Heart rate at lactate threshold and cycling time trials

Area of Science:

• Exercise Physiology
• Sports Science
• Cardiovascular Research

Background:

• Assessing exercise intensity is crucial for training and performance.
• Lactate threshold and heart rate (HR) are common physiological markers.
• Different methods exist to determine lactate threshold, yielding varied results.

Purpose of the Study:

• To correlate heart rate and lactate responses during simulated cycling time trials (TT) with incremental laboratory tests.
• To evaluate the predictability of laboratory-derived thresholds for maximal effort cycling durations.
• To compare physiological responses between 30-minute and 60-minute maximal cycling efforts.

Main Methods:

• Ten subjects underwent incremental tests to determine maximal oxygen uptake (VO2max) and lactate threshold (LT) using lactate deflection point (LaT), onset of blood lactate accumulation (OBLA), and Dmax methods.
• Subjects then performed 30-minute (30TT) and 60-minute (60TT) maximal cycling time trials, with measurements of lactate, HR, and perceived exertion (RPE).
• Statistical analyses, including correlations, were used to compare methods and trial conditions.

Main Results:

• Lactate threshold power output and HR were significantly lower for LaT compared to OBLA and Dmax.
• The 30TT elicited significantly higher lactate levels, %HRmax, and RPE than the 60TT.
• VO2 was similar between TTs, but VO2CO2, ventilation, and respiratory exchange ratio were higher during the 30TT.
• Significant correlations were found between HR at threshold methods and the 60TT, but not the 30TT.
• HR was consistently ~90% of maximum for 30TT and ~85% for 60TT, approximating OBLA/Dmax and LaT, respectively.

Conclusions:

• Heart rate during 30-minute and 60-minute cycling time trials can be approximated by specific lactate threshold measures determined in laboratory settings.
• The 30-minute time trial represents a higher relative intensity than the 60-minute time trial, indicated by higher HR and lactate.
• Different lactate threshold determination methods provide varying results, with OBLA and Dmax being more representative of higher intensity efforts like the 30TT.