The two major fractions of blood cholesterol are low-density-lipoprotein (LDL) cholesterol and high-density-lipoprotein (HDL) cholesterol. LDL increases the risk of heart-disease because it is readily deposited in arterial walls and can result in a blood clot that shuts off the blood supply to the heart muscle. In contrast, LDL removes cholesterol from arterial walls. The ratio of total cholesterol (TC) to HDL cholesterol is a risk-index for heart-disease. The higher the ratio, the greater the risk. The average ratio is 4.5, but doctors recommend it be below 4.0 and preferably below 3.0.
Endurance exercise has been shown to improve the TC/HDL ratio, but interval training (sprint running interspersed with rest periods) has not been shown effective in this regard. However, a recent study by Musa et al. (Journal of Strength and Conditioning Research, vol 23, no 2, 2009, pages 587-592) showed that interval training using longer running intervals (500 meters ~ half-mile) can be effective for improving the ratio.
20 college age males ran 4 half-mile intervals at high intensity (90% of max heart rate) seperated by rest periods equal in time (3-5 min) to the running intervals, 3 times a week for 8 weeks. Their TC/HDL ratio improved by 18%, reducing their risk of heart-disease by an estimated 37%. The training also improved their 2.4 km (1.5 mi) running time by 9%.
Interval training using running distances of 0.5 miles and rest periods equal to run time can effectively enhance blood cholesterol profiles, reducing risk for heart-disease. Thus, for individuals healthy enough to withstand the strain of high-intensity running, longer-distance interval training can have a valuable place in a physical fitness program.