According to the World Health Organization (WHO), cardiovascular diseases cause approximately 18 million deaths worldwide, each year. This is almost one third of all deaths worldwide. In the European Union, 49 million people live with cardiovascular disease and every year, about 1.8 million people die from these diseases, which represents about 37% of all deaths. High blood pressure is estimated to be responsible for almost half of these deaths, or 13% of deaths worldwide (more than 8 million deaths per year). The WHO estimates that by 2025, 1.56 billion people will have high blood pressure. Increased blood pressure is an important risk factor for cardiovascular diseases, including stroke and coronary heart disease.
Blood pressure is quantified by two values, systolic (maximum pressure in the systemic circulation when blood is ejected from the heart) and diastolic (minimum pressure in the systemic circulation when the heart "relaxes"). For most adults, a normal blood pressure is 100-130/60-80 mmHg. But when these values exceed 140/90 mmHg at rest on a daily basis, it is called hypertension (or high blood pressure). Many factors influence systolic and diastolic blood pressure, including blood volume, arterial wall compliance, and peripheral resistance. While certain genetic factors and diseases can lead to hypertension, the main cause is often behavioural : diet, alcohol consumption, smoking, sedentary lifestyle, etc.
In addition to pharmacological treatments, physical activity (endurance or muscle strengthening) is often recommended for the prevention, treatment and control of hypertension. It improves various muscular functions (see also: Resistance training and Hypertension : Improving Cardiovascular Health) and cardiovascular functions (including endothelial function) which result in a decrease in blood pressure. And the clinical effects of training are as good as or better than those obtained with drug treatments (See also: High blood pressure : Exercise vs. Drugs). However, traditional strength training or cardiovascular endurance training are not always the most appropriate solutions for all people, especially those with limited mobility. In addition, adherence is often poor. As 50% of people with high blood pressure do not have their blood pressure properly managed and below the recommended limits, it is important to implement effective and simple solutions. Isometric training is a simple solution to implement at home and does not require too much time for patients (10 to 40 minutes / week). But how effective is isometric training in reducing blood pressure? Is this method effective for people with high blood pressure under medication ?
To answer these questions, an international team of researchers carried out an individual participant data meta-analysis. Traditional meta-analyses sum up the overall results of studies, with their uncertainty (standard error or confidence interval). Whereas individual participant data meta-analyses, as the name suggests, consider the individual data of all patients, with their own characteristics. Thus, the heterogeneity of data that is often a problem in classical meta-analyses becomes an advantage in individual participant data meta-analyses, allowing many factors to be considered. The data collection and associated statistics, however, are more complex.
For this purpose, the researchers collected data from 12 randomised (and non-randomised) controlled studies, involving 326 participants, 191 of whom were in the experimental groups and 135 in the control groups. The participants were all at least 18 years old, with or without hypertension, on or off medication and the duration of the isometric training programme was at least 3 weeks. The exercises performed were grip training, leg extension or both. The isometric intensity was equal to 30% of the maximum voluntary contraction for 124 people, 21% for 26, 18% for 10, 14% for 11, 10% for 11 and 8% for 9, over 4 sets of 2 minutes (with inter-set rests varying from 1 to 3 minutes). The frequency of the sessions was 3 times a week for all the studies, except for one which carried out the sessions every day.
The main results of this individual participant data meta-analysis showed that isometric training significantly reduces systolic (-6.22 to -7.35 mmHg), diastolic (-2.78 to -3.29 mmHg) and mean (-4.12 to -4.63 mmHg) blood pressure. The reduction in mean arterial blood pressure demonstrated here has real clinical significance since scientific data show that a 3 mmHg reduction can reduce the risk of coronary heart disease by 5%, stroke by 8% and all-cause mortality by 4%. Moreover, these gains are quite comparable to those obtained with drug treatments or cardiovascular or strength training programmes.
There were no differences between women and men, between people under and over 45 years old, between people without and those with hypertension, and between people with different body mass indexes. Although no significant difference was observed between those not taking blood pressure medication and those taking it, there was a trend that people without medication would improve their health more with isometric training. This could be explained by the similarity between the mechanisms of medication and training. It is proposed that isometric training increases endothelium-induced vasodilation, which lowers blood pressure by reducing total peripheral resistance, as does cardiovascular endurance training.
A few tens of minutes per week of isometric work on 1 or 2 exercises at relatively low intensity (20-30% of maximal voluntary contraction) is sufficient to bring clinical benefits on the health status of people with hypertension. Grip exercises can generally be performed anywhere, anytime, in a seated position and are easily accessible to all audiences, including people with mobility problems who would not be able to start immediately with a cardiovascular training programme (walking, running, cycling, swimming, etc.) or a strength training programme.
The benefits of isometric training are numerous, not limited to neuromuscular performance and have a significant clinical impact on the health of people with hypertension. Further studies are needed to better define optimal protocols (optimal intensity, optimal frequency, optimal exercise mix, etc.). In the meantime, if you have family members or clients with hypertension, isometric grip work can help them.
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