VO2pk is measured by an incremental exercise cycle test whereby subjects begin at very light warm up loads and the workload is gradually increased until maximum; optimal test time is 8-15 minutes, thus requiring different incremental exercise protocols based on subject characteristics (body size, fitness, gender, etc). It is generally believed that optimal testing involves small gradual increases in workload versus fewer large steps in workload. Assessment of VT requires small gradual increases in workload, thus the investigators proposed to pilot test four different "ramp" protocols.
The primary purpose of this study was to identify a peak cycle protocol that elicits a true VO2pk and allows for the determination of VT in subjects of varying gender, body weight, and training status. In order to meet this objective a method for technicians to determine whether VO2pk was achieved and for identifying VT needed to be defined.
Ten healthy, non-smoking males (n=5) and females (n=5), 26-48 years of age, with varied fitness levels participated in the evaluation. All test subjects successfully passed a modified Air Force Class III physical exam and gave written informed consent prior to participation in the study. This study was approved by the NASA-JSC Committee for the Protection of Human Subjects (CPHS).
Subjects were asked to complete 2-4 cycle ergometer tests to peak exertion. Each protocol consisted of a three minute warm-up stage, followed by either 30 second or 60 second stages at increasing workloads until peak exertion. Selection of the protocols was based on the subject's weight. Subjects weighing less than 65 kg completed protocols A and B, and subjects weighing more than 65 kg completed protocols C and D.
Protocol A: The exercise test session included three minutes of warm-up at 0 watts followed by one minute stages, increasing 15 watts each stage until peak exertion.
Protocol B: The exercise test session included three minutes of warm-up at 0 watts followed by thirty second stages, increasing 7.5 watts each stage until peak exertion.
Protocol C: The exercise test session included three minutes of warm-up at 50 watts followed by one minute stages, increasing 25 watts each stage until peak exertion.
Protocol D: The exercise test session included three minutes of warm-up at 50 watts followed by thirty second stages, increasing 12.5 watts each stage until peak exertion.
Expired gases were collected and analyzed using a Parvomedics TrueOne™ Metabolic Cart. Expired gas fractions of oxygen (VO2) and carbon dioxide (VCO2), rate of ventilation (VE), and respiratory exchange ratio (RER) were averaged in 30 second increments during exercise. Heart rate was monitored throughout testing via ECG. Borg rating of perceived exertion (RPE) was recorded at the end of each exercise stage.
The tests were completed using Level I medical monitoring. Testing was performed in the Exercise Physiology and Countermeasures Project Laboratory (EXL). The determination of VO2pk was defined by meeting two of the following three criteria: 1) HR = 90% age predicted maximum (220-age), 2) RER = 1.1, and 3) RPE = 19.
A total of 26 peak cycle tests were completed in this investigation. The criteria for achieving VO2pk were met in all tests. In general, VO2pk was higher in males than in females; however, when the male and female data were combined, VO2pk values were not different between the 30 and 60 second stage protocols.
Upon inspection of the four VT determination methods, the majority of the VT values produced by the RER and ParvoMedics V-slope method were outside the reasonable acceptable range. Therefore, VT was determined using only the technician defined V-slope and VEQ method. VEQ produced a higher VT than V-slope; however, within each method there were no significant differences in VT between the three technicians.
Taking the results together with the subject preference for 60 second stages, it is recommended that future bed rest and flight studies implement Protocol A for individuals that are less than 65 kg and demonstrate lower levels of fitness; and Protocol C for individuals that are above 65 kg and exhibit higher levels of fitness. Determination of VT can be achieved in peak cycle tests as defined by these protocols, and by implementing the data analysis methods used in this study.
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