In a study published this month in the journal Medicine and Science in Sports and Exercise, a team led by Greg Wells and Andrew Redington at the the University of Toronto’s Hospital for Sick Children, demonstrated that highly-trained swimmers that used a blood pressure cuff to restrict blood flow to their arms a few minutes before maximum-effort time trials improved their performance in a 100-meter race by 0.7 seconds.

So in just a few minutes’ time and with minimal effort, athletes were able to significantly boost their performance, making gains that — according to the authors — would normally take an average of two years of intense training to accomplish.

The study builds off research first conducted in the 1980s by cardiovascular pioneer Keith Reimer that examined infarcts, areas of dead cardiac tissue that resulted after heart attacks, when blood flow (and, hence, oxygen) were cut off for extended periods of time. Reimer and his colleagues discovered that much less heart muscle deteriorated when the tissue had previously experienced a few training sessions where blood flow was slightly reduced. It was as if practice makes perfect, and the previous bouts of low blood flow, which researchers refer to as ischemic preconditioning, primed the heart muscle to endure more serious, even catastrophic, events. When a life-threatening heart attack transpired, instead of shriveling away, the preconditioned heart muscle seemed to stand strong.

In 2009, a research team led by Maria Hopman from Radbound University in The Netherlands posed a question: If Reimer’s team was able to use ischemic preconditioning to protect the cardiac muscle during a heart attack, would the technique protect different types of muscle tissue from the stress and damage that occurs during another type of ischemic event, like exercise?

Though immensely different than a heart attack, exercise is technically an ischemic event, as athletic performance hinges on how much blood reaches a tissue. And insufficient blood flow, which also translates to reduced oxygen and nutrient delivery, can be one factor that limits exercise duration and intensity.

Hopman recruited 15 healthy, trained cyclists, asking each participant to complete two maximum effort bicycling tests, where the intensity was slowly ramped up over time. But before one of the bicycling tests, the subjects underwent three 5-minute rounds where an inflatable cuff, similar to what’s used to measure blood pressure, limited the circulation to their legs, followed by a five-minute rest period where the cuff was deflated.

The researchers found that the subjects performed better when they underwent ischemic preconditioning before the exercise trial, touting gains in both maximum power (1.6 percent) and peak oxygen consumption (3 percent). Yet the performance improvements were not due to differences in heart rate, respiration, or lactate levels, all of which seemed to stay the same, regardless if ischemic preconditioning was used or not. Rather, it seemed possible that the ischemic preconditioning treatment may have given the participants their edge.

While Hopman’s work recorded the benefits conferred to the average athlete, the latest research from Wells and Redington pushes the understanding of ischemic preconditioning one step further, looking at whether the technique works in elite, highly trained athletes, a group whose bodies run with machine-like efficiency.

Using a group of 16 to 18 swimmers who previously competed at the national or international level, the research team devised a double-blind crossover study where the same athletes swam mid-intensity and maximum-effort trials, but on two different days. To counterbalance one of the main criticisms of the earlier studies conducted by Hopman — that the study design potentially allowed the placebo effect to creep in, inadvertently making participants try harder when they had an inflatable cuff strapped to their legs preceding exercise — Wells and Redington decided to alter their protocol: On both days of the experiment, a cuff would be inflated on every athlete’s arm. To induce ischemic preconditioning, the cuff would be pumped up enough to surpass the systolic blood pressure, slowing the flow of blood to the arms for four cycles of five minutes. The other day, the cuff was still inflated, but only enough to slightly squeeze the muscles for each 5-minute period, which provided a better sham, or control condition, than Hopman used.

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Authors: Brian Mossop

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