min⁻¹] performed a 50-km steady-state ride on a cycle ergometer at a workload corresponding to ∼60% of V˙O_2max followed by a 2000-m time trial. For 7 days prior to each ride, subjects daily ingested either a placebo (PL) or a combination of 1 g of allithiamin and 1.8 g of a 55%/45% pantethine/pantothenic acid compound (AP). Treatments were administered using a randomized, double-blind, counter-balanced design. During the 50-km ride, measures of heart rate, respiratory gas exchange and ratings of perceived exertion were recorded at 5, 15, 25, 35 and 45 km. Blood samples were collected at 10, 20, 30, 40 and 50 km and analyzed for lactate, glucose and free fatty acids. Blood samples for the analysis of lactate were also collected 3 and 5 min after the completion of the 2000-m time trial. There were no significant differences in any of the measured parameters between experimental conditions. Time to complete the 2000-m time trial was also not significantly different between experimental conditions [PL 178.2 (8.4), AP 170.7 (10.2) s; P = 0.58]. These results suggest that, despite the reported enhanced absorption properties, supplementation with allithiamin and pantethine does not alter exercise metabolism or exercise performance. Accepted: 9 October 1997     

A comparison of physiological responses and rating of perceived exertion between high-impact and low-impact aerobic dance sessions

The aim of this study was to compare the exercise intensity and rating of perceived exertion (RPE) of a high-impact (HIP) and a low-impact (LIP) university aerobic dance session. Ten women [mean (SD) age 22.9 (2.6) years] took part in the study. An incremental treadmill test was performed by each subject to determine maximum oxygen consumption (V˙O_{2 max} ) and maximum heart rate (HR _max ). The measured V˙O_{2 max} [mean (SD)] was 49.0 (7.5) ml · kg⁻¹ · min⁻¹. The subjects were randomly assigned to LIP and HIP sessions (i.e. five of the subjects participated in the HIP session first, and the other five participated in the LIP session first). In a laboratory, heart rate, oxygen uptake and RPE were measured throughout each session for each subject. Expired air was collected continuously throughout the sessions using Douglas bags (ten bags over a 30-min period). The sessions consisted of 20 min of aerobic exercise (bags 1–7) followed by 5 min of local muscular endurance exercise (bags 8 and 9) and 5 min of flexibility exercises (bag 10). The mean intensity of the aerobic section of the LIP and HIP sessions was 51.6% and 64.7% V˙O_{2 max} , respectively. Ninety-five percent confidence intervals for the average difference between the HIP and LIP sessions demonstrate that the %V˙O_{2 max} was between 12% and 14% higher for the HIP session. The mean %HR _max for the LIP and HIP sessions was 71.4% and 76.7%, respectively, with the %HR _max in the HIP session being between 5.4% and 7.2% higher on average than that of the LIP session. On average, the RPE for the aerobic section of the HIP session (12.1) was consistently higher than that of the LIP session (11.1). HIP activity has the potential to maintain/improve the aerobic fitness of its participants. According to the literature, the exercise intensity elicited by LIP activity may have a limited training effect for the population utilised in this study, and for some individuals may result in detraining. Conversely, LIP activities may be an appropriate mode of exercise for overweight and unfit individuals. Accepted: 5 January 1998     

Effect of cold exposure (?15°C) and Salbutamol treatment on physical performance in elite nonasthmatic cross-country skiers

The effects of whole-body exposure to ambient temperatures of −15°C and 23°C on selected performance-related physiological variables were investigated in elite nonasthmatic cross-country skiers. At an ambient temperature of −15°C we also studied the effects of the selective β₂-adrenergic agonist Salbutamol (0.4 mg × 3) which was administered 10 min before the exercise test. Eight male cross-country skiers with known maximal oxygen uptakes (V˙O_{2 max} ) of more than 70 ml · kg⁻¹ · min⁻¹ participated in the study. Oxygen uptake (V˙O₂), heart rate (f _c), blood lactate concentration ([La⁻]_b) and time to exhaustion were measured during controlled submaximal and maximal running on a treadmill in a climatic chamber. Lung function measured as forced expiratory volume in 1 s (FEV₁) was recorded immediately before the warm-up period and at the conclusion of the exercise protocol. Submaximal V˙O₂ and [La⁻]_b at the two highest submaximal exercise intensities were significantly higher at −15°C than at 23°C. Time to exhaustion was significantly shorter in the cold environment. However, no differences in V˙O_{2 max} or f _c were observed. Our results would suggest that exercise stress is higher at submaximal exercise intensities in a cold environment and support the contention that aerobic capacity is not altered by cold exposure. Furthermore, we found that after Salbutamol inhalation FEV₁ was significantly higher than after placebo administration. However, the inhaled β₂-agonist Salbutamol did not influence submaximal and maximal V˙O₂, f _c, [La⁻]_b or time to exhaustion in the elite, nonasthmatic cross-country skiers we studied. Thus, these results did not demonstrate any ergogenic effect of the β₂-agonist used. Accepted: 18 August 1997     

The influence of either no fluid or carbohydrate-electrolyte fluid ingestion and the environment (thermoneutral versus hot and humid) on running economy after prolonged, high-intensity exercise

This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (V˙O_2max). Tests were undertaken in either a thermoneutral (22–23°C; 56–62% relative humidity, RH) or a hot and humid natural environment (Singapore: 25–35°C; 66–77% RH). The subjects were 15 young adult male Singaporeans [V˙O_2max = 55.5 (4.4 SD) ml kg⁻¹ min⁻¹]. The RE was measured at 3 m s⁻¹ [65 (6)% V˙O_2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined from prior tests, to maintain body mass (group mean = 17.4 ml min⁻¹). The V˙O₂ during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase in V˙O₂ from RE1 to RE2 ranged from 3.4 to 4.7 ml kg⁻¹ min⁻¹ across treatments. In conclusion, the deterioration in RE at 3 m s⁻¹ (65% V˙O_2max) after 60 min of running at 80% V˙O_2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or electrolytes, in both a thermoneutral and in a hot, humid environment. Accepted: 30 October 1997     

The effect of a low-carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal exercise

The aim of this study was to find out whether a low-carbohydrate diet (L-CHO) affects: (1) the capacity for all-out anaerobic exercise, and (2) hormonal and metabolic responses to this type of exercise. To this purpose, eight healthy subjects underwent a 30-s bicycle Wingate test preceded by either 3 days of a controlled mixed diet (130 kJ/kg of body mass daily, 50% carbohydrate, 30% fat, 20% protein) or 3 days of an isoenergetic L-CHO diet (up to 5% carbohydrate, 50% fat, 45% protein) in a randomized order. Before and during 1 h after the exercise venous blood samples were taken for measurement of blood lactate (LA), β-hydroxybutyrate (β-HB), glucose, adrenaline (A), noradrenaline (NA) and insulin levels. Oxygen consumption (V˙O₂) was also determined. It was found that the L-CHO diet diminished the mean power output during the 30-s exercise bout [533 (7) W vs 581 (7) W, P < 0.05] without changing the maximal power attained during the first or second 5-s interval of the exercise. In comparison with the data obtained after the consumption of a mixed diet, after the consumption of a L-CHO diet resting plasma concentrations of β-HB [2.38 (0.18) vs 0.23 (0.01) mmol · l⁻¹, P < 0.001] and NA [4.81 (0.68) vs 2.2 (0.31) nmol · l⁻¹, P < 0.05] were higher, while glucose [4.6 (0.1) vs 5.7 (0.2) mmol · l⁻¹, P < 0.05] and insulin concentrations [11.9 (0.9) vs 21.8 (1.8) mU · l⁻¹] were lower. The 1-h post-exercise excess of V˙O₂ [9.1 (0.25) vs 10.6 (0.25) l, P < 0.05], and blood LA measured 3 min after the exercise [9.5 (0.4) vs 10.6 (0.5) mmol · l⁻¹, P < 0.05] were lower following the L-CHO treatment, whilst plasma NA and A concentrations reached higher values [2.24 (0.40) vs 1.21 (0.13) nmol · l⁻¹ and 14.30 (1.41) vs 8.20 (1.31) nmol · l⁻¹, P < 0.01, respectively]. In subjects on the L-CHO diet, the plasma β-HB concentration decreased quickly after exercise, attaining ≈30% of the pre-exercise value within 60 min, while insulin and glucose levels were elevated. The main conclusions of this study are: (1) a L-CHO diet is detrimental to anaerobic work capacity, possibly because of a reduced muscle glycogen store and decreased rate of glycolysis; (2) reduced carbohydrate intake for 3 days enhances activity of the sympathoadrenal system at rest and after exercise. Accepted: 31 January 1997     

Energetics of swimming at maximal speeds in humans

The energy cost per unit of distance (C _s, kilojoules per metre) of the front-crawl, back, breast and butterfly strokes was assessed in 20 elite swimmers. At sub-maximal speeds (v), C _s was measured dividing steady-state oxygen consumption (V˙O₂) by the speed (v, metres per second). At supra-maximal v, C _s was calculated by dividing the total metabolic energy (E, kilojoules) spent in covering 45.7, 91.4 and 182.9 m by the distance. E was obtained as: E = E _an+V˙O_2max t _p−V˙O_2max(1−e^{−( t p/)}), where E _an was the amount of energy (kilojoules) derived from anaerobic sources, V˙O_2max litres per second was the maximal oxygen uptake, α (=20.9 kJ · l O₂ ⁻¹) was the energy equivalent of O₂, τ (24 s) was the time constant assumed for the attainment of V˙O_2max at muscle level at the onset of exercise, and t _p (seconds) was the performance time. The lactic acid component was assumed to increase exponentially with t _p to an asymptotic value of 0.418 kJ · kg⁻¹ of body mass for t _p ≥ 120 s. The lactic acid component of E _an was obtained from the net increase of lactate concentration after exercise (Δ[La]_b) assuming that, when Δ[La]_b = 1 mmol · l⁻¹ the net amount of metabolic energy released by lactate formation was 0.069 kJ · kg⁻¹. Over the entire range of v, front crawl was the least costly stroke. For example at 1 m · s⁻¹, C _s amounted, on average, to 0.70, 0.84, 0.82 and 0.124 kJ · m⁻¹ in front crawl, backstroke, butterfly and breaststroke, respectively; at 1.5 m · s⁻¹, C _s was 1.23, 1.47, 1.55 and 1.87 kJ · m⁻¹ in the four strokes, respectively. The C _s was a continuous function of the speed in all of the four strokes. It increased exponentially in crawl and backstroke, whereas in butterfly C _s attained a minimum at the two lowest v to increase exponentially at higher v. The C _s in breaststroke was a linear function of the v, probably because of the considerable amount of energy spent in this stroke for accelerating the body during the pushing phase so as to compensate for the loss of v occurring in the non-propulsive phase. Accepted: 14 April 1998