Background and Aim: Stroke survivors have low levels of fitness and physical activity that contribute to reduced ability to perform everyday activities. Oxygen uptake kinetics measure the time to adapt to a steady state sub-maximal exercise workload (on-kinetics), as well as the time to recover from a steady state sub-maximal work load (off-kinetics). It describes the rate of change in oxygen uptake (VO₂) in response to a submaximal exercise bout. The relationship between oxygen uptake kinetics, physical functional performance, and ambulatory activity has not been explored in stroke survivors. Therefore, the aim of this study was to explore the associations amongst the on-and-off kinetics time constants, physical functional performance, and ambulatory activity outcomes.

Materials and Methods: This was a cross sectional, case control study involving 10 stroke survivors (time since stroke: 7.5+/-8.3 years; gender: 4 male, 6 female) and 10 control subjects matched for age and physical activity level. Oxygen uptake kinetics (on and off kinetics) were measured in response to sub maximal exercise on a recumbent cycle. The exercise protocol followed 5 minutes of quiet rest to determine baseline VO₂, and involved an abrupt pedaling start to an intensity corresponding to the VO₂ ranging from 75 to 90% of the ventilatory threshold. The exercise period lasted 5 minutes and measurement on the metabolic cart continued for 7 minutes following exercise cessation The continuous-scale physical functional performance test (CS-PFP10) was used to measure functional ability and includes 10 everyday tasks that progress from easy (personal tasks) to moderate (household tasks) to difficult (mobility tasks). Ambulatory activity outcomes including steps per day, number of activity bouts and length of activity bouts were measured using a Step Activity Monitor (Orthocare Innovations, Oklahoma City) and averaged over 4 days of monitoring.

Results: Stroke survivors took significantly longer to recover from submaximal exercise (i.e. off-kinetics constant) compared to control participants. Shorter ambulatory activity bouts were significantly associated with longer off-kinetics time constants. Also in stroke survivors, the association between on-kinetics and total activity in steps per day, approached significance (p=0.068) with longer on-kinetics related to fewer steps per day. There were no significant associations between physical functional performance with either on or off kinetics time constants.

Conclusions: In stroke survivors, there is a need for activity interventions to improve functional ability and the ability to recover from functional abilities (i.e. quantified by time to adapt to or recover from an activity).