A new single-stage step test for the clinical assessment of maximal oxygen consumption.

A New Single-Stage Step Test for the Clinical Assessment of Maximal Oxygen Consumption Substantial evidence has accumulated delineating the positive metabolic and health consequences of regularly conducted physical activity. [1,2] Consequently, it is becoming increasingly important to include assessments of cardiorespiratory fitness (eg, measurements of maximal oxygen consumption [[Vo.sub.2.max]]) in any health-assessment program or routine involving variables that may be influenced by an individual's level of physical fitness or ability to sustain an exercise program.

A number of testing methods have been devised for environments in which equipment is limited or time is a priority. These tests predict [Vo.sub.2.max] indirectly from a submaximal work-performance test without the requirement of maximal exertion. These tests are appealing for clinical situations because they offer the attractiveness of simplicity, safety, and validity within an economy of time management. [3] The most popular clinical methods of submaximal testing have been those that predict [Vo.sub.2max] by extrapolation from the relationship of oxygen consumption and heart rate values recorded during or immediately following a session of steady-state submaximal exercise. [4-6]

A testing device that is generally suitable for submaximal testing in the clinic is the simple bench step. [7,8] Of the many procedures that use steps for the estimation of [Vo.sub.2max], the single-stage protocol is one of the easiest to adminiter. The earliest and most popular single-stage step test was the Harvard Step Test. [9] Whereas in its original form the test was useful in determining cardiorespiratory fitness in selected groups of subjects, the strenous protocol of stepping at an elevated height of 50.8 cm at a rate of 30 steps per minute for 5 minutes limited its usefulness for general testing.

Accordingly, a variety of modifications of one or both of these tests' variables have been attempted in order to make the tests more inclusive of distinct individuals. The resulting adaptations have been reflected in a diversity of tests that use bench heights ranging from 30 to 50 cm and stepping frequencies of 18 to 36 step-ups/min (KT Francis, R. Feinstein; unpublished research). [10-12] Although these modifications have enhanced the applicability of the single-stage step test, the important consideration of adjustment of the step height to accommodate for individual differences in stature has been overlooked.

Recently, a new single-stage step test was introduced that uses a height-adjustable platform to normalize the height of stepping for individuals of varying stature (KT Francis, R Feinstein; unpublished research). [10-12] The determination of the adjusted step height was modeled from anatomical studies and consideration of efficiency of stepping with respect to hip angles. [13] This test, which has been validated in groups of subjects ranging in age from 6 to 47 years, [10-12] provides some of the highest correlation values between predicted and measured values of [Vo.sub.2max] of any reported single-stage step test (Tab. 1). The following computer program is designed to simplify the use of this test and to facilitate the implementation in clinical environments where equipment or time is limited, yet accuracy and validity are essential.

Description of the Test

The platform height used for testing each subject is based on the height of the foot when the hip is flexed at an angle of 73.3 degrees. This value is determined from a geometric relationship of an individual's stature and femur length and expressed in the formula:

(1) [H.sub.f = (L.sub.f X I.sub.h) X 0.7162]

where [H.sub.f] is foot height (in centimeters), [I.sub.h] is stature (in centimeters), and [L.sub.f] is the ratio of femur length to stature. The corresponding ratios of femur length to stature, categorized by age and sex, are shown in Table 2. A more detailed description of the development of the formula is available from the author.

The step test is administered by having the patient step up and down on the height-adjusted platform for 3 minutes to a cadence established by a metronome set at 104 clicks per minute (26 ascents per minute) for adults or 88 clicks per minute (22 ascents per minute) for children. Immediately after stepping for a period of 3 minutes, the patient remains standing while a recovery pulse rate is determined for a 15-second period starting 5 seconds into recovery. Maximal oxygen consumption is estimated using the following equations:

Adults:

(2) [Vo.sub.2max] = 71.97 - (0.776 X 15-second recovery heart rate)

Children and adolescents:

(3) [Vo.sub.2max] = 103.42 - (1.588 X 15-second recovery heart rate)

Even though the height-adjusted, single-stage step test is an attractive means of assessing [Vo.sub.2max] in a clinical setting, there remains the relative inconvenience following the performance of the test of calculating and collating the results. The data must be entered into the appropriate equation and the results summarized in a format that is useful for consulting with the patient.

The use of the accompanying program provides an attractive alternative to the traditional methods of data acquisition, reduction, and summary. The computer performs the related task of data reduction and calculations and organizes the results into a tabular and graphical format for rapid perusal and interpretation. In addition, simple instructions for the performance of the test are included within the program. A sample printout of a typical patient is shown in the Figure.

The program is written in Microsoft BASIC for IBM-PCs (*1) and IBM-PC- compatible computers. The program can easily be adapted for other computer dialects with minimal changes. RE-Mark statements are included to facilitate the adaptation.

(*1) International Business Machines Corp, 1000 NW 51st St, Boca Raton, FL 33432.

References

[1] Kannel W. Some health benefits of physical activity. Arch Intern Med. 1979;139:857-861.

[2] Leon A. Physical activity levels and coronary heart disease. Med Clin North Am. 1985;69:3-20.

[3] American College of Sports Medicine. Guidelines for Exercise Testing and Prescription. 3rd ed. Philadelphia, Pa: Lea & Febiger; 1986.

[4] Astrand P, Rhyming I. A nomogram for the calculation of aerobic capacity (physical fitness) from pulse rate during submaximal work. J Appl Physiol. 1954;7:218-221.

[5] Bailey DA, Shephard RJ, Mirwald RL. VAlidation of a self-administered home test of cardiorespiratory fitness. Can J Appl Sports Sci. 1976;1:1-9.

[6] Watkins J. Step tests of cardiorespiratory fitness suitable for mass testing. Br J Sports Med. 1984;18:84-89.

[7] Bruce R. Methods of exercise testing. Am J Cardiol. 1974;33:715-720.

[8] Shapiro A, Shapiro Y, Magazanik A. A simple test to predict aerobic capacity. J Sports Med Phys Fitness. 1976;16:209-214.

[9] Brouha L. The step test: a simple method of measuring physical fitness for muscular work in young men. Research Quarterly. 1943:14:34-38.

[10] Francis KT, Culpepper M. Height-adjusted, rate-specific, single-stage step test for predicting maximal oxygen consumption. South Med J. 1989;82:602-606.

[11] Feinstein, R, Francis KT. Standardization of step-height for fitness testing using stature and hip angle of children and adolescents. Pediatr Res. 1989;25:5A. Abstract.

[12] Francis KT, Brasher JD. A height-adjusted step test for predicting maximal oxygen consumption in males. In: Abstracts of Platform and Poster Presentations: 65th Annual Conference of the American Physical Therapy Association; June 24-28, 1990; Anaheim, California. Alexandria, Va: American Physical Therapy Association; 1990:87. Abstract.

[13] Culpepper M, Francis KT. An anatomical model to determine step height in step testing for estimating aerobic capacity. J Theor Biol. 1987;129:1-8.

K Francis, PhD, is an exercise physiologist, Division of Physical Therapy, The University of Alabama at Birmingham, SHRP Bldg, Rm B41, Birmingham, AL 35294 (USA).