***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 purpose of this study was to test the hypothesis that athletes having a slower oxygen uptake ( V̇O2 ) kinetics would benefit more , in terms of time spent near V̇O2max , from an increase in the intensity of an intermittent running training ( IT ) . After determination of V̇O2max , vV̇O2max ( i.e. the minimal velocity associated with V̇O2max in an incremental test ) and the time to exhaustion sustained at vV̇O2max ( Tlim ) , seven well-trained triathletes performed in r and om order two IT sessions . The two IT comprised 30-s work intervals at either 100 % ( IT100 % ) or 105 % ( IT105 % ) of vV̇O2max with 30-s recovery intervals at 50 % of vV̇O2max between each repeat . The parameters of the V̇O2 kinetics ( td1 , τ1 , A1 , td2 , τ2 , A2 , i.e. time delay , time constant and amplitude of the primary phase and slow component , respectively ) during the Tlim test were modelled with two exponential functions . The highest V̇O2 reached was significantly lower ( P<0.01 ) in IT100 % run at 19.8 ( 0.9 ) km.h−1 [ 66.2 ( 4.6 ) ml.min−1.kg−1 ] than in IT105 % run at 20.8 ( 1.0 ) km.h−1 [ 71.1 ( 4.9 ) ml.min−1.kg−1 ] or in the incremental test [ 71.2 ( 4.2 ) ml.min−1.kg−1 ] . The time sustained above 90 % of V̇O2max in IT105 % [ 338 ( 149 ) s ] was significantly higher ( P<0.05 ) than in IT100 % [ 168 ( 131 ) s ] . The average Tlim was 244 ( 39 ) s , τ1 was 15.8 ( 5.9 ) s and td2 was 96 ( 13 ) s. τ1 was correlated with the difference in time spent above 90 % of V̇O2max ( r=0.91 ; P<0.01 ) between IT105 % and IT100 % . In conclusion , athletes with a slower V̇O2 kinetics in a vV̇O2max constant-velocity test benefited more from the 5 % rise of IT work intensity , exercising for longer above 90 % of V̇O2max when the IT intensity was increased from 100 to 105 % of vV̇O2max The objective of this study was to analyze the effect of two different high-intensity interval training ( HIT ) programs on selected aerobic physiological indices and 1500 and 5000 m running performance in well-trained runners . The following tests were completed ( n=17 ) : ( i ) incremental treadmill test to determine maximal oxygen uptake ( VO2 max ) , running velocity associated with VO2 max ( vVO2 max ) , and the velocity corresponding to 3.5 mmol/L of blood lactate concentration ( vOBLA ) ; ( ii ) submaximal constant-intensity test to determine running economy ( RE ) ; and ( iii ) 1500 and 5000 m time trials on a 400 m track . Runners were then r and omized into 95 % vVO2 max or 100 % vVO2 max groups , and undertook a 4 week training program consisting of 2 HIT sessions ( performed at 95 % or 100 % vVO2 max , respectively ) and 4 submaximal run sessions per week . Runners were retested on all parameters at the completion of the training program . The VO2 max values were not different after training for both groups . There was a significant increase in post-training vVO2 max , RE , and 1500 m running performance in the 100 % vVO2 max group . The vOBLA and 5000 m running performance were significantly higher after the training period for both groups . We conclude that vOBLA and 5000 m running performance can be significantly improved in well-trained runners using a 4 week training program consisting of 2 HIT sessions ( performed at 95 % or 100 % vVO2 max ) and 4 submaximal run sessions per week . However , the improvement in vVO2 max , RE , and 1500 m running performance seems to be dependent on the HIT program at 100 % vVO2 max Context : A high number of recreational runners sustain a running-related injury each year . To reduce injury risk , alterations in running form have been suggested . One simple strategy for running stride frequency or length has been commonly advocated . Objective : To characterize how running mechanics change when stride frequency and length are manipulated . Data Sources : In January 2012 , a comprehensive search of PubMed , CINAHL Plus , SPORTD iscus , PEDro , and Cochrane was performed independently by 2 review ers . A second search of the data bases was repeated in June 2012 to ensure that no additional studies met the criteria after the initial search . Study Selection : Inclusion criteria for studies were an independent variable including manipulation of stride frequency or length at a constant speed with outcome measures of running kinematics or kinetics . Study Design : Systematic review . Level of Evidence : Level 3 . Data Extraction : Two review ers independently appraised each article using a modified version of the Quality Index , design ed for assessing bias of nonr and omized studies . Results : Ten studies met the criteria for this review . There was consistent evidence that increased stride rate result ed in decreased center of mass vertical excursion , ground reaction force , shock attenuation , and energy absorbed at the hip , knee , and ankle joints .  All but 1 study had a limited number of participants , with several method ological differences existing among studies ( eg , overground and treadmill running , duration of test conditions ) . Although speed was held constant during testing , it was individually self-selected or fixed . Most studies used only male participants . Conclusion : Despite procedural differences among studies , an increased stride rate ( reduced stride length ) appears to reduce the magnitude of several key biomechanical factors associated with running injuries The purpose of this study was to examine physiological strain and muscular performance responses of well trained athletes during two intermittent running exercise protocol s at the velocity associated with VO2max . Ten national level middle-distance runners ( VO2max 69.4+/-5.1 ; mean+/-SD ) performed in r and om order  two 28 min treadmill running exercises : 14 bouts of 60 s runs with 60 s rest ( IR60 ) and 7 bouts of 120 s runs with 120 s rest between each run ( IR120 ) . During IR120 peak oxygen uptake ( 12 % ) , peak heart rate ( 3 % ) and peak blood lactate ( 79 % ) were significantly higher than during IR60 ( P < 0.001 ) and almost the same as in the VO2max test . In IR120 the relative aerobic energy release calculated on the basis of the accumulated oxygen deficit during the running bouts was significantly higher than in IR60 ( 81.5+/-2.7 vs. 70.2+/-2.6 % , P<0.001 ) likewise the sum oxygen consumption during the 14 min running ( P < 0.001 ) , while during the 14 min recovery it was as much lower ( P < 0.001 ) . There were no changes either during or between the IR60 and IR120 protocol s with regard to the muscular performance parameters , stride length or height of maximal vertical jumps . In conclusion , during intermittent running at the velocity associated with VO2max doubling the duration of work and rest bouts from 60 s to 120s increased the physiological strain of well trained athletes to the same level as at exhaustion in the VO2max test but the muscular performance variables were not influenced PURPOSE To quantify the relationship between total training load and running performance during the most important competitions of the season ( national cross-country championships , 4.175- and 10.130-km races ) . METHODS Eight well-trained , subelite endurance runners ( age ( mean+/-SD ) : 23+/-2 yr ; VO2max : 70.0+/-7.3 mL.kg.min ) performed a maximal cardiorespiratory exercise test before the training period to determine ventilatory threshold ( VT ) and respiratory compensation threshold ( RCT ) . Heart rate was continuously recorded using telemetry during each training session over a 6-month macrocycle , design ed to achieve peak performance during the aforementioned cross-country races , lasting from late August to the time that these races were held , that is , mid-February . This allowed us to quantify the total cumulative time spent in three intensity zones calculated as zone 1 ( low intensity , lower than the VT ) ; zone 2 ( moderate intensity , between VT and RCT ) ; and zone 3 ( high intensity , above the RCT ) . RESULTS Total training time in zone 1 ( 4581+/-979 min ) was significantly higher ( P<0.001 ) than that accumulated in zones 2 ( 1354+/-583 min ) and 3 ( 487+/-154 min ) . Total time in zone 2 was significantly higher than time in zone 3 ( P<0.05 ) . A correlation coefficient of r=-0.79 ( P=0.06 ) and r=-0.97 ( P=0.008 ) was found between the total training time spent in zone 1 and performance time during the short and long cross-country races , respectively . CONCLUSIONS Our findings suggest that total training time spent at low intensities might be associated with improved performance during highly intense endurance events , especially if the event duration is approximately 35 min . Interventional studies ( i.e. , improving or reducing training time in zone 1 ) are needed to corroborate our findings and to eluci date the physiological mechanisms behind them Beneficial systemic effects of regular physical exercise have been demonstrated to reduce risks of a number of age-related disorders . Antioxidant capacity adaptations are amongst these fundamental changes in response to exercise training . However , it has been cl aim ed that acute physical exercise performed at high intensity ( > 60 % of maximal oxygen uptake ) may result in oxidative stress , due to reactive oxygen species being generated excessively by enhanced oxygen consumption . The aim of this study was to evaluate the effect of high-intensity discontinuous training ( HIDT ) , characterized by repeated variations of intensity and changes of redox potential , on oxidative damage . Twenty long-distance masters runners ( age 47.8±7.8 yr ) on the basis of the individual values of gas exchange threshold were assigned to a different 8-weeks training program : continuous moderate-intensity training ( MOD , n = 10 ) or HIDT ( n = 10 ) . In both groups before ( PRE ) and after ( POST ) training we examined the following oxidative damage markers : thiobarbituric acid reactive substances ( TBARS ) as marker of lipid peroxidation ; protein carbonyls ( PC ) as marker of protein oxidation ; 8-hydroxy-2-deoxy-guanosine ( 8-OH-dG ) as a biomarker of DNA base modifications ; and total antioxidant capacity ( TAC ) as indicator of the overall antioxidant system . Training induced a significant ( p<0.05 ) decrease in resting plasma TBARS concentration in both MOD ( 7.53±0.30 and 6.46±0.27 µM , PRE and POST respectively ) and HIDT ( 7.21±0.32 and 5.85±0.46 µM , PRE and POST respectively ) . Resting urinary 8-OH-dG levels were significantly decreased in both MOD ( 5.50±0.66 and 4.16±0.40 ng mg−1creatinine , PRE and POST respectively ) and HIDT ( 4.52±0.50 and 3.18±0.34 ng mg−1creatinine , PRE and POST respectively ) . Training both in MOD and HIDT did not significantly modify plasma levels of PC . Resting plasma TAC was reduced in MOD while no significant changes were observed in HIDT . In conclusion , these results suggest that in masters runners high-intensity discontinuous does not cause higher level of exercise-induced oxidative stress than continuous moderate-intensity training , inducing similar beneficial effects on redox homeostasis This study compared running velocity , physiological responses , and perceived exertion during self-paced interval training bouts differing only in work bout duration . Twelve well-trained runners ( nine males , three females , 28+/-5 years , VO2 max 65+/-6 mL min(-1 ) kg(-1 ) ) performed preliminary testing followed by four " high-intensity " interval sessions ( Latin squares , 1 session week(-1 ) over 4 weeks ) consisting of 24 x 1 , 12 x 2 , 6 x 4 , or 4 x 6-min running bouts with a 1:1 work-to-rest interval ( total session duration 48 min ) . The average running velocity decreased ( 93 % , 88 % , 86 % , 84 % vVO2 max , P < 0.01 ) with increasing work duration . Peak VO2 averaged about 92+/-4 % of VO2 max for 2- , 4- , and 6-min intervals compared with only 82+/-5 % for 1-min bouts ( P < 0.001 ) . Six of 12 athletes achieved their highest average VO2 and heart rate during 4-min intervals . The average RPEpeak ( rating scale of perceived exertion ) was approximately 17+/-1 for all four interval sessions . RPE increased by 2 - 4 U during an interval 
    Output:
    
Conclusion HIIT-based running plans ( 2 to 3 HIIT sessions per week , combining HIIT and CR runs ) show athletic performance improvements in endurance runners by improving maximal oxygen uptake and running economy along with muscular and metabolic adaptations .