Eur J Appl Physiol (2000) 82: 245±249
Ó Springer-Verlag 2000
ORIGINAL ARTICLE
Mathias Reiser á Tim Meyer á Wilfried Kindermann Reinhard Daugs
Transferability of workload measurements between three different types of ergometer
Accepted: 16 February 2000
Abstract The aim of this study was to test the transferability of workload measurements between three dierent types of bicycle ergometer. Two common ergometers (Lode Excalibur and Avantronic Cyclus 2) were compared with a powermeter (Schoberer SRM system) that enables the measurement of power output during road cycling. Twelve well-trained subjects participated in this study. Within 12 h, each subject carried out three separate graded incremental exercise tests on each of the ergometric devices, and their oxygen uptake (V_ O2 ) and heart rate were determined. The three test protocols were identical: after warm-up, four stages of 4 min each at exercise intensities of 100, 150, 200, and 250 W. Pedalling frequency was controlled and there was no dierence between the three ergometers. Tests were administered in a random order. Neither V_ O2 nor heart rate was aected by the type of ergometer used. For a given intensity, the same values were found in the two laboratory tests and in the ®eld test (V_ O2 : P 0.425; heart rate: P 0.845). Thus, the transferability of workload measurements between two dierent laboratory cycling ergometers and an ambulatory device was proven. Equivalency was determined using V_ O2 and heart rate as indices of metabolic and cardiovascular strain, respectively. Key words Spiroergometry á Stress testing á Cycling á Oxygen uptake á Validation
M. Reiser á R. Daugs Institute of Sports Science, University of Saarland, Department of Movement and Training Science, 66041 SaarbruÈcken, Germany T. Meyer (&) á W. Kindermann Institute of Sports and Preventive Medicine, Faculty of Clinical Medicine, University of Saarland, 66041 SaarbruÈcken, Germany e-mail:
[email protected] Tel.: +49-681-3023747; Fax: +49-681-3024296
Introduction It is common to use laboratory tests in order to evaluate the performance of competitive road cyclists. Usually these athletes carry out incremental tests on cycle ergometers to allow the determination of their ventilatory parameters, heart rate, and lactate levels. Subsequently, performance descriptors are calculated from plots of these measurements. If exercise prescription for training is to be deduced from these laboratory values, one has to consider diering ®eld conditions. These comprise variable environmental conditions (i.e. wind, temperature or humidity), as well as biomechanical dierences between the movement patterns that take place during road and ergometer cycling. To our knowledge, there is no study in which both conditions are adequately compared. Thus, it is not known to what extent dierences in muscular activity (e.g. caused by dierent requirements) in¯uence the physiological strain. With respect to the biomechanical aspect, the systematic manipulation of seat tube angles (Too 1991), body orientation (Too 1994), or seat-to-pedal distance (Too 1993), have shown that dierent ankling patterns can aect maximal cycling performance. Varying movement patterns (e.g. ankling pattern, steering movements or balancing) might imply dierences in the metabolic cost, which is best described by the whole-body oxygen uptake (V_ O2 , Wasserman et al. 1999). It has been shown that mean V_ O2 and power output eciency during submaximal cycling are in¯uenced by the dierent ankling patterns that result from adjustments in seat tube angle and seat height (Price and Donne 1997). This suggests a slight in¯uence of body position and/or movement variations on the metabolic cost of cycling, which may have implications for testing elite athletes on dierent ergometers. For decades, the prescription of exercise intensities for cycling had to be performed using heart rate or, more rarely, velocity on even ground. Recent technological developments have enabled a direct measurement of the actual power output on a racing bicycle.
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Ambulatory powermeters allow the determination of the force that is developed at the pedals. Combined with the registration of the pedalling rate, a calculation (and online display) of the actual cycling workload (in Watts) has become accessible. Thus, it is possible to obtain a direct prescription of workloads from the cycle ergometer. However, with a powermeter, the realization of a given workload is more dicult than on a standard cycle ergometer. Due to ®eld conditions, athletes permanently have to adapt their pedalling frequency and/or strength to maintain the required intensity. Thus, in¯uences on the metabolic cost still cannot be ruled out completely. A second technological innovation has led to new options in performance diagnostics under ®eld conditions. The development of lightweight ambulatory spiroergometers enables the measurement of ventilatory parameters under real training (and eventually competition) conditions (e.g. in a road-cycling situation). The precise determination of V_ O2 requirements has become possible. For the present study, both techniques ± ambulatory measurement of workload and gas exchange ± were combined. It was our goal to test whether the choice of ergometer type (i.e. ``classical'' stationary ergometer vs stationary ergometry using a ¯exible ®xation of a racing bicycle vs ambulatory measurements under ®eld conditions) signi®cantly in¯uences metabolic cost and cardiovascular strain. Therefore, we compared performance on two common stationary cycle ergometers with that using the SRM-system. As a primary criterion variable V_ O2 was measured, and was considered as a gold standard to indicate dierences in metabolic cost. In addition, heart rate evaluation served as a way of assessing cadiovascular strain.
Methods Subjects Twelve healthy males volunteered as subjects for this study. Their anthropometric data are presented in Table 1. All of the subjects had been tested earlier and had a maximal workload above 300 W, which was achieved in incremental stage tests. They were requested to refrain from strenuous physical activities for the 24 h prior to the experimental session. Thus, they were expected to be able to perform at workloads of up to 250 W without great diculty. Experimental design and procedures Subjects performed identical exercise tests on three dierent cycle ergometers in a randomised order. V_ O2 and heart rate were determined at four exercise intensities (100, 150, 200, and 250 W). Table 1 Anthropometric data of the subjects (means and SD; n = 12). Maximum oxygen uptake (V_ O2max ) values were estimated from tests on Lode using the Astrand-Rhyming nomogram (Astrand and Rodahl 1986) Data
Age (years)
Body mass (kg)
Height (cm)
V_ O2 max (ml á min)1 á kg)1)
Mean SD
29.0 5.9
75.4 6.3
182.2 5.9
64.2 7.0
After a 4-min warm-up period at a work rate of 50 W, each test started with a power output of 100 W. Work rate was then increased by 50 W every 4 min until the 250-W stage was ®nished. The 4-min stage duration was chosen to guarantee stable values for V_ O2 and heart rate, at least for the three lowest intensities. Pedalling rate was controlled and subjects were asked to cycle at similar frequencies in all tests. Each subject performed all three tests on 1 day. In order to maintain comparable cycling positions on each ergometer, seat tube angle, seat-to-handlebars distance and seat-to-pedal distance were individually adjusted prior to each test. Between two tests, subjects had a rest period of 4 h. It was assumed that this time period was long enough to allow for sucient regeneration. Subjects ®nished exercise clearly before exhaustion and performed no longer than 8 min at an intensity above their estimated aerobic-anaerobic transition. Therefore glycogen depletion should have been ruled out completely, particularly since subjects were told to replenish their stores with meals rich in carbohydrates between tests. To minimise water loss due to sweating, subjects were instructed to ingest at least 500 ml of ¯uid during the resting periods. The rather small increase in average resting heart rate (®rst test 66.6 beats á min)1; second test 69.3 beats á min)1; third test 71.7 beats á min)1) demonstrates that subjects showed no eminent hypohydration. Bicycle ergometers Cycling ergometer tests were carried out on a Lode Excalibur (Groningen, The Netherlands), a Cyclus 2 (Avantronic, Leipzig, Germany), and with an SRM Training System (Schoberer, JuÈlichWelldorf, Germany). The Lode is a stationary, electronically braked ergometer. Before the beginning of the investigation it was mechanically calibrated according to the manufacturer's instructions. Cyclus 2 is a stationary training device for competitive and recreational cyclists. A racing bike frame is placed on an electronic brake, and the bicycle chain over the pinion drives the braking mechanism. The axles, which ingest fork and rear, are constructed elastically. Thus, a more ``natural'' cycling movement can be simulated. The SRM-system is a mobile ergometer. It enables workload measurements to be made outside the laboratory. It makes use of a force transducer integrated into the gear rim for measuring tangential pedalling forces, and a speed sensor that measures the speed of the pedal. Power output is calculated from these raw data. The SRMsystem can be attached to each racing bike. In contrast to both stationary ergometers, to maintain a given workload with the SRMsystem, subjects have to permanently adapt their pedalling frequency or the chosen gear according to changing environmental conditions (e.g. wind, or road gradient). To help in achieving this goal, the actual work done on the ergometer is displayed digitally. The data are stored in a mini computer for later analysis. It is essential in these types of experimental protocols that the actual braking power of an ergometer is set precisely at the chosen level, and that an accurate and constant workrate is ensured. Giezendanner et al. (1983) showed that at the level of the braking system, thermal changes resulting from cycling can lead to errors in the power output. When ®xing the actual braking torque, the Lode system takes such changes into account. For an (indirect) evaluation of that eect on the Cyclus 2, the same bike frame was used for all tests, and the SRM-system was installed simultaneously. Therefore, the work load performed by the subjects could be recorded with both systems at the same time and be compared directly. The mean dierence between the two systems ± above all measurements ± was 0.8 W (SD=5.3 W). Such a small deviation is considered to be irrelevant for practical purposes. Regarding the technological aspects and the measured data, it can be concluded that ergometers used in this study oer sucient accuracy, in terms of both absolute calibration and stability. Spiroergometry and heart rate Respiratory parameters were measured using a MetaMax I metabolic system (Cortex, Leipzig, Germany), which was calibrated
247 according to the manufacturer's instructions. The spirometer is based on a mixing chamber system, and measures ventilatory and gas exchange raw data every 10 s. The fraction of oxygen in expiratory air was determined using a cirkonium cell. Expiratory volume was recorded digitally with a Triple V-sensor. The apparatus weighs about 1.8 kg. If used in a ®eld test, the spirometer can be placed in a back pack and carried by the subject (Fig. 1). The weight of the whole system adds up to 3 kg. It has been shown previously that even for running trials, the in¯uence on heart rate of this additional weight is negligible (Coen et al. 1999). V_ O2 was de®ned as the mean of the last three measured V_ O2 values for every workload. This was done to reduce the in¯uence of unsystematic ¯uctuations. The corresponding time frames are marked in Fig. 2. Due to the environmental in¯uences mentioned above, the real work done in the ®eld tests with the SRM-system was not absolutely identical to the intended intensities (see Results). V_ O2 values were interpolated by linear regression (all r > 0.99, P £ 0.001, n 12). The V_ O2 values for the workloads of interest (100, 150, 200 and 250 W) were taken for statistical calculations. Heart rates were measured using a portable device (Polar, Finland). The mean value of the 4th min during each of the stages was taken as the heart rate for that stage. Correction of the heart
rate values for the SRM-system was carried out in the same way as for the V_ O2 values. Statistics Analysis of variance for repeated measures (three ergometers ´ four intensities) was used to determine whether V_ O2 and heart rate diered among the ergometers. When the homogeneity of variance was violated, the degrees of freedom were corrected with an e in accordance with the Greenhouse-Geisser-procedure. Data are presented as means SD. An a-level of P < 0.05 was considered signi®cant.
Results Exact work rates with the SRM-system Table 2 shows the real workloads realised by the subjects with the SRM-system for given work intensities. In the ®rst three stages the intended intensities were reproduced almost exactly. The average deviation was below 1 W. For the 250-W stage, the average absolute deviation was a little higher, however, the error was still below 1%. Pedalling rates As depicted in Fig. 3, the pedalling frequency increased with cycling intensity (P < 0.001). Similar values for Table 2 Exact values of the exercise intensities produced in the ®eld test (SRM-system). Data are given as the means and SD (n = 12)
Fig. 1 Spiroergometry in the ®eld test situation. The battery-driven spiroergometer is placed in a back pack Fig. 2 Oxygen uptake (V_ O2 ) of one representative subject during an incremental test. At the start of the test, work rate was set at 100 W, and then increased by 50 W every 4 min. Steady states can be identi®ed at all stages for this subject
Data
100 W
150 W
200 W
250 W
Mean SD
100.7 3.1
149.7 1.4
200.1 4.0
247.8 7.0
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Fig. 3 Mean pedalling frequencies (PF) on dierent ergometers (Cyclus squares, Lode triangles, SRM-system circles), at dierent exercise intensities (n 12)
pedalling rates were obtained regardless of the type of ergometer used. There was no signi®cant dierence among the three ergometric devices (F(ergometer) 0.351, P 0.708), nor was the interaction signi®cant. Oxygen uptake As can be seen in Fig. 4a, no signi®cantly dierent values for V_ O2 were measured for the three ergometers in the incremental exercise tests (i.e. for a given intensity, V_ O2 was not aected by the type of ergometer; F(ergometer) 0.753, P 0.425). For each subject, V_ O2 increased linearly with exercise intensity in each of the three tests (all r > 0.99, P < 0.001, n 36). The interaction ``ergometer ´ intensity'' was not signi®cant. Heart rate A similar picture was observed with heart rate (Fig. 4b). Heart rate increased linearly with cycling intensity (all r > 0.99, P < 0.001, n 33). However, there was no signi®cant dierence among the three types of ergometer (F(ergometer) 0.170, P 0.845). The interaction was not signi®cant.
Discussion The purpose of this study was to evaluate the comparability of three dierent types of bicycle ergometer with respect to power output measurements. This was thought to be warranted because dierences in the movement patterns induced by varying principles of ergometric measurement (two dierent stationary ergometers vs an ambulatory device) might imply differences in metabolic cost and/or dierences in cardiovascular strain.
Fig. 4 V_ O2 (a) and heart rate (b) for the Lode (horizontal stripes), Cyclus 2 (black), and SRM-system (white) ergometers. Each bar in a represents the mean value of 12 subjects, and in b the mean for 9 subjects (the automatic storage of heart rate data for three subjects failed during one stage, therefore the number of cases available for heart rate analysis was reduced)
The main ®nding of this study is that there were no dierences between ergometers in metabolic (V_ O2 ) and cardiovascular (HR) responses for given work intensities. This was true for the range of work intensities of 100±250 W, which covers a wide range of workloads relevant to the training of athletes. It is possible to transfer intensities calculated from laboratory measurements directly to the ®eld situation. This is of importance for trainers and physicians who prescribe exercise intensities on the basis of laboratory tests. Threshold models for prescription, which result in intensity recommendations, gain applicability. To estimate the entire metabolic cost contributing to the actual work accomplished, V_ O2 was measured. This is considered to be a sensitive and valid parameter that will highlight such dierences. Heart rate was measured to evaluate the cardiovascular response. This is an easily applicable parameter that is capable of describing satisfactorily the net strain for the heart and circulation. We used a type of ``biological validation'' procedure to investigate our issue. This relies on the constancy of the subjects' physiological reaction to given workloads,
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and has been demonstrated several times before. Even under varied circumstances (e.g. participating in a triathlon before ergometry) and in older subjects and sick persons, this procedure provides an adequate reproducibility of respiratory raw data and of deduced parameters (Le Gallais et al. 1999; Lehmann and KoÈlling 1996; Marburger et al. 1998; Meyer et al. 1997). Other investigators have made use of related methods to compare workloads under changing conditions, for example walking with varying kinds of rucksacks (Lloyd and Cook 2000). Steady states in V_ O2 were observed only in the ®rst three stages. For comparisons among ergometers, however, this does not represent a problem. During the trials, subjects were allowed to cycle at their individual comfortable pedalling rate, but were instructed to maintain similar frequencies for all tests. It has been demonstrated previously that V_ O2 increases with pedalling rate (Casaburi et al. 1978; Chavarren and Calbet 1999). However, this eect is rather small and can be shown only if pedalling rate varies over a wide range. Considering the very small and insigni®cant dierences in pedalling rates observed in the present study, it can be concluded that there was no relevant in¯uence of pedalling inconsistencies on the criterium variables. In the laboratory situation, the work done on the cycle ergometer is almost independent of the pedalling rate, therefore exercise intensity can be reproduced exactly. In contrast, during the ®eld situation with the SRM-system, in order to keep the required exercise intensity, subjects permanently had to adapt their pedalling frequency (for a given translation ratio). However, after a short period of familiarization, the desired exercise intensities could be accomplished precisely. In addition, as noted in the Methods section, to optimise comparability, the V_ O2 values measured on the SRMsystem were corrected for the exact stage intensity. In this study, we held the assumption that exercise with identical power output on three ergometers leads to varying physiological strain. Consequently, the level of statistical signi®cance for testing the statistical hypothesis was set at P 0.05. However, the ®nding that there are no dierences between the ergometric devices is not equivalent to evidence that exercise on the ergometers leads to identical physiological strains. In order to hypothesise equality, one would have to test against the b-error. For unspeci®c alternative hypotheses, this is principally impossible. However, alternatively it can be tested with an adjusted a-level (e.g. P > 0.20; Bortz 1993). Even this criterion is ful®lled by our results. In summary, the validity of measuring power outputs under ®eld conditions was substantiated by our investigation. V_ O2 and heart rate are not in¯uenced by the dierences between two modes of stationary ergometer,
and ambulatory ergometry. For the purposes of monitoring training, it can be concluded that test results may be transferred from the laboratory to ®eld situations without the necessity of adjusting the measurements. The use of the types of cycle ergometer tested in this study is widespread in the area of sports medicine. Therefore, our results have implications for a variety of researchers, trainers, and physician/exercise physiologists. They justify the interchangeable application of these ergometers. Acknowledgements The authors wish to acknowledge the technical assistance provided by Oliver Faude and Dominik Schammne.
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