PORSZASZ, J., R. CASABURI, A. SOMFAY, L. J. WOODHOUSE, and B. J. WHIPP. A Treadmill Ramp Protocol Using Simultaneous Changes in Speed and Grade. Med. Sci. Sports Exerc., Vol. 35, No. 9, pp. 1596-1603, 2003.
Introduction: A treadmill exercise test requiring a low initial metabolic rate that then increments the work rate linearly to reach the subject's limit of tolerance in approximately 10 min would have significant advantages for exercise testing and rehabilitation of subjects with impaired exercise tolerance.
Methods: We developed such a treadmill protocol that uses a linear increase in walking speed coupled with a curvilinear increase in treadmill grade to yield a linear increase in work rate.
Results: Twenty-two healthy, sedentary subjects performed both this new treadmill protocol and a standard cycle ergometry ramp protocol eliciting similar work rate profiles. The low initial treadmill speed and grade resulted in a low initial metabolic rate, commensurate with unloaded pedaling on a cycle ergometer (average V̇O2 = 0.54 ± 0.16 vs 46 ± 0.12 L·min-1). This combination of simultaneous increase in speed and grade yielded a linear work rate and its oxygen uptake response (R2 = 0.96 ± 0.03) with a slope of 11.4 ± 2.4 mL·min-1·W-1-slightly, but significantly, higher than on the cycle (9.6 ± 2.0 mL·min-1·W-1). This difference was attributed to unmeasured work associated, for example, with additional limb movements and frictional losses. As previously demonstrated, both the peak oxygen uptake and the estimated lactate threshold were higher on the treadmill than for cycle ergometry (averaging 23% and 27%, respectively, in these subjects).
Conclusion: This treadmill protocol provides a linear profile of work rate as is currently standard for cycle ergometry and is appropriate for testing of subjects with low exercise tolerance.
An incremental exercise test that linearly spans the tolerable work rate range has become the recommended procedure for initial assessment in clinical exercise testing (11,13,29). In these tests, work rate maybe advanced either as a ramp function (i.e., continuous increase) or using frequent stepwise increases in work rate. These tests are normally performed using either a cycle or treadmill ergometer. It has been argued that the treadmill has the advantage of educing a higher maximum metabolic rate and of using a mode of exercise that more closely approximates aspects of activities of daily living (5,11,13). Others prefer the cycle ergometer for this task, citing safety aspects of the test performance, ease of both blood sampling, and auscultation of blood pressure as well as the ability to precisely quantify work rate throughout the test (9,16,29). Because the linearity of the pattern of the oxygen uptake response is a major discriminating feature for assessing a cardiovascular basis for exercise intolerance (3,17,20,22, 28,30), it is naturally important to be confident of the linearity of the work rate profile that yielded the response.
For severely impaired patients, the metabolic cost of even normal walking or unloaded cycling can be a significant proportion of their maximum metabolic rate, which in turn limits the duration of the test and, consequently, the available range of data for interpretation. An incremental treadmill test starting at a slow and constant walking speed would provide a sufficiently low initial metabolic rate (12), but keeping the speed constant as the test progresses results in an inappropriately long test duration. Conversely, a faster and constant walking speed, although shortening the test, has the disadvantage of a high initial metabolic cost (5,34). We reasoned that the combination of an initially slow walking speed that is increased progressively in concert with an increasing grade would meet the demands of both an initially low exercise metabolic rate and optimum test duration. The simultaneous combination of change in speed and grade, however, does not directly provide a linear increase in work rate, thereby complicating the interpretation of the oxygen uptake profile, unless more complex methods of deconvoluting the oxygen uptake response are applied (14).
It was therefore the purpose of this study to design and implement a treadmill exercise test that a) requires a low initial metabolic demand; b) provides a constant rate of change in work rate (i.e., linear increase as a function of time) utilizing continuous changes in both speed and grade; and c) brings subjects to the limit of tolerance in approximately 10 min, i.e., meeting the requirements recommended for clinical exercise testing by the relevant major international organizations (1,2,9,15). Although this new protocol was thought to have its most valuable application in subjects with severely limited exercise tolerance (e.g., those with severe heart or lung disease), we chose to perform our initial validation in a group of healthy subjects with widely differing exercise tolerances, so that the robustness of the method might be evaluated. We evaluated this new treadmill protocol by comparing the cardiopulmonary and metabolic response profiles of healthy sedentary individuals with those from a cycle ramp test with an equivalent work rate incrementation profile.