Of the 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.
After five years, the overall mortality rate was 4.6%, or 72 participants, the researchers wrote in a study pubished this week in the journal The BMJ.
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 training groups.
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 trial was not without limitations, the researchers noted. 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," they wrote.
The large number of participants and the long monitoring period were two of its strengths.
“This study suggests that combined MICT and HIIT has no effect on all cause mortality compared with recommended physical activity levels,” the researchers wrote.