Effect of 8 weeks of high-intensity interval training versus traditional endurance training on the blood lipid profile in humans
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INTRODUCTION: High-density lipoprotein (HDL) plays an important role in the prevention of atherosclerosis and coronary heart disease (CHD), which is the leading cause of death in the United States. While the importance of adequate concentrations of HDL is recognized, HDL must exhibit anti-inflammatory properties and participate in reverse cholesterol transport to be beneficial. Chronic C-reactive protein (CRP) levels may indicate whether HDL can function in this manner, with reductions in CRP being associated with greater HDL function and thus protection from CHD. Traditional endurance training (ET) is an effective way to reduce chronic CRP concentration, increase HDL function, and increase HDL concentration. However, High-intensity Interval Training (HIIT) is equal or superior to ET for improving measures of cardiovascular health across a wide range of populations, and may be more beneficial than ET for improving inflammatory status, HDL function, and HDL concentration. PURPOSE: To compare the effects of duration- and work-matched ET and HIIT on HDL function and concentration, as well as on CRP, the acute IL-6 response to exercise, and cardiovascular fitness. METHODS: Twelve young males (age 21.6 ± 1.6 years, HDL 34 ± 8 mg/dL, VO2max 41.6 ± 5.4 ml/kg/min) divided into 2 matched groups (HIIT or ET) based on HDL concentration and VO2max completed 8 weeks of duration- and work-matched exercise training 3 days per week. Each exercise session lasted 30 min, with a progression in average intensity from 70 to 80% of VO2max. HDL function and concentration, resting CRP, acute IL-6 response to exercise, VO2max, body composition, and blood pressure were determined before and after the 8 weeks of training. RESULTS: After 8 weeks of training, there were no significant differences in HDL function, resting CRP, HDL concentration, or VO2max within or between groups (p>0.05). HIIT lowered plasma triglyceride (TRG) concentrations (-31 ± 28 mg/dL, p=0.04) significantly more than ET (p=0.009). HIIT also significantly increased treadmill Vmax (0.6 ± 0.5 mph, p=0.02) and reduced HRmax (-5 ± 3 bpm, p=0.01) from baseline levels, but there was no significant difference between the groups. ET resulted in significant reductions in the percentage of android fat (-2.60 ± 2.41%, p=0.045) and TC:HDL ratio (-0.60 ± 0.41, p=0.02), but neither were significantly different from HIIT. CONCLUSION: When average intensity, workload, and duration are equal, these results indicate no difference between HIIT and ET for improving HDL function, HDL concentrations, or resting CRP. However, in this time period HIIT was significantly better than ET for reducing plasma TRG concentrations. Also, HIIT alone improved Vmax and reduced HRmax, while only ET was beneficial for reducing the percentage of android fat. A larger sample size, longer training period, or different exercise protocols may be necessary to alter HDL function and chronic inflammation.
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