Omega-3 fatty acids are essential in the human diet, as there is no mechanism in humans for producing these fats from other substances. Omega-3 fatty acids serve as precursors to prostaglandins, which are powerful hormone-like substances that reduce inflammation and improve blood flow (Calder, 2006). For example, prostaglandin E3, which is produced from dietary omega-3 fatty acids, decreases swelling, reduces sensitivity to pain, and lessens the recruitment of inflammatory white blood cells (Maroon and Bost, 2006a). In addition, when humans ingest the omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), there is a decrease in both the production of thromboxane A2, a potent platelet aggregator and vasoconstrictor, and leukotriene B4 formation, an inducer of inflammation (Weber et al., 1986).
In light of the well-known involvement of omega-3 in the biology of inflammation, it is not surprising that more than 7,000 scientific studies, including 900 human clinical trials, have provided evidence supporting the effectiveness of fish oil and omega-3 fatty acids in the prevention and treatment for inflammatory conditions (Maroon and Bost 2006a). For example, omega-3 supplementation has been found effective for treating rheumatoid arthritis (Cleland et al., 2003; Kremer et al., 1990; Lau et al., 1993;Volker et al., 2000), osteoarthritis (Curtis et al. 2002), inflammatory bowel disease, Crohn's disease, ulcerative colitis (Kim, 1996; Ross, 1993; Salomon et al., 1990; Stenson et al., 1992), and psoriasis (Bittiner et al., 1988; Kojima et al., 1989). Despite the extensive literature on the effect of omega-3 supplementation on inflammatory disease conditions, no studies have assessed the effects of omega-3 supplements on the inflammatory responses to exercise. The potential implications of reducing post-exercise inflammation would be reduced pain and quicker recovery time from intense exercise.
The purpose of the present study was to determine if one week of omega-3 supplementation reduces clinical markers of localized inflammation as measured 48 hours after eccentric arm curl exercise. As localized inflammation is characterized by pain, swelling, and increased temperature, we hypothesized that omega-3 supplementation attenuates the increases in subjective ratings of muscle soreness, arm circumference and volume (as indices of swelling), and skin temperature.
This study was a repeated measures intervention trial in which subjects were assessed for inflammatory responses to eccentric exercise on two occasions: once after 14 days on a low omega-3 fatty acid diet (control trial) and again after seven days of omega-3 fatty acid supplementation (omega-3 trial). The participants reported to the laboratory on 5 occasions. During the first visit, a muscular strength test was conducted to determine 1-repetition maximum (1RM) weight for both arms. The study dietitian provided diet instructions pertaining to a restricted omega-3 diet and participants immediately started the diet and continued it throughout their involvement in the study. During the control trial, which was conducted after 14 days on the omega-3 restricted diet, the participants underwent baseline assessments of signs of inflammation, performed unilateral eccentric biceps curls to induce inflammation, and returned for follow-up measures of inflammation signs 48 h after eccentric exercise. During the omega-3 trial, which was conducted after 7 d of omega-3 supplementation, the participants underwent baseline assessments of inflammation signs, performed eccentric biceps curls using the contralateral arm, and returned for follow-up measures 48 h after eccentric exercise. The pairing of treatment conditions (control vs. omega-3) with arm dominance (dominant arm vs. non-dominant arm) was counterbalanced, such that half of the participants underwent the control trial using their dominant arm followed by the omega-3 trial with the non-dominant arm. The remaining half of the participants used the nondominant arm for the control trial and the dominant arm for the omega-3 trial.
Eleven healthy, 18- to 60-year old men (n = 3) and women (n = 8) were recruited from the Saint Louis, Missouri metropolitan area. Candidates for the study were excluded if they had allergies to fish or fish oil, or a self-reported history of diabetes, cardiovascular disease, significant pulmonary disease, hypertension, malignancy, musculoskeletal problems, or clotting disorders. In addition, candidates were excluded if currently taking nonsteroidal anti-inflammatory drugs, aspirin or anticoagulants.
All participants gave their informed written consent to participate in the study, which was approved by the Institutional Review Board at Saint Louis University.
Dietary and exercise control: To minimize the possibility of diet and exercise habits confounding the results, the participants were instructed to keep a 2 d food diary and exercise journal during the control trial and to use this information to replicate their diet and exercise during the subsequent omega-3 trial. Additionally, the participants were instructed to refrain from stretching their arms to overcome the soreness induced by the eccentric exercise.
Strength assessment: Muscular strength (1RM) for preacher bench bicep curls was estimated for each arm individually by using the 1RM Berger Prediction table (Berger 1961). Prior to the strength assessment on each arm, the subject was allowed to practice the arm curl exercise for 3-5 repetitions with a light (2.3 kg) dumbbell.
Then, the subject selected a dumbbell weight so at least one repetition could be performed, but no more than 15 repetitions before reaching fatigue. The subject then performed as many complete repetitions as possible. The number of repetitions and the weight were used to predict 1RM based on the Berger Prediction Table (Berger 1961).
Eccentric exercise: The goal of the exercise intervention was to induce bicep inflammation and soreness to a degree where change could be measured 48 hours post exercise. Eccentric exercise, especially for the elbow flexors, is a safe and commonly used means for experimentally inducing muscle inflammation (Friden and Lieber, 1992; Hirose et al., 2004; Nosaka and Clarkson, 1996; Trappe et al., 2001). Using 120% of the subject's 1RM, two sets of eccentric biceps curls were performed on a preacher bench, with 60 s of rest between sets. During each repetition, the technician lifted the weight for the subject to the fully flexed elbow position, while the subject lowered the weight over a 4 s period until the elbow was fully extended. Repetitions were executed without rest until the subject was not able to lower the weight slowly and in a controlled manner (i.e. [greater than or equal to] 4 s) due to fatigue for 2 consecutive repetitions.
Signs of inflammation: Measures of signs of inflammation were made immediately before and 48 h after eccentric exercise. Assessments were performed 48 hours after exercise based upon evidence that shows peak soreness and inflammation occur in this time frame (Miles et al. 2008). Our assessment of inflammatory signs included measures of swelling, increased temperature and soreness, as these are hallmark characteristics of localized inflammation (Friden and Lieber 1992).
Swelling was assessed by measuring the circumference of the upper arm at the mid-brachium with a spring-loaded anthropometric tape. Swelling was also assessed by measuring arm volume, utilizing the water...