When is fit, fit enough? The impact of cardiorespiratory fitness on daily-life activities after stroke

The cardiorespiratory fitness of individuals after stroke is lower compared to their peers. Also, the aerobic energy expenditure of daily-life activities is higher after stroke. However, to define the experienced cardiorespiratory strain of an activity, cardiorespiratory fitness and aerobic energy expenditure should be assessed together. The fraction of cardiorespiratory fitness that an individual needs to use to perform an activity- the relative aerobic load - defines the experienced cardiorespiratory strain of that activity. Performing activities at a high relative aerobic load will likely lead to earlier fatigue or induce a slower movement speed. To gain insight in the impact of cardiorespiratory fitness on performance of daily-life activities, this thesis investigated the relative aerobic load of daily-life activities after stroke. In chapter 2, we provided reference values of cardiorespiratory fitness post-stroke in clinical rehabilitation based on more than 400 individuals. The results of this study can give individuals after stroke insight in their cardiorespiratory fitness compared to their peers. Also, they could help guide rehabilitation treatment, for example by identifying patients for whom training cardiorespiratory fitness should be prioritized to increase functioning. In chapter 3 we showed that individuals after stroke experience a higher relative aerobic load during walking at preferred walking speed on a treadmill. We also showed that walking faster, although being more economic, would lead to unsustainable relative aerobic loads for individuals after stroke. It might be that individuals after stroke choose a pace that enables them to walk as fast as possible within sustainable relative aerobic load values. Thus, they appear limited in movement speed by a high relative aerobic load. In chapter 4 we assessed relative aerobic load in daily-life activities such as walking and sweeping. This showed a similar pattern of higher relative aerobic loads for individuals after stroke at lower self-selected movement pace. In addition, we found indications that individuals with the lowest functional ambulation were not limited by relative aerobic load, but might have been limited more by a decreased motor function. In chapter 6 we explored relative aerobic load in 4 mock-up settings of daily-activities such as grocery shopping and cleaning. Since these activities were non-cyclic, we could not use commonly used methods of estimating aerobic energy expenditure. Therefore we used a novel method, described in chapter 5. We estimated aerobic energy expenditure of short walking bouts by taking into account the oxygen consumption of the activity and the excess post-exercise oxygen consumption. This method was shown to be as reliable as steady-state measurements for longer activities, and could therefore be used in the experimental setting of chapter 6. In accordance with previous chapters, chapter 6 shows a higher relative aerobic load of non-cyclic, functional, daily-life activities in individuals after stroke even though their time to complete the activities was increased compared to able-bodied individuals. We also found indications that the individuals with lower motor ability were not primarily limited by a relative aerobic load. To conclude, individuals after stroke experience a higher relative aerobic load during daily-life activities, while they move slower than able-bodied peers. Potentially, they limit their movement pace to experience a sustainable relative aerobic load. Moving faster would likely induce early fatigue or make it impossible to perform the activity. Reducing relative aerobic load might make it possible to move faster and more economically. Therefore, training cardiorespiratory fitness should be considered in rehabilitation after stroke to enhance functioning. Especially in individuals with a low cardiorespiratory fitness who are not limited in movement speed by motor ability. Reference values of cardiorespiratory fitness and aerobic energy expenditure could help to define which patients would benefit most from aerobic training.