Active Voice: Exercise Volume is Paramount for Improving Health in Unfit Individuals with Metabolic Syndrome
By Ricardo Mora-Rodriguez, Ph.D., and Felix Morales-Palomo, Ph.D.
Hypertension, abdominal obesity, fasting hyperglycemia and dyslipidemia (high blood triglycerides and low HDL-cholesterol) are the components of metabolic syndrome (MetS). MetS is an increasingly prevalent clinical condition that, if untreated, often leads to type 2 diabetes and cardiovascular diseases. Lifestyle interventions that include exercise training have demonstrated positive health outcomes for people with MetS, including favorable changes in multiple measures associated with the condition (see Ostman et al., Cardiovasc Diabetol 2017). For example, 12-24 weeks of aerobic exercise training, carried out three days per week, has been shown to result in successful reductions in MetS components. However, debate continues about the type of aerobic exercise training that is more effective on reversing and halting MetS progression.
Because lack of time is one barrier to engaging in regular exercise, aerobic training programs using low-volume, high intensity interval training (HIIT) have enjoyed increased popularity. Recent data supports that HIIT is as effective as moderate-intensity continuous training (MICT) for boosting cardiorespiratory fitness (CRF), lowering blood pressure and achieving cellular oxidative adaptations. Even HIIT composed of one-minute bouts of very intense exercise (1HIIT), near an individual’s peak aerobic capacity, will increase muscle mitochondrial capacity. However, the effects of 1HIIT in the improvement of MetS components are unclear. On the other hand, a seminal study analyzing different continuous aerobic training protocols (STRRIDE study) suggests that training volume is a stronger determinant than exercise intensity for achieving improvements in the MetS components.
In our investigation, as reported in the September 2019 issue of Medicine & Science in Sports & Exercise®, we studied 121 individuals with MetS. Our overall sample was comprised of middle-aged men and women, 57 years old, regarded as low-fit (VO2peak 24 ml·kg-1·min-1) and obese (BMI 32.5 kg/m2). Approximately 47% of the subjects were women. Subjects were randomized into four groups for the study. Three of the groups completed four months of exercise training, while one group remained sedentary (control). One of the training groups underwent MICT (one x 50 minutes at 70% HRMAX), while the other two exercise groups completed one of two forms of HIIT. One of those groups did four-minute bouts (4HIIT; four x four minutes at 90% HRMAX for 43 minutes) and the other did one-minute bouts (1HIIT; 10 x one minute at 100%HRMAX for 35 minutes). We measured the evolution of the MetS components over the training period using a compound score (MetS Z score), as well as CRF (VO2peak as the surrogate).
Analysis of our findings showed no differences in CRF improvements among training programs (11%, 12% and 14% gains for 4HIIT, MICT and 1HIIT, respectively), when compared to the sedentary control group. Thus, any aerobic training program lasting 16 weeks, with a frequency of three times per week, is enough stimulus to raise CRF in low-fit individuals with MetS. However, we also found that the more intense but shorter 1HIIT training program was not effective for improving MetS.
The reasons why 1HIIT did not reduce the MetS Z score are unclear. Although the 1HIIT was very intense (100% HRMAX), the exercise sessions were only 35 minutes and less energy-demanding than the other two exercise types. Energy expenditures were 873 versus 1,320 kcals·week-1 for 1HIIT vs MICT-4HIIT, respectively. Thus, exercise volume and/or the associated energy expenditure seem to be the main factors for improving MetS. The exercise type (continuous versus intermittent) or intensity (70% versus 100% HRMAX) seem to be of lesser importance for achieving outcomes in this population of low-fit, obese individuals with MetS.
Our findings simplify exercise advice in this population to aerobic training (any type) that amounts to a weekly energy expenditure above 1,000 kcals. It also discourages the use of 1HIIT and thus, resolves the concerns about using very intense HIIT as a training mode for people with a deteriorated cardiovascular system.
About the authors:
Ricardo Mora-Rodriguez, Ph.D., is a professor of exercise physiology in the department of sport sciences at the University of Castilla-La Mancha in Spain. During the last decade, his research has focused on understanding how exercise improves the health of obese-metabolic syndrome individuals. Dr. Mora-Rodriguez is a member of ACSM.
Felix Morales-Palomo is a recent Ph.D. graduate from the department of sport sciences at the University of Castilla-La Mancha. He currently holds a post-doctoral research position in the department.
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