Training & Testing
Authors
L. Eriksen1, J. S. Tolstrup1, S. Larsen2, M. Grønbæk1, J. W. Helge2
Affiliations
1
2
Key words ▶ cardiorespiratory fitness ● ▶ reproducibility ● ▶ exercise test ● ▶ physical fitness ● ▶ cycle ergometer ● ▶ measurement ●
Abstract
National Institute of Public Health, University of Southern Denmark, Copenhagen, Denmark Centre of Healthy Aging, Department of Biomedical Sciences, University of Copenhagen, Copenhagen N, Denmark
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In 11 680 individuals (18–85 years) maximal oxygen consumption (VO2max) was estimated indirectly in a maximal cycle test using a prediction model developed in a young population (15–28 years). A subsample of 182 individuals (23–77 years) underwent 2 maximal cycle tests with VO2max estimated indirectly in both tests and measured directly in one test. Agreement between the direct measurement and the indirect estimate of VO2max and repeatability of the indirect estimates of VO2max were examined by Bland-Altman plots, limits of agreement (LOA) and coefficient of repeatability (CR). The indi-
Introduction
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accepted after revision April 22, 2014 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1376973 Published online: 2014 Int J Sports Med © Georg Thieme Verlag KG Stuttgart · New York ISSN 0172-4622 Correspondence Louise Eriksen National Institute of Public Health University of Southern Denmark Øster Farimagsgade 5A 1353 Copenhagen Denmark Tel.: + 45/655/07 728 Fax: + 45/392/08 010
[email protected]
Maximal oxygen consumption (VO2max) is the criterion measure of cardiorespiratory fitness, which is an independent predictor of morbidity and mortality [16]. Direct measurement of VO2max implies measurement of oxygen and carbon dioxide in expired air and is considered the gold standard physiological test [1]. Direct measurement is time-consuming and requires expensive equipment and specific expertise. Thus, several indirect and simpler procedures based on heart rate during exercise [5], covered distance for a given time [10], maximal speed in shuttle run [19, 20] and maximal time and/or power on treadmill or ergometer cycle [3, 4, 9, 14, 29] have been developed to predict VO2max. Indirect tests may be maximal (performed to voluntary exhaustion) or sub-maximal, the latter considered less precise. In the Danish Health Examination Survey 2007–2008 (DANHES) [11] 11 680 participants ages 18–85 years performed a maximal cycle exercise test. VO2max was estimated indirectly based on maximal power output (MPO) obtained by the participants in the cycle test. The prediction model of
rect method (mean VO2max = 3 132 ml · min − 1) underestimated VO2max as compared to the direct method (mean VO2max = 3 190 ml · min − 1) in men (bias: 58 ml · min − 1 (95 % LOA − 450 and 565)) and overestimated VO2max in women (mean VO2max = 2 328 vs. 2 258 ml · min − 1, bias: − 70 ml · min − 1 (95 % LOA − 468 and 328)). The mean difference between the 2 indirect estimates was non-significant (men: − 11.9 ml · min − 1, women: 18.3 ml · min − 1) with a CR of 279 ml · min − 1 (8.9 %) in men and 274 ml · min − 1 (11.7 %) in women. The validity of the indirect method was good despite minor sex-specific bias. Owing to this bias we suggest a new prediction model of VO2max. The maximal cycle test was highly repeatable.
VO2max was originally developed by Andersen [4] from directly measured VO2max among 535 men and women ages 15–28 years. Nonetheless, this model might not be suitable for our population with a wider age range, since age has been found to contribute significantly to the prediction of VO2max independent of MPO with lower values of VO2max for older ages [4, 25]. In large population studies like DANHES, it is inevitable that physiological tests are performed under the instruction and guidance of several test leaders due to the huge number of participants. This will most likely induce a higher variation in the results, and it is therefore important to investigate whether such tests have high repeatability, even when being carried out under the guidance of different test leaders. The objective of the present study was to assess the agreement between VO2max estimated indirectly (applying a prediction model originally developed in adolescents and young adults) and measured directly (gold standard) among an adult population spanning a wide age range. A second objective was to test the repeatability of the maximal cycle test under the guidance of different test leaders. Eriksen L et al. A Maximal Cycle Test … Int J Sports Med
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A Maximal Cycle Test with Good Validity and High Repeatability in Adults of All Ages
Methods
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Study population
A random subsample of adult citizens 18 years and older (n = 180 103) from 13 Danish municipalities was invited to participate in the Danish Health Examination Survey in 2007–2008 [11]. A total of 18 065 individuals (10 %) accepted the invitation, and based on a screening interview on health status and results of blood pressure measurements participants were eligible for participation in a maximal exercise test (n = 11 680), a sub-maximal test (n = 4 403) or no test (n = 1 982) for indirect estimation of maximal oxygen consumption (VO2max). Out of those 11 680 participants eligible for the maximal test 10 973 (94 %) completed the test with a valid test result. In 3 municipalities a sexand age-stratified sample of participants (n = 182) who underwent the maximal test with a valid test result were invited to come back after a week to perform a retest with indirect estimation as well as direct measurement of VO2max. Informed consent was obtained from all participants, and the protocol was reviewed by the Scientific Ethical Committee B for the Capital Region of Denmark (H-B-2007-050). The study was conducted in accordance with the ethical standards of the International Journal of Sports Medicine [13].
Measurement of VO2max
In order to ensure safe participation and achieve optimal risk minimisation in the maximal cycle, test participants were subjected to a screening by means of an interview and measurement of blood pressure. In brief, one or more of the following conditions contraindicated participation in the cycle test: any heart-related disease; chest pain or pressure; moderate hypertension; consumption of antihypertensives; cardiac or pulmonary medication; pregnancy; muscle, joint or skeletal problems. On the first test day (test day 1) VO2max was estimated indirectly using an ergometer cycle (Ergomedic 839E, Monark Exercise AB, Vansbro, Sweden). Heart rate was monitored with chest strap and watch (Polar RS100, Polar Electro Oy, Kempele, Finland). The test started with a 5-min warm-up at a load of 75 watts for women and 100 watts for men. After the warm-up the work load was increased by 35 watts every 2 min until voluntary exhaustion. The size of the initial load and increments were chosen given the notion that younger as well as elderly participants should be able to complete the test within a reasonable time frame [2, 21]. Pedal frequency was freely chosen by participants within the limits 60–80 rpm, while trained participants were allowed to exceed 80 rpm. The participants were verbally encouraged to continue for as long as possible, and the perceived exertion of the participants was evaluated using Borg’s scale [8]. VO2max was estimated from MPO, that is, the highest achieved load adjusted for the proportion of the last stage completed: VO2max (l · min − 1) = 0.16 + (0.0117 · MPO (watt)) [4]. The maximal cycle tests were managed by trained scientific personnel. On the second test day (test day 2) the following week a similar test procedure was followed, yet on a different exercise ergometer cycle of the same model as on the first test day (Ergomedic 839E, Monark Exercise AB, Vansbro, Sweden). During this cycle test direct measurement of pulmonary VO2 as well as indirect estimation of VO2max was performed, enabling assessment of repeatability of the cycle test on 2 different test days as well as
Eriksen L et al. A Maximal Cycle Test … Int J Sports Med
agreement between the indirect and direct measurement conducted in one and the same test. The measurements were performed continuously using an automated metabolic cart (Quark b2, Cosmed Srl., Rome, Italy), calibrated before each test according to the manufacturer’s specifications. Before each test a volume calibration and a calibration of the gas analysers were performed using gases of known composition. The respiratory variables were averaged every 20 s. The greatest 20-s averaged VO2 (l · min − 1) value during the test was taken as the VO2max. Achievement of VO2max was accepted when a respiratory exchange ratio of 1.15 and/or maximal heart rate (220 − age) were present, or a levelling off or decline in VO2 was reached [15, 22]. All tests on test day 2 were managed by one experienced and formally qualified exercise physiologist. No attempt was made to control the participants’ food and beverage intake and physical activity prior to the tests.
Statistics
To obtain a visual assessment of the relationship between the different measurements of VO2max, scatterplots and Pearson’s correlation coefficient were used. Bland-Altman plots [7] were used to illustrate the extent of agreement between the direct and indirect measurement of VO2max in the maximal cycle test on test day 2 by plotting the difference between the direct and indirect measurements for each individual against their direct measurement (the gold stand) instead of against the mean of the direct and indirect measurements, since the gold standard is expected to be closer to the “true value” [17]. The mean difference (bias) represents the degree of systematic error between the 2 measurements [7]. The hypothesis of zero bias was tested using a paired t-test. Stepwise multiple regression analysis with the direct measurement as the dependent variable was performed to derive a new equation for indirect estimation of VO2max. The repeatability of the cycle test was evaluated by the coefficient of repeatability (CR) (CR = 1.96 · standard deviation (SD) of the mean difference between the 2 indirect estimates of VO2max) and Bland-Altman plots with the difference between estimates by the 2 indirect methods for each individual against their mean value of the 2 indirect estimates. The significance level was set at P
