title: Cardiopulmonary, blood metabolite and rating of perceived exertion responses to constant exercises performed at different intensities until exhaustion.
abstract: OBJECTIVE
  This study analysed cardiopulmonary, metabolic and rating of perceived exertion (RPE) responses during exercise bouts performed below, at and above the second lactate threshold (LT2) intensity.
  
  
  METHODS
  10 healthy men performed constant workloads to exhaustion at the first lactate threshold (LT1), LT2 and 25% of the difference between LT2 and maximal aerobic power output (TW(25%)) identified during an incremental test. The time to exhaustion (TE) was 93.8 (18.0), 44.5 (16.0) and 22.8 (10.6) min at LT1, LT2 and TW(25%), respectively (p < 0.001). Metabolic and cardiopulmonary parameters and RPE data were time normalised to the exercise bout duration. The correlation between the slope of these variables and TE was calculated.
  
  
  RESULTS
  Differences were found for respiratory exchange ratio (RER), RPE and potassium at LT1; RER, RPE, norepinephrine and potassium at LT2; and ventilation, respiratory rate (RR), RPE, lactate and potassium at TW(25%). Except for RR, no cardiopulmonary or metabolic parameter increased significantly after 50% of the exercise duration, indicating a physiological steady state. VO₂, heart rate and lactate at exhaustion in all exercise bouts were significantly lower than values reached in the maximal incremental test. The slope of most metabolic variables was not correlated to TE in LT1, LT2 and TW(25%), whereas the slope of RPE was significantly correlated to TE (r = -0.72 to -0.84; p < 0.05) for the three exercise intensities.
  
  
  CONCLUSIONS
  Contrary to traditional suggestions, exercise at LT1, LT2 and TW(25%) intensities is performed and terminated in the presence of an overall physiological steady state.
authors.affiliation: Department of Sports, School of Physical Education and Sport, University of São Paulo, São Paulo, Brazil. piresfo@usp.br
authors.forename: Flávio O
authors.initials: FO
authors.lastname: Pires
authors.forename: Timothy D
authors.initials: TD
authors.lastname: Noakes
authors.forename: Adriano E
authors.initials: AE
authors.lastname: Lima-Silva
authors.forename: R
authors.initials: R
authors.lastname: Bertuzzi
authors.forename: Carlos
authors.initials: C
authors.lastname: Ugrinowitsch
authors.forename: Fabio S
authors.initials: FS
authors.lastname: Lira
authors.forename: Maria Augusta P D M
authors.initials: MA
authors.lastname: Kiss
mesh_terms: D000328:Adult; D004734:Energy Metabolism / Q000502:physiology; D015444:Exercise / Q000502:physiology* / Q000523:psychology; D017079:Exercise Tolerance / Q000502:physiology*; D005221:Fatigue / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D010101:Oxygen Consumption / Q000502:physiology; D010465:Perception; D005082:Physical Exertion / Q000502:physiology; D011188:Potassium / Q000378:metabolism; D011659:Pulmonary Gas Exchange / Q000502:physiology; D056152:Respiratory Rate / Q000502:physiology; D055815:Young Adult
chemical_list: D019344:Lactic Acid; D011188:Potassium; D009638:Norepinephrine