Cardiorespiratory fitness adaptations to exercise in sedentary men
Clarke, Gregory John
MetadataShow full item record
Cardiorespiratory Fitness (CRF) classically measured by maximal oxygen consumption (VO2max), is a strong predictor of morbidity and mortality. However, there is substantial inter-individual variation in CRF response with exercise training. Several lines of evidence suggest that the measurement of CRF using VO2peak alone may be masking some of the submaximal cardiorespiratory adaptations, such as exercise tolerance, that occur as a result of regular physical activity. Our goal is to assess the relationship between changes in CRF and exercise tolerance in inactive men of varying age. We studied 25 inactive men between the ages of 30 and 60 years ([mean (SD)] age = 44.3 (9.1)) from Kingston, Canada. Participants completed 4 weeks of moderate intensity exercise in accordance with the Canadian Physical Activity Guidelines. All measurements were obtained at baseline and post exercise. CRF was assessed using a maximal, graded treadmill test. Exercise tolerance was assessed using a 12 minute time trial on a treadmill, where participants were instructed to cover as much distance as possible through self-selection of speed. Twenty four hour physical activity data was obtained at baseline and during the final week of exercise using accelerometry. In a secondary analysis, we compared the changes in exercise tolerance between responders and non-responders of CRF. Both CRF and exercise tolerance improved significantly over the intervention. There was no association between absolute CRF values and exercise tolerance at baseline or post exercise. Relative CRF showed a strong association with exercise tolerance at baseline and post exercise, r = 0.85 and r = 0.75, respectively (p<0.05). However, there was no association between changes in CRF and exercise tolerance (p >0.05). Furthermore, there was no difference in change in exercise tolerance when comparing responders to non-responders of CRF (p > 0.05). Alternative measures of fitness such as exercise tolerance may capture cardiovascular and muscle metabolic adaptations not seen when CRF alone is measured. As such, these alternative measures may be of clinical relevance in assessing changes in fitness in conjunction with CRF, which has been well-established as a key risk factor of all-cause morbidity and mortality.