Changes in plasma lipids and lipoproteins following 10-days of prolonged walking: influence of age and relationship to physical activity level.

The aim of the present study was to examine (1) the influence of 10 days of prolonged walking on plasma total-cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) concentrations, (2) the effect of age on any changes in plasma cholesterol and lipoprotein concentration, and (3) whether any changes in cholesterol and lipoprotein concentrations are correlated to the participants' physical activity level (PAL). Seventeen male participants were divided into two groups according to their age. The nine participants in group 1 constituted the younger group (age 24 +/- 3 (SD) years), whereas eight older participants were in group 2 (age 56 +/- 3 years). Both groups completed 10 consecutive days of high-intensity hill walking. Mean (range) daily distances and ascent were 21 km (10-35 km) and 1,160 m (800-2,540 m), respectively. Identical distances and ascents were covered by each group. For each participant, PAL was calculated from energy expenditure, assessed by the doubly-labeled water technique, divided by the individual's basal metabolic rate. Venous blood was sampled immediately prior to, and following, the 10 consecutive days of walking. Following these 10 days, the older group showed a greater decrease in both TC (-25 +/- 11% vs. -10 +/- 11%; P < 0.05) and LDL-C (-26 +/- 12% vs. -4 +/- 13%; P < 0.05) when compared with the young. Likewise, the older group showed a greater increase in HDL-C (38 +/- 15%; P < 0.05), after the 10 days, whereas no significant change was evident in the younger group. In the older participants, there were strong positive relationships between PAL and the decreases in TC (r = 0.79, P < 0.05) and LDL-C (r = 0.74, P < 0.05). Conversely, in the younger group there were strong negative relationships between PAL and the decreases in TC (r = -0.74, P < 0.05) and LDL-C (r = -0.86, P < 0.01). These correlations persisted when changes in lipid concentrations were corrected for changes in plasma volume. These data suggest an 'age-dependant' threshold for PAL, rather than a specific exercise intensity or duration, may be critical for inducing favourable changes in HDL-C, LDL-C and TC.