Exercising with Asthma: A Slow Burn or a Quick HIIT?

Long-term asthma control is determined both by adherence to an appropriate pharmacologic regimen and by lifestyle contributors. Aerobic exercise is a prominent example of how healthy lifestyle can affect the disease course of asthma. Patients with asthma who consistently engage in physical activity have improved disease control, quality of life, and lung function parameters.¹ On the other hand, low levels of physical activity in asthma are associated with increased health care utilization and associated costs.¹ Most asthma providers recognize the positive effects of physical activity and recommend that their patients engage in it.² The “right” type of aerobic exercise is likely to vary between individual patients with asthma; however, little is known about the relative effects of exercise intensity level on asthma outcomes.

High-intensity interval training (HIIT) is a form of cardio-aerobic exercise in which an individual’s activity routine is divided into discrete periods of variable exertion, alternating between high-exertion phases that approach the person’s physiologic threshold and lighter-exertion, or “recovery,” phases. The advantages of HIIT include a higher maximal level of intensity than other exercise regimens and, thus, the ability to achieve a targeted level of effort over shorter time. Accordingly, a 2021 work group report of the American Academy of Allergy, Asthma, and Immunology’s Sport, Exercise and Fitness Committee noted that HIIT may be a particularly good option for patients with limited time to pursue physical activity.³ Prior studies have demonstrated that, like constant-load exercise (CLE), HIIT interventions promote improved health outcomes in patients with asthma.⁴ A recent systematic review found that HIIT and a similar type of exercise, sprint interval training, were comparable to other exercise methods in the degree of improvement seen across numerous clinical asthma outcomes.⁵ The review also acknowledged that no significant improvements in lung function measures, including forced expiratory volume in 1 second (FEV1), forced vital capacity, and forced expiratory flow at 25% to 75% of forced vital capacity, could be consistently achieved with HIIT. The review authors concluded that high-quality randomized controlled trials are needed before conclusions can be drawn about the beneficial effects of HIIT over traditional CLE in asthma.

In “Constant-load exercise versus high-intensity interval training on aerobic fitness in moderate to severe asthma,” Da Silva et al⁶ randomized patients with moderate or severe asthma into 2 intervention arms: HIIT and CLE. Twenty-eight patients in the HIIT group and 27 in the CLE group participated in 40-minute training sessions, twice weekly, for a 12-week period. Aerobic exercise was performed on a cycle ergometer. Although the exercise workload in each intervention arm was gradually increased over the study period, there was a large difference in maximum work levels attained. By week 12, participants randomized to HIIT were performing bursts of exercise at 140% of their baseline maximum intensity, whereas participants randomized to CLE were performing a continuous session at 100% of their baseline maximum.

Da Silva et al examined a varied set of outcomes, including exercise tolerance, asthma control, quality of life, pulmonary function measurements, pulmonary inflammation, and systemic inflammation. Both HIIT and CLE produced improvements in aerobic fitness and some clinical outcomes, such as reduced anxiety. Neither intervention led to a change in the pulmonary or systemic inflammatory profile. Although HIIT participants expended greater energy over the study period, there was no significant difference between them and CLE participants in physical activity level, pulmonary function, asthma control, or health-related quality of life (HRQOL). However, where changes from baseline were observed, the magnitude of effect was larger in the HIIT group in 7 of 9 outcomes. As a result, only HIIT participants reached the minimal clinically important difference in asthma control and HRQOL scores. Interestingly, the most persistent improvement observed in the HIIT group was in psychosocial distress, with a lasting reduction in depression and anxiety scores noted 3 months after the intervention.

The mechanisms behind the larger asthma benefits with HIIT are unclear. The benefits of HIIT exercise in other respiratory diseases (chronic obstructive pulmonary disease [COPD]) have been attributed to a reduction in systemic inflammation.⁷ Yet no changes in airway or systemic inflammation were observed in the Da Silva et al study. In addition to being an inflammatory lung disorder, asthma is also a disease of the airway smooth muscles. However, the authors do not directly address the possibility that respiratory mechanics and inspiratory muscles may change in response to exercise modalities that vary in their maximum intensity. In contrast to the evidence in asthma, a systematic review in patients with COPD after HIIT revealed modest improvement in FEV1 and other lung function parameters.⁸ It is unclear whether this discrepancy between asthma and COPD is attributable to differences in inflammatory profile or respiratory mechanics between the 2 pathologies.

The exercise instrument used in this study was a cycle ergometer, which the authors note, “.allows for increases in the workload and quick interruptions during the training exercise ” However, it is not known if other modes of HIIT exercise, for instance running or rowing, would produce similar results. Further, the study had a high dropout rate with almost 30% of participants dropping out of both groups. The reasons for this are unknown, but in participants who are new to exercise, HIIT can cause greater distress and injury (eg, dizziness, muscle soreness) and lead people to stop or avoid exercise. Qualitative data on patient preference, ability, experience, and/or the use of validated questionnaires that assess exercise self-efficacy and outcome expectations for exercise should be incorporated into future studies of physical activity interventions in asthma to better understand preferences and reasons for dropping out.^9,10 Additional research questions remain, such as “What is the effective ‘dose’ of exercise needed to generate improved asthma outcomes?” and “What is the sustainability of exercise interventions such as HIIT?” Answers to these and more questions will help researchers to develop an exercise prescription that health care providers can give to their patients with asthma and integrate into the management of asthma.