Interval Training for the Diabetic Heart

A new randomized-controlled trial has shown that exercise training can improve cardiac structure and function, and possibly reverse cardiac damage, in type 2 diabetes (T2DM).

 “This study demonstrates, for the first time, that exercise can begin to reverse some of the early cardiac changes that are commonly found in people with type 2 diabetes. Interestingly, the data also suggest that this type of high intensity intermittent exercise benefits both the heart and diabetes control, but the benefits appear to be greatest in the heart. The strong positive effect of exercise on the heart is, although completely logical, a message that needs to be communicated to people with type 2 diabetes more clearly,” said lead author Michael Trenell, PhD, and colleagues at Newcastle University, UK.

Heart disease is the leading cause of morbidity and mortality in diabetes. The damage can appear early, even before overt clinical disease develops. Abnormalities in diastolic function represent the most common dysfunction of the diabetic heart, and are an independent predictor of mortality. Patients with diabetes often show ventricular abnormalities, such as pathological hypertrophy of the left ventricle due to collagen accumulation. They also show increased torsion, which can indicate impaired contraction at the level of the endocardium and potential perfusion defects, according to background information in the article.

In the 12-week study, 23 people with type 2 diabetes were randomized to standard care (n=11) or three sessions of stationary cycling three times per week (n=12). At the beginning of the study, participants did intervals of 2 minutes, followed by 3 minute recovery periods. The exercise intervals increased by 10 seconds each week, reaching 3 minutes 50 seconds by the end of the study.

Cardiac function was evaluated using advanced magnetic resonance imaging, and liver fat was assessed with magnetic resonance spectroscopy. Researchers checked diabetes control with oral glucose tolerance tests.

Regular exercisers and participants with clinical heart disease who took beta blockers, or had contraindications to stress testing, could not participate in the study.

Results showed that cardiac structure as well as both systolic and diastolic function significantly improved in the high intensity intermittent training (HIIT) group compared to controls.

After doing HIIT participants had:

• Improved cardiac structure:

♦ 12% increased ventricular wall mass

• Improved systolic function

♦ Significantly improved left ventricular ejection fraction and stroke volume

♦ 15% decrease in peak torsion

• Improved diastolic function

♦ 24% increased early diastolic filling rate

• 39% decrease in liver fat

• Modest decrease in HbA1c (from 7.1 to 6.8, p < 0.05)

• No significant change in whole body fat, fasting glucose, fasting insulin, insulin sensitivity, or beta cell function

• No reported adverse events 

The authors pointed out that the increase in left ventricular wall mass following HIIT likely represents “physiological hypertrophy” that often develops with exercise, and is not linked to increased mortality found with the “pathological hypertrophy” of heart disease. 

“The data reinforce how important a physically active lifestyle is for people with type 2 diabetes. Our findings also suggest that exercise does not have to be 30 minutes of continuous exercise – repeated short bouts of higher intensity exercise give strong benefits to the heart,” the authors emphasized, “Getting more physically active is, quite literally, at the heart of good diabetes control.”

Take-home Points

• The leading cause of morbidity and mortality in T2DM is heart disease.

• A randomized controlled trial has suggested that high intensity intermittent exercise training can improve cardiac structure and functioning, and potentially reverse damage, in the diabetic heart.

• Exercise does not have to be continuous to benefit the heart in patients with T2DM; short bouts of high intensity exercise may also do the trick

Reference: Cassidy S, et al. High intensity intermittent exercise improves cardiac structure and function and reduces liver fat in patients with type 2 diabetes: a randomised controlled trial. Diabetologia. 2015 Sep 9. [Epub ahead of print]