Impact of exercise duration on maximal and sub-maximal markers during clinical cardio-pulmonary exercise testing

Alhowikan, Abdulrahman M. (2012) Impact of exercise duration on maximal and sub-maximal markers during clinical cardio-pulmonary exercise testing. PhD thesis, University of Glasgow.

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Currently, the American College of Sports Medicine (ACSM) recommends that protocols for cardiopulmonary exercise testing (CPET) should last between eight and twelve minutes. However, the justification for these exercise durations rely on limited experimental data. These recommendations have a significant impact on the ability of frail patients to be assessed using CPET and should conform to evidence based practice. This thesis begins by assessing the validity of these recommendations in relation to maximal exercise responses before assessing the consequences of these recommendations on sub-maximal exercise measurements. These studies were conducted in a relatively large cohort (compared to the study that underpins the ACSM guidelines) of heterogeneous volunteers (they are both men and women, with a significant age range and varied functional capacity) to make the data more relevant to clinical exercise testing.
The data presented in chapter three demonstrate that it is very difficult to obtain exercise duration conforming to the current ACSM guidelines by using a standardised ramp exercise protocol on both treadmill and cycle ergometer exercise. However, sub-group analyses for those subjects who achieved moderate (8-12 minutes) and short (less than 8 minutes) exercise durations. In addition, a separate analysis was carried out for a different sub-group of those who achieved moderate (8-12 minutes) and long (more than 12 minutes) of durations of exercise. Despite this, it was possible to demonstrate in sub-group analysis that there was no significant difference in peak oxygen uptake, peak carbon dioxide output, peak heart rate, peak ventilation and peak power output when exercise duration was less or more than that prescribed by the ACSM recommendations. In addition, the effects of long, moderate or short duration exercise per se were also analysed in this chapter and again exercise duration was shown to be without effect on the main maximal markers of exercise performance.
In chapters four, five and six, the initial findings were extended to determine the effects of exercise duration on a range of clinically relevant sub-maximal markers of exercise performance. It was likely, since exercise duration did not affect maximal exercise that the physiological determinants of maximal performance were not significantly altered during short or long duration exercise and consequently it was likely that sub-maximal markers of functional capacity would not be affected. However, the quality of the data obtained during CPET can obviously influence the accurate measurement physiological responses during exercise and much of the analysis in these chapters focused on the validity of the data analysis.
Chapter four investigated the limitations to measuring the break point in the relationship between oxygen uptake and carbon dioxide output during progressive exercise (the so called ventilatory threshold or ‘V-slope’). The accurate measurement of this break point was determined by standard gas exchange criteria and the effects of reducing the data available for analysis (by reducing the amount of breaths available for comparison at reduced exercise durations) were examined. The data showed that reducing the data available for analysis had an impact on the quality of the data (decreasing the goodness of fit) but no significant effect on the determination of the ventilatory threshold.
Chapter five determined the effects of exercise duration on the oxygen uptake efficiency slope (OUES). As expected, the effects of exercise duration were not significant but additional investigation into the commonly employed data analysis procedures was performed. These data show that the log transformation of the relationship between ventilation and oxygen uptake allows reliable assessment of ventilatory efficiency in most cases, however, the impact of the lactate threshold on ventilation and the biological variability in where the threshold occurs as a proportion of functional capacity can impact on the sensitivity of this measurement to predict aerobic and/or anaerobic capacity.
Chapter six determined the effects of exercise duration on the breathing reserve index and found no significant difference during short, moderate or long exercise duration exercise. Further analysis was performed to demonstrate limitations in the use of predicted maximum voluntary ventilation (rather than direct measurement).
Taken together, these data demonstrate that the current ACSM recommendations for CPET are too restrictive and may limit the application of such testing in populations that cannot exercise for between eight and twelve minutes. The data further suggest that the testing and analysis procedures used during CPET are central to producing valid maximal and sub-maximal markers of functional capacity and the recommendations should focus include guidelines in relation to such aspects.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Exercise, exercise duration, oxygen consumption, anaerobic threshold, oxygen uptake efficiency slope, breathing reserve index
Subjects: R Medicine > R Medicine (General)
Q Science > QP Physiology
Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cardiovascular & Metabolic Health
Supervisor's Name: Macfarlane, Dr. Niall
Date of Award: 2012
Depositing User: DR Abdulrahman Alhowikan
Unique ID: glathesis:2012-3224
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 05 Mar 2012
Last Modified: 02 Mar 2015 08:34

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