There is serious research behind the advice to do most of your training at an easy pace, add two sessions of very hard work each week, and avoid spending time in between.

But I think this research answers a different question from the one that matters to most of us over 65. Are we trying to maximize endurance or racing performance—or stay healthy, capable and independent for as many years as possible?

What is polarised training?

The idea comes mainly from endurance sport. Polarised training means doing most exercise at a comfortable intensity, a smaller amount at a very demanding intensity, and relatively little sustained work in between.

What matters more after 65?

The goal should not be to perfect a zone distribution. It should be to preserve the ability to walk further, climb stairs or hills, carry shopping, maintain strength and balance, and recover well enough to do it again.

The World Health Organization recommends 150–300 minutes of moderate aerobic activity per week, or 75–150 minutes of vigorous activity, or a combination, alongside strength and balance training. It does not tell older people to avoid intermediate intensities.

What does the research actually tell us?

A 2025 review of 13 studies involving 348 endurance athletes found no overall significant advantage for polarised training over other training distributions for improving VO₂max or time-trial performance. There were indications that competitive athletes and recreational athletes may respond differently. Importantly, this was research on athletic performance, largely involving much younger people—not healthy lifespan after 65.

A 2024 analysis of 29 trials involving 1,227 older adults found that both high-intensity intervals and continuous moderate-intensity exercise improved several fitness and health measures. Hard intervals sometimes produced larger gains in aerobic fitness, but most of the health outcomes examined improved similarly.

High Intensity Interval Exercise (HIIT) - Norwegian 4*4 the holy grail for You Tubers

In the Generation 100 trial, 1,567 Norwegians aged 70–77 were assigned to high-intensity intervals, moderate continuous exercise, or standard physical-activity advice for five years.

This trial is the most referenced reason for doing HIIT and the protocol is one of the most demanding types of HIIT. The HIIT group was assigned two sessions each week: an easy 10-minute warm-up followed by four demanding four-minute efforts, each separated by three minutes of active recovery. The hard intervals targeted roughly 85–95% of peak heart rate. Participants were encouraged to remain active on other days too. This was a sustained commitment, not an occasional sprint.

I have always been skeptical about how many participants were able to keep doing HIIT at the level required in this study. I know I can’t do 4*4 hard intervals once, yet alone twice a week. I lack the will power to push myself this hard. Maybe as part of a group with regular help the situation would be different?

“The researchers offered supervised outdoor training twice weekly and exercise-bike sessions every six weeks to check intensity.”

What happened to the HIIT group?

Of 400 participants, 132 (33%) dropped out of the study by year five, including deaths, withdrawals and exclusions. Only 187 (47%) met the prescribed exercise-adherence criterion, completing at least half their assigned sessions.

The moderate-exercise group had a 26% dropout rate and 51% met its exercise target. The activity-advice group had a 20% dropout rate and 69% met national activity guidelines.

Why did people withdraw?

A separate analysis of withdrawals across all three groups during the first three years found that, among 123 people who gave reasons, 71 cited health problems, 25 loss of interest, 21 lack of time and six family responsibilities. Another 102 provided no reason.

These findings do not establish that HIIT caused health problems or how many participants stopped HIIT altogether.

At five years, mortality was 3.0% in the HIIT group, 5.9% in the moderate group and 4.7% in the activity-advice group. The differences were not statistically conclusive.

The trial supports HIIT as an option for many relatively healthy older adults. It does not establish that HIIT is the best route to longevity.

Participants in the Standard activity advice (control) were encouraged to undertake 30 minutes of moderate exercise on most days, without supervised training. Importantly, 69% were still meeting national activity recommendations after five years, and some voluntarily undertook high-intensity exercise.

Perhaps the most interesting finding was that participants receiving only standard physical activity advice experienced remarkably little decline in aerobic fitness over five years.

The finding challenges the assumption that structured high-intensity training is necessary to maintain aerobic fitness as we age. Regular, sustainable physical activity may be sufficient to preserve much of that capacity, although the trial cannot establish which particular activities were responsible.

What does the research show?

None of these studies demonstrates that avoiding Zones 3 and 4 helps people live longer.

For most of human history, people walked, climbed, carried things and worked over uneven ground. They did not arrange their days around a heart-rate-zone chart. That observation is not proof of the ideal training program — but it confirms my understanding that avoiding Zones 3 & 4 does not reflect the reality anyone who lives an active outdoor life. When I walk up the hills around my place I go up and down the zones depending on the steepness of the slope and the duration of the walk.

What matters more after 65?

The goal should not be to perfect a zone distribution. It should be to preserve the ability to walk further, climb stairs or hills, carry shopping, maintain strength and balance, and recover well enough to do it again.

Vigorous activity is essential for improving aerobic capacity, where medically appropriate. I try and have two harder sessions each week but I definitely do not go close to a 4*4 regime.

The one lesson I have learnt over the last year though, is avoiding injury is the most important skill to learn. Muscles regain strength in a few weeks, tendons can take months and I now have to manage two on-going tendon problems because I didn’t understand this golden rule.

Personally, walking harder up the steeper slopes near my house has made a big difference to my health and now that my tendon injury in my right knee has settled down I am excited to start walking up hills again. Comfortably paced activity, brisk walking, sustained climbs and strength work all have a place. Anyone returning after a long break, or living with a cardiovascular condition, should build intensity gradually and seek professional advice before hard intervals.

ChatGPT’s conclusion

Polarised training is a useful training strategy. It is not an established law of healthy ageing. The evidence supports staying active, including some appropriately challenging exercise, and maintaining strength, balance and mobility. It does not support dismissing Zones 3 and 4 as wasted time.

For those of us interested in living well into our 70s, 80s and beyond, the important question is not “Did I spend the right percentage of time in each zone?” It is “Am I maintaining the physical capacity to enjoy the life I want to lead?”

Next steps

I know how important having a regular training approach is to how I feel and how it enables me to stay active and mobile. After drafting this story a few days ago I spent a good amount of time working with Codex and Claude to see if there is a business case to invest in an opt-in program for people 65+ and older to stay active. What I found out will be explained in the following story which also really calls out some of the limitations of the current versions of these models. I will be writing and posting more about my living well experiences.