***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: The effect of hypoxia on the response to interval exercise was determined in eight elite female cyclists during two interval sessions : a sustained 3 x 10-min endurance set ( 5-min recovery ) and a repeat sprint session comprising three sets of 6 x 15-s sprints ( work-to-relief ratios were 1:3 , 1:2 , and 1:1 for the 1st , 2nd , and 3rd sets , respectively , with 3 min between each set ) . During exercise , cyclists selected their maximum power output and breathed either  atmospheric air ( normoxia , 20.93 % O(2 ) ) or  a hypoxic gas mix ( hypoxia , 17.42 % O(2 ) ) . Power output was lower in hypoxia vs. normoxia throughout the endurance set ( 244+/-18 vs. 226+/-17 , 234+/-18 vs. 221+/-25 , and 235+/-18 vs. 221+/-25 W for 1st , 2nd , and 3rd sets , respectively ; P < 0.05 ) but was lower only in the latter stages of the second and third sets of the sprints ( 452+/-56 vs. 429+/-49 and 403+/-54 vs. 373+/- 43 W , respectively ; P<0.05 ) . Hypoxia lowered blood O(2 ) saturation during the endurance set ( 92.9+/-2.9 vs. 95.4+/-1.5 % ; P<0.05 ) but not during repeat sprints . We conclude that , when elite cyclists select their maximum exercise intensity , both sustained ( 10 min ) and short-term ( 15 s ) power are impaired during hypoxia , which simulated moderate ( approximately 2,100 m ) altitude PURPOSE Lower barometric air pressure at altitude can affect competitive performance of athletes in some sports . Reported here are the effects of various altitudes on elite track- and -field athletes ' performance . METHODS Lifetime track- and -field performances of athletes placed in the top 16 in at least 1 major international competition between 2000 and 2009 were downloaded from the data base at tilastopaja.org . There were 132,104 performances of 1889 athletes at 794 venues . Performances were log-transformed and analyzed using a mixed linear model with fixed effects for 6 levels of altitude and r and om quadratic effects to adjust for athlete age . RESULTS Men 's and women 's sprint events ( 100 - 400 m ) showed marginal improvements of ~0.2 % at altitudes of 500 - 999 m , and above 1500 m all but the 100- and 110-m hurdles showed substantial improvements of 0.3 - 0.7 % . Some middle- and long-distance events ( 800 - 10,000 m ) showed marginal impairments at altitudes above 150 m , but above 1000 m the impairments increased dramatically to ~2 - 4 % for events > 800 m. There was no consistent trend in the effects of altitude on field events up to 1000 m ; above 1000 m , hammer throw showed a marginal improvement of ~1 % and discus was impaired by 1 - 2 % . Above 1500 m , triple jump and long jump showed marginal improvements of ~1 % . CONCLUSIONS In middle- and long-distance runners , altitudes as low as 150 to 299 m can impair performance . Higher altitudes ( ≥1000 m ) are generally required before decreases in discus performance or enhancements in sprinting , triple and long jump , or hammer throw are seen Purpose To investigate the interaction between the development of peripheral locomotor muscle fatigue , muscle recruitment and performance during repeated-sprint exercise ( RSE ) . Method In a single-blind , r and omised and cross-over design , ten male team-sport athletes performed two RSE ( fifteen 5-s cycling sprints interspersed with 25 s of rest ; power self-selected ) in normoxia and in acute moderate hypoxia ( FIO2 0.138 ) . Mechanical work , total electromyographic intensity ( summed quadriceps electromyograms , RMSsum ) and muscle ( vastus lateralis ) and pre-fontal cortex near-infrared spectroscopy ( NIRS ) parameters were calculated for every sprint . Blood lactate concentration ( [ Lac- ] ) was measured throughout the protocol . Peripheral quadriceps fatigue was assessed via changes in potentiated quadriceps twitch force ( ΔQtw , pot ) pre- versus post-exercise in response to supra-maximal magnetic femoral nerve stimulation . The central activation ratio ( QCAR ) was used to quantify completeness of quadriceps activation . Results Compared with normoxia , hypoxia reduced arterial oxygen saturation ( -13.7 % , P=0.001 ) , quadriceps RMSsum ( -13.7 % , P=0.022 ) , QCAR ( -3.3 % , P=0.041 ) and total mechanical work ( -8.3 % , P=0.019 ) . However , the magnitude of quadriceps fatigue induced by RSE was similar in the two conditions ( ΔQtw , pot : -53.5 % and -55.1 % , P=0.71 ) . The lower cycling performance in hypoxia occurred despite similar metabolic ( muscle NIRS parameters and blood [ Lac- ] ) and functional ( twitch and M-wave ) muscle states . Conclusion Results suggest that the central nervous system regulates quadriceps muscle recruitment and , thereby , performance to limit the development of muscle fatigue during intermittent , short sprints . This finding highlights the complex interaction between muscular perturbations and neural adjustments during sprint exercise , and further supports the presence of pacing during intermittent sprint exercise PURPOSE To underst and the role of O2 utilization in the sex differences of fatigue during intermittent activity , we compared the cerebral ( prefrontal lobe ) and muscle ( vastus lateralis ) oxygenation of men and women during repeated-sprint exercise ( RSE ) . METHODS Ten men and 10 women matched for initial-sprint mechanical work performed ten , 10 s cycle sprints ( with 30 s of rest ) under normoxic ( NM : 21 % FIO2 ) and acute hypoxic ( HY : 13 % FIO2 ) conditions  in a r and omized single-blind and crossover design . Mechanical work was calculated and  arterial O2 saturation ( SpO2 )  was estimated via pulse oximetry during every sprint . Cerebral and muscle oxy- ( O2Hb ) and deoxy-hemoglobin ( HHb ) were monitored continuously by near-infrared spectroscopy . RESULTS Compared with NM , work decrement was accentuated ( P = 0.01 ) in HY for both men ( -16.4 ± 10.3 % ) and women ( -16.8 ± 9.0 % ) . This was associated with lower SpO2 and lower cerebral Δ[O2Hb ] in both sexes ( -13.6 ± 7.5 % , P = .008 , and -134.5 ± 73.8 % , P = .003 , respectively ) . These HY-induced changes were nearly identical in these men and women matched for initial-sprint work . Muscle Δ[HHb ] increased 9-fold ( P = .009 ) and 5-fold ( P = .02 ) in men and women , respectively , and plateaued . This muscle deoxygenation was not exacerbated in HY . CONCLUSIONS Results indicate that men and women matched for initial-sprint work experience similar levels of fatigue and systemic , cerebral , and peripheral adjustments during RSE performed in NM and HY . These data suggest that cerebral deoxygenation imposes a limitation to repeated-sprint performance The study examined the influence of cerebral ( prefrontal cortex ) and muscle ( vastus lateralis ) oxygenation on the ability to perform repeated , cycling sprints . Thirteen team-sport athletes performed ten , 10-s sprints  ( with 30 s of rest ) under normoxic ( FIO2 0.21 ) and acute hypoxic ( FIO2 0.13 ) conditions  in a r and omised , single-blind fashion and crossover design . Mechanical work was calculated and arterial O2 saturation ( SpO2 ) was estimated via pulse oximetry for every sprint . Cerebral and muscle oxy-(O2Hb ) , deoxy-(HHb ) , and total haemoglobin ( THb ) were monitored continuously by near-infrared spectroscopy . Compared with normoxia , hypoxia induced larger decrements in SpO2 and work ( 11.6 and 7.6 % , respectively ; P < 0.05 ) . In the muscle , we observed a fairly constant level of deoxygenation across sprints , with no effect of the condition . In normoxia , regional cerebral oxygenation increased during the first two sprints and slightly fluctuated thereafter . In contrast , this initial cerebral hyper-oxygenation was attenuated in hypoxia . Changes in [ O2Hb ] and [ HHb ] occurred earlier and were larger in hypoxia compared with normoxia ( P < 0.05 ) , while regional blood volume ( Δ[THb ] ) remained unaffected by the condition . Changes in cerebral [ HHb ] and mechanical work were strongly correlated in normoxia and hypoxia ( R2 = 0.81 and R2 = 0.85 , respectively ; P < 0.05 ) , although the slope of this relationship differed ( normoxia , −351.3 ± 183.3 vs. hypoxia , −442.4 ± 227.2 ; P < 0.05 ) . The results of this NIRS study show that O2 availability influences prefrontal cortex , but not muscle , oxygenation during repeated , short sprints . By using a hypoxia paradigm , the study suggests that cerebral oxygenation contributes to the impairment of repeated-sprint ability Athletes regularly compete at 2,000–3,000 m altitude where peak oxygen consumption $ $ ( \dot{V}\hbox{\rm O}_{2{\rm peak}})$$ declines ∼10–20 % . Factors other than $ $ \dot{V}\hbox{\rm O}_{2{\rm peak}}$$ including gross efficiency ( GE ) , power output , and pacing are all important for cycling performance . It is therefore imperative to underst and how all these factors and not just $ $ \dot{V}\hbox{\rm O}_{2{\rm peak}}$$ are affected by acute hypobaric hypoxia to select athletes who can compete successfully at these altitudes . Ten well-trained , non-altitude-acclimatised male cyclists and triathletes completed cycling tests at four simulated altitudes ( 200 , 1,200 , 2,200 , 3,200 m ) in a r and omised , counter-balanced order . The exercise protocol comprised 5 × 5-min submaximal efforts ( 50 , 100 , 150 , 200 and 250 W ) to determine submaximal $ $ \dot{V}\hbox{\rm O}_{2}$$ and GE and , after 10-min rest , a 5-min maximal time-trial ( 5-minTT ) to determine $ $ \dot{V}\hbox{\rm O}_{2{\rm peak}}$$ and mean power output ( 5-minTTpower ) . $ $ \dot{V}\hbox{\rm O}_{2{\rm peak}}$$ declined 8.2 ± 2.0 , 13.9 ± 2.9 and 22.5 ± 3.8 % at 1,200 , 2,200 and 3,200 m compared with 200 m , respectively , P < 0.05 . The corresponding decreases in 5-minTTpower were 5.8 ± 2.9 , 10.3 ± 4.3 and 19.8 ± 3.5 % ( P < 0.05 ) . GE during the 5-minTT was not different across the four altitudes . There was no change in submaximal $ $ \dot{V}\hbox{\rm O}_{2}$$ at any of the simulated altitudes , however , submaximal efficiency decreased at 3,200 m compared with both 200 and 1,200 m. Despite substantially reduced power at simulated altitude , there was no difference in pacing at the four altitudes for athletes whose first trial was at 200 or 1,200 m ; whereas athletes whose first trial was at 2,200 or 3,200 m tended to mis-pace that effort . In conclusion , during the 5-minTT there was a dose – response effect of hypoxia on both $ $ \dot{V}\hbox{\rm O}_{2{\rm peak}}$$ and 5-minTTpower but no effect on GE The present study examined the effect of oxygen fraction in inspired air ( FIO2 ) on exercise performance and maximum oxygen consumption ( VO2max ) .  Six national level male rowers exercised three 2500-m all-out tests on a Concept II rowing ergometer . Each subject performed one test in normoxia ( FIO2 20.9 % ) , one in simulated hyperoxia ( FIO2 62.2 % ) and one in simulated hypoxia ( FIO2 15.8 % ) in a r and om 
    Output:
    
TT ( −16.2 ± 4.3 % ; 95 % CI −22.9 % to −9 % ) and TTE ( −44.5 ± 6.9 % ; 95 % CI −51.3 % to −36.7 % ) elicited a negative effect , whilst indicating a quadratic relationship between hypoxic magnitude and both TTE and TT performance .
Furthermore , exercise less than 2 min exhibited no ergolytic effect from acute hypoxia .
Summary / Conclusion : This review highlights the ergolytic effect of acute hypoxic exposure , which is curvilinear for TTE and TT performance with increasing hypoxic levels , but short duration intermittent and sprint exercise seem to be unaffected