The longitudinal development of running economy in males and females aged between 13 and 27 years: The Amsterdam Growth and Health Study

The purpose of this study was to describe the longitudinal development of running economy [defined as the oxygen uptake (V˙O₂) at a submaximal running speed] in males and females from teenage to young adult age using data from the Amsterdam Growth and Health Study. Submaximal V˙O₂ (in ml · kg^?1· min^?1) was measured in 84 males and 98 females while they ran on a treadmill at a constant speed of 8 km · h^?1 for 6 min at three different treadmill slopes (0%, 2.5% and 5%). This test was carried out six times, on the same subjects at the ages of 13, 14, 15, 16, 21, and 27 years. The longitudinal development of running economy in males and females was analysed using a two-way analysis of variance for repeated measurements. At all three slopes, a significant decrease in V˙O₂ with increasing age was found for both males and females, implying a significant increase in running economy for both sexes. Males showed significantly higher V˙O₂ values than females at all ages measured and for all three slopes, suggesting that females have a significantly higher running economy than males. In order to make a better comparison of the V˙O₂ of individuals of different sizes, allometric models were used; power function ratios were constructed in which body mass was expressed to an exponential power. Following this analysis the difference in submaximal V˙O₂ and running economy between males and females appeared even larger.     

Gender comparison of peak oxygen uptake: repetitive box lifting versus treadmill running

The gender differences in peak oxygen uptake (V˙O_2peak) for various modes of exercise have been examined previously; however, no direct gender comparisons have been made during repetitive lifting (RL). In the present study the V˙O_2peak between RL and treadmill running (TR) was compared between 20 men [mean (SD) age, height, body mass and body fat: 21 (3) years, 1.79 (0.06)?m, 81 (9)?kg, 19 (6)%, respectively] and 20 women [mean (SD) age, height, body mass and body fat: 21 (3) years, 1.63 (0.05)?m, 60 (7)?kg, 27 (6)%, respectively]. V˙O_2peak (l?·?min^?1), defined as the highest value obtained during exercise to volitional fatigue, was determined using discontinuous protocols with treadmill grade or box mass incremented to increase exercise intensity. For RL V˙O_2peak, a pneumatically driven shelf was used to lower a loaded box to the floor, and subjects then lifted the box, at a rate of 15 lifts?·?min^?1. V˙O_2peak (l?·?min^?1 and ml?·?kg^?1?·?min^?1) and minute ventilation (V˙ _E, l?·?min^?1) were determined using an on-line gas analysis system. A two-way repeated measures analysis of variance revealed significant gender effects, with men having higher values for V˙O_2peak (l?·?min^?1 and ml?·?kg^?1?·?min^?1) and V˙ _E, but women having higher values of the ventilatory equivalent for oxygen (V˙ _E/V˙O₂). There were also mode of exercise effects, with TR values being higher for V˙O_2peak (l?·?min^?1 and ml?·?kg^?1?·?min^?1) and V˙ _E and an interaction effect for V˙O_2peak {1?·?min^?1 and ml?·?kg^?1?·?min^?1) and V˙ _E/V˙O₂. The women obtained a greater percentage (≈84%) of their TR V˙O_2peak during RL than did the men (≈79%). There was a marginal tendency for women to decrease and men to increase their V˙ _E/V˙O₂ when comparing TR with RL. The magnitude of the gender differences between the two exercise modalities appeared to be similar for heart rate, V˙ _E and R, but differed for V˙O_2peak (1?·?min^?1 and ml?·?kg^?1?·?min^?1). Lifting to an absolute height (1.32?m for the RL protocol) may present a different physical challenge to men and women with respect to the degree of involvement of the muscle groups used during lifting and ventilation.     

Changes in performance,maximal oxygen uptake and maximal accumulated oxygen deficit after 5, 10 and 15 days of live high:train low altitude exposure

Nineteen well-trained cyclists (14 males and 5 females, mean initial V˙O_2max 62.3 ml kg^–1 min^–1) completed a multistage cycle ergometer test to determine maximal mean power output in 4 min (MMPO_4min), maximal oxygen uptake (V˙O_2max) and maximal accumulated oxygen deficit (MAOD). The athletes were divided into three groups, each of which completed 5, 10 or 15 days of both a control condition (C) and live high:train low altitude exposure (LHTL). The C groups lived and trained at the ambient altitude of 610 m. The LHTL groups spent 8–10 h night^–1 in normobaric hypoxia at a simulated altitude of 2,650 m, and trained at the ambient altitude of 610 m. The changes to MMPO_4min, V˙O_2max and MAOD in response to LHTL altitude exposure were not significantly different for the 5-, 10- and 15-day treatment periods. For the pooled data from all three treatment periods, there were significant increases in MMPO_4min [mean (SD) 5.15 (0.83) W kg^–1 vs 5.34 (0.78) W kg^–1] and MAOD [50.1 (14.2) ml kg^–1 vs 54.9 (13.1) ml kg^–1] in the LHTL athletes between pre- and post-altitude exposure. There were no significant changes in MMPO_4min [5.09 (0.76) W kg^–1 vs 5.16 (0.86) W kg^–1] or MAOD [50.5 (14.1) ml kg^–1 vs 49.1 (13.0) ml kg^–1] in the C athletes over the corresponding period. There were significant increases in V˙O_2max in the athletes during both the LHTL [63.2 (9.0) ml kg^–1 min^–1 vs 64.1 (9.0) ml kg^–1 min^–1] and C [62.0 (8.6) ml kg^–1 min^–1 vs 63.4 (9.2) ml kg^–1 min^–1] conditions. In these athletes, there was no difference in the impact of 5, 10 or 15 days of LHTL on the increases observed in MMPO_4min, V˙O_2max or MAOD; and LHTL increased MMPO_4min and MAOD more than training at low altitude alone. Electronic Publication     

Relationship between isocapnic buffering and maximal aerobic capacity in athletes

This study was performed to clarify the relationship between isocapnic buffering and maximal aerobic capacity (V˙O_{2 max} ) in athletes. A group of 15 trained athletes aged 21.1 (SD 2.6) years was studied. Incremental treadmill exercise was performed using a modified version of Bruce's protocol for determination of the anaerobic threshold (AT) and the respiratory compensation point (RC). Ventilatory and gas exchange responses were measured with an aeromonitor and expressed per unit of body mass. Heart rate and ratings of perceived exertion were recorded continuously during exercise. The mean V˙O_{2 max} , oxygen uptake (V˙O₂) at AT and RC were 58.2 (SD 5.8)?ml?·?kg^?1?·?min^?1, 28.0 (SD 3.3)?ml?·?kg^?1?·?min^?1 and 52.4 (SD 6.7)?ml?· kg^?1?·?min^?1, respectively. The mean values of AT and RC, expressed as percentages of V˙O_{2 max} , were 48.3 (SD 4.2)% and 90.0 (SD 5.2)%, respectively. The mean range of isocapnic buffering defined as V˙O₂ between AT and RC was 24.4 (SD 4.5) ml?·?kg^?1?·?min^?1, and the mean range of hypocapnic hyperventilation (HHV) defined as V˙O₂ between RC and the end of exercise was 5.8 (SD 3.0)?ml?·?kg^?1?·?min^?1. The V˙O_{2 max} per unit mass was significantly correlated with AT (r?=?0.683, P?V˙O_{2 max} /mass was closely correlated with both the range of isocapnic buffering (r?=?0.803, P?r?=?0.878, P?V˙O_{2 max} per unit mass and the range of HHV (r?=?0.011, NS.). These findings would suggest that the prominence of isocapnic buffering, in addition to the anaerobic threshold, may have been related to V˙O_{2 max} of the athletes. The precise mechanisms underlying this proposed relationship remain to be elucidated.     

Vascular volumes and hematology in male and female runners and cyclists

To examine the hypothesis that foot-strike hemolysis alters vascular volumes and selected hematological properties is trained athletes, we have measured total blood volume (TBV), red cell volume (RCV) and plasma volume (PV) in cyclists (n?=?21) and runners (n?=?17) and compared them to those of untrained controls (n?=?20). TBV (ml?·?kg^?1) was calculated as the sum of RCV (ml?·?kg^?1) and PV (ml?·?kg^?1) obtained using ⁵¹Cr and ¹²⁵I-labelled albumin, respectively. Hematological assessment was carried out using a Coulter counter. Peak aerobic power (V˙O_2peak) was measured during progressive exercise to fatigue using both cycle and treadmill ergometry. RCV was 15% higher (P?n?=?12] and runners [35.3 (0.98); n=9] compared to the controls [30.7 (0.92); n?=?12]. Similar differences existed between the female cyclists [28.2 (2.1); n?=?9] and runners [28.4 (1.0); n?=?8] compared to the untrained controls [24.9 (1.4); n?=?8]. For the male athletes, PV was between 19% (cyclists) and 28% (runners) higher (P?P?V˙O_2peak (ml?· kg^?1?·?min^?1) was higher (P?V˙O_2peak for both cyclists and runners, no differences were found between the athletic groups within a gender. Since the vascular volumes were not different between cyclists and runners for either the males or females, foot-strike hemolysis would not appear to have an effect on that parameter. The significant correlations (P?V˙O_2peak and RCV (r?=?0.64 and 0.64) and TBV (r?=?0.82 and 0.63) for the males and females, respectively, suggests a role for the vascular system in realizing a high aerobic power.     

Do gender differences exist in the ventilatory response to progressive exercise in males and females of average fitness?

Gender differences in lung volumes and flow rates, and in respiratory control have been documented previously. How these gender differences affect exercise responses in normal subjects is less clear, particularly as many studies involved highly fit subjects. This study aimed to investigate potential gender differences occurring during progressive exercise in healthy males and females of average fitness. Fourteen males and ten females of mean (SD) age 23 (0.35) years completed a progressive exercise test to exhaustion on a cycle ergometer, with a ramp increase of 15 W min⁻¹ (female) or 20 W min⁻¹ (male). All females were studied during the follicular phase of their menstrual cycle. Cardiorespiratory variables were measured, breath by breath, and values were compared at rest, at 40 W, at physiologically equivalent workloads below, at and above the gas exchange threshold and at peak oxygen uptake (V̇O_2peak). Mean V̇O_2peak (SEM) was 32.4 (2.01) ml kg⁻¹ min⁻¹ for the females and 41.9 (1.80) ml kg⁻¹ min⁻¹ for the males. Females had a significantly lower end-tidal partial CO₂ pressure at rest and throughout exercise. Increases in exercise minute ventilation were achieved by a significantly greater tidal volume in males, whereas females adopted a significantly greater breathing frequency. Ratings of respiratory discomfort were significantly greater in the male group at physiologically equivalent workloads compared to the female group. This study shows gender differences exist in the ventilatory and sensory response to progressive exercise in untrained subjects. Further work is required to ascertain if these effects are altered during the luteal phase of the menstrual cycle.     

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??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??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?V˙O₂, HR and R were independent of the recovery duration between the repetitions.     

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.     

A physiological description of critical velocity

Although critical velocity (CV) provides a valid index of aerobic function, the physiological significance of CV is not known. Twelve individuals performed exhaustive runs at 95% to 110% of the velocity at which V˙O₂max was attained in an incremental test. V˙O₂max was elicited in each run. Using the time to exhaustion at each velocity, CV was calculated for each participant. Using the time to achieve V˙O₂max at each velocity, which was shorter at higher velocities, a parameter we have designated as CV′ was calculated for each participant. During exercise at or below CV′, V˙O₂max cannot be elicited. CV (238?±?24?m?·?min^?1) and CV′ (239?±?25?m?·?min^?1) were equal (t?=?0.60, p?=?0.56) and correlated (r?=?0.97, p?<?0.01). These results demonstrate that CV is the threshold intensity above which exercise of sufficient duration will lead to attainment of V˙O₂max.     

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?相似文献   

The perceptually regulated exercise test is sensitive to increases in maximal oxygen uptake

The aim of this study was to assess the sensitivity of a perceptually regulated exercise test (PRET) to predict maximal oxygen uptake ( $ \dot{V} $ O₂max) following an aerobic exercise-training programme. Sedentary volunteers were assigned to either a training (TG n = 16) or control (CG n = 10) group. The TG performed 30 min of treadmill exercise, regulated at 13 on the Borg Rating of Perceived Exertion (RPE) Scale, 3× per week for 8 weeks. All participants completed a 12-min PRET to predict $ \dot{V} $ O₂max followed by a graded exercise test (GXT) to measure $ \dot{V} $ O₂max before and after training. The PRET required participants to control the speed and incline on the treadmill to correspond to RPE intensities of 9, 11, 13 and 15. Predictive accuracy of extrapolation end-points RPE19 and RPE20 from a submaximal RPE range of 9–15 was compared. Measured $ \dot{V} $ O₂max increased by 17 % (p < 0.05) from baseline to post-intervention in TG. This was reflected by a similar change in $ \dot{V} $ O₂max predicted from PRET when extrapolated to RPE 19 (baseline $ \dot{V} $ O₂max: 31.3 ± 5.5, 30.3 ± 9.5 mL kg^?1 min^?1; post-intervention $ \dot{V} $ O₂max: 36.7 ± 6.4, 37.4 ± 7.9 mL kg^?1 min^?1, for measured and predicted values, respectively). There was no change in CG (measured vs. predicted $ \dot{V} $ O₂max: 39.3 ± 6.5; 40.3 ± 8.2 and 39.2 ± 7.0; 37.7 ± 6.0 mL kg^?1 min^?1) at baseline and post-intervention, respectively. The results confirm that PRET is sensitive to increases in $ \dot{V} $ O₂max following aerobic training.     

V˙O2peak and the gas-exchange anaerobic threshold during incremental arm cranking in able-bodied and paraplegic men

Resting energy expenditure, peak oxygen uptake (V˙O_2peak) and the gas-exchange anaerobic threshold (Th_an) were measured during incremental arm cranking (15?W?·?min^?1) in six able-bodied (AB) and six paraplegic (P) subjects. Only male subjects with traumatic spinal cord injuries in the area of the 10–12th thoracic segment were included in the P group. All AB and P subjects were physically active. Mean (SE) values for age and body mass were 28 (2)?years and 78.9 (3.9)?kg for the AB group and 32 (4)?years and 70.8 (7.9)?kg for the P group (P?>?0.05). Resting energy expenditure values were not found to be significantly different between AB [5.8 (0.2)?kJ?·?min^?1] and P [5.1 (0.3)?kJ?·?min^?1] subjects. Mean V˙O_2peak values were 29.3 (2.4)?ml?· kg^?1?· min^?1 and 29.6 (2.2)?ml?·?kg^?1?·?min^?1 for the AB and P groups, respectively (P?>?0.05). Absolute oxygen uptake values measured at two gas-exchange anaerobic threshold (Th_an) were not significantly different between the two groups. However, the Th_an occurred at a significantly higher percentage of V˙O_2peak in the P [58.9 (1.7)%] group than in the AB [50.0 (2.8)%] group (P?R) values obtained at the Th_an and at 15, 45, 60, 75 and 90?W of incremental exercise were significantly lower in the P group than in the AB group. Heart rates were significantly elevated at every submaximal work stage (15–120?W) in the P group compared to the AB group (P?R) during arm exercise. These local adaptations may be in part responsible for the significantly higher Th_an observed for arm exercise in P subjects, even though V˙O_2peak values were essentially the same for both groups.     

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.     

Maximal aerobic power in trained youths at high altitude

The sample for this study consisted of 25 males and 19 females between the ages of 8·8 and 19·5 years. The subjects were healthy, well nourished and trained swimmers residing in La Paz, Bolivia (mean altitude 3700 m). The purpose of this study was to provide normative values for the work capacity of high-altitude youths. Mean V˙O₂max was 46·9 ml/kg/min in males and 39·3 ml/kg/min in females. V˙O₂max increased significantly with age in males but not in females. Mean V˙O₂max tended to be 10 20% lower in the swimmers than in sea-level athletes.     

Stroke volume response to cycle ergometry in trained and untrained older men

The aims of this study were threefold: (1) to investigate the stroke volume (SV) response of trained older male cyclists [Cyclists: 65 (2.1) years; n?=?10] during incremental cycle ergometry (20 W?·?min^?1); (2) to determine the SV dynamics and total peripheral resistance response of untrained, but healthy and active older male controls [Controls: 66 (1.1) years; n?=?10]; (3) to compare the maximum oxygen consumption (˙VO_2max) and SV response of trained older male runners [Runners: 65 (3.4) years; n?=?11] with that of age-matched Cyclists. Impedance cardiography was used to assess the response of cardiac output (CO), SV and total peripheral resistance to exercise involving cycle ergometry. The mean ˙VO_2max of the trained Cyclists [54 (1.6) ml?·?kg^?1?·?min^?1] was significantly higher (P??1?·?min^?1], whereas both groups possessed a significantly higher ˙VO_2max than the Controls [28 (1.3) ml?·?kg^?1?·?min^?1]. During exercise, at a heart rate of 90 beats?·?min^?1, the SV of the Cyclists increased by 41%, that of the Runners increased by 47%, and that of the Controls increased by 31%. However, the Cyclists' and Runners' SV response was significantly greater than that of the Controls. The SV for cyclists and controls peaked at 30% of ˙VO_2max. This early increase in SV was a major factor underlying the increase in CO during exercise in both the trained and the untrained subjects. In addition, all three groups showed a significant decrease in total peripheral resistance throughout exercise. The finding that older male runners possessed a large exercise SV and high ˙VO_2max suggests that run training results in enhanced cardiovascular performance during cycle ergometry.     

An alternative method to determine maximal accumulated O2 deficit in runners

An accepted measure of anaerobic capacity is the maximal O₂ deficit. But it is not feasible to use O₂ deficit if ≥10 submaximal runs are needed to extrapolate the O₂ demand of high velocity running (Medbø et al. 1988). Recently, an alternative method to determine O₂ deficit was proposed (Hill 1996) using only results of supramaximal cycle ergometer tests. The purpose of this study was to evaluate this alternative method with data from treadmill tests. Twenty-six runners ran at 95%, 100%, 105%, and 110% of their velocity at VO₂max. Times to exhaustion, velocity, and accumulated oxygen uptake (VO₂) from each individual's four tests were fit to the following equation using iterative nonlinear regression: The mean values derived for O₂ demand and O₂ deficit were 0.198?±?0.031?ml?·?kg^?1?·?m^?1 and 42?±?22?ml?· kg^?1. SEE for the parameters were 0.007?±?0.007?ml?· kg^?1?·?m^?1 and 8?±?10?ml?·?kg^?1, respectively. Mean R² was 0.998?±?0.003. It was concluded that O₂ deficit can be determined from all-out treadmill tests without the need to perform submaximal tests.     

Breath-to-breath “noise” in the ventilatory and gas exchange responses of children to exercise

The purposes of this investigation were to quantify the noise component of child breath-by-breath data, investigate the major determinants of the breath-to-breath noise, and to characterise the noise statistically. Twenty-four healthy children (12 males and 12 females) of mean (SD) age 13.1 (0.3) years completed 25?min of steady-state cycle ergometry at an exercise intensity of 50?W. Ventilatory and gas exchange variables were computed breath-by-breath. The mean (SD) oxygen consumption (V˙O₂) ranged from 0.72 (0.16) to 0.92 (0.26) l?·?min^?1; mean (SD) carbon dioxide production (V˙CO₂) ranged from 0.67 (0.20) l?·?min^?1 to 0.85 (0.16) l?·?min^?1; and mean (SD) minute ventilation ranged from 17.81 (3.54) l?·?min^?1 to 24.97 (5.63) l?·?min^?1. The majority of the breath-to-breath noise distributions differed significantly from Gaussian distributions with equivalent mean and SD parameters. The values of the normalised autocorrelation functions indicated a negligible breath-to-breath correlation. Tidal volume accounted for the majority of the V˙O₂ (43%) and V˙CO₂ (49%) variance. The breath-to-breath noise can be explained in terms of variations in the breathing pattern, although the large noise magnitude, together with the relatively small attainable response amplitudes in children reduces the certainty with which ventilatory and gas exchange kinetics can be measured.     

A comparison between laddermill and treadmill maximal oxygen consumption

Maximal O₂ consumption (V˙O_2max) is an index of the capacity for work over an 8 h workshift. Running on a treadmill is the most common method of eliciting it, because it is an easy, natural exercise, and also, by engaging large muscle masses, larger values are obtained than by other exercises. It has been claimed, however, that climbing a laddermill elicits a still higher V˙O_2max, probably because more muscle mass is apparently engaged (legs + arms) than on the treadmill (legs only). However, no data in support of this claim have been presented. To see if differences exist, we conducted progressive tests to exhaustion on 44 active coal miners, on a laddermill (slant angle 75°, vertical separation of rungs 25?cm) and on a treadmill set at a 5% gradient. The subjects' mean (range) age was 37.4 (31–47) years, height 174.3 (164–187) cm, body mass 82.2 (64–103) kg. Mean (range) V˙O_2max on the laddermill was 2.83 (2.31–3.64) l?·?min^?1 and 2.98 (2.03–4.22)?l?·?min^?1 on the treadmill (P?t-test). Mean (range) of maximal heart rate f _cmax (beats?·?min^?1) on the laddermill and on the treadmill were 181.0 (161–194) and 181.3 (162–195), respectively (NS). Laddermill:treadmill V˙O_2max was negatively related to both treadmill V˙O_2max?·?kg body mass^?1 (r?=??0.410, P?r?=??0.409, P< 0.01). Laddermill:treadmill f _cmax was negatively related to treadmill V˙O_2max?·?kg body mass^?1 (r?=??0.367, P?r?=??0.166, P?=?0.28). Our data would suggest that for fitter subjects (V˙O_2max > 2.6?l?·?min or V˙O_2max?·?kg body mass^?1 > 30?ml?·?min^?1?·?kg^?1) and/or higher body masses (>70?kg), exercise on the laddermill is not dynamic enough to elicit a V˙O_2max as high as on the treadmill. For such subjects, treadmill V˙O_2max would overestimate exercise capacity for jobs requiring a fair amount of climbing ladders or ladder-like structures.     

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.     

Myocardial function and aerobic fitness in adolescent females

A recent report indicated that variations in myocardial functional (systolic and diastolic) responses to exercise do not contribute to inter-individual differences in aerobic fitness (peak VO₂) among young males. This study was designed to investigate the same question among adolescent females. Thirteen highly fit adolescent football (soccer) players (peak VO₂ 43.5 ± 3.4 ml kg⁻¹ min⁻¹) and nine untrained girls (peak VO₂ 36.0 ± 5.1 ml kg⁻¹ min⁻¹) matched for age underwent a progressive cycle exercise test to exhaustion. Cardiac variables were measured by standard echocardiographic techniques. Maximal stroke index was greater in the high-fit group (50 ± 5 vs. 41 ± 4 ml m⁻²), but no significant group differences were observed in maximal heart rate or arterial venous oxygen difference. Increases in markers of both systolic (ejection rate, tissue Doppler S′) and diastolic (tissue Doppler E′, mitral E velocity) myocardial functions at rest and during the acute bout of exercise were similar in the two groups. This study suggests that among healthy adolescent females, like young males, myocardial systolic and diastolic functional capacities do not contribute to inter-individual variability in physiologic aerobic fitness.