Exercise as it relates to Disease/Obesity-exercise dose response - How much is enough?

This is a critique of the research paper Effects of the Amount of Exercise on Body Weight, Body Composition, and Measures of Central Obesity: STRRIDE - A Randomized Controlled Study. Slentz, C. et al, 2004, Arch Intern Med, Vol 164, Jan 12, 2004 submitted as an assignment in the unit Health, Disease and Exercise at the University of Canberra, September 2019.

What is the background to this research?

Obesity can be defined as an excess of body-fat mass and is considered to affect over 30% of adults in the USA and account for on third of total mortality. In Australia, rates of obesity are similar to the USA.  Persons who are obese are at increased risk of developing a host of disorders including cardiovascular disease, high blood pressure, diabetes, high levels of blood cholesterol, and stroke.

The financial and social cost of obesity to the Australian economy was estimated to be of the order of $58 billion in 2008. Thus, finding cost-effective and appropriate ways to manage and limit the health and financial costs of obesity is an important social issue. Central obesity, i.e. excess abdominal fat, is of particular concern, as it is strongly linked to a greater increased risk of disease than that associated with excess fat stored elsewhere

The role of exercise in weight management programs has been the subject of much research. The STRRIDE (Studies of a Targeted Risk Reduction Intervention through Defined Exercise) program investigated the impact of exercise volume and/or intensity on a range of cardiovascular risk factors.

The research was conducted between February 1999 and July 2002 and was understood to be the first clinical trial that was designed to assess the separate and combined effects of exercise volume and intensity on various measures of central obesity. As such, the article is critiqued against the level of understanding at the time of publication.

Where is the research from?

The authors are part of the Duke University Medical Center, Durham, North Carolina.

What kind of research was this?

The research comprised a randomised control clinical trial.

A total of 302 persons living the Durham area of NC, who met the following criteria:

• sedentary at commencement of study, i.e. exercised less than once per week
• aged between 40 and 65 years old;
• calculated BMI in the range 25 to 35 (overweight to moderately obese); &
• diagnosed with mild to moderate lipid irregularities

were initially assessed for inclusion in the study. Of these, 182 were included and randomised into one of four groups.

Excluding criteria included:

• high blood pressure and diabetes;
• currently dieting (or intending to diet);
• heart disease, presence of musculoskeletal problems; &
• taking of medication that may cause confounding issues.

Of the 182 persons who commenced the study, roughly 50% were female and 20% were from ethnic minorities.

Exercise sessions were supervised or monitored using a heart rate monitor.

The trials were eventually completed by 120 persons

What did the research involve?

Qualifying participants were randomly split between four groups: Three groups that exercised at different levels of volume and intensity; and a control group that did no exercise.

The three exercise groups were as follows:

• High volume/vigorous intensity - equivalent to 32km per week at 65% to 85% peak VO₂;
• Low volume/vigorous intensity - equivalent to 19.2km per week at 65% to 85% peak VO₂; &
• Low volume/moderate intensity - equivalent to 19.2km per week at 40% to 55% peak VO₂

Specifically, the high volume/vigorous intensity group were required to use 13kcal/kg of body weight per week and the other two groups were required to use 14kcal/kg of body weight per week.

The volume and intensity of the exercise sessions started at lower levels and was increased to the specified level over a period of 2 to 3 months. Once participants had reached the specified levels of volume and intensity, this was maintained for a period of 6 months.

The dietary intake of each participant was controlled. It was a requirement of the study that participants try to maintain body weight throughout the trial and not lose weight. Any change in baseline weight greater than 2.5%, led to a nutritionist reviewing their calorific intake and making recommendations to return body weight to the baseline.

Prior to commencement and at conclusion of the trial the following parameters were measured:

• Height (to nearest 0.64cm);
• Weight (in light clothing without shoes to nearest 100g);
• Body composition - sum of 4 skinfolds (triceps, suprailiac, abdominal, and thigh);
• Abdominal waist circumference;
• Minimum waist circumference;
• Hip circumference; &
• Thigh circumference.

What were the basic results?

Participants in all of the exercise groups generally showed improvements or stability in some or all measures of central obesity when compared with the control, non-exercising group.

A clear dose-response was demonstrated, with the high-volume/high-intensity group realising the best results, followed by low-volume/high-intensity and then the low-volume-moderate-intensity groups.

The results showed that the non-exercising group gain weight during the study, with no corresponding increase in calorific intake.

The non-exercising group also showed an increase in excess abdominal fat.

What conclusions can we take from this research?

The research indicates that even a low level of regular exercise at moderate intensity can stabilise and maintain measures of central obesity. Increased levels of exercise both in terms of volume and intensity may be necessary for weight loss and reductions in other measures.

One outcome that contradicts other research was that exercise did not appear to specifically reduce levels of excess abdominal fat. However, it was observed that the non-exercise group increased levels of excess abdominal fat from baseline. This result appears to indicate that even low levels of exercise can stabilise markers of central obesity. Stabilisation and maintaining markers of central obesity can be considered to be a positive outcome as risk factors are not increasing.

Practical advice

The research led to evidenced based information to support recommendations relating to the levels of exercise (volume and intensity) required to either maintain or reduce weight, assuming no change in calorific intake. This was an important as it could guide physicians when making recommendations to patients about how exercise can help managing their risk profile. It also provided evidence based information to help health authorities develop guidelines on exercise and health.

Further information/resources

This research formed part of the STRRIDE clinical trials. Several other papers of interest were also published relating to this research. A good introduction to the trials is provided by Kraus et al. Several other papers present specific findings from the trials.

Of particular interest is a paper published by Johnson et al in 2019 reporting on the ten-year legacy effects of the STRRIDE trials. This article discusses the findings of a ten-year follow-up study of 161 participants of the original STRRIDE clinical trials. A major question around exercise (and other short-term, supervised interventions) is whether there are any long-term benefits or whether gains would be lost overtime as participants returned to previous behaviour patterns. The findings of the 10-year Legacy Study indicate that:

• all participants from the exercise groups experienced smaller increases in waist circumference than the control group members;

• participants in the vigorous exercise group demonstrated a lower reduction in peak VO₂, when compared to the other groups;
• members of the moderate intensity group and high volume/high intensity group had significantly lower mean arterial blood pressure than before the intervention began; &
• participants who continued to exercise post trial showed a significantly lower reduction in peak VO₂ than participants who did not.