Norwegian 4x4 interval workout

• New to hard intervals? Do 2 efforts for the first week or two, then 3, then 4 (our suggestion). Do it once or twice a week with easier days between; the trials used 2 or 3 sessions a week.
• Heart rate lags behind effort, so judge the first minute or two by feel; by the end of each 4 minutes you should be down to a few words.
• On a beta blocker, go by how hard it feels, not your heart rate.
• If your blood pressure is high and not yet under control, keep to moderate effort until it is.
• If you have a heart condition, or get chest pain, faintness or unusual breathlessness when active, see your GP first; people with heart disease do this kind of training within cardiac rehabilitation.
• If you take insulin or a sulfonylurea such as gliclazide, check your blood sugar before and after: hard intervals can raise it for a while and lower it later. Skip intervals with proliferative diabetic retinopathy.
• Outdoors: walk or run hard up a long, steady hill for the 4 minutes and walk back down for the 3 (our suggestion).

The doses are suggested starting points, not a prescription. Choose a range you can control and stop for sharp or increasing pain, numbness or tingling. Get individual advice after an injury or surgery, or if you are pregnant or managing a health condition.

• HIIT guide
• VO2 max guide

• Cardio and conditioning exercises