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     

Running economy deteriorates following 60?min of exercise at 80% V˙O2max

Fifteen young adult Singaporean male physical education students maximum oxygen consumption [(V˙O_2max) = 56 (4.7) ml · kg⁻¹ · min⁻¹] performed three prolonged runs in a counterbalanced design. The running bouts varied in time (40 vs 60 min) and intensity (70% vs 80% V˙O_{2 max} ). Each prolonged run was separated by 7 days. The running economy (RE) at 10.8 km · h⁻¹ during 10-min running bouts was measured before (RE1) and after (RE2) each prolonged run. A control study involved monitoring RE at 10.8 km · h⁻¹ before and after 60 min rest. There were no differences between RE1 and RE2 values during the control run. However, there were differences between RE1 and RE2 values when separated by a prolonged run. For example, the mean (SD) changes in oxygen consumption (ml · kg⁻¹ · min⁻¹) values were 38.2 (2.5) versus 40.1 (2.6) (40 min at 80% V˙O_{2 max} ), 38.9 (2.8) versus 41.5 (2.6) (60 min at 70% V˙O_{2 max} ), and 39.0 (3.1) versus 42.7 (2.9) (60 min at 80% V˙O_{2 max} ; P < 0.01). The results of this investigation support the hypothesis that RE deteriorates during prolonged running, and that the magnitude of the deterioration in RE increases with both increasing exercise intensity and duration. Accepted: 14 July 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     

Temperature dependence of habituation of the initial responses to cold-water immersion

The initial responses to cold-water immersion, evoked by stimulation of peripheral cold receptors, include tachycardia, a reflex inspiratory gasp and uncontrollable hyperventilation. When immersed naked, the maximum responses are initiated in water at 10°C, with smaller responses being observed following immersion in water at 15°C. Habituation of the initial responses can be achieved following repeated immersions, but the specificity of this response with regard to water temperature is not known. Thirteen healthy male volunteers were divided into a control (C) group (n = 5) and a habituation (H) group (n = 8). Each subject undertook two 3-min head-out immersions in water at 10°C wearing swimming trunks. These immersions took place at a corresponding time of day with 4 days separating the two immersions. In the intervening period the C group were not exposed to cold water, while the H group undertook another six, 3-min, head-out immersions in water at 15°C. Respiratory rate (f _R), inspiratory minute volume (V˙ _I) and heart rate (f _H) were measured continuously throughout each immersion. Following repeated immersions in water at 15°C, the f _R, V˙ _I and f _H responses of the H group over the first 30 s of immersion were reduced (P < 0.01) from 33.3 breaths · min⁻¹, 50.5 l · min⁻¹ and 114 beats · min⁻¹ respectively, to 19.8 breaths · min⁻¹, 26.4 l · min⁻¹ and 98 beats · min⁻¹, respectively. In water at 10°C these responses were reduced (P < 0.01) from 47.3 breaths · min⁻¹, 67.6 l · min⁻¹ and 128 beats · min⁻¹ to 24.0 breaths · min⁻¹, 29.5 l · min⁻¹ and 109 beats · min⁻¹, respectively over a corresponding period of immersion. Similar reductions were observed during the last 2.5 min of immersions. The initial responses of the C group were unchanged. It is concluded that habituation of the cold shock response can be achieved by immersion in warmer water than that for which protection is required. This suggests that repeated submaximal stimulation of the cutaneous cold receptors is sufficient to attenuate the responses to more maximal stimulation. Accepted: 6 February 1998     

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     

Effect of intense interval workouts on running economy using three recovery durations

The purposes of this study were to determine whether running economy (RE) is adversely affected following intense interval bouts of 10 × 400-m running, and whether there is an interaction effect between RE and recovery duration during the workouts. Twelve highly trained male endurance athletes [maximal oxygen consumption; V˙O_{2 max} =72.5 (4.3) ml·kg⁻¹·min⁻¹; mean (SD)] performed three interval running workouts of 10 × 400 m with a minimum of 4 days between runs. Recovery duration between the repetitions was randomly assigned at 60, 120 or 180 s. The velocity for each 400-m run was determined from a treadmill V˙O_{2 max} test. The average running velocity was 357.9 (9.0) m · min⁻¹. Following the workout, the rating of perceived exertion (RPE) increased significantly (P < 0.01) as recovery duration between the 400-m repetitions decreased (14.4, 16.1, and 17.7 at 180s, 120s, and 60 s recovery, respectively). Prior to and following each workout, RE was measured at speeds of 200 and 268 m · min⁻¹. Changes in RE from pre- to post-workout, as well as heart rate (HR) and respiratory exchange ratio (R) were similar for the three recovery conditions. When averaged across conditions, oxygen consumption (V˙O₂) increased significantly (P < 0.01) from pre- to post-test (from 38.5 to 40.5 ml · kg⁻¹ · min⁻¹ at 200 m · min⁻¹, and from 53.1 to 54.5 ml · kg⁻¹ · min⁻¹ at 268 m · min⁻¹, respectively). HR increased (from 124 to 138, and from 151 to 157 beats · min⁻¹ respectively) and R decreased (from 0.90 to 0.78, and from 0.93 to 0.89, respectively) at 200 and 268 m · min⁻¹, respectively (P < 0.01). This study showed that RE can be perturbed after a high-intensity interval workout and that the changes in V˙O₂, HR and R were independent of the recovery duration between the repetitions. Accepted: 23 June 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 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     

Human energy expenditure when walking on a moving platform

The assumption that working on board ship is more strenuous than comparable work ashore was investigated in this study. Various physiological parameters (V˙O₂, V˙CO₂, V˙ _E and HR) have been measured to determine the energy expenditure of subjects walking slowly on a moving platform (ship motion simulator). Twelve subjects (eight men and four women) walked either freely on the floor or on a treadmill at a speed of 1 m · s⁻¹. Platform motion was either in a heave, pitch or roll mode. These three conditions were compared with a control condition in which the platform remained stationary. The results showed that during pitch and roll movements of the platform, the energy expenditure for the same walking task was about 30% higher than under the stationary control condition (3.6 J · kg⁻¹ · m⁻¹ vs 2.5 J · kg⁻¹ · m⁻¹, P < 0.05) for both walking on a treadmill and free walking. The heart rate data supported the higher energy expenditure results with an elevation of the heart rate (112 beats · min⁻¹ vs 103 beats · min⁻¹, P < 0.05). The heave condition did not differ significantly from the stationary control condition. Pitch and roll were not significantly different from each other. During all experimental conditions free walking resulted in a higher energy cost of walking than treadmill walking (3.5 J · kg⁻¹ · m⁻¹ vs 2.7 J · kg⁻¹ · m⁻¹, P < 0.05) at the same average speed. The results of this experiment were interpreted as indicating that the muscular effort, needed for maintaining balance when walking on a pitching or rolling platform, resulted in a significantly higher work load than similar walking on a stable or a heaving floor, independent of the mode of walking. These results explain in part the increased fatigue observed when a task is performed on a moving platform. Accepted: 3 October 1997     

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     

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     

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     

Heritability of running economy: a study made on twin brothers

Running economy (RE), defined as the steady-state of oxygen uptake (V˙O₂) for a given running velocity, is a factor of sports performance the genetic component of which has seldom been reported to date. We studied this component using a heritability index (HI) in a group of 32 male twins, 8 monozygotic (MZ) and 8 dizygotic (DZ) pairs, all sportsmen with similar perinatal and environmental backgrounds. Zygocity was determined by the identity of erythrocytic antigenic, protein and enzymatic polymorphism, and human leucocyte antigen serologic types between co-twins. The subjects exercised twice on a treadmill, once until exhaustion and again at submaximal intensities. Pulmonary gas exchange was measured continuously using an automatic analyser system during both tests. Blood samples were obtained during the recovery period to determine lactate concentrations. No significant differences were observed between MZ and DZ, in respect of RE at any speed or in maximal V˙O₂ relative to body mass. Nevertheless, significant HI (P < 0.05) was found in maximal lactate concentrations (HI = 0.75) and in respiratory equivalent for oxygen at two speeds, 7 km · h⁻¹ (HI = 0.71) and 8 km · h⁻¹ (HI = 0.79), differences which probably suggest that there are differences in RE. In conclusion, we did not detect a genetic component in RE or in maximal oxygen uptake, but a genetic component for markers of anaerobic metabolism was present. Accepted: 5 November 1997     

Sex-related differences in thermoregulatory responses while wearing protective clothing

This study examined the thermoregulatory responses of men (group M) and women (group F) to uncompensable heat stress. In total, 13 M [mean (SD) age 31.8 (4.7) years, mass 82.7 (12.5) kg, height␣1.79␣(0.06) m, surface area to mass ratio 2.46␣(0.18) m² · kg⁻¹ · 10⁻², Dubois surface area 2.01 (0.16) m², %body fatness 14.6 (3.9)%, V˙O_2peak 49.0 (4.8) ml · kg⁻¹ · min⁻¹] and 17 F [23.2 (4.2) years, 62.4 (7.7) kg, 1.65 (0.07) m, 2.71 (0.14) m² · kg⁻¹ · 10⁻², 1.68 (0.13) m², 20.2 (4.8)%, 43.2 (6.6) ml · kg⁻¹ · min⁻¹, respectively] performed light intermittent exercise (repeated intervals of 15 min of walking at 4.0 km · h⁻¹ followed by 15 min of seated rest) in the heat (40°C, 30% relative humidity) while wearing nuclear, biological, and chemical protective clothing (0.29 m² ·°C · W⁻¹ or 1.88 clo, Woodcock vapour permeability coefficient 0.33 i _m). Group F consisted of eight non-users and nine users of oral contraceptives tested during the early follicular phase of their menstrual cycle. Heart rates were higher for F throughout the session reaching 166.7 (15.9) beats · min⁻¹ at 105 min (n = 13) compared with 145.1 (14.4) beats · min⁻¹ for M. Sweat rates and evaporation rates from the clothing were lower and average skin temperature () was higher for F. The increase in rectal temperature (T _re) was significantly faster for the F, increasing 1.52 (0.29)°C after 105 min compared with an increase of 1.37 (0.29)°C for M. Tolerance times were significantly longer for M [142.9 (24.5) min] than for F [119.3 (17.3) min]. Partitional calorimetric estimates of heat storage (S) revealed that although the rate of S was similar between genders [42.1 (6.6) and 46.1 (9.7) W · m⁻² for F and M, respectively], S expressed per unit of total mass was significantly lower for F [7.76 (1.44) kJ · kg⁻¹] compared with M [9.45 (1.26) kJ · kg⁻¹]. When subjects were matched for body fatness (n = 8 F and 8 M), tolerance times [124.5 (14.7) and 140.3 (27.4) min for F and M, respectively] and S [8.67 (1.44) and 9.39 (1.05) kJ · kg⁻¹ for F and M, respectively] were not different between the genders. It was concluded that females are at a thermoregulatory disadvantage compared with males when wearing protective clothing and exercising in a hot environment. This disadvantage can be attributed to the lower specific heat of adipose versus non-adipose tissue and a higher percentage body fatness. Accepted: 31 October 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     

Failure to obtain a unique threshold on the blood lactate concentration curve during exercise

The purpose of this study was to compare various methods and criteria used to identify the anaerobic threshold (AT), and to correlate the AT obtained with each other and with running performance. Furthermore, a number of additional points throughout the entire range of lactate concentrations [La⁻] were obtained and correlated with performance. A group of 19 runners [mean age 33.7 (SD 9.6) years, height 173 (SD 6.3) cm, body mass 68.3 (SD 5.4) kg, maximal O₂ uptake (V˙O_{2 max} ) 55.2 (SD 5.9) ml · kg⁻¹ · min⁻¹] performed a maximal multistage treadmill test (1 km · h⁻¹ every 3.5 min) with blood sampling at the end of each stage while running. All AT points selected (visual [La⁻], 4 mmol · l⁻¹ [La⁻], 1 mmol · l⁻¹ above baseline, log-log breakpoint, and 45° tangent to the exponential regression) were highly correlated one with another and with performance (r > 0.90) even when there were many differences among the AT (P < 0.05). The additional points (ranging from 3 to 8 mmol · l⁻¹ [La⁻], 1 to 6 mmol · l⁻¹ [La⁻] above the baseline, and 30 to 70° tangent to the exponential curve of [La⁻]) were also highly correlated with performance (r > 0.90). These results failed to demonstrate a distinct AT because many points of the curve provided similar information. Intercorrelations and correlations between AT and performance were, however, reduced when AT were expressed as the percentage of maximal treadmill speed obtained at AT or percentage of V˙O_{2 max} . This would indicate that different attributes of aerobic performance (i.e. maximal aerobic power, running economy and endurance) are measured when manipulating units. Thus, coaches should be aware of these results when they prescribe an intensity for training and concentrate more on the physiological consequences of a chosen [La⁻] rather than on a “threshold”. Accepted: 22 October 1997     

Ca2+ regulation of heart contractility in Octopus

Isometric force development of electrically paced preparations isolated from the systemic heart of Octopus vulgaris were utilized to examine the regulation of contractility by Ca²⁺. Increases in extracellular Ca²⁺, to the physiological level, resulted in enhancement of twitch force. For instance, at 36 beats · min⁻¹ an increase in Ca²⁺ from 3 to 9 mmol · l⁻¹ resulted in a threefold increase in twitch force development. When steady-state contraction at 12 beats · min⁻¹ was followed by a rest period of either 5 or 10 min, the first contraction always exhibited either an increase in twitch force or stayed unchanged such that post-rest twitch force was about 133% of the last value in the steady-state train. Ryanodine (12.5 μmol · l⁻¹), which is considered to be a specific inhibitor of the Ca²⁺ storage and release capabilities of the sarcoplasmic reticulum (SR), was applied to further assess Ca²⁺ handling. Twitch force fell to about 22% of the preteatment level in preparations paced at either 12 or 36 beats · min⁻¹. In all preparations the frequency transition from 12 to 36 beats · min⁻¹ was associated with an increase in resting tension. The␣increase␣was 37 ± 14% prior to ryanodine treatment and was significantly elevated to 127 ± 33% following treatment. When steady-state contraction at 36 beats · min⁻¹ was followed by a rest period of 10 s, the first contraction was not significantly different from the last beat in the train prior to ryanodine; however, with ryanodine treatment, post-rest twitch force development significantly decreased. Twitch force development was regular at pacing rates of up to 300 beats · min⁻¹. Twitch force was maintained up to rates of 84 beats · min⁻¹ but␣decreased thereafter and reached a value of about 10% at 300 beats · min⁻¹. Resting tension increased substantially as frequency was elevated from 12 to 36 beats · min⁻¹ and then gradually increased as frequency was further elevated to 180 beats · min⁻¹. In conclusion, the Octopus ventricle is dependent upon extracellular Ca²⁺ for contraction. A post-rest potentiation of force development, the negative impact of ryanodine, and the ability to respond regularly at high pacing rates imply a strong reliance on the SR in Ca²⁺ cycling based on criteria established for vertebrate hearts. Accepted: 19 January 1997     

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     

Cold induced vasodilatation and cardiovascular responses in humans during cold water immersion of various upper limb areas

To study the physiological responses induced by immersing in cold water various areas of the upper limb, 20 subjects immersed either the index finger (T1), hand (T2) or forearm and hand (T3) for 30 min in 5°C water followed by a 15-min recovery period. Skin temperature of the index finger, skin blood flow (Q_sk) measured by laser Doppler flowmetry, as well as heart rate (HR) and mean arterial blood pressure (ˉBP_a) were all monitored during the test. Cutaneous vascular conductance (CVC) was calculated as Q_sk / ˉBP_a. Cold induced vasodilatation (CIVD) indices were calculated from index finger skin temperature and CVC time courses. The results showed that no differences in temperature, CVC or cardiovascular changes were observed between T2 and T3. During T1, CIVD appeared earlier compared to T2 and T3 [5.90 (SEM 0.32) min in T1 vs 7.95 (SEM 0.86) min in T2 and 9.26 (SEM 0.78) min in T3, P < 0.01]. The HR was unchanged in T1 whereas it increased significantly at the beginning of T2 and T3 [+13 (SEM 2) beats · min⁻¹ in T2 and +15 (SEM 3) beats · min⁻¹ in T3, P < 0.01] and then decreased at the end of the immersion [−12 (SEM 3) beats · min⁻¹ in T2, and −15 (SEM 3) beats · min⁻¹ in T3, P < 0.01]. Moreover, ˉBP_aincreased at the beginning of T1 but was lower than in T2 and T3 [+9.3 (SEM 2.5) mmHg in T1, P < 0.05;  +20.6 (SEM 2.6) mmHg and 26.5 (SEM 2.8) mmHg in T2 and T3, respectively, P < 0.01]. The rewarming during recovery was faster and higher in T1 compared to T2 and T3. These results showed that general and local physiological responses observed during an upper limb cold water test differed according to the area immersed. Index finger cooling led to earlier and faster CIVD without significant cardiovascular changes, whereas hand or forearm immersion led to a delayed and slower CIVD with a bradycardia at the end of the test. Accepted: 26 November 1996     

The effect of a thiamin derivative on exercise performance

The purpose of this study was to investigate the effect of a thiamin derivative, thiamin tetrahydrofurfuryl disulfide (TTFD), on oxygen uptake (˙VO₂), lactate accumulation and cycling performance during exercise to exhaustion. Using a randomized, double-blind, cross-over design with a 10-day washout between trials, 14 subjects ingested either 1 g · day⁻¹ of TTFD or a placebo (PL) for 4 days. On day 3, subjects performed a progressive exercise test to exhaustion on a cycle ergometer for the determination of ˙VO_2submax, ˙VO_2peak, lactate concentration ([La⁻ ]), lactate threshold (Th_La) and heart rate ( f _c). On day 4, subjects performed a maximal 2000-m time trial on a cycle ergometer. A one-way analysis of variance (ANOVA) with repeated measures was used to determine significant differences between trials. There were no significant differences detected between trials for serial measures of ˙VO_2submax, [La⁻] or f _c. Likewise, ˙VO_2peak [PL 4.06 (0.19) TTFD 4.12 (0.19) l · min⁻¹, P = 0.83], Th_La [PL 2.47 (0.17), TTFD 2.43 (0.16) l · min⁻¹, P = 0.86] and 2000-m performance time [PL 204.5 (5.5), TTFD 200.9 (4.3) s, P = 0.61] were not significantly different between trials. The results of this study suggest that thiamin derivative supplementation does not influence high-intensity exercise performance. Accepted: 19 December 1996