Assessment of Cardiorespiratory Fitness and High-Intensity Interval Training after Stroke

Abstract

More than 11,000 people suffer a stroke in Norway each year, and the majority are left with residual impairments like hemiparesis, cognitive deficits, and reduced balance and walking ability. These consequences may result in a sedentary lifestyle with a negative impact on their cardiovascular health, which further increases stroke risk. Almost 30% of stroke survivors experience a recurrent stroke within 5 years. Physical activity guidelines recommend that stroke survivors be physically active with a minimum of 150 minutes per week of moderate intensity exercise or 75 minutes per week at vigorous intensity. However, very few stroke survivors adhere to these recommendations. Stroke survivors often have a low aerobic capacity and experience increased effort in performing the activities of daily life, which also contributes to an inactive lifestyle. The primary aim of stroke rehabilitation is to improve function. In the clinical setting, most attention is paid to the motor impairments and physical disabilities following stroke, with less focus on maintaining and improving aerobic capacity. Maximal oxygen uptake (VO2peak) is a strong and independent predictor for the risk of a recurrent stroke. High-intensity interval training (HIIT) at 85-95% of maximal heart rate has been found to increase VO2peak more than moderate and low intensity training in healthy people and people with cardiovascular disease. An increasing number of HIIT studies of the stroke population have emerged. However, most of these studies have few participants, lack a control group, have the intensity control often based on indirect calculations, and there are differences in the HIIT protocols that make these studies difficult to interpret. This doctoral thesis is based on two separate studies with people after stroke, with the aim of attaining a better understanding of the aerobic capacity of stroke survivors and the potential effects of HIIT on VO2peak, as well as physical and cognitive functions both after training and in the longer term. In the first study, the primary aim was to determine the test-retest reliability of a portable ergospirometry system (MetaMax II) during a functional test course, which simulated the activities of daily life. In addition, we wanted to assess the amount of oxygen consumed during these activities in relation to their VO2peak level assessed during a graded exercise test. A total of 31 participants were included. Our results demonstrated good to very good testretest reliability of portable ergospirometry, indicating that the MetaMax II for the most important cardiopulmonary performance variables, could be used outside the laboratory also in the stroke population. Furthermore, the results showed that the participants spent more than 60% of their VO2peak during activities frequently encountered in daily life. The main part of this thesis reports the results of the HIIT Stroke study. This was a single blinded, randomized, clinically controlled, multicenter study in collaboration with three hospitals in Norway. The intervention group (n=36) received 8 weeks of individualized and supervised treadmill HIIT delivered 3 times per week at 85 to 95% of peak heart rate in 4x4 work periods. The control group (n=34) received standard care only. Participants were tested at three time points: 1) at baseline, 2) posttest after 8 weeks, and 3) at 12 months after inclusion in the study. First, we reported the results from treadmill HIIT intervention in combination with standard care, and compared to standard care alone on VO2peak, blood pressure, and blood lipid profiles. There was a significant increase in VO2peak immediately after the intervention, when compared to standard care. However, there was no difference between the groups in the primary outcome, which was VO2peak at the 12-months follow-up. There was no difference between groups in blood pressure or blood profiles at any time point. In a second paper from the study, we presented results of the HIIT intervention on physical, cognitive, and health-related quality of life measures as compared to standard care alone. The main finding was that HIIT in combination with standard care significantly improved walking capacity, balance, and cognitive function when compared to standard care alone. However, these effects were not maintained in the long term except for results of the Trail- Making Test Part B at the 12-months follow-up. In conclusion, our findings support the use of the portable MetaMax II ergospirometry equipment in measuring oxygen uptake during functional activities in persons with stroke and found that an HIIT program resulted in a higher increase in VO2peak than did standard care alone in people with stroke. However, the effect was not maintained at the 12-month follow-up. Future studies should investigate follow-up programs aiming to maintain the positive effects achieved after HIIT into the long term.