Exercise has been well established as an important factor in the prevention and management of chronic disease in humans,1 including cardiovascular disease (CVD).2 According to the American Heart Association, CVD comprises hypertension, stroke, heart failure, and coronary heart disease.3 In 2018, the prevalence of CVD in the U.S. for those 20 years of age or older was a staggering 49.2%.4 A 2020 report indicated 1 person dies every 33 seconds from CVD.5 With nearly half of the adult U.S. population having CVD, health care professionals including physical therapists will treat, either directly or indirectly, patients with CVD.
EXERCISE PRESCRIPTION
Prescribing the appropriate exercise intensity is based on a patient’s ability to perform a resisted exercise utilizing a percentage of their one repetition maximum (%1RM), the rating of perceived exertion (RPE) of the exercise, and/or a percentage of their maximum heart rate (% HRmax) or peak heart rate (% peak HR).6,7 Other factors such as exercise volume (i.e., how much), exercise frequency (i.e., how often), duration, and rest periods also should to be considered when prescribing exercise.7
Several studies have found high intensity interval training (HIIT) in patients with 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.8-14 Nevertheless, the optimal parameters (i.e., duration, volume, and weekly frequency) for HIIT workouts in individuals with CVD has not yet been established despite the growing body of research supporting its use.9-18
INTENSITY DEFINED
HIIT requires higher submaximal effort for a given task than MICT, and is characterized by the patient performing tasks with >75% maximal power output or the patient’s attainment of 85-95% HRmax with a subjective RPE of 15-17 on the Borg scale, with the RPE taking precedence over the measured HR when discrepancies occur (i.e., the patient may rate the intensity at 15 but the HRmax is measuring 75%).19-20
Although determining exercise intensity is based on HRmax, an overestimation can occur in untrained individuals and in individuals taking beta blockers.21-22 The Borg scale may be a better predictor for these patients. Notably, obtaining direct maximal oxygen consumption (VO2max) measurements is not pragmatic for most clinical settings; therefore, use of the below formulas from the 2019 guidelines23 is recommended as an objective way to prescribe and monitor HIIT in clinical populations.
FORMULAS FOR ESTIMATING HRmax
For patients not taking a beta blocker, the estimated HRmax = 211 – (0.64 x age)24
For patients taking a beta blocker, the estimated HRmax = 164 – (0.7 x age)25
TYPE OF HIIT – DOES IT 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.26-29 These findings encourage clinicians to adjust exercise modes that introduce variability and/or promote additional safety into the plan of care. Clinicians may be able to continue to promote and improve cardiovascular fitness for patients with neuromusculoskeletal injuries using HIIT while reducing loads on injured tissue (e.g., a runner with plantar fasciitis may benefit from the aerobic and anaerobic benefits of HIIT workouts with rowing and/or cycling while progressing with a rehabilitation program geared towards a return to running). This may be a useful strategy to maximize patient compliance because added variety to an exercise program may generate greater patient satisfaction and engagement with the plan of care.30
VOLUME AND FREQUENCY
Guidelines on exercise duration and volume regarding HIIT for patients with CVD support the continued use of 3 exercise duration categories (short duration, medium duration, and long duration) to assist with proper patient assignment to their respective exercise capacity category.15 Short duration high intensity intervals are defined as lasting 15-60 seconds with an active recovery period of 15-120 seconds. Medium duration high intensity intervals are defined as lasting 1-2 minutes with an active recovery period of 1-4 minutes. Long duration high intensity intervals are defined as lasting 3-4 minutes with an active recovery period of 3-4 minutes.
During the active recovery period, regardless of duration type (i.e., short, medium, or long), the patient’s target HR is recommended to be between 50-75% HRmax with a RPE of 12-14 on the Borg scale.15 Additionally, the number of sets performed (i.e., the high intensity interval plus the active recovery period) should be adjusted based on the duration type.
For those performing short duration HIIT, the recommended number of sets is 10, whereas for the medium and long duration intervals, the number of recommended sets is 8 and 4, respectively.15 Notably, HIIT for 7-12 weeks has been found to elicit the largest change in cardiorespiratory fitness, suggesting rehabilitation protocols of less than 7 weeks may be suboptimal.9
| Duration Type | High Intensity Interval (85-95% HRmax and 15-17 RPE) | Active Recovery (50-75% HRmax and 12-14 RPE) | Number of Sets Performed | Proposed Timeline of Progression |
| Short (low exercise capacity) | 15-60 sec | 15-120 sec | 10 | 0-3 weeks |
| Medium (intermediate exercise capacity) | 1-2 min | 1-4 min | 8 | 4-12 weeks |
| Long (high exercise capacity) | 3-4 min | 3-4 min | 4 | >12 weeks |
SAFETY CONCERNS FOR HIIT
Despite the real concern for adverse events occurring in those with CVD while performing HIIT, one retrospective study of 4,864 patients with CVD found 1 fatal event per 129,456 hours of MICT and 2 non-fatal events per 23,182 hours of HIIT. Notably, ; n
Additional measures and precautions should be undertaken by physical therapists to reduce the incidence of adverse events both during and following exercise. Absolute contraindications must be adhered to (see below), and at a minimum, the patient’s heart rate, blood pressure, peripheral capillary oxygen saturation, and weight should be recorded before, during, and following the HIIT activity.23 Other considerations include clearance from a physician to begin physical activity, a greater than 3-minute warm up and cool down, an extended and carefully monitored cool down period for patients taking antihypertensive medication (due to sudden excessive reductions in BP post exercise), and for patients with known angina, a 10 minute warm up and cool down may be necessary.23 Additionally, blood pressure should be monitored during the last 2 minutes of the first high intensity interval, especially during the first HIIT session.23
| Contraindications | |
| 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 |
Several clinical trials have also found HIIT to be an effective form of exercise in other populations, including those with limited exercise tolerance, diabetes mellitus, congestive heart failure, chronic obstructive pulmonary disease,intermittent claudication, long distance runners, sarcopenia, and women over 65 years of age.16-18,32-40
CONCLUSIONS
Although the specific frequencies and durations have not yet been established, the use of HIIT in patients with CVD is considered a safe and effective management strategy. Due to the variety of exercises employed and the shorter time commitments required, HIIT exercise may generate greater patient satisfaction and engagement with the plan of care.
AUTHORS
David Didlake, PT, DPT, Cert. DN, CSCS
Fellow in Training, AAMT Fellowship in Orthopaedic Manual Physical Therapy
Integrative Therapeutics, Ellisville, MO
Casey Charlebois, PhD(c), DPT, MSc, FAAOMPT, Dip. Osteopractic
Director of Clinical Research, AAMT Fellowship in Orthopaedic Manual Physical Therapy
PhD Candidate, Nova Southeastern University, Fort. Lauderdale, FL
James Dunning, PhD, DPT, MSc, FAAOMPT, Dip. Osteopractic
Director, AAMT Fellowship in Orthopaedic Manual Physical Therapy
Montgomery Osteopractic Physical Therapy & Acupuncture, Montgomery, AL
Paul Bliton, DPT, OCS, SCS, FAAOMPT, Dip. Osteopractic
Associate Director, AAMT Fellowship in Orthopaedic Manual Physical Therapy
William S. Middleton Memorial Veterans’ Hospital, Madison, WI
Patrick Gorby, DPT, MPH, FAAOMPT, Dip. Osteopractic
Assistant Director, AAMT Fellowship in Orthopaedic Manual Physical Therapy
Gorby Osteopractic Physiotherapy & Wellness, Colorado Springs, CO
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OSTEOPRACTIC 