What is HIIT?

Why HIIT Workouts May Be Right for You

It is well documented in the literature that exercise is important for the prevention of chronic (non-curable) illness.  HIIT workouts are a great way to maintain and improve cardiovascular and musculoskeletal fitness in a healthy population.

 However, what if you are already diagnosed with an illness? What type of exercise is safe and effective to improve strength, endurance, and overall stamina to reduce the risk of the illness getting worse? 

Several clinical trials have found that High Intensity Interval Training (HIIT) to be an effective and safe form of exercise in populations including those with limited exercise tolerance, diabetes, congestive heart failure, chronic obstructive pulmonary disease, intermittent claudication and sarcopenia.   Additionally, it has been found to be effective in women over the age of 65, as well as, long distance runners.7-9,24  

Why participate in HIIT training?

Participation in HIIT for at least 7-12 weeks has been found to elicit the largest change in cardiorespiratory fitness as comparted to more traditional exercise.  Also, several studies have found high intensity interval training (HIIT) in patients with Cardiovascular disease (CVD) to be as safe as moderate intensity continuous training (MICT), yet more effective with regards to improving aerobic capacity, heart rate response, myocardial function, and quality of life.8- There are no specific parameters in the research for those with CVD to follow, therefore working with a qualified Physical Therapist that can monitor blood pressure, heart rate, and form is important.1-9

HIIT Defined

HIIT requires higher submaximal effort for a given task than other forms of exercise.  It is characterized by an individual performing exercise tasks with a Rating of Perceived Exertion (RPE) of 15-17 on the Borg scale.

What is the RPE Scale?



Percieved Exertion Level



Very, very light



Very light



Fairly light



Somewhat hard






Very hard



Very, very hard



Does The Type of HIIT Routine Matter?

Numerous clinical trials have found that the type of HIIT task performed (i.e., cycling, calisthenics, rowing, running, or functional activities/functional training) does not significantly change cardiovascular fitness outcomes.19-22 It is more important to participate in activities you enjoy in order for this type of training to be a long term solution to your health goals.

Can I Still Participate in HIIT While Injured?

Even when recovering from an injury, you may still be able to safely training cardiovascular fitness by changing the load on the injured area to one that is tolerable.  For example, a runner with a foot injury might still be able to get on a rower, stationary bike, or swim.  This will help keep the participant’s cardiovascular fitness level high while still allowing the injury to heal, which results in improved personal satisfaction and faster return the preferred activity, which in this example is running.23  It is important to note, working with a Physical Therapist to set a personalized plan of care for injury recovery and correctly dose the cross-training is important to avoid further injury and recover as quickly as possible.

What are the 3 Categories of HIIT Workouts?

Duration Type

High Intensity Interval

(15-17 RPE)

Active Recovery

(12-14 RPE)

Number of Sets Performed

Proposed Timeline of Progression


(low exercise capacity)

15-60 sec

15-120 sec


0-3 weeks

Medium (intermediate exercise capacity)

1-2 min

1-4 min


4-12 weeks


(high exercise capacity)

3-4 min

3-4 min


>12 weeks

 Dun Y, Smith JR, Liu S, Olson TP. High-Intensity Interval Training in Cardiac Rehabilitation. Clin Geriatr Med. 2019, Nov;35(4):469-487. doi: 10.1016/j.cger.2019.07.011. Epub 2019 Jul 12. PMID: 31543179; PMCID: PMC6760312

What Is an Active Recovery Period?

Complete lighter level activity that still keeps the heart rate (HR) elevated.  The Rating of Perceived Exertion (RPE) should range between 12-14 on the Borg scale.6

  • Examples of active recovery exercises:some text
    • Walking
    • Jumping Jax
    • Jogging in place
    • Standing squats
    • Walking Lunges
    • Stationary bike
    • Rower

Are There Safety Concerns for Participating in HIIT?

If you are diagnosed with a chronic illness it is important that you be cleared from a physician to begin physical activity.  

  • Key Ingredients to a Safe HIIT Workout:some text
    • Greater than 3-minute warm up
    • Greater than a 3 min cooldown that is carefully monitored. 
    • People taking antihypertensive medication- may have a sudden excessive reductions in blood pressure following exercise.   
    • People with known angina- a 10 minute warm up and cool down may be necessary.25
    • During the first HIIT Workout- blood pressure should be monitored during the last 2 minutes of the first high intensity interval, to ensure normative changes to exercises demands.23

Are There Contraindications to HIIT Workouts?

Quick Answer, Yes!


Uncontrolled resting BP (>180 mmHg systolic and/or >110 mmHg diastolic)

<90% SPO₂ before or during exercise

Progressive worsening of exercise tolerance

Unstable HF

≥2 kg increase in weight previous 1-3 days

Signs and symptoms of hypovolemia

Exercising BP ≥220 mmHg systolic and/or≥105 mmHg diastolic BP

Resting supine HR >100 bpm

Taylor JL, et al. Guidelines for the delivery and monitoring of high intensity interval training in clinical populations. Prog in Cardio Dis. 2019 Mar;62(2):140-146.

To Sum It Up

The use of HIIT Workouts are a safe and effective way to progress and maintain fitness levels in a healthy population, as well as, with those diagnosed with chronic illness.  If you are diagnosed with chronic illness, it is important to be cleared by your physician for exercises and then work with a qualified Physical Therapist to assess vitals before, during and after training sessions, to ensure participation is safe and dosed properly.

 Exercise can be enjoyed by the vast majority of our population; it is important to support each other in order to help create the healthiest community as possible.


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10. Hwang CL, Lim J, Yoo JK, Kim HK, Hwang MH, Handberg EM, Petersen JW, Holmer BJ, Leey Casella JA, Cusi K, Christou DD. Effect of all-extremity high-intensity interval training vs. moderate-intensity continuous training on aerobic fitness in middle-aged and older adults with type 2 diabetes: A randomized controlled trial. Exp Gerontol. 2019 Feb;116:46-53. doi: 10.1016/j.exger.2018.12.013. Epub 2018 Dec 18. PMID: 30576716; PMCID: PMC6404965.

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20. Gjellesvik TI, Becker F, Tjønna AE, Indredavik B, Lundgaard E, Solbakken H, Brurok B, Tørhaug T, Lydersen S, Askim T. Effects of High-Intensity Interval Training After Stroke (The HIIT Stroke Study) on Physical and Cognitive Function: A Multicenter Randomized Controlled Trial. Arch Phys Med Rehabil. 2021 Sep;102(9):1683-1691. doi: 10.1016/ j.apmr.2021.05.008. Epub 2021 Jun 6. PMID: 34102144.

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