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High-Intensity Interval Training for Hypertension

Program Design and Application

Uken, Brent M.S.; Lee, Matthew M.S., ACSM-EP; Wright, Gage M.S.; Feito, Yuri Ph.D., MPH, FACSM, ACSM-CEP

Author Information
ACSM's Health & Fitness Journal: 9/10 2021 - Volume 25 - Issue 5 - p 28-34
doi: 10.1249/FIT.0000000000000706
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Abstract

INTRODUCTION

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Hypertension (HTN) is a significant risk factor for cardiovascular disease (CVD) and a leading cause of disability and death in the United States and globally (1). The prevalence of HTN among U.S. adults over 20 years of age is estimated to be 116 million, divided nearly equally between men and women (1). The most recent estimates of the total direct and indirect cost to society associated with HTN in the United States is more than $55 billion (annual average), and projections show that by 2035, the total costs of HTN could increase to more than $220 billion (1).

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The high prevalence of HTN creates a significant likelihood that health and fitness professionals will regularly encounter individuals who have HTN — diagnosed or not. Table 1 presents blood pressure categories and their corresponding systolic blood pressure (SBP) and diastolic blood pressure (DBP) levels.

TABLE 1 - Blood Pressure Categories
Blood Pressure Category SBP (Upper Number), mm Hg DBP (Lower Number), mm Hg
Normal <120 and <80
Elevated 120–129 and <80
High blood pressure (HTN stage 1) 130–139 or 80–89
High blood pressure (HTN stage 2) ≥140 or ≥90
Hypertensive crisis (consult physician immediately) >180 and/or >120
Source: American Heart Association (2020).

HTN develops gradually and is generally the product of lifestyle choices concerning diet and exercise. These same lifestyle choices also frequently lead to other chronic diseases, such as diabetes, dyslipidemia, overweight, and obesity — all common comorbidities with HTN. Although HTN is routinely treated with pharmacological intervention (e.g., beta-blockers, diuretics, angiotensin II receptor blockers, and angiotensin-converting enzyme inhibitors), lifestyle intervention is a primary therapeutic option for most who have been newly diagnosed with hypertension (2,3). Pharmacological interventions and dietary changes, which are effective for controlling blood pressure, are beyond the scope of this article; therefore, our focus is on the role of exercise in mitigating or possibly reversing HTN. More specifically, our focus is on the role of high-intensity interval training (HIIT) as an element of the exercise prescription (ExRx) in addressing HTN.

Current ExRx for HTN

The American College of Sports Medicine (ACSM), along with the American Heart Association, the World Health Organization, and other prominent groups, universally endorses aerobic exercise for the treatment of HTN, with specific details outlined in its Exercise and Hypertension Position Stand (4) and in ACSM’s Guidelines for Exercise Testing and Prescription (5). The consensus is that ExRx for adults with HTN should comprise 30 to 60 minutes per day and at least 150 minutes per week of moderate-intensity aerobic exercise, supplemented with moderate-intensity dynamic resistance training 2 to 3 days per week (6). The current ACSM frequency, intensity, time, tand type (FITT) recommendations for individuals with HTN are summarized in Table 2.

TABLE 2 - FITT Recommendations for Individuals with HTN
FITT Element Aerobic Exercise Resistance Exercise
Frequency ≥5–7 days/week ≥2–3 days/week
Intensity Moderate (i.e., 40%–59% O2R or HRR; RPE 12–13 on a 6–20 scale) Moderate (i.e., 60%–70% 1-RM; may progress to 80% 1-RM; for older individuals and novice exercisers, begin with 40%–50% 1-RM)
Time ≥30 minutes/day of continuous or accumulated exercise 2–4 sets of 8–12 repetitions for each of the major muscle groups per session to total ≥20 minutes per session with rest days interspersed depending on the muscle groups being exercised
Type Prolonged, rhythmic activities using large muscle groups (e.g., walking, cycling, swimming) Resistance machines, free weights, resistance bands, and/or functional bodyweight exercise
Source: ACSM’s Guidelines for Exercise Testing and Prescription, 11th edition (2021).
1-RM, one repetition maximum; HRR, heart rate reserve; O2R, oxygen uptake reserve; RPE, rating of perceived exertion.

TABLE 3 - Pros, Cons, and Considerations of HIIT for HTN at a Glance
Pros Cons Considerations
• HIIT has been shown to lower blood pressure in hypertensive individuals
• HIIT effectively addresses common HTN comorbidities, such as diabetes, overweight, and obesity
• HIIT may increase participant motivation and facilitate a higher level of exercise compliance
• HIIT allows for virtually unlimited variability in programming when considering the combinations of modality, work intensity, WRR, recovery activity, recovery intensity, total session duration, etc.
• Unsupervised or improperly executed HIIT is a riskier form of exercise for hypertensive individuals relative to current guidelines
• For clinicians and health and fitness professionals, initiating HIIT may be a more time-intensive approach to patient wellness relative to traditional ExRx due to additional risk factors and considerations
• Clearance: Has the individual received physician clearance to participate in HIIT?
• Fitness level: Does the individual have sufficient baseline fitness to safely perform HIIT?
• Motivation level: Is the individual motivated to begin the incorporation of HIIT into his/her exercise regimen?
• Tolerance: Is the individual willing and able to tolerate the unique and high level of discomfort associated with HIIT?
• Modality: What will be most effective for an individual given his/her goals, preferences, abilities, and limitations?

TABLE 4 - Measures of Exercise Intensity
Intensity %HRR or %V·O2R %HRmax %V·O2max RPE scale (6–20) METs (absolute)
Vigorous 60% to 89% 77% to 95% 64% to 90% 14–17 6.0 to 8.7
Near maximal to maximal ≥90% ≥96% ≥91% ≥18 ≥8.8
Source: ACSM’s Guidelines for Exercise Testing and Prescription, 11th edition (2021).

TABLE 5 - Recommendations for Hypertensive Individuals
Absolute contraindication • Exercise of any type is an absolute contraindication for an individual experiencing a hypertensive crisis.
Client goals and attributes • Evaluate HIIT in the context of an individual’s goals and desired health outcomes
• Identify and discuss any physical limitations that may interfere with HIIT (including past or current injuries)
• Discuss the unique elements of HIIT concerning motivation and levels of discomfort/pain; transparency on these elements of HIIT will position individuals to make informed decisions and better calibrate training expectations
Modality • Identify and discuss modality options
• Consider alternating modalities day to day and week to week to avoid concurrent high-impact sessions, especially for older adults
Acclimation and progression • Start an individual on an MICT or modified HIIT protocol to establish baseline fitness
• Modified HIIT could involve a more generous WRR (e.g., 1:5) or a lower-intensity level during work intervals (e.g., 75% HRmax instead of 90% HRmax)
• Progress gradually to higher intensities (increase work and/or reduce recovery)
• Progress gradually from 1 session per week to a maximum of 3 sessions per week

The American College of Sports Medicine (ACSM), along with the American Heart Association, the World Health Organization, and other prominent groups, universally endorses aerobic exercise for the treatment of HTN, with specific details outlined in its Exercise and Hypertension Position Stand (4) and in ACSM’s Guidelines for Exercise Testing and Prescription (5).

Although the generally accepted ExRx for HTN does not include HIIT, the effectiveness and benefits of HIIT are worthy of consideration as a therapeutic option. Consequently, the purpose of this article is to explore HIIT as an emerging approach to ExRx for individuals with hypertension.

HIIT

Over the past few decades, there has been an increased emphasis on HIIT in support of various physiological outcomes, including fat loss and improved athletic performance (7,8). Controlled and observational research and field results have shown that HIIT is efficacious across various populations (9). HIIT is often characterized along two primary axes: (i) intensity level (e.g., aerobic capacity and percent of age-predicted heart rate) and (ii) the work-to-recovery ratio (WRR), or the duration of work performed to recovery allowed between repetitions and sets. Intensity levels approach, and may even exceed, V·O2max or age-predicted maximum heart rate (HRmax), and recovery periods are tightly controlled. The intensity and the WRR variables are modified depending on the individual goals, ability, and motivation.

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The Case for HIIT

There is an emerging body of evidence showing that exercise-induced reductions in SBP and DBP are dose dependent and related to exercise intensity. As a result, HIIT can be viewed as an alternative to moderate-intensity continuous training (MICT) for addressing HTN (10). In short, MICT is characterized by longer-duration, lower-intensity exercise (e.g., rhythmic exercises, such as jogging), whereas HIIT is characterized by short-duration, high-intensity movements (e.g., sprinting).

Research supports the implementation of aerobically based HIIT and MICT for inducing similar reductions in SBP and DBP in adults with pre-HTN and/or HTN (11,12). In fact, each 10% increase in relative V·O2peak corresponds to a decrease in resting blood pressure of 1.5 mm Hg SBP and 0.6 mm Hg DBP, respectively (13). In comparison, commonly prescribed antihypertensive drugs can produce reductions in SBP and DBP up to 9.1 and 5.5 mm Hg, respectively. Therefore, overall blood pressure reductions resulting from HIIT have the potential to reduce SBP and DBP up to 11 and 7 mm Hg, respectively, similar to pharmaceuticals, and thus HIIT embodies the phrase Exercise is Medicine® (14).

Currently, MICT is considered the gold standard for exercise-based HTN treatment, given the volume of research over the past few decades supporting its positive effects on cardiovascular fitness. However, MICT has some inherent impracticalities because of the duration of both individual and collective weekly exercise sessions. This considerable time commitment often leads to reductions in program adherence. Alternatively, and promisingly, the shorter duration sessions, coupled with the inherent exercise variety found in HIIT protocols, may facilitate higher compliance rates and corresponding results (15). Furthermore, HIIT also has been shown to address common comorbidities (e.g., diabetes, dyslipidemia, overweight, and obesity) seen in hypertensive individuals (8,15,16).

Safety and Risk Profile

Safety is essential when considering exercise for any population and even more so when implemented for individuals with known CVD. Although at first glance HIIT may appear to be problematic for those with CVD or other HTN-related conditions, mounting evidence indicates that individuals in various states of CVD respond well to HIIT (8,10–17). Furthermore, research shows that the rate of serious adverse events during HIIT (e.g., cardiac arrest) is not statistically different from traditional MICT exercise programs (18).

HIIT Programming Variables

The FITT framework, a model with which most health and fitness professionals have experience, can be used to develop HIIT-centric ExRx.

Frequency

HIIT for any client must be introduced gradually — and deliberately — over time. The introduction of HIIT should start with a single, brief set of HIIT (e.g., a few minutes of HIIT) to evaluate the client’s readiness and receptivity to the approach. A safe and effective progression would build to a single HIIT session per week (e.g., multiple sets of HIIT comprising 20 to 40 minutes of activity) and remain at this level of frequency while initial neuromuscular and other physiological adaptations occur. Over time, clients may progress to multiple HIIT sessions per week, allowing for at least one day of rest between sessions.

HIIT for any client must be introduced gradually — and deliberately — over time. The introduction of HIIT should start with a single, brief set of HIIT (e.g., a few minutes of HIIT) to evaluate the client’s readiness and receptivity to the approach.

Intensity

Intensity within the context of HIIT comprises two elements: physical exertion (also referred to as “work”) and the WRR. Physical exertion can be measured in many ways: heart rate reserve, HRmax, V·O2max, V·O2 reserve, rate of perceived exertion, and metabolic equivalents (METs) (5). It is important to note, however, that HIIT research varies in the definition of “high intensity” with respect to both the primary measure (e.g., V·O2max) and range of values (e.g., range of % of maximum). What is used is a blend of the ACSM-defined categories “vigorous” and “near maximal to maximal” (e.g., 70% to 95% of V·O2max) (5).

WRR consists of several methodologies, usually consisting of a ratio (e.g., 1 minute of work to 3 minutes of recovery = 1:3 WRR) or a focus on the absolute time between repetitions or sets without regard to the time spent working (e.g., 30 seconds of recovery between sprints). Either approach is within the generally accepted concept of HIIT. The critical element is to vary the amount of recovery: (i) intensity of the work (i.e., maximal effort requires more recovery time than vigorous effort), (ii) ability and training status of the individual, and (iii) limiting the potential of injury. Recovery during HIIT can be the main modifiable variable for generating increases in workout intensity, even in the absence of changes to exercise effort. For example, doing sets of (1 minute on/1 minute rest) can be modified to (1 minute on/30 seconds rest), where the “on” remains at the same intensity, but the shorter recovery makes the effort more challenging. It is also important to note that recovery in this context does not necessarily mean an individual is inactive; recovery also may encompass light or moderate activity. Consequently, the concept of recovery is best defined as the period over which an individual develops readiness to perform the next repetition or set with maximal effort.

In research and practice, some of the most common WRR protocols include the following:

  • 4 sets × 4 minutes of work × 3 minutes of recovery (4:3 WRR) (11,18,19,20)
  • 4 sets × 4 minutes of work × 4 minutes of recovery (1:1 WRR) (12,20)
  • 10 sets × 1 minute of work × 1 minute of recovery (1:1 WRR) (11,16,18,19,20)

The key variables, number of sets, minutes of work, and recovery periods, can be modified to create any number of combinations of HIIT sessions to meet individual client objectives. Initially, it is recommended to implement these protocols at lower intensities or at a more generous WRR to allow clients appropriate acclimation to HIIT.

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In addition, multiset protocols should be introduced slowly, only after clients become comfortable with initial high-intensity sessions. HIIT — and especially multiset HIIT — can produce significant fatigue and delayed onset muscle soreness (DOMS). Because fatigue and DOMS are likely to occur, at least initially, it is best to initiate HIIT with no more than one set or session once a week so as to minimize the risk of reduced client engagement and adherence to exercise.

Time

HIIT sessions are of short duration by design. HIIT sessions can be completed in less than 5 minutes, but also can exceed 60 minutes, all depending on individual preference. Most published research concerning individuals with hypertension have reported total session length of 25 to 45 minutes, inclusive of warm-up and cool-down (20).

Type

The selection of training type should focus on individual preference, while also considering realities of available time, equipment, etc. Common modalities for HIIT include the cycle ergometer and treadmill, but the possibilities are numerous. Rowing machines, battle ropes, burpees, kettle bells, and similar exercises are used in HIIT programs, and as long as the intensity stays high, physiological adaptations will occur. Ultimately, the selection of modality depends on several factors that include a client’s ability, preference, and physical limitations (i.e., consideration of low- vs high-impact exercises; overweight or obese individuals may find cycle ergometers more suitable for exercise given their low-impact nature, for example).

Examples of HIIT Session Programs

Table 6 provides three examples of HIIT sessions. Each of these examples highlight the WRR and combined work and recovery periods relative to total sets performed. Although we have presented three program examples, there are a vast number of combinations possible across these elements. In addition to the variety this affords a health and fitness professional in developing client workouts, it also yields a level of variety that may supercharge a client’s level of motivation, exercise program compliance, and — most importantly — results (e.g., lower SBP and lower DBP).

TABLE 6 - HIIT Programming Examples
Program a Common Modalities Sets Protocol Frequency Time b
Example A • Cycle ergometer
• Treadmill
• Rowing machine
4 sets 4 × 4 minutes (1:1 WRR) c 1–3 sessions per week 28 minutes
Example B • Cycle ergometer
• Treadmill
• Rowing machine
10 sets 1 × 1 minute (1:1 WRR) c 1–3 sessions per week 19 minutes
Example C • Cycle ergometer
• Treadmill
• Rowing machine
8 sets 30 × 60 seconds (1:2 WRR) c 1–3 sessions per week 11 minutes
aAll programs assume that clients are physically able to participate in high-intensity exercise and have developed a base level of fitness to engage in these types of protocols.
bLiteral time elapsed (sets × work duration × recovery period); actual session time will be longer than the time shown when including training sessions elements such as warm-up, transition time between sets, switching modalities (if applicable), and cooldown.
cRecovery may range from no activity (complete rest) to moderate activity.

TABLE 7 - Key Considerations for Health and Fitness Professionals
• Properly address the need for medical clearance (as-if necessary)
• Review and understand the implications of all medications
• Evaluate suitability (physical and psychological)
• Appreciate that MICT and HIIT are not mutually exclusive
• Identify the appropriate modality
• Start slowly and monitor performance
• Make progressions deliberately and slowly

CONCLUSION

Although moderate-intensity aerobic exercise is a long-established therapeutic modality for HTN, a growing body of evidence suggests that HIIT is an alternative exercise protocol yielding similar clinical benefits. For the health and fitness professional, using HIIT with the hypertensive population is a safe and effective means of exercise that many clients may find as an engaging addition to their exercise routines.

BRIDGING THE GAP

HTN is a significant risk factor for CVD and is a leading cause of disability and death globally. In the United States alone, the prevalence of HTN among adults is estimated to be 116 million, divided nearly equally between men and women. HTN develops gradually over several years and is generally the product of lifestyle choices concerning diet and exercise. Fortunately, improvements in these same two areas can be used to mitigate, and potentially reverse, HTN. The current ExRx for HTN is continuous, aerobic, moderate-intensity exercise. However, a growing body of evidence highlights the effectiveness of HIIT for this population. In addition to its blood pressure-lowering effect, HIIT offers individuals unique programming flexibility and variety that many find invigorating and challenging, therefore leading to increased exercise compliance, usually resulting in improved blood pressure.

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Keywords:

Hypertension; Systolic Blood Pressure; High Intensity; HIIT; Interval Training

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