Effect of high-intensity exercise on cardiorespiratory fitness in stroke survivors: A systematic review and meta-analysis





Abstract


Background


Knowledge of the optimal protocol and safety of particularly high-intensity exercise applied to individuals with stroke is lacking.


Objective


This systematic review and meta-analysis aimed to investigate the effect of high-intensity exercise on cardiorespiratory fitness in stroke survivors.


Methods


We performed a systematic electronic search for articles in MedLine via PubMed, EMBASE, Web of Science, Cochrane Central Register of Controlled Trials, CINAHL, and SPORTSDiscus up to April 1, 2019. Peak oxygen consumption (VO 2 peak), 6-min walk test (6MWT), fastest 10-m walk test (10MWT), and adverse events were assessed. The standardized mean difference (SMD), weighted mean difference (WMD), and odds ratios (ORs) were used to compute the effect size, and subgroup analysis was conducted to test the consistency of results as well as sensitivity analysis to assess the robustness of the results. The quality of evidence was assessed with the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system.


Results


We included 17 studies (PEDro score ≥ 4) in the meta-analysis. Post-intervention, high-intensity exercise had a significant effect on peak oxygen uptake (VO 2 peak; SMD = 0.56, P < 0.01, I 2 = 8%; WMD = 2.53 mL/kg/min; high quality of evidence) and 6MWT (SMD = 0.26, P < 0.01, I 2 = 40%; WMD = 17.08 m; moderate quality of evidence) but not fastest 10MWT (SMD = 0.33, P = 0.27, I 2 = 77%; WMD = 0.05 m/s; low quality of evidence). Subgroup analysis showed better effects of higher-intensity treadmill training (≥ 70% heart rate reserve/VO 2 peak) for a longer duration (≥ 12 weeks) on VO 2 peak and 6MWT in sub-acute or chronic stroke survivors. The high-intensity exercise and control groups did not differ in adverse events including falls [odds ratio (OR) 1.40, P = 0.35, I 2 = 11%; low quality of evidence], pain (OR 3.34, P = 0.09, I 2 = 0%; moderate quality of evidence), or skin injuries (OR 1.08, P = 0.90, I 2 = 0%; low quality of evidence).


Conclusions


Our meta-analysis suggests that high-intensity exercise is beneficial for cardiorespiratory fitness in stroke survivors and might be safe as a novel intervention in cardiopulmonary rehabilitation after stroke.


1


Introduction


Each year, approximately 795,000 people experience stroke, the second leading global cause of death after ischemic heart disease . All adverse conditions besides fatigue, low mood and motivation, and cognitive impairments lead to physical inactivity and de-conditioning . As compared with older adults without stroke, stroke patients’ steps per day average 79% fewer steps (1536–3035 vs. 7250 steps/day), far below that in the “sedentary lifestyle index” (5000 steps/day) . Physical inactivity contributes to further de-conditioning , recurrent stroke , and high long-term risk for cardiovascular diseases .


Cardiorespiratory fitness (CRF) reflects the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained, moderate- to high-intensity exercise physical activity. CRF is impaired after stroke, with VO 2 peak values ranging from 8 to 22 mL/kg/min, equivalent to 26% to 87%, respectively, of that of healthy age- and sex-matched individuals .


Post-stroke exercise is an important component in reducing the risk of future cardiovascular events and recurrent stroke . Meta-analysis showed that aerobic exercise contributed to improving aerobic capacity and walking performance . The use of a treadmill , cycle ergometer , and recumbent stepper during training has also been found beneficial for cardiopulmonary health. However, most traditional stroke rehabilitation programs lack essential training time and sufficient exercise intensity . A series of clinical studies suggested that higher-intensity exercise could result in significantly greater improvement in aerobic fitness among healthy adults , heart disease patients , and stroke patients . However, despite the evidence regarding the known benefits, confusion remains regarding the different impacts of specific intensity, duration, and frequency across high-intensity exercise regimes on CRF after stroke.


Several previous meta-analyses confirmed that post-stroke aerobic exercise has a significant positive effect on CRF . One study found that higher aerobic intensity was significantly associated with greater improvements in VO 2 peak than lower-intensity aerobics . However, all of these studies failed to explicitly investigate the optimal protocol and safety of high-intensity exercise applied to individuals with stroke systematically.


Thus, our review aimed to explore the effect of different intensity, duration, type, and duration of high-intensity exercise on CRF gains and walking ability by a consecutive sensitivity analysis and whether high-intensity exercise effects differ between post-stroke stages. Furthermore, we explored the safety of high-intensity exercise during stroke recovery. This systematic review will provide specific information on high-intensity exercise programs and their efficacy in improving CRF in individuals with stroke.




2


Methods


The review and analysis were conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) . The systematic review protocol was registered in PROSPERO (CRD42019130311). Details of the definitions, search strategy, inclusion and exclusion criteria, risk of bias and quality of evidence, data extraction, and statistical analysis are in the online Data Supplement.


2.1


Definitions


An exercise intervention with high intensity includes high-intensity training (HIT) and high-intensity interval training (HIIT). HIT refers to a high intensity exercise program performed continuously. HIIT is characterized by maximum exercise intensity by short bursts of concentrated effort alternating with low activity or rest. The classification of relative intensity exercise modified from American College of Sports Medicine is shown in Table 1 . The target intensity of high-intensity exercise is ≥ 60% heart rate reserve (HRR)/VO 2 peak, ≥ 70% peak HR, or ≥ 14 Borg RPE (6–20 scale). There are 2 methods to measure CRF: the progressive exercise test, and clinical tests such as the 6-min walk test (6MWT) . Measurement of the peak/maximum level of oxygen uptake (VO 2 peak/VO 2 max), the capacity oxygen consumption during progressive exercise (exercise of increasing intensity), is the gold standard for evaluating an individual’s CRF . In addition, we tried to indirectly reflect the changes of CRF by measuring the fastest but not comfortable 10-m walk (10MWT).



Table 1

American College of Sports Medicine classification of exercise relative intensity.














































Intensity %HRR or VO 2 R %peak VO 2 %peak HR RPE Borg Scale
Very light < 20 < 25 < 35 < 10
Light 20–39 25–44 35–54 10–11
Moderate 40–59 45–59 55–69 12–13
Heavy 60–84 60–84 70–89 14–16
Very heavy ≥ 85 ≥ 85 ≥ 90 17–19
Maximal 100 100 100 20

HRR: heart rate reserve; VO 2 R: VO 2 reserve; HR: heart rate; RPE: rating of perceived exertion.


The primary outcome measures were changes in the peak/maximum level of oxygen uptake (VO 2 peak/VO 2 max), 6MWT, and fastest 10MWT. Secondary outcome measures were any adverse events (e.g. falls, pain, injuries). We distinguished 4 stages following the onset of stroke: the hyper-acute or acute phase (0–7 days), early sub-acute phase (7 days until 3 months), late sub-acute phase (3–6 months), and chronic phase ( > 6 months) .


2.2


Search strategy


We performed a systematic search for articles in the databases MEDLINE via PubMed (1966 to April 2019), EMBASE (1988 to April 2019), Web of Science (1900 to April 2019), Cochrane Central Register of Controlled Trials (CENTRAL; April 2019), CINAHL (EBSCOhost; 1982 to April 2019), and SPORTSDiscus (EBSCOhost; 1949 to April 2019). Search terms are in Supplemental Table 1 . We included articles that described randomized controlled trials (RCTs) or clinical controlled trials of individuals ≥ 18 years of age in the acute, sub-acute, or chronic stages of stroke recovery. Articles had to include a detailed description of the exercise intervention, including intensity, duration, and frequency with the target intensity of exercise achieved ≥ 60% HRR/VO 2 peak, ≥ 70% peak HR, or ≥ 14 Borg RPE (6–20 scale). Controls had to have low- to moderate-intensity training (< 60% HRR/VO 2 peak, < 70% peak HR, or < 14 RPE), no exercise intervention or no specific exercise intervention. One or more of the study outcomes had to evaluate CRF (e.g. VO 2 peak, VO 2 max, 6MWT, fastest 10MWT). The secondary outcome measures included adverse events (e.g. falls, pain, and injuries).




3


Risk of bias and quality of evidence


The methodological quality of each study was independently assessed by using the Physiotherapy Evidence Database (PEDro) Scale (range 0–10). A total PEDro score ≥ 6 was considered high quality, 4 or 5 moderate quality, and < 4 low quality . Studies with a score < 4 were excluded. The quality of evidence was assessed by using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system. The GRADE approach specifies 4 levels of quality: high, moderate, low, or very low. The highest quality rating is for randomized trial evidence. However, review authors can downgrade randomized trial evidence to moderate-, low-, or even very low-quality evidence, depending on the presence of several factors .




4


Statistical analysis


Stata v14.0 and Revman v5.3.4 were used for the meta-analysis. For all studies that reported continuous data, we chose the standardized mean difference (SMD) with the 95% confidence interval (CI) as summary statistics for the meta-analysis. The weighted mean difference (WMD) of the aerobic capacity from pre- to post-intervention between groups in each study was calculated. For dichotomous data (i.e. adverse events), the Mantel-Haenszel method was used to calculate pooled odds ratios (ORs). Six analyses with subgroups were planned: intervention type (HIT vs HIIT), time since stroke (sub-acute, < 6 months, vs. chronic, ≥ 6 months), intensity (< 70% vs ≥ 70% HRR/VO 2 peak), mode (i.e. treadmill, cycle ergometer, recumbent stepper), and frequency of the intervention (< 12 vs ≥ 12 weeks) in the experimental group, and type of intervention in the experimental and control groups (the same or different type of training between experimental and control groups). With the Cohen classification, effect sizes were defined as small (0.2–0.5), medium (0.5–0.8) and large (≥ 0.8). .




5


Results


5.1


Search results


A flow chart detailing the study selection process is in Fig. 1 . Reports for 17 studies (707 participants) were eligible for inclusion in the meta-analysis. The initial searches returned a total of 4932 articles, of which 1987 were duplicated articles. Additional records identified through reference lists returned 72 articles. Titles and abstracts of the retrieved articles were assessed for suitability, leading to the retrieval of 112 full texts. Of these, 95 did not fulfil the inclusion criteria and the remaining 17 studies were analyzed. Supplemental Table 2 describes the characteristics of the 17 studies.




Fig. 1


PRISMA flowchart of the search process.


5.2


Characteristics of included studies


The 17 articles described 16 RCTs and 1 controlled trial. All studies were published from 2000 onward; most were published after 2010 ( n = 11). The 17 studies were performed in 7 countries, predominantly North America [USA ( n = 8) and Canada ( n = 3) ]. Study inclusion/exclusion criteria often included the following: > 6 months post-stroke ( n = 9 studies) , stable cardiovascular/cardiopulmonary condition ( n = 15) , no serious musculoskeletal problems or pain ( n = 11) , no previous history of peripheral or central nervous system injury ( n = 10) , independent in ambulation with or without a walking aid ( n = 15) , no significant cognitive or communication issues ( n = 8) , and not currently participating in formal rehabilitation or any physical training within the last few months ( n = 4) .


5.3


Participants


The 17 articles described results for 707 participants (467 [66.1%] males). The mean (SD) age ranged from 45 (no SD provided) to 69 (9) years, with the mean age being in the 60’s for most. The mean (SD) time since stroke ranged from 17.8 (3.1) days to 5.2 (2.93) years: within 6 months ( n = 3) and > 6 months ( n = 14) .


5.4


Interventions


Information regarding the interventions is in Table 2 . Three studies adopted HIIT, and we considered that 14 studies adopted HIT because of no report of interval intensity and time. Eleven studies used treadmill walking and 6 a cycle ergometer. HRR, VO2peak, and work rate (WR) were used to define the intensity of exercise. The intensity in the experimental group ranged from 60% to 85% HRR/VO 2 peak, and the control group performed 28 to 45 min of aerobic exercise (i.e. treadmill walking, stretching exercise, conventional physical therapy) at planned intensities < 50% HRR/VO 2 peak. Sessions ranged from 25 to 50 min, with most lasting 30 to 40 min ( n = 14) . The frequency ranged from 2 to 5 times per week, most occurring 3 times per week ( n = 8) . Overall, 7 studies did not report the frequency of training. The program length ranged from 4 to 24 weeks, with the program for 7 studies being 8 to 12 weeks. In total, 14 studies reported the training settings. Interventions were undertaken in outpatient or inpatient rehabilitation institutions.


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Mar 10, 2020 | Posted by in PHYSICAL MEDICINE & REHABILITATION | Comments Off on Effect of high-intensity exercise on cardiorespiratory fitness in stroke survivors: A systematic review and meta-analysis

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