HIIT-ing Health: Positive Effects of High Intensity Training on Symptoms of Metabolic Syndrome

There is a demarcation-line within the fitness community: The low-intensity steady state veterans on one side of the divide, and the high-intensity revolutionizers on the other. A recent study by Shepherd et al. (Shepherd. 2010) plays into the hands of the revolutionizers, as the scientists found that 6 weeks of HIIT improves whole-body fat oxidation and insulin sensitivity in young sedentary males.

Eight participants (23±2 years; body mass index 24.5±1.5 kg/m²; VO₂ peak 43.0±1.5 ml/min/kg) with normal glucose tolerance undertook 6 weeks of HIT consisting of between four and six 30-s Wingate tests separated by 4.5 min rest, performed three times per week. [...] VO₂ peak increased 18% (pre 43.0±1.5 ml/min/kg², post 50.8±1.8 ml/min/kg²; p<0.05). A 5% reduction in relative fat content in the body was observed (pre 19.6±2.2%, post 18.8±2.1%, p<0.05), which was attributed to a 6% decrease in relative fat content in the legs. Absolute carbohydrate oxidation was reduced after HIT (pre 1.75±0.11 g/min, post 1.49±0.11 g/min; p=0.04), while relative fat oxidation showed a tendency to increase (pre 35.2±5.7%, post 43.3±3.6%; p=0.078). Plasma glucose and insulin area under the curve in response to the OGTT was reduced by 17% and 31% (p<0.05) posttraining, respectively, which corresponded with a 27% improvement in the Matsuda index of insulin sensitivity (pre 4.0±0.5, post 5.1±0.6, p=0.066).

With an increase in exercise capacity, a decrease in body fat and a shift from carbohydrate to fat oxidation, all that still would have been changed is the nutrition from what I suspect was still the typical western high carb diet to a low/moderate carb diet high in protein and fats.