This study investigated the effect of consuming EPA-enriched fish oil for 4 weeks on temporal muscular dysfunction and soreness following ECCs. As a result, the 4-week ingestion of 600-mg EPA and 260-mg DHA attenuated the loss of joint flexibility after 60 ECCs in the elbow flexors. Moreover, the present regimen reduced the blood CK level, suggesting increased owing to damage to muscle fibers. However, no effects were observed on loss of muscle strength, delayed onset muscle soreness, muscle swelling, echo intensity, and blood IL-6. These results suggest that supplementation with EPA-enriched fish oil for 4 weeks is effective to a certain extent for attenuating acute exercise-induced muscular damage. These results support our hypothesis.
Herein, we confirmed that EPA (600 mg/day) and DHA (260 mg/day) consumed for 4 weeks significantly attenuated reduced ROM after 60 ECCs in the elbow flexors. The decreased ROM after ECCs has been attributed to the increased passive muscle stiffness due to inflammatory response in myofibrils, elevated cytoplasmic calcium levels, and muscle swelling due to inflammatory reactions 16, 17. In our previous study, 30 isokinetic ECCs produced by elbow flexion with maximum effort were loaded after 600-mg EPA and 260-mg DHA per day for 8 weeks before exercise 7. As a result, the reduction of ROM in the elbow joint until 3 days after exercise in EPA and DHA group was significantly less compared with that in the placebo group 7. In a different study, the 8-week consumption of 600 mg/day EPA and 260 mg/day DHA significantly reduced elbow ROM until 5 days after 60 ECCs using dumbbells at 100% MVC 11. As a study investigating the effectiveness of supplementation for a period shorter than 8 weeks, Lenn et al. 13 tested the effect of 30-day consumption of 1,800-mg/day omega-3 fatty acids (398-mg EPA and 269-mg DHA) on muscle damage following 50 ECCs by elbow flexions in 21 untrained men and women. The results of that study show no differences in the loss of ROM in the elbow between the omega-3 fatty acid group and the placebo group. As consumption of 2,400-mg/day omega-3 fatty acids (600-mg EPA and 260-mg DHA) was effective in this study, the dose, rather than the duration of administration, appears to be a more important factor determining the preventive effect on joint flexibility. In addition, a study involving 24 healthy young men has reported that reduced ROM in the knee joint after loading ECCs of quadriceps through a 40-min bench stepping exercise was significantly reduced in those who consumed 324-mg/day EPA and 216-mg/day DHA for 30 days 10. In that study, ingestion of lower EPA and DHA was effective presumably because the multi-joint movement in lower limbs for a long period of time was a relatively low-intensity exercise. These data suggest that the effectiveness of short-term supplementation with EPA and DHA (28–30 days) on joint flexibility may differ depending on the omega-3 fatty acid dose, mode of exercise, and specific muscles involved.
In the present study, no differences in IL-6 between the groups were observed, and blood CK elevation in the EPA group was significantly reduced. The increase in CK following ECCs is attributable to micro-damage to muscle fibers 3, 5. A study involving mice has reported that the amount of omega-3 fatty acids in the cell membrane significantly increased after 3-week administration of omega-3 fatty acids 18. Therefore, a possible reason why the exercise-induced CK elevation was mitigated herein is that omega-3 fatty acids were incorporated into and protected cell membrane in muscle fiber. Similarly, Tartibian et al 10 have reported that consumption of EPA and DHA for 30 days reduced CK elevation after ECCs from 40 min of the bench stepping exercise. A different study has also showed that 2,000-mg/day DHA ingestion for 4 weeks reduced CK elevation after ECCs through elbow flexions using dumbbells 19. Some studies have reported controversial observations indicating that supplementation with EPA and DHA did not reduce the CK level in blood 7, 20, 21. Furthermore, some studies have demonstrated that consumption of EPA and DHA reduced the elevation of IL-6, an inflammatory cytokine 7, 12, 19, 20. Possible reasons why our results did not agree with these previous studies were used different modes and time points. Future studies considering these factors are necessary.
The present study also indicated no effect of 4-week supplementation with EPA and DHA on DOMS. A study has reported that the results of daily ingestion of 2,000-mg EPA and 1,000-mg DHA for 2 weeks significantly mitigated DOMS in the upper arm after two sets of ECCs (until exhaustion) via elbow flexions using dumbbells at an intensity of 120% 1RM 22. Similarly, as a result of 3,600 mg of EPA and DHA ingested for 2 weeks have also been reported to mitigate DOMS in the upper arm and thigh after 10 sets of ECCs (until exhaustion) through elbow flexions and knee extensions at an intensity of 50% 1RM 23. Studies using 8-week consumption of EPA and DHA at lower doses (600 mg/day of EPA and 260 mg/day of DHA) have reported significant mitigation of DOMS after 30 isokinetic ECCs by elbow flexions 7 and DOMS after isotonic ECCs using dumbbells at an intensity of 40% 1RM 9. In contrast, 30-day consumption of 287-mg/day EPA and 194-mg/day DHA 13 and 6-week consumption of 1,300-mg/day EPA and 300-mg/day DHA 24 have been demonstrated to be ineffective for DOMS following isokinetic ECCs. Therefore, we suggest that ingestion at a high daily dose or for a long period of time appears to be important for EPA and DHA to exert the mitigation effect on DOMS.
Herein, loss of muscle strength, muscle swelling, and increased echo intensity after exercise were not prevented by the 4-week ingestion of EPA and DHA. In a previous study, we have reported that the results of 8-week ingestion at similar doses to those used in the present study reduced the loss of muscle strength 7, 9, 11. Furthermore, 30-day ingestion of 287-mg/day EPA and 194-mg/day DHA 13 and 6-week ingestion of 1,300-mg EPA and 300-mg DHA 24 have been shown to be ineffective against loss of muscle strength. Considering the results of our present and previous studies, the duration of EPA and DHA intake is an important determinant of the effectiveness for muscle strength after exercise. In addition, no consensus has been obtained thus far on the swelling of muscles. Consumption of EPA (600 mg/day) and DHA (260 mg/day) for 8 weeks has been reported to attenuate muscle swelling after ECCs through elbow flexions at an intensity of 100% MVC 11. Ingestion of 324-mg EPA and 216-mg DHA per day for 30 days has been reported to mitigate muscle swelling after ECCs in lower limbs 10. Several previous studies show that consumption of EPA and DHA for 2–8 weeks did not attenuate muscle swelling after ECCs 7, 9, 22, 23. In many studies, muscle swelling was not evaluated directly and was measured using a measuring tape. The use of MRI or ultrasonography may be necessary for evaluation in the future. In the ultrasound measurement, an increased echo intensity reflects the amount of free water or edema due to disintegration of the extracellular matrix 6. Our previous study has shown that consumption of EPA and DHA for 8 weeks resulted in a smaller increase in echo intensity following elbow flexions 11. Therefore, more studies are needed to clarify the effect on echo intensity after ECCs because pf the paucity of data; regardless, the available data suggest the importance of the duration of consumption.