High Intensity Interval Training (HIIT) has gained popularity globally, promising to burn more calories and increase fitness in a shorter time. [1,2] Building more muscles also helps to increase the resting metabolic rate and add to the afterburn benefits of excess post-exercise oxygen consumption (EPOC). Similarly, other forms of aerobic classes such as Les Mills workouts, Bodyweight Tabata classes and Spin classes are trending in popularity, with many of these being highly enjoyable with loud party music and motivational coaches.


Photo: Sport Singapore

Is there a downside to HIIT?

Possible onset of Rhabdomyolysis

Intense and unaccustomed workouts can cause muscle damage, with reports of rhabdomyolysis associated with activities such as spin classes rising across Emergency Departments around the world.

Physicians locally have also raised concerns over the numerous Spin Classes induced rhabdomyolysis especially during their first lesson. Rhabdomyolysis occurs when there is damage and breakdown of muscle cells, releasing enzymes and cell contents into the bloodstream, which may then cause multi-organ failure. Common symptoms include muscle pain, fatigue, as well as darkened urine. Rhabdomyolysis is more common during the first Spin class in untrained participants and is also more common in women compared to men.

Bone, joint, muscle and tendon injuries

Unaccustomed exercise in a previously sedentary individual can also cause injuries such as muscle and tendon tears, stress fractures or joint damage. This may be due to lack of flexibility, strength and endurance, as well as poor form.

What should I look out for before starting high intensity workouts?

Am I healthy enough?

Do complete the Get Active Questionnaire (GAQ) to help determine if you’re ready to start a new exercise routine. This step is applicable not just for HIIT but for pre-exercise participation in general. The questionnaire is available on the Sport Singapore website at


Am I fit enough? 

Do start aerobic training 3 to5 times a week for 20 to 60mins per session to achieve a basal fitness level prior to engaging in HIIT workouts. Start with once a week HIIT workout and gently increase the sessions to the maximum of three sessions per week with adequate space in between for your body to recover.


Photo: Sport Singapore

Do not undertake HIIT over consecutive days. If you can do more than three sessions a week, then you probably are not doing it right. When you do start, remember to start low, and go slow. Participants new to spin classes should start slow with lower resistance before cranking up the intensity gradually.

Other useful tips

Eat and drink well

Ensure adequate nutrition with carbohydrates for the quick energy release, and hydration before HIIT or Spin classes to reduce the risk of rhabdomyolysis.

Look out for red flags

Look out for symptoms of rhabdomyolysis, including fatigue, muscle pain and darkened urine. See a doctor for blood and urine tests if necessary.

Avoid anti-inflammatories before a workout

Do not take anti-inflammatories (NSAIDS) such as Voltaren or Neurofen prior to exercising as these can affect your kidney function.

Listen to your body

Don’t over-train if you are not feeling up to it or if you are unwell with a fever or viral illness.


Photo: Sport Singapore

Check the safety aspects of your gym

Ensure that the equipment is ergonomic, and the weights and machines used are appropriate and well-maintained to prevent injuries.

Ensure that the coaches or personal trainers are trained in basic first aid and resuscitation skills (CPR and AED).

Ensure that an AED is readily available, and that an Emergency Action Plan with emergency phone numbers and proper evacuation plans are place.

Participants should be properly registered. Details of the next-of-kin in case of medical emergencies should be accessible.

High-intensity workouts are great, and with proper safety measures and knowledge, we can all aspire for a fitter body and a healthier life.

Keen to find out more about high-intensity interval training? You can click here for a resource produced by American College of Sports Medicine (ACSM)


This article was contributed by Dr Cheah Si Oon, an Emergency Physician from Urgent Care Clinic International. Dr Cheah is also a member of the Sports Safety Committee and can be reached at sioon@urgentcareclinic.sg



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  2. Martin-Smith R, Cox A, Buchan DS, Baker JS, Grace F, Sculthorpe N. High Intensity Interval Training (HIIT) Improves Cardiorespiratory Fitness (CRF) in Healthy, Overweight and Obese Adolescents: A Systematic Review and Meta-Analysis of Controlled Studies. Int J Environ Res Public Health. 2020 Apr 24;17(8):2955. doi: 10.3390/ijerph17082955. PMID: 32344773; PMCID: PMC7215828.
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