Which of the Following is Monitored Continuously During the Clinical Maximal Exercise Test Quizlet

The maximal rate at which oxygen can be processed by muscle cells ⁽²⁴⁾ is termed maximum oxygen uptake (V˙O_2peak) and involves the integration of functions of the neuromuscular, cardiovascular, and pulmonary systems. V˙O_2peak is used to classify individuals into categories of cardiovascular fitness ^(2,4) and is frequently used as the basis for exercise prescription. It can be measured from standardized protocols using the treadmill, leg cycle ergometer, or arm crank ergometer ^(2,6,7). Owing to the specificity of the metabolic response to an exercise mode, it is ideal to measure V˙O_2peak on the same mode as the one with which the participant exercises.

There are several limitations of"maximal" stress testing including the need for trained personnel, length of time needed to conduct the tests, expensive equipment, and a possible health hazard for some subjects ^(2,8). Therefore, submaximal exercise testing is often used for the purpose of predicting V˙O_2peak when testing large populations, individuals over 40 yr of age, if time and equipment are limited, and when safety is an issue ^(2,3,13). Exercise modes that have been used for submaximal exercise testing include treadmill, leg ergometer, arm ergometer ^(5,13,14,23), and all-extremity ergometry ^{(11,13,17,18,22)}.

In previous work, the principal investigator found that a submaximal all-extremity ergometry test estimated a higher V˙O_2peak than a leg ergometer test in college-aged females. The higher value was closer to that expected from a treadmill test and, therefore, judged to be a better mode for submaximal testing. All-extremity ergometers are particularly desirable for many populations with extremity weakness or disability who would benefit from maximizing the muscle mass involved in exercise. A submaximal testing protocol has been validated for the Schwinn Air-Dyne, one of the first all-extremity ergometers to become commercially available ⁽¹³⁾. However, its primary use has been with individuals involved in cardiac rehabilitation, and it may be inappropriate for some clinical populations such as those with impaired balance. The SciFit Pro II Power Trainer is an all-extremity ergometer that is ideal for testing a wide variety of clinical populations because it has a high-back semirecumbent chair, foot straps that can accommodate to ankle-foot orthoses, and a removable seat that allows room for a wheelchair. Therefore, it would be useful for individuals who have limited function of the arms and/or legs ⁽¹⁰⁾.

Presently, no submaximal exercise test exists that utilizes the Pro II Power Trainer. The purpose of this study was to develop and validate a submaximal exercise test protocol and regression equation using this equipment with ablebodied women. This protocol will allow clinicians to estimate V˙O_2peak and prescribe appropriate and safe guidelines for exercise without the drawbacks of maximal testing. A second goal was to determine the relationship between V˙O_2peak values measured during a maximal treadmill and a maximal all-extremity ergometer test. It was hypothesized that the all-extremity test would prove to be a valid predictor of V˙O_2peak.

METHODS

Subjects. A group of 33 healthy female subjects between the ages of 30 and 60 yr were recruited to participate in this study. Ages of the 33 females ranged from 32 to 57 yr with the mean age ± SD of 45.30 ± 8.05. The subjects had no musculoskeletal, neuromuscular, or cardiopulmonary impairment and were heterogeneous with respect to general physical activity level and cardiovascular fitness category. Individuals had medical clearance to perform a maximal exercise test, and written informed consent was obtained in accordance with university guidelines for human experimentation. Fitness level was estimated using a nonexercise estimate of V˙O_2peak ⁽¹⁶⁾ based on activity level, age, height, and weight. The subject was then classified into a high, medium, or low fitness level, based upon this equation. The distribution of subjects is listed in Table 1.

TABLE 1:

Demographic information of subjects.

SUBJECT INFORMATION

Experimental Design

Each subject performed three exercise tests: a submaximal all-extremity test, a maximal all-extremity test, and a maximal treadmill test. The tests were performed in a randomized order, and each subject completed her three tests within a 2-wk period, with each testing day separated by at least 48 h.

Heart rate was monitored throughout testing using the Polar Vantage XL heart rate monitor (Polar CIC, Port Washington, NY). Blood pressure was taken before and after each test for safety precautions with a standard sphygmomanometer and stethoscope.

The maximal treadmill test was performed on a Quinton 55 treadmill. The maximal and submaximal all-extremity exercise tests were performed on a Pro II Power Trainer (SciFit, Tulsa, OK). To measure V˙O_2peak during the two maximal tests, a SensorMedics 2900 metabolic measurement system was used to measure respiratory and metabolic responses during exercise. Expired gases were collected continuously through a mouthpiece and tubing connected to an adjustable head set. A nose clip was fastened to the subject's nose to direct all ventilation through the mouth. Calibration of the instrumented metabolic system was performed (gas flowmeter, and O₂ and CO₂ analyzers) before each test. Subjects were asked to rate their perceived exertion (RPE) using Borg's 0-10 scale at the end of each stage of the exercise tests.

Submaximal all-extremity test. The submaximal allextremity test was a two-stage test in which the subject worked continuously at a set power output and self-selected pedaling cadence between 50 and 90 rpm for 6 min, after which the power output was increased for an additional 3 min (Table 2). Power output was specified depending on fitness level determined from the nonexercise V˙O_2max estimate ⁽¹⁶⁾. The protocol is presented in Table 2.

TABLE 2:

Submaximal all-extremity protocol.

The subject began the test at the predetermined power output. Heart rate (HR) was monitored continuously and recorded during the last 10 s of every minute. If, after 3 min, the HR was greater or equal to 70% HR_max, the load was considered adequate and the test continued for an additional 3 min. If the HR was below 90 bpm, the load was increased by 25 W for the remaining 3 min. The subject was expected to achieve a physiologic steady state during the fifth and sixth minutes. Criteria for steady state were HR greater than 70% HR_max with less than a 5-bpm difference in HR between the fifth and sixth minutes. After 6 min, the power output was increased by 25 W, and the subject rode for an additional 3 min until a second steady-state heart rate was achieved. If necessary, the test was continued one or more additional minutes until the steady-state requirements were met.

Maximal all-extremity test. The maximal all-extremity test was a discontinuous test beginning with a no-load 2-min warm-up phase. The test progresses with an increase of 35 W every 2 min followed by a 2-min rest period. Pedaling cadence was self-selected between 50 and 90 rpm. Heart rate and oxygen consumption was measured continuously, and blood pressure was measured during the last 30 s of every minute of exercise. Rate of perceived exertion (RPE) was also monitored for every stage of exercise using the Borg scale to assess intensity level. The test was terminated when the subject could not maintain the exercise pedaling cadence or asked to stop the test despite encouragement to continue. A maximal test was defined as a 2.0 mL·kg·min⁻¹ plateau of V˙O₂, an R value >1.1, and maximal HR within 10 beats of predicted maximum. The test varied in length from 10 to 30 min depending on the fitness level of the individual. Figure 1 is a photograph of an individual performing the all-extremity ergometry test.

Figure 1:

Maximal all-extremity bicycle test setup.

Maximal treadmill test. The maximal treadmill test utilized the continuous Bruce protocol, the most frequently used validated test for measuring V˙O_2peak ⁽¹⁾. It involved an increase in speed and grade every 3 min. The major advantage of the Bruce protocol is relative brevity and validation across a wide range of fitness levels. Heart rate and oxygen consumption were measured continuously, and blood pressure was measured pre- and postexercise. Maximal critieria were consistent as described in the maximal all-extremity test.

Statistical Analysis

Descriptive analyses were performed on subjects' age, height, weight, and activity level. A regression equation was developed from a step-wise regression analysis utilizing the submaximal test information of two exercise power outputs (W), age (years), and two submaximal HR (bpm) as independent variables, and V˙O_2peak from the maximal all-extremity test as the dependent variable. Predicted residual sum of squares (PRESS) was calculated to derive R² and standard error of estimate (SEE). The PRESS approach is appropriate for small data sets and should yield the most stable prediction equation ^(15,19).

A Pearson correlation coefficient was utilized to correlate the V˙O_2peak value from each of the maximal tests, and the treadmill V˙O_2peak values to the submaximal all-extremity predicted V˙O_2peak. Alpha was set at 0.05 with a 0.80 power level. A paired t-test was performed between maximal all-extremity V˙O_2peak values and maximal treadmill V˙O_2peak values. Mean heart rate peak values were calculated for both maximal tests and were tested for a significant difference using a t-test for paired samples.

RESULTS

Table 3 displays the age group, fitness level, and total results of all exercise tests. Maximal oxygen consumption for treadmill test ranged from 1.34 to 3.21 L·min⁻¹ with mean ± SD value of 2.18 ± 0.41. V˙O_2peak for the maximal all-extremity test ranged from 1.37 to 3.19 L·min⁻¹ with the mean value of 2.04 ± 0.41.

TABLE 3:

Results of V˙O_2max values from the three testing modes.

The linear regression derived for the submaximal allextremity test was V˙O_2peak L·min⁻¹ = −0.01(age in years) − 0.0029(HR 1) − 0.0099(HR2) − 0.0029(WK1) + 0.0151(WK2)+ 3.010. (HR1 is the first heart rate value after 6 min of exercise; WK1 is the initial 6-min power output and is measured in W; HR2 and WK2 are the heart rate and power output during the last 2-3 min of exercise.) Predicted residual sum of squares of the linear equation revealed an R² value of 0.722 and standard error of estimate of 0.216 L·min⁻¹, which is equivalent to 10.6%.

The predicted all-extremity values ranged from 1.30 to 3.10 L·min⁻¹ with mean value of 2.06 ± 0.35 L·min⁻¹. Treadmill V˙O_2peak values correlated significantly with all-extremity V˙O_2peak values (r= 0.91) and with the predicted all-extremity values (r = 0.85). There was no significant difference between all-extremity and treadmill V˙O_2peak values at P< 0.05. Table 3 displays the results from the three exercise tests by age, group, and fitness level.

Table 4 displays the heart rate peak reached during the three exercise tests divided by age, group, and fitness level. Average peak heart rate was 174 ± 9 bpm for the treadmill test and 170 ± 9 bpm for the maximal all-extremity test. These values are not significantly different.

TABLE 4:

Results of HR_peak values from the three testing modes.

DISCUSSION

The goal of this investigation was to validate a submaximal all-extremity ergometer protocol to predict V˙O_2peak in healthy females ages 30-60. The nonexercise estimate of V˙O_2peak proved to be accurate with this population as presented inTable 3. V˙O_2peak values were highest in the high fitness level groups for all age groups. Individuals of varied age and fitness level were sought for this study to develop a submaximal regression equation that would work for a variety of individuals. From the spread of V˙O_2peak values, it seems that this goal was accomplished.

Use of an all-extremity ergometer allows for use of large muscle groups and enables optimal performance and should elicit a greater cardiopulmonary and metabolic response than use of legs alone ⁽²⁰⁾. The all-extremity device used in this study was the SciFit Power Trainer, which allows for a single work output divided between the upper and lower extremities. The ergometer included an adjustable seat to account for differences in leg length and adjustable pedal lengths. The removable high-back seat could move forward/backward and up/down. Pedal toe clips and heel straps are available to support the foot. Positioning of the arm cycle was made possible by adjusting the vertical height and horizontal distance of the seat back and arm and leg crank length. This device allows for use in a variety of populations. the SciFit Power Trainer has a high seat back, removable seat for use with wheelchairs, and adjustable pedals for use with ankle-foot orthoses.

Other studies that have used all-extremity devices, such as Hagan ⁽¹³⁾, found no difference in V˙O_2max values between maximal treadmill and maximal combined allextremity test. The maximal all-extremity test utilized in the present study was a discontinuous protocol that allowed for temporary relief from muscular fatigue ^(9,12). The allextremity test correlated well with the maximal treadmill values and statistically was not different at the 0.05 level. Peak heart rate between the treadmill and all-extremity was also not statistically different. Although not the primary focus of the study, the maximal all-extremity exercise protocol proved to be a reliable and valid testing protocol and an alternative to treadmill testing.

Submaximal exercise testing gives the investigator an option when maximal testing is not ideal, i.e., with a special population, lack of equipment, safety, expense, or personnel. An all-extremity test that utilizes large muscle groups can produce similar treadmill V˙O₂ and HR values. The submaximal protocol used in this study was designed to accommodate a variety of subjects including individuals with disabilities. The protocol utilized two submaximal power outputs, two submaximal heart rates, and age to estimate V˙O_2peak in L·min⁻¹. Other all-extremity testing protocols that have been studied have primarily utilized maximal testing ^(20,21) or the Schwinn Air-Dyne, which does not offer a semirecumbent position that may accommodate a wider range of patients ⁽¹³⁾. This protocol used an ergometer with one power output independent of the amount of work used by the arms or legs. If the lower extremity fatigues, the upper extremity can help to compensate.

The predicted residual sum of squares yielded an R² value of 0.722, indicating a moderately strong relationship. The SEE of 10% is clinically insignificant, and therefore the submaximal all-extremity test can be a valid measurement of maximal oxygen consumption.

CONCLUSION

One advantage of using an all-extremity ergometer with clinical populations is the potential for distributing the exercise load over a large muscle mass, thus reducing the absolute load on one extremity or only the two lower extremities that may possess some sort of pathology. The results of this study revealed the all-extremity ergometer was valid for apparently healthy females aged 30 to 60 yr. Future study will test the protocol on individuals with disabilities such as cerebral vascular accidents, amputation, spinal cord injury, and arthritis.

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Keywords:

AEROBIC CAPACITY; FITNESS ESTIMATION; ERGOMETER; EXERTION

© Williams & Wilkins 1998. All Rights Reserved.

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