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Original articles  EXERCISE PHYSIOLOGY AND BIOMECHANICS


The Journal of Sports Medicine and Physical Fitness 2002 Dicembre;42(3):396-402

lingua: Inglese

Physiological variables at lactate threshold under-represent cycling time-trial intensity

Kenefick R. W., Mattern C. O., Mahood N. V., Quinn T. J.

Uni­ver­sity of New Hamp­shire Depart­ment of Kin­e­sio­logy Exer­cise Phys­iology Labor­a­tory Durham, New Hamp­shire, USA


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Back­ground. The impor­tance of lac­tate ­threshold (LT) as a deter­mi­nant of per­for­mance in endu­rance ­sports has ­been estab­lished. In addi­tion, it has ­been ­shown ­that ­during run­ning and ­selected ­other endu­rance com­pe­ti­tions, ath­letes per­form at a ­velocity and VO2 ­slightly ­above LT for the dura­tion of the ­event. ­Prior ­work indi­cates how­ever, ­that ­this may not be ­true ­during a ­cycling ­time-­trial (TT). ­This inves­ti­ga­tion ­sought to com­pare phys­io­log­ical var­i­ables ­during a 20-k TT ­with ­those cor­re­sponding to the ­athlete’s LT.
­Methods. Thir­teen ­male ­cyclists (22.7±0.8 yrs; 180.6±8.0 cm; 77.1±10.0 kg; 8.3±2.5% fat; 4.9±2.2 l·min-1, VO2max) par­tic­i­pated in the ­study. Sub­jects per­formed a ­graded pro­tocol ­starting at 150 ­Watts (W) to deter­mine LT (2 ­mmol·L-1 ­above base­line) ­which con­sisted of 20 W ­increases ­every 4-min. Fol­lowing an 8 min-­recovery, sub­jects ­cycled at the ­wattage cor­re­sponding to LT-20 W for 1 min and ­then work­load ­increased 20 W ­every ­minute ­until voli­tional exhaus­tion to deter­mine VO2max. On a sep­arate occa­sion a ­self-­paced, 20-k TT was com­pleted.
­Results. ­Mean ­values of ­blood lac­tate, HR and % ­HRmax, VO2 and % VO2max, and ­power ­output ­throughout the 20-k TT ­were ­greater (p<0.01) ­than ­those at LT. ­During the TT ­these ­cyclists per­formed at an inten­sity ­well ­above LT (­blood lac­tate=252.0±0.1%, HR=9.4±0.03%, %­HRmax=9.2±0.15%, VO2=26.5±0.7%, %VO2max=17.2±0.08% and ­power ­out-put=14.8±0.14% ­above LT) for ­over 30 min.
Con­clu­sions. There­fore, ­while LT may be ­highly cor­re­lated to per­for­mance, it may not be rep­re­sen­ta­tive of ­race ­pace for a ­cycling TT, and may be ques­tion­able as a bench­mark ­used to pre­scribe ­training inten­sity for com­pet­i­tive TT-­cycling.

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