Research Review By Demetry Assimakopoulos©

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Date Posted:

December 2011

Study Title:

Comparison of Aerobic Versus Resistance Exercise Training on Metabolic Syndrome (from the Studies of a Targeted Risk Reduction Intervention Through Defined Exercise – STRRIDE-AR/RT)

Authors:

Bateman LA, Slentz CA, Willis LH et al.

Author's Affiliations:

Division of Cardiovascular Medicine and Geriatric Medicine at the Duke University Medical Centre; Department of Exercise and Sports Science and Human Performance at East Carolina University.

Publication Information:

American Journal of Cardiology 2011; 108(6):838-44.

Background Information:

While a lot of research exists concerning the efficacy of aerobic training (AT) for reducing cardiometabolic risk factors, little has been conducted on the efficacy of resistance training (RT) as a therapy for improving cardiometabolic health. The intent of this study, therefore, is to compare AT to RT in obese adults for the purposes of improving various diagnostic and health indicators of metabolic syndrome (MS). Also, this study attempted to assess whether or not a combination of AT and RT (AT/RT) are more effective than any of the interventions alone. The authors of this study conducted the Studies of Target Risk Reduction Intervention through Defined Exercise (STRRIDE-AT/RT) in an attempt to identify the effectiveness of the three therapies in obese adults.

Pertinent Results:

  • No significant differences were found between subjects at baseline. 196 subjects were randomized – 86 provided complete datasets that were full analyzed.
  • There was a reported 26.5% drop out rate across all groups.
  • All of the study groups experienced an increase in peak oxygen consumption, with the AT/RT group yielding the greatest increase (??by 3.67±3.61 mL/Kg/min); the AT and RT groups followed, with increases of 3.33±3.95 and 1.23±3.14 mL/Kg/min, respectively.
  • BMI significantly decreased in the AT and AT/RT groups, but did not in the RT group. Waist circumference did not change in the RT group; however, the AT group showed a trend towards significance, while the AT/RT group actually showed significant changes (-2.48±3.78 cm at the level of the iliac crest).
  • Triglyceride levels significantly decreased in the AT/RT and AT groups, but did not change significantly in the RT group. Surprisingly, no changes were seen in HDL, cholesterol, fasting plasma glucose or systolic blood pressure in any exercise group.
  • Diastolic blood pressure and mean arterial pressure both decreased significantly in the AT/RT group. However, these two measurements did not change significantly in the AT or RT groups.
  • The AT/RT groups realized a significant improvement in the metabolic syndrome (MS) z-score (see methods). Shockingly, the AT group only showed a trend towards significance in this score, while the RT group failed to show significance.
  • The AT/RT group also showed a significant decrease in the Adult Treatment Panel (ATP) III scores (see methods and weaknesses). Only the RT showed a trend towards significance with regard to this score, while AT group, surprisingly, did not achieve significance.

Clinical Application & Conclusions:

The most important findings of this study are as follows:
  1. The RT group did not significantly improve the clinical markers of MS or the MS z-score
  2. AT improved the overall MS z-score
  3. AT/RT showed largely significant improvements in the MS z-score
  4. The AT intervention was superior to RT at improving clinical markers of MS
  5. The combination of RT/AT will lead to longer workouts and therefore more calories consumed
  6. AT produced greater improvements in VO2peak (or Max), and other parameters of cardiometabolic and cardiorespiratory health than RT
  7. AT is more effective than RT at modifying the health status of individuals with cardiovascular disorders
  8. When weighing the time commitment versus cardiometabolic health benefit, aerobic exercise is the most efficient mode of exercise for addressing the various health issues that exist as a result of MS.
(Clinical note: this does not preclude trainers and therapists from prescribing resistance training to their clients and patients with MS. As shown above, the combination of interventions showed the greatest improvements in all health parameters. However, when time and motivation are issues, the biggest bang for your buck will come from AT based on the results of this study.)

Study Methods:

This study included individuals aged 18-70, who were sedentary (exercised < 2x/week), overweight or moderately obese (BMI 25-35 kg/m2) with mild to moderate dyslipidemia (either high LDLs or low HDLs) – essentially metabolic syndrome. Subjects were excluded if they smoked, had a history of diabetes mellitus, blood pressure greater than 160mmHg systolic and 90mmHg diastolic, were taking hypertension medications at the time of the study, a history of musculoskeletal disorders and coronary artery disease, or if they were dieting or intending to diet and if they were imbibing any confounding medications. Seventy-five percent of the subjects were recruited at Duke University, while the remaining 25% were recruited from East Carolina University (ECU).

The patients included were asked to not change their lifestyle for 4 months. The participants were randomized into one of the three treatment groups: RT, AT or RT/AT. The exercise groups were described as follows:
  • The RT patient group performed 3 days/week, 3 sets/day of 8-12 repetitions/set
  • The AT group performed the equivalent of ~ 12 miles/week of aerobic exercise at 65-80% of their VO2peak
  • The AT/RT therapy group performed both the RT and AT interventions described above.
The aerobic exercise program consisted of a ramp-up period of 8-10 weeks, where the subjects gradually became acclimatized to exercise over time. Subsequently, the subjects participated in 5-6 months of training at the appropriate intensity. Once the ramp-up period was finished, those in the AT and the AT/RT groups completed approximately 12 miles/week of walking or jogging (or approximately, 14 kcal/kg body mass/week). The duration of each session was dependent on the fitness level of the subject. Caloric expenditure was calculated with a formula, where, put simply, each liter of oxygen consumed during exercise corresponded to 5 kcal burned – expired gas was measured using a metabolic cart. Each subject could choose between using a treadmill, elliptical or a cycle ergometer. Also, all exercise sessions were performed under direct supervision and within a specified heart rate range.

The RT and AT/RT groups started with a ramp-up period of their own, consisting of 1 set during weeks 1 and 2. Subsequently, they increased their exercise volume by performing 2 sets during weeks 3 and 4 and finally 3 sets by week 5. The full training program for those at Duke University consisted of 3 sessions/week, where 3 sets of 8-12 repetitions were performed on 8 Cybex weight lifting machines; 4 upper body and 4 lower body. The composite of exercises was designed to target all major muscle groups. Those at ECU were asked to perform the same routine, only 2 free weight exercises and abdominal crunches were added. Eight Cybex machines were used at Duke throughout the study. Similarly, the same 8 machines were used at ECU, until week 14 of the study, where they began performing free-weight exercises for the upper body rather than using the Cybex. The weight amounts were increased by 2.3Kg (5 lbs) each time the subject performed 12 repetitions consecutively with flawless form, for all 3 sets throughout two consecutive workout sessions.

In addition to body mass index, waist circumference measurements were taken in each patient at the level of the iliac crest. This measurement was taken twice and averaged for accuracy. Two blood pressure readings were taken approximately 20 minutes apart, and then averaged for consistency.

Cardiovascular exercise tests to determine VO2peak were performed with a 12-lead ECG and a metabolic cart to analyze expired gases while the patient exercised on a treadmill. From these, peak oxygen consumption was determined in L/min. Additionally, respiratory exchange ratio (RER) was measured – an RER of greater than or equal to 1.10 was required and achieved during 86% of all the pre-training VO2peak tests and 74% of all post-training VO2peak tests.

An MS z-score was calculated using the 5 MS variables included in this study to create a composite score for MS. A modified z-score was calculated for each variable using individual subject data, the Adult Treatment Panel (ATP) III Criteria and standard deviations, using data from the entire STRRIDE-AT/RT study population at baseline. Additionally, an MS risk factor score using the ATP III guidelines was calculated for each patient using the sum of the number of ATP III criteria met by each subject before and after the intervention.

Study Strengths / Weaknesses:

Weaknesses:
  • No specific indication was given as to the standards used to identify individuals with metabolic syndrome (Canadian/American Diabetes Association, National Cholesterol Education Program, etc.)
  • The authors made no effort to explain what exactly the ATP III score is. It is inferred that it is the National Cholesterol Education Program (NCEP) criteria for the diagnosis of metabolic syndrome.
  • Perhaps the study intervention period needed to be longer to realize positive changes in triglycerides and HDL.
  • The researchers may have been better off to measure insulin resistance in addition to blood glucose levels, seeing as frank diabetes is not a feature of metabolic syndrome – only pre-diabetes or insulin resistance.
  • If the researchers had measured glycosylated hemoglobin and insulin resistance, there may have been better results for RT, as prior research has shown improvements in both these important factors while using this mode of exercise.
  • High intensity interval training has been shown to produce the best results for improving blood glucose levels and glycemic control (despite the fact that it does not experimentally improve weight, waist circumference and blood lipid profile). Integrating this mode of exercise into the study may have provided even more valuable information regarding the treatment of MS.
  • The authors did not offer to discuss why RT was superior to AT in lowering the ATP III Scores.
Strengths:
  • The specificity in prescribing exercise intensity
  • Fairly intense workouts, idealized for the individual patient
  • Large number of subjects
  • The addition of a combination therapy group (AT/RT)