When it comes to burning fat, nothing torches calories or helps you work up a sweat quite like a bit of HIIT Training. HIIT (which stands for high intensity interval training), as the name suggests, involves short maximum effort exercise intervals, followed by rest periods of similar durations.
HIIT has quite a few advantages over continuous, moderate intensity exercise (i.e. running 5km at a steady pace), particularly when it comes to weight loss and cardiovascular fitness. Specifically, studies have shown that HIIT training (1):
Improves fat-burning efficiency, supporting exercise performance and weight loss
Elevates post-exercise metabolic rate by as much as 6-15%, for up to 24 hours.
Extends exercise tolerance and cardiovascular fitness.
Prevents fitness plateaus by ‘shocking’ your body with each interval, and avoiding efficiencies in energy expenditure.
With all of these benefits in mind, it may be tempting to start planning daily HIIT routines. But rather than reaching your goals faster, overdosing on HIIT may be a one-way ticket to injury, burnout, or worse. You could say - high intensity exercise requires high intensity recovery!
Why? Firstly - high intensity exercise can stimulate the release of cortisol, a stress hormone. Chronic elevated cortisol from daily HIIT training may contribute towards elevated heart rate and blood pressure, anxiety, reduced immunity, impaired digestion, acne and even infertility. What’s more, it can increase appetite and fat storage – overshadowing the ‘good work’ you’re doing in the gym (2).
Secondly, a recent study by Rutgers University found that the ‘extreme’ nature HIIT training can increase your risk of injury, especially in the knees and shoulders. Injury risk is further increased if muscles and joints are not permitted at least 24 hours of recovery time (4).
Thirdly, experts agree that the best fitness regimes include a combination of HIIT, resistance training, and moderate intensity exercise. The variety of workouts allows you to train all muscle groups and energy-burning systems for better whole-body results. It also facilitates better recovery between sessions.
So - what is the recommended number of HIIT sessions per week?
Guidelines suggest no more than 30-40 minutes of training with your heart rate above 90% per week. This can be achieved by limiting your HIIT sessions to two or three sessions per week. In between, you may choose to include days of resistance training and moderate-intensity cardio, with one or two days of low intensity exercise or total rest (5).