Exercise as it relates to Disease/Treating the metabolic syndrome: aerobic interval training vs. continuous moderate exercise
This Wikibooks page is an analysis of the journal article "Aerobic interval training vs. continuous moderate exercise as a treatment for the metabolic syndrome - “A Pilot Study”" (2008)
What is the background to this research?
The metabolic syndrome is a cluster of cardiovascular and metabolic risk factors with formal definitions varying worldwide. The World Health Organisation (WHO) has defined the metabolic syndrome as the presence of one of diabetes mellitus, impaired glucose tolerance, impaired fasting glucose, or insulin resistance in the presence of two of high blood pressure, dyslipidaemia, central obesity or microalbuminuria. With increasing worldwide prevalence, the metabolic syndrome is of great importance due to its links to type 2 diabetes mellitus, cardiovascular disease and all-cause mortality.
A mounting body of evidence states that exercise can reverse the negative effects of the metabolic syndrome due to improvements in endothelial function, insulin sensitivity and aerobic capacity. Despite this, it is still unclear which form of exercise is best for the treatment of the metabolic syndrome.
Studies have investigated aerobic interval training (AIT) and continuous moderate exercise (CME) for improving VO2max. VO2max is an indicator of how efficiently the body can utilise oxygen at peak aerobic performance. Low VO2max is strongly linked to cardiovascular mortality. Evidence shows that AIT is more effective for improving VO2max than CME. However, it is yet to be determined which type of exercise is best for targeting the metabolic syndrome. In this study, the authors have addressed this question and have highlighted the need for future studies in this area.
Where is the research from?
This study was conducted by researchers from the Norwegian University of Science and Technology, Trondheim, Norway and the University of Toledo College of Medicine, Ohio, USA. The research was led by Arnt Erik Tjønna, an engineer/researcher at the Norwegian University of Science. Since 2002, he has been involved in numerous studies into the effects of aerobic interval training and physiological adaptations to exercise training.
What kind of research was this?
This study was a randomised controlled trial (RCT). RCTs are considered by the National Health and Medical Research Council evidence hierarchy as level 2 evidence. Systematic reviews are the highest form of evidence, as they review of a number of RCTs. This study had a relatively small sample size of 32. This number could have been increased to improve the strength of the study. However, as a pilot study, the authors were not seeking to make definitive results, but rather to justify future large studies.
What did the research involve?
Participants with metabolic syndrome as defined by the WHO criteria were included for the trial. Participants were randomised to one of three groups: AIT, CME or no intervention. VO2max testing was conducted on all subjects to determine baseline fitness data and to calculate maximum heart rate (HRMax). Blood samples, endothelial function, blood pressure and tissue biopsies of the vastus lateralis muscle and gluteal fat pad were taken of all participants in accordance with clinical guidelines.
The AIT group completed exercise sessions 3 times per week for 16 weeks. During each session, the participants completed a 10-minute warm up consisting of treadmill running at 70% HRMax. Participants completed 4x4 minute intervals of treadmill exercise at 90% HRMax with 3-minutes recovery at 70% HRMax between intervals. Participants finished with a 5-minute cool down period.
The CME group also exercised 3 times per week for 16 weeks. Their workouts consisted of continuous treadmill running or walking for 47 minutes while maintaining their heart rate at 70% HRMax.
The control group had no intervention from the researchers. Instead, they followed advice from family physicians.
After the 16-week period, measures were taken of VO2max, blood profiles, blood pressure and tissue biopsies. Statistical analysis was then conducted on the results using a paired T-test.
The authors have detailed their protocols well throughout the study. Using a patient specific variable like HRMax is an effective way to differentiate between the AIT and CME protocols rather than using set exercise protocols. The control group was not well regulated and may have exercised throughout the duration of the study. Tighter regulation of the control group would strengthen comparisons between groups. Several thorough investigations provided the researchers with an array meaningful data with a focus on VO2max.
What were the basic results?
Tjonna and colleagues  found participants were comparable at baseline for body weight, body mass index, waist-to-hip circumference, blood profiles and blood pressures. 4 participants were unable to complete the study or withdrew from the study. As 87.5% of participants were followed up, the margin for bias here is low.
After the 16-week program, there was a 46% reduction in the number of participants with metabolic syndrome in the AIT group. The CME group was comparatively worse with a 37% reduction. Improvements in endothelial flow mediated dilation of 9% and 5% for the AIT and CME groups respectively were recorded. Insulin sensitivity and fasting glucose levels were also improved in the AIT group compared to the CME group, however both groups improved. The authors correctly claim that these results are valid and significant.
VO2max increased in the AIT and CME groups by 35% and 16% respectively. PGC-1a, a coordinator of metabolic genes responsible for muscle activity increased by 138% in the AIT group. This resulted in increased Ca2+ uptake by the sarcoplasmic reticulum, which is an important adaptation related to VO2max. The authors appropriately draw attention to VO2max given its link to mortality. It is clearly appropriate for the authors to claim that AIT is more effective than CME in improving VO2max in people with the metabolic syndrome.
What conclusions can we take from this research?
Both AIT and CME clearly have an effect in reducing the prevalence of clinically diagnosed metabolic syndrome. AIT and CME have also been shown to improve VO2max in people diagnosed with the metabolic syndrome. This study indicates that AIT is more effective in attaining these adaptations than CME.
The researchers have conducted a study with well targeted interventions and thorough measurements of important variables. From this, we can gain a further understanding of the most effective exercise treatment for the metabolic syndrome. However, this study has some clear limitations. The small sample size influences the strength of the findings. Therefore, these findings should be interpreted with some caution. Future large studies are needed to conclusively determine whether AIT is more effective in treating the metabolic syndrome than CME.
For people diagnosed with metabolic syndrome per the WHO criteria, AIT and CME exercise are both effective in reversing the condition. AIT may be more beneficial, although further large studies are needed. Before undertaking exercise, consult your doctor for exercise pre-screening.
For further information regarding the metabolic syndrome and aerobic interval training, click on the links below:
- What is Metabolic Syndrome? https://www.nhlbi.nih.gov/health/health-topics/topics/ms
- Definition of Metabolic Syndrome: http://circ.ahajournals.org/content/109/3/433.long
- High Intensity Interval Training: http://www.acsm.org/docs/default-source/files-for-resource-library/high-intensity-interval-training.pdf
- Tjonna AE, Lee SJ, Rognmo O, Stolen TO, Bye A, Haram PM, et al. Aerobic interval training versus continuous moderate exercise as a treatment for the metabolic syndrome: a pilot study. Circulation. 2008;118(4):346-54.
- Alberti KG, Zimmet PZ. Definition, diagnosis and classification of diabetes mellitus and its complications. Part 1: diagnosis and classification of diabetes mellitus provisional report of a WHO consultation. Diabet Med. 1998;15(7):539-53.
- Lakka HM, Laaksonen DE, Lakka TA, Niskanen LK, Kumpusalo E, Tuomilehto J, et al. The metabolic syndrome and total and cardiovascular disease mortality in middle-aged men. JAMA. 2002;288(21):2709-16.
- Meigs JB. Metabolic syndrome: in search of a clinical role. Diabetes Care. 2004;27(11):2761-3.
- Rognmo O, Hetland E, Helgerud J, Hoff J, Slordahl SA. High intensity aerobic interval exercise is superior to moderate intensity exercise for increasing aerobic capacity in patients with coronary artery disease. Eur J Cardiovasc Prev Rehabil. 2004;11(3):216-22.
- Helgerud J, Hoydal K, Wang E, Karlsen T, Berg P, Bjerkaas M, et al. Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sports Exerc. 2007;39(4):665-71.
- Huang PL. A comprehensive definition for metabolic syndrome. Dis Model Mech. 2009;2(5-6):231-7.
- Tjonna AE. Employees 2017 [Available from: https://www.ntnu.edu/employees/arnt.e.tjonna.
- Merlin T, Weston A, Tooher R. Extending an evidence hierarchy to include topics other than treatment: revising the Australian 'levels of evidence'. BMC Med Res Methodol. 2009;9:34.