Too Much High-Intensity Exercise May Be Bad for Your Health

During week two, the riders added a 3rd HIIT session and ramped up the size of a few of their intervals to a draining eight minutes. In week three, they labored out 5 instances, with a mixture of four-minute and eight-minute spurts of all-out pedaling. Finally, in week 4, for restoration, they successfully halved the quantity and depth of their train. Each week, the researchers repeated all testing.

Then they in contrast how folks’s our bodies had modified week over week.

At first, the findings had been encouraging. By the top of week two, the riders had been pedaling tougher and seemed to be getting fitter, with higher each day blood-sugar management and extra complete mitochondria of their muscle cells. Each of those mitochondria was additionally extra environment friendly now, producing higher quantities of vitality than in the beginning.

But one thing started to go improper throughout week three. The volunteers’ skill to generate energy whereas biking flattened, and their subsequent muscle biopsies confirmed sputtering mitochondria, every of which was now producing solely about 60 % as a lot vitality as through the earlier week. The riders’ blood-sugar management additionally slipped, with seesawing spikes and dips all through the day.

After per week of lower-intensity driving, their mitochondria began to bounce again, producing extra vitality, however nonetheless 25 % lower than throughout week two. Their blood-sugar ranges additionally stabilized, however once more, to not the identical extent as earlier than. The riders may pedal, nevertheless, with the identical — and even higher — vigor as in week two.

Taken as an entire, the monthlong experiment means that “HIIT exercise should not be excessive if increased health is a desired outcome,” says Mikael Flockhart, a doctoral scholar on the Swedish School of Sport and Health Sciences, who performed the examine together with his adviser, Filip Larsen, and others.

The examine was not centered on athletic efficiency, however even for critical athletes, he says, piling on a number of, intense, interval exercises every week, with little relaxation between them, is more likely to result in a tipping level, after which efficiency, in addition to indicators of metabolic well being, slip.

The researchers should not positive exactly what adjustments inside their volunteers’ our bodies and muscle tissue precipitated the detrimental ends in week three. They examined a number of potential molecular causes, Mr. Flockhart says, however didn’t isolate an apparent, single instigator. He and his colleagues suspect {that a} cascade of biochemical adjustments inside folks’s muscle tissue through the hardest week of train overwhelmed the mitochondria then, and the weakened mitochondria contributed to the disruptions in folks’s blood-sugar management.

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