High-Intensity Interval Training can Activate Ischemic Preconditioning

Take Away Message

High-Intensity Interval Training (HIIT) but not endurance training can produce ischemic preconditioning.

High-intensity interval training is repeated exercise lasting for seconds but intense enough to make the heartbeat go up to 85 to 95% of maximum. The high-intensity exercises are separated by intervals that are shorter than the exercise durations. The rest periods allow the cells to recover partially to execute the exercise duration.

Ischemic preconditioning (IPC) was introduced in this article, What is Ischemic Preconditioning? IPC is a method to increase the resistance of the different body organs against ischemia. Ischemia is a condition wherein the blood and oxygen supply is inadequate. IPC provides fewer complications and increased survival in strokes, heart attacks, and major surgeries.

In the article, What is Ischemic Preconditioning?, studies used a blood pressure cuff to restrict blood flow either to the upper or the lower extremity to limit the blood flow and induce IPC. But interval training can also cause IPC without applying any constricting devices to the arms or legs.

The following is a description of a study to find out whether HIIT or Endurance exercises can induce ischemic preconditioning.

Step 1: HIIT vs. Endurance Exercise

In a study of 17 healthy young subjects, the HIIT group performed ten 1-minute cycle exercise bouts at 100% of the maximum workload. These 100% bouts were separated by
2-min recovery periods at with cycle exercise at 25% of the maximum workload.

The endurance group was done at moderate intensity. After a 10 minute warm-up, a 28-minute exercise at 50% of maximum workload was done. The recovery period was the same. The study made sure that the exercise workload is the same for both groups.

The control group rested supine for 43 minutes.

Step 2: Ischemic and Reperfusion Injury

A device similar to a blood pressure cuff was put around the right upper arm of all the subjects and inflated at 220 mm Hg for 20 minutes, followed by 20 minutes of reperfusion.

This step simulates a blockage to an artery. Ischemia caused by an arterial occlusion leads to low oxygen levels. It is the mechanism of injury in strokes and heart attacks. Afterward, the reperfusion of blood after the reopening of the arteries causes cellular changes leading to more damage to the lining of the blood vessels giving a double whammy. That is called reperfusion injury.

Step 3: Testing of the Arteries

After the exercise and arterial occlusion, a doppler ultrasound was used to measure the diameter of the brachial artery of all groups. The blood vessel diameter is a measure of the ability of the inner lining of the blood vessels or endothelium to maintain its integrity and functionality. The larger the width, the more blood can flow. In ischemia/reperfusion injuries, the arteries lose their elasticity and size and therefore limit blood flow.

The results showed that ischemia/reperfusion injuries were prevented in the HIIT group but not on the endurance and control group. In real life, if all the groups will have a heart attack or stroke, the HIIT will have fewer complications and mortality than the endurance and control group.

photo-1546749876-2088f8b19e09 — Photo by Inspired Horizons Digital Marketing on Unsplash

Mechanisms of Protection by HIIT

During interval training, but not endurance exercise, the body is subjected to ischemia or low blood supply. Training leads to the release of β-endorphins, as evidenced by the higher lactate levels. The β-endorphins has an effect on the opioid receptors that lead to ischemic preconditioning.

HIIT also causes an upregulation of nitric oxide production. Nitric oxide is essential in maintaining healthy blood vessels.

Interval training also causes changes to the mitochondria, the fuel source of the cell, making it more resistant to ischemia, thus preventing early cell death.

Although the conclusions of this particular study are limited because the subjects were all healthy, it may explain the findings of other studies that showed an association between intense exercise and higher survival from all causes of deaths. They can be found in the following articles: Physical Activity Correlates with Life Span

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