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Objective: Long before clinical complications of type 1 diabetes (T1D) develop, oxygen supply and use can be altered during activities of daily life. We examined in patients with uncomplicated T1D all steps of the oxygen pathway, from the lungs to the mitochondria, using an integrative ex vivo (muscle biopsies) and in vivo (during exercise) approach., Research Design and Methods: We compared 16 adults with T1D with 16 strictly matched healthy control subjects. We assessed lung diffusion capacity for carbon monoxide and nitric oxide, exercise-induced changes in arterial O 2 content (SaO 2 , PaO 2 , hemoglobin), muscle blood volume, and O 2 extraction (via near-infrared spectroscopy). We analyzed blood samples for metabolic and hormonal vasoactive moieties and factors that are able to shift the O 2 -hemoglobin dissociation curve. Mitochondrial oxidative capacities were assessed in permeabilized vastus lateralis muscle fibers., Results: Lung diffusion capacity and arterial O 2 transport were normal in patients with T1D. However, those patients displayed blunted exercise-induced increases in muscle blood volume, despite higher serum insulin, and in O 2 extraction, despite higher erythrocyte 2,3-diphosphoglycerate. Although complex I- and complex II-supported mitochondrial respirations were unaltered, complex IV capacity (relative to complex I capacity) was impaired in patients with T1D, and this was even more apparent in those with long-standing diabetes and high HbA 1c . [Formula: see text]O 2max was lower in patients with T1D than in the control subjects., Conclusions: Early defects in microvascular delivery of blood to skeletal muscle and in complex IV capacity in the mitochondrial respiratory chain may negatively impact aerobic fitness. These findings are clinically relevant considering the main role of skeletal muscle oxidation in whole-body glucose disposal., (© 2019 by the American Diabetes Association.)

This study aimed to compare the effect of active recovery (AR) versus passive recovery (PR) on time to exhaustion and time spent at high percentages of peak oxygen uptake ( peak V ˙ O 2 ) during short, high-intensity intermittent exercises in children. Twelve children (9.5 [0.7] y) underwent a graded test and 2 short, high-intensity intermittent exercises (15 s at 120% of maximal aerobic speed) interspersed with either 15 seconds of AR (50% of maximal aerobic speed) or 15-second PR until exhaustion. A very large effect (effect size = 2.42; 95% confidence interval, 1.32 to 3.52) was observed for time to exhaustion in favor of longer time to exhaustion with PR compared with AR. Trivial or small effect sizes were found for peak V ˙ O 2 , peakHR, and peak ventilation between PR and AR, while a moderate effect in favor of higher average V ˙ O 2 values (effect size = -0.87; 95% confidence interval, -1.76 to -0.01) was found using AR. The difference between PR and AR for the time spent above 80% (t80%) and 90% (t90%) of peak V ˙ O 2 was trivial. Despite the shorter running duration in AR, similar t80% and t90% were spent with AR and PR. Time spent at a high percentage of peak V ˙ O 2 may be attained by running 3-fold shorter using AR compared with using PR.

The aim of the study was to characterize aerobic responses to high intensity intermittent (HIIE) and continuous (CE) exercises in prepubertal children. 26 children aged 8 to 11-year-old took part in a preliminary session to determine peakVO 2 and Maximal Aerobic Velocity (MAV). In 5 subsequent experimental visits, the participants completed 2 CE and 3 HIIE sessions in a randomized order. HIIE consisted of short intermittent 10-s and 20-s running bouts at 100 to 130% MAV, interspersed with recovery periods of equal duration (S-HIIE1 and S-HIIE2 respectively) and 5-s of sprinting and jumping at maximal intensity with 15-s recovery periods (S-HIIE3). CE consisted of 2 10-min running periods at 80% and 85% MAV with a 5-min recovery period. CE protocols elicited higher average VO 2 and exercise time spent above 95% of peakVO 2 compared to the HIIE protocols. S-HIIE 1 and S-HIIE 2 elicited similar average VO 2 response, higher than S-HIIE 3. Our study shows that CE activated the aerobic system to a greater extent than S-HIIE in prepubertal children, as reflected by the time above 95% of peakVO 2 during exercise. However, isotime S-HIIE protocols comprising 10-s or 20-s exercise bouts at an intensity above MAV result in similar times above 95% of peakVO 2 during exercise., Competing Interests: Conflicts of interest: The author have no conflict of interes to declare., (© Georg Thieme Verlag KG Stuttgart · New York.)

This study aimed to examine if the faster pulmonary oxygen uptake (VO2p) phase 2 in children could be explained by increased O2 availability or extraction at the muscle level. For that purpose, O2 availability and extraction were assessed using deoxyhemoglobin (HHb) estimated by near-infrared spectroscopy during moderate-intensity constant load cycling exercise in children and young adults. Eleven prepubertal boys and 12 men volunteered to participate in the study. They performed one maximal graded exercise to determine the power associated with the gas exchange threshold (GET) and four constant load exercises at 90% of GET. VO2p and HHb were continuously monitored. VO2p , HHb, and estimated capillary blood flow (Qcap) kinetics were modelled after a time delay and characterized by the time to achieve 63% of the amplitude (τ) and by mean response time (MRT: time delay + τ), respectively. Mean values of τ for VO2p (P < 0.001), of MRT for HHb (P < 0.01) and of MRT for Qcap (P < 0.001) were significantly shorter in children. Faster VO2p kinetics have been shown in children; these appear due to both faster O2 extraction and delivery kinetics as indicated by faster HHb and Qcap kinetics, respectively., (© 2012 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The aim of this investigation was, first, to examine comparatively the changes in first and second ventilatory thresholds (VT1 and VT2 ) and, secondly, to compare with peak oxygen uptake (${\dot {\rm {V}}}&#95;{{\rm O}&#95;{{\rm 2}} {\rm peak}} $) changes following high-intensity interval training (HIT) in prepubescent children. Eighteen prepubescent children (aged 10.1 ± 0.7 years) performed an incremental exhaustive exercise on a cycle ergometer with pulmonary gas exchange measurements before and after an 8-week period. During this period, nine children (five girls and four boys; initial ${\dot {\rm {V}}}&#95;{{\rm O}&#95;{{\rm 2}} {\rm peak}} $: 39.6 ± 6.0 ml O2  · min(-1)  · kg(-1) ) took part in a HIT and nine other children (three girls and six boys; initial ${\dot {\rm {V}}}&#95;{{\rm O}&#95;{{\rm 2}} {\rm peak}} $: 39.8 ± 7.8 ml O2  · min(-1)  · kg(-1) ), considered as controls, were not trained. After the training period, VT1 , VT2 , and ${\dot {\rm {V}}}&#95;{{\rm O}&#95;{{\rm 2}} {\rm peak}} $ were significantly (P < 0.01) improved (21%, 24%, and 14%, respectively) without significant changes in the control group. However, the changes in VT1 (ΔVT1 = +4.35 ± 4.36 ml O2  · min(-1)  · kg(-1) ), VT2 (ΔVT1 = +7.17 ± 5.17 ml O2  · min(-1)  · kg(-1) ), ${\dot {\rm {V}}}&#95;{{\rm O}&#95;{{\rm 2}} {\rm peak}} $ ($\Delta {\dot {\rm {V}}}&#95;{{\rm O}&#95;{{\rm 2}} {\rm peak}} $ = +5.51 ± 4.17 ml O2  · min(-1)  · kg(-1) ) induced by HIT in trained children were not related. In conclusion, for prepubescent children, in addition to VT1 and ${\dot {\rm {V}}}&#95;{{\rm O}&#95;{{\rm 2}} {\rm peak}} $, VT2 can also be significantly improved by training. Therefore, HIT represents a good way to obtain great improvement in these parameters in only 8 weeks. However, the time courses of these aerobic fitness parameters are dissociated, which implies the need to differentiate among them during aerobic fitness exercise testing., (Copyright © 2012 Wiley Periodicals, Inc.)

The aim of the study was to compare time spent at a high percentage of VO2max (>90% of VO2max) (ts90%), time to achieve 90% of VO2max (ta90%), and time to exhaustion (TTE) for exercise in the severe intensity domain in children and adults. Fifteen prepubertal boys (10.3 ± 0.9 years) and 15 men (23.5 ± 3.6 years) performed a maximal graded exercise to determine VO2max, maximal aerobic power (MAP) and power at ventilatory threshold (PVTh). Then, they performed 4 constant load exercises in a random order at PVTh plus 50 and 75% of the difference between MAP and PVTh (PΔ50 and PΔ75) and 100 and 110% of MAP (P100 and P110). VO2max was continuously monitored. The P110 test was used to determine maximal accumulated oxygen deficit (MAOD). No significant difference was found in ta90% between children and adults. ts90% and TTE were not significantly different between children and adults for the exercises at PΔ50 and PΔ75. However, ts90% and TTE during P100 (p < 0.05 and p < 0.01, respectively) and P110 (p < 0.001) exercises were significantly shorter in children. Children had a significantly lower MAOD than adults (34.3 ± 9.4 ml · kg vs. 53.6 ± 11.1 ml · kg). A positive relationship (p < 0.05) was obtained between MAOD and TTE values during the P100 test in children. This study showed that only for intensities at, or higher than MAP, lower ts90% in children was linked to a reduced TTE, compared to adults. Shorter TTE in children can partly be explained by a lower anaerobic capacity (MAOD). These results give precious information about exercise intensity ranges that could be used in children's training sessions. Moreover, they highlight the implication of both aerobic and anaerobic processes in endurance performances in both populations.

This study was designed to test the hypothesis that subjects having faster oxygen uptake (VO(2)) kinetics during off-transients to exercises of severe intensity would obtain the smallest decrement score during a repeated sprint test. Twelve male soccer players completed a graded test, two severe-intensity exercises, followed by 6 min of passive recovery, and a repeated sprint test, consisting of seven 30-m sprints alternating with 20 s of active recovery. The relative decrease in score during the repeated sprint test was positively correlated with time constants of the primary phase for the VO(2) off-kinetics (r = 0.85; p < 0.001) and negatively correlated with the VO(2) peak (r = -0.83; p < 0.001). These results strengthen the link found between VO(2) kinetics and the ability to maintain sprint performance during repeated sprints.

This study examines the effect of prior heavy exercise on the spatial distribution of muscle deoxygenation kinetics at the onset of heavy-intensity cycling exercise. Young untrained male adults (n = 16) performed two consecutive bouts of 6 min of high intensity cycle exercise separated by 6 min at 35 W. Muscle deoxygenation (HHb) was monitored continuously by near-infrared spectroscopy at eight sites in the quadriceps. Prior heavy exercise reduced the delay before the increase in HHb (9 +/- 2 vs. 5 +/- 2 s; P < 0.001). The standard deviation of TD HHb of the eight sites was decreased by the performance of prior exercise (1.1 +/- 0.5 vs. 0.8 +/- 0.4 s; P < 0.05). The transient decrease in HHb during the first 10 s of exercise was less during the second bout than during the first bout (0.6 +/- 0.6 vs. 0.3 +/- 0.3 A.U.; P < 0.01). The standard deviation of this decrease was also reduced by prior exercise (0.5 +/- 0.3 vs. 0.3 +/- 0.2 A.U.; P < 0.01). Lastly, prior exercise decreased significantly the standard deviation of the HHb rise during the time period corresponding to the pulmonary VO(2) slow component. These results indicate that prior heavy exercise reduced the spatial heterogeneity of muscle deoxygenation kinetics at the early onset of heavy exercise and during the development of the pulmonary VO(2) slow component. It indicates that the distribution of the VO(2)/O(2) delivery ratio within muscle was improved by the performance of a prior exercise.

In this study, we examined the effects of three recovery intensities on time spent at a high percentage of maximal oxygen uptake (t90[Vdot]O(2max)) during a short intermittent session. Eight endurance-trained male adolescents (16 +/- 1 years) performed four field tests until exhaustion: a graded test to determine maximal oxygen uptake ([Vdot]O(2max); 57.4 +/- 6.1 ml x min(-1) . kg(-1)) and maximal aerobic velocity (17.9 +/- 0.4 km x h(-1)), and three intermittent exercises consisting of repeat 30-s runs at 105% of maximal aerobic velocity alternating with 30 s active recovery at 50% (IE(50)), 67% (IE(67)), and 84% (IE(84)) of maximal aerobic velocity. In absolute values, mean t90[Vdot]O(2max) was not significantly different between IE(50) and IE(67), but both values were significantly longer compared with IE(84). When expressed in relative values (as a percentage of time to exhaustion), mean t90[Vdot]O(2max) was significantly higher during IE(67) than during IE(50). Our results show that both 50% and 67% of maximal aerobic velocity of active recovery induced extensive solicitation of the cardiorespiratory system. Our results suggest that the choice of recovery intensity depends on the exercise objective.

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 (VO2max) i.e. above 90% of VO2max (t90VO2max) and above 95% of VO2max (t95VO2max) 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 VO2max (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 t90VO2max and t95VO2max 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), t90VO2max and t95VO2max 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 t90VO2max or t95VO2max 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 VO2max.

The purpose of this study was to apply the "critical velocity" concept to short intermittent high-intensity running exercises in prepubescent girls and boys and to compare the running performances obtained either by intermittent or continuous exercise runs. Eleven 8 to 11-year-old children underwent a maximal graded field test to determine peak oxygen uptake (peakVO2) and maximal aerobic velocity (MAV). During the six following sessions, they randomly performed three continuous runs (90, 100, and 110% of MAV) and three intermittent runs (120, 130, and 140% of MAV) until exhaustion. Intermittent exercises consisted of repeated 15 s runs each one separated by a 15 s passive recovery interval. For continuous as well as intermittent exercises, distance versus time to exhaustion (TTE) relationships were calculated to determine continuous (CVc) and intermittent (CVi) critical velocities. Values for peakVO2 and MAV were 45.8 +/- 5.3 ml x kg(-1) x min(-1) and 10.5 +/- 1.0 km h(-1), respectively. For the whole population, a significant relationship was found between the distance to exhaustion (DTE) and TTE for continuous (r2= 0.99, P < 0.05) and intermittent exercises (r2 = 0.99, P < 0.05). Significant relationships were found between peakVO2 and both CVc (r2= 0.60, P < 0.01) and CVi (r2= 0.47, P < 0.05). In conclusion, as for continuous exercises, a linear relationship was found between DTE and TTE for short high-intensity intermittent exercises. CVc was significantly related to peakVO2, while a significant lower relationship was found between peakVO2 and CVi.

The purpose of this study was to test the hypothesis that subjects having a shorter time constant for the fast component of VO2 kinetics in a transition from rest to constant exercise would maintain their speed for a longer time during repeated sprint exercise (RSE). Eleven male soccer players completed a graded test, two constant exercises at 60% maximal aerobic speed and RSE, consisting of fifteen 40-m sprints alternated with 25 s of active recovery. All the tests were performed on the field (200 m indoor track). The parameters of the VO2 kinetics (time delay, time constant, and amplitude of the primary phase) during the two constant exercises were modeled. All subjects elicited VO2 during the RSE. A significant correlation was found between VO2 and the relative decrease in speed during the 15 sprints (r=0.71; p < 0.05), but not between VO2 and the cumulated time for the 15 sprints (r=0.48; p > 0.05). There were significant correlations between the time constant of the primary phase and the relative decrease in speed during the 15 sprints (r=0.80; p < 0.01) and the cumulated time for the 15 sprints (r=0.80; p < 0.01). These results suggest that individuals with faster VO2 kinetics during constant load exercise might also have a faster adjustment of VO2 during RSE leading to a shorter cumulated time and a lower relative decrease in speed during the 15 sprints.

The purpose of this study was to compare the effects of recovery type (active vs. passive) on the time spent at VO(2)max and above 90 % of VO(2)max during short intermittent runs (15 s) at 120 % of maximal aerobic speed. Twelve male subjects performed a graded test and intermittent runs (15 s) alternated with 15 s of active recovery (50 % of maximal aerobic speed) or with 15 s of passive recovery to exhaustion. The time to exhaustion during the intermittent runs with active recovery (445 +/- 79 s) was significantly shorter (p < 0.001) compared with passive recovery (745 +/- 171 s). No significant difference was found between time spent at VO(2)max and above 90 % of VO(2)max for intermittent runs alternated with active recovery (180 +/- 121 s and 282 +/- 117 s, respectively ) and intermittent runs alternated with passive recovery (191 +/- 135 s and 317 +/- 132 s, respectively ). The times spent at VO(2)max (p < 0.05) and above 90 % of VO(2)max (p < 0.001), expressed in percentage of time to exhaustion, were significantly longer for intermittent runs alternated with active recovery (41 +/- 27 % and 64 +/- 24 %, respectively) than with passive recovery (25 +/- 16 % and 43 +/- 16%, respectively). In conclusion, the present study has shown that the time to exhaustion during repeated high-intensity exercise was significantly greater for passive compared with active recovery, despite no difference in absolute time spent at a high percentage of VO(2)max. However, the time spent at a high percentage of VO(2)max, expressed as a percentage of time to exhaustion, was significantly higher for active compared with passive recovery.

The aim of this study was to investigate the development of exercise-induced hypoxemia (EIH defined as an exercise decrease > 4 % in oxygen arterial saturation, i. e. SaO (2) measured with a portable pulse oximeter) in twelve sportsmen and ten sportswomen (18.5 +/- 0.5 years) who were non-elite and not initially engaged in endurance sport or training. They followed a high-intensity interval-training program to improve V.O (2)max for eight weeks. The training running speeds were set at approximately 140 % V.O (2)max running speed up to 100 % 20-m maximal running speed. Pre- and post-training pulmonary gas exchanges and SaO (2) were measured during an incremental running field-test. After the training period, men and women increased their V.O (2)max (p < 0.001) by 10.0 % and 7.8 %, respectively. Nine subjects (seven men and two women) developed EIH. This phenomenon appeared even in sportsmen with low V.O (2)max from 45 ml x min (-1) x kg (-1) and seemed to be associated with inadequate hyperventilation induced by training: because only this hypoxemic group showed 1) a decrease in maximal ventilatory equivalent in O (2) (V.E/V.O (2), p < 0.01) although maximal ventilation increased (p < 0.01) with training, i. e. in EIH-subjects the ventilatory response increased less than the metabolic demand after the training program; 2) a significant relationship between SaO (2) at maximal workload and the matched V.E/V.O (2) (p < 0.05, r = 0.67) which strengthened a relative hypoventilation implication in EIH. In conclusion, in this field investigation the significant decrease in the minimum SaO (2) inducing the development of EIH after high-intensity interval-training indicates that changes in training conditions could be accompanied in approximately 40 % non-endurance sportive subjects by alterations in the degree of arterial oxyhemoglobin desaturation developing during exercise.

This study was designed to propose a standardised procedure to determine the time spent at VO2max (tVO2max) based on the VO2max of the day (i. e. the VO2max value measured the day of the test). Ten male subjects first performed a graded field test, followed by a continuous running exercise to exhaustion, at the velocity of the Université de Montréal Track Test (V(UMTT)) plus 1 km x h(-1) (V(UMTT)(+1)). The second test consisted of an exhaustive run at 100 % of V(UMTT), followed by a V(UMTT)(+1) test. Different methods were used to compare time spent at VO2max, based on the VO2max of the graded field test, and time spent at VO2max, based on the VO2max of the day, during an exhaustive run at 100 % of V(UMTT). Results have shown that V(UMTT)(+1) tests were of sufficient intensity and duration to identify the VO2max of the day. Time spent at VO2max ranged from 25 +/- 53 s to 139 +/- 76 s according to the method used. However, the tVO2max method based on the sum of each value higher than 95 % of VO2max of the day appeared more robust than methods based on the time to exhaustion minus time to reach VO2 reference value, or the method based on the sum of values higher than VO2max minus 2.1 ml x kg(-1) x min(-1).

This study was designed to examine peak VO(2) responses of prepubescent children following a 7-week aerobic training. Twenty-three boys and thirty girls (9.7 +/- 0.8 years) were divided into a high intensity experimental group (HIEG: 20 girls and 13 boys) and a control group (CG: 10 girls and 10 boys). A graded 20-m shuttle run with measurement of gas exchange values was performed prior to and after the 7-week training program. The test consisted of a 3-min run at 7 km x h(-1) to determine energy cost of running, immediately followed by a 20-meter shuttle run test. HIEG had two 30 min-sessions of short intermittent aerobic training per week at velocities ranging from 100 up to 130 % of the maximal aerobic speed. For HIEG, absolute peak VO(2)(9.1 %) and relative to body mass peak VO(2)(8.2 %) increased significantly (p < 0.001); it was unchanged in the CG. Similarly, maximal shuttle run improved significantly in HIEG (5.1 %, p < 0.001). In contrast, there was no significant change for CG. For both groups energy cost of running remained unchanged. These findings show that prepubescent children could significantly increase their peak VO(2) and maximal shuttle velocity with high intensity short intermittent aerobic exercises.

This study was designed to determine the intermittent critical velocity, the time spent at maximal oxygen uptake (VO2max) and the time spent above 90% of VO2max for short intermittent runs of 15 s at supramaximal velocities, alternating with 15 s of passive recovery. Nine male subjects performed 5 field-tests to exhaustion (tlim): 4 intermittent runs at 110%, 120%, 130% and 140% of maximal aerobic speed (MAS) and 1 continuous run at 100% of MAS. Results have shown the mean intermittent critical velocity (4.82 +/- 0.41 m.s-1) was not significantly different from MAS (4.63 +/- 0.37 m.s-1). Intermittent runs at 110% and 120% of MAS and the continuous run at 100% of MAS lead all subjects to reach VO2max. However, intermittent runs at 120% of MAS (202 +/- 66 s) allowed subjects to spend a significantly longer time at VO2max (p < .05) than intermittent runs at 110% (116 +/- 42 s), 130% (50 +/- 47 s), 140% (48 +/- 59 s) of MAS and continuous run at 100% of MAS (120 +/- 42 s). The time spent between 90 and 100% of VO2max was significantly longer (p < .05) for intermittent runs at 110% (383 +/- 180 s) and for 120% (323 +/- 272 s) of MAS than for intermittent runs at 130% (135 +/- 133 s), 140% of MAS (77 +/- 96 s) and for continuous run at 100% of MAS (217 +/- 114 s). Consequently, this kind of intermittent exercise with intensities from intermittent critical velocity to 120% of MAS could be introduced in a training program when the purpose is to increase VO2max.

The aim of the present study was to explain the inter-individual variability in running time to exhaustion (tlim) when running speed was expressed as a percentage of the velocity, associated with maximal oxygen uptake (vVO2max). Indeed for the same percentage of vVO2max the anaerobic contribution to energy supply is different and could be dependent on the critical velocity (Cv) and also on the maximal running velocity (vmax). Ten subjects ran four tlim at 90, 100, 120, and 140% of vVO2max; mean and standard deviation for tlim were 839 +/- 236 s, 357 +/- 110 s, 122 +/- 27 s, and 65 +/- 17s, respectively. Each velocity was then expressed 1) as a percentage of the difference between vVO2max and Cv (%AeSR); 2) as a percentage of the difference between vmax and Cv (%MSR); 3) as a percentage of the difference between vmax and vVO2max (%AnSR). Highest correlations were found between tlim90 and tlim100 and velocity expressed as %MSR (r = -0.82, p < 0.01 and r = -0.75, p < 0.01), and between tlim120 and tlim140 and velocity expressed as %AnSR (r = -0.83, p < 0.01 and r = -0.94, p < 0.001). These results show that the same intensity relative to aerobic contribution did not represent the same absolute intensity for all and could partly explain variability in tlim. Therefore expressing intensity as a percentage of MSR for sub-maximal and maximal velocities and as a percentage of AnSR for supra-maximal velocities allows individual differences in anaerobic work capacity to be taken into account and running times to exhaustion to be predicted accurately.

The purpose of this study was to characterise the relationship between running velocity and the time for which a subject can run at maximal oxygen uptake (VO2max), (tlimVO2max). Seven physical education students ran in an incremental test (3-min stages) to determine VO2max and the minimal velocity at which it was elicited (vVO2max). They then performed four all-out running tests on a 200-m indoor track every 2 days in random order. The mean times to exhaustion tlim at 90%, 100%, 120% and 140% vVO2max were 13 min 22 s (SD 4 min 30 s), 5 min 47 s (SD 1 min 50 s), 2 min 11 s (SD 38 s) and 1 min 12 s (SD 18 s), respectively. Five subjects did not reach VO2max in the 90% vVO2max test. All the subjects reached VO2max in the runs at 100% vVO2max. All the subjects, except one, reached VO2max in the runs at 120% vVO2max. Four subjects did not reach VO2max in the 140% vVO2max test. Time to achieve VO2max was always about 50% of the time to exhaustion irrespective of the intensity. The time to exhaustion-velocity relationship was better fitted by a 3- than by a 2-parameter critical power model for running at 90%, 100%, 120%, 140% vVO2max as determined in the previous incremental test. In conclusion, tlimVO2max depended on a balance between the time to attain VO2max and the time to exhaustion tlim. The time to reach VO2max decreased as velocity increased. The tlimVO2max was a bi-phasic function of velocity, with a peak at 100% vVO2max.

The so-called velocity associated with VO2max, defined as the minimal velocity which elicits VO2max in an incremental exercise protocol (v(VO2max)), is currently used for training to improve VO2max. However, it is well known that it is not the sole velocity which elicits VO2max and it is possible to achieve VO2max at velocities lower and higher than v(VO2max). The goal of this study was to determine the velocity which allows exercise to be maintained the longest time at v(VO2max). Using the relationship between time to exhaustion at VO2max in the all-out runs at 90%, 100%, 120% and 140% of v(VO2max) and distance run at VO2max, the velocity which elicits the longest time to exhaustion at VO2max (CV') was determined. For the six subjects tested (physical education students), this velocity was not significantly different from v(VO2max) (16.96+/-0.92 km x h(-1) vs 17.22+/-1.12 km x h(-1), P = 0.2 for CV' and v(VO2max), respectively) and these two velocities were correlated (r = 0.88, P = 0.05).

Background: The purpose of the study was to test the ability to determine the velocity associated with peak oxygen uptake for adolescents by means of a simple field test, the Université de Montréal Track Test (UMTT)., Methods: Fifteen adolescents, 13.4 +/- 1.0 years, performed two maximal field tests where oxygen uptake and heart rate were continuously monitored. The first test (graded field test, first stage 8 km.h-1, increment 1.5 km.h-1, duration 3 min) allowed the subjects to reach a steady-state oxygen uptake. Then, the velocity associated with peak oxygen uptake was calculated from the ratio between peak oxygen uptake above resting level to energy cost of running. The calculated velocity was kept as the criterion velocity. For the second test (UMTT, first stage 8 km.h-1; increment 1 km.h-1; duration 2 min), the velocity measured at the last completed stage was retained., Results: The measured peak oxygen uptake for the graded field test (51.8 +/- 6.5 ml.kg-1.min-1) and for the UMTT (51.0 +/- 7.9 ml.kg-1.min-1) were not significantly different. The calculated velocity (12.9 +/- 1.0 km.h-1) and the measured velocity (12.7 +/- 0.9 km.h-1) were not significantly different and were significantly correlated (r = 0.80, p < 0.001)., Conclusions: It was concluded that, for adolescents, the velocity measured at the last completed stage of the UMTT allows a valid estimation of the velocity associated with peak oxygen uptake.

During 20 m shuttle tests, obese adolescents may have difficulty achieving maximum cardiorespiratory performance due to the presence of braking-relaunch phases (BRP). Nineteen obese adolescents aged 15.2 ± 1.5 years (body mass index [BMI] = 39.7 ± 5.9 kg.m−2) performed three graded walking exercises on a 50 m track at speeds between 3 and 6 km/h: a continuous-straight-line protocol (C), a continuous protocol that required turning back every 30 sec (C-BRP) and an intermittent protocol that consisted of successively walking then resting for 15 sec (15–15). Oxygen uptake (VO2), aerobic cost of walking (Cw), ventilation (VE) and rating of perceived exertion (RPE) were measured at each stage during the protocols. During C-BRP, the responses were not significantly higher compared with C (p > 0.30). During 15–15, the VO2, Cw and VE were ~ 15 to 25% lower than during C beginning at 4 km/h (p < 0.05). In obese adolescents, the respiratory impact of sudden directional changes during the 20 m shuttle-type test appeared to be minor at walking speeds. During the 15–15 test, the intensity increases more progressively, and this design may encourage obese adolescents to walk further than during a continuous test. [ABSTRACT FROM AUTHOR]

Type 1 diabetes (T1D) can have a significant impact on brain function, mostly ascribed to episodes of hypoglycemia and chronic hyperglycemia. Exercise has positive effects on acute and chronic glycemic control in T1 D, and has beneficial effects on cognitive function by increasing neurotrophins such as BDNF and IGF-I in non-diabetic humans. The present study examines the effects of different types of exercise intensities on neurotrophins in T1D. 10 participants with type 1 diabetes were evaluated in 3 sessions: high-intensity exercise (10x[60s 90%Wmax, 60s 50W]), continuous exercise (22min, 70% VO2 max) and a control session. Blood glucose, serum free insulin, serum BDNF and IGF-I were assessed pre/post all the trials and after recovery. Blood glucose significantly decreased after both exercise intensities and BDNF levels increased, with a dose-response effect for exercise intensity on BDNF. IGF-I changed over time, but without a difference between the different exercise protocols. Both exercise intensities change neurotrophins in T1 D, but also exhibit a dose response effect for BDNF. The intensity-dependent findings may aid in designing exercise prescriptions for maintaining or improving neurological health in T1D, but both types of exercise can be implemented. [ABSTRACT FROM AUTHOR]