Eur J Appl Physiol (1982) 49:359-368 European Journal of

Applied Physiology and Occupational Physiology �9 Springer-Verlag 1982

Square-Wave Endurance Exercise Test (SWEET) for Training and Assessment in Trained and Untrained Subjects* I. Description and Cardiorespiratory Responses

Manuel Gimenez 1, Emilio Servera 2, and Willy Salinas 2

1 Laboratoire de Physiologie de l'Exercice Musculaire Unit6 14 INSERM, C.O. 10, F-54511 Vandoeuvre les Nancy Cedex, France 2 Recipients of a CIES grant: E. Servera, on leave from the Medical School, Valencia, Spain; W. Salinas, on leave from the IBBA, La Paz, Bolivia

Summary. A new 45 min Square-Wave Endurance Exercise Test (SWEET) performed on a cycle ergometer and designed for endurance training was studied in 43 normal subjects: Untrained (U), twelve women and seven men and Trained (T), eight women and 16 men. Among them seven were elite sportsmen (E). Preliminary measurements were made of 1;102 max by constant power and Maximal Tolerated Power (MTP) in a progressive test (+ 30 W/3 rain). To the SWEET's base, established as a % of individual MTP, a peak of 1 rain at MTP was added every 5 minutes. Maximum Intensity of Endurance during the SWEET (MIE45) is defined by both maximal heart rate ( H R ) a t the end of the test and the impossibility of maintaining 5% above the percent MTP of the MIE45 for 45 min. Exhaustion was reached at the end of the MIE45 , which could be expressed as % MTP, as total energy expenditure (TEE) in liters of 02, or as total mechanical work (TMW) in kiloJoules per kg of weight (kJ. kg-1). ~z E, /VCO2, VO2 and H R were continuously measured. VO2 max, TMW and % MTP were signifi- cantly higher in T than in U subjects. The E subjects show the highest values of those parameters. TMW and TEE were well correlated (r = 0.992, p < 0.001, n = 43) indicating good efficiency. TMWin T (r = 0.453) and in E men (r = 0.442) were however less well correlated to the VO2 max. MIE45 therefore gives different information in the evaluation of "endurance capacity" at the time of measurement than that provided by ~zO 2 max. Because of the high TEE per session it could be useful for endurance training of T and U subjects.

Key words: Maximal energy expenditure - Total mechanical work - Maximal intensity of endurance - Ventilation - Respiratory exchanges - 1)O2 max - Men - Women - Athletes - Untrained

* Supported in part by the European Economic Community (EEC) Luxembourg Offprint requests to: M. Gimenez, MD (address see above)

0301-5548/82/0049/0359/$ 02.00

360 M. Gimenez et al.

Introduction

One of the factors contributing to the improvement of athletic performances and setting of new records has been better training techniques (Astrand and Rodahl 1970; Mathews and Fox 1976). The improvement can be attributed largely to interval training (Fox et al. 1975; Eddy et al. 1977). There is no standard ergometric method of training which demands an appropriate caloric output. The essential factors in training must include its intensity (from 60 to 90% of the reserve heart rate) and the duration of the exercise (from 15 to 60 min of aerobic activity) (Sharkey 1970; Shephard 1970; Davies and Knibbs 1971; Mathews and Fox 1976; Kearney et al. 1976). Most authors propose either constant exercise levels, the duration of which is a function of intensity (Astrand and Rodahl 1970; Gleser and Vogel 1973), or intermittent exercise of diverse modality (Fox et al. 1975; Mathews and Fox 1976; Eddy et al. 1977). No type of exercise test simulates competitive conditions well, nor does any test simulate the training protocols of endurance athletes.

The aim of this study is to establish the validity of a new exercise test, which would permit evaluation of a given exercise pattern as a controlled interval training technique, not only for endurance athletes, but also for sedentary subjects wishing to acquire and maintain a good physical condition.

Material and Methods

Forty-three normal subjects, 20 women and 23 men, voluntered for this study after having been informed of the protocol involved. Nineteen were untrained (U) (12 women and seven men) and 24 (eight women and 16 men) had practiced sport, between 4 - 8 h per week for more than 3 months (T). Among them, seven were endurance sportsmen of national level who trained regularly and participated in national competitions. They are considered in this work as a group of "elite sportsmen" (E). They completed a medical questionnaire and underwent a cardiopulmonary and electrocardiographic examination, all of which were normal for all subjects.

Firstly, maximal oxygen uptake or 1702 max was measured directly in duplicate with a constant and a progressive test: an initial load of 30 W was increased by 30 W every 3 min (Gimenez et al. 1981). It should be noted that in progressive exercise the highest level maintained for 2 or 3 min, referred to as "maximum tolerated power" (MTP) is an essential measurement for the test to be described later.

Total ventilation (17E, BTPS), oxygen uptake @02, STPD), carbon dioxide production (17CO2, STPD), respiratory frequency (f) and tidal volume (Vr) were measured continuously every 30 s using a Jaeger Ergo-Pneumotest with a Dataspir EDV 70 processing system (E. Jaeger, Wtirzburg, FRG). Heart rate (HR) was also monitored continuously on an electrocardiogram (EKG) (Siemens Cardiostat 3T). Arterial blood pressure was measured at rest, at 1702 max, and every 15 min (before and after the peaks) of the test to be described later. The tests were performed on a Fleisch or Jaeger cycle ergometer at 60 revolutions per minute (rpm).

Square Wave Exercise Endurance Test (SWEET). In order to simulate the conditions encountered by endurance athletes (cross country, long distance running and skiing, soccer, e tc . . . ) as closely as possible, the tests of 45-rain duration (Fig. 1) consisted of a submaximal base level, chosen at the beginning of the study as 50% of the MTP. A 60-s peak at MTP was superimposed on the base level activity every 5 min. This was achieved by increasing both the load and the pedalling rate from 60 rpm (endurance training) to 90 rpm (resistance training) to simulate a true acceleration (Fig. 1). Maximum Intensity of Endurance during the SWEET (MIEn5) is defined by both maximal heart rate

New Test for Endurance Training (SWEET) 361

% MTP RPM

lO0_B[

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Time (min) Fig. 1. Diagram representing the square-wave endurance exercise test (SWEET). At a submaximal base level (endurance training) working at 60 revolutions per minute (RPM) on a cycle ergometer, a 60-s peak of maximal tolerated power (MTP) was superimposed on the base level activity, every 5 min, at 90 RPM (resistance training)

(220-age) at the end of the test and the impossibility of maintaining 5% above the percent MTP of the MIE4s. Exhaustion would be reached at the end of MIE4s which could be expressed as % MTP, as total energy expenditure (TEE) in liters of oxygen, or as total mechanical work (TMW) in kJ �9 kg -1. At least two sessions were necessary to obtain an accurate value of MIE45. The level of base exercise varied as a multiple of 15 W increments for MTP ~ 240 W and 10 W increments for MTP ~ 210 W, which represents about + 5% variation from the base level of exercise. In untrained women, since MTP could be 150 or 120 W, the step variation may reach 6 - 8 % .

The term endurance or "the possibility of maintaining a submaximal exercise for as long a possible" is usually used in the field of sport physiology. Because of this vague definition, each author uses his own interpretation. In this work, "endurance capacity" has been interpreted, according to the MIE4s, as total mechanical work (TMW).

Before starting the tests, the subjects were asked to make a manual signal when they experienced signs of fatigue, or before stopping the exercise. Verbal encouragement was given to urge the subjects to maintain their maximal effort for another half, I or 2 rain depending on the test. Body weight was measured before and after exercise, to an accuracy of + 20 g.

Pulmonary and cardiac examination, arterial blood pressure, EKG and the subjective impressions of the subjects were monitored by the physician during the SWEET. Twenty-four hours later the subjects answered a questionnaire about subjective complaints. Statistical analysis included comparison of two mean values and the paired t-test.

Results

There were no adverse clinical effects during the various maximal tests. The mean (X + SEM) and range of age, weight and height of the different

groups of subjects are represented in Table 1. VO 2 max was lower in women than in men in untrained subjects. There were significant differences between trained and untrained women (p < 0.001) and men (p < 0.001); the difference between trained women and men was less (p < 0.05). The elite sportsmen showed the highest values of /dO 2 max, which were significantly different from all other groups.

362 M. Gimenez et al.

Table 1. Physical characteristics and lkO2 max of trained and untrained subjects

(~ • SEM) Age Weight Height ~rO 2 max yr kg cm ml �9 kg -1 �9 min -1

Untrained n

Women 12

Men 7

Trained Women

Men

32.6 • 2.8 58.8 • 2.1 163 • 2 (21-51) (49-67) (154-170)

34.9 • 4.2 70.3 • 3.1 172 • 2 (22-50) (56-83) (165-177)

8 33.1 • 2.5 54.9 • 2.6 164 • 3 (24-42) (46-66) (152-172)

9 28.1 • 3.1 69.9 • 2.5 176 • 3 (16-48) (58-82) (160-181)

Eli te

Men 7 23.3 + 3.6 65.9 + 2.6 173 • 1.4 (14-41) (54-77) (166-176)

-33.4 + 0.75 1

:38.7 + 2.20] ***

/ 48.5 + 1.95 ~

3 *

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Range is bracketed * p < 0.05 ** p < 0.01 *** p < 0.001

The SWEET lower than MIE45 was subjectively considered as easy, while on the other hand exercise greater than MIE45 was considered difficult. In the easy exercise HR was submaximal, while in the latter, HR was maximal, (220-age) before the subject stopped the SWEET. The subjects always stopped before the 45th minute from fatigue and exhaustion. The subjects considered the MIE45 as three successive stages of exercise. In the first stage, between the first and the 15th or 20th rain most subjects (36/43) thought that they could not continue the test till the 45th min. After the first 15 min the second "transition phase" takes place with the subject feeling better, a mechanism we can not explain physiologically. This will probably correspond to the well known "second wind". Finally, in the third stage, the hardest peaks are those corresponding to the 35th and 40th rain. No adverse effects were detected immediately after or 24 h later. Systolic arterial blood pressure varied very little before and after the peaks. The values at the 45th min of the MIE45 were distinctly lower in women (ranging between 150-200 mmHg) than in men (ranging between 160-240 mmHg). Sweat output, as clinically assessed, and weight loss as measured, were higher in the trained (1.05 + 0.07 kg) than in the untrained subjects (0.25 + 0.05 kg, p < 0.01). Perspiration started around the 10th rain of exercise in T subjects (Henane et aI. 1977).

Ventilation increased regularly with the duration of MIE45. It increased somewhat during the peaks, but more after them, and tended to return to the base level of exercise at about the 3rd or the 4th min in between the peaks. Ventilation during the MIE45 was higher in trained than in the untrained subjects, an example being given in Fig. 2. The difference of HR between the peaks and bases during MIE45 was dissimilar among the three groups: the

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while a slight tendency to decrease is observed in the base level of the T and U subjects. VO2 increases moderately throughout MIE45.

Using an energy equivalent of 20.195 kJ per litre of oxygen, the total energy expenditure (TEE), per session of 45 min, is represented in Fig. 4. TEE, TMW and % MTP are higher in the trained subjects (Fig. 4), the highest values occurring in the elite sportsmen. As for VO2 max, those variables tend to diminish according to age, especially in untrained subjects (Pollock et al. 1972). As comparative data, the second measurement of MIE45 and MIE45 + 5% MTP, performed 15 days later in four women and six men, shows a good reproducibility for TEE, TMW and % MTP.

Discussion

Preliminary accurate measurement of 1?O2 max at MTP was necessary for the precise assessment of MIE45. The notion that MlE45 always corresponds to a maximum level by the 45th min of exercise is supported by the behavior of the heart rate, which rises progressively and achieves an almost maximal value by the eighth exercise peak (Fig. 3). At the 9th peak (45th min of exercise) heart rate reaches the maximum observed during the two tests used for the determination of the 1?O 2 max (Gimenez et al. 1981). Whether the MIE is at or near maximum is also indicated by the fact that the subjects were unable to

New Test for Endurance Training (SWEET) 365

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maintain a value of exercise power higher than 4 - 6 % of MTP over the MIE45, for the full 45 rain, as shown in Fig. 2. These two elements, which define the MIE45 , assure a good reproducibility as pointed out in the results.

Another factor to be considered in the MIE45 is the total amount of work performed in each session. The energy output during the course of the test is higher in the trained than in the untrained subjects (Fig. 4). Also the % of MTP is significantly higher in trained; but more so in E subjects (Fig. 4). As a consequence, T subjects have higher total ventilation (Fig. 2), and higher oxygen transport, as measured by the oxygen pulse (Fig. 3), during the MIE45. Moreover, the lactate level at the end of MIE45 is significantly greater in E subjects (Gimenez et al. 1982). Consequently T subjects had better endurance capacity of skeletal and respiratory muscles (Gimenez et al. 1982b). For a training technique to be of a sufficient duration and intensity, and include a significant amount of work in order to be reliable and effective, the proposed MIE45 should satisfy these conditions. It is important to point out that, despite a significant amount of intense work, arterial pH and oxygen saturation remain constant at the end of the MIE45 (Gimenez et al. 1982a).

366 M. Gimenez et al.

Table 2. Correlations (r) between l)O~ max total energy expenditure (TEE) and total mechanical work (TMW) of maximal intensity of endurance (45 rain) of SWEET (MIE45)

n 1)O2 max (ml- kg -1) TEE (kJ. kg -1)

TMW (kJ. kg -1) TMW (kJ- kg -1)

Untrained Women 12 0.607*** 0.903*** Men 7 0.792*** 0.987***

Trained Women 8 0.790*** 0.913"** Men 9 0.453*** 0.869***

Trained Men 7 0.442 0.974"**

*** = p < 0.001

Prior testing in endurance capacity had already been undertaken using exercises at constant levels in percent of the 1)O2 max either at 80% (for about 1 h), 95% (for 20 min) and 100% for about 5 min (~strand and Rodahl 1970; Gleser and Vogel 1973; Lacour and Flandrois 1977). In the first case (80% of 1)O2 max for 1 h), the regularity of the course in the treadmill, or of pedalling in the cycle ergometer, for a longer period does not correspond to the rapid acceleration that endurance athletes do voluntarily or are obliged to do in a short space of time. In addition, the physiological and metabolic responses must be different for constant or "interval-training" work schedules (Mathews and Fox 1976). In the last two examples (95 or 100% of 1)O 2 max for 20 or 5 min) what is measured is tolerance to lactic acidosis. In effect, those levels are equivalent or higher than the aerobic capacity, and the lactate level in the blood increases progressively when the exercises last longer, i.e., until the subject can tolerate no more. Furthermore, starting at maximal power without warm-up (De Bruin-Prevost and Lefebvre 1980) is not appreciated by athletes, who also worry about muscular complications. The MIE45 which has a base level of intense endurance, and periodical maximum overloading, (Fig. 1) is nearer to competitive reality. The exercise starts at a submaximum level, which serves for an initial warm-up, and the regular peaks eliminate the monotony of constant level exercises. The peaks give the subject an impression of maximal exercise, and objectively it demands ventilatory (Fig. 2), cardiocirculatory (Fig. 3) acid-base balance and metabolic readjustments. (Gimenez et al. 1982a).

For the classification of endurance athletes, VO2 max has been proposed as the best test. Consideration must be given to the possibility that changes in 1)O2 max may not be a complete index of adaptation to endurance training (Daniel et al. 1978). Our results suggest that VO2 max reflects endurance capacity less faithfully than MIE45. Table 2 shows the correlation coefficients obtained between VO2max and the MIE45 (kJ. kg-1). The correlation coefficients differ in the different groups, but in all cases they are lower than 0.8.

New Test for Endurance Training (SWEET) 367

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However, in r o f 0 0 2 max/TMW is the lowest in the groups of trained and elite sportsmen. Figure 5 shows the correlation between these two variables for the 43 subjects. Many subjects with similar l)O2max had different endurance capacities (TMW), and !nversely other subjects with similar endurance capacity (TMW) had different VO 2 max. This disparity is not due to methodological artefacts (Gimenez et al. 1981). Concerning the maximum level of MIE45 , the mechanical calibration of the cycle ergometers, and the excellent correlation coefficient found between the TEE and the TMW of the MIE45 (r = 0.992, p < 0.001) show the validity of the total mechanical work measured, and indicate great efficiency in this particular test. Finally we have shown that a substantial improvement in endurance capacity, as measured by MIE45, can be observed in athletes without significant variations in. 002 max (Gimenez et al. 1982b). It appears, therefore, that in this study VO2 max does not always indicate the endurance of the subject.

Though the SWEET offers certain advantages, it can also have certain drawbacks. For a good assumptive value of MIE4~ it is necessary firstly to measure MTP carefully, and then carry out SWEET two or three times. This takes time. In our opinion the % MTP applied is in rapport with the degree of training and age. In Fig. 4 it can be seen that the % MTP usually varied between 40-52% in untrained subjects, between 55-65% in trained subjects and higher than 70% in the elite subjects. With those results in mind, and knowing the training rate of the subjects, it is easier and faster to approach the % MIE45, than using the standard 50% of MTP chosen at the beginning of the study. In practice, and for training purposes in sedentary subjects, it will be possible to approach the MIE45 in only two sessions: one for MTP and the other for SWEET, in which

368 M. Gimenez et al.

HR would permit adjustment to the correct MIE45 in the next session of training.

In summary, the 45-rain square-wave endurance exercise test is a useful tool for physical training in the laboratory, as will be discussed in another paper of this issue (Gimenez et al. 1982), and could be a practical method for the assessment of endurance athletes, according to their degree of training.

Acknowledgements. We are greatly indebted to Doctor B. Dull and Miss S. Horlick for their assistance in preparing the English manuscript. We wish also to thank Miss F. Poincelot and Mr. J. C. Henquel for technical assistance, and the secretaries Miss M. C. Rohrer for illustrations and Miss B. Clement and Mrs. P. Ulmer for typing the manuscript.

References

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training. Eur J Appl Physiol 39:249-254 Davies CTM, Knibbs AV (1971) The training stimulus. The effects of intensity duration and

frequency of effort on maximum aerobic power output. Int Z Angew Physiol 29:299-305 De Bruyn-Prevost P, Lefebvre F (1980) The effects of various warming up intensities and durations

during a short maximal anaerobic exercise. Eur J Appl Physiol 43:101-107 Eddy DO, Sparxs KL, Adelizi DA (1977) The effects of continuous and interval training in women

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Gimenez M, Salinas W, Servera E, Kuntz E (1981) VO2 max during progressive and constant bicycle exercise in sedentary men and women. Eur J Appl Physiol 46:237-248

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Kearney JT, StuU GA, Ewing Jr JL, Strein JW (1976) Cardiorespiratory responses of sedentary college women as a function of training intensity. J Appl Physiol 41:822-825

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Muller EA (1950) Ein Leistungs-Puls-Index als Mag der Leistungsffihigkeit. Arbeitsphysiologie 14 : 271- 284

Pollock ML, Broida J, Kendrick Z, Miller HS, Janeway R, Linnerud AC (1972) Effects of training two days per week at different intensities on middle-aged men. Med Sci Sports 4: 192-197

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Shephard RJ (1970) Intensity, duration and frequency of exercise as determinants of the response to training regime. Int Z Angew Physiol 26:272-278

Accepted March 22, 1982