The effects of running mileage and duration on plasma lipoprotein levels.

Eighty-one healthy, sedentary men aged 30 to 55 years were randomly assigned to supervised running (n = 48) or to sedentary control groups (n = 33) and followed up in a one-year trial. Measurements of plasma lipoproteins, fitness, and percent body fat were made at three-month intervals. Results and conclusions from this study are (1) that cross-sectional studies of lipoprotein concentrations in exercisers may be biased by a self-selection effect, since study participants with initially higher high-density lipoprotein cholesterol (HDL-C) and lower triglyceride concentrations were more easily persuaded to run more miles; (2) that plasma concentrations of HDL-C and low-density lipoprotein cholesterol (LDL-C) generally did not begin to change until a threshold exercise level (ten miles run per week) was maintained for at least nine months; and (3) that fitness increased and percent body fat decreased sooner and at lower exercise levels than required for HDL-C and LDL-C concentration changes.