Lack of time is often the main reason people don’t exercise regularly. But a type of interval workout recently popularised by actress Jessica Biel could be the solution – with research showing it can improve fitness faster than traditional, steady-pace workouts, such as jogging or cycling.

The Norwegian 4x4 workout has traditionally been used by athletes. It’s a form of high-intensity interval training (Hiit) that involves four-minute sets of very intense cardio exercise, followed by three minutes of very light exercise. A typical training session includes a five-minute warm-up, four high-intensity intervals and a five-minute cool-down.

The 4x4 workout format follows the same format as other Hiit workouts, which alternate periods of high-intensity exercise with periods low-intensity exercise (or rest). Most Hiit workouts involve work intervals that last anything from ten seconds up to a couple of minutes. In contrast, the 4×4 workout employs four minute work periods, which raises your heart rate for longer than most Hiit protocols.

Decades of research has shown that regular Hiit workouts are often more effective than moderate-intensity workouts (such as running or cycling at a steady pace continuously) in improving cardiovascular fitness and other health outcomes (such as improving blood sugar and cholesterol levels). Hiit is even effective for improving health in adults with type 2 diabetes and cardiovascular disease.

Hiit also offers these benefits with less training time than........

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