Gender differences in the progression of metabolic responses during incremental exercise.

AIM: The present investigation was undertaken to elucidate the differences in the progression of metabolic responses during incremental exercise between men and women of similar maximal aerobic capacity. METHODS: Twenty males and 20 females served as subjects for the study. Each subject was randomly assigned to perform a graded exercise test on either a cycle ergometer or a treadmill. Of the 20 subjects within each gender, 10 were tested on the cycle ergometer, whereas the other half was tested on the treadmill. During each test, absolute VO2, relative VO2, and HR were recorded during the last 15 seconds of every minute throughout the test. These variables were then plotted separately as a function of work rate so that a best-fit linear regression equation was generated for each of the three plots. RESULTS: Under the cycle condition, we found no difference in slope of increment in absolute VO2 between genders. However, the slope of increment in relative VO2 and HR was greater (P<0.05) in women than men. A negative correlation (r=-0.858, P<0.05) was found between body mass and slope of increment in relative VO2 in men and women combined. Under the treadmill condition, the slope for absolute VO2 were greater (P<0.05) in men than women. However, in terms of relative VO2 and HR, no between-gender differences were observed in the slope of increment. A positive correlation (r=0.769, P<0.05) was found between body mass and slope of increment in absolute VO2 in men and women combined. CONCLUSIONS: These results indicate that the progression of metabolic responses during incremental exercise differs between men and women despite a similar fitness. These gender differences may be further attributed to body mass that seems to play a distinctive role when the incremental exercise is conducted on a cycle ergometer and treadmill.

Physiological comparisons among three maximal treadmill exercise protocols in trained and untrained individuals.

The present investigation was undertaken to examine whether maximal oxygen uptake (VO2max) and anaerobic threshold (AT) measured during incremental treadmill exercise would be affected by the exercise protocol in trained and untrained individuals. Fifteen untrained men, 10 untrained women, and 12 trained individuals participated in this study. The Astrand, Bruce, and Costill/Fox protocols were selected for comparison. Each subject was tested using all three protocols and the three tests were conducted in a randomized counterbalanced order. During each test, oxygen uptake was measured every 30 s and the test was terminated according to the standard criteria. The VO2max was determined by averaging the two consecutive highest measurements, whereas AT was determined using ventilatory parameters following the V-slope technique. The Astrand, Bruce, and Costill/Fox protocols produced test durations of 9.8 (SEM 0.5), 12.4 (SEM 0.4), and 4.9 (SEM 0.3) min, respectively, in the untrained men, 9.0 (SEM 0.8), 11.0 (SEM 0.6), and 5.3 (SEM 0.6) min, respectively, in the untrained women, and 14.5 (SEM 0.5), 17.0 (SEM 0.5) and 10.4 (SEM 0.4) min, respectively, in the trained men. In the untrained men and women, no differences in VO2max were observed among the three different protocols, but AT was lower when using the Bruce compared to the Astrand protocol. In the trained men, VO2max and AT were lower when using the Bruce protocol than either the Astrand or Costill/Fox protocols. In conclusion, VO2max measured during treadmill exercise is not affected by the protocol of the test and using a running protocol of short duration (i.e. about 5 min) could be a time-efficient way of assessing VO2max in healthy untrained subjects. In trained subjects, however, a protocol consisting of running with small increments in gradient is effective in eliciting a higher VO2max. The lower AT associated with the Bruce protocol seen in both untrained and trained groups suggests this aerobic parameter is protocol dependent and this protocol dependency is not affected by training status.

Metabolic and cardiorespiratory responses to continuous box lifting and lowering in nonimpaired subjects.

STUDY DESIGN: A within-subject experimental design. OBJECTIVES: To compare the magnitude of metabolic and cardiorespiratory changes produced during box lifting and lowering among combinations of lift technique (leg lift and leg-torso lift) and lift weight (10.8 and 15.4 kg). BACKGROUND: Continuous box lifting and lowering can be used as an exercise in a low-back rehabilitation program. Awareness of the possible cardiovascular stress of this activity is important to the clinician because some patients may have existing cardiovascular pathologies or possess unknown risk factors for cardiovascular disease. METHODS AND MEASURES: A group of 17 nonimpaired men 26 +/- 8 years of age (mean +/- SD) performed the 4 experimental trials on different days in a counterbalanced order determined by a Latin Square design. Lifting and lowering was performed for 6 continuous minutes at a rate of 12 cycles per minute. Physiologic variables were oxygen uptake, minute ventilation, heart rate, systolic blood pressure, diastolic blood pressure, metabolic equivalent, and rate-pressure product. RESULTS: There were stepwise increases in the values for oxygen uptake, minute ventilation, heart rate, metabolic equivalent, and rate-pressure product from the leg-torso lift to the leg lift and from 10.8 to 15.4 kg of weight within each lift technique (with the exception that minute ventilation and heart rate did not differ between the leg-torso lift at 15.4 kg and the leg lift at 10.8 kg). For the 4 lifts, values (mean +/- SD) varied from 20.3 +/- 5.4 to 28.8 +/- 5.8 mL x kg x min(-1) for oxygen uptake, 42.2 +/- 11.1 to 66.4 +/- 15.2 L x min(-2) for minute ventilation,129 +/- 20.6 to 156 +/- 16.5 beats x min(-1) for heart rate, 5.8 +/- 1.6 to 8.2 +/- 1.6 for metabolic equivalent, and 197 +/- 49.4 to 245 +/- 41.2 for rate-pressure product (x10(-2)). CONCLUSION: The leg lift with the 15.4-kg weight produced the greatest physiologic stress. Because of the magnitude of the increase in the variables measured for all 4 types of lifts, clinicians should closely monitor patients' response to this type of exercise.

Physiological responses to upper body exercise on an arm and a modified leg ergometer.

PURPOSE: The present study was undertaken to compare cardiorespiratory, metabolic, and perceptual responses to upper body exercise on an arm ergometer (AE) and a modified leg ergometer (LE). METHODS: Seventeen male and seven female subjects completed two experimental trials. During each trial, the subjects performed two successive 8-min steady-state arm crank exercises on either an AE or an LE. The crank frequency was kept constant at 50 rev x min(-1) during all exercise bouts. The two power outputs selected were 50 and 75 W for male subjects and 25 and 50 W for female subjects. To achieve these power outputs, the brake resistance was set at 1, 2, and 3 kg at a power output of 25, 50, and 75 W, respectively, for the AE and 0.5, 1, and 1.5 kg at a power output of 25, 50, and 75 W, respectively, for the LE. Oxygen uptake (VO2), heart rate (HR), respiratory exchange ratio (RER), expired ventilation (VE), gross efficiency (GE), and ratings of perceived exertion (RPE) were measured every minute during the last 2 min of each exercise bout. RESULTS: In male subjects, VO2, HR, RER, VE, and RPE were higher (P < 0.05), whereas GE was lower (P < 0.05) during arm crank exercise on an AE than an LE at power outputs of 50 and 70 W. In female subjects, similar differences in these variables between the two ergometers were also observed when exercise was performed at 50 W. However, VO2, RER, VE, and GE did not differ between the two ergometers when exercise was performed at 25 W. CONCLUSIONS: Upper body exercise elicits greater cardiorespiratory, metabolic, and perceptual responses on an AE than an LE at the same power output when power output is computed according to the manufacturer's instructions.

Regulating exercise intensity using ratings of perceived exertion during arm and leg ergometry.

The purpose of this investigation was to examine the validity of regulating exercise intensity using ratings of perceived exertion (RPEs) during arm crank and leg cycle exercise at 50 and 70% peak oxygen consumption (VO2peak). Ten men and seven women [26 (1) years old; mean (SE)] participated in this study. Each subject completed a maximal estimation trial and two submaximal exercise bouts (production trials) on both an arm and leg ergometer. During each maximal estimation trial, subjects were asked to give a RPE for each stage of the exercise. RPEs, heart rates (HR), and power outputs (PO) equivalent to 50 and 70% VO2peak for each exercise mode were then estimated from plots of RPE versus oxygen consumption (VO2), HR versus VO2, and PO versus VO2, respectively. During the submaximal trials, subjects were instructed to select workloads on an arm and leg ergometer that produced the previously estimated RPEs. Comparisons were made for VO2, HR, and PO between the estimation and production trials for each mode at each exercise intensity. HR did not differ between the trials at either 50 or 70% VO2peak during arm and leg ergometry. In addition, VO2 and PO did not differ between the trials at either 50 or 70% VO2peak during arm ergometry and at 50% VO2peak during leg ergometry. However, these two parameters were lower (P < 0.05) during the production trial [1.88 (0.15) l x min(-1) and 89.1 (10.1) W, respectively] as compared to the estimation trial [2.08(0.14) l x min(-1) and 102.4 (6.5)W, respectively] during leg ergometry at 70% VO2peak. In conclusion, using RPEs to regulate exercise intensity is physiologically valid during arm ergometry at both 50 and 70% VO2peak and during leg ergometry at 50% VO2peak. However, this prescriptive approach remains questionable during leg cycle exercise at 70% VO2peak.

Cardiorespiratory and metabolic responses during forward and backward walking.

Level and incline backward treadmill walking techniques are used in the rehabilitation of certain lower extremity injuries (eg., anterior cruciate ligament reconstruction). Of interest to clinicians is the maintenance of cardiorespiratory fitness resulting from these activities. The purpose of the present study was to determine the cardiorespiratory and metabolic stress of backward walking compared with forward walking. The metabolic cost of backward incline walking above a 1% grade has previously not been reported. Seventeen volunteers (11 males and six females, age = 25 +/- 2 years) underwent a forward maximal running test and four random-ordered 6-minute submaximal walking bouts at 93.8 m/min (3.5 mph). The bouts consisted of forward walking at 0% and 5% elevation and backward walking at 0% and 5% elevation. Measurements taken for each exercise session were oxygen uptake, expired ventilation, heart rate, and rating of perceived exertion. Statistical analysis of these dependent variables indicates that: 1) at a given elevation, backward walking elicited greater cardiorespiratory, metabolic, and perceptual responses than forward walking and 2) backward walking at 5% elevation could provide a sufficient stimulus to maintain cardiorespiratory fitness.

Oxygen cost during exercise in simulated subgravity environments.

Oxygen cost (VO2) and heart rate (HR) were determined during treadmill walking in simulated subgravity environments. The long axis of the subject's body was suspended parallel to the floor in a slow rotation room with feet aligned on the surface of a treadmill mounted 90 degrees on the wall. Without rotation, the subjects were virtually weightless against the treadmill; with centrifugation, environments of 0.25, 0.5 and 1 G were simulated. VO2 (open circuit) and HR (ECG) were measured during the 5th minute of walking at 3.2, 4.7 and 6.1 km/h. Similar measurements were also determined during walking at 1/2-G using the inclined plane technique. VO2 per unit mass and HR were significantly reduced in all subgravity environments. However, net VO2 per unit weight carried and, therefore, mechanical efficiency was found to be independent of gravity. This supports the idea that the most probable cause for the decreased O2 cost with reduced gravity is less body weight carried.