According to the World Health Organization, chronic diseases are the leading cause of death and disability worldwide (1). Chronic diseases (e.g., heart disease, stroke, cancer, diabetes) are defined broadly as conditions that last one year or more, require ongoing medical attention, and limit activities of daily living (2). For individuals living with chronic disease, exercise training is paramount in the management of disease conditions. Yet despite the well-established benefits of exercise, many individuals with chronic disease remain physically inactive. Accumulated physical inactivity leads to the unfortunate initiation of a downward cycle of physical deconditioning, loss of functional capacity, and marked reductions in the ability to perform activities of daily living, ultimately culminating in further deteriorations of health (3). As an alternative, incorporating exercise training can be a fundamental strategy to enhance health and improve quality of life, as evidenced by ACSM’s global health initiative, Exercise is Medicine®. As such, fitness professionals and health care providers who work with individuals living with chronic disease are tasked with improving the cardiorespiratory fitness (CRF) of their clients and patients. Although the efficacy of exercise to improve CRF is not in question, the mechanisms on how to get there vary greatly.
For readers of ACSM’s Health & Fitness Journal®, the popularity and widespread utilization of high-intensity interval training (HIIT) is well known, as HIIT has firmly cemented itself as one of the top five fitness trends since 2014 (4). In healthy populations, the appeal of HIIT is largely centered on the marked reduction in total exercise volume and total exercise time, both of which are a result of HIIT’s prioritization on the intensity component of a given exercise bout (5). Likewise, for individuals with chronic disease, HIIT is emerging as a safe and viable option for therapeutic exercise prescription to maximize health outcomes (6).
Throughout this specially themed issue of ACSM’s Health & Fitness Journal®, a challenge for each of the authors was to provide the reader with a consistent definition of terms associated with interval training. When reviewing the literature, a proverbial alphabet soup of abbreviations such as HIIT, SIT, and MICT can be found, all of which may confuse the most well-read fitness professionals. As such, throughout this themed issue, the following terms will be operationally defined, which are consistent with ACSM’s Guidelines for Exercise Testing and Prescription, 11th edition (5):
- Interval training — intermittent periods of intense exercise separated by periods of recovery (7).
- High-intensity interval training (HIIT) — a form of interval training that is characterized by near-maximal efforts, is often performed at an intensity close to that which elicits ≥ 80% to 100% peak HR (7).
- Sprint interval training (SIT) — a form of interval training characterized by an all-out, supramaximal effort equal to or greater than the pace that elicits ≥100% peak oxygen uptake (V˙O2peak) (7).
- Moderate-intensity continuous training (MICT) — used for comparative purposes to describe exercise that is performed in a continuous manner without interruptions and at lower intensities, allowing for prolonged maintenance of the activity (e.g., below the second ventilatory threshold) (8).
During interval training, the exercise prescription is primarily centered around the work-to-rest ratio (work–rest) of 1) the intensity and duration of the work bout, 2) the intensity and duration of the recovery/rest intervals, and 3) the total number of intervals performed (e.g., a ratio of 1 min at 85% HRmax to 1 min at 65% HRmax × 10) (7). It is important to note that there is no consensus regarding the most appropriate method to assign exercise intensity; therefore, several maximal and submaximal anchor measurements are used and are listed below (9):
- maximal/peak oxygen uptake (V˙O2max, V˙O2peak)
- maximal/peak heart rate (HRmax, HRpeak)
- maximal work rate (power W˙max or velocity V˙max)
- ventilatory and lactate thresholds (VT, LT1, LT2)
- maximal lactate steady state
- critical power and critical speed
Although all the above methods can be used to create an individualized exercise prescription, for individuals with chronic disease, the interaction of medications and therapeutic treatments with subsequent chronic disease-related fatigue may contraindicate the use of commonly used measurements, such as HRmax, and may necessitate more subjective measures of intensity, such as ratings of perceived exertion and the talk test (5).
In the pages that follow, this specially themed issue of ACSM’s Health & Fitness Journal® will provide evidence-based and practical recommendations on how to best incorporate interval training from experts in mental health and cognition, neurodegenerative conditions, hypertension, cardiovascular disease, cancer, and metabolic disease. We hope health and fitness professionals will find the information useful to provide their clients with additional exercise options specific to their goals and needs.
In the pages that follow, this specially themed issue of ACSM’s Health & Fitness Journal® will provide evidence-based and practical recommendations on how to best incorporate interval training from experts in mental health and cognition, neurodegenerative conditions, hypertension, cardiovascular disease, cancer, and metabolic disease.
1. World Health Organization. Chronic diseases and health promotion. Integrated chronic disease prevention and control. [cited 2021 March 12]. Available from: https://www.who.int/chp/about/integrated_cd/en/
2. Centers for Disease Control and Prevention. About Chronic Diseases. [cited 2021 March 12]. Available from: https://www.cdc.gov/chronicdisease/about/index.htm
3. Ross LM, Porter RR, Durstine JL. High-intensity interval training (HIIT) for patients with chronic diseases. J Sport Health Sci
4. Thompson WR. Worldwide survey of fitness trends for 2021. ACSMs Health Fit J
5. Liguori G; American College of Sports Medicine. ACSM’s Guidelines for Exercise Testing and Prescription
. 11th ed. Philadelphia (PA): Wolters Kluwer; 2021.
6. Karlsen T, Aamot IL, Haykowsky M, Rognmo Ø. High intensity interval training for maximizing health outcomes. Prog Cardiovasc Dis
7. MacInnis MJ, Gibala MJ. Physiological adaptations to interval training and the role of exercise intensity. Review J Physiol
. 2017 May 1;595(9):2915–30.
8. Andreato LV. High-intensity interval training: methodological considerations for interpreting results and conducting research. Trends Endocrinol Metab
. 2020 Nov;31(11):812–7.
9. Jamnick NA, Pettitt RW, Granata C, Pyne DB, Bishop DJ. An examination and critique of current methods to determine exercise intensity. Sports Med