European Journal o f

Europ. J. appl. Physiol. 37, 297-304 (1977)

Applied

Physiology

and OccuDational Physiology 9 by Springer-Verlag 1977

Heart Rate and Perceptual Response to Exercise with Different Pedalling Speed in Normal Subjects and Patients* H. L611gen, H. V. Ulmer 1, and G. v. Nieding Krankenhaus Bethanien fiir die Grafschaft Moers, D-4130 Moers, Federal Republic of Germany

Summary. The perceived exertion rating (RPE) scale of Borg was used to investigate the relationship between perceived exertion and pedalling rate. Normal subjects and patients with chronic obstructive lung disease (Cold) were studied in repeated test series. Work load, applied in a random order, varied from 2.5 to 10 mkp/s (patients) and 5 to 20 mkp/s (normals). Pedalling rate varied from 40 to 60, 80, 100 rpm. At constant work load, RPE decreases during increasing pedalling rate. With respect to validity, RPE, showing a closer relationship to work load than to heart rate, seems to reflect perception of physical stress rather than perception of physiological strain. In addition, the results raise the question of standardization of pedalling rate in bicycle ergometry. Key words: Bicycle ergometry - Perceived exertion - Pedalling rate.

Introduction For determination of physical fitness, the bicycle ergometer is widely used as the ergometer of choice. In addition to some physiological factors, psychological aspects are of interest in ergometric tests as well. In bicycle ergometry, motivation determines, whether a subject will push himself to reach a maximum effort. Older women or men, especially patients, proceed with caution sitting on a bicycle or even are anxious. Compensation claimants often are unwilling to do their best. One factor affecting the interplay of performance and cooperation in bicycle ergometry is rate of pedalling. Previous studies pointed out that higher pedalling rates (about 70 rpm) are more convenient to sportsmen and normal subjects (Ulmer, 1969; Stegemann et al., 1968; Skinner et al., 1973). Even patients, when to choose pedalling speed, prefer * Preliminary results have been presented at the XXth World Congress of Sports Medicine, Melbourne, 1974 1 Sportphysiolog.Abteilung, FB 26, University of Mainz, D-6500 Mainz, FRG Offprints request to: H. Ltllgen, M. D., II. Med. Klinik, Langenbeckstr. 1, D-65 MAINZ, FRG

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higher pedalling rates (70 r p m a n d more) ( L t l l g e n et al., 1973). These results d e m o n strate a d i s c r e p a n c y between o p t i m a l speed c o n c e r n i n g the efficiency of effort a n d the preferred speed w h e n speed is freely selected. These conflicting findings are t h o u g h t to d e p e n d o n a decrease of perception o f exertion at higher pedalling rates ( S t e g e m a n n et al., 1968; L t l l g e n et al., 1973; Ulmer, 1973). I n order to c o n f i r m this a s s u m p t i o n , this study was designed to determine perceived exertion in e r g o m e t r y tests with different pedalling speeds b y m e a n s of the rating scale i n t r o d u c e d b y Borg (1962). F u r t h e r m o r e , the purpose o f the present study was to evaluate some factors c o n c e r n i n g validity o f R P E , to c o n t r i b u t e some e x p l a n a t i o n s of the u n d e r l y i n g mecha n i s m of perception o f exertion a n d to clarify the above m e n t i o n e d d i s c r e p a n c y b e t w e e n optimal efficiency a n d preferred pedalling rate.

Methods Detailed informations about methodical aspects have been given previously (Ltllgen et al., 1975).

Instruments The bicycle tests were performed with a mechanically braked ergometer (Fa. Monark, Sweden) with a normal rotating mass (7.5 kg). Braking force and pedalling rate were recorded as described previously (Ulmer et al., 1975). The pedalling rate was indicated by a metronome. Physical working capacity (PWC, Wahlund, 1948) was determined with an electrically braked ergometer (Fa. Lode, Groningen/The Netherlands). The work load during the PWC-test increased within 1 min continuously by 1 mkp/s, starting from 5 mkp/s (patients) and 10 mkp/s (normals), respectively, up to heart rate of 150 beats/min (patients) and 170 beats/min (normal subjects). The work load at that moment was considered as PWC150 or PWC170. Pedalling rate was kept constant at 60 rpm. Heart rate was measured by a rate meter (Pulsemeter, Fa. SanEi, Tokyo/Japan). All tests took place in an air-conditioned laboratory, they were performed at the same hour in the day in order to avoid circadian variation. Perceived exertion rating (RPE) was estimated by a rating scale given by Borg.

Procedure Eight subjects volunteerd to participate in the study: 4 healthy male subjects (aged 23-35 yrs.) and 4 patients with obstructive lung disease (aged 34-51 yrs.; mean raw = 3.7 cm H20/1/s). During the time of investigation, the patients were not given any heart influencing drugs. All subjects had to perform four test series comprising 16 tests of 1 min duration. During the first series the subjects had to get familiar with the test procedure, the results of this series were disregarded. Each series started with a resting period of 5 min with the subject sitting on the ergometer. Each of the following 16 tests had to be performed for 1 rain ending with the question for the number of the RPE scale. Between every test there was a pause of 90 s. In the 16 tests of one series, work load changed from 2.5, 5.0, 7.5 to 10.0 mkp/s (patients) and from 5.0, 10.0, 15.0 to 20.0 mkp/s (normals). Pedalling rates (40, 60, 80 and 100) were combined randomly with the different power outputs.

Statistics For statistical evaluation, conventional methods were applied using a PDP 12 computer (Digital Equipment, Maynard/Mass.). All computations were done with single values. Levels of significance are described as follows: 0.01 < P < 0.05: *, P < 0.01: **

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Results

Relationship between Heart Rate and Work Load In this test arrangement heart rate was considered to be the indicator of physiological strain. As a consequence of the experimental setup, only peak heart rate values at the end of an one minute's test have been ascertained. Heart rate increased both with increasing work load (normals: r = 0.737**; patients: r = 0.575**) and less markedly with increasing pedalling rate (Fig. 1). Mean heart rate values at the four pedalling speeds did not differ significantly.

Relationship between RPE and Work Load For every subject, coefficients of correlation have been calculated beween RPE and work load irrespective of pedalling rate. All individual relationships proved significant (Table 2) with the coefficients less closer in the patients than in the normals. In computations of interindividual correlations, based on all values, between RPE and work load, the obtained coefficients were similar as for the single subjects (normals: r = 0.714"*; patients: r = 0.349**; n = 192).

Relationship between RPE and Pedalling Rate In the normals, RPE commonly decreases with increasing pedalling speed with a more marked decline from 40 to 60 rpm. The course of the relationship is not linear,

Peak heart rate (min "1)

Work load (mkp//sec)

Peak heart rate (min"1)

140

140 20 15 10

130

130 10.0

120

120

715 (" 5

110

2.5

100 al~subjecis 90

110

no (n=4, rest: 66/min)

do 6'0 ~

100

5.0

lOO (rpm)

patients (n=4,rest.'85/min)

90

4'0 ~o do t~o (rpm)

Fig. 1. Interindividual means and standard deviation of heart rate vs. pedal frequency for differentpower outputs. Left: normal subjects, right: patients. SD is shown in one direction only

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Heart rate (min-1)

i

160-

/ = /"

150-

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+'-'+ LUNG PATIENTS ~'NORMAL" SUBJECTS ~= LUMBER WORKERS a . - a "NORMAL- SWEDES o--o CORONARY PATIENTS * - ~ "NORMAL" ISRAELIS L . . . MIXED GROUP

90-

31-51 YEARS 23-35 45-63 40-59 50-67 36-44 41-60

8070-

~,

7

,

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113 14

115 ;6

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;7

Fig. 2. Heart rate (ordinate) vs. KPE (abscissa). The figure shows mean values obtained in studies by seVeral authors (modified fromBaf-Or et al., 1972). Own subjects are: Lung patients, "normal" subjects, top of the list Table 1. Means and SD of RPE for normal subjects and patients for all work loads Group

40 rpm

60 rpm

80 rpm

100 rpm

Normalsu~ects

J sx

11.1 3.3

10.3 2.9

10.1 2.8

9.6 2.8

P~e~s

~ sx

11.4 3.4

10.6 2.6

10.5 2.9

11.6 4.0

-

Mean work load: Normals 12.5 mkp/s; Patients 6.25 mkp/s; n = 16 for each pedalling rate

so that linear correlation computation yield low significant or insignificant coefficients only. The coefficient of correlation for the RPE-pedalling rate relation including all work load steps is 0.205** (n = 192). In the patients, speed dependent R P E values also demonstrate a nonlinear, parabolic relationship with a minimum about 60 to 80 r p m (Table 1).

Relationship between RPE and Heart Rate In each subject, R P E was closely related to heart rate (Table 2). However, the same calculations for all values o f one group revealed significant results in the normals

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Table 2. Coefficientsof correlation between RPE and work load and RPE and heart rate for the eight subjects. These intraindividual values are based on three tests series (n = 48) Subjects

Coefficient of correlation RPE vs. work load

RPE vs. heart rate

Normals 1 2 3 4

0.880** 0.804** 0.869** 0.894**

0.903** 0.682** 0.849** 0.772**

Patients 5 6 7 8

0.719"* 0.616'* 0.659** 0.649**

0.742** 0.485** 0.502** 0.514"*

Table 3. Coefficients of correlation and of partial correlation for the both groups (n = 192) Relationship

Coefficient of correlation (r)

Coefficient of partial correlationa

Heart rate-work load

N P

0.737** 0.575**

0.525** 0.627**

RPE-work load

N P

0.714"* 0.349**

0.472** 0.452**

RPE-heart rate

N P

0.634** 0.036**

0.228** 0.308**

Abbreviations: N: normal subjects; P: patients a After eliminating the effect of the third variable

only (r -- 0.634**; n = 192). I n the patients, significant correlations could not be detected between R P E and heart rate for the values of the group (r = 0.036; n -192) nor when separating the data according to pedalling rate or work load.

Partial Correlation between RPE, Heart Rate, and Work Load I n a further analysis, partial correlation calculations were done for the R P E -- heart rate relationship with eliminating the effect of work load (Table 3) and for the R P E - work load relationship with eliminating the effect of heart rate. The latter procedure yielded higher coefficients of correlation than eliminating the effect of work load.

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Discussion

The results of the present study demonstrate that for normal subjects RPE at constant work load mainly depends on pedalling speed: increasing pedalling rate decreases perception of exertion. In the patients, 100 rpm again leeds to an increase showing a parabolic relationship between RPE and speed. These findings intervenes between those of Pandolf et al. (1973) and Stamford et al. (1974), and giving additional explanations on the influence of speed on RPE. According to the own results, the RPE-speed relationship does not seem to be linear (Pandolf et al.) but curvilinear or parabolic, as has been suggested by Stamford et al., who analyzed the relationship up to 80 rpm. Further measurements including 120 rpm in normal subjects demonstrate an increase of RPE thus confirming the parabolic relationship also in normal subjects (Lfllgen et al., unpublished). The discernable difference between normals and patients in this study, and referring to the above noted studies in well-trained subjects, points out that speed dependence of RPE is influenced by the selection of the subjects. However, physical fitness and illness are assumed to influence the rating of perceived exertion (Arstila, 1972; Bar-Or et al., 1972; Borg, 1970). Figure 2 illustrates that age and illness only moderately shift the heart rate-RPE relationship to the left and downwards. RPE decreased after an eight weeks training program, but RPE remained unchanged if related to the relative values of oxygen uptake and heart rate (Ekblom et al., 1971). In conclusion of these findings the question of validity of RPE is raised, meaning that RPE is appropriate to measure exertion as physiological or psychological strain (subjective feeling of stress). The insignificant relationship of heart rate to RPE in the patients and the decrease of RPE at increasing speed while heart rate increases moderately is an evidence that RPE is related to work load (physical stress) rather than to heart rate (physiological strain). This is confirmed by partial correlation analysis. Eliminating heart rate, correlation of RPE to work load is higher than to heart rate with eliminated work load. These conclusion meet those of other authors who stated that "heart rate, per se, is not the primary factor in the subjective estimate of exercise exertion" (Ekblom, 1971). However, it should be admitted, that this comes only true for normal or trained subjects. In the patients, having airway obstruction, dyspnoe may also be involved in grading the exertion. Contribution of ventilation to perception of exertion is likewise thought to be important in patients with limited ventilatory capacity (Edwards et al., 1972). The presented results indicate that RPE does not derive from strain of exercise but may originate from perception of force and speed in the working muscles. High braking force and slow muscular movements lead to muscular fatigue (Petrofsky et al., 1975). This then may explain the decrease of RPE with increasing pedalling speed. However, it is yet unknown, whether perceived exertion depends on metabolic rate or mechanoreceptors activity in the working muscles. In several studies, muscular efficiency has been shown to change in a parabolic way when speed increases with a minimum about 50 rpm (Eiselt, 1965; Israel et al., 1967; Ulmer, 1969; Arstila, 1972; Gaessler et al., 1975). The divergence of RPE and heart rate in this study highlights the discrepancy in ergometry : pedalling rate

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with respect to m a x i m u m of efficiency differs from pedalling rate with respect to minimum o f perceived exertion. The reasons for this difference are widely obscure. F r o m the present results, evidence is given that R P E depends on local factors, whereas muscular efficiency, determined b y the f , ' O J w o r k load ratio, is mainly inflenced b y t h e overall working capacity. Measurements of local metabolism m a y render definitive explanations. F r o m a practical standpoint, higher pedalling rates support motivation and cooperation o f a subject in m a x i m a l performance tests. In athletes, m a x i m u m of oxygen u p t a k e will be achieved only with higher pedalling rates (Israel et al., 1967; H e r m a n s e n et al., 1969; Shephard, 1970; Schfirch et al., 1976). This fact is well known in exercise tests in sports medicine. Some authors refer to higher pedalling rates (even up to 90 rpm) in exercise tests when examining athletes (Bannister et al., 1967; Sz6gy et al., 1972; Sch6nholzer et al., 1973; Ulmer, 1975). These results therefore raise the question o f pedalling rate and standard guidelines in ergometry.

Acknowledgements. This study was supported by the Bundesinstitut ffir Sportwissenschaft KSln, FRG, VF-1124/10/73.

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Received March 11, 1977~Accepted August 10, 1977