The effects of HIIT appear to be comparable to those of continuous exercise in relation to functional and cardiovascular responses .
OBJECTIVE To evaluate the effects of high-intensity interval training ( HIIT ) , in comparison with those of continuous exercise , on functional capacity and cardiovascular variables in patients with COPD , through a systematic review and meta- analysis of r and omized controlled trials .
Interval versus Continuous High-Intensity Exercise in Chronic Obstructive Pulmonary Disease
Context Exercise training improves quality of life in patients with chronic obstructive pulmonary disease , but many of these patients can not tolerate continuous exercise . The effects of intermittent exercise are not known . Contribution The authors r and omly assigned 100 in patients with chronic obstructive pulmonary disease in a 3-week respiratory rehabilitation program to receive either high-intensity continuous exercise or high-intensity exercise alternating with low-intensity exercise ( interval exercise ) . After 5 weeks , the 2 groups had similar respiratory symptoms in daily activities and 6-minute walking distance , but the interval exercise group adhered better to the exercise protocol . Caution s The study focused on initiation of exercise and not on outpatient or home-based maintenance of exercise . Implication s For pulmonary rehabilitation , interval exercise is as effective as continuous high-intensity exercise and is better tolerated . The Editors Low exercise capacity is an important systemic manifestation of advanced chronic obstructive pulmonary disease ( COPD ) associated with poor health-related quality of life , exacerbations , and death ( 14 ) . Physical exercise , therefore , represents an important element of COPD management ( 5 , 6 ) . If performed under supervision during respiratory rehabilitation , exercise training improves health-related quality of life and may improve prognosis ( 79 ) . Dyspnea and leg fatigue limit the ability of patients with COPD to exercise , and patient response to exercise is highly variable ( 10 ) . It is challenging to find endurable exercise programs that are still effective . Current guidelines recommend endurance exercise at constant and high intensity ( 70 % of maximum exercise capacity ) ( 11 , 12 ) . For example , if a patient achieves 100 watts in an incremental exercise test , workload would be set at 70 watts for the entire exercise session of at least 20 minute 's duration . Strong evidence from r and omized trials shows that patients achieve clinical ly important improvements of health-related quality of life and exercise capacity with a continuous exercise protocol ( 1316 ) . However , patients with severe COPD are often unable to tolerate continuous exercise ( 17 ) , which can be frustrating for them and can limit their long-term adherence to exercise programs . Effective alternatives to continuous exercise are required to offer this important intervention to more patients with COPD . The American Thoracic Society and the European Respiratory Society state , on the basis of 2 r and omized trials ( 18 , 19 ) , that interval exercise may be an alternative . The benefits of interval exercise may be similar to those of continuous training , but this method is associated with less dyspnea ( 11 , 12 ) . Although studies indicated that interval exercise is well tolerated ( 1821 ) , evidence about its effectiveness relative to continuous exercise is inconclusive ; previous trials had method ological limitations and were small ( 22 ) . Because of perceived better tolerability of interval exercise , r and omized trials should be explicitly design ed to show that interval exercise is no less effective ( clinical noninferiority ) ( 22 ) . Thus , the aim of our trial was to assess whether interval exercise is no less effective than high-intensity continuous exercise in patients with severe COPD and whether patient tolerance of the interval exercise protocol is superior to that of continuous exercise . Methods Design Overview We conducted a r and omized , controlled noninferiority trial to compare the effects of interval exercise with those of high-intensity continuous exercise in patients with severe COPD . We previously described the detailed study protocol ( 23 ) and report this trial following the recommendations of the extended Consoli date d St and ards of Reporting Trials ( CONSORT ) statement for noninferiority and equivalence trials ( 24 ) . Setting The trial took place in a public rehabilitation clinic , Klinik Barmelweid , in Aargau , Switzerl and . The ethics committee of the Kantonsspital Aarau , Aargau , Switzerl and , approved the study protocol , and all study participants provided written informed consent . Participants We screened patients admitted to the respiratory medicine unit and included consecutive patients following inclusion criteria similar to those of previous respiratory rehabilitation trials ( 7 ) : COPD as defined by FEV1FVC ratio less than 70 % of predicted , FEV1 less than 50 % of predicted after bronchodilation corresponding to Global Initiative for Chronic Obstructive Lung Disease ( GOLD ) stage III to IV ( 5 ) , and German as first or daily language . Exclusion criteria included cardiovascular , musculoskeletal , or neurologic disorders that inhibited physical exercise or the performance of exercise tests ( 6 ) . We also excluded patients who had received a diagnosis of cancer ( excluding skin cancer ) within the past 2 years and were undergoing treatment . R and omization and Interventions A third party not involved in the execution of the trial ( DatInf GmbH , Tuebingen , Germany ) provided online central r and omization using a computerized minimization procedure , thereby ensuring concealment of r and omization ( 25 ) . Stratification variables were exercise capacity ( 6-minute walking distance < 300 or 300 meters ) , the presence of affective disorders ( Hospital Anxiety Depression Scale scores < or 8) , stability of pulmonary condition ( stable or exacerbation within the last 8 weeks ) , and the need for oxygen at rest ( Pao 2 < 55 mm Hg or 55 mm Hg ) . Patients followed an inpatient respiratory rehabilitation of approximately 3 week 's duration that included 12 to 15 exercise sessions . On weekdays , patients usually participated in 1 exercise session .  Twelve physical therapists worked with an approximately equal number of patients from both treatment groups . Apart from exercise , the rehabilitation program was identical for both groups and included breathing therapy , relaxation therapy , guided walking tours , and patient education ( 23 ) . At discharge , physiotherapists prescribed home-based exercise for each patient . Patients with cycle ergometers at home were instructed to exercise for at least 20 minutes per day . If no cycle ergometers were available , daily walking , swimming , or stair climbing was prescribed . High-Intensity Continuous Exercise Patients r and omly assigned to this intervention exercised on electromagnetically braked cycle ergometers ( Ergometrics 900S , Ergoline , Bitz , Germany ) with a target workload of 70 % or more of maximum exercise capacity ( Figure 1 ) . This exercise protocol has been used in earlier respiratory rehabilitation trials ( 7 ) . To determine maximum exercise capacity , patients pedaled unloaded for 3 minutes at 20 watts to warm up . Then , we used increments of 7.5 watts per minute until patients had to stop because of symptoms or cardiovascular stopping criteria . In each exercise session , patients completed a warm-up period of 2 minutes at 20 % of maximum exercise capacity , high-intensity exercise for 20 minutes , and a run-out phase of 2 minutes ( gradual decrease from 70 % to 0 % ) . If patients could not sustain the workload because of perceived dyspnea ( modified Borg [ 26 ] ratings > 5 on a scale from 0 to 10 ) or because heart rate exceeded safety limits , physical therapists let patients rest for 1 minute before continuing in the assigned phase . If patients had to rest more than twice per session , physical therapists lowered the workload by steps of 10 % of baseline maximum exercise capacity for the following exercise sessions . If workload was too low ( modified Borg ratings < 3 or patients or physical therapists considered the workload to be too low ) , physical therapists increased the workload by steps of 10 % of baseline maximum exercise capacity . Figure 1 . Exercise protocol s. Interval Exercise The target workload for this group was 50 % ( high-intensity intervals ) and 10 % ( low-intensity intervals ) of short-term maximum exercise capacity as determined by a steep ramp test ( 27 , 28 ) . The steep ramp test is an incremental cycle ergometer test in which patients pedal cycle ergometers unloaded for 2 minutes and then at increments of 25 watts every 10 seconds until they can not maintain a pedaling frequency above 50 pedals per minute or their heart rate exceeds the limit set by the normal incremental exercise test . We used the steep ramp test because workload for interval exercise can be underestimated if it is based on normal incremental exercise tests ( 28 ) . Fifty percent of short-term maximum exercise capacity corresponds , on average , to 90 % to 100 % of normal maximum exercise capacity ( 27 ) . We chose a workrecovery ratio of 1:2 that prevents high lactate accumulation and is well tolerated by patients ( 28 ) . In each session , patients had a warm-up period of 2 minutes at 10 % of the short-term maximum exercise capacity and then exercised for 20 minutes alternating between high-intensity intervals for 20 seconds and low-intensity intervals for 40 seconds ( Figure 1 ) . Patients also had a slowdown period of 2 minutes before completing the training session . We adjusted the exercise load for each patient individually if workload was too high or too low as described earlier ; physiotherapists lowered or increased the workload by steps of 10 % of short-term maximum exercise capacity , but the length of intervals remained constant ( 23 ) . Outcomes and Measurements Our primary outcome for effectiveness was the difference from baseline in Chronic Respiratory Question naire ( CRQ ) scores 5 weeks after r and omization as measured by the self-administered German- language version ( 29 , 30 ) with st and ardized dyspnea questions ( 31 ) . The CRQ is a widely used instrument in respiratory rehabilitation and measures dyspnea , fatigue , emotional functioning , and ability to cope with COPD ( 7 , 32 ) . Domain and total ( average of domains ) scores are presented on a Likert-type scale from 1 ( most severe impairment ) to 7 ( no impairment ) . We selected assessment at 5 weeks after r and omization as the primary outcome
The effects of HIIT appear to be comparable to those of continuous exercise in relation to functional and cardiovascular responses .
OBJECTIVE To evaluate the effects of high-intensity interval training ( HIIT ) , in comparison with those of continuous exercise , on functional capacity and cardiovascular variables in patients with COPD , through a systematic review and meta- analysis of r and omized controlled trials .