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00005768-199606000-0001400005768_1996_28_752_foster_independent_6miscellaneous-article< 73_0_9_4 >Medicine & Science in Sports & Exercise©1996The American College of Sports MedicineVolume 28(6)June 1996pp 752-756Predicting functional capacity during treadmill testing independent of exercise protocol[Applied Sciences: Physical Fitness and Performance]FOSTER, CARL; CROWE, AMY J.; DAINES, ERIN; DUMIT, MAURICE; GREEN, MEGAN A.; LETTAU, STACEY; THOMPSON, NANCY N.; WEYMIER, JEANMilwaukee Heart Institute, Milwaukee, WISubmitted for publication December 1995.Accepted for publication March 1996.Address for correspondence: Carl Foster, Ph.D., Milwaukee Heart Institute, P.O. Box 342, Milwaukee, WI 53201-0342; E-mail:cfoster@facstaff.wisc.edu.ABSTRACTClinically useful estimates of ˙VO2max from treadmill tests(GXT) may be made using protocol-specific equations. In many cases, GXT may proceed more effectively if the clinician is free to adjust speed and grade independent of a specific protocol. We sought to determine whether˙VO2max could be predicted from the estimated steady-state˙VO2 of the terminal exercise stage. Seventy clinically stable individuals performed GXT with direct measurement of ˙VO2. Exercise was incremented each minute to optimize clinical examination. Measured˙VO2max was compared to the estimated steady-state ˙VO2 of the terminal stage based on ACSM equations. Equations for walking or running were used based on the patient's observed method of ambulation. The measured ˙VO2max was always less than the ACSM estimate, with a regular relationship between measured and estimated ˙VO2max. No handrail support: ˙VO2max = 0.869·ACSM - 0.07; R2 = 0.955, SEE = 4.8 ml·min-1·kg-1 (N = 30). With handrail support: ˙VO2max = 0.694·ACSM + 3.33; R2 = 0.833, SEE = 4.4 ml·min-1·kg-1(N = 40). The equations were cross-validated with 20 patients. The correlation between predicted and observed values was r = 0.98 and 0.97 without and with handrail support, respectively. The mean absolute prediction error (3.1 and 4.1 ml·min-1·kg-1) were similar to protocol-specific equations. We conclude that ˙VO2max can be predicted independent of treadmill protocol with approximately the same error as protocol-specific equations.Determination of functional exercise capacity is an important outcome of clinical graded exercise testing. Functional exercise capacity is an important index of prognosis independent of other factors(5-7,16,21). Although direct measurement of ˙VO2max is the definitive index of functional exercise capacity, in the majority of clinical situations it is inconvenient to directly measure ˙VO2max. Accordingly, functional exercise capacity usually is estimated on the basis of protocol-dependent prediction equations(2-4,7-9,11,12,14,17-19,24-26). Unfortunately, in many cases, standard exercise protocols do not provide a patient-friendly format for conducting exercise examinations. Frequently, the initial workload is too high or the increments between stages are too large to provide for an orderly test. In many cases we have found that a better test is obtained if frequent, small, patient-specific increments in the velocity and grade of the treadmill belt are made. Similarly, others have found that a large number of very small changes in speed/grade (ramping) makes for a smoother exercise test (22,23).As useful as these strategies might be in allowing for a patient-friendly exercise test, they make estimating functional exercise capacity difficult because conventional prediction equations cannot be used and˙VO2max is virtually always less than the estimated steady-state aerobic requirements of the terminal exercise stage(10,13). This problem is further complicated by the influence of handrail support on the relationship between exercise performance and ˙VO2max(13,15,19). Various investigators have demonstrated that there is a systematic difference between the measured˙VO2max and the estimated steady-state aerobic requirements of the last treadmill stage attained (estimated from the speed and grade of the treadmill belt)(10,13,15,20,22,27). The estimated steady-state aerobic requirements of the last stage attained almost always grossly overestimate the achieved ˙VO2max. This may be attributable either to the lack of time during the terminal exercise stage for oxygen uptake to adapt or to the emergence of the classical plateau of˙VO2 during incremental exercise testing. However, some authors have suggested that there might be a regular relationship between the estimated steady-state aerobic requirements of the terminal exercise stage and the achieved ˙VO2max sufficient to allow prediction of˙VO2max, particularly if a small increment protocol (i.e., ramping) is used (22,23).Accordingly, the intent of this study was to determine whether˙VO2max could be predicted from the estimated steady-state aerobic requirements of the last treadmill stage attained during an exercise test with comparatively small workload increments between stages. We hypothesized that there would be a consistent difference between the estimated steady-state aerobic requirements of the terminal exercise stage and measured˙VO2max sufficient to allow prediction of ˙VO2max with clinically acceptable accuracy.METHODSSubjectsThe subjects for this study were 70 patients (38 males, 32 females) (mean age = 44.6 ± 12.5 yr) referred for exercise testing either to evaluate cardiorespiratory disease or for exercise prescription. They represented a wide variety of exercise capacities from very debilitated patients to competitive athletes. All patients were clinically stable and provided informed consent. Manipulation of medications prior to the test was conducted according to the instructions of the referring physician. A separate group of similarly referred patients (12 males, 8 females) (mean age = 48.5 ± 13.8 yr) was used as a cross-validation group to test the regression equations developed. There were no systematic differences between the validation and cross-validation groups (≈50% of each group had documented coronary artery disease that was clinically stable at the time of testing; ≈30% of each group was taking medications (beta blockers, calcium channel blockers), which might influence the heart rate response to exercise).ProtocolAll patients exercised to clinically relevant endpoints on a motor-driven treadmill. Patients were given a brief period of habituation to the treadmill and instructed to ambulate without holding onto the handrails if possible. However, if they could not ambulate smoothly without handrail support, we encouraged the patients to use as little handrail pressure as possible. The presence/absence of handrail support was noted and used in the subsequent analysis of the data.The exercise protocol was individually adjusted to conclude the test in 8-12 min. The workload was changed every minute. In many cases we consulted the patient regarding whether he/she preferred to go faster or up a steeper incline during the next stage. The magnitude of increments in treadmill velocity and elevation was selected based on the experience of the individual monitoring the test. Generally, velocity increments ranged from 0.2 to 0.5 mph(0.089-0.223 m·s-1) and grade increments ranged from 2 to 5%. During the concluding minute of the test, we noted the velocity and grade, whether the patient was walking or running on the treadmill belt, and whether or not handrail support was used. Alternating walking/running was considered to be running. Test termination was based on conventional symptoms (fatigue, angina pectoris (3 on a 4-point scale), dyspnea) and signs (progressive ST segment depression ≥0.03 mV, hemodynamically significant arrhythmias, or a decrease in systolic BP with exercise). In all fatigue-limited tests the patient had achieved ≥85% of the age-predicted HRmax. Gas exchange criteria were not used to decide when to terminate the test.Pulmonary oxygen uptake (˙VO2) was measured throughout the exercise test using open-circuit spirometry (Quinton Q-Plex).˙VO2max was taken as the ˙VO2 measured during the last full minute of exercise. Patients for whom the terminal exercise stage was less than a full minute were analyzed relative to the last full minute that they did complete.The estimated steady-state ˙VO2 for the terminal treadmill stage was calculated on the basis of equations published by the ACSM(1). However, the ordinary velocity constraints of these equations were set aside. Thus, if a patient was walking (at whatever velocity) during the last stage of the test, we used the ACSM walking equation: EquationEquation 3CIf the patient was jogging/running or alternating walking/jogging (at whatever velocity) during the last stage of the test, we used the ACSM running equation: EquationEquation 3DIt should be noted that the estimated steady-state aerobic requirements of the terminal exercise stage represent a population average that has its own intrinsic variability. Because we never achieved steady-state conditions during any portion of this test, we made no attempt to correct for individual differences in the aerobic requirements of treadmill ambulation.Statistical AnalysisThe steady-state ˙VO2 requirement of the last stage achieved and the measured ˙VO2max were compared using simple regression and ANOVA. A prediction equation relating the steady-state ˙VO2 requirement of the last stage completed to the measured ˙VO2max was calculated using a curve-fitting program. The predicted ˙VO2max using this regression equation was then compared with the measured˙VO2max in the cross-validation group. The correlation between predicted and measured ˙VO2max was computed together with the mean absolute error.RESULTSThere was a significant difference between the estimated steady-state aerobic requirements of the terminal exercise stage and the measured˙VO2max, both without (55.3 ± 16.4 vs 47.1 ± 14.6 ml·min-1·kg-1, P < 0.01) and with(37.8 ± 13.7 vs 29.8 ± 10.4 ml·min-1·kg-1, P < 0.01) handrail support allowed. In all but one individual case, the estimated steady-state aerobic requirements of the terminal stage were greater than the measured˙VO2max. However, there was a regular relationship between the estimated steady-state aerobic requirements of the terminal exercise stage and the measured ˙VO2max. This relationship was well described by a linear regression equation. The R2 was high (0.995 and 0.833, for nonhandrail-supported and handrail-supported exercise, respectively) and the standard error of estimate comparatively low (4.8 and 4.4 ml·min-1·kg-1, respectively)(Fig. 1). The relationship between the measured˙VO2max and the estimated aerobic requirements of the terminal exercise stage can be represented by linear regression equations:˙VO2max = 0.869·ACSM - 0.07 (nonhandrail supported) or˙VO2max = 0.694·ACSM + 3.33 (handrail supported).Figure 1-Relationship between ˙VO2max estimated on the basis of the aerobic requirements of the last exercise stage completed and the measured ˙VO2max in the validation group.When the protocol-independent prediction equations were used in the cross-validation group, there was no significant difference between predicted and measured ˙VO2max for either nonhandrail-supported (46.6± 15.8 vs 46.6 ± 15.3 ml·min-1·kg-1) or handrail-supported (31.3 ± 12.4 vs 33.7 ± 15.1 ml·min-1·kg-1) exercise. The correlation between predicted and measured ˙VO2max in the cross-validation group was high for both nonhandrail-supported (r = 0.98) and handrail-supported (r = 0.97) exercise, and the mean absolute error was low (3.1 and 4.1 ml·min-1·kg-1, respectively)(Fig. 2).Figure 2-Relationship between predicted ˙VO2max (from the regression equations developed in the validation group) and measured˙VO2max in the cross-validation group.DISCUSSIONThe results of this study demonstrate that the estimated steady-state aerobic requirements during the last stage achieved of a treadmill exercise test can be used as a basis for calculating the functional exercise capacity independent of exactly how that stage was reached (exercise protocol). A comparison of the correlation and standard error of estimate using this approach compares favorably with a number of other protocol-specific prediction equations published in the literature(4,8,9,11,12,17-19,23,25,26). This new approach may allow calculation of functional exercise capacity even when a specific exercise protocol must be abandoned, or when the clinician chooses to custom design the exercise protocol to fit the needs of each patient. The overall relationship between the estimated aerobic requirements of the terminal exercise stage and measured ˙VO2max (in the group using handrail support) is very similar to that observed by Myers et al.(22,23). We interpret this as suggesting that our empirical approach to incrementing the workload is substantially similar to a predetermined ramping protocol.The equation derived for the nonhandrail-supported condition has a much higher correlation and better “fit” of the data than the equation for handrail-supported exercise. This is consistent with previous findings(15,19). It doubtless represents the effect of variability in the magnitude of handrail support, which can significantly influence not only time to fatigue but the time course of the heart rate and˙VO2 response to exercise (28).Our protocol is in many respects reminiscent of branching protocols that were briefly popular 20 yr ago. Formal branching protocols have the advantage of also being responsive to how the patient is responding to the exercise test. However, the requirement to calculate heart rate and refer to a table to select the appropriate branch takes attention away from the patient. Additionally, since most branching protocols operate on the basis of heart rate responses, patients taking medications known to influence the heart rate response to exercise will not be able to be appropriately stressed using a branching protocol. Our approach relies upon perceived exertion and the clinical experience of the individual conducting the exercise test to select(and scale) an appropriate “branch.” Our experience in this group of subjects indicated that the patients were very comfortable with the protocol and we were usually able to coordinate ending the test at the end of a full minute of exercise.The precision of estimating functional exercise capacity is adequate for many clinical purposes. In very debilitated patients the effective confidence window for estimating exercise capacity (≈1 MET) may represent too large an error to be clinically acceptable. Additionally, in patients where more exact knowledge of exercise capacity is important (e.g., transplant candidates, disability assessment), direct measurement of respiratory gas exchange is clearly necessary. Nevertheless, we feel that the present data support the concept of using patient-customized exercise protocols, and that functional exercise capacity can be estimated with as much accuracy using this approach as with conventional clinical exercise protocols. Because estimation of functional exercise capacity depends on only a few variables, it is comparatively easy to note the terminal velocity and grade of the treadmill belt, whether or not the patient is using handrail support, and whether the patient is walking or running. Then, by using either tables or a handheld calculator, the functional exercise capacity can be rapidly calculated.REFERENCES1. American College OF Sports Medicine. Guidelines for Exercise Testing and Prescription, 5th Ed. Baltimore: Williams & Wilkins, 1995, pp 277. [Context Link]2. Balke, B. An experimental study of physical fitness of Air Force personnel. U. S. Armed Forces Med. J. 10:675-688, 1959. [Context Link]3. Bruce, R. A. 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Exercise2003351145-149JAN 2003Accuracy of V̇O2max Prediction Equations in Older AdultsPETERSON, MJ; PIEPER, CF; MOREY, MChttp://journals.lww.com/acsm-msse/Fulltext/2003/01000/Accuracy_of_V_O2max_Prediction_Equations_in_Older.22.aspx138http://pdfs.journals.lww.com/acsm-msse/2003/01000/Accuracy_of_V_O2max_Prediction_Equations_in_Older.00022.pdfInternalThe Journal of Strength & Conditioning Research10.1519/JSC.0b013e3181c02bce20092392425-2429DEC 2009Translation of Submaximal Exercise Test Responses to Exercise Prescription Using the Talk TestFoster, C; Porcari, JP; Gibson, M; Wright, G; Greany, J; Talati, N; Recalde, Phttp://journals.lww.com/nsca-jscr/Fulltext/2009/12000/Translation_of_Submaximal_Exercise_Test_Responses.1.aspx287disablehttp://dx.doi.org/10.1519%2fJSC.0b013e3181c02bce