JOURNAL OF SPORTS SCIENCE & MEDICINE
EFFECT OF TIME OF DAY ON THE RELATIONSHIP BETWEEN LACTATE AND VENTILATORY THRESHOLDS: A BRIEF REPORT
Faculty of Uludag Univeristy, Department of Sports Medicine, Bursa, Turkey
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purpose of this investigation was to study the effect of time of day on
the relationship between lactate (LT) and ventilatory thresholds (VT) of
pulmonary oxygen uptake (VO2). Seven moderately active male volunteers
(26.3±3.0 years, 1.74±0.08 m, 76±5 kg) performed a maximal incremental test
(increases of 30 W every 2 min) on a cycle ergometer on consecutive days
at 0900 h, 1400h and 1900 h in a randomized fashion. The anaerobic threshold
was determined using both ventilatory gas analysis and blood lactate measures.
Each of the following variables was recorded both at VT and the LT; heart
rate (HR, beats.min-1), minute ventilation (VE, L.min-1),
respiratory exchange ratio (RER), time to threshold (Time, sec), oxygen
uptake (VO2, ml.kg-1.min-1) and VO2
as a percentage of maximal oxygen uptake (%VO2max). The correlations
between VT and LT variables analyzed by Pearson product moment correlations
for each time of day. ANOVA was used to compare the data obtained at different
times of the day. There were no significant differences for the data related
to time of day either for ventilatory gas analysis or lactate measurements.
The correlation coefficients between VT and LT variables were moderate to
high (r=0.56-0.94) for time of day. However, the correlations for HR, VO2,
and %VO2max (r=0.81-0.94) were slightly stronger compared with Time, VE
and RER (r=0.56-0.88). It was concluded that, the data at VT and LT were
not influenced by time of day.
KEY WORDS: Anaerobic threshold, circadian rhythm.