Physical activity is the mantra of our time. Before we get carried away, we should remember that birds do not live forever. Nevertheless, there is overwhelming evidence that physical inactivity is bad for our health. Stroke is an event with often devastating consequences, and stroke survivors are at high risk for recurrent stroke. Other than medication, physical activity might be one possibility of reducing that risk. As yet, the evidence for this assumption is lacking.
Association between physical activity & stroke
Two meta-analyses on the association between physical activity and risk of stroke found a beneficial effect of physical activity Citation[1,2]. The studies included, dating back to the late 1970s, were observational studies, with the majority being cohort and some being case–control studies. Some found an association between increased level of physical activity and reduced risk of stroke, while others found a u-shaped relationship or no association. So far, no study has shown that a higher level of physical activity increases the risk of stroke. Physical activity was measured using a variety of questionnaires, which makes individual comparison difficult.
The Nord-Trøndelag Health Survey from Norway investigated 14,101 women, aged 50 years or older who were free from stroke Citation[3]. In a multivariable logistic regression model, the results showed that an increasing level of physical activity was associated with a decreased risk of stroke (ptrend = 0.0027). The association was consistent across all age groups. Data from the Copenhagen City Heart Study on 7060 women showed a small protective effect of physical activity on the avoidance of stroke (p = 0.04) Citation[4]. Wannamethee et al. followed 7735 men aged between 40 and 59 years for 9.5 years Citation[5]. Physical activity was categorized into three groups at baseline: inactivity, moderate activity and vigorous activity. The results showed a linear association between increased levels of physical activity and decreased risk of stroke (ptrend = 0.008). The relationship between physical activity and myocardial infarctions was u-shaped. The authors concluded that moderate physical activity was sufficient to produce a beneficial effect on reducing cardiovascular risk. An increased level of physical activity was associated with a decreased risk of both ischemic and hemorrhagic stroke. Furthermore, there was a dose–response relationship, so patients with a high level of physical activity had a greater risk reduction compared with patients with a moderate level of physical activity. Since the publication of the two meta-analyses Citation[1,2], a Finnish study on the association between physical activity and risk of stroke analyzed leisure time-, occupational-, and commuting physical activity separately Citation[6]. A total of 22,481 men and 24,880 women were included in the analyses. Increasing levels of leisure time, occupational or commuting physical activity were independently associated with a decreased risk of stroke (ptrend < 0.0001, 0.007 and 0.002, respectively). There are not many studies that have focused on the association between cardio–respiratory fitness and the risk of stroke. In the Aerobic Center Longitudinal Study, 20,728 men and 5909 women free of cardiovascular disease completed a maximal treadmill exercise test in order to assess cardio–respiratory fitness Citation[7]. Based on the test results, the cohort was grouped into three groups of cardio–respiratory fitness (low, moderate or high). The cohort was followed for an average of 10 years. Patients with a high or moderate cardio–respiratory fitness had a decreased risk of cardiovascular disease, including stroke (ptrend = 0.001). When considering the risk of stroke alone, the trend was significant (ptrend = 0.04).
We have analyzed the physical activity of stroke patients as they recalled it during the week preceding their mild ischemic stroke Citation[8]. Physical activity was measured by the Physical Activity Scale for the Elderly (PASE) in which a higher score means a higher level of activity. The mean PASE value was low as compared with age-matched controls. As in other case–control studies, we found that risk of stroke increased with decreasing PASE values Citation[8]. In patients who suffered a stroke, we found that a higher level of physical activity was associated with a less severe stroke and a better recovery 2 years later Citation[9].
Observational evidence support the beneficial effects of physical activity in the prevention of first ever stroke. However, it has to be mentioned that the hypothesis has never been tested in a randomized setting. Therefore, we cannot exclude that individuals with a high level of physical activity in general lead more healthy lives than individuals with a low physical activity, which may account for the reduced risk of stroke.
Physical activity & risk factors for ischemic stroke
The causal risk factors for stroke include hypertension, hypercholesterolemia, carotid stenosis and atrial fibrillation. There is evidence, not only from observational studies but also from randomized controlled trials, that treating these risk factors reduces the incidence of ischemic stroke. Other risk factors, such as diabetes mellitus, ischemic heart disease and cigarette smoking, are probably also causal risk factors; however, no studies have shown that treating these risk factors reduces the incidence of ischemic stroke Citation[10].
Physical activity has been shown to positively modify almost all known risk factors, including the most prominent ones, such as high blood pressure, diabetes mellitus/impaired glucose metabolism and high cholesterol levels. Most studies of the beneficial effects of physical activity on risk factors have been carried out in the general population, in patients with hypertension and those with coronary heart disease, but not in stroke patients.
Trainability of stroke patients
Following stroke, sequelae such as hemiparesis and ataxia may limit the trainability of stroke patients and lead to decreasing levels of physical activity and physical performance. A Cochrane review from 2004 Citation[11] reviewed the literature until 2002 and aimed to evaluate the effect of exercise on a number of outcomes (mortality, recurrent stroke, muscle strength, physical fitness, mobility and physical function). In total, 12 trials including 289 stroke patients were identified. All studies were small randomized trials and none of them assessed the effect of exercise on recurrent stroke or mortality. Two studies investigated the effect of physical exercise on cardio–respiratory fitness Citation[12,13]. In both studies it was concluded that cardio–respiratory fitness could be increased. In a meta-analysis of the two studies a significant effect of physical exercise on cardio–respiratory fitness measured as peak oxygen uptake, VO2 after exercise could, however, not be confirmed. Mobility, measured as walking speed, was assessed in five studies Citation[14–18]. A meta-analysis of those five studies showed a significant effect of physical exercise on walking speed. Walking speed could be improved by 0.42 m/s (95% confidence interval: 0.04–0.79). The effect of isokinetic strength training on muscle strength was investigated in a randomized study of 22 stroke patients Citation[19]. No significant effect of strength training on muscle strength was shown.
Since 2002, not many studies have been published that could further clarify the effect of physical training on cardio–respiratory fitness and muscle strength in stroke patients. In a nonrandomized study, walking speed was increased using an outpatient exercise protocol for 2 months Citation[20]. Patients randomized to mixed training (resistance and endurance training) for 12 weeks obtained a significantly better timed-up-and-go (time to raise from chair and walk 6 m) and walking economy (O2 ml/kg/m) compared with the control group Citation[21]. However, the effect was lost at 7 months. In 222 stroke patients with a paretic upper extremity the effect of 2 weeks constraint-induced movement therapy (ipsilesional arm restraint while training of paretic arm is conducted) showed a significant improvement of the function of the paretic arm Citation[22].
Conclusion
Current evidence shows that a higher level of physical activity is associated with a decreased risk of stroke, has beneficial effects on stroke risk factors, and results in lesser stroke severity and a better long-term outcome following stroke. As yet there is no study to show that increased physical activity after stroke reduces risk of recurrent stroke. That is, however, likely to be the case. To demonstrate such an effect will need a large clinical trial where participants are randomized to a training program or to a control group. The challenge will be to get stroke survivors to exercise. Supervised training programs will probably be necessary. Simply advising stroke patients to exercise will probably not be effective.
Financial & competing interests disclosure
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
No writing assistance was utilized in the production of this manuscript.
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