Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The purpose of this thesis was to determine which factors influence oxygen uptake (VO{dollar}\sb2){dollar} kinetics during exercise in old individuals. These factors may include central {dollar}\rm O\sb2{dollar} delivery (i.e. cardiac output kinetics), the rate of O{dollar}\sb2{dollar} delivery at the exercising muscle, and the rate at which mitochondria can use O{dollar}\sb2.{dollar} Fitness level may also influence VO{dollar}\sb2{dollar} kinetics, by affecting the above factors. These factors were estimated by measuring heart rate (HR) kinetics, muscle capillarization, and citrate synthase (CS) activity, respectively, in groups of old ({dollar}\sim{dollar}65y) and young ({dollar}\sim{dollar}26y) individuals. Capillarization and CS activity of the lateral gastrocnemius were compared to VO{dollar}\sb2{dollar} an PCr kinetics (which reflect kinetics of muscle O{dollar}\sb2{dollar} consumption), measured during ankle plantar flexion, while HR kinetics were compared to VO{dollar}\sb2{dollar} kinetics during plantar flexion, cycling, and treadmill exercise. The influence of fitness levels on VO{dollar}\sb2{dollar} kinetics during cycling was also assessed in old an young groups of individuals. Old and young individuals had similar measures for capillarization, CS activity, and HR, PCr, and VO{dollar}\sb2{dollar} kinetics during plantar flexion exercise, compared to young adults. Old individuals, who were relatively fit for their age, had VO{dollar}\sb2{dollar} kinetics which were similar to fit young subjects.;These studies show that peripheral muscle oxidative capacity (as determined by enzyme activities, capillarization and PCr dynamics), and VO{dollar}\sb2{dollar} kinetics during exercise of a small muscle mass (plantar flexors), accustomed to daily activity, are maintained with age. Cardiorespiratory kinetics of the old individuals are slower during exercise involving large muscle mass (i.e. treadmill walking or cycling), which places a greater demand on central O{dollar}\sb2{dollar} delivery; however these kinetics can be greatly improved with moderate improvements in fitness level.;It is speculated that peripheral oxidative capacity (i.e. mitochondrial capacity or capillarization) is dominant in controlling VO{dollar}\sb2{dollar} kinetics during exercise of a small muscle mass in old individuals, since these measures were similar, along with VO{dollar}\sb2{dollar} kinetics, in the old compared to yound subjects. Central O{dollar}\sb2{dollar} transport (cardiac output kinetics, as estimated by HR kinetics) appears to limit VO{dollar}\sb2{dollar} kinetics during larger muscle mass exercise (cycling and treadmill walking) in older individuals.



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