Cross Training Reduces the Markers of Insulin Resistance

ABSTRACT & COMMENTARY

Synopsis: This report provides evidence that strength training is an additive to endurance exercise in its benefits for change in percent fat, insulin concentrations, triglycerides, and systolic blood pressure.

Source: Wallace MD, et al. Med Sci Sports Exer 1997;29: 1170-1175.

This study examined, through a randomized controlled trial, the effects of combined resistance and endurance exercise (cross-training) on markers of insulin resistance (e.g., dyslipidemia, intra-abdominal obesity, hyperinsulinemia, and hypertension), body composition, and performance in hyperinsulinemic individuals.

Sedentary adult males characterized as hyperinsulinemic (fasting insulin > 20 uV-mL-1), randomly assigned to two groups (n = 8 each), completed 14 weeks of training at three days a week. An endurance-only (E) group performed both continuous cycle exercise and walking (30 minutes each at 60-70% heart rate reserve). A cross-training (C) group performed both endurance and resistance exercise (8 exercises, 4 sets/exercise, 8-12 repetitions/set) in a single session. Both E and C groups demonstrated similar increases in VO2max (25% and 27%, respectively), while only C demonstrated an increase in 1 RM bench press (19%) and leg press (25%). The changes induced by C training were significantly greater than those from E training alone in percent fat (6.9), insulin concentration (8.5 vs 5.5 uU mL), glucose levels (11.1 vs 5.9 mg dL-1), HDL-C levels (5.1 vs 2.9 mg dL-1), triglyceride concentration (43.8 mg dL-1), and systolic blood pressure (14.6 vs 8.3 mmHg). Results indicate that the addition of resistance training to an endurance training program will induce significantly greater differences in markers of insulin resistance and body composition in individuals with hyperinsulinemia than endurance training alone.

COMMENT BY RALPH R. HALL, MD, FACP

This report is interesting and encouraging in that it provides evidence that strength training is an additive to endurance exercise in its benefits for change in percent fat, insulin concentrations, triglycerides, and systolic blood pressure. As the authors point out, heretofore, there has been sparse evidence regarding the effects of combined endurance and strength training (cross training) on the manifestation of the prevalent insulin resistance syndrome. There was no improvement in VO2max as has been the case with other weight training studies.

It has been demonstrated that there is a favorable dose-dependent effect of endurance exercise (running) on blood lipoprotein levels.1 The American College of Sports Medicine2 and the NIH consensus statement regarding exercise recommend a combination of endurance, flexibility, and strength training to improve health-related fitness. This study supports this approach and is encouraging in that the strength training was an additive to endurance training as measured by body fat distribution, blood lipid levels, and blood pressure.

The one disappointing aspect of this research is the failure to include a third group of subjects who performed an amount of endurance exercise equal to the amount of time spent on both the endurance and the strength training. Would the benefits have been greater? Would there have been more injuries and dropouts among the subjects? Further, how do you induce your patients to do this amount of strenuous exercise?

References

1. Barinaga M. Science 1997;276:1324-1327.

2. ACSM Guidelines for Exercise Testing and Prescription. Baltimore, MD: Williams & Wilkins; 1995.

Gemfibrozil treatment of post-CABG patients with isolated low HDL has been associated with marked reduction in subsequent clinical events despite lack of any demonstrated angiographic benefit.

Which of the following statements is true?

a. The strength training doubled the increase in fitness as measured by the VO2max.

b. The percent of body fat reduction was greater with the endurance training alone.

c. The effect of combined training was more effective than the endurance training alone on blood pressure changes.

d. Insulin resistance was decreased to a greater degree with the endurance training alone.