Do enough curls and you’ll start to see your biceps grow.

Walk up enough staircases and you’ll no longer get so out of breath.

Swim enough laps and you might start noticing you’re sleeping better.

But what about the less noticeable effects of exercise?

How do you become healthier in other less visible but critical ways?

Exactly how exercise can affect your tiniest components — your cells — is still being uncovered.

A recent study published in Cell Metabolism sheds some light on the mystery, finding that high-intensity interval training (HIIT) during exercises like biking and walking increased the capacity of the mitochondria.

Those are the organelles that produce the energy in cells that keeps us going.

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What researchers discovered

This energy generation capacity decreases as we get older, but the researchers found that, due to exercise, the cells in study participants made more mitochondrial proteins as well as the proteins responsible for muscle growth.

This, the researchers said, essentially reversed the effects of aging at the cellular level.

“We always knew exercise could have an impact on cell function,” the study’s senior author, Dr. Sreekumaran Nair, of the Mayo Clinic, told Healthline. “Many age-related changes are related to lack of exercise. But if you deliberately do it, then you can really reverse most it.”

Specifically, interval training — brief bursts of high-intensity cardio followed by longer period of lighter activity or rest — led to a 49 percent increase in mitochondrial capacity in the muscle cells of volunteers ages 18 to 30.

It also produced a 69 percent increase in participants ages 65 to 80.

Those were the two age groups included in the research.

The study divided volunteers — 36 men and 36 women — into a group that did high-intensity interval cycling, one that lifted weights, and another that did both. Researchers then took biopsies from the participants’ thigh muscles.

The benefits went beyond interval training causing mitochondrial improvements.

The quicker, more intense exercises also reduced insulin sensitivity and, thus, susceptibility to diabetes.

Nair said the study was intended to help uncover how exercise affects cell functioning, not necessarily to find the best exercises.

But he would recommend combining HIIT with strength training to maximize both the age-reversing cellular benefits and the muscle strength improvement.

He said to stick with the interval training if you only have time for one.

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Broader benefits

The broader benefits to health and longevity from exercise have been well established for more than 70 years, said Jennifer Turgiss, Ph.D., vice president of behavioral science and advanced analytics at Johnson & Johnson Health and Wellness Solutions.

She rattles off a list of ailments that exercise is known to decrease the likelihood of developing. These include stroke, hypertension, hyperlipidemia, cardiovascular disease, type 2 diabetes, breast and colon cancers, depression, and anxiety.

But, she says, through new research methods we are starting to learn more about how physical activity affects us at the cellular level.

“It is early days for this type of research, so there would be no changes in [exercise] recommendations yet,” Turgiss told Healthline. “But keep on the watch.”

She notes that updates to the government’s Physical Activity Guidelines are currently in the works. Those guidelines don’t currently mention cellular health or interval training.

Most athletes already use interval training in their exercise programs and the approach appears to be growing in popularity among non-athletes as well.

For some ideas on how to apply it in your own exercise routines, look to a last year that put 27 sedentary men through 12 weeks of HIIT consisting of three 20-second sprints on a stationary bike, each followed by 2 minutes of easier riding.

The group, which biked for 10 minutes a day total, saw the same benefits in terms of aerobic fitness, regulation of blood sugar, and improved function of muscle cells as men who biked for 45 minutes at 70 percent of their maximal heart rate.

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