Physical activity is recognized as one factor that affects polyunsaturated fatty acid status.5 Physical activity per se induces changes in the phospholipid fatty acid composition of muscle membranes.5,95 The effects of an aerobic exercise program (55% VO2 peak) on phospholipid fatty acid composition of ro-3 and ro-6 fatty acids in the skeletal muscle have been examined in sedentary subjects.95 Six weeks of physical training showed changes in the levels of ro-3 (EPA, DHA, and docosapen-taenoic acid) fatty acids, decreased the proportion of ro-6 (linoleic acid, dihomo-y-linolenic acid, and arachidonic acid) fatty acids in muscle phospholipids, and reduced the ro-6 to ro-3 ratio.96 Similar results were reported by Helge et al.95 when investigating the effect of endurance training of the knee extensor of one leg for 4 weeks on the muscle membrane phospholipid fatty acid composition. After 4 weeks of training, the phospholipid fatty acid contents of oleic acid and DHA were higher in the trained than the untrained leg, and the ratio of ro-6 to ro-3 was lower in the trained than in the untrained leg.95 The beneficial effect of exercise on lipoproteins and subfractions has been reported previously. The ro-3 fatty acid role in physiological metabolism includes an amelioration of lipid profiles, specifically triglycerides and cholesterol fractions, and increased fluidity in membranes, of which similar effects have been attributed to regular aerobic exercise.97 It has been indicated that a single session of aerobic exercise has shown effects on triglyceride concentrations similar to those shown by ro-3 supplementation.98
Brilla and Landerholm97 assessed the effect of aerobic exercise for 1 hour three times a week (mean range VO2 max post-exercise: 35.6 to 49.5 ml kg1 min1), and fish oil supplementation (4 g/day of ro-3 fatty acids) on serum lipids and aerobic fitness on healthy sedentary males for 10 weeks. Subjects in the exercise only and fish oil plus exercise groups had significantly higher VO2 max. Subjects in the fish only, exercise only, and fish oil plus exercise groups had significantly higher ventilatory anaerobic thresholds (VATs) than controls; however, there were no differences in blood lipid values among all groups.97 The improvement in aerobic indicators may be explained by incorporation of ro-3 fatty acids into membranes and their effect on the increase of the deformability of red blood cells, enhancing oxygen transport, and probably improving exercise performance.9799 Contrasting results on plasma lipoproteins were reported on recreationally active males who completed an aerobic exercise session of 60 min on the treadmill (60% VO2 max) and were supplemented with 4 g/day of ro-3 fatty acids (600 mg of EPA and 400 mg of DHA/g) for 4 weeks. Supplementation increased plasma EPA and DHA, supplementation or exercise each affected HDL and subfractions (HDL2 for supplementation and HDL3 for exercise), exercise increased LDL, and the combined treatments affected HDL3 and LDLj.100 The lowering effect of ro-3 fatty acids in the form of fish oil on triglycerides is thought to involve the suppression on enzymes engaged in the triglyceride synthesis and stimulation of ^-oxidation in the liver.101102 Chronic supplementation with fish oil of 4 g/day (600 mg of EPA and 400 mg of DHA/g) rather than an acute high dose of 16 to 22 g/day (600 mg of EPA and 400 mg of DHA/g) has been reported to increase fat oxidation during 60 min of aerobic exercise (60% VO2 max) in recreationally active males.103 The effect on fat oxidation may be linked to the activation of skeletal muscle peroxisomal poliferator-activated receptor-a (PPAR-a) by EPA and DHA, resulting in decreased accumulation of triglycerides in myo-tubes.103
Contrary to studies that reported improvement in ventilatory indicators, Raastad et al.104 showed that the effect of ro-3 fatty acids supplementation on cardiac output and peripheral blood flow on increasing aerobic performance did not show positive results. Well-trained soccer players supplemented with 5.2 g/day of fish oil (1.60 g/day EPA and 1.04 g/day DHA) for 10 weeks did not demonstrate an improvement in maximal aerobic power, anaerobic threshold, and running performance. However, supplemented subjects had significantly reduced plasma triglycerides and elevated plasma concentrations of EPA and DHA.
Omega-3 fatty acid supplementation has been utilized for muscle inflammation and soreness, and its use is based on the anti-inflammatory response that these polyunsaturated fatty acids have shown through modulation of the eicosanoid pathways.28 Intakes of ro-3 fatty acids to reduce joint tenderness in patients with rheumatoid arthritis28 105 and myalgic pain106 have been reported, and intake of cod liver oil to mitigate musculoskeletal pain has been examined in a cross-sectional study that included nonathletic males and females older than 18 years.107 However, supplementation of ro-3 fatty acids (1.8 g/day) for 30 days before and during iso-kinetic eccentric elbow flexion exercise was not effective in decreasing the physical parameters linked with delayed-onset muscle soreness (DOMS).108
The effect of ro-3 fatty acids, specifically EPA and DHA, has been tested on cytokine production during strenuous exercise due to their modulation on the production of pro-inflamatory and immunoregulatory cytokines.109 Strenuous exercise induces an acute-phase response with increased plasma concentration of IL-6,110 IL-1 receptor antagonist,111 and TNF-a.112 It is also thought that the anti-inflammatory cytokine, and transforming growth factor (TGF)-^1, is increased in physiological states similar to strenuous exercise.109 Therefore, the effect of 6.0 g/day of fish oil supplementation containing 3.6 g of ro-3 fatty acids (approximately 1.9 g of EPA and 1.1 g of DHA), and tocopherol for 6 weeks on male runners before participating in a marathon was examined.109 The study aimed to investigate whether fish oil supplementation could modulate the acute-phase response to strenuous exercise. Subjects supplemented with fish oil showed incorporation of ro-3 fatty acids and less arachidonic acid in blood mononuclear cells than the nonsupplemented group, and although cytokine concentrations increased as a result of exercise, the cytokine concentrations of the supplemented and nonsupplemented groups did not differ.109 Omega-3 fatty acids supplementation on the effect of exercise-induced bron-choconstriction (EIB) in athletes has gained attention lately.113116 Fish oil supplementation in doses of 3.2 g/day of EPA and 2.0 to 2.2 g/day of DHA for 3 weeks has been reported to reduce the severity of EIB in athletes challenged to aerobic exercise (treadmill) until exhaustion, as seen by decreases in the forced expiratory volume (FEV1) pre- and post-exercise of 64 to 80% at 15 min after exercise.114116 Inflammatory mediators of urinary LTE4 and 9a, 11^-PGF2, blood LTB4, TNF-a, and IL-1P,114 and sputum LTC4-LTE4, PGD2, IL-1p, and TNF-a116 were decreased in subjects on the ro-3 fatty acid diet compared to placebo and after exercise,114 and before and following exercise in the fish oil group compared to placebo.116
Supplementation intakes of ro-3 fatty acids have ranged from 1.8 to 6 g/day, and one study reported using an acute high dose of up to 22 g/day. To our knowledge, there are no existing studies that have addressed the effect of inadequate or toxic intakes on physical performance or reported the use and effects of ro-6 fatty acids supplementation on athletes.
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