Gas exchange responses to continuous incremental cycle ergometry exercise in primary pulmonary hypertension in humans

In patients suffering from primary pulmonary hypertension (PPH), a raised pulmonary vascular resistance may limit the ability to increase pulmonary blood flow as work rate increases. We hypothesised that oxygen uptake (V˙O₂) may not rise appropriately with increasing work rate during incremental cardiopulmonary exercise tests. Nine PPH patients and nine normal subjects performed symptom-limited maximal continuous incremental cycle ergometry exercise. Mean peak V˙O₂ [1.00 (SD 0.22) compared to 2.58 (SD 0.64) l · min⁻¹] and mean V˙O₂ at lactic acidosis threshold [LAT, 0.73 (SD 0.17) compared to 1.46 (SD 0.21 · l) ml · min⁻¹] were much lower in patients than in normal subjects (both P < 0.01, two-way ANOVA with Tukey test). The mean rate of change of V˙O₂ with increasing work rate above the LAT [5.9 (SD 2.1) compared to 9.4 (SD 1.3) ml · min⁻¹ · W⁻¹, P < 0.01)] was also much lower in patients than in normal subjects [apparent δ efficiency 60.3 (SD 38.8)% in patients compared to 31.0 (SD 4.9)% in normal subjects]. The patients displayed lower mean values of end-tidal partial pressure of carbon dioxide than the normal subjects at peak exercise [29.7 (SD 6.8) compared to 42.4 (SD 5.8) mmHg, P < 0.01] and mean oxyhaemoglobin saturation [89.1 (SD 4.1) compared to 93.6 (SD 1.8)%, P < 0.05]. Mean ventilatory equivalents for CO₂ [49.3 (SD 11.4) compared to 35.0 (SD 7.3), P < 0.05] and O₂ [44.2 (SD 10.7) compared to 29.9 (SD 5.1), P < 0.05] were greater in patients than normal subjects. The sub-normal slopes for the V˙O₂-work-rate relationship above the LAT indicated severe impairment of the circulatory response to exercise in patients with PPH. The ventilatory abnormalities in PPH suggested that the lung had become an inefficient gas exchange organ because of impaired perfusion of the ventilated lung. Accepted: 17 April 2000     

Influence of ultra-long-term fatigue on the oxygen cost of two types of locomotion

The aim of this study was to examine the effects of fatigue induced by a 65-km ultramarathon on the oxygen cost of running (C_r) and cycling (C_cycl). The day before and immediately after the race, a group of nine well-trained male subjects performed two sub-maximal 4-min exercise bouts: one cycling at a power corresponding to 1.5 W · kg⁻¹ body mass on an electromagnetically braked ergometer, and one running at 11 km · h⁻¹ on a flat asphalt roadway. Before oxygen cost determinations, the subjects performed 12 “ankle” jumps at a given frequency that was fixed by an electronic metronome (2.5 Hz). From the non-fatigued to the fatigued condition, there was a significant increase in minute ventilation for both running (P < 0.01) and cycling (P < 0.0001). Significant changes were also found in respiratory exchange ratio both for running (P=0.01) and cycling (P < 0.0001). However, running and cycling differed in that C_cycl increased significantly by [mean (SD)] 24.2 (11.5)% (P < 0.001), suggesting an alteration of muscle efficiency, while C_r did not change with fatigue [186.8 (14.1) mlO₂ · kg⁻¹ · km⁻¹ vs 186.8 (18.7) mlO₂ · kg⁻¹ · km⁻¹]. In addition, contact times during hopping increased significantly from 0.173 (0.019) ms to 0.194 (0.027) ms (P < 0.01). Analysis of the factors that determine C_r indicate that the subjects modified their movement pattern in order to decrease the mechanical cost of running in such long-term fatigue conditions. Accepted: 7 August 2000     

In vivo 4-androstene-3,17-dione and 4-androstene-3β,17β-diol supplementation in young men

To determine if known androgenic hormone precursors for testosterone in the androgen pathway would be readily transformed to testosterone, eight male subjects [mean age 23.8 (SEM 3) years, bodymass 83.1 (SEM 8.7) kg, height 175.6 (SEM 8.5) cm] underwent a randomized, double-blind, cross-over, placebo-controlled oral treatment with 200 mg of 4-androstene-3,17-dione (Δ4), 4-androstene-3β,17β-diol (Δ4Diol), and placebo (PL). The periods of study were separated by 7 days of washout. Blood was drawn at baseline and subsequently every 30 min for 90 min after treatment. Analysis revealed mean area-under-the-curve (AUC) serum Δ4 concentrations to be higher during Δ4 treatment [2177 (SEM 100) nmol · l⁻¹] than Δ4Diol [900 (SEM 96) nmol · l⁻¹] or PL [484 (SEM 82) nmol · l⁻¹; P < 0.0001]. The Δ4 treatment also revealed a significant effect on total testosterone with a mean AUC [1632.5 (SEM 121) nmol · l⁻¹] that was greater than PL [1418.5 (SEM 131) nmol · l⁻¹; P < 0.05] but not significantly different from those observed after Δ4Diol treatment [1602.9 (SEM 119) nmol · l⁻¹; P = 0.77]. Free testosterone concentrations followed a similar pattern where mean AUC for the Δ4 treatment [6114.0 (SEM 600) pmol · l⁻¹] was greater than after PL [4974.6 (SEM 565) pmol · l⁻¹; P < 0.06] but not significantly different from those observed after Δ4Diol [5632.0 (SEM 389) pmol · l⁻¹; P = 0.48]. The appearance and apparent conversion to total and free testosterone over 90 min was stronger for the Δ4 treatment (r = 0.91, P < 0.045) than for Δ4Diol treatment (r = 0.69, NS) and negatively correlated for PL (r = −0.90, P < 0.02). These results would suggest that Δ4, and perhaps Δ4Diol, taken by month are capable of producing in vivo increases in testosterone concentrations in apparently healthy young men as has already been observed in women after treatment with Δ4. Accepted: 26 August 1999     

An improved estimation of mean body temperature using combined direct calorimetry and thermometry

The conventional method used to estimate the change in mean body temperature (dMBT) is by taking X% of a body core temperature and (1−X)% of weighted mean skin temperature, the value of X being dependent upon ambient temperature. This technique is used widely, despite opposition from calorimetrists. In the present paper we attempt to provide a better method. Minute-by-minute changes in dMBT, as assessed using calorimetry, and 21 (20 if esophageal temperature was unavailable) various regional temperatures (dRBTs), as assessed using thermometry, including 6 subcutaneous measures, were collected from 7 young male adults at 6 calorimeter temperatures. Since a calorimeter measures only changes in heat storage, which can be converted to dMBT, all body temperatures are expressed as changes from the reasonably constant pre-exposure temperatures. The following three aspects were investigated. (1) The prediction of dMBT from the 21 (or 20) dRBTs with multi-linear regression analysis (MLR). This yields two results, model A with rectal temperature (dT _re) alone, and model B with dT _re and esophageal temperature (dT _es). (2) The prediction of dMBT from dT _re with or without dT _es and 13 skin surface temperatures combined to one weighted mean skin temperature (dTˉ _sk), using MLR. This results in models C and D. Six more models (E–J) were added, representing the above two sets in various combinations with four factors. (3) The conventional method calculated with four values for X. Model A predicted better than 0.3 °C in 70% of the cases. Model I was the best amongst the models with 13 weighted skin temperatures (better than 0.3 °C in 60% of the cases). The conventional method was erratic. Accepted: 14 January 2000     

Effects of gradient and load carried on human haemodynamic responses during treadmill walking

This study examined the effects of different loads carried and gradients, on haemodynamic and cardiovascular responses during 45 min of treadmill walking. A group of 20 male endurance-trained athletes [mean maximal oxygen uptake 61.4 (SD 4) ml · kg⁻¹ · min⁻¹] volunteered for this study. The subjects took part in three separate trials. The first involved a backpack weighing 25 kg , the second a 35 kg backpack, and the third trial, unladen, while walking on a treadmill at a speed of 5 km · h⁻¹. The subjects began walking on the treadmill with the randomized load at 0% gradient. After 15 min, the gradient was increased by 5% every 15 min for a total of 45 min. The order of the loads carried was randomized among subjects. No significant differences were noted for all the variables measured attributable to loads between 25 kg and 35 kg. However, significant (P < 0.05) differences were seen for all variables each time the gradient was increased. Cardiac output increased from 11.4 (SD 0.6) l · min⁻¹ at 0% to 13.6 (SD 0.8) l · min⁻¹ at 5% and to 17.6 (SD 1.3) l · min⁻¹ at 10% carrying the 35 kg load. Similarly, lactic acid concentrations in the blood increased from 2.8 (SD 0.2) to 3.1 (SD 0.6) and to 5.3 (SD 1.3) mmol · l⁻¹, respectively. Similar changes were observed for all variables while carrying the 25 kg load. In addition, steady states in oxygen uptake and other physiological variables were obtained throughout the course of the tests. These data suggest that during isodynamic exercise, one of the main factors determining metabolic and haemodynamic responses will be the change in gradient and to a lesser extent, the mass of the load carried. Accepted: 12 May 2000     

The oxygen consumption with unloaded walking and load carriage using two different backpack designs

The purpose of this study was to assess the energy expenditure associated with load carriage using both a traditional rucksack and a new rucksack design, the AARN rucksack, which incorporates front balance pockets. Nine volunteers walked at 3 km h⁻¹ at various uphill and downhill gradients on a treadmill without a load and carrying a load of 25.6 kg in each of the rucksacks. The oxygen consumption associated with both of the loading conditions was significantly (P < 0.001) higher than that associated with unloaded walking at all downhill gradients tested, although there was no significant difference between the two loading conditions. During the uphill gradients the oxygen consumption associated with the AARN pack was significantly (P < 0.05) lower than that associated with the traditional pack at the 0%, 5%, 10% and 20% gradients. The mean (%) differences at these gradients, expressed in ml · kg⁻¹ · min⁻¹ were 1.18 (9%), 1.45 (8%), 1.76 (8%) and 1.88 (6%), respectively. On average for the whole protocol, the oxygen consumption associated with the AARN rucksack was 5% lower than that associated with the traditional rucksack [mean (SD) 17.28 (7.46) ml · kg⁻¹ · min⁻¹ for the AARN pack and 18.20 (7.84) ml · kg⁻¹ · min⁻¹ for the traditional pack]. The findings of the present study suggest that a load carriage system that allows the load to be distributed between the back and font of the trunk is more appropriate for carrying relatively heavy loads than a system that loads the back only. Accepted: 22 November 1999     

Physiological and metabolic responses of female games and endurance athletes to prolonged, intermittent, high-intensity running at 30° and 16°C ambient temperatures

Eight female games players (GP) and eight female endurance athletes (EA) ran intermittently at high-intensity and for prolonged periods in hot (30°C) and moderate (16°C) ambient temperatures. The subjects performed a two-part (A, B) test based on repeated 20-m shuttle runs. Part A comprised 60 m of walking, a maximal 15-m sprint, 60 m of cruising (90% maximal oxygen uptake, V˙O_2max) and 60 m of jogging (45% V˙O_2max) repeated for 75 min with a 3-min rest every 15 min. Part B involved an exercise and rest pattern of 60-s running at 100% V˙O_2max and 60-s rest which was continued until fatigue. Although the GP and EA did not respond differently in terms of distances completed, performance was 25 (SEM 4)% less (main effect trial, P < 0.01) in the hot (HT) compared with the moderate trial (MT). Sprints of 15 m took longer to complete in the heat (main effect, trial, P < 0.01), and sprint performance declined during HT but not MT (interaction, trial × time, P < 0.01). A very high correlation was found between the rate of rise in rectal temperature in HT and the distance completed [GP, r =−0.94, P < 0.01; EA (n = 7), r = −0.93, P < 0.01]. Blood lactate [La⁻ ]_b and plasma ammonia [NH₃]_p1 concentrations were higher for GP than EA, but were similar in HT and MT [La⁻ ]_b, HT: GP vs EA, 8.0 (SEM 0.9) vs 4.9 (SEM 1.1) mmol · l⁻¹; MT: GP vs EA, 8.0 (SEM 1.3) vs 4.4 (SEM 1.2) mmol · l⁻¹; interaction, group × time, P < 0.01; [NH₃]_p1, HT: GP vs EA, 70.1 (SEM 12.7) vs 43.2 (SEM 6.1) mmol · l⁻¹; MT: GP vs EA, 76.8 (SEM 8.8) vs 32.5 (SEM 3.8) μmol · l⁻¹; interaction, group × time, P < 0.01. Ad libitum water consumption was higher in HT [HT: GP vs EA, 18.9 (SEM 2.9) vs 13.5 (SEM 1.7) ml · kg⁻¹ · h⁻¹; MT: GP vs EA, 12.7 (SEM 3.7) vs 8.5 (SEM 1.5) ml · kg⁻¹ · h⁻¹; main effect, group, n.s.; main effect, trial, P < 0.01]. These results would suggest that elevated body temperature is probably the key factor limiting performance of prolonged, intermittent, high-intensity running when the ambient temperature is high, but not because of its effect on the metabolic responses to exercise. Accepted: 19 July 1999     

Extracellular pH defense against lactic acid in normoxia and hypoxia before and after a Himalayan expedition

The extracellular pH defense against the lactic acidosis resulting from exercise can be estimated from the ratios −Δ[La] · ΔpH⁻¹ (where Δ[La] is change in lactic acid concentration and ΔpH is change in pH) and Δ[HCO₃ ⁻] · ΔpH⁻¹ (where Δ[HCO₃ ⁻] is change in bicarbonate concentration) in blood plasma. The difference between −Δ[La] · ΔpH⁻¹ and Δ[HCO₃ ⁻] · ΔpH⁻¹ yields the capacity of available non-bicarbonate buffers (mainly hemoglobin). In turn, Δ[HCO₃ ⁻] · ΔpH⁻¹ can be separated into a pure bicarbonate buffering (as calculated at constant carbon dioxide tension) and a hyperventilation effect. These quantities were measured in 12 mountaineers during incremental exercise tests before, and 7–8 days (group 1) or 11–12 days (group 2) after their return from a Himalayan expedition (2800–7600 m altitude) under conditions of normoxia and acute hypoxia. In normoxia −Δ[La] · ΔpH⁻¹ amounted to [mean (SEM)] 92 (6) mmol · l⁻¹ before altitude, of which 19 (4), 48 (1) and 25 (3) mmol · l⁻¹ were due to hyperventilation, bicarbonate and non-bicarbonate buffering, respectively. After altitude −Δ[La] · ΔpH⁻¹ was increased to 128 (12) mmol · l⁻¹ (P < 0.01) in group 1 and decreased to 72 (5) mmol · l⁻¹ in group 2 (P < 0.05), resulting mainly from apparent large changes of non-bicarbonate buffer capacity, which amounted to 49 (14) mmol · l⁻¹ in group 1 and to 10 (2) mmol · l⁻¹ in group 2. In acute hypoxia the apparent increase in non-bicarbonate buffers of group 1 was even larger [140 (18) mmol · l⁻¹]. Since the hemoglobin mass was only modestly elevated after descent, other factors must play a role. It is proposed here that the transport of La⁻ and H⁺ across cell membranes is differently influenced by high-altitude acclimatization. Accepted: 14 September 2000     

Plasma catecholamine responses and neural adaptation during short-term resistance training

Low exercise-induced plasma adrenaline (A) responses have been reported in resistance-trained individuals. In the study reported here, we investigated the interaction between strength gain and neural adaptation of the muscles, and the plasma A response in eight healthy men during a short-term resistance-training period. The subjects performed 5 resistance exercises (E1–E5), consisting of 6 sets of 12 bilateral leg extensions performed at a 50% load, and with 2 days rest in between. Average electromyographic (EMG) signal amplitude was recorded before and after the exercises, from the knee extensor muscles in isometric maximal voluntary contraction (MVC) as well as during the exercises (aEMG_max and aEMG_exerc, respectively). Total oxygen consumed during the exercises (V˙O_2tot) was also measured. All of the exercises were exhaustive and caused significant decreases in MVC (34–36%, P < 0.001). As expected, the concentric one-repetition maximum (1-RM), MVC and aEMG_max were all higher before the last exercise (E5) than before the first exercise (E1; 7, 9 and 19%, respectively, P < 0.05). In addition, in E5 the aEMG_exerc:load and V˙O_2tot:load ratios were lower than in E1 (−5 and −14%, P < 0.05), indicating enhanced efficiency of the muscle contractions, However, the post-exercise plasma noradrenaline (NA) and A were not different in these two exercises [mean (SD) 10.2 (3.8) nmol · l⁻¹ vs 11.3 (6.0) nmol · l⁻¹, ns, and 1.2 (1.0) nmol · l⁻¹ vs 1.9 (1.1) nmol · l⁻¹, ns, respectively]. However, although NA increased similarly in every exercise (P < 0.01), the increase in A reached the level of statistical significance only in E1 (P < 0.05). The post-exercise A was also already lower in E2 [0.7 (0.7) nmol · l⁻¹, P < 0.05) than in E1, despite the higher post-exercise blood lactate concentration than in the other exercises [9.4 (1.1) mmol · l⁻¹, P < 0.05]. Thus, the results suggest that the observed attenuation in the A response can not be explained by reduced exercise-induced strain due to the strength gain and neural adaptation of the muscles. Correlation analysis actually revealed that those individuals who had the highest strength gain during the training period even tended to have an increased post-exercise A concentration in the last exercise as compared to first one (r=0.76, P < 0.05). Accepted: 10 February 2000     

The use of magnetic resonance images to investigate the influence of recruitment on the relationship between torque and cross-sectional area in human muscle

The purpose of the present study was to investigate the effect of recruitment on the relationship between peak torque and physiological cross-sectional area (PCSA) in human muscle. A group of 11 healthy men participated in this study. Isokinetic knee extension torques at seven (0, 30, 60, 120, 180, 240, and 300° · s⁻¹) velocities were determined. Magnetic resonance imaging (MRI) was performed to calculate PCSA of right quadriceps femoris (QF) muscle. Exercise-induced contrast shifts in spin-spin relaxation time (T2)-weighted MRI were taken at rest and immediately after repetitive knee-extension exercise and T2 of QF were calculated. The MRI pixels with T2 values more than 1 SD greater than the means at rest were considered to represent QF muscle that had contracted. The area of activated PCSA within the total in QF was expressed as percentage activated PCSA and used as an index of muscle recruitment. The PCSA correlated with peak torque at 0° · s⁻¹ (r=0.615, P < 0.05); in contrast, activated PCSA correlated with peak torque at 120° · s⁻¹ (r=0.603, P < 0.05) and 180° · s⁻¹ (r=0.606, P < 0.05). Additionally, there was a significant difference in correlation coefficients between the activated PCSA-peak torque relationship and the PCSA-torque relationship (P < 0.05). These results suggested that muscle recruitment affects the PCSA-torque relationship. Accepted: 11 August 2000     

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

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

Investigation of the effects of the pre-cooling on the physiological responses to soccer-specific intermittent exercise

Whole-body cooling prior to activity has the potential to reduce thermal strain and fatigue during subsequent endurance exercise. Intermittent activity is associated with greater increases in rectal temperature compared with continuous exercise. Thus, the effect of pre-cooling on thermoregulatory responses was examined during an intermittent test under “normal” environmental conditions. Six male university soccer players [mean (SD) age 27 (2) years; height 1.77 (0.3) m; mass 72.2 (1.5) kg; maximal oxygen consumption 58.9 (3.5) ml · kg⁻¹ · min⁻¹] completed a 90-minute soccer-specific intermittent exercise protocol on a non-motorised treadmill. The run was completed with and without pre-cooling under normal laboratory conditions (20°C) and without pre-cooling in a heated laboratory (26°C). The pre-cooling strategy involved exposure to a cold shower (26°C) for 60 min. The pre-cooling manipulation lowered rectal temperature prior to exercise [−0.6 (0.6)°C, range −1.5°C; P < 0.05]. The rectal temperature response to exercise was significantly lower following pre-cooling than in the heated condition [pre-cooled 38.1 (0.6)°C, heated 38.6 (0.3)°C]. The increase in rectal temperature during the second half of the protocol following pre-cooling was significantly greater than the increase observed under normal or heated conditions (P < 0.05). No significant differences were observed between the three conditions for oxygen consumption, heart rate, minute ventilation, rating of perceived exertion and plasma lactate, glucose or free fatty acid concentrations. Based on the current investigation, it can be concluded that there is no evidence for the beneficial effects of pre-cooling on the physiological responses to soccer-specific intermittent exercise under normal environmental conditions. Accepted: 30 June 1999     

Effect of strenuous strength training on the Na-K pump concentration in skeletal muscle of well-trained men

This study examined how strenuous strength training affected the Na-K pump concentration in the knee extensor muscle of well-trained men and whether leg muscle strength and endurance was related to the pump concentration. First, the pump concentration, taken as ³H-ouabain binding, was measured in top alpine skiers since strength training is important to them. Second, well-trained subjects carried out strenuous eccentric resistance training either 1, 2, or 3 times · week⁻¹ for 3 months. The Na-K pump concentration, the maximal muscle strength in a full squat lift (one repetition maximum, 1 RM), and the muscle endurance, taken as the number of full squat lifts of a mass of 70% of the 1 RM load, were measured before and after the training period. The mean pump concentration of the alpine skiers was 425 (SEM 11) nmol · kg⁻¹ wet muscle mass. The subjects in part two increased their maximal strength in a dose-dependent manner. The muscle endurance increased for all subjects but independently of the training programme. From a mean starting value of 356 (SEM 6) nmol · kg⁻¹ the mean Na-K pump concentration increased by 54 (SEM 15) nmol · kg⁻¹ (+15%, P < 0.001) when the results for all subjects were pooled. The effect was larger for those who had trained twice a week than for those who had trained only once a week (P=0.025), suggesting that the effect of strength training depended on the amount of training carried out. The muscle strength and endurance were not related to the pump concentration, suggesting that the pumping power of this enzyme did not limit the performance during heavy lifting. However, the individual improvements in the endurance test during the training period correlated with the individual changes in the pump concentration (r _Spearman=0.5; P=0.01) which could mean that a common factor both increases the pump concentration and makes the muscles more adapted to repeated heavy lifting. Accepted: 8 August 2000     

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

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

Time to exhaustion during severe intensity running: response following a single bout of interval training

 The primary aim of this study was to examine any change in performance caused by a fatiguing interval training session (TS). A secondary aim of this study was to examine the change in oxygen uptake (V˙O₂) during moderate and severe intensity running, and the relationship with the change in performance. Seven male runners [mean age 24 (SD 6) years, height 1.79 (SD 0.06) m, body mass 67.9 (SD 7.6) kg, maximal oxygen uptake (V˙O_2max) 4.14 (SD 0.49) l · min⁻¹] were studied. The V˙O₂ during moderate and severe intensity running and running performance were studied immediately prior to, 1 h following, and 72 h following TS. The TS was performed on a treadmill, and consisted of six bouts of 800 m at 1 km · h⁻¹ below the velocity at V˙O_2max (v _V˙ O_2max), with 3-min rest intervals. Performance was also assessed at 1 km · h⁻¹ below v _V˙ O_2max, in the form of time to exhaustion (t _lim). The V˙O₂ and heart rate (f _c) were assessed both during the severe intensity performance trial, and the moderate intensity run at 50% v _V˙ O_2max. Whilst a significant change was observed in running performance and the V˙O₂ during both moderate and severe intensity running prior to and following TS, no relationship was observed between the magnitude of change in these variables. At 1 h following TS, t _lim had decreased by 24%, V˙O₂ during moderate intensity running had increased by 2%, and the difference in V˙O₂ between 2 min 45 s and the end of severe intensity running had increased by 91% compared with values recorded prior to TS. At 1 h following TS, ƒ_c had also increased significantly during moderate intensity running by 5% compared to the value recorded prior to TS. These findings demonstrated that TS resulted in a reduction in performance, and that the relationship between running performance and V˙O₂ during running may be altered under conditions of prolonged fatigue. Accepted: 16 September 1999     

The effects of 3000-m swimming on subsequent 3-h cycling performance: implications for ultraendurance triathletes

The purpose of this study was to examine the physiological effects of 3000-m swimming on subsequent 3-h cycling time trial performance in ultraendurance triathletes. Eight highly trained ultraendurance triathletes [mean (SEM) age 34 (2) years, body fat 12.5 (0.8)%, maximum oxygen consumption 63.2 (2.1) ml · kg⁻¹ · min⁻¹] completed two randomly assigned trials 1 week apart. The swim/bike trial (SB) involved 3000 m of swimming [min:s 52:28 (1:48)] immediately followed by a 3-h cycling performance at a self-selected time-trial pace. The control trial (CON) consisted of an identical 3-h cycling time trial but without prior swimming. Subjects consumed an 8% carbohydrate (CHO)/electrolyte beverage during both trials at the rate of 60 g CHO · h⁻¹ and 1 l · h⁻¹. No significant differences were evident between CON and SB on the dependent measures (CON vs SB): power output [W˙, 222 (14) W vs 212 (13) W], heart rate [f _c, 147 (5) beats · min⁻¹ vs 143 (4) beats · min⁻¹; %f _cmax 80.0 (1.6)% vs 78.4 (1.5)%], oxygen uptake [3.10 (0.12) l · min⁻¹ vs 2.97 (0.15) l · min⁻¹], minute ventilation [82.5 (4.4) l · min⁻¹ vs 77.3 (3.7) l · min⁻¹], rating of perceived exertion [14.6 (0.4) vs 14.0 (0.1)], blood lactate [6.1 (0.5) mmol · l⁻¹ vs 4.8 (0.5) mmol · l⁻¹], and blood glucose [5.0 (0.2) mmol · l⁻¹ vs 5.3 (0.1) mmol · l⁻¹; all non-significant at the P > 0.05 level]. However, the CON respiratory exchange ratio was significantly greater than for SB [0.91 (0.01) vs 0.89 (0.01); P < 0.05], suggesting that the SB trial required a greater reliance on lipid as a fuel substrate. Hence, the main finding in the present study was that 3000 m of swimming had no significant performance effect (in terms of W˙) on subsequent 3-h cycling performance in ultraendurance triathletes. Accepted: 2 March 2000     

Effect of exercise on the mitochondrial DNA content of peripheral blood in healthy women

Exercise decreases insulin resistance and increases maximal exercise capacity as estimated from maximal oxygen uptake (V˙O_2max). Recent reports have demonstrated that the mitochondrial DNA (mtDNA) content of blood is correlated with V˙O_2max in healthy subjects (mean age 31 years) and is inversely correlated with insulin resistance parameters. The aim of this study was to determine the effect of regular exercise on the mtDNA content in the peripheral blood of 16 healthy young women of mean age 24.8 (SD 6.2) years and 14 healthy older women of mean age 66.7 (SD 5.8) years. The exercise programme lasted for 10 weeks and consisted of three sessions a week, each of 1 h and aiming to attain 60%–80% of V˙O_2max. The mtDNA content of peripheral blood was measured by competitive polymerase chain reaction. The V˙O_2max had significantly increased following the exercise programme [from 33.1 (SD 3.4) to 35.2 (SD 3.4) ml · kg⁻¹ · min⁻¹ in the young and from 24.3 (SD 5.3) to 30.3 (SD 7.3) ml · kg⁻¹ · min⁻¹ in the older women, both P < 0.05]. Exercise decreased systolic blood pressure, and concentrations of triglyceride, low density lipoprotein-cholesterol (LDL-C), glucose and insulin in the blood of the young and of total cholesterol, LDL-C and glucose in that of the older women. High density lipoprotein-cholesterol (HDL-C) in the young women was increased by exercise. The mtDNA content significantly increased following the exercise programme in both groups [from 27.1 (SD 17.9) to 52.7 (SD 44.6) amol · 5 ng⁻¹ genomic DNA in the young and from 15.3 (SD 10.2) to 32.1 (SD 30.0) amol · 5 ng⁻¹ genomic DNA in the older women, both P < 0.05]. There was a significant positive correlation between the change in mtDNA content and the change in V˙O_2max (r=0.74 in the young and r=0.71 in the older women, both P < 0.01). In conclusion, 10 weeks of moderate intensity, regular exercise increased the mtDNA content in peripheral blood and decreased insulin resistance parameters. This data suggests that increase in the mtDNA content may be associated with increased insulin sensitivity. Accepted: 15 April 2000     

The effects of drafting on stroking variations during swimming in elite male triathletes

The aim of this study was to determine the effects of drafting behind another swimmer on the metabolic response and stroke characteristics. Six highly trained male triathletes performed two maximal 400-m swims, one in a drafting (D) and one in a non-drafting condition (ND). Their metabolic response was assessed by measuring the oxygen uptake (V˙O₂) and the blood lactate concentration at the end of each 400 m. Swimming velocity, stroke frequency, stroke length, and stroke index (velocity multiplied by stroke length) were recorded every 50 m. In the D and ND conditions, there was no difference in V˙O₂ [66.7 (1.7) ml · kg⁻¹ · min⁻¹ vs 65.6 (1.2) ml · kg⁻¹ · min⁻¹, respectively], however, the lactate concentrations were lower in D than in ND [9.6 (0.9) mM vs 10.8 (0.9) mM, respectively, P < 0.01]. In D, the performance [1.39 (0.02) m · s⁻¹ vs 1.34 (0.02) m · s⁻¹, respectively, P < 0.01] and the stroking parameters (i.e., stroke length and stroke index) increased significantly, while the stroke frequency remain unchanged. In D, a stable pace was maintained, while in ND, velocity decreased significantly throughout the 400 m. In D, the performance gains were related to the 400-m D velocity (r=0.78, P < 0.05), and to the body fat mass (BFM, r=0.99, P < 0.01). The stroke index in D was also related to BFM (r=0.78, P < 0.05). Faster and leaner swimmers achieved greater performance gains and stroke index when drafting. Thus, drafting during swimming increases the performance and contributes to the maintenance of stable stroking parameters such as stroke frequency and stroke length during a 400-m swim. Accepted: 10 April 2000     

Measurement and prediction of peak shivering intensity in humans

Prediction equations of shivering metabolism are critical to the development of models of thermoregulation during cold exposure. Although the intensity of maximal shivering has not yet been predicted, a peak shivering metabolic rate (Shiv_peak) of five times the resting metabolic rate has been reported. A group of 15 subjects (including 4 women) [mean age 24.7 (SD 6) years, mean body mass 72.1 (SD 12) kg, mean height 1.76 (SD 0.1) m, mean body fat 22.3 (SD 7)% and mean maximal oxygen uptake (V˙O_2max) 53.2 (SD 9) ml O₂ · kg⁻¹ · min⁻¹] participated in the present study to measure and predict Shiv_peak. The subjects were initially immersed in water at 8°C for up to 70 min. Water temperature was then gradually increased at 0.8 °C · min⁻¹ to a value of 20 °C, which it was expected would increase shivering heat production based on the knowledge that peripheral cold receptors fire maximally at approximately this temperature. This, in combination with the relatively low core temperature at the time this water temperature was reached, was hypothesized would stimulate Shiv_peak. Prior to warming the water from 8 to 20 °C, the oxygen consumption was 15.1 (SD 5.5) ml · kg⁻¹ · min⁻¹ at core temperatures of approximately 35 °C. After the water temperature had risen to 20 °C, the observed Shiv_peak was 22.1 (SD 4.2) ml O₂ · kg⁻¹ · min⁻¹ at core and mean skin temperatures of 35.2 (SD 0.9) and 22.1 (SD 2.2) °C, respectively. The Shiv_peak corresponded to 4.9 (SD 0.8) times the resting metabolism and 41.7 (SD 5.1)% of V˙O_2max. The best fit equation predicting Shiv_peak was Shiv_peak (ml O₂ · kg⁻¹ · min⁻¹)=30.5 + 0.348 ×V˙O_2max (ml O₂ · kg⁻¹ · min⁻¹) − 0.909 × body mass index (kg · m⁻²) − 0.233 × age (years); (P=0.0001; r ²=0.872). Accepted: 7 September 2000     

Total energy expenditure of elite synchronized swimmers measured by the doubly labeled water method

To determine the daily energy requirement of elite synchronized swimmers during moderate-intensity training, the average daily energy expenditure measured by the doubly labeled water method, was calculated for nine female Japanese national team synchronized swimmers [four senior; mean (SD) 22.5 (1.0) years old, 52.2 (3.6) kg, and five junior; 17.6 (1.1) years old, 52.8 (2.3) kg]. Their total energy expenditure (TEE) was 11.5 (2.8) MJ · day⁻¹ [2738 (672) kcal · day⁻¹]. When compared with estimated energy requirements derived from “Recommended Dietary Allowances for the Japanese”, 12.1 (0.6) MJ · day⁻¹ [2897 (139) kcal · day⁻¹], there was no difference between mean actual and estimated energy requirements. However, there were considerable differences observed on an individual basis. Their energy intake, estimated from 7- day self-reported dietary records, was 8.9 (1.7) MJ · day⁻¹ [2128 (395) kcal · day⁻¹], which was significantly lower than their TEE (P < 0.05). Resting energy expenditure (REE), as determined by indirect calorimetry, was 5.2 (0.3) MJ · day⁻¹ [1247 (75) kcal · day⁻¹]. Their physical activity level (TEE/REE) was 2.18 (0.43). These results demonstrate that the TEE values of elite female synchronized swimmers are not dissimilar to those reported for athletes participating in other sports, especially competitive swimmers during moderate-intensity training. Accepted: 26 May 2000