ORIGINAL ARTICLE

Magaly Tardieu-Berger Æ Delphine Thevenet

Hassane Zouhal Æ Jacques Prioux

Effects of active recovery between series on performance duringan intermittent exercise model in young endurance athletes

Accepted: 8 June 2004 / Published online: 27 July 2004� Springer-Verlag 2004

Abstract The purpose of our study was to compare timeto exhaustion (tlim) and time spent at a high level ofoxygen uptake ( _V O2) during two high-intensity shortintermittent exercises (30 s-30 s) realized with or withoutseries. Eleven young endurance-trained athletes [16.6(0.4) years] took part in three field tests until exhaustion:(1) a maximal graded test to measure their maximalaerobic velocity (MAV) and maximal oxygen uptake( _V O2max); (2) and (3) two randomized intermittentexercises (30 s at 110% of MAV alternated with 30 s at50% of MAV): one alternating repetitions non-stop (IE)and another including 4 min recovery every six repeti-tions (IEs). The mean tlim measured during IEs wassignificantly longer than IE [respectively 960.0 (102.0) svs 621.8 (56.2) s]. The time spent at _V O2max(t _V O2max)and the time spent above 90% of _V O2max(t90% _V O2max)did not differ significantly according to the type ofexercise: with or without series [respectively t _V O2max was158.2 (59.7) s vs 178.0 (56.5) s and t90% _V O2max was 290.4(84.3) s vs 345.0 (61.6) s] but when expressed as a rela-tive value, t90% _V O2max during IEs was significantly lowerthan during IE [respectively 36.4 (10.4)% tlim vs 58.3(8.7)% tlim]. Despite a significant decrease (P<0.005) oftime to achieve 90% of _V O2max at the start of each seriesduring IEs [respectively 165.0 (43.1) s for the first seriesand 82.5 (15.8) s for the second series (n=6)] the timespent under 90% of _V O2max limited the t90% _V O2max

during each series. In conclusion, our results showedthat intermittent exercise with series does not permit an

increase in the time spent at a high level of _V O2; how-ever, the athletes performed more repetitions of shortintense exercise.

Keywords Intermittent exercise run Æ Time spent at_VO2max Æ Time to exhaustion Æ Lactatemia Æ Oxygenuptake kinetics

Introduction

It is clearly established that maximal oxygen uptake( _V O2max) is one of the parameters correlated with middleand long distance performance (800 m to 10 km)(Brandon and Boileau 1987). Wenger and Bell (1986)hypothesized that the optimal development of _V O2max

occurs when a high level of oxygen uptake is maintainedduring exercise. Hence, in the last few years, studies onexercise efficiency to develop aerobic performance haveanalyzed the time spent at _V O2max (t _V O2max; Hill andRowell 1997; Hill et al. 1997; Billat et al. 1999, 2000a,2001; Dupont et al. 2002; Millet et al. 2003). However,protocols for data collection to calculate the t _V O2max

differ between studies. According to Dupont et al.(2003), a lower coefficient of variation is obtained whenthe calculation of t _V O2max is based on _V O2 values higherthan 95% of _V O2max. Moreover, we still do not know ifit is more efficient to maintain _V O2max for a few minutesor 90% of _V O2max for a longer period (Astrand andRodahl 1986). Therefore, calculation of the time spent at_V O2max and also above 90% of _V O2max (t90% _V O2max) willbe of interest for the evaluation of an exercise model todevelop _V O2max.

Among the intermittent exercise models used todevelop _V O2max, the 30 s-30 s, composed of a 30 sintensive exercise alternated with a 30 s recovery per-iod, is commonly practiced. This intermittent exercisemodel has been reported to be efficient for theimprovement of the _V O2max (Gorostiaga et al. 1991;

M. Tardieu-Berger (&) Æ D. Thevenet Æ J. PriouxLaboratory ‘‘Motricite, Interactions, Performance’’,UFR S TAPS, 25 bis bd Guy Mollet, BP 72206,44322 Nantes Cedex 3, FranceE-mail: magaly.tardieu@staps.univ-nantes.frFax: +33-2-51837210

H. ZouhalLaboratory ‘‘Physiologie et biomecanique de l’exercicemusculaire’’, UFRAPS, Universite de Rennes 2,Campus la Harpe, 2 av Charles Tillon, CS 24414, 35044 RennesCedex, France

Eur J Appl Physiol (2004) 93: 145–152DOI 10.1007/s00421-004-1189-z

Overend et al. 1992). However, we still do not knowwhich is the best format of the exercise model (workand recovery interval intensity, working with series ornot, number of intervals per series or number of ser-ies) leading to an optimal improvement of aerobiccapacity. In the literature, the 30 s-30 s is currentlyanalyzed by alternating the repetitions without stop-ping until exhaustion (Billat et al. 2000a), or during afixed period, also without stopping (Astrand et al.1960; Gorostiaga et al. 1991; Ballor and Volovsek1992). However, a second form of 30 s-30 s is alsoregularly practiced. It consists of interspersing a longer(generally 4–5 min) recovery period (active and/orpassive) between a fixed number of repetitions. Eachgroup of repetitions is called a ‘‘series’’. To ourknowledge, the influence of series on time to exhaus-tion (tlim) and on time spent at a high percentage of_V O2max has never been studied. Margaria et al. (1969)demonstrated that the time to exhaustion increased asrecovery periods between short exercises increased.Hence tlim will be higher when intermittent exercise isrealized in series. Moreover, according to Millet et al.(2003), during recovery periods between series, _V O2

may decrease to low values. Hence, a progressive timecourse of _V O2 should be observed at the start of eachseries (Whipp 1987; Barstow 1994). However, it hasalso been well established that a prior bout of heavyexercise (above the lactate threshold) reduces the mean_V O2 response time during the subsequent exercise andincreases the mean _V O2 level (Jones et al. 2003). Thisphenomenon occurs independently of the level of thebaseline _V O2 measured at the start of the exercise(Burnley et al. 2001). Based on these results, ourhypothesis was that intermittent exercise realized inseries should result in an increase of the time spentnear _V O2max due to an increase of the time toexhaustion combined with the enhancement of _V O2

kinetics during each series. The purpose of our studywas to compare tlim, t _V O2max and t90% _V O2max duringtwo high-intensity short intermittent exercises realizedwith or without series.

Methods

Subjects

Eleven endurance-trained male adolescents volunteeredto participate in this study. All were familiar with supra-maximal intermittent runs. The subjects were aged from15 to 18 years old [16.6 (0.4) years]. Their mean andstandard error (SEM) for body mass and height were63.0 (2.2) kg and 177.2 (2.0) cm respectively. Prior toparticipation, they underwent a medical examinationand were fully informed about the experimental proce-dures. Parental consent (for the under-age athletes) andwritten consent were obtained in accordance with theguidelines of the University of Nantes which had

approved the experimental protocol and the proceduresinvolved.

Overview

All subjects performed three field-tests on a 400-m out-door tartan track calibrated with cones, exercising untilexhaustion at the same time of the day, with 48 h restbetween each test. The subjects were required to havetheir last light meal (not standardized) 3 h before thetests. All tests were completed within 2 weeks. For eachtest, the subjects were verbally encouraged to continuefor as long as possible. Tests were stopped when subjectscould not maintain the required speed (3 consecutivedelays from the cones) or when the subjects stopped theexercise, judging themselves to be exhausted. Before thetests, the subjects were familiarized with the exerciseprocedure and with the gas exchange measuring appa-ratus. Atmospheric conditions were checked before eachtest ensuring that all sessions were carried out undersimilar conditions (temperature range from 15 to 20�Cand humidity range from 45% to 65%).

Athletes first performed a maximal graded test todetermine their _V O2max and maximal aerobic velocity(MAV) and then, in random order, two intermittentexercises composed of 30 s at 110% of MAV alternatingwith 30 s active recovery at 50% of MAV. A 30 sintensive run (110% of MAV) with 30 s active recovery(50% of MAV) formed one repetition. One of these twotests consisted of alternating repetitions without stop-ping until exhaustion (IE) whereas during the other test(IEs) a period of 4 min mixed recovery (30 s rest +3 min at 50% MAV + 30 s rest) was interspersed every6 repetitions (Fig. 1).

Maximal graded test

Cones were set at 50-m intervals along the track (in-side the first line). The running pace was set by anexperimenter, equipped with a whistle and a chro-nometer, who made a brief sound at the momentwhen the subject had to pass near a cone to maintaina constant speed. A longer sound marked the changein the running stage. This test was preceded by awarm-up composed of 10 min continuous jogging and5 min stretching. The initial speed was 12 km.h-1 andthis was increased by 1 km.h-1 every 2 min. Thismethod is in accordance with previous publications(Berthoin et al. 1996; Lacour et al. 1991). The velocityat the last completed stage was considered as theMAV. If the velocity at exhaustion was only main-tained for 1 min (half of the stage duration), then theMAV was considered to be equal to the velocityduring the previous stage plus half the velocityincrease between the last two stages (Kuipers et al.1985). The accuracy of MAV was 0.5 km.h-1.

146

Intermittent exercises

The two intermittent exercises consisted of repeating a30 s run at 110% of MAV alternated with 30 s activerecovery at 50% of MAV for as long as possible (Fig. 1).For these exercises, the running pace was again set by anexperimenter making sounds at regular intervals (30 s)up to the end of the exercise. During the 30 s exerciseand the 30 s active recovery, the subjects had to cover adistance determined from their own MAV. During therecovery period, a longer sound was made at mid-period(15 s) to inform the athletes. During IE the subjectsalternated repetitions until exhaustion whereas duringIEs a period of 4 min of mixed recovery (30 s rest then3 min at 50% MAV and 30 s rest) was interspersed ev-ery 6 repetitions. These last two tests were preceded by astandardized warm-up which consisted of 10 min ofcontinuous running at 12 km.h-1, followed by 5 min ofstretching exercises and three short bursts of accelera-tion on the track.

Respiratory gas exchanges and heart rate measures

During all tests, respiratory gas exchanges were mea-sured breath-by-breath using a portable telemetric sys-tem in order to determine ventilation ( _V E), _V O2 andcarbon dioxide production (Cosmed K4b2, Rome, Italy;McLaughlin et al. 2001). Before each test, the O2 andCO2 analysis systems were calibrated using ambient airand a gas of known O2 and CO2 concentrations (16%and 5% respectively). The calibration of the K4b2 tur-bine flow-meter was performed using a 3-1 syringe(Quinton Instruments, Seattle, Wash., USA). Heart rate(HR) was continuously monitored (Polar Electro,Kempele, Finland). The cardio-respiratory values wereaveraged over a 5-s period.

Determination of _V O2max

The _V O2max corresponded to the highest _V O2 attained intwo successive 5-s periods for the maximal graded test. Itwas judged that subjects had reached their _V O2max whenthree or more of the following criteria were met: 1. Asteady state of _V O2 despite increasing running speed.This plateau of _V O2 was defined as being when thechange in _V O2 was less than 150 ml.min-1 or 2.1 ml.kg-1.min-1 between successive stages (Taylor et al. 1955). 2. Afinal respiratory exchange ratio (R) higher than 1.1. 3.Visible exhaustion. 4. A HR within the 10 bpm of thepredicted maximum (220-age). 5. A lactate concentra-tion higher than 8 mmol.l-1.

Fig. 1 Schematic illustration of the intermittent exercise tests.The top panel shows the structure of the intermittent exercise test(IE), consisting of a 30 s intensive run at 110% of the maximalaerobic velocity (MAV) followed by a 30 s active recovery (at50% of MAV) forming one repetition, repeated until exhaustion.The bottom panel shows the structure of the intermittent exercisetest with series (IEs), which was identical to test IE except thatafter the 6th repetition, a period of 4 min mixed recovery (30 srest + 3 min at 50% MAV + 30 s rest) was included. Whitebars represent exercise at 110% MAV, diagonally hashed barsrepresent exercise at submaximal values of MAV

147

Determination of _V O2 peak and _V O2 mean

During both intermittent tests, the _V O2 peak wasdetermined as the maximal _V O2 attained in two suc-cessive 5-s periods and the _V O2 mean corresponded tothe mean _V O2 values measured from the start of the testand at exhaustion. During IEs, the recovery periodsbetween series were not included in the determination ofthe _V O2 mean.

Blood sample collection

Fingertip blood samples were obtained at rest before thewarm-up and 2 min after each test. During IEs bloodsamples were also taken during a 30-s period at the startand the end of each series. Even if the sample was notcompleted, it did not last more than 30 s. These sampleswere taken with the subject at rest. Hence, over 4 min ofrecovery, the subject spent 1 min at rest (30 s at thebeginning and 30 s at the end of recovery) and 3 minrunning at a low intensity (50% of MAV). For eachblood sample, 20 ll of arterialized blood was collectedinto a heparinized micro-tube kept on ice for measure-ment of the blood lactate concentration ([La]). [La] wasdetermined by an enzymatic method (Microzym-L, SGI,France).

Determination of time to exhaustion, time spent at_V O2max or above 90% of _V O2max, and time to achieve90% of _V O2max

The tlim value corresponds to the delay between the startand the end of the exercise. During IEs, the 4 min mixedrecovery between series was not included in the deter-mination of tlim. The t _V O2max and t90% _V O2max values weredetermined from the _V O2 values higher or equal to 95%and 90% of _V O2max respectively. The tt90% _V O2max valuecorresponds to the time spent to achieve 90% of _V O2max

after the start of exercise.

Statistical analysis

All results were expressed as means (SEM). Mean valuesfor _V O2 peak, _V O2 mean, [La] and tlim measured duringIE and IEs were compared using a paired t test (n=11).Differences in time spent above 95% of _V O2max or 90%of _V O2max between both intermittent exercises were alsodetermined by paired t tests (n=11). A Pearson corre-lation was used to assess the relationship between [La]and tlim measured during both intermittent exercises. Apaired t-test was finally used to compare: (1) thett90% _V O2max measured in the subjects who attained 90%of _V O2max during both IE and IEs (n=8); and (2) thett90% _V O2max measured in the subjects who attained 90%of _V O2max during both the first series and the secondseries of IEs (n=6). Normal Gaussian distribution of the

data was verified with the Kolmogorov-Smirnov test(with Lilliefor’s correction). For all statistical analyses,the level of significance was fixed at P=0.05.

Results

Maximal graded test

The mean values for MAV, _V O2max, HRmax and Rmax

were: 17.7 (0.3) km.h�1, 62.6 (1.1) ml.min�1.kg�1, 196.3(2.1) bpm and 1.1 (0.01) respectively. The mean value of[La] obtained at the end of this test was 10.2(0.6) mmol.l�1.

Intermittent exercise

The mean values for the parameters measured during theintermittent tests are presented in Table 1. The values of_V O2 peak and [La] were not significantly different be-tween IEs and IE whereas _V O2 mean measured duringIEs was significantly lower (P<0.05) than during IE.The mean value for tlim measured during IEs was sig-nificantly higher (P<0.005) than that during IE butt _V O2max and t90% _V O2max (both expressed as absolutevalues) were not significantly different during IEs andIE. However, when expressed as relative values (%tlim),t90% _V O2max measured during IEs was significantly lowerthan during IE (P<0.05).

A significant relationship (P<0.05) was found be-tween tlim IE and [La] measured at the end of IE(r=0.76) whereas no correlation was found between tlimand [La] during IEs (Fig. 2). Figure 3 presents twoexamples of lactate kinetics obtained during IEs. Weobserved that [La] tended to increase during each seriesand tended to decrease or stabilize during recoveryperiods between series.

From the 11 subjects tested, 10 reached 95% of_V O2max during IE whereas only 7 reached 95% of_V O2max during IEs (8 subjects reached 90% of _V O2max

during IEs). Seven subjects reached 95% of _V O2max

during both IE and IEs and 8 reached 90% of _V O2max

during both of those tests. The mean values fortt90% _V O2max (n=8) measured during IE and IEs were notsignificantly different: 114.4 (19.2) s and 148.1 (34.9) srespectively. Of the 10 subjects who realized more thanone series during IEs, only 6 reached 90% of _V O2max

during the first and also the second series. Figure 4presents the mean _V O2 kinetics obtained at the start ofthe first and the second series of IEs and at the beginningof IE (n=6). We observed that at the beginning of thesecond series of IEs, _V O2 kinetics tended to be morerapid when compared with those seen in the first series.This result is confirmed by the tt90% _V O2max mean value:this was significantly higher (P<0.05) for the first seriesthan the second series [165.0 (43.1) s and 82.5 (15.8) srespectively].

148

Discussion

Most of the studies on short intermittent exercise imposerepetitions until exhaustion (Billat et al. 2000a; Dupontet al. 2002). However, intermittent exercise can also beprescribed in a fixed number of series composed of afixed number of intervals. Each series is then separatedby recovery periods lasting 3–5 min. The purpose of ourstudy was to analyze the effects on tlim and t _V O2max ofincluding series in an intermittent exercise session. Thechoice of 6 repetitions per series was based not only onprevious investigations that we have made with the samesubjects but also on the literature. Firstly, for youngendurance athletes, coaches often propose intermittentexercise sessions with 6–7 repetitions per series. Sec-ondly, during preliminary tests, one of our subjects wasunable to maintain more than 6 repetitions of 30 s at110% of MAV alternating with active recovery (30 s at50% of MAV). Thirdly, Billat et al. (2000a) have ob-served that during a 30 s-30 s intermittent exercisemodel (100% of v _V O2max alternated with 50% ofv _V O2max) a _V O2max steady state was observed from the

fifth repetition until the end of the exercise. Finally,Millet et al. (2003) proposed a mean of 8 repetitions of30 s at 100% of MAV per series for well trained adultsubjects. If the time to reach _V O2max decreases as thevelocity increases (Billat et al. 2000b), then the numberof repetitions per series should be lower in our studythan in that of Millet et al. (2003). Consequently, ourchoice of 6 repetitions per series was based on athleticpractice as well as the findings reported in the literature.

Effects of series on time to exhaustion

Our results show that long recovery between series ofshort interval exercises delays the onset of exhaustionsince tlim for IEs is significantly longer than tlim for IE.No data exist concerning the influence of series on totalexercise duration. However, our results are in agreementwith those of Margaria et al. (1969) who observed anincrease in the time to exhaustion with an increase in theduration of the pause between the exercise bursts.

A reduction of phosphocreatine (PCr) availabilitycan be advanced to explain the appearance of fatigueduring IE. Indeed, in a study of eight male subjects,Bogdanis et al. (1998) have observed a rapid rate ofdecrease of PCr during the initial 10 s of a sprint on acycle ergometer. Moreover, they demonstrated that aftera 2 min recovery, PCr was resynthesized to 86 (3)% and76 (3)% of the resting values following 10 s and 20 ssprints, respectively. Thus during IEs in our study, the4 min mixed recovery between each series should permitan important PCr resynthesis, delaying exhaustion.Acidosis could also be responsible for a decrease ofmuscular performance (Sahlin et al. 1998) Some studieshave reported a significant decrease in the blood pHafter intense exercise (Handschuh et al. 1991) or afterintermittent intense exercises (Callier and Candau 1994).This metabolic acidosis is often related to lactate accu-mulation in working muscles (Spangenburg et al. 1998).Although blood lactate concentration does not alwaysreflect the level of muscle acidosis (Brooks 1985), it hasbeen reported that it provides a good index of themuscular lactate concentration (Hirvonnen et al. 1987).In our study, a negative correlation (r=0.76, P< 0.05)was observed between [La] and the tlim measured duringIE (Fig. 2). This result suggests that the subjects with the

Fig. 2 Regression analysis of the blood lactate concentrationversus the time to exhaustion

Table 1 Data [mean (SEM)] measured during and after the twointermittent tests realized without (IE) and with series (IEs)(n=11). The peak equals the maximal 5 s averaged O2 uptakemeasured in the test, the mean _V O2 equals the mean O2 uptake

value obtained between the start of the test and exhaustion (for IEsthe 4 min recovery between series was not included). [La] Lactateconcentration obtained 2 min after the end of the test, tlim time toexhaustion

_V O2 peak(% _V O2max)

_V O2 mean(% _V O2max)

[La](mmol.l�1)

tlim (s) Time spent above 95% of_V O2max

Time spent above 90% of_V O2max

(s) (% tlim) (s) (% tlim)

IE 96.5 (1.5) 90.3 (1.4) 10.7 (1.0) 621.8 (56.2) 178.0 (56.5) 29.7 (8.3) 345.0 (61.6) 58.3 (8.7)IEs 93.5 (3.0) 84.6* (2.7) 11.5 (1.0) 960.0** (102.0) 158.2 (59.7) 21.7 (8.1) 290.4 (84.3) 36.4* (10.4)

*P<0.05, **P< 0.005

149

highest blood lactate concentration are those who ranthe least time. During continuous exercise (5 min at 90%of _V O2max), Messonnier et al. (2002) observed the samenegative correlation between tlim and the arterializedblood lactate concentration measured at the end ofexercise. They concluded that the duration of highintensity exercise is closely correlated with high lactateexchange and removal abilities. In our study, when serieswere included in intermittent exercise, the time toexhaustion was no longer correlated with [La] (Fig. 2).Moreover, the mean [La] obtained at the end of IEs andIE did not differ significantly between both exerciseswhereas the total exercise duration was significantlylonger after IEs than after IE (Table 1). Thus, lactateaccumulation seems to play an important role in totalexercise duration during IE, probably because of itsrelationship with metabolic acidosis (Spangenburg et al.1998).

No data exist concerning the effect of active recoverybetween series on lactate kinetics during short intermit-tent exercise. However, the literature largely demon-strates that active recovery activates lactate removalfollowing submaximal exercise of intermediate duration(Belcastro and Bonen 1975; Boileau et al. 1983) and alsofollowing short duration high intensity exercise (Bogd-anis et al. 1996). Hence we can suppose that in thepresent study the 4 min mixed recovery between series,which was the only element that differed between IE andIEs, played an important role in lactate removal. Thishypothesis is supported by the lactate kinetics obtainedduring IEs. Figure 3 demonstrates that [La] tended toincrease during the series, but decreased (or stabilized)during the 4 min mixed recovery period between eachseries. Bogdanis et al. (1996) proposed that the beneficial

effects of active recovery could be due to an increasedblood flow to the previously exercised muscles, enhanc-ing oxygen delivery and therefore lactate removal (Saltinet al. 1992) and resulting in a faster recovery of muscleperformance (Messonnier et al. 2002).

Effects of series on the time spent at _V O2max or above90% of _V O2max

An important result of the present study is that theeffective time spent at _V O2max or above 90% of _V O2max

did not differ significantly according to the exerciseformat (with or without series) (Table 1). Moreover,when t90% _V O2max was related to the total exercise dura-tion, it was significantly lower during IEs than IE. Inother terms, intermittent exercise realized with seriesmay not be more effective when the objective of trainingis to improve the _V O2max. Indeed, to spend the sameamount of time above 90% of _V O2max, short intermit-tent exercise with series obliges the athlete to maintainthe exercise for a longer duration (1.5-fold longer) thanwhen repetitions are alternated without stopping. Toexplain this result, we have calculated tt90% _V O2max at thestart of IE and at the start of each series for IEs. For the8 subjects who reached 90% of _V O2max during IE andalso during the first series of IEs, the mean values oftt90% _V O2max were not significantly different [114.4(19.2) s and 148.1 (34.9) s, respectively]. Nevertheless,the _V O2 kinetics at the start of the second series of IEstends to be faster than those of the first series (Fig 4).Indeed, for the 6 subjects who attained 90% of _V O2max

during the first and also the second series of IEs, themean tt90% _V O2max values are significantly different: 165.0(43.1) s and 82.5 (15.8) s, respectively. This result is inaccordance with numerous recent studies which havedemonstrated that the _V O2 kinetics are modified byprior heavy exercise (Jones et al. 2003). For example, apreliminary 6 min of heavy exercise followed by 6 min

Fig. 3 Two examples of lactate kinetics obtained during IEs.Diagonally hashed bars represent each exercise series

150

of complete recovery significantly speeded the monoex-ponential kinetics during a subsequent 6 min of heavyexercise (Gerbino et al. 1996). This increase in the _V O2

kinetics following prior heavy exercise has severalexplanations which are still under debate. One physio-logical mechanism could be an increase in the aerobicenergy turnover in subsequent high-intensity exercisedue to an increase of oxygen availability at the beginningof the exercise (Gerbino et al. 1996). This could explainthe increased exercise tolerance generally observed dur-ing the subsequent exercise (Jones et al. 2003). In thepresent study, the first series during the IEs formatcertainly influenced the _V O2 response during the secondand subsequent series. However, during the 4 min mixedrecovery, the _V O2 kinetics were largely decreased. Forexample, the mean _V O2 attained before the start of thesecond series was 22.4 (1.7)% of _V O2max. This result is inaccordance with the study of Millet et al. (2003). Hence,at the start of each series, a progressive elevation of _V O2

(Barstow 1994; Whipp 1987) is systematically observed.Indeed, 90% of _V O2max is never immediately attained(Fig. 4) and time spent under 90% of _V O2max remainsconsiderable. This may explain why the mean _V O2 wassignificantly lower during IEs than IE (Table 1) whereasthe _V O2 peak did not differ. Finally, a recovery periodimposed every 6 repetitions may limit the t90% _V O2max

during the overall series. Moreover, the increase in tlimassociated with the speeding up of the _V O2 kinetics wasnot sufficient to compensate for the time spent under90% of _V O2max at the beginning of each series.

Conclusion

In conclusion, our results demonstrate that seriesduring a model of high intensity short intermittentexercise (30 s-30 s) permits the improvement of the

total duration of exercise at high intensity. This benefitgained in terms of total distance ran per session isprobably due to the recovery allowed between series.According to Noakes (1991), the effectiveness oftraining also depends on the distance covered at ahigh velocity, which determines the muscular adapta-tions. Hence longitudinal studies should be carried outto confirm the interest of series during short inter-mittent training to develop running performance.Finally, and in accordance with other studies (Billatet al. 2000a; Millet et al. 2003), neither _V O2max nor90% of _V O2max were reached by some subjectswhatever the exercise format chosen in this study (withor without series). Hence, if the goal of the training isto be able to sustain _V O2max in order to improve it(central adaptation), this exercise model (30 s-30 s)may not be an optimal exercise for these subjects. It isprobable that the interactions between intensity,recovery period, exercise period and number of repe-titions by series should be more individualized.

References

Astrand I, Astrand PO, Christensen EH, Hedman R (1960) Inter-mittent muscular work. Acta Physiol Scand 48:448–453

Astrand PO, Rodahl K (1986) Textbook of work physiology, 3rdedn. McGraw Hill, New York

Ballor DL, Volovsek AJ (1992) Effect of exercise to rest ratio onplasma lactate concentration at work rates above and belowmaximum oxygen uptake. Eur J Appl Physiol 65:365–369

Barstow TJ (1994) Characterization of _V O2 kinetics during heavyexercise. Med Sci Sports Exerc 26:1327–1334

Belcastro AN, Bonen A (1975) Lactic acid removal rates duringcontrolled and uncontrolled recovery exercise. J Appl Physiol39:932–936

Berthoin S, Pelayo P, Lensel-Corbeil G, Robin H, Gerbeaux M(1996) Comparison of maximal aerobic speed as assessed withlaboratory and field measurements in moderately trained sub-jects. Int J Sports Med 17:525–529

Billat VL, Blondel N, Berthoin S (1999) Determination of thevelocity associated with the longest time to exhaustion atmaximal oxygen uptake. Eur J Appl Physiol 80:159–161

Billat VL, Slawinski J, Bocquet V, Demarle A, Lafitte L, ChassaingP, Koralsztein JP (2000a) Intermittent runs at the velocityassociated with maximal oxygen uptake enables subjects to re-main at maximal oxygen uptake for a longer time than intensebut submaximal runs. Eur J Appl Physiol 81:188–196

Billat VL, Morton RH, Blondel N, Berthoin S, Bocquet V, Ko-ralsztein JP, Barstow TJ (2000b) Oxygen kinetics and modellingof time to exhaustion whilst running at various velocities atmaximal oxygen uptake. Eur J Appl Physiol 82:178–187

Billat VL, Slawinksi J, Bocquet V, Chassaing P, Demarle A, Ko-ralsztein JP (2001) Very short (15 s) interval-training aroundthe critical velocity allows middle-aged runners to maintain_V O2max for 14 minutes. Int J Sports Med 22:201–208

Bogdanis GC, Nevill ME, Lakomy HK, Graham CM, Louis G(1996) Effects of active recovery on power output during re-peated maximal sprint cycling. Eur J Appl Physiol 74:461–469

Bogdanis GC, Nevill ME, Lakomy HKA, Boobis LH (1998) Poweroutput and muscle metabolism during and following recoveryfrom 10 and 20 s of maximal sprint exercise in humans. ActaPhysiol Scand 163:261–272

Boileau RA, Misner JE, Dykstra GL, Spitzer TA (1983) Bloodlactic acid removal during treadmill and bicycle exercise atvarious intensities. J Sports Med Phys Fitness 23:159–167

Fig. 4 Mean _V O2 kinetics obtained at the start of the IE test,and at the beginning of the first and the second series of the IEstest.The open circles represent the mean _V O2 values for IE, theopen triangles the mean _V O2 values for the first IEs series, andthe filled circles the values for the second series

151

Brandon LJ, Boileau RA (1987) The contribution of selectedvariables to middle and long distance run performance. J SportsMed Phys Fitness 27:157–164

Brooks GA (1985) Anaerobic threshold: review of the concept anddirections for future research. Med Sci Sports Exerc 17:22–34

Burnley M, Doust JH, Carter H, Jones AM (2001) Effects of priorexercise and recovery duration on oxygen uptake kinetics dur-ing heavy exercise in humans. Exp Physiol 86:417–425

Callier J, Candau R, Magnin P (1994) The effect of induced alka-losis on endurance time during repeated bouts of maximalexercise. Cinesiologie 154:45–50

Dupont G, Blondel N, Lensel G, Berthoin S (2002) Critical velocityand time spent at a high level of _V O2 for short intermittent runsat supramaximal velocities. Can J Appl Physiol 27:103–115

Dupont G, Blondel N, Berthoin S (2003) Time spent at _V O2max: amethodological issue. Int J Sports Med 24:291–297

Gerbino A, Ward SA, Whipp BJ (1996) Effects of prior exercise onpulmonary gas-exchange kinetics during high-intensity exercisein humans. J Appl Physiol 80:99–107

Gorostiaga EM, Walter CB, Foster C, Hickson RC (1991)Uniqueness of interval and continuous training at the samemaintained exercise intensity. Eur J Appl Physiol 63:101–107

Handschuh R, Rakotoambinina B, Desnus B, Fraisse F (1991)Study of the participation of anaerobic metabolism of the en-ergy requirement according to the duration and intensity ofexercise. Sci Sports 6:15–24

Hill DW, Rowell AL (1997) Responses to exercise at the velocityassociated with _V O2max. Med Sci Sports Exerc 29:113–116

Hill DW, Williams CS, Burt SE (1997) Responses to exercise at92% and 100% of the velocity associated with _V O2max. Int JSports Med 18:325–329

Hirvonnen J, Rehumen S, Rusko H, Harkonen M (1987) Break-down of high-energy phosphate compounds and lactate accu-mulation during short supramaximal exercise. Eur J ApplPhysiol 56:253–259

Jones AM, Wilkerson DP, Burnley M, Koppo K (2003) Priorheavy exercise enhances performance during subsequent peri-maximal exercise. Med Sci Sports Exerc 35:2085–2092

Kuipers H, Verstappen FT, Keizer HA, Geurten P, van Kranen-burg G (1985) Variability of aerobic performance in the labo-ratory and its physiologic correlates. Int J Sports Med 6:197–201

Lacour JR, Padilla-Magunacelaya S, Chatard JC, Arsac L, Bar-thelemy JC (1991) Assessment of running velocity at maximaloxygen uptake. Eur J Appl Physiol 62:77–82

Margaria R, Oliva RD, Di Prampero PE, Cerretelli P (1969) En-ergy utilization in intermittent exercise of supramaximalintensity. J Appl Physiol 26:752–756

McLaughlin JE, King GA, Howley ET, Bassett DR Jr., AinsworthBE (2001) Validation of the COSMED K4 b2 portable meta-bolic system. Int J Sports Med 22:280–284

Messonnier L, Freund H, Denis C, Dormois D, Dufour AB, La-cour JR (2002) Time to exhaustion at _V O2max is related to thelactate exchange and removal abilities. Int J Sports Med23:433–438

Millet GP, Candau R, Fattori P, Bignet F, Varray A (2003) _V O2

responses to different intermittent runs at velocity associatedwith _V O2max. Can J Appl Physiol 28:410–423

Noakes TD (1991) Lore of running. Leisure Press, Champaign,p 450

Overend TJ, Paterson DH, Cunningham DA (1992) The effect ofinterval and continuous training on the aerobic parameters.Can J Sport Sci 17:129–134

Sahlin K, Tonkonogi M, Soderlund K (1998) Energy supply andmuscle fatigue in humans. Acta Physiol Scand 162:261–266

Saltin B, Bangsbo J, Graham TE, Johansen L (1992) Metabolismand performance in exhaustive intense exercise: different effectsof muscle glycogen availability, previous exercise and muscleacidity. In: Marconnet P, Komi PV, Saltin B, Sejersted OM(eds) Muscle fatigue mechanisms in exercise and training, vol26. Karger, Basel, pp 98–109

Spangenburg EE, Ward CW, Williams JH (1998) Effects of lactateon force production by mouse EDL muscle: implicationsfor the development of fatigue. Can J Physiol Pharmacol76:642–648

Taylor H, Buskirk E, Henschel A (1955) Maximal oxygen intake asan objective measure of cardiorespiratory performance. J ApplPhysiol 8:73–80

Wenger HA, Bell GJ (1986) The interactions of intensity, frequencyand duration of exercise training in altering cardiorespiratoryfitness. Sports Med 3:346–356

Whipp BJ (1987) Dynamics of pulmonary gas exchange. Circula-tion 76:VI18–28

152