90 Seconds A Day of HIIT Might Be All You Need

man and woman passing an exercise ball while doing sit ups at a gym

Evan Stevens

We know that HIIT can be used to improve parameters of health in diseased individuals, but can it work in healthy individuals/a whole population, and if so, how might it work?

The first talk of the session examined just that by having individuals perform single leg cycling tests; one leg would perform short, higher intensity intervals (4 x 5 minutes at 65% of max wattage) and the other leg would perform longer, continuous exercises ( 30 minutes at 50% max wattage).

Biopsies from each leg were taken and analyzed, as well, whole body measures were taken during each exercise protocol to see how the body changed when stressed differently.

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90 Seconds A Day Study

Legs that underwent HIIT showed increases in mitochondrial protein markers greater than moderate intensity continuous training (MICT) in the whole muscle but did not lead to changes in muscle fibre type (type I being slow and type II being fast twitch).

On a whole body level HIIT led to an increased heart rate and increased amount of lactate production (a by-product of working harder).

The researchers wanted to push the workload even shorter and see if the effects of HIIT were still beneficial. They had participants conduct a specific workout:

Two minute warm up + 30 second work + two minute rest + 30 second work + two minute rest + 30 second work + three minute cool down, three times a week.

Work was done at 86% of the participants’ max heart rate.

So can less than 15 minutes of exercise (90 seconds of total hard work) three times a week translate to better health outcomes even when compared to continuous?

The results seem to indicate so; as little at 90 seconds of hard work resulted in a 19% increase in VO₂ Max (in regular, non-elite individuals) over the MICT comparison group, there was an increase in insulin sensitivity that was on par with the MICT group as well as matched increases in stroke volume and cardiac output.

The only area where MICT was better than this HIIT protocol was in body composition where small but significant changes to muscle mass and body fat percentages were noted in the MICT group that were not seen in the HIIT group.

So, form a pure metabolic health standpoint it would seem that HIIT is a viable alternative to improving population health, which goes in the face of most public health models of exercise that calls for moderate continuous exercise. Less work can be used to get the same health outcomes which is great news for people who don’t have the time for or are easily discouraged by longer bouts of exercise.

Take Away:

As little as 90 seconds of really hard work, three times a week can be just as beneficial for metabolic health as longer continuous exercise.

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Related Article: How HIIT Changes Our Body

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