Skeletal muscle properties and performance in elite female track athletes

Summary Selected biochemical and physiological properties of skeletal muscle were studied in light of performance capabilities in 24 elite female track athletes. The feasibility of quantifying end point histochemistry and relating oxidative staining density (reduced nicotinomide adenine dinucleotide diaphorase: NADH-D) to whole body maximal oxygen consumption ( max) was also investigated, while muscle fiber types, classified according to alkaline APTase stains, were studied and related to muscle oxidative capacity (succinate dehydrogenase: SDH), max and “in vivo” torque-velocity properties. Muscle biopsies were taken from the vastus lateralis of each subject and maximal knee extensor torques were recorded at 30‡ from full extension at four selected velocities. While results confirm earlier reports on skeletal muscle properties and performance it was concluded that end point histochemistry could be reliably quantified and that an “oxidative” stain such as NADH-D correlates extremely well with max (r=0.86,p<0.001) whereas correlations between %slow twitch fibres (alkaline ATPase stain) and max were lower (r=0.44,p<0.05). Additionally, as knee extension velocity increased from 0–1.7 rad·s⁻¹ angle specific extensor torque production did not decline as observed in vitro and pentathletes displayed significantly larger torques at all velocities when compared to the other athletes. These data confirm that while myofibrillar ATPase staining correlates with force-velocity properties of muscle, max is better correlated with quantified oxidative staining. Supported in part by a Public Health Service Biomedical Research Support Grant to UCLA, Public Health Service Grant 10423 and by the National Aeronautics and Space Administration (NASA)     

The slope of the oxygen pulse curve does not depend on the maximal heart rate in elite soccer players

INTRODUCTION:

It is unknown whether an extremely high heart rate can affect oxygen pulse profile during progressive maximal exercise in healthy subjects.

OBJECTIVE:

Our aim was to compare relative oxygen pulse (adjusted for body weight) curves in athletes at their maximal heart rate during treadmill cardiopulmonary exercise testing.

METHODS:

A total of 180 elite soccer players were categorized in quartiles according to their maximum heart rate values (n  =  45). Oxygen consumption, maximum heart rate and relative oxygen pulse curves in the extreme quartiles, Q1 and Q4, were compared at intervals corresponding to 10% of the total duration of a cardiopulmonary exercise testing.

RESULTS:

Oxygen consumption was similar among all subjects during cardiopulmonary exercise testing; however subjects in Q1 started to exhibit lower maximum heart rate values when 20% of the test was complete. Conversely, the relative oxygen pulse was higher in this group when cardiopulmonary exercise testing was 40% complete (p<.01). Although the slopes of the lines were similar (p = .25), the regression intercepts differed (p<.01) between Q1 and Q4. During the last two minutes of testing, a flat or decreasing oxygen pulse was identified in 20% of the soccer players, and this trend was similar between subjects in Q1 and Q4.

CONCLUSION:

Relative oxygen pulse curve slopes, which serve as an indirect and non-invasive surrogate for stroke volume, suggest that the stroke volume is similar in young and aerobically fit subjects regardless of the maximum heart rate reached.     

Incidence of exercise induced hypoxemia in elite endurance athletes at sea level

Summary Recent evidence suggests that exercise-induced hypoxemia (EIH) may occur in healthy trained endurance athletes. However, at present, no data exist to describe the regularity of EIH in athletes or non-athletes. Therefore, the purpose of the present investigation was to determine the incidence of EIH during exercise in healthy subjects varying in physical fitness. Subjects (N=68) performed an incremental cycle ergometer test to volitional fatigue with percent arterial oxyhemoglobin saturation (%SaO₂) measured min-by-min. For the purpose of data analysis subjects were divided into three groups according to their level of physical training: 1) untrained (N=16), 2) moderately trained (N=27), and 3) elite highly trained endurance athletes (N=25). EIH was defined as a %SaO₂ of 91% during exercise. EIH did not occur in any of the untrained subjects or the moderately trained subjects. However, EIH occurred in 52% of the highly trained endurance athletes tested and was highly reproducible (r=0.95; P<0.05). These findings further confirm the existence of EIH in healthy highly trained endurance athletes and suggests a rather high incidence of EIH in this healthy population. Hence, it is important that the clinician or physiologist performing exercise testing in elite endurance athletes recognize that EIH can and does occur in the elite endurance athlete in the absence of lung disease.     

Role of psychological stress in cortisol recovery from exhaustive exercise among elite athletes

Life-event stress (LES) was used to classify elite athletes (n = 39) into high-and low-LES groups. A repeated measures analysis of variance revealed higher Cortisol concentration after a graded exercise test among the high-LES group relative to the low-LES group, which was maintained for up to 20 hr. Subsequent prospective analyses further indicated that high-LES athletes were more likely to be symptomatic than low-LES athletes and that elevated Cortisol level was positively correlated with symptomatology. To the extent that Cortisol is a marker of exercise recovery in competitive atbletes, our results suggest that chronic stress prolongs the recovery process, which may potentially widen a window of susceptibility for illness and injury among competitive athletes. This article was supported in part by the Division of Sport Science and Technology of the United States Olympic Training Center and by NIMH research training Grant MHI8917.     

Respiratory responses of elite oarsmen,former oarsmen,and highly trained non-rowers during rowing,cycling and running

The position of the body and use of the respiratory muscles in the act of rowing may limit ventilation and thereby reduce maximal aerobic power relative to that achieved in cycling or running, in spite of the greater muscle mass involved in rowing. This hypothesis was investigated for three groups of male subjects: nine elite senior oarsmen, eight former senior oarsmen and eight highly trained athletes unskilled in rowing. The subjects performed graded exercise to maximal effort on a rowing ergometer, cycle ergometer and treadmill while respiratory minute volume and oxygen consumption were monitored continuously. The VE at a given during intense submaximal exercise (greater than 75% of maximal ) was not significantly lower in rowing compared with that in cycling and treadmill running for any group, which would suggest that submaximal rowing does not restrict ventilation. At maximal effort, and for rowing were less than those for the other types of exercise in all the groups, although the differences were not statistically significant in the elite oarsmen. These data are consistent with a ventilatory limitation to maximal performance in rowing that may have been partly overcome by training in the elite oarsmen. Alternatively, a lower maximal VE in rowing might have been an effect rather than a cause of a lower maximal if maximal was limited by the lower rate of muscle activation in rowing.     

Maximum oxygen consumption in dogs during muscular exercise and cold exposure

Maximum oxygen consumption for a short exhaustive work (Ex max) and for a severe cold stress (Ex max) were investigated in 8 dogs. Heart rate, plasma catecholamines and substrate concentrations were measured under both conditions. Mean C was lower than mean Ex max. Heart rate and plasma lactate were also lower during cold exposure than during exercise. Average plasma epinephrine concentrations were not significantly different and average plasma norepinephrine concentrations were similar under C and Ex max conditions. A positive correlation was found between plasma lactate and epinephrine concentrations measured under both conditions.It may be assumed that maximum oxygen consumption during muscular exercise is higher than during shivering thermogenesis. This difference does not seem to be due to differences in the involvement of the sympathico-adreno-medullary system.     

Impact of the exercise mode on heart rate recovery after maximal exercise

Heart rate recovery 1 min after exercise termination (HRR-1) is a prognostic predictor. However, the influence of the exercise mode on HRR-1 is incompletely characterised. Twenty-nine young and healthy subjects and 16 elderly patients with chronic heart failure underwent cardiopulmonary exercise testing using cycle ergometer and treadmill ramp protocols in random order. HRR-1 and heart rate recovery 2 and 3 min after exercise (HRR-2, HRR-3) during active recovery and peak oxygen consumption (peak VO₂) were measured. In both healthy subjects (32 ± 14 vs. 27 ± 10 bpm) and HF patients (19 ± 8 vs. 14 ± 9 bpm), HRR-1 was faster after cycle exercise (p = 0.029; p for between group difference 0.94). In contrast, HRR-2 and HRR-3 were similar after both tests in both groups. Peak VO₂ was lower during cycle as compared to treadmill exercise in both groups. In conclusion, in both healthy subjects and HF patients, HRR-1 depends on the mode of exercise as peak VO₂ does.     

The effects of dietary manipulation upon the respiratory exchange ratio as a predictor of maximum oxygen uptake during fixed term maximal incremental exercise in man

Summary This study examined the effects of dietary manipulation upon the respiratory exchange ratio ( ) as a predictor of maximum oxygen uptake ( ). Seven healthy males performed fixed term maximal incremental treadmill exercise after an overnight fast on three separate occasions. The first test took place after the subjects had consumed their normal mixed diet (45±5% carbohydrate (CHO)) for a period of three days. This test protocol was then repeated after three days of a low CHO diet (3±2% CHO), and again after three days of a high CHO diet (61±5% CHO). Respiratory gases were continuously monitored during each test using an online system. No significant changes in mean exercise oxygen uptake ( ), or maximum functional heart rate (FHR_max) were found between tests. Mean exercise carbon dioxide output ( ) and R were significantly lower than normal after the low CHO diet (bothp<0.001) and significantly higher than normal after the high CHO diet (bothp<0.05). Moreover, compared with the normal CHO diet, the R-time relationship during exercise was at all times significantly (p<0.001) shifted to the right after the low CHO diet, and shifted to the left, being significantly so (p<0.05) over the final 5 min of exercise, after the high CHO diet. As a result, predictions of based on the R-time relationship were similar to recorded after the normal CHO dietary condition (-1.5±1.9%), but higher after the low CHO diet (+14.8±3.9%,p<0.001) and lower after the high CHO diet (–7.0±4.5%,p<0.01). These results indicate that dietary manipulation can significantly affect respiratory gas exchanges during fixed term maximal incremental exercise, and by doing so can significantly influence predictions of based on R.     

Oxygen uptake and blood flow of the lower limb in maximal treadmill and bicycle exercise

Summary The present study was undertaken to compare the effects of maximal treadmill and bicycle exercise on maximum oxygen uptake and blood flow in the lower extremity. Mean maximum oxygen uptake in maximal treadmill exercise was higher than that in bicycle exercise (p<0.001). Mean values and standard errors of blood flow measured immediately after maximal treadmill and bicycle exercise in the thigh were 39.1±4.0 and 44.2±2.8 ml/100 ml·min, the difference not being significant. However, a significant difference in blood flow in the calf measured immediately after both types of exercise was observed (p< 0.001). Blood flow in the thigh immediately after bicycle exercise was significantly higher than that in the calf (p<0.001), whereas the difference between thigh and calf in treadmill exercise was small and statistically not significant. Leg blood flow, the average value of blood flow of the thigh and calf added together, was used as an index of blood flow in the lower extremity. It was found that the leg blood flow was significantly higher on the treadmill than with bicycle exercise (p<0.05). From these results, it is suggested that the lower maximum oxygen uptake observed during bicycle exercise as compared with treadmill exercise seems to be due to a lower blood flow in the lower limb.     

Age and training effects on the lactate kinetics of master athletes during maximal exercise

Summary To study the effects of age and training on lactate production in older trained subjects, the lactate kinetics of highly trained cyclists [HT,n = 7; 65 (SEM 1.2) years] and control subjects with low training (LT,n = 7) and of similar age were compared to those of young athletes [YA,n = 7; 26 (SEM 0.7) years], during an incremental exercise test to maximum power. The results showed that the lactacidaemia at maximal oxygen uptake ( ) was lower for HT than for LT (P<0.05) and, in both cases, lower than that of YA (P<0.001). The respective values were HT: 3.9 (SEM 0.51), LT: 5.36 (SEM 1.12), and YA: 10.3 (SEM 0.63) mmol·1^–1. At submaximal powers, however, the difference in lactacidaemia was not significant between HT and YA, although the values for lactacidaemia at calculated per watt and per watt normalized by body mass were significantly lower for HT (P<0.001) and LT (P< 0.02). These results would indicate that the decline in power with age induced a decline in lactacidaemia. Yet this loss in power was not the only causative factor; indeed, our results indicated a complementary metabolic influence. In the older subjects training decreased significantly the lactacidaemia for the same submaximal power (P<0.01) and from 60% of onwards (P<0.05); as for YA it postponed the increase and accumulation of lactates. The lactate increase threshold (Th_1a–,1) was found at 46% for LT and at 56% for HT. The lactate accumulation threshold (Th_1a–,₂) was observed at approximately 80% for all three groups but at a value significantly different in each group. At Th_1a–,2 the lactate value of HT was 2 (SEM 0.19) mmol · 1^–1 thus closer to the value normally associated with the increase threshold instead of the accumulation threshold. In conclusion, the reduction in lactacidaemia was enhanced by training. Furthermore, the modification in the lactate kinetics with aging indicated that training at an intensity corresponding to a lactacidaemia of 2 and 4 mmol·1^–1 was inadequate for master endurance athletes.     

Influence of exercise intensity on time spent at high percentage of maximal oxygen uptake during an intermittent session in young endurance-trained athletes

The purpose of this study was to compare, during a 30s intermittent exercise (IE), the effects of exercise intensity on time spent above 90% and time spent above 95% in young endurance trained athletes. We hypothesized that during a 30sIE, an increase in exercise intensity would allow an increase in due to a decrease in time to achieve 90% or 95% of Nine endurance-trained male adolescents took part in three field tests. After determination of their and maximal aerobic velocity (MAV), they performed, until exhaustion, two intermittent exercise sessions alternating 30s at 100% of MAV (IE₁₀₀) or 110% of MAV (IE₁₁₀) and 30s at 50% of MAV. Mean time to exhaustion (t _lim) values obtained during IE₁₀₀ were significantly longer than during IE₁₁₀ (p < 0.01). Moreover, no significant difference was found in expressed in absolute or relative (%t _lim) values between IE₁₀₀ and IE₁₁₀. In conclusion, an increased of 10% of exercise intensity during a 30s intermittent exercise model (with active recovery), does not seem to be the most efficient exercise to solicit oxygen uptake to its highest level in young endurance-trained athletes.     

Predictive value of allergy and pulmonary function tests for the diagnosis of asthma in elite athletes

BACKGROUND: Asthma is frequently found in athletes, often associated with rhinitis and allergy. AIM: To study the predictive value of allergy and pulmonary function tests for the diagnosis of asthma in athletes. SUBJECTS AND METHODS: Ninety-eight national preOlympic athletes underwent an accurate medical examination including a validated questionnaire for asthma and rhinitis, spirometric recordings and skin prick testing with a panel of the most frequent inhalant allergens. Bronchodilator and/or exercise challenge were also performed in asthmatic subjects. RESULTS: Clinical asthma was present in 20.4% of athletes, rhinitis in 35.3% (in 21.4% of cases alone and in 13.9% associated with asthma). Positive prick tests were recorded in 44.4% of athletes (in 60.5% of asthmatics, in 95.2% of rhinitics and in 21.0% of nonasthmatic - nonrhinitic subjects). Mean spirometric values and distribution of abnormal values were not different among asthmatics, rhinitics and nonasthmatics - nonrhinitic patients. Skin-tests positivity was not related to the abnormal spirometric data found in individual cases. Provocation tests with bronchodilators or exercise did not appear sensitive enough to diagnose mild forms of asthma in subjects with normal basal spirometric values. CONCLUSIONS: Allergy testing and spirometry should be performed routinely in athletes because of the high prevalence of allergy, rhinitis and asthma in this population. However, the predictive value of these tests and of the bronchial provocation tests performed in this study seems too low to document mild or subclinical asthma in athletes.     

Influence of hypoxic ventilatory response on arterial O2 saturation during maximal exercise in acute hypoxia

The aim of this study was to evaluate the influence of peripheral chemosensitivity estimated by hypoxic ventilatory response (HVR) on arterial oxygen saturation (S _aO₂) during maximal exercise in acute hypoxia. A group of 16 healthy men performed maximal exercise in two conditions of partial pressure of inspired oxygen (P _IO₂/149 and 70 mm Hg, 19.8 and 9.3 kPa). Measurements of maximal oxygen uptake ( ) andS _aO₂ using an ear-oximeter were carried out in both conditions ofP _IO₂. The HVR was measured at rest by progressive isocapnic hypoxia and evaluated by the slope of the linear regression between the ventilatory flow ( ) and theS _aO₂ ( ). The absolute value of HVR (in litres per minute per percentage saturation per kilogram) was correlated to maximal expired (r = 0.85,P < 0.001), ventilatory equivalent for CO₂ (r = 0.83,P < 0.001) andS _aO₂ (r = 0.60,P < 0.05) determined during maximal exercise in hypoxia: a significant decrease in (37%) andS _aO₂ (32%) forP _IO₂ of 70 mm Hg (9.3 Pa) was observed (P < 0.001). The correlation between the decline of and arterial oxygen desaturation failed to reach statistical significance (r = 0.47, P = 0.1). The present findings indicated that the peripheral ventilatory chemosensitivity contributed to the interindividual variability of andS _aO₂ during maximal exercise in acute hypoxia.     

The effect of shuttle test protocol and the resulting lactacidaemia on maximal velocity and maximal oxygen uptake during the shuttle exercise test

Summary The purpose of this study was to investigate the influence of the shuttle test protocol (20-MST) and the resulting lactacidaemia on maximal velocity (V _max) and maximal oxygen uptake (VO_2max). Firstly, three randomly assigned tests to exhaustion were performed by 12 subjects: the treadmill test, the 20-MST, and a continuous running track test using the same prerecorded 1-min protocol as in the 20-MST (T1). One week later, subjects performed another track test, which was conducted up to the same level of effort as attained during the 20-MST (T2). For each test, V _max, VO_2max) lactate concentration at rest and during recovery, maximal heart rate, and distance covered were determined. The results indicated that the 20-MST underestimated V _max; only Tl satisfactorily assessed V _max (F=15.49, P<0.001). At the same level of effort, the peak blood lactate concentration (t=2.7, P<0.02) and VO_2max (t=11.35, P<0.001) values were higher for the shuttle than for the continuous protocol. It was concluded that V _max was limited by the running backwards and forwards in the protocol of the shuttle test. The higher values of peak blood lactate concentration and its earlier appearance obtained for the shuttle may have been one of the limiting factors of V _max. However, the higher values of VO_2max obtained for the 20-MST were most likely due to a combination of the relative hyperlactacidaemia and the biomechanical complexities required for this type of protocol.     

The upper limit of physiological cardiac hypertrophy in elite male and female athletes: the British experience

Establishment of upper normal limits of physiological hypertrophy in response to physical training is important in the differentiation of physiological and pathological left ventricular hypertrophy. The genetic differences that exist in the adaptive response of the heart to physical training and the causes of sudden cardiac death in young athletes indicate the need for population-specific normal values. Between September 1994 and December 2001, 442 (306 male, 136 female) elite British athletes from 13 sports were profiled. Standard two-dimensional guided M-mode and Doppler echocardiography were employed to evaluate left ventricular morphology and function. Eleven (2.5%) athletes, competing in a range of sports including judo, skiing, cycling, triathlon, rugby and tennis, presented with a wall thickness >13 mm, commensurate with a diagnosis of hypertrophic cardiomyopathy. Eighteen (5.8%) male athletes presented with a left ventricular internal diameter during diastole (LVIDd) >60 mm, with an upper limit of 65 mm. Of the 136 female athletes, none where found to have a maximum wall thickness >11 mm. Left ventricular internal diameter was <60 mm in all female athletes. Systolic and diastolic function were within normal limits for all athletes. Upper normal limits for left ventricular wall thickness and LVIDd are 14 mm and 65 mm for elite male British athletes, and 11 mm and 60 mm for elite female British athletes. Values in excess of these should be viewed with caution and should prompt further investigation to identify the underlying mechanism.     

Effects of intermittent hypoxia on SaO2, cerebral and muscle oxygenation during maximal exercise in athletes with exercise-induced hypoxemia

In a placebo-controlled study, the effects of intermittent hypoxic exposures (IHE) or a placebo control for 10 days, were examined on the extent of exercise-induced hypoxemia (EIH), cerebral and muscle oxygenation (near-infrared spectroscopy) and [Formula: see text] Eight athletes who had previously displayed EIH (fall in saturation of arterial oxygen (SaO(2)) of >4% from rest) during an incremental maximal exercise test, volunteered for the present research. Prior to (baseline), and 2 days following (post) the IHE or placebo, an incremental maximal exercise test was performed whilst SaO(2), heart rate, cerebral and muscle oxygenation and respiratory gas exchange were measured continuously. After IHE, but not placebo, EIH was less pronounced at [Formula: see text] (IHE group, SaO(2) at [Formula: see text] baseline 91.23 +/- 1.10%, post 94.10 +/- 2.19%; P < 0.01, mean +/- SD). This reduction was reflected in an increased ventilation (NS), a lower end-tidal CO(2) (P < 0.01), and lowered cerebral TOI during heavy exercise [Formula: see text] Conversely, muscle tHb at maximal exercise, was increased (2.4 +/- 1.8 DeltamuM, P = 0.01, mean +/- 95 CL) following IHE, whilst de-oxygenated Hb at 90% of [Formula: see text] was reduced (-0.9 +/- 0.8 DeltamuM, P = 0.02). These data indicate that exposure to IHE can attenuate the degree of EIH. Despite a potential compromise in cerebral oxygenation, exposure to IHE may induce some positive physiological adaptations at the muscle tissue level. We speculate that the unchanged [Formula: see text] following IHE might reflect a balance between these central (cerebral) and peripheral (muscle) adaptations.     

Respiratory gas exchange indices used to detect the blood lactate accumulation threshold during an incremental exercise test in young athletes

Summary The time course of changes in blood lactate concentration and ventilatory gas exchange was studied during an incremental exercise test on a cycle ergometer to determine if the lactate accumulation threshold (LT₂) could be accurately estimated by the use of respiratory indices (VT₂) in young athletes. LT₂ was defined as the starting point of accelerated lactate accumulation. VT₂ was identified by the second exponential increase in _E and the ventilatory equivalent for O₂ uptake with a concomitant nonlinear increase in the ventilatory equivalent for CO₂ output. Twelve trained subjects, aged 18–22 years, participated in this study. The initial power setting was 30 W for 3 min with successive increases of 30 W every minute except at the end of the test when the increase was reduced. Ventilatory flow ( _E), oxygen uptake ( O₂), carbon dioxide output ( CO₂), and ventilatory equivalents of O₂ and CO₂ were determined during the last 30 s of every minute. Venous blood samples were drawn at the end of each stage of effort and analysed enzymatically for lactate concentration. After each test, LT₂ and VT₂ were determined visually by two investigators from the graphic results using a double-blind procedure. The results [mean (SEM)] indicate no significant difference between LT₂ and VT₂ expressed as O₂ [43.98 (1.70) vs 44.93 (2.39) ml - min^– - kg^–], lactataemia [4.01 (0.28) vs 4.44 (0.37) mM - 1^–], or heart rate [171 (3.36) vs 173 (3.11) min^–]. In addition, strong correlations were noted between the two methods for O₂ (r=0.90,P<0.001), lactataemia (r=0.75,P<0.01), and heart rate (r=0.96,P<0.001). It is concluded that VT₂ coincides with LT₂ determination and that the ventilatory gas exchange method can thus satisfactorily evaluate the lactate accumulation threshold in young athletes.     

The effect of maximal exercise on the activity of neutrophil granulocytes in highly trained athletes in a moderate training period

Summary Leucocyte cell counts and the phagocytic and chemotactic activities of neutrophil granulocytes were investigated in highly endurance-trained long-distance runners (n = 10) and triathletes (n = 10) during a moderate training period and compared with untrained subjects (n= 0) before and up to 24 h after a graded exercise to exhaustion on a treadmill. After exercise a leucocytosis was noted with a significant increase in lymphocyte (P0.01) and neutrophil (P0.01) counts in all groups. In neutrophils the number of ingested inert latex beads was significantly increased (P 0.01) from 0.21 (SD 0.09) to 0.45 (SD 0.22) in controls, from 0.20 (SD 0.12) to 0.56 (SD 0.16) in long-distance runners and from 0.25 (SD 0.08) to 1.03 (SD 0.42) particles per cell in triathletes 24 h after exercise, compared with resting values. The capability of neutrophils to produce microbicidal reactive oxygen species fell (P:_ 0.05) immediately after exercise in all subjects and then increased by 36 (SD 8) %, 31 (SD 6) % and 19 (SD 9) % in controls, runners and triathletes respectively up to 24 h after exercise (P 0.05) compared with pre-start values. With respect to the absolute number of neutrophils, ingestion capacity, production of superoxide anions and chemotactic activity, no significant differences were found between athletes and control subjects at rest and after exercise. These data indicate, on the one hand, no impairment of the granulocyte system during a moderate training period in long-distance runners and triathletes but, on the other, that the prolonged activation of the phagocytosis reaction after exercise might impair the granulocyte system in periods of intensive training with high training frequency.     

Influence of recovery mode (passive vs. active) on time spent at maximal oxygen uptake during an intermittent session in young and endurance-trained athletes

The aim of this study was to analyze the effects of recovery mode (active/passive) on time spent at high percentage of maximal oxygen uptake i.e. above 90% of and above 95% of during a single short intermittent session. Eight endurance-trained male adolescents (15.9 ± 1.4 years) performed three field tests until exhaustion: a graded test to determine their (57.4 ± 6.1 ml min⁻¹ kg⁻¹), and maximal aerobic velocity (MAV; 17.9 ± 0.4 km h⁻¹), and in a random order, two intermittent exercises consisting of repeated 30 s runs at 105% of MAV alternated with 30 s passive (IE_P) or active recovery (IE_A, 50% of MAV). Time to exhaustion (t _lim) was significantly longer for IE_P than for IE_A (2145 ± 829 vs. 1072 ± 388 s, P < 0.01). No difference was found in and between IE_P (548 ± 499–316 ± 360 s) and IE_A (746 ± 417–459 ± 332 s). However, when expressed as a percentage of t _lim, and were significantly longer (P < 0.001 and P < 0.05, respectively) during IE_A (67.7 ± 19%–42.1 ± 27%) than during IE_P (24.2 ± 19%–13.8 ± 15%). Our results demonstrated no influence of recovery mode on absolute or mean values despite significantly longer t _lim values for IE_P than for IE_A. In conclusion, passive recovery allows a longer running time (t _lim) for a similar time spent at a high percentage of