Exercise Oncology

High-Intensity Interval Training for Cancer Survivors

Abstract

Apply It! 

• Recommendations for incorporating HIIT for cancer survivors are made.

• Contraindications for exercise training for cancer survivors also are made.

In Brief

Based on the currently available evidence, high-intensity interval training (HIIT) training is safe, tolerable, and effective as part of a comprehensive cancer rehabilitation program. Incorporating HIIT should be tailored to the individual based on their goals and current level of fitness.

INTRODUCTION

Exercise is a significant component of primary cancer prevention and for improving the health and well-being of cancer survivors after treatment. In addition, there is a growing body of evidence that post–cancer treatment exercise reduces the risk of recurrence and increases longevity (¹). Accordingly, exercise guidelines that reduce the risk of developing cancer have been established (²), and exercise guidelines after cancer treatment have primarily been developed over the last two decades (¹). The 2019 ACSM consensus statement on exercise guidelines for cancer survivors provides an excellent review of “evidence-based guidelines for exercise testing, prescription, and delivery in cancer survivors” and should be considered a must read. In general, there is moderate to strong evidence that exercise after treatment is well tolerated, safe, and improves physical and mental well-being in cancer survivors (¹).

The goal of exercise programming for cancer survivors is to improve physical fitness, physical functioning, quality of life, and cancer-related fatigue through individualized exercise plans (¹). As an individual’s response to cancer and cancer treatment is unique, there may be survivors who are unable to tolerate minimal levels of exercise while there also may be a select population of cancer survivors who are able to tolerate a more aggressive approach to rehabilitation. Therefore, defining the optimal exercise load for a cancer survivor who has completed treatment has remained elusive, in part due to the many independent variables associated with health that are adversely affected by cancer. These late and long-term effects are presented in Table 1.

TABLE 1 - Late and Long-Term Effects of Cancer Treatment Where Physical Activity Can Have a Positive Impact

Cancer Treatment	Physical Changes
Surgery	↓	Pulmonary function
Radiation	↓	Cardiac function
Chemotherapy	↓	Muscle mass
Immunotherapy	↑	Fat mass
Hormone therapy	↑	Body weight or body mass index
Steroid therapy	↓	Muscle strength/power
	↑	Inflammation
	↓	Immune function
	↓	Bone health
	↑	Trauma and scarring
	↑	Lymphedema
	Psychological and behavioral changes
	↓	Exercise/physical activity
	↑	Physical symptom and pain
	↑	Depression
	↓	Cognitive function
	↓	Quality of life (multiple domains)

There is emerging evidence in exercise oncology that manipulating the duration and intensity of exercise sessions may be a time-effective strategy in improving the clinical outcomes of cancer survivors. It is therefore the purpose of this article to review the efficacy and safety of implementing high-intensity interval training (HIIT) for cancer survivors and to provide the reader/practitioner practical advice when constructing HIIT exercise prescriptions for this group.

Herein, we define cancer survivors as individuals 18 years and older and include all cancer types, stages of diagnosis, and individuals who have undergone any one or combination of treatments, including surgery, hormonal therapy, chemotherapy, radiotherapy, and adjuvant therapy. Emerging data on the effectiveness of exercise training during treatment (e.g., chemotherapy) are forthcoming, yet at this time, they are insufficient to make recommendations and are excluded from this discussion.

Efficacy of Exercise for Cancer Survivors

According to the evidence-based recommendations found in the 2019 ACSM consensus statement on exercise guidelines for cancer survivors, “based on the current literature, an effective exercise prescription that most consistently addresses health-related outcomes experienced due to a cancer diagnosis and cancer treatment includes moderate-intensity aerobic training at least three times per week, for at least 30 minutes, for at least 8 to 12 wk. The addition of resistance training to aerobic training, at least two times per week, using at least two sets of 8 to 15 repetitions at least 60% of one repetition maximum, appears to result in similar benefits” (¹, p. 2385). The recommendations did not include specifics with regards to HIIT training as the evidence to evaluate randomized controlled trials of low- and high-intensity exercise was insufficient.

There is emerging evidence that the addition of HIIT may be beneficial for cancer survivors (^3–5). In general, these collective papers indicated that HIIT was superior to usual care in improving aerobic capacity (V˙O_2peak) but not superior to participating in moderate-intensity aerobic exercise. Mugele et al. (³) further concluded that there was no difference between HIIT compared with moderate-intensity aerobic training for changes in cardiorespiratory fitness, lean mass, and patient-reported outcomes. However, the general consensus was that HIIT may be a time-efficient mode of training for cancer survivors at any point during or after treatment (⁴). This is an important consideration as time is often cited as a significant barrier to exercise participation (⁶).

Training Programs

In addition to the reviews mentioned above, additional observational studies that detail duration, intensity, and efficacy of HIIT exercise for cancer survivors were reviewed for this article and are presented in Table 2.

TABLE 2 - Summary of Selected Studies on HIIT, Including Age Range, Exercise Prescription, Outcome Measures, and Safety

Study	Entity	Sample	Training Duration/Frequency	Exercise Rx	Outcomes	Safety
Adamsen et al. (7)	Various cancers	M/F, n = 269, mean = 47	6 weeks, 9 hours/week	HIIT: 30-minute WU, 45-minute resistance, 15-minute CV; resistance: 3 × 5–8 reps at 70%–100% 1RM; CV: cycle at 85%–95% HRmax	Decrease in fatigue; increase in leg press	No adverse events; adherence = 70.8%
Klika et al. (8)	Various cancers	Females, 41; Males, 13; N = 54; mean = 53.8 ± 10.3 years	12 weeks, 5× per week	Intervals at 100%–115%; LT = 24% of the time	Increase in V˙O2max by 5% males, 14% females; females: decrease in BMI, percentage fat down, peak power, threshold power, heart rate max lower; males: PPO up, PP, PTlact up, no change in body comp	No adverse events
van Waart et al. (9)	Breast and colon	N = 230 (228 females), mean = 50. 7 ± 9.1	2× week till end of chemotherapy	UC, low intensity and moderate to high intensity; JIIT included 2 × 8 RM and 30 minutes of aerobic activity at 50%–80% max workload	Increased peak O2 uptake, strength, fatigue, and chemotherapy completion rate	48%–71% compliancy for all three groups
Edvardsen et al. (10)	Lung	Females, 33; Males, 28; RCT, N = 61	20 weeks, 3× per week	Walking uphill at 80%–95% of HRmax and 3 × 6–12 RM	Increases in 1-RM, peak O2 uptake, chair stand, muscle mass, QoL	Adherence = 88%
Heinrich et al. (11)	Various cancers	Females, 6; Males, 2; N = 8; mean 53.5 ± 5.0	5 weeks, 3× per week, 60 minutes	HIFT: session based on CrossFit template (e.g., rowing, running, or jumping rope), gymnastic (e.g., push-ups, squats, or pull-ups), and weightlifting (e.g., presses, deadlifts, and kettlebell swings) exercises and were scaled as necessary	Increased emotional function, FFM increase, FM decrease, decreased body fat 4.7%, increased balance, lower body strength, power, aerobic capacity, and endurance	Adherence = 75%
Schmitt et al. (12)	Breast	Female, N = 26	3 weeks; LMIE: 6× per week, 75-minute session; HIIT: 3× per week, ~27 minutes	LMIE: 60 minutes walking outdoors, 15 minutes cycling indoors at 60% HRpeak; HIIT: 5-minute warm-up at 70% HRpeak, 8 × 1-minute intervals at >95% HRpeak, 2-minute slow walking between intervals; 24-hour rest between sessions	Both groups improved work economy and QOL while decreasing fatigue; LMIE: improved peak O2, muscle mass, and FFM; HIIT: improved peak O2 greater than LMIE; decrease in total body fat mass	No adverse events
Toohey et al. (13)	Various cancers	Female, N = 16, mean = 51.6 ± 13.01 years	12 weeks, 36 sessions	CLMIT: 20 minutes continuous at ≤55% maximal heart rate, 5-minute warm-up and cool-down; LVHIIT: ≥85% maximal heart rate, 5-minute warmup/cool-down; 7 × 30-second intervals; 1-minute rest between intervals; *progressed to 7 intervals by session 5	Both interventions improve QoL, functional capacity, and select CVD risk factors; LVHITT: increase in 6MWT distance	No adverse events
Toohey et al. (4)	Various cancers	Female, N = 16, mean = 51.6 ± 13.01 years	12 weeks, 36 sessions	CLMIT: 20 minutes continuous at ≤55% maximal heart rate, 5-minute warm-up and cool-down; LVHIIT: ≥85% maximal heart rate, 5-minute warm-up/cool-down; 7×30-second intervals; 1-minute rest between intervals; *progressed to 7 intervals by session 5	Both interventions improve QoL, functional capacity, and select CVD risk factors; LVHITT: increase in 6MWT distance	No adverse events
Adams et al. (14)	Testicular	N = 63, mean = 43.7 ± 10.8	12 weeks, 3× per week	4 × 4 minutes with 3 minutes between intervals at 75%–95% V˙O2peak	Increased V˙O2peak and decreases in CAD risk factors	Adherence = 99%
Mijwel et al. (15)	Breast	Female, N = 240, mean = 52–54 years	16 weeks, 2× per week	Resistance: 2–3 sets × 8–12 reps at 70% estimated 1RM, progressed to 80% 1RM; aerobic: 3 × 3-minute intervals of HIIT exercise on cycle ergometer, RPE of 16–18; 1-minute recovery between bouts at low intensity	HIIT: prevented increase in fatigue compared with UC; decrease in symptom burden during treatment; increase in role functioning	No adverse events; adherence: RT, 75%; AT, 83%
Kampshoff et al. (16)	Various cancers	M/F, N = 277, mean = 54 years	12 weeks	Resistance: 6 exercises, 2 sets × 10 reps, HI = 70%–85% 1RM, LMI = 40%–55% 1RM; endurance interval (part A): 8-minute alternating workload (MSEC), 60 seconds recovery at 30%, HI = 30 seconds at 65%, LMI = 30 seconds at 45%; endurance intervals (part B): 3 × 5-minute constant workload; HRR: HI ≥ 80%, LMI = 40%–50%	Both HI and LMI improved peakV˙O2 and fatigue compared with WLC	No adverse events
Lee et al. (17)	Breast	Female, N = 30, mean = 46.9 ± 9.8 years	8 weeks, 3× per week, 30 minutes	7 × 1-minute intervals at 90% PPO; 2-minute RBIs at 10% PPO	No change in V˙O2 in intervention but decreased V˙O2max in the control group	No adverse events; adherence = 82.3%
Devin et al. (18)	Colorectal	M/F, N = 47, mean = 61	4 weeks, 3× per week	Cycle ergometry; MIE, 50 minutes at 50%–70% HRpeak; HIE, 10-minute warm-up at 50%–70% HRpeak; 4 × 4 min bouts at 85%–95% HRpeak; 3-minute recovery at 50%–70% HRpeak	HIE: significantly increased V˙O2peak and lean body mass; significant decrease in fat mass and percent fat; MIE: no significant changes; both: significant increase in PPO	No adverse events; some aggravate on of sciatica and knee pain with HIE

CVD, cardiovascular disease; HR, heart rate; MIE, moderate-intensity exercise; RPE, rating of perceived exertion; RM, repetition maximum; PPO, peak power output; QoL, quality of life; RBI, rest between intervals.

Based on the summary data in Table 2, on average, the research has shown that using high-intensity exercise in cancer survivors increases aerobic capacity (V˙O_2peak), peak power output, and quality of life. For the selected studies, favorable body composition changes after HIIT are equivocal, most likely as a result of the relatively short training periods (4 to 12 weeks). The data presented indicate relatively few adverse events after HIIT training, and adherence rates of ~70%–99%.

From the summary data, frequency of interval training appears to be optimal at 2 or 3 sessions per week, but this is highly dependent on the initial fitness level. Intensity levels of HIIT are variable but generally in agreement with the definition of HIIT of 80%–100% of peak heart rate. An important note here is that peak heart rate after cancer treatment in an untrained individual is most likely lower than age-predicted maximal heart rate or a true maximal heart. This creates a situation whereby the “high” intensity level for a cancer survivor HIIT program may be relatively low compared with HIIT training programs for a healthy individual.

Most exercise oncology HIIT studies have used treadmill walking or running or cycle ergometry as a mode of exercise during the training sessions. On average, individual training sessions in the studies presented ranged from 45 to 90 minutes. Most studies reviewed did not detail exercise progression. The totality of the data on HIIT for cancer survivors is small and generally appears safe for cancer survivors, but making assumptions that HIIT is safe for all cancer survivors is not advised.

Risks and Contraindications for Exercise Training for Cancer Survivors

Cancer and cancer treatment create an enormous emotional, physical, and financial burden for most survivors. As a result, survivors nearer to the end of treatment are most likely deconditioned and emotionally fatigued. It is recommended that exercise trainers working with cancer survivors have a solid understanding of the contraindications to exercise testing and training and be able to recognize the signs and symptoms of changes in health status. These are presented in Table 3.

TABLE 3 - Contraindications and Precautions to Exercise Testing and Training for Patients with Cancer

	Contraindications to Exercise Testing and Training	Precautions Requiring Modification and/or Physician Approval
Factors related to cancer treatment	No exercise on days of intravenous chemotherapy (recommendation changing)	Caution if on treatments that affect the lung and/or heart: recommend medically supervised exercise testing and training
	No exercise before blood draw	Mouth sores/ulcerations: avoid mouthpiece for maximal testing: use face mask
	Severe tissue reaction to radiation therapy	Lymphedema: wear appropriate compression garments
Hematologic	Platelet count <50,000	Platelets >50,000–150,000: avoid tests or exercise (contact sports) that increase risk of bleeding
	Hemoglobin level <10.0 g/dL	White blood cells >3,000-4,000: ensure proper sterilization of equipment
	Absolute neutrophil count <0.5 × 109/L	Hemoglobin >10 g/dL to 11.5–13.5 g/dL: caution with maximal tests
		Avoid activities that may increase the risk of bacterial infection (swimming)
Musculoskeletal	Extreme fatigue/muscle weakness	Any pain or cramping: investigate
	Bone, back, or neck pain	Osteopenia: avoid high-impact exercise if risk of fracture
	Severe cachexia (loss of >35% premorbid weight)	Loss of muscle mass limits exercise to mild intensity
	Karnofsky performance status score <60%; poor functional status: avoid exercise testing	Cachexia: multidisciplinary approach to exercise
Systemic	Acute infections	May indicate systemic infection and should be investigated; avoid high-intensity exercise
	Febrile illness: fever >100 F	Avoid exercise until asymptomatic for >48 hours
	General malaise
Gastrointestinal	Severe nausea	Compromised fluid and/or food intake: recommend multidisciplinary approach/consultation with nutritionist
	Dehydration	Ensure adequate nutrition with electrolyte drinks and water (avoid hyponatremia)
	Vomiting or diarrhea within 24–36 hours
	Poor nutrition: inadequate fluid and/or intake
Cardiovascular	Chest pain	Exercise is contraindicated (refer to physician)
	Resting HR >100 BPM or <50 BPM	Caution: recommend medically supervised exercise testing and training
	Resting SBP >145 mmHg and/or DBP >95 mmHg
	Resting SBP <85 mmHg
	Irregular HR	Exercise is contraindicated (refer to physician)
	Swelling of ankles	Lymphedema: wear appropriate compression garments
Pulmonary	Dyspnea	Mild to moderate dyspnea: avoid maximal tests
	Cough, wheezing	Avoid activities that require significant oxygen transport (high-intensity X)
	Chest pain increased by deep breath
Neurologic	Ataxia/dizziness/peripheral sensory neuropathy	Avoid activities that require significant balance and coordination (treadmill)
	Significant decline in cognitive performance	Ensure patient is able to understand and follow instructions
	Disorientation	Use well-supported positions for exercise
	Blurred vision

Adapted from McNeely et al. (¹⁵).

When there is doubt about the survivor’s health status or a decline in physical functioning, the exercise specialist should refer their clients to their primary care physician or oncologist for further evaluation or clearance to continue with the exercise program.

Practical Advice

Medical History

When prescribing exercise for cancer survivors, a careful review of an extensive medical and cancer history (including stage based on TNM status, treatment including all drugs, radiation treatment [dose and time course], surgery, and any adjuvant therapy) is required (^19,20). In addition, because cancer is typically a disease of older individuals, comorbidities, such as cardiovascular, pulmonary disease, and diabetes, should be evaluated and appropriate precautions taken to ensure survivor safety.

Monitoring

It is important to monitor hematologic abnormalities, and it is recommended that cancer survivor assessment includes complete blood counts, physical assessment (cardiovascular health, muscular strength and endurance, balance/coordination, body composition, and range of motion), and quality of life assessment (¹). Clinical assessments may include pulmonary function testing to evaluate potential pulmonary fibrosis, heart function assessed by echocardiography to detect subclinical cardiomyopathy, neurologic examination to assess the severity of chemotherapy-induced peripheral neuropathy and pain, and a DXA scan to evaluate bone mineral density (²¹). Physician (oncologist or primary care) assent should be obtained for all cancer patients starting an exercise program that includes vigorous exercise intensity.

Sidebar: Definitions

Cancer — A term for diseases in which abnormal cells divide without control and can invade nearby tissues. Carcinoma is a cancer that begins in the skin or in tissues that line or cover internal organs. Sarcoma is a cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue. Leukemia is a cancer that begins in blood-forming tissue, such as the bone marrow, and causes too many abnormal blood cells to be made. Lymphoma and multiple myeloma are cancers that begin in the cells of the immune system. Central nervous system cancers are cancers that begin in the tissues of the brain and spinal cord.

Cancer survivor — A person is considered to be a survivor from the time of diagnosis until the end of life.

Cancer survival rate — The survival rate is often stated as a 5-year survival rate, which is the percentage of people in a study or treatment group who are alive 5 years after their diagnosis or the start of treatment.

Exercise oncology — evaluation of physical activity on cancer treatment and prognosis

Exercise prescription

Individualized exercise prescriptions for cancer survivors should address all components of fitness based on the recommendations from the 2019 ACSM consensus statement on exercise guidelines for cancer survivors (¹). However, cardiovascular conditioning should be a focus of the training plan for cancer survivors as there is a clear relationship between cardiorespiratory fitness and decreased mortality in this group (²²).

In general, the classification of aerobic fitness based on cancer survivor–specific V˙O_2peak values are typically well below healthy age-matched peers and therefore would be considered “poor.” Low aerobic fitness due to complications from cancer treatment may require physical therapy and modification to the exercise prescription. Regardless, aerobic training for all fitness levels should be incorporated at least three times per week for ~30 minutes at low to moderate intensity for 8 to 12 weeks at the beginning phase of rehabilitation. This time allows for the evaluation of heart rate and blood pressure responses to exercise and to gauge whether an individual has the endurance capacity to complete future 30- to 60-minute aerobic sessions. In general, the cancer survivor should be able to complete 30 minutes of continuous exercise in a single session before starting HIIT.

After a general aerobic base training of 2 to 3 months, HIIT sessions can then be incorporated into the exercise program. HIIT can be prescribed twice per week with approximately 48 hours between each HIIT session with each session 30 to 60 minutes in duration. Each session should consist of a dynamic warm-up of 5 to 10 minutes at low to moderate intensity, followed by the interval conditioning phase of the session and culminating with a 10-minute cool-down period and/or stretching.

The intensity of the interval should be based on a percentage of peak heart rate (measured), V˙O_2peak (measured), or heart rate reserve whereby maximal heart rate is measured rather than estimated. Ranges for effective interval intensity are from 80% to 100% of peak heart rate (measured), 60% to 90% heart rate reserve when maximal heart rate and resting heart are available, and 60% to 90% of V˙O_2peak (measured). Rating of perceived exertion has been used effectively to prescribe exercise intensity and should be between 7 and 9 on a modified Borg CR-10 scale or between 14 and 17 on the original 6 to 20 scale.

The number of intervals in a session is dependent on the work-to-rest ratio, and in the literature, it ranges from 15- and 30-second sprint intervals to 1-, 2-, 3-, 4-, and 5-minute high-intensity intervals followed by 1 to 3 minutes of recovery between repetitions. Superior increases in aerobic capacity were seen with programs consisting of 4 × 4-minute intervals with a 3-minute rest between repetitions (^14,18).

The rate of progression is based on client fitness, training response, and individual goals. Progression for interval training can include increasing the number of intervals and/or decreasing the rest duration and increasing the length of each interval. Progression volume should not exceed 10% in the subsequent week to minimize risk of injury, muscle soreness, undue fatigue and long-term risk of overtraining (²³). This is especially a concern if the cancer survivor is anemic or has low red blood cell counts (Table 4).

TABLE 4 - Summary of HIIT for Cancer Survivors after an 8- to 12-wk Aerobic Base Conditioning Program

Frequency	2× per Week	Minimum 48 Hours between Sessions
Intensity	80%–100% HRpeak	60%–90% HRreserve	60%–90% V˙O2peak
Time (total)	30–60 minutes	Dynamic warm up 5 minutes	Interval session (variable set and reps)	Cool-down 5–10 minutes
Type	Treadmill walking (inclined)	Jogging/running	Stationary cycling
Volume	1–4 sets	2–4 minutes duration	~3-minute rest between intervals or sets
Progression	≤10% increase in volume from previous week

Precautions

Client safety is crucial when working with cancer patients who may have compromised immune systems, subclinical cardiomyopathy, and other comorbidities. Practitioners should monitor heart rate, blood pressure, and if available, oxygen saturation, during a client’s first HIIT session to ensure appropriate hemodynamic response to exercise. Clients should be instructed to decrease and/or stop the workload if they are dizzy, are ataxic, have chest pain, and/or have serious difficulty breathing. Appropriate emergency equipment, including oxygen, should be available for cancer patients who are exercising in a commercial setting.

Future Research

Exercise oncology has produced tremendous advances in exercise programming for cancer survivors. Through trial and error, observation, and a limited number of randomized controlled exercise training studies, evidence is moderate to strong that exercise is both beneficial and safe for cancer survivors after treatment. Advances in the dosing of exercise and addition of strategies such as HIIT show promise and should be considered as part of a practitioner’s approach to exercise prescription. For researchers working in exercise oncology, reporting the dose of exercise used in interventional studies should clearly address frequency, intensity, time, type, volume, and progression (FITT-VP principle). Other areas of interest in exercise oncology include prehabilitation strategies (^19,24) to increase fitness before chemotherapy treatment and exercise training during chemotherapy infusion.

BRIDGING THE GAP

Based on the currently available evidence, HIIT training is safe, tolerable, and effective as part of a comprehensive cancer rehabilitation program. Cancer survivors who are relatively healthy after treatment can add vigorous intensity to their rehabilitation/training programs to be time efficient. An extensive medical and cancer history and physician clearance should be obtained before prescribing HIIT training to your clients.