Interval training confers greater gains than continuous training

Blikk på forskning utarbeides i samarbeid med Journal of Physiotherapy (Australia), som trykker forskningspresentasjonene under betegnelsen Critically appraised Papers, CAPs.

Synopsis

Summary of: Wisloff U et al (2007) Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients: a randomized study.Circulation115: 3086–3094. [Prepared by Kylie Hill, CAP Editor.] 

Question: Is aerobic interval training (AIT) more effective than moderate continuous training (MCT) at enhancing aerobic fitness and myocardial remodelling in patients with stable heart failure?

Design: Randomised controlled trial in which participants were allocated to AIT, MCT, or a control group.

Setting: Hospital in Trondheim, Norway.

Participants: Adults with stable heart failure post myocardial infarction with left ventricular ejection fraction (EF) < 40% on optimal medical management. Exclusion criteria comprised: unstable angina pectoris, uncompensated heart failure, myocardial infarction within four weeks, complex ventricular arrhythmias, no use of β-blockers and ACE inhibitors or, any other limitation to exercise. Randomisation of 27 patients allocated nine to each group.Interventions: The AIT and MCT groups completed two supervised exercise training sessions and one home training session each week for 12 weeks. Those in AIT completed uphill treadmill walking that comprised a warm-up and cool down interspersed with 4 × 4 minute exercise intervals completed at 90–95% of peak heart rate. Intervals were separated by three minutes of walking at 50–70% of peak heart rate (total exercise time = 38 minutes). The MCT participants walked continuously for 47 minutes at 70–75% of peak heart rate. Weekly home training comprised outdoor hill walking. The control group completed 47 minutes of supervised treadmill walking at 70% of peak heart rate once every three weeks.

Outcome measures: The primary outcomes related to exercise capacity (eg, peak rate of oxygen uptake; VO2peak); secondary outcomes comprised measures of echocardiography and endothelial function.

Results: Outcomes were available from 26 participants. The VO2peak achieved on completion of training was greater in the AIT group compared with the MCT group (mean difference 4.1; 95% CI 2.4 to 5.8 ml/kg/min) and the control group (5.8, 95% CI 3.8 to 7.8 ml/kg/min). Compared with the other groups, AIT also conferred greater gains in measures of systolic and diastolic function and endothelial function.

Conclusion: In adults with stable heart failure, AIT conferred greater gains than MCT in improving aerobic capacity and measures reflecting left ventricular and endothelial function.

[Mean difference and 95% CIs calculated by the CAP Editor] 

Commentary

A key objective of clinical exercise prescription is optimising physiological adaptations without placing the patient at risk of exercise-induced events. In patients with heart failure, who are at the higher end of the risk spectrum, exercise has historically been prescribed at moderate intensities approximating 60% of measured peak VO2peak (70% of HRpeak) (Pina et al 2003). This intensity is well tolerated, with no exercise-related deaths reported in a systematic review of published exercise training involving over 100 000 patient hours of exercise (Smart 2011). Wisloff et al (2007) evaluated a novel, high intensity aerobic interval training (AIT) approach and found this produced significant benefits over moderate, continuous aerobic exercise. These findings raise the question: has the traditional approach been too conservative? Before exercise practitioners rush to adopt high intensity exercise prescription in clinical groups, such as heart failure, several salient points related to the study should be considered: first, the investigators were a highly trained and specialised group which included cardiologists; second, the study was performed in carefully screened and selected patients who were clinically stable and on optimal medical therapy; and third, all participants were at least 12 months post myocardial infarction. Accordingly, their risk of adverse events is markedly less than for many patients referred to clinical programs. Importantly, the study documents only 200 hours of experience with AIT, a ‘drop in the ocean’ compared with that of moderate continuous aerobic exercise, so assumptions about safety are premature. Also noteworthy is that perceived exertion levels during AIT averaged 17 (‘very hard’). Ongoing adherence to such effort requires high personal motivation, a trait less common in the broader patient population than study volunteers. The study by Wisloff et al (2007) challenges convention. However, practitioners should always apply due prudence when translating research into clinical practice. 

Andrew Maiorana, Advanced Heart Failure and Cardiac Transplant Service, Royal Perth Hospital and Curtin University, Australia 

References

Pina IL et al (2003)Circulation107: 1210–1225.

Smart N (2011)Cardiol Res Pract: Article ID 837238.

Wisloff U (2007)Circulation115: 3086–3094.