Insulin resistance in the presence of obesity, especially high abdominal fat levels (of which men are particularly prone), are prime risk factors for type II diabetes and metabolic syndrome (MetS), and a sedentary lifestyle is a known contributor for these. Walking is accessible exercise for the majority of the population but there is still relatively little empirical research looking directly at its effect upon all prime MetS risk factors.
PURPOSE: To determine whether 24 weeks of walking for 30 min·d-1 on at least 5 d·wk-1 affected prime MetS risk factors and insulin sensitivity in previously sedentary men.
METHODS: 48 (28.4±3.2 BMI) low-active/sedentary men were randomly selected into controls (n=19, 52.4±8.0) or walkers (n=29, 54.9±8.0 years). Walking diaries indicated intensity, duration and compliance. Pre- and post-intervention criterion MetS measures were taken in addition to insulin (insulin sensitivity index (ISI) derived) and treadmill-walking VO2max. Fasted venous blood samples were taken. The GLM was employed using baseline covariate measures. Bonferroni correction was applied which set statistical significance at P<0.006.
RESULTS: Over 24-weeks 156.4±26.5 min·walking·wk-1 was performed in 7.2±2.9 sessions·wk-1 for a mean of 25.1±10.3 min·session-1 at 50.6±9.1% estimated VO2max mL·kg-1·min-1. Significant post-intervention changes were observed in waist circumference (WC) (walkers -2.0±2.7 vs. controls +1.3±3.1 cm, F=15.27, P<0.0001); W/H ratio (-0.02 ±0.03 vs. +0.01±0.03, F=19.82, P<0.0001), serum insulin (-1.7±1.5 vs. +2.0±6.0, F=8.40, P<0.006 μU·ml-1) and ISI (+2.0±6.0 vs. -0.4±0.7, F=10.82, P<0.002 M·mU-1·L-1, respectively). No significant effect was observed in levels of triglyceride, high-density lipoprotein cholesterol, blood pressure, or blood glucose. Post-intervention changes for insulin correlated with WC (R=0.441; R2=0.19: P<0.002); and ISI negatively with WC (R=-0.433; R2=0.19: P<0.003).
CONCLUSIONS: Given the importance of insulin resistance in the presence of abdominal obesity, these findings demonstrate around 30 min·d-1 of walking on at least 5 d·wk-1 at an easily attainable intensity for most adults (∼51% VO2max) can reduced WC, which appeared to enhance insulin sensitivity, thereby helping reduce risk of type II diabetes and MetS.