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.     

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

Elevated oxygen uptake (V˙O₂) during moderate-intensity running following a bout of interval running training has been studied previously. To further investigate this phenomenon, the V˙O₂ response to high-intensity exercise was examined following a bout of interval running. Well-trained endurance runners were split into an experimental group [maximum oxygen uptake, V˙O_{2 max} 4.73 (0.39) l?·?min^?1] and a reliability group [V˙O_{2 max} 4.77 (0.26) l?·?min^?1]. The experimental group completed a training session (4?×?800?m at 1?km?·?h^?1 below speed at V˙O_{2 max} , with 3?min rest between each 800-m interval). Five minutes prior to, and 1?h following the training session, subjects completed 6?min 30?s of constant speed, high-intensity running designed to elicit 40% Δ (where Δ is the difference between V˙O₂ at ventilatory threshold and V˙O_{2 max} ; tests 1 and 2, respectively). The slow component of V˙O₂ kinetics was quantified as the difference between the V˙O₂ at 6?min and the V˙O₂ at 3?min of exercise, i.e. ΔV˙O₂₍₆₃₎. The ΔV˙O₂₍₆₃₎ was the same in two identical conditions in the reliability group [mean (SD): 0.30 (0.10) l?·?min^?1 vs 0.32 (0.13) l?·?min^?1]. In the experimental group, the magnitude of the slow component of V˙O₂ kinetics was increased in test 2 compared with test 1 by 24.9% [0.27 (0.14) l?·?min^?1 vs 0.34 (0.08)?l?·?min^?1, P?V˙O₂₍₆₃₎ in the experimental group was observed in the absence of any significant change in body mass, core temperature or blood lactate concentration, either at the start or end of tests 1 or 2. It is concluded that similar mechanisms may be responsible for the slow component of V˙O₂ kinetics and for the fatigue following the training session. It has been suggested previously that this mechanism may be linked primarily to changes within the active limb, with the recruitment of alternative and/or additional less efficient fibres.     

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.     

Cardiorespiratory responses to underwater treadmill walking in healthy females

This study compared the cardiorespiratory responses of eight healthy women (mean age 30.25 years) to submaximal exercise on land (LTm) and water treadmills (WTm) in chest-deep water (Aquaciser). In addition, the effects of two different water temperatures were examined (28 and 36°C). Each exercise test consisted of three consecutive 5-min bouts at 3.5, 4.5 and 5.5?km?·?h^?1. Oxygen consumption (V˙O₂) and heart rate (HR), measured using open-circuit spirometry and telemetry, respectively, increased linearly with increasing speed both in water and on land. At 3.5?km?·?h^?1 V˙O₂ was similar across procedures [χ?=?0.6 (0.05) l?·?min^?1]. At 4.5 and 5.5?km?·?h^?1 V˙O₂ was significantly higher in water than on land, but there was no temperature effect (WTm: 0.9 and 1.4, respectively; LTm: 0.8 and 0.9?l?·?min^?1, respectively). HR was significantly higher in WTm at 36°C compared to WTm at 28°C at all speeds, and compared to LTm at 4.5 and 5.5?km?·?h^?1 (P?≤?0.003). The HR-V˙O₂ relationship showed that at a V˙O₂ of 0.9?l?·?min^?1, HR was higher in water at 36°C (115?beats?·?min^?1) than either on land (100?beats?· min^?1) or in water at 28°C (99?beats?·?min^?1). The Borg scale of perceived exertion showed that walking in water at 4.5 and 5.5?km?·?h^?1 was significantly harder than on land (WTm: 11.4 and 14, respectively; LTm: 9.9 and 11, respectively; P?≤?0.001). These cardiorespiratory changes occurred despite a slower cadence in water (the mean difference at all speeds was 27?steps/min). Thus, walking in chest-deep water yields higher energy costs than walking at similar speeds on land. This data has implications for therapists working in hydrotherapy pools.     

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.     

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   

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.     

Aerobic and anaerobic energy during a 2-km race simulation in female rowers

The maximal aerobic power (V˙O_2max) and maximal anaerobic capacity (AOD_max) of 16 female rowers were compared to their peak aerobic power (V˙O_2peak) and peak anaerobic capacity (AOD_peak, respectively) during a simulated 2-km race on a rowing ergometer. Each subject completed three tests, which included a 2-min maximal effort bout to determine the AOD_max, a series of four, 4-min submaximal stages with subsequent progression to V˙O_2max and a simulated 2-km race. Aerobic power was determined using an open-circuit system, and the accumulated oxygen deficit method was used to calculate anaerobic capacities from recorded mechanical power on a rowing ergometer. The average V˙O_2peak (3.58?l?·?min^?1), which usually occurred during the last minute of the race simulation, was not significantly different (P?>?0.05) from the V˙O_2max (3.55?l?· min^?1). In addition, the rowers' AOD_max (3.40?l) was not significantly different (P?>?0.05) from their AOD_peak (3.50?l). The average time taken for the rowers to complete the 2-km race simulation was 7.5?min, and the anaerobic system (AOD_peak) accounted for 12% of the rowers' total energy production during the race.     

Energetics of kayaking at submaximal and maximal speeds

The energy cost of kayaking per unit distance (C_k, kJ?·?m^?1) was assessed in eight middle- to high-class athletes (three males and five females; 45–76?kg body mass; 1.50–1.88?m height; 15–32 years of age) at submaximal and maximal speeds. At submaximal speeds, C_k was measured by dividing the steady-state oxygen consumption (V˙O₂, l?·?s^?1) by the speed (v, m?·?s^?1), assuming an energy equivalent of 20.9?kJ?·?l O^?1 ₂. At maximal speeds, C_k was calculated from the ratio of the total metabolic energy expenditure (E, kJ) to the distance (d, m). E was assumed to be the sum of three terms, as originally proposed by Wilkie (1980): E?=?AnS?+?αV˙O_2max?·?t?αV˙O_2max?·?τ(1?e ^?t·τ?1), were α is the energy equivalent of O₂ (20.9?kJ?·?l?O₂ ^?1), τ is the time constant with which V˙O_2max is attained at the onset of exercise at the muscular level, AnS is the amount of energy derived from anaerobic energy utilization, t is the performance time, and V˙O_2max is the net maximal V˙O₂. Individual V˙O_2max was obtained from the V˙O₂ measured during the last minute of the 1000-m or 2000-m maximal run. The average metabolic power output (E˙, kW) amounted to 141% and 102% of the individual maximal aerobic power (V˙O_2max) from the shortest (250?m) to the longest (2000?m) distance, respectively. The average (SD) power provided by oxidative processes increased with the distance covered [from 0.64 (0.14) kW at 250?m to 1.02 (0.31) kW at 2000?m], whereas that provided by anaerobic sources showed the opposite trend. The net C_k was a continuous power function of the speed over the entire range of velocities from 2.88 to 4.45?m?·?s^?1: C _k ?=?0.02?·?v ^2.26 (r?=?0.937, n?=?32).     

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?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?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.     

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.     

Relative exercise intensity of long-distance marching (120 km in 4 days) in 153 subjects aged 69–87 years

The aim of this study was to determine the relative exercise intensity (oxygen uptake during the march/maximal oxygen uptake, V˙O_{2 march}/V˙O_{2 max} ) during a long-distance march in subjects or over 70 years of age. Secondly, the effect of hypertension, cardiovascular and pulmonary diseases on the relative exercise intensity was evaluated. One hundred and fifty-three subjects, 97 men aged 76.7 (4.6) years and 56 women aged 72.8 (3.6) years who completed the 1993 Nijmegen–day long-distance march (30?km?·?day^?1 on 4 consecutive days) participated in the study. Oxygen uptake (V˙O₂) during walking at different velocities () was measured in a subgroup of nine men and nine women, selected randomly from the population under study. With these data, regression equations describing the relationship between V˙O₂ and were made. V˙O_{2 march} was estimated with the obtained regression equations from an average of the _march measured in all participants. V˙O_{2 max} was determined using incremental cycle ergometry in all subjects. V˙O_{2 march} was 13.7 (1.8) ml?·?kg^?1?·?min^?1 in men and 15.2 (1.3) ml?·?kg?·?min^?1 in women at a mean of 5?km?·?h^?1 in both sexes. This corresponded to 52% of V˙O_{2 max} in men and 63% in women. In both sexes subjects with cardiovascular and/or pulmonary diseases walked at a slower and thus lower V˙O_{2 march} compared to subjects without these diseases. Due to the lower V˙O_{2 max} in subjects with these diseases there was no difference in the relative exercise intensity between the groups. A multiple linear regression analysis showed that and not age on the prevalence of hypertension, cardiovascular and/or pulmonary that V˙O_{2 max} was the most important predictor of the variance in self-selected _march. This study demonstrates that these active people aged over 70 years could maintain a high relative exercise intensity during endurance walking on 4 subsequent days. Furthermore, it shows that the relative exercise intensity of marching is within the range recommended for improving fitness and reducing the risk of cardiovascular diseases. Finally, these results demonstrate that V˙O_{2 max} has a more important influence on performance than does age or chronic diseases in active elderly people.     

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.     

Determination of the velocity associated with the longest time to exhaustion at maximal oxygen uptake

The so-called velocity associated with V˙O_2max, defined as the minimal velocity which elicits V˙O_2max in an incremental exercise protocol (v _{V˙ O2max}), is currently used for training to improve V˙O_2max. However, it is well known that it is not the sole velocity which elicits V˙O_2max and it is possible to achieve V˙O_2max at velocities lower and higher than v _{V˙ O2max}. The goal of this study was to determine the velocity which allows exercise to be maintained the longest time at V˙O_2max. Using the relationship between time to exhaustion at V˙O_2max in the all-out runs at 90%, 100%, 120% and 140% of v _{V˙ O2max} and distance run at V˙O_2max, the velocity which elicits the longest time to exhaustion at V˙O_2max (CV′) was determined. For the six subjects tested (physical education students), this velocity was not significantly different from v _{V˙ O2max} (16.96?±?0.92?km?·?h^?1 vs 17.22?± 1.12?km?·?h^?1, P?=?0.2 for CV′ and v _{V˙ O2max}, respectively) and these two velocities were correlated (r?=?0.88, P?=?0.05).     

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 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.     

Metabolic and cardioventilatory responses during a graded exercise test before and 24 h after a triathlon

Previous studies have reported respiratory, cardiac and muscle changes at rest in triathletes 24?h after completion of the event. To examine the effects of these changes on metabolic and cardioventilatory variables during exercise, eight male triathletes of mean age 21.1 (SD 2.5) years (range 17–26 years) performed an incremental cycle exercise test (IET) before (pre) and the day after (post) an official classic triathlon (1.5-km swimming, 40-km cycling and 10-km running). The IET was performed using an electromagnetic cycle ergometer. Ventilatory data were collected every minute using a breath-by-breath automated system and included minute ventilation (V˙ _E), oxygen uptake (V˙O₂), carbon dioxide production (V˙CO₂), respiratory exchange ratio, ventilatory equivalent for oxygen (V˙ _E/V˙O₂) and for carbon dioxide (V˙ _E/V˙CO₂), breathing frequency and tidal volume. Heart rate (HR) was monitored using an electrocardiogram. The oxygen pulse was calculated as V˙O₂/HR. Arterialized blood was collected every 2 min throughout IET and the recovery period, and lactate concentration was measured using an enzymatic method. Maximal oxygen uptake (V˙O_{2 max} ) was determined using conventional criteria. Ventilatory threshold (VT) was determined using the V-slope method formulated earlier. Cardioventilatory variables were studied during the test, at the point when the subject felt exhausted and during recovery. Results indicated no significant differences (P>0.05) in V˙O_{2 max} [62.6 (SD 5.9) vs 64.6 (SD 4.8) ml?·?kg^?1?·?min^?1], VT [2368 (SD 258) vs 2477 (SD 352) ml?·?min^?1] and time courses of V˙O₂ between the pre- versus post-triathlon sessions. In contrast, the time courses of HR and blood lactate concentration reached significantly higher values (P<0.05) in the pre-triathlon session. We concluded that these triathletes when tested 24?h after a classic triathlon displayed their pre-event aerobic exercise capacity, bud did not recover pre-triathlon time courses in HR or blood lactate concentration.     

Serum insulin-like growth factor I and physical performance in prepubertal Bolivian girls of a high and low socio-economic status

The aim of the study was to determine if a decrease in serum insulin-like growth factor I (Igf-I) levels under marginal malnutrition is responsible for the lower physical performance of girls of a low socio-economic status (LSES). Girls were selected after physical examination (Tanner's stage 1) and anthropometric measurements (height, body mass or m _b, body mass index or BMI?=?m _b height²). Lean body mass m _b,l was measured after skinfold thickness determination; serum IGF-I, by radioimmunoassay; maximal O₂ consumption, (V˙O_2max), directly during incremental exercise up to exhaustion; and maximal aerobic power (W˙ _max), using the force-velocity test. LSES girls (n?=?31) had been malnourished in the past and, currently, were suffering from marginal malnutrition: they were smaller (135.2?±?5.5 vs 146.1?±?4.3 cm), lighter (31.7?±?3.9 vs 37.6?±?5.0 kg), exhibited a lower m _b,l (24.2?±?2.5 vs 27.5?±?3.0 kg) but same BMI compared with HSES (high socio-economic status) girls (n?=?32). Igf-I levels (27.7?±?7.9 vs 34.1?±?6.5 nmol?·?l^?1), V˙O_2max (45.26 ±?4.72 vs 50.74?±?6.02 ml?·?min^?1?·?kg^?1 LBM) and W˙ _max (6.00?±?1.15 vs 8.70?±?1.53 W?·?kg^?1 m _b,l were lower in LSES girls. Moreover, the differences in every parameter were not the consequence of the younger age (10.8?±?0.9 vs 11.2?±?0.6 years) of the LSES girls. Our results provide evidence that the lower W˙ _max of undernourished prepubertal girls was partly the consequence of alterations in muscle function at the qualitative level, as a result of a decrease in Igf-I levels. Conversely, under normal nutritional conditions, anthropometric characteristics only are explicatory factors for physical performances.     

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??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”.     

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+? _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 ? _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).