Key takeaways
Generation 100 randomised 1,567 Norwegians aged 70 to 77 to HIIT, moderate training or guideline advice for five years
Deaths were 3% with HIIT, 5.9% with moderate training and 4.7% in controls, but the differences were not statistically significant
HIIT gave slightly higher fitness, and no cardiovascular events occurred during supervised sessions
High-intensity interval training (HIIT) used to be seen as something for young athletes. That view keeps being challenged, and interest is growing as more people look for ways to stay fit and independent into their 70s and 80s. The largest and longest trial on the question is Generation 100 from Norway. Here is what it found — and what it did not.
The trial
Researchers in Trondheim invited everyone in the city born between 1936 and 1942. 1,567 adults aged 70 to 77 (mean age about 73, half women) were randomised to one of three groups for five years:
- HIIT: two sessions a week of 4×4 intervals — four minutes at about 90% of peak heart rate, with active recovery between — the protocol described in our Norwegian 4×4 guide.
- Moderate continuous training (MICT): two 50-minute sessions a week at about 70% of peak heart rate.
- Control: advice to follow the national physical activity guidelines of about 30 minutes a day.
Both exercise groups were offered supervised sessions regularly, and fitness was measured in the lab at the start and during follow-up.
Mortality: an encouraging trend, not proof
After five years (Stensvold et al., BMJ, 2020):
| Group | Training | Deaths after 5 years |
|---|---|---|
| HIIT | 2×/week, 4×4 min at ~90% peak HR | 3.0% |
| Moderate (MICT) | 2×/week, 50 min at ~70% peak HR | 5.9% |
| Control | National guidelines | 4.7% |
The HIIT group had the fewest deaths, but none of the differences was statistically significant. The confidence intervals were wide because few people died: participants were healthier and fitter than average for their age, so the trial had limited power to detect differences in mortality.
Two other issues blur the comparison. Only about half of the participants in each exercise group stuck to the prescribed programme over five years, and many people in the control group exercised at high intensity on their own. When the "control" group exercises too, differences between groups shrink.
Fitness and quality of life
HIIT produced the clearest gains in peak oxygen uptake (VO2peak), and the authors reported better fitness and quality of life in the HIIT group than in the controls. Given the strong link between fitness and survival in observational research (see VO2max and longevity), that is a meaningful result in itself.
Cardiovascular risk: the 2022 follow-up
Letnes et al. (European Heart Journal, 2022) analysed blood pressure, blood fats, blood sugar, body composition and other risk factors in the same participants. Five years of supervised exercise did not significantly improve the overall cardiovascular risk profile compared with controls, although there was a signal in favour of HIIT for several risk factors, and the HIIT group had a slightly higher VO2peak (about 0.8 ml/kg/min) than controls.
The safety finding was reassuring: no cardiovascular events occurred during supervised training sessions, including the HIIT sessions at 90% of peak heart rate. The trial did record a few fractures from slips during outdoor sessions, so for older adults the practical risk is often the surface, not the heart: train indoors or on dry, even ground in winter.
What it means
- Generation 100 does not prove that HIIT makes older adults live longer.
- It does show that two interval sessions a week are feasible and appear safe for screened people in their 70s, and they deliver at least as much — and probably more — fitness benefit than moderate training.
- Fitness declines with age (see VO2max and ageing), but it remains trainable; read more in VO2max trainability.
A 4×4 session adapted for older adults
Get medical clearance first, especially if you have heart disease, high blood pressure, diabetes, joint problems or have been inactive. Then:
- Warm up 10 minutes at an easy pace on a bike, treadmill (walking uphill works well) or cross-trainer.
- Interval: 4 minutes hard. You should be breathing heavily and able to say only a few words. Beginners can start at 80–85% of peak heart rate, or with 2–3 intervals instead of 4.
- Recovery: 3 minutes of easy movement between intervals.
- Cool down 5 minutes.
- Frequency: once a week at first, building to twice a week. Keep other days easy, as in 80/20 training, and add two strength sessions to protect muscle and balance.
Choose low-impact equipment, and stop if you feel chest pain, dizziness or unusual breathlessness. To see whether it is working, estimate your fitness with the VO2max calculator or check your fitness age every couple of months. For how HIIT compares with steady exercise in general, see HIIT vs steady cardio.
Frequently asked questions
Is HIIT safe for people over 70?
In Generation 100, no cardiovascular events occurred during supervised training in adults aged 70 to 77. Participants were screened and relatively healthy, so get medical clearance first.
Does HIIT help older adults live longer?
The HIIT group had the fewest deaths over five years, but the difference was not statistically significant, so the trial does not prove that HIIT lowers mortality.
How often should older adults do HIIT?
Generation 100 used two sessions a week. A 4x4 interval session once or twice a week, alongside easy activity and strength training, is a reasonable target after medical clearance.
Sources
- Stensvold D, et al. Effect of exercise training for five years on all cause mortality in older adults—the Generation 100 study: randomised controlled trial. BMJ, 2020.
- Letnes JM, et al. Effect of 5 years of exercise training on the cardiovascular risk profile of older adults: the Generation 100 randomized trial. Eur Heart J, 2022.