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.

Study design
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 non-dominant arm for the control trial and the dominant arm for the omega-3 trial.

Subjects
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.

Procedures
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. > 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 displacement method. This method is commonly used for monitoring lymphedema in breast cancer patients and has been shown to be sensitive to day-to-day fluctuations in arm volume that are associated with changes in edema (Lette, 2006). In brief, the volumeter is a vertical cylinder (100 cm tall, 15 cm in diameter) with a small spout at the top through which water can spill out. After filling the volumeter to the top with water, the subject slowly inserted their arm into the volumeter until a pre-marked area on the arm (near the insertion of the deltoid muscle) was at the water's surface. The water that spilled out of the volumeter was captured in a container and weighed. Water density was assumed to equal 1 g·mL-1; therefore, arm volume (in mL), was equal to the mass (in grams) of the displaced water. To ensure that the arm was inserted into the volumeter to the same level between baseline and 48-hr post exercise assessments, the subjects were advised to not wash off the reference mark on their arm between tests.

Temperature was measured using an infrared skin sensor (Dermatemp^TM Infrared Temperature Scanner. Model # DT1000, Exergen Corp, Newton, Mass). A total of five temperatures were taken on the bicep mid brachii and the mean of all readings were used. Infrared thermometers are highly reliable and valid devices for measuring skin surface temperature (Burnham et al., 2006).

Soreness was measured using a visual analog scale on which the participants placed a tick mark on a 10 cm line to indicate the degree of soreness. The distance in centimeters from the left end of the scale to the tick mark was used to reflect soreness. Several studies have assessed the validity and reliably of the visual analog scale as a means for measuring subjective soreness (Gallagher et al., 2002). Muscle soreness was rated three ways: "Weighted" measures were made while the participants flexed and extended the elbow while holding a 1.1 kg weight; "Palpated" soreness was assessed with the participant relaxing their arm and while the technician palpated/massaged the bicep muscle ~2 cm inferior to the olecranon-to-acromion midpoint; "Fully extended" soreness ratings were made while the participants attempted to fully extend their elbow.

Omega-3 supplementation protocol: For the entire study subjects were placed on a restricted omega-3 fatty acid diet. The subjects were provided with a specific list of omega-3 containing foods to avoid. This ensured that dietary omega-3 fatty acid intake was minimized. During the omega-3 trial, participants took 2,000 mg EPA and 1,000 mg DHA per day (Rx Omega-3 Factors, Natural Factors, Everett, Washington; 400 mg EPA and 200 mg DHA per softgel capsule). Previous research has used omega-3 fatty acid supplements in a ratio of EPA:DHA of 2:1 (Simopoulos, 2007). A supplement diary was given to each subject so they could record when they took the daily supplements. Additionally, pill counts were performed to assess compliance with the supplementation regimen. To maintain consistency with the amount of omega-3 fatty acids among subjects, the supplements were the only source of omega-3 fatty acids in the diet, as subjects continued to follow an omega-3 restricted diet.

Statistical analysis
Primary statistical analysis was performed on all subjects to assess the physiologic efficacy of the omega-3 supplementation. Change scores were calculated for each of the inflammatory markers by subtracting the final values (48 hr post exercise) from the baseline values (as measured immediately prior to eccentric exercise) for each trial. Paired t-tests were used to compare the change in inflammation from the control trial to the change in inflammation for the omega-3 trial. Statistical analysis was performed using SPSS software. A p-value of ?0.05 was considered significant. Values are presented as mean ± SE unless indicated otherwise.

Participants
Eight women (73%) and three men (27%) completed the study. Mean age (± SD) was in the middle to lower end of the targeted age range for the study (Table 1). BMI was 22.9 ± 2.0 kg·m^-2, reflecting that most of the participants were lean to normal weight. As expected, men had greater 1RM than women. Strength in the dominant and non-dominant arms was similar for both men and women (Table 1). Pill counts indicated 100% compliance with the supplementation regimen.

Eccentric exercise performance
There was no difference (p = 1.00) in the weight used for eccentric exercise in the control trial (11.3 ± 4.2 kg) and the omega-3 trial (11.3 ± 4.6 kg). However, in the omega-3 trial, subjects completed more repetitions in set 1 (18 ± 3 vs. 21 ± 7 reps, p = 0.05) and set 2 (8 ± 3 vs. 10 ± 4 reps, p = 0.02), thereby resulting in greater total eccentric exercise volume (280 ± 73 vs. 321 ± 66 kg·repetitions, p= 0.01).

Post-exercise soreness
All three measures of muscle soreness showed very large increases in soreness between baseline and 48 h follow-up (Table 2), indicating that the exercise protocol induced significant arm soreness. Omega-3 supplementation attenuated the soreness based on the "weighted" and "fully extended" measures. Omega-3 supplementation also attenuated the "palpated" soreness, although this did not achieve statistical significance (p = 0.11).

Post-exercise swelling
Arm volume, did not change significantly between baseline and the 48 h follow up visit in either the control or omega-3 trial (Table 2). Although arm circumference increased significantly in the control trial but not in the omega-3 trial, the magnitude of increase in arm circumference was not different between trials (Table 2).

Post-exercise temperature
No statistical difference between baseline and 48 h follow-up measures of skin temperature were found. Furthermore, there was no difference found between the control and omega-3 trail with respect to changes in temperature in response to eccentric exercise.

Results from the present study indicate that omega-3 fatty acid supplementation decreases muscle soreness after high-intensity eccentric exercise. This effect could be beneficial to athletes who undergo high-intensity strength training, which often produces delayed-onset muscle soreness. Furthermore, although we did not study lower intensity eccentric exercise, such as that which occurs during running, it is also possible that omega-3 fatty acid supplementation might attenuate the post exercise muscle soreness that occurs after activities such as marathon running. An omega-3 fatty acid dose of < 3000 mg·day^-1 (DHA+EPA) has been designated as safe for general consumption by the US Food and Drug Administration (Food and Drug Administration 2004). Until further research is done, one should abide by these recommendations if using fish oil for decreasing soreness and/or pain from exercise.

Pain, heat and swelling are signs associated with localized inflammatory process and can be measured noninvasively. We assessed the effect of omega-3 fatty acid supplementation on these hallmark characteristics of inflammation. Muscle soreness increased substantially after eccentric exercise, as evidenced by the soreness ratings. It is also noteworthy that most participants had such severe soreness that they struggled to achieve full elbow extension 48 h after exercise. Despite the severe soreness induced by eccentric exercise, arm volume, as a measure of swelling, and skin temperature did not change significantly in response to eccentric exercise, even in the control trial, indicating that these measures are not sensitive enough to change in response to eccentric biceps curls. Consequently, this precluded the possibility of determining if omega-3 fatty acid supplementation affects swelling and warmth as inflammatory characteristics.

One previous study found that a supplement containing the omega-3 fatty acid DHA attenuated the inflammatory response to eccentric exercise (Phillips et al., 2003). However, it is not clear if the beneficial effect was attributed to DHA, as the supplement also contained mixed tocopherols and flavonoids, which might have their own anti-inflammatory effects. Numerous other studies have demonstrated that omega-3 supplementation can act as a natural anti-inflammatory agent for people taking non steroidal anti-inflammatory drugs (NSAIDs) for medical conditions (Maroon and Bost, 2006a; Maroon and Bost, 2006b).

An unanticipated finding was that the participants performed more eccentric exercise after omega-3 supplementation. One explanation for this is that omega-3 supplementation increased muscle strength and/or decreased fatigue. Omega-3 fatty acids have anabolic properties in muscle tissue of healthy humans (Smith et al., 2011) and omega-3 rich fatty fish consumption is associated with grip strength in older adults (Robinson et al., 2008). Furthermore, EPA attenuates muscle wasting that is associated with cancer cachexia (Ryan et al., 2009), bacterial endotoxin exposure (Supinski et al., 2010), and arthritis (Castillero et al., 2009). However, these are not likely the main cause for the effects seen in the present study, especially in light of the short, weeklong supplementation period. An alternative explanation is that there was a "repeated bout effect" in which adaptations occurred between the first (control) and second (omega-3) trial (McHugh, 2003) (because of long washout time for omega-3 (Cerbone et al., 1999) we designed the study so that the omega-3 trial always occurred last). We intended to preclude this possibility by using opposite arms for the control and omega-3 trials. However, while some research suggests that the repeated bout effect does not affect the contralateral limb (Connolly et al., 2002; Clarkson et al., 1987), a more recent study suggests that it does, at least partially (Howatson and van Someren, 2007). Nonetheless, it is intriguing that despite the fact that more eccentric work was performed in the omega-3 trail, soreness was significantly less.

The present study is limited in that the lack of a placebo group precludes the ability to rule out a potential psychological impact on subjective soreness ratings. However, anecdotally, most of the study participants did not have interest in the study outcome and those who did were skeptical about the potential soreness reducing effects of omega-3s. Thus, it seems unlikely that a placebo effect could explain our findings. Another limitation is that our sample size was small, thereby increasing the chances of a "false-positive" finding. Future research, using a larger sample and a randomized controlled design will be important for providing more definitive evidence. Finally, it is important to recognize that the beneficial effects seen in the present study were achieved with a EPA/DHA ratio of 2:1 and a fairly large 3000 mg/d dose, requiring 1-2 softgel capsules to be taken at each meal. We cannot determine whether smaller, more economical, and more convenient dosing regimens would provide similar benefits. However, it is noteworthy that we saw beneficial effects after only 7-days of supplementation. This suggests that chronic supplementation is not necessary for protection against muscle soreness and that supplementation could be initiated in the ~7 days prior to activity that might cause soreness, such as a marathon or intensified period of strength training.

Muscle microtrauma, inflammation, and soreness are often caused by increases in physical activity such as vigorous training or competition in an elite athlete or physical therapy for rehabilitation from a hip fracture in an elderly patient. While NSAIDs are often used to treat post-exercise muscle soreness, omega-3 fatty acid supplementation could be a safer and healthier alternative (Maroon and Bost, 2006b). In addition to attenuating muscle soreness, omega-3 fatty acids may protect against cardiovascular disease (Lavie et al., 2009) and cardiac arrhythmias (Richardson et al., 2011), slow the age-related decline in cognitive function (Fotuhi et al., 2009), and protect against some forms of cancer (Rose and Connolly, 1999). In contrast, there appear to be very few adverse effects from omega-3 fatty acid supplementation, with the main concern being increased bleeding time (and theoretically an increased risk of hemorrhagic stroke) at intakes > 3000 mg·d^-1 (Food and Drug Administration 2004), an effect which might have important ramifications for individuals on anticoagulation therapies. However, this effect has not been substantiated in clinical trials (Bays, 2007). Other concerns about omega-3 fatty acid supplementation are related the possible presence of pollutants (from fish sources) (Bourdon et al., 2010) and the proneness to oxidation. However, these issues are not directly related to omega-3 fatty acid consumption, per se, and can be managed with proper manufacturing methods (i.e. fish source monitoring or use of algal sources), and storage techniques (for example, using vitamin E as an antioxidant preservative).

We are grateful to the study participants for their cooperation and time.

• Dietary supplementation with omega-3 fatty acids has been shown to reduce inflammation in numerous inflammatory diseases such as rheumatoid arthritis, inflammatory bowel disease, and Chrohn's disease.
• Although strenuous exercise is known to cause acute increases in inflammation, it is not clear if omega-3 fatty acid supplementation attenuates this adverse response to exercise.
• Our research demonstrates that 3000 mg·d-1 omega-3 fatty acid supplementation minimizes the severe, delayed-onset muscle soreness that results from strenuous eccentric strength exercise.
• This information, along with a plethora of information showing that omega-3 fatty acid supplementation has other health benefits, demonstrates that a readily available over the counter nutritional supplement (i.e. omega-3 fatty acids) reduces delayed-onset soreness caused by strenuous strength exercise.
• This information has obvious relevance to athletic populations but also to other groups such as physical therapy patients and newly admitted cardiac rehabilitation patients, as muscle soreness, if left unchecked, can slow the progress in adapting to a new exercise program.
• Furthermore, as inflammation is known to be involved in the pathogenesis if numerous diseases, including heart disease, cancer, and diabetes, it is likely prudent for individuals to use inflammation-attenuating interventions, such as omega-3 supplementation, to keep inflammatory responses to physical activity at a minimum.