High-Intensity Interval Training Improves Diabetic Hearts

Veronica Hackethal, MD

September 11, 2015

A UK study has found that high-intensity interval training (HIIT) improves cardiac structure and function in patients with type 2 diabetes. Control of diabetes also improved with the training, but to a lesser extent.

The findings were published online on September 9 in Diabetologia by Sophie Cassidy of the University of Newcastle, United Kingdom, and colleagues.

The study is the first to suggest that an exercise intervention could improve cardiac function in patients with diabetes.

"Our data highlight the importance of exercise, beyond solely thinking about diabetes control and HbA1c. Exercise can begin to target key organs, like the heart, and help adapt their physiology," commented senior author Michael Trenell, PhD, professor of metabolism and lifestyle medicine at the University of Newcastle.

Patients with diabetes represent nearly one-quarter of all hospital admissions for heart failure in Westernized countries, making heart disease the leading cause of death and illness in type 2 diabetes.

And diabetes begins to affect the heart early, even before clinical cardiovascular disease becomes apparent. Diabetics have few treatment options, though, to improve cardiac structure and function, according to background information in the article.

HIIT Improves Left Ventricular Function

In the study, researchers randomized 23 patients with type 2 diabetes to 12 weeks of HIIT (n=12) or standard care (n=11). HIIT consisted of three sessions per week of stationary cycling at a local gym. Participants started with initial intervals of 2 minutes with 3-minute recovery periods, increasing in 10-second increments each week, and reaching 3 minutes 50 seconds by week 12. The initial session was supervised. Participants used voice-recorded instructions on an iPod for subsequent sessions and completed an exercise diary.

The researchers measured cardiac function with advanced MRI and hepatic fat with magnetic resonance spectroscopy. They used oral glucose tolerance tests to evaluate diabetes control.

The study excluded patients who already had heart disease, who exercised regularly, took beta-blockers, or had contraindications to exercise stress testing.

Compared with controls, HIIT significantly improved cardiac structure and function. The left ventricle is often impaired in diabetes, and left ventricular wall mass increased by 12% in HIIT participants.

The authors point out that this "physiological hypertrophy" of increased left ventricular wall mass that occurs with exercise is different from "pathological hypertrophy" that occurs with heart disease. Only the latter is linked to increased wall thickness due to collagen accumulation, which can predict death.

Systolic function, including stroke volume (P < .01) and left ventricular ejection fraction (P < .05), also improved in the HIIT group.

In addition, HIIT participants had improved diastolic function, the most common heart abnormality in diabetes and a predictor of mortality.

Early diastolic filling rate increased by 24% in the HIIT group, and peak torsion, which can indicate endocardial damage, decreased by 15%.

And after HIIT, liver fat in participants decreased by about 39%. The HIIT group also experienced a decrease in visceral fat and a modest, though significant, decrease in HbA1c (from 7.1 to 6.8, P < .05).

HIIT did not significantly alter whole body fat, fasting glucose, fasting insulin, insulin sensitivity, or beta-cell function however.

There were no reported adverse events.

Screen Patients Before Prescribing Exercise

"The adverse events associated with exercise predominantly relate to undiagnosed heart disease, so screening for heart disease is advised. For those for whom HIIT may not be appropriate, lower-intensity exercise may also be advised," Dr Trenell pointed out.

"Exercise is recommended as part of the standard treatment pathways for everyone with type 2 diabetes. Our data reinforce this but also highlight the specific benefits to the heart," he emphasized, "Everyday physical movement is a hugely underutilized therapy for the management of type 2 diabetes."

The authors report no relevant financial relationships.

Diabetologia. Published online September 9, 2015.Article


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