Effect of free versus constant pace on performance and oxygen kinetics in running

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Effect of free versus constant pace on performance and oxygen kinetics in running
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  Effect of free versus constant pace onperformance and oxygen kinetics in running VE´RONIQUE LOUISE BILLAT, JEAN SLAWINSKI, MATHIEU DANEL, and JEAN PIERRE KORALSZTEIN Faculty of Sport Science, University of Lille 2, Lille, FRANCE; and the Sport Medicine Center C.C.A.S., Paris, FRANCE  ABSTRACT BILLAT, V. L., J. SLAWINSKI, M. DANEL, and J. P. KORALSZTEIN. Effect of free versus constant pace on performance andoxygen kinetics in running.  Med. Sci. Sports Exerc. , Vol. 33, No. 12, 2001, pp. 2082–2088.  Purpose:  This study tested the hypothesisthat free versus constant pace enhanced the performance (i.e., distance run) in suprathreshold runs between 90 and 105% of the velocityassociated with the maximal oxygen consumption determined in an incremental test (vV˙O 2max ). Moreover, we hypothesized thatvariable pace could decrease the slow phase of oxygen kinetics by small spontaneous recoveries during the same distance run at anaverage velocity.  Method:  Eleven long-distance runners performed nine track runs performed until exhaustion. Following anincremental test to determine vV˙O 2max , the runners performed, in a random order, four constant-velocity runs at 90, 95, 100, and 105%of vV˙O 2max  to determine the time to exhaustion (tlim90, tlim95, tlim100, and tlim105) and the distance limit at 90, 95, 100 and 105%of vV˙O 2max  (dlim90, dlim95, dlim100, and dlim105). Finally, they performed the distance limit determined in the constant velocity runsbut at variable velocity according to their spontaneous choice.  Results:  The coefficient of variation of velocity (in percent of the averagevelocity) was small and not significantly different between the four free pace dlim (4.2    1.3%, 4.8    2.4%, 3.6    1.1%, and 4.6   1.9% for dlim90, dlim95, dlim100, and dlim105, respectively;  P    0.40). Performances were not improved by a variable pace exceptedfor the dlim at 105% vV˙O 2max  (4.96    0.6 m·s  1 vs 4.86    0.5 m·s  1 ,  P    0.04). Oxygen kinetics and the volume of oxygen consumedwere not modified by this (low) variation in velocity.  Conclusion:  These results indicate that for long-distance runners, variable pacemodifies neither performance nor the oxygen kinetics in all-out suprathreshold runs.  Key Words:  OXYGEN CONSUMPTION,EXHAUSTION, EXERCISE O n a track where the goal is to run a given distanceas quickly as possible, athletes spontaneouslychoose to modulate their pace during the race toavoid becoming overfatigued before reaching the finishingline (1). Sports records are performed with free and notconstant paces even during long-distance running, and anathlete in any event lasting more than 2 min has the oppor-tunity to use energy available from the cleavage of phosph-agen and from glycolysis in a flexible manner (15). If oneconsiders the last three world records for middle- and long-distance running (1500 m, 3000 m, 5000 m, and 10,000 m),it can be observed that the range of the coefficient of variation of velocity is 1 to 5% (unpublished data computedfrom the International Amateur Athletic Federation books).However, in a review on pacing strategy and athletic per-formance, Foster et al. (14) recall that since the initial studyof Robinson et al. (25) during a 1200-m run, there have beenfew systematic studies to determine how various pacingstrategies might influence the outcome of competitive per-formance. The studies were true pacing studies (1,2,14,20) or controlled stochastic investigations (23,24).It has been demonstrated that under competitive condi-tions the physiological responses of athletes might be sig-nificantly greater than suggested by the conventional incre-mental test (9,12). Moreover, in a run at 90% of the velocityassociated with V˙O 2max  in an incremental test (vV˙O 2max ),oxygen consumption continues to increase with time bymeans of a V˙O 2  slow component (i.e., the second amplitudeof the oxygen biexponential kinetics model) (6,16,26). Fos-ter et al. (14) suggested that athletes learn how to sense lowvalues of muscle pH and adjust their pace accordingly sothat they ideally reach critically low values of pH near theend of a race. During an all-out event of 3–15 min, theincrease of type II fiber recruitment, which is correlatedwith the lactate accumulation, could increase V˙O 2  towardV˙O 2max . Therefore, a spontaneous decrease in the velocityaround the third minute could prevent the development of the V˙O 2  slow component (26). Indeed, above the criticalpower, V˙O 2  rises inexorably until fatigue ensues, at V˙O 2max (5). Therefore, the purpose of this study was to examinewhether a free versus a constant pace produces differentperformance results and, if so, whether this related to theslow V˙O 2  response. METHODS Subjects Eleven male long-distance runners (age, 41    10 yr;height, 175    5 cm; weight, 71    5 kg) participated in thisstudy. They trained five times per week (70    20 km·wk   1 ).These subjects were long-distance runners training for thehalf-marathon. They were chosen to avoid a strategy (long-term planned) and to get a stochastic pace (i.e., a variation 0195-9131/01/3312-2082/$3.00/0MEDICINE & SCIENCE IN SPORTS & EXERCISE ® Copyright © 2001 by the American College of Sports MedicineSubmitted for publication August 2000.Accepted for publication February 2001. 2082  of pace involving probability arising from chance). Beforeparticipation in this study, all subjects provided voluntarywritten informed consent in accordance with the guidelinesof the University of Lille. Experimental Design Subjects performed nine tests performed until exhaus-tion. Only one test was carried out on a given day. Alltests were performed on a synthetic 400-m track at thesame time of day in a climate of 19° to 22°C without windaccording to the immobility of the flags surrounding thetrack. On the day separating the two tests, subjects wereasked either to rest or to do light training (i.e., 30 min at60% of vV˙ O 2max ). They were also asked to refrain fromfood or beverages containing caffeine before testing.Runners followed a pacing cyclist traveling at the re-quired velocity. The cyclist received audio cues via aWalkman; the cue rhythm determined the speed needed tocover 20 m. Visual marks were set at 20-m intervals alongthe track (inside the first lane).The first test was needed to determine V˙O 2max , the ve-locity associated with V˙O 2max  (vV˙O 2max ), and the runningvelocity at the lactate threshold (vLT) (3,9). After thispreliminary incremental test, runners performed, in a ran-dom order, four constant pace runs at 90, 95, 100, and 105%of vV˙O 2max  with time (tlim) and distance limits (dlim) beingdetermined at each velocity (Table 1). Then, they per-formed, also in a random order, a free paced run on eachfour distance limits (dlim) set by the time limit (tlim) at 90,95, 100, and 105% of vV˙O 2 max. For instance, if they ran300 s at 100% of vV˙O 2max  equal to 5 m·s  1 , they performeda distance limit equal to 1500 m. Therefore, they performedtheir variable pace run on the same distance limit (i.e.,1500 m) to compare the average velocity with the constantpace trial. Hence, the runners performed free paced runs atthe same four distance limits: dlim90, dlim95, dlim100, anddlim105. Data Collection ProceduresProtocol of V ˙O 2max  and vV ˙O 2max  determination. The initial speed was set at 10 km·h  1 and was increased by1 km·h  1 every 2 min. Each stage was separated by a 30-srest during which a capillary blood sample was obtainedfrom the fingertip and analyzed for lactate concentration(YSI 27 analyzer, Yellow Spring Instruments, YellowSpring, OH). Measurement of V˙O 2  was carried out through-out each test using a telemetric system (K4 b 2 , COSMED,Rome, Italy) (17,21). Expired gases were measured breathby breath and were averaged every 5 s. Before each test, theO 2  analysis system was calibrated using ambient air, whosepartial O 2  composition was assumed to be 20.9% and a gasof known CO 2  concentration (5%) (K4 b 2 instruction man-ual). The calibration of the turbine flow- meter of the K4 b 2 was performed with a 3-L syringe (Quinton Instruments,Seattle, WA). In the incremental tests, the maximal oxygenconsumption (V˙O 2max ) was defined as the highest V˙O 2 obtained in two successive 15-s intervals. In this incremen-tal protocol, vV˙O 2max  was defined as the lowest runningspeed maintained for more than 1 min that elicited V˙O 2max (8). If, during the last stage, an athlete achieved V˙O 2max  thatwas not sustained for at least 1 min, the speed during theprevious stage was recorded as his vV˙O 2max . If this velocitythat resulted in fatigue was only sustained for  1 min and   2 min, then vV˙O 2max  was considered to be equal to thevelocity during the previous stage plus the half velocityincrease between the last two stages (i.e., 1 km·h  1  /2    0.5km·h  1 ) (19). The lactate threshold (LT) was defined as theV˙O 2  value that corresponded to the starting point of anaccelerated lactate accumulation between 3.5 and 5mmol·L  1 (3). Constant and free paces on distances limit at 90,95, 100, and 105% vV ˙O 2max .  The constant and free paceruns on dlim90, dlim95, dlim100, and dlim105 were pre-ceded by 15 min of warming-up at 50% vV˙O 2max  and 5 minof rest to obtain basal oxygen consumption and blood lactateconcentration. For the constant velocity runs, the subjectsfollowed a pacing cyclist traveling at the required velocity.The cyclist received audio cues via a Walkman; the cuerhythm determined the speed needed to cover 20 m. Visualmarks were set at 20-m intervals along the track (crossingperpendicular to the first lane). The runners were asked tomaintain the tempo as long as possible. This allowed thetime and distance limit at 90, 95, 100, and 105% vV˙O 2max to be determined. For the free pace runs, the runners wereasked to run as fast as possible the same distance they hadpreviously covered at 90, 95, 100, and 105% of vV˙O 2max (dlim90, dlim95, dlim100, and dlim105). Subjects had noway of knowing their velocities. Every 20 m, the time wasregistered by two cyclists with a chronometer (DigisportsInstruments, Seyssins, France) set exactly on the runner’sside avoiding the parallax error when crossing the visualtrack marks. Thereafter, these data were downloaded into amicrocomputer. Since it was operated manually, the regis-tration of the two operators was checked for similarity (itwas the case). In all the distance limit runs, six successive TABLE 1. Experimental design of the nine tests performed until exhaustion and eachseparated by 1 day. Tests Purpose 1. Incremental tests To determine vV˙O 2max Then, in random order:2. Constant pace run at 90% vV˙O 2max  To determine dlim903. Constant pace run at 95% vV˙O 2max  To determine dlim954. Constant pace run at 100%vV˙O 2max To determine dlim1005. Constant pace run at 105%vV˙O 2max To determine dlim105Then, in random order:6. Free pace run over dlim90 To determine average velocity on dlim90with free pace7. Free pace run over dlim95 To determine average velocity on dlim95with free pace8. Free pace run over dlim100 To determine average velocity on dlim100with free pace9. Free pace run over dlim105 To determine average velocity on dlim105with free pace EFFECT OF VARIABLE PACE ON OXYGEN KINETICS Medicine & Science in Sports & Exercise   2083  5-s intervals runs (for a period of 30 s as in the incrementaltests) were recorded as the maximal V˙O 2  obtained duringthe dlim run.Blood lactate samples were collected after the warm-upand at 1, 3, and 5 min after the exercise. The highest of thesevalues was taken as the maximal blood lactate value for eachtest. The rating of perceived exertion (RPE) was based onthe Borg scale from 6 to 20 (10). The runners were asked togive their RPE at each lap with hand signals. Another cyclisthad the scale board on his back and asked the runners fortheir RPE at every lap and at the end of the all-out run. Therunner answered with a hand signal because of the K4 b 2 mask on his face. Subjects had been previously familiarizedwith the use of the Borg scale during the incremental test. Data AnalysesOxygen uptake kinetics.  The V˙O 2  kinetics were fitby a monoexponential function (5) for the short exercisebouts on dlim100 and dlim105 according to the followingequation: V˙O 2  (t)  V˙O 2baseline  A *   1 – e  (t/    )   (1) where V˙O 2  (t) is the oxygen uptake at time (t); theV˙O 2baseline  is the oxygen uptake at the end of the warm-up;A is the amplitude of oxygen uptake (V˙O 2max   V˙O 2baseline ), which subjects reached at the end of thedlim100 and dlim105 all-out runs; and     is the time constant(5).For runs long (90% of vV˙O 2max ), it was checked that allthe subjects developed a V˙O 2  slow component. Hence, thekinetics of V˙O 2  were fit by a triple exponential function(4,5) of the form: V˙O 2  (t)  V˙O 2baseline  A 0  *   1 – e  (t/    0)   A 1  *   1 – e (–(t –    1) /    1)   A 2  *   1 – e (–(t –    2) /    2)   (2) where V˙O 2  (t) is the oxygen uptake at time (t), V˙O 2baseline is the oxygen uptake at the end of the warm-up, A is theamplitude of oxygen uptake for each component during thetest (I, II, and slow),     is the time delay before the onset of each exponential component (I, II, and slow), and     is thetime constant of each component (5). Initial estimates of theparameter values were made by inspection of the experi-mental V˙O 2max  time points. Sigma Plot (SPSS, Inc., Chi-cago, IL) was used to determine the best-fit estimates foreach parameter. Calculation of the time limit at VO 2max  in all-outruns at 90, 95, 100, and 105% vV ˙O 2max .  The time toreach 95% of V˙O 2max  in the incremental test (TA95%V˙O 2max ) was calculated according to the following equa-tions used for the mono (equation 1) or triple exponential(equation 2).1. For the mono exponential starting from equation 1,solving for time t: t  –    ln   1 –   V˙O 2  (t) – V˙O 2baseline   /A   (3) Specifically, when V ˙O 2  (t) has reached 95% V ˙O 2max   , TA95% V˙O 2max  –    ln   1 –   0.95 V˙O 2max  – V˙O 2baseline   /A   (4) 2. For the triple exponential, a similar approach is used: TA95% V˙O 2max    2  t  (5) Where    2 is given in equation 2 as the time delay of the thirdexponential of the V˙O 2  kinetics and t  –   2  ln   1 –   0.95 V˙O 2max  – A1   – V˙O 2baseline   /A2   (6) Where A1'    A1    A0 * (1    e -(  1/    0) )Combining equations 5 and 6 yields TA95% V˙O 2max    2 –    2 * ln   1 –   0.95 V˙O 2max  – A1   – V˙O 2baseline   /A2   (7) Time limit at V˙O 2max  (tlim @ V˙O 2max ) can be computedaccording to equation 8: tlim @ V˙O 2max  tlim – TA95% V˙O 2max  (8) where TA95% V˙O 2max  is derived from the mono or tripleexponential models as described above (equations 1 or 2),and tlim is the total time to exhaustion (time limit) of theall-out runs performed at constant or variable paces. Oxygen consumed.  The aerobic component of the to-tal energy requirement for the all-out tests was computed byintegrating the area under the curve V˙O 2  time until exhaus-tion. The volume of oxygen consumed is the definite inte-gral of equations 1 and 2 performed with Mathcad 8 soft-ware (MathSoft, Cambridge, MA) (7). Statistical Analysis The results are presented as mean    standard deviation(SD). A two-way analysis of variance (constant vs freepace) for four levels (four speeds: 90, 95, 100, and 105%vV˙O 2max ) was used to compare the average velocities be-tween the constant versus variable paces in dlim90, dlim95,dlim100, and dlim105. Significant differences were identi-fied by Scheffe´  post hoc  tests. Oxygen kinetics parameters(time delay, time constant, amplitude, and V˙O 2baseline ) inconstant versus variable paces were compared using theStudent’s  t  -test. The results are presented as mean    SD.Statistical significance has been set at  P    0.05. RESULTS The individual characteristics of the subjects obtainedduring the incremental test are presented in Table 2. In allfree pace runs (dlim90, dlim95, dlim100, and dlim105), therunners accelerated in the second part of the run, especiallyduring the last lap (Fig. 1). In all the free pace runs, thevariation of velocity were very small and not significantlydifferent between the four dlim. Indeed, the coefficient of variation (in percentage of the average velocity) was lessthan 5% dlim (4.2    1.3%, 4.8    2.4%, 3.6    1.1%, and 4.6   1.9% for dlim90, dlim95, dlim100, and dlim105, respec-tively;  P    0.40). Figure 2 shows a typical subject. More-over, the coefficient of variation of the speed was muchlower during all the race but the last lap (3.8    1.6%, 2.3   1.7%, 2.5    0.8%, and 3.2    2.9% for dlim90, dlim95,dlim100, and dlim105, respectively;  P    0.32).2084  Official Journal of the American College of Sports Medicine http://www.acsm-msse.org  These velocity variations were ineffective in improvingperformance (i.e., to decrease the time for running the dis-tance limits) (Table 3). Indeed, there was no significantdifference in time to exhaustion between free and constantpace on the same dlim. Hence, performances (i.e., averagevelocity on dlim) were not improved by variable pace ex-cepted in dlim at 105% vV˙O 2max  (4.96    0.6 m·s  1 vs 4.86   0.5 m·s  1 ,  P    0.04).All the subjects developed a slow phase of oxygen kinet-ics in dlim90, long enough to observe it. The oxygen kinet-ics and the volume of oxygen consumed during dlim werenot modified in the free pace runs except for the time delayin the onset of the slow phase of oxygen kinetics, whichappears earlier in the dlim90 variable velocity run (134   64 s vs 180    94 s,  P    0.05) (Table 4). Indeed, at 90% of vV˙O 2max , the time delay for the oxygen slow phase (   2 ) wassignificantly shorter in the free than in the constant pace(134    64 s vs 180    94 s,  P    0.05), but in this case, FIGURE 1—Velocity (expressed as a percent of the average velocity ondlim90, dlim95, dlim100, and dlim105) in the first and second half of the time limit tests and in the last lap of the runs at free pace.FIGURE 2—Time course of oxygen consumption in the free (  black squares ) and constant pace (  open squares ) all-out runs on dlim90,dlim95, dlim100, and dlim105 (from top to bottom). Velocity is indi-cated as a  narrow line  (constant velocity) and  squares  (free velocity).This is an example in a typical subject for each distance limit: dlim90,dlim95, dlim100, and dlim105. TABLE 2. Individual incremental test data. SubjectsAge(yr)vV˙O 2max (m  s –1 )V˙O 2max (mL  min –1  kg –1 )HR max (bpm)BloodLactate(mmol  L –1 )vLT(m  s –1 )vLT (%vV˙O 2max ) 1 45 4.72 60.1 191 15.9 3.88 82.22 36 5.27 58.3 175 17.8 4.44 84.33 26 5.55 57.4 187 17.3 4.72 85.04 40 4.72 53.8 171 11.4 4.16 88.15 38 5.13 58.0 193 16.7 4.30 83.86 22 5.55 64.0 193 13.0 4.72 85.07 54 4.02 43.3 174 12.9 3.33 82.88 41 4.44 57.4 186 15.6 3.61 81.39 44 4.16 51.0 179 9.3 3.47 83.410 48 4.16 47.0 172 14.7 3.47 83.411 55 4.16 47.9 161 10.5 3.61 86.8Mean 41 4.72 54.4 180 14.5 3.97 84.2Standard deviation 10 0.58 6.0 11 2.8 0.62 2.0HR max , maximal heart rate; vLT, lactate threshold velocity; V˙O 2max , maximal oxygen uptake. EFFECT OF VARIABLE PACE ON OXYGEN KINETICS Medicine & Science in Sports & Exercise   2085  subjects had run this 130 s faster than in the constantvelocity dlim90 (92% vs 90% of vV˙O 2max ). The time spentat V˙O 2max  in each of the dlim run at constant versus freepace was not significantly different (Table 4).Maximal blood lactate did not differ significantly be-tween free and constant paces ( P    0.86) (Table 3). TheRPE was not influenced either by spontaneous velocity ( P   0.53) or by the interaction between intensity (90, 95, 100,and 105% vV˙O 2max ) and (small) variation of pace in freepace runs ( P    0.32). RPE response at 25, 50, 75, and 100%of time to exhaustion, independent of the distance limit, wasnot influenced by constant or variable velocity ( P    0.90).In both cases, RPE was close to its maximum at the end of the exercise whatever the intensity and was not significantlydifferent according to the type of pace (constant or variable)(19.9    0.4 vs 19.5    0.8 for constant and variable velocity,respectively;  P    0.34). DISCUSSION This study showed that in free pace runs performed bylong-distance runners unfamiliar with these middle dis-tances (1000–3000 m), pace variations were small, espe-cially if we only consider all of the distance that is runexcept the last lap. Consequently, the oxygen kinetics andblood lactate were not affected by the free pace versusconstant runs except for the time delay for the oxygen slowcomponent, which was shorter because the first part of thedistance run was faster than in the constant pace run (92%vs 90% of vV˙O 2max ).This study clearly shows that a variable versus a constantpacing in all-out runs on dlim90, dlim95, dlim100, ordlim105 produces similar performances in these subjectswho are not middle-distance runners. Moreover, the oxygenkinetics and the slow V˙O 2  response were not affected by thevariable versus constant pace. Indeed, this study showedthat the oxygen kinetics was not modified by the smallvariation in velocity except at 90% of vV˙O 2max , where therewas a shorter time delay for the V˙O 2  slow componentbecause of the first 3 min run at 92% versus 90% of vV˙O 2max . This is in accordance with Hughson et al. (18),who recently reported that there was an inverse relationshipbetween the time delay to reach V˙O 2max , the V˙O 2  slowcomponent, and the intensity of exercise. Pace and performance in variable velocity stud-ies.  The literature has generally focused on performanceand physiological responses in a one-time trial (1,2,12) or insubsequent all-out exercise (23,24). Using a self-pace ap-proach as in our study, Foster et al. (13) examined the pacein a 5-km simulated competition where no pacing constraintwas applied in order to examine the physiological responsesof the cyclists. Each subject was instructed to complete the5 km as rapidly as possible, as in a competition. Throughoutthe first half of the 5-km time trial (of the same duration asour dlim90 and dlim95), cycling velocity increased progres-sively to remain relatively constant throughout the last 2 km.In our study carried out on running performance, where theenergy cost is nonaerodynamic (11), all of the runnersaccelerated during the second part of the distance limit andin particular during the last lap. This may be because they TABLE 4. Influence of free pace versus constant pace on oxygen kinetics parameters. SubjectsA  0 (mL  min –1 )    1  (s)A  1 (mL  min –1 )    1  (s)    2  (s)A  2 (mL  min –1 )    2  (s) V˙O 2  (L) dlim90  a  Constant 765  112 5.1  0.8 2799  602 28  4 180  94 417  151 94  72 39.9  7.1Free 733  167 5.5  0.9 2710  660 26  9 134  64 414  241 64  54 38.0  6.4dlim95Constant 728  207 5.8  1.1 2788  635 25  10 126  43 333  171 54  14 21.3  4.1Free 683  162 6.0  1.0 2784  658 22  6 119  36 375  156 53  20 21.3  4.3dlim100Constant 737  162 6.0  1.1 2994  849 25  10 — — — 13.2  4.3Free 716  137 6.2  1.0 2858  670 24  8 12.6  4.1dlim105Constant 948  166 7.1  1.0 2749  632 22  7 — — — 11.0  3.9Free 876  320 6.5  1.1 2973  800 22  9 11.0  3.7A  0 , A  1 , and A  2  are the amplitudes of the three exponentials at times    1  and    2  and at 95% V˙O 2max . Time delay of the second and third exponentials (   1  and    2 ) and time constantof the second and third exponentials (   1  and    2 ); V˙O 2 , total volume of oxygen consumed during the dlim90, dlim95, dlim100, and dlim105; —, for dlim100 and dlim105, the V˙O 2  timecourse was better fitted by mono exponential model. a  P     0.05. TABLE 3. Individual performance (time limit), time spent at V˙O 2max , and maximal blood lactate in the dlim90, dlim95, dlim100, and dlim105 run at constant andspontaneous paces. DistanceLimitTime Limit atConstantPace (s)Time Limit atVariablePace (s)tlim atV˙O 2max  atConstantPace (s)tlim atV˙O 2max  atVariablePace (s)Max Blood Lactateat Constant Pace(mmol  L –1 )Max Blood Lactateat Variable Pace(mmol  L –1 )Distance Limit(m) dlim90 640  172 634  177 396  265 423  253 11.1  2.0 11.3  2.0 2738  982dlim95 386  93 370  111 206  139 176  178 10.5  1.7 12.1  2.4 1745  509dlim100 237  42 237  44 102  76 74  82 10.7  3.1 10.8  2.5 1118  305dlim105 200  41 194  30 89  78 107  65 12.3  2.9 10.8  2.1 945  203dlim90, distance limit at 90% of vV˙O 2max  equal to 90% vV˙O 2max  tlim90 at 90% of vV˙O 2max ; Max Blood lactate, maximal blood concentration at the end of the all-out run on dlim90,dlim95, dlim100, and dlim105. 2086  Official Journal of the American College of Sports Medicine http://www.acsm-msse.org
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