Significance of skeletal muscle properties on fitness, long-term physical training and serum lipids.
The percentage of slow-twitch (ST) fibers in a person's skeletal muscle, e.g. muscle fiber composition (ST-%), may have a significant impact on physical activity, fitness level, serum high density lipoprotein cholesterol (HDL-C) concentration, and ultimately, on the risk of coronary heart disease (CHD). We studied the effect of a 12 month home-based exercise training program on skeletal muscle metabolic activity, serum lipids, and hormones in 12 healthy middle-aged men (sedentary men) with a low level of fitness and leisure-time physical activity (LTPA). Their parameters and changes in them were compared with 12 men of the same age with defined CHD and with two groups (15 each) of physically active men, who had either a high ST-% (high-ST-men) or a low ST-% (low-ST-men). In the sedentary men, CHD-patients and low-ST-men, the mean ST-% (42, 44, and 49%, respectively) was similar but was significantly higher in the high-ST-men (73%). The sedentary men whose LTPA mean was 34 and 19% of the mean of low-ST-men (mean of 2137 kcal/week) and high-ST-men (mean of 3845 kcal/week), respectively, increased their LTPA from a mean of 728-1526 kcal/week (P < 0.01). After training, we found an increase in serum HDL-C by 21%, (P < 0.01) and apo A-I by 36% (P < 0.01), and a decrease in serum LDL-C by 8%. The cholesterol/HDL-C ratio decreased by 17(% (P < 0.01) and the LDL-C/HDL-C ratio decreased by 22% (P < 0.01). Skeletal muscle lipoprotein lipase (LPL) activity increased by 65% (P < 0.001). Moreover, the increase in LPL as well as in HDL-C concentration tended to be more pronounced the higher the level was before training. The oxidative enzyme activity of alpha-ketoglutarate dehydrogenase (KGDH) in skeletal muscle and the activity of carnitine palmitoyltransferase (CPT) in lipid metabolism increased, whereas glycolytic phosphofructokinase (PFK) did not change but the PFK to CPT ratio decreased, which was reflected as a decrease of lactate accumulation during exercise. Increase in CPT activity correlated significantly (r(s) = 0.81, P < 0.01) with the increase in HDL-C concentration. In all men (n = 54), the CPT activity correlated negatively with serum triglyceride concentration (r(s) = -0.34, P < 0.05) but positively with serum HDL-C concentration and ST-% (r(s) = 0.34, P < 0.05 and r(s) = 0.47, P < 0.01, respectively). In all healthy men, (n = 42) LTPA correlated with both Vo2max, and ST-% (r(s) = 0.76, P < 0.001 and r(s) = 0.54, P < 0.001, respectively) and with serum HDL-C and apo A-I concentrations (r(s) = 0.35, P < 0.05 and r(s) = 0.54, P < 0.001, respectively). Serum sex hormones did not show significant associations with serum lipids, but in sedentary men, serum total and free testosterone as well as the ratio of free testosterone to free estradiol decreased significantly after training. These findings confirm the pronounced effects of a home-based exercise training program on CHD risk factors and they underline the importance of considering skeletal muscle properties when studying serum lipids and lipoproteins and their modifications in the field of health-related fitness and physical activity.
Department of Clinical Chemistry, Helsinki University Central Hospital, Finland. heikki.tikkanen@dlc.fi
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Tikkanen
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Hämäläinen
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Härkönen
D000328:Adult; D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism; D003327:Coronary Disease / Q000097:blood / Q000517:prevention & control; D015444:Exercise / Q000502:physiology*; D005500:Follow-Up Studies; D012739:Gonadal Steroid Hormones / Q000097:blood; D006801:Humans; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism; D019344:Lactic Acid / Q000097:blood; D008055:Lipids / Q000097:blood*; D008071:Lipoprotein Lipase / Q000378:metabolism; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology*; D010732:Phosphofructokinase-1 / Q000378:metabolism; D010809:Physical Fitness / Q000502:physiology*; D012016:Reference Values; D014280:Triglycerides / Q000097:blood
D012739:Gonadal Steroid Hormones; D008055:Lipids; D014280:Triglycerides; D019344:Lactic Acid; D007655:Ketoglutarate Dehydrogenase Complex; D002334:Carnitine O-Palmitoyltransferase; D010732:Phosphofructokinase-1; D008071:Lipoprotein Lipase