The level of exercise intensity appears to make no difference to risk of mortality in older adults, according to a new trial.

Published in the BMJ, the study evaluated the effect of five years of supervised exercise training compared with recommendations for physical activity on mortality in older adults aged 70-77 years.

The trial involved 1,567 participants (790 women and 777 men) living in Trondheim, Norway, with an average age of 73 years. In total, 87.5% of participants reported overall good health and 80% reported a medium or high level of physical activity at the start of the trial.

Of these 1,567 participants, 400 were assigned to two weekly sessions of high intensity interval training (HIIT), 387 were assigned to moderate intensity continuous training (MICT), and 780 to follow the Norwegian guidelines for physical activity (control group), all for five years. 

It found that combined MICT and HIIT has no effect on all cause mortality compared with recommended physical activity levels. However, we observed a lower all cause mortality trend after HIIT compared with controls and MICT. After five years, the overall mortality rate was 4.6% (72 participants).

Recommended physical activity levels 

The researchers found no difference in all cause mortality between the control group (4.7%, 37 participants) and combined HIIT and MICT group (4.5%, 35 participants).

They also found no differences in cardiovascular disease or cancer between the control group and the combined HIIT and MICT group. For example, the total proportion of participants with cardiovascular disease after five years was 15.6%, with 16% (125 participants) in the control group, 15% (58 participants) in the MICT group, and 15.3% (61 participants) in the HIIT group.

The researchers point to some limitations. For example, highly active participants in the control group could have hampered finding differences between groups, and many participants were healthier than expected at the start of the study, which may have limited the potential to increase activity levels further. 

However, strengths include the large number of older adults, and the long intervention period and monitoring throughout the study.

The authors added: "This study suggests that combined MICT and HIIT has no effect on all cause mortality compared with recommended physical activity levels."