Leading cause of death worldwide, cardiovascular disease is a group of disorders that affect the heart and vascular system, and includes coronary heart disease (affecting the vessels that feed the heart), cerebrovascular disease (affecting the vessels that feed the brain), rheumatic disease, venous thrombosis and many others. In 2016, the number of deaths from these diseases was 840,000 in the United States and 17.9 million worldwide, representing 31% of total global mortality. They are linked to genetics, ageing and our behaviour: smoking, alcohol consumption, level of physical activity & dietary hygiene.
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Arterial stiffness is an independent risk factor for the development of cardiovascular disease. Increased arterial stiffness is associated with increased mortality risk in the elderly and in people with chronic diseases such as hypertension or diabetes, for example. Schematically, arterial stiffness means a loss of elastin fibres and an accumulation of stiffer collagen fibres on the arterial wall, which in turn affects the vasomotricity of the endothelium (the inner layer of our blood vessels), and thus the vaso-constriction/dilatation and regulation of our blood pressure. Arterial stiffness is measured via the pulse wave velocity which is the speed at which the pulse travels along an artery. The higher this speed, the more rigid the artery.
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Many studies have found that arterial stiffness is correlated with the level of physical activity. Thus, spending more time in sedentary activities would be associated with higher arterial stiffness while spending more time in physical activities would be associated with lower arterial stiffness. Cardiovascular endurance activities such as walking or running appear to have a positive impact on arterial stiffness, regardless of age and health status. Whereas for activities such as weight training, the results of studies are contradictory, with some reporting positive effects, others negative and some finding no impact. What is the reality ?
To clarify this question, Chinese researchers carried out a meta-analysis of 20 randomised controlled studies involving 981 participants (462 for the control group and 519 for the experimental group), aged between 18 and 88 years. Each study used a training program lasting between 8 and 12 weeks with a frequency of 1 to 5 weekly sessions and an intensity ranging from 30 to 90% of the 1RM. In all studies, pulse wave velocity measurement was used either between the carotid and femoral arteries (which measures central arterial stiffness) or between the brachial and tibial arteries (which measures whole-body arterial stiffness).
The main results of this meta-analysis showed that resistance training had no significant effect on pulse wave velocity. However, as resistance training is dependent on so many parameters, the researchers went further and performed regression analyses to see if certain variables influenced pulse wave velocity more than others. The results showed that only intensity was significantly correlated with changes in pulse wave velocity.
Based on this result, the researchers performed further analyses by grouping the studies according to 2 intensities: light-moderate (30-70% 1RM) and high (> 70% 1RM). The light-to-moderate intensity significantly decreased pulse wave velocity, while the high intensity had no significant effect.
The researchers then analysed the results according to the age of the participants: under 40 and over 40. The results showed that resistance training significantly reduced arterial stiffness in participants over 40.
Finally, the researchers analysed the impact of age and intensity. They observed that only light to moderate intensities significantly reduced arterial stiffness in both the under 40 and over 40 age groups.
Increasing pulse wave velocity by 1 m/s can increase the risk of cardiovascular events by 12-14% and mortality by 13-15%. And it would seem that even for training intensities below 70% of 1RM, it is possible to achieve a significant reduction in this variable. But the exact mechanisms of the impact of muscle strengthening on arterial stiffness are not yet fully understood. The authors of this study hypothesise that light-moderate intensity muscle training (30-70% 1RM) would activate the sympathetic nervous system less and would not increase muscle tone, which would have a beneficial effect on blood circulation via improved endothelial function (including better production of nitrogen oxide).
Regarding the impact of higher intensities, the lack of significant results does not necessarily mean that lifting heavier does not provide health benefits (nor that it would be bad). Especially since randomised controlled trials have already shown the positive impact of heavy weight training on blood pressure in people with chronic health problems, not to mention other health benefits such as gains in maximal strength, muscle mass, mobility, bone mineral density, etc. However, pulse wave velocity is an independent risk factor, and further studies are needed to better understand these results and the impact of strength training.
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