The exercise prescription for endurance training is often defined in terms of a target heart rate (HR) based on relative HR (%HRmax or %HR Reserve) or relative exercise capacity (%maximal metabolic equivalents [METs] or %maximal MET Reserve) (1,15). However, both participants and exercise leaders are often as interested in the absolute dimensions of the exercise prescription (e.g., walking speed and grade to achieve the target HR or MET intensity) as in the target HR or MET value itself. This is particularly true in beginning exercisers who may be at risk for both cardiovascular complications (11) and subjective responses during early training sessions that might be so unpleasant as to limit the likelihood of continuing an exercise program. Thus, during the first few weeks of an exercise program, until the exerciser has learned the appropriate self-monitoring strategies, guidance regarding the appropriate absolute exercise training intensity is highly valuable. Previous work from our laboratory has demonstrated that maximal exercise test-derived parameters could be “translated” into absolute exercise intensities that could provoke a given HR response during training (7,8). However, this approach requires a maximal exercise test, which is often not available in fitness programs or which may be conducted with handrail support, which fundamentally confounds the process of translating exercise test results to the exercise prescription (2). Thus, there is a need for an objective method for translating submaximal exercise test responses into training prescriptions.
The Talk Test
The Talk Test (TT) has emerged as a technique applicable to submaximal exercise that is a reasonable surrogate for estimating the ventilatory threshold (VT) in a variety of populations (6,13,16,17) and of the ischemic threshold in patients who develop exertional ischemia (4). The Talk Test technique has been shown to be sensitive enough to reflect changes in VT attributable to blood loss and to training (12). However, we have also shown that the HR response during steady-state or interval exercise training may be systematically higher (e.g., cardiovascular drift) than predicted from the Talk Test during incremental exercise (12).
Accordingly, we thought it would be useful to determine the amount of reduction in absolute exercise intensity from the intensity during incremental exercise which would allow comfortable speech during a 20-minute exercise bout in sedentary individuals.
Experimental Approach to the Problem
The study was conducted as a within-subjects experimental trail observing physiological, subjective, and TT responses during counterbalanced steady-state exercise bouts, with the intensity of the bouts driven from TT responses during incremental exercise.
The subjects were 14 healthy, sedentary young adults (7 men, 7 women) (age = 25 ± 6 years). Although the subjects carried out normal daily activities, none had performed any systematic exercise training during the last 2 years, nor were any active in recreational/intermural sports competition. They provided written informed consent, and the protocol had been approved by the university human subjects committee.
After a familiarization session designed to habituate them to treadmill walking, the subjects performed an incremental exercise test to fatigue using a Balke-type protocol. Each subject walked at a constant speed (3.0 mph for women, 3.5 mph for men), beginning at 0% grade and incremented by 2.5% grade every 2 minutes until volitional exhaustion. Handrail support was not allowed. Exercise capacity was estimated from protocol-independent equations based on the terminal speed and grade achieved during the last minute of exercise (9). Heart rate was measured by radiotelemetry (Polar Electro Oy, Finland). During the last 30 seconds of each stage the subjects recited a standard paragraph (The Pledge of Allegiance) out loud and responded to the question “Can you speak comfortably?” Possible answers were “yes,” some sort of equivocation (equivocal), and “no” (negative). The speed and grade at the last time that the subject responded with “yes” was noted and used as a reference point (LP) for subsequent exercise training bouts (described later).
On subsequent days, separated by at least 48 hours, the subjects performed three 20-minute exercise training bouts. The subject warmed up by following the incremental treadmill protocol until they achieved the stage prior to the last positive stage (LP-1) during the incremental test, the LP, or the stage following the last positive stage (e.g., first equivocal stage [EQ]). For the remainder of the 20-minute exercise bout, the speed and grade of the treadmill remained constant. Handrail support was not allowed. The order of presentation of the 3 exercise bouts was counterbalanced. During the last 30 seconds of each 2-minute period of this “warm-up and workout,” the subject recited the standard paragraph and responded to the “Can you speak comfortably?” question. From this we ranked the speech difficulty according to the following scheme: “Yes, I can speak comfortably” = 1; equivocal response = 2; and “No, I can't speak comfortably” = 3. Heart rate and the rating of perceived exertion (RPE) using the category ratio scale (3) were measured every 2 minutes.
Comparisons of both absolute and relative exercise intensity (METs, HR), RPE, and speech difficulty during the last 6 minutes of the steady-state exercise bouts among the 3 TT-defined exercise intensities were compared using repeated-measures analysis of variance (ANOVA). When statistically significant (p < 0.05) differences were observed using ANOVA, post hoc comparisons were made using the Tukey test. We hypothesized that both objective and subjective exercise responses would differ during steady-state exercise from those observed during incremental exercise and that steady-state conditions might not be observed during workloads rated “equivocal” during the incremental test.
The absolute and relative exercise intensities, calculated as METs and %maximal METs, are presented in Figure 1. All 3 strategies for prescribing exercise resulted in exercise intensities within the recommended training range (50-85% of maximal METs) based on calculation of exercise intensity at a given speed and grade (1,15). The calculated value for METs (5.1 ± 1.7, 5.9 ± 1.9, and 6.6 ± 1.8) and % maximal METs (59 ± 3, 68 ± 4, and 76 ± 3) were significantly different among all the training bouts.
The absolute and % maximal HR values are presented in Figure 2. All 3 strategies for prescribing exercise intensity from the incremental exercise TT markers resulted in exercise HRs within the recommended training range (65-94% of HRmax). The strategies based on LP-1 and LP stages of the Talk Test resulted in stable HR values, whereas the HR response at the intensity of the EQ stage of the Talk Test resulted in a progressive HR drift throughout the exercise bout. The terminal values for both absolute HR and % maximal HR were significantly different between all training bouts.
The RPE during the training sessions is presented in Figure 3. Training bouts based on the LP-1 and on the LP stage of the TT resulted in terminal RPE values that were within the recommended range (3-5, e.g., moderate to hard). Training bouts based on the EQ stage of the Talk Test resulted in very high terminal values for RPE (∼7, e.g., very hard), with some subjects barely able to finish the 20-minute exercise bout. The terminal values for RPE (3.8 ± 1.7, 4.4 ± 1.8, and 6.6 ± 2.2) were significantly different among all 3 training bouts. Based on the scoring of speech comfort during the training bout, training sessions based on the LP-1 stage of the Talk Test allowed comfortable speech in most of the subjects (Figure 3). By the end of the training session, based on the LP stage of the Talk Test, most of the subjects were beginning to express some difficulty with speaking. In the exercise session based on the EQ stage of the Talk Test, most subjects were not able to speak at all during the terminal portion of the bout. The terminal values for speech difficulty (1.4 ± 0.5, 1.8 ± 0.4, and 2.6 ± 0.5) were significantly different among all 3 exercise bouts.
Although our previous work has documented that TT responses during incremental exercise testing can successfully identify exercise intensities relative to the VT, we have not previously demonstrated how the actual exercise intensity “translates” when the Talk Test responses are applied to steady-state exercise training. The main result of this study was that, to be able to speak comfortably throughout a 20-minute exercise bout, in previously untrained individuals the absolute exercise intensity must be decreased from that during which comfortable speech is last observed during an incremental exercise test. Although all 3 exercise prescriptive strategies produced steady-state exercise responses within the rather broad MET and % HRmax ranges recommended by the American College of Sports Medicine (1,15), the subjective intensity of the training bouts (based on RPE and the Talk Test) was excessive in most subjects unless the intensity was decreased by about the magnitude of 1 exercise stage (1.0-1.2 METs or ∼10-12% based on a mean 8.8 MET exercise capacity) below the LP stage during the incremental exercise test. With this amount of reduction in the absolute exercise intensity, appropriate objective and subjective intensity criteria can be achieved, based entirely on the responses during the purely submaximal portions of the incremental exercise test.
This ability to use submaximal exercise responses to derive absolute exercise training intensity may be particularly useful to those responsible for the early training sessions in previously sedentary individuals. Unaccustomed strenuous exercise is associated not only with poor compliance with exercise training programs, but also with increased risk for catastrophic events (11). Further, because exercise test responses at the intensity of the Talk Test are known to be fairly reproducible (14), the calculation of the MET value at the EQ stage of the TT may provide a reasonable estimate of improvement during exercise programs (9), essentially serving as a surrogate for changes in VT, which may be a very good marker of sustainable exercise capacity (10).
The results, indicating a step down of ∼10 to 12% in the exercise intensity from the exercise test to the exercise training session, are in substantial agreement with our earlier findings, based on the step down necessary to achieve a defined target HR derived from a maximal exercise test using either the Bruce treadmill or a cycle ergometer protocol (7,8). In the present study, the combination of speed and grade at which the HR was the same during the exercise training bout calculated to be 1.1 ± 0.3 METs lower than during the exercise test. In a recent study from our laboratory (12), we demonstrated that when the exercise intensity was rapidly transitioned to approximately that of the equivocal stage of the Talk Test, it took ∼4 minutes before the subject was able to sense that the intensity was too high for comfortable speech. We believe that this finding supports the results of this study, where there was a continual upward drift in both RPE and perceived speech difficulty, particularly during the heaviest workload.
The ability to speak comfortably is probably related to the ability to control breathing frequency. Given that the tidal volume is nearly maximal at even modest workloads, most of any progressive increases in pulmonary ventilation must occur at the expense of increases in breathing frequency. During steady-state exercise at intensities in excess of VT, there is a progressive increase in O2 and VE, the slow component (5). Because the EQ stage of the Talk Test is very close to the intensity of the VT, it seems reasonable that sustained exercise at this intensity would provoke a slow component of O2 kinetics, leading to increases in breathing frequency and a progressive loss in the ability to speak comfortably. Because we were interested in the ability of the subjects to speak comfortably, we did not measure respiratory gas exchange in the present study. It would be of interest to collect gas exchange data to demonstrate the stability of the breathing pattern during the kinds of exercise performed in this study.
This study was limited to individuals who were sedentary, in that we felt that a major need within the exercise community is to find ways to not only encourage people to start exercise programs, but also to allow them to have a good-enough early experience with exercise so that there is a reasonable chance that they will continue with an exercise program. Beyond the small risk of catastrophic events from inappropriately hard exercise (11), high-intensity exercise in sedentary individuals is likely to be so unpleasant that they quit the exercise program before achieving the benefits of exercise. In the usual model of exercise prescription, a rather wide range of exercise intensities are prescribed. However, sedentary individuals have little understanding of the specific behavior (e.g., walking speed and grade) necessary to achieve a target training intensity. Further, as was evident in the present data, even when objectively correct exercise intensities are achieved, the range of subjective responses is large, often including effort that is not sustainable. We believe that the present results, demonstrating the degree to which exercise intensity needs to be reduced from subjective submaximal markers observed during exercise testing, provides needed guidance toward making early exercise sessions more tolerable, particularly until the beginning exerciser acquires a sense of the appropriate “feel” (e.g., RPE) of exercise training that will result in reasonable values for %maximal METs or % maximal HR.
The results of this study demonstrate that appropriate objective and subjective responses during exercise training can be achieved from data observed during the purely subjective portions of an incremental exercise test. If the exercise intensity during the stage proceeding the LP stage of the Talk Test is chosen, from a submaximal exercise test that is terminated at the EQ stage of the Talk Test, not only can a defensible marker of exercise capacity be generated, but also an intensity for training that will result in both objectively and subjectively appropriate exercise responses during training can be defined. This information may be particularly important to the beginning exerciser during the first weeks of an exercise program to not only ensure adequate levels of exercise, but also to guard against inappropriately high levels of exertion. The present data obviously apply to young and healthy individuals of both sexes and need to be extended to other populations. As a result, we believe that these data may allow a rational basis for evaluating progress in exercise programs and prescribing exercise, in a highly individual manner, and without the necessity for a maximal exercise test.
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