The influence of walking on risk factors associated with metabolic syndrome

Metabolic syndrome (MetS) represents a cluster of metabolic abnormalities, characterised by the presence of 3 or more of 1) abdominal obesity, 2) insulin resistance, 3) hypertension, 4) dyslipidaemia, and 5) emerging risk factors, such as pro-thrombotic and pro-inflammatory states, which are each independent cardiovascular disease (CVD) risk factors. This clustering of risk factors is reported to increase the odds ratio forcardiovascular and all-cause mortality above the risk associated with the individual components (Wilson, 2004). The precise aetiology of MetS is currently unknown, however an energy-dense diet, particularly high in carbohydrate, and an inactive lifestyle or low fitness may interact with a genetic susceptibility to contribute to the pathophysiology ofMetS (Bouchard, 2007). Therefore the purpose of the studies included in this thesis were to determine whether accumulative brisk walking may improve risk factors associated with MetS and whether one single session of brisk walking at a moderate intensity may improve risk factors associated with MetS in middle-aged men at risk of MetS. Study one recruited 85 males aged 38-73 onto a 24-week randomised controlled trial with participants allocated to control (CON), single 30 minute daily brisk walking (SBW) or accumulative 30 minutes of daily brisk walking (ABW; 3×10 min or 2×15 min) groups. Measures included aerobic fitness (OO2max), body composition and selected blood variables. The main findings were that 24 weeks of accumulating 150 min·wk-1 of brisk walking at ~65% HRmax significantly improved insulin sensitivity, which was associated with decreased abdominal adiposity, assessed by waist circumference, and was at least as effective as a single daily session of equal volume in middle-aged men at risk of MetS. Study two investigated the 24-hour effect of walking for 30 minutes at 50% OO2max (30×50%), 30 minutes at 65% OO2max (30×65%) and 60 minutes at 50% OO2max (60×50%) compared to rest (CON) on cardiovascular control, resting metabolism and selected blood variables. The main findings were that a single 30 minute walking session at 50% OO2max favourably improved cardiovascular control, indicated by decreased heart rate and systolic blood pressure, thus decreasing the workload of the heart, whereas increasing the intensity of the walk to 65% OO2max attenuated this effect, while increasing the duration to 60 minutes had no additional effect compared to 30 minutes at 50% OO2max in men at risk of MetS.