Magnitude of the Heart Rate
Threshold Is Not Explained by VO2max, the Lactate Threshold, Or Endurance
Cycling Performance
Robert A. Robergs, Daryl L. Parker, Roberto
Quintana, Cristopher C. Frankel.
Center For Exercise and Applied Human
Physiology, The University of New Mexico, Albuquerque NM 87131-1258.
Introduction: The HRT is purported
to represent the lactate threshold and therefore be an indicator of exercise
performance (1-4). The intent of this study was to statistically explain
the occurrence of HRT in subjects using absolute and relative indices of
cardiovascular fitness. Methods: Twenty two subjects (11 males)
of varying fitness first completed an incremental exercise test to VO2max
on an electronically braked cycle ergometer. During the maximal exercise
test blood lactate was measured each minute, and heart rate was measured
every 15 s. Expired gas was collected continuously and analyzed every
30 seconds by an automated expired gas collection system. In another trial,
subjects performed a 30 minute isokinetic cycling performance test (PERF).
Statistics:
Data
for HRT, LT, and mean performance (PERF) were compared by separate one-way
repeated measures ANOVA (p=0.05/3=0.0166). Stepwise multiple regression
analyses were used to explain the between subjects variability in the HRT
(%VO2max, VO2
(L/min)) and VO2 (L/min) during PERF.
Stepwise discriminant analysis was used to determine if any one factor
or combination of factors could discern subjects with or without a HRT.
The error for detecting a difference of 5% VO2max
between the HRT and LT for the 22 subjects of this study was 0.3. Results:
The heart rate profiles exhibited were exponential (n=1), linear (n=8),
and sigmoidal (n=13). Subsequent assessment of the heart rate response
to exercise resulted in a HRT in 13 of 22 subjects (59%). The mean values
for blood lactate, HR, VO2, and %VO2max
at the HRT, LT and PERF are presented in Figure 1. The only predictor to
enter in the discriminant function analysis was %VO2max
at the LT (p<0.01), accounting for 32.38% of the variance with HRT categories,
and classified groups correctly by 76.2 %. None of the variables, VO2max,
%VO2max at LT, and hours exercised per
week had a sufficient F to be entered into a multiple regression equation.
Discussion:
We hypothesized that the HRT would be related to, or be predicted by indices
of cardiovascular endurance based upon previous findings (1-4). However,
our results indicated that VO2max, LT,
or hours trained per week were not related to HRT, and that for individuals
who have a HRT, it occurs at a significantly higher intensity than the
LT. We conclude that cardiorespiratory fitness is not related to
the exercise intensity at the HRT. Further studies are needed to
identify the physiological variables that explain or cause the HRT phenomenon.
References:
1. Gledhill N. et al. Med Sci Sports Exerc. 26: 1116-1121,
1994. 2. Hofmann P. et al. Int J Sports Med. 15:232-237, 1994. 3.
Pokan R. et al. Eur J Appl Physiol. 67: 385-388, 1993.
4. Pokan R. et al. Eur J Appl Physiol. 70: 175-179, 1995.
Note: Send
the abstract to the ASEP National Office. The address is:
c/o Dr. Tommy Boone
Department of Exercise Physiology
1200 Kenwood Avenue
Duluth, MN 55811
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