Discussion
After pooling data from 79 studies, this systematic review and meta-analysis suggests short-term AET significantly reduces PWV in adults with and without LTC by a similar magnitude. The participant factors were not associated with greater improvement in PWV, however, cohorts of older age had a greater reduction in PWV following AET than younger cohorts. The impact of PWV was independent of all recorded aspects of the exercise prescription. Similarly, the technique used to measure PWV, which includes cfPWV, brachial-ankle PWV and carotid-brachial PWV, did not affect the findings and neither did the equipment used to measure PWV.
The magnitude of the change in PWV from this review is −0.63 m/s across health and disease, which is potentially associated with a risk reduction of 9.3% for cardiovascular events, 10.0% for cardiovascular and all-cause mortality over 7 years, extrapolated from existing data.3 The subanalyses showed that the presence of LTC does not impact the influence AET has on PWV. This implies that the beneficial effects of AET on vascular stiffness is not limited to healthy adults and exercise programmes incorporating AET could be of benefit for adults regardless of their health status to reduce the risk of cardiovascular events.
Eleven conditions have been collated in this review to explore the effect of AET on PWV, however, it is evident that this association has not been investigated in various conditions, including inflammatory disorders and mental health conditions associated with high levels of sedentary behaviour. Considering inflammatory markers are associated with AS and patients with primary inflammatory disorders have increased vascular stiffness,30 an AET programme could reduce the risk of cardiovascular events in adults with inflammatory conditions. AET programmes could also benefit conditions such as depression and anxiety that are associated with decreased levels of physical activity, often linked to a rise in cardiovascular risk. Rehabilitation programmes for people with chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF) usually target improvements in exercise capacity and quality of life rather than improvements in cardiovascular risk, and therefore, the effect of AET on AS has rarely been studied in these populations.
AET was chosen as the intervention as this modality confers beneficial effects on the heart and increases exercise capacity. Reduction in central and peripheral stiffness has been reported following AET in healthy populations31–35 and hypertensive adults.36 The underlying mechanisms by which AET reduces vascular stiffness is unknown, however, evidence suggests it may be via arterial remodelling, improved endothelial function and decreased sympathetic tone.31
Previous systematic reviews comparing the influences of aerobic, resistance and combined (aerobic and resistance) exercise training on a range of measures of vascular stiffness collectively report that AET significantly improves vascular stiffness whereas resistance and combined exercise had no effect in a mixed cohort of adults with and without LTC.9 11 A common hypothesis suggests the resistance exercise component of the combined exercise could limit the improvement in AS, as resistance training has been linked to increased PWV.37 Despite the influence of resistance exercise on vascular stiffness, this mode of exercise is associated with many cardiometabolic benefits including reduction of resting blood pressure and prevention and management of type 2 diabetes.38
In contrast to previous systematic reviews,9–11 this review collates studies with supervised AET rather than concurrent aerobic and resistance exercise training interventions. Despite the similar change in PWV after AET across the systematic reviews, updated studies have been added to this review alongside US enabling a clear understanding of the impact that AET has on PWV. This review also differs from the previous reviews as it explores whether any aspect of the exercise prescription or the population demographics influences the change in PWV.
The quality of evidence in this review was graded very low with the main reason being the inclusion of observational studies (non-RCTs) alongside the RCTs. The high heterogeneity may also contribute to the low grading.
Strengths and limitations
The main strength of this systematic review was the focus on AET in isolation to remove the possible confounding of resistance training, and the inclusion of US to provide a larger dataset for meta-regression, allowing exploration of the impact of patient and programme factors on change in PWV.
The main limitation of this study is that it explores the effect of an exercise intervention on PWV when it is unknown whether the reduction in cardiovascular events associated with AET is mediated by AS or an alternative mechanism.
The mean duration of the AET programmes in the included studies was 11 weeks. Although a reduction in PWV was observed, the long-term benefits of AET on PWV, cardiovascular health and the effect of detraining on PWV remain unknown. One trial reported that PWV returned to baseline levels after 1 month of detraining.39
Poor reporting of exercise interventions, specifically training intensity, potentially reduced the power of the meta-regression to detect an effect for patient and programme factors. There was a greater change in PWV observed in studies where SD was estimated using presented test statistics compared with using correlation coefficient. A potential explanation is that studies reporting test statistics often show significant results demonstrating precise results with greater effects.
The included studies possessed small sample sizes (number of participants range: 6–71), indicating the studies could be predominantly underpowered. High risk of bias was present in study designs other than RCTs due to a lack of participant blinding, potentially leading to performance bias, however, this is very difficult to avoid in studies of exercise training. The presence of publication bias could indicate successful trials are more likely to be published, supported by the three positive studies that had a large influence on the change in PWV. The number of studies in individual diseases was small, suggesting the need for further exploration in these diseases.
Narrowing the focus of this review to AET restricts the application of these results to interventions that combine AET with other factors (eg, resistance training or dietary modification). In turn, this excludes populations with LTC, such as COPD and CHF, for whom rehabilitation programmes lead to beneficial effects on symptoms often include resistance and AET.40 41 Pharmacological interventions, includinganti-hypertensive and lipid-lowering medications, can influence PWV but were not taken into consideration in this review.
Finally, confining the measure of AS to PWV could limit the generalisability of the results. Although combining different measures of AS such as PWV, carotid-intima thickness and flow‐mediated vasodilation would illustrate the overall picture of AS, these parameters cannot be compared as each measure assesses a different aspect of vascular stiffness.