Durstine and Haskell36 reported that in cross-sectional studies endurance athletes have 20 percent to 30 percent higher levels of HDL cholesterol when compared to inactive controls. Cross-sectional studies also suggest a dose-response relationship between amount of exercise and HDL-C concentrations. However, exercise-training studies, according to Durstine and Haskell, have not been as consistent, as many studies have reported a significant training benefit on HDL-C levels, while many other studies did not find the effect to be significant. Leon and Sanchez,37 in their meta-analysis, reported a marked inconsistency of the effects of aerobic-exercise training on blood lipids in general, and they suggested that the most frequent finding was of a significant (P < 0.05) increase in HDL-C. However, this significant beneficial effect was reported in only 24 of the 51 studies (47 percent) included in the review. The exercise-induced change in HDL-C ranged from a decrease of 5.8 percent to an increase of 25 percent. Nevertheless, overall there was an average increase of 4.6 percent across the studies (P < 0.05).
Some help in understanding the variability in the lipid response has recently been reported in an eight-month exercise training study by Kraus et al.38 In the first randomized controlled study of the effect of two different amounts of exercise training on HDL-C, they reported that only the larger amount of exercise (an amount of exercise calorically equivalent to ~ 17 miles of jogging per week) was found to have a significantly increased HDL-C, compared to an inactive control group. The two lower amounts of exercise training (both calorically equivalent to ~ 11 miles per week, one group at a moderate exercise intensity and the other group at a more vigorous exercise intensity) had small, nonsignificant, increases in HDL-C. Thus, the Kraus study confirmed the earlier analysis of Durstine and Haskell, which reported that cross-sectional studies suggested that there was a dose-response effect of exercise training on HDL-C improvement.
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