- Previous research has shown isometric resistance training (IRT) to lower systolic and diastolic blood pressure, but there have been safety concerns.
- A new meta-analysis of 24 primary studies reexamines the effectiveness of this form of exercise and assesses its safety.
- The study findings suggest that IRT is both safe and effective in lowering blood pressure.
Research has suggested that IRT may reduce systolic and diastolic blood pressure. However, concerns about its safety have stopped doctors from widely prescribing it. The concerns stem from the fact that IRT can increase blood pressure during exercise, especially when it involves large muscle groups or is high in intensity.
Researchers from the University of New South Wales (UNSW) in Sydney, Australia, recently led a new analysis of previous studies to explore the question of IRT’s safety.
The meta-analysis suggests that IRT can safely lower blood pressure and may even be safer than other forms of exercise for some people.
The senior author of the study, Dr. Matthew Jones, is an accredited exercise physiologist and lecturer in the School of Health Sciences, Faculty of Medicine & Health at UNSW.
Dr. Jones explains, “IRT is a time-efficient means of reducing blood pressure, needing only 12 minutes a day, 2 to 3 days per week to produce the effects we found in our review.”
The study features in the journal Hypertension Research.
What is isometric resistance training?
IRT involves applying tension to muscles without movement of the surrounding joints. For instance, a person contracts a muscle or muscle group and holds it in place for a specified period.
“While the studies included in our review normally used a specialized handgrip device,” says Dr. Jones, “it’s possible we would see the same effects simply by asking participants to make a fist and squeeze it at a certain intensity for the prescribed amount of time. This means IRT could easily be performed while participants are sitting down watching TV.”
Analyzing existing research
The researchers included 24 randomized control trials in their analysis, which involved 1,143 participants with an average age of 56 years. Of the total group, 56% were female.
The participants in the study were individuals who had either:
- High-normal blood pressure: A systolic blood pressure (SBP) of 130–139 millimeters of mercury (mm Hg).
- Grade 1 hypertension: An SBP of 140–159 mm Hg.
- Grade 2 hypertension: An SPB over 160 mm Hg or a diastolic blood pressure (DBP) of more than 100 mm Hg.
The researchers only included IRT trials that had lasted at least 3 weeks, which previous research suggests is the minimum length of time to produce a blood pressure change.
The effect of IRT on blood pressure
The study produced promising results. Dr. Jones recalls:
“We were interested in how IRT reduced blood pressure in people with high blood pressure. We also wanted to know whether IRT was safe. We found that IRT was very safe and caused meaningful changes in blood pressure — almost as much as what you’d expect to see with blood pressure-lowering medications.”
Looking at measurements taken as part of regular clinical practice, the researchers found that SBP reduced by an average of 6.97 mm Hg among the IRT group compared with controls. DBP also decreased by an average of 3.86 mm Hg.
The researchers also found that aorta, or central, blood pressure — an important indicator of cardiovascular disease — reduced by an average of 7.48 mm Hg for SBP and 3.75 mm Hg for DBP. Average DBP over 24 hours also went down, although to a lesser degree, with a reduction of 2.39 mm Hg.
In an email, University of Washington cardiologist Dr. Alec J. Moorman, M.D., FACC, who was not involved in this research, pointed out to Medical News Today that the study included three comparisons of IRT vs. aerobic exercise in which the aerobic exercise produced a more significant reduction in blood pressure.
He noted, “The ACC/AHA Prevention guidelines recommend 150 minutes of moderate intensity aerobic activity or 75 minutes of vigorous intensity aerobic activity per week, as this volume (“dose”) of exercise lowers [cardiovascular] risk by about 30%.”
IRT may still be of value for people unable to engage in aerobic exercise, says Dr. Jones :
“It’s particularly exciting for people who may have difficulty performing more ‘traditional’ exercise, such as walking, cycling, or strength training, knowing they have another exercise type in their toolkit to help manage their high blood pressure.”
“In fact,” Dr. Jones adds, “there were actually lower rates of adverse events in older adults, making it a very appealing mode of exercise, especially in those with mobility restrictions who may not be able to do other exercises like aerobic or dynamic resistance training.”
Cardiologist Dr. Jennifer Wong of MemorialCare Heart and Vascular Institute at Orange Coast Medical Center in Fountain Valley, CA, who was not involved in the study, spoke with MNT. “Speaking to our patients about it,” she said, “I’m sure we have a much easier time telling them to do a handgrip for 15 minutes.”
Dr. Wong also suggested that IRT “may even have an additive effect in combination with hypertensive medications. I do think it’s reasonable to try in conjunction with the other therapies like low salt diet and (…) medication that’s been well-studied.”
IRT safety
The analysis found no serious adverse events in the IRT trials. Out of the two dozen included studies, there were only seven reported adverse events — predominately joint or muscle pain — and none was severe enough to cause a participant to leave the study. Individuals in most of the studies exercised with handgrips.
“Importantly, this meta-analysis demonstrates that IRT is safe,” said Dr. Moorman, although, he added, “I would recommend something like a handgrip device or doing wall sits.”
Said Dr. Wong:
“I would feel comfortable recommending the handgrip exercise, especially given that most of the trials they looked at here were using hand exercises, and very few adverse effects seem to have been seen in these trials. I might even recommend it with additional aerobic exercise.”
She noted that the two lower-limb trials that the study included also produced no adverse effects.
Limitations of the study
“All included trials were at a high risk of bias, downgrading the quality of the evidence,” write the study’s authors.
As a result, the authors reduced all reported reductions in SBP and DBP by 2 mm Hg to reflect the high likelihood of bias in the original studies.
They also lowered the values by an additional 1 mm Hg to account for inconsistencies between the methods and measurements that the 24 different sets of researchers employed.
Although Dr. Moorman said that he still considers the study to have value, he agreed that some caution is warranted, saying, “The advantage is combining several studies to pool data, but these types of analyses can be prone to several types of bias and error, and that can be amplified.”
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