Athletes use nutrition strategies to improve their training and performance through increasing their metabolic capacity, delaying the onset of fatigue, and improving muscle hypertrophy by enhancing recovery, improving immune function, and decreasing oxidative stress. Krill oil is rich in long-chain omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), which have been found to have positive effects on inflammation [
Krill oil contains astaxanthin, a red carotenoid pigment and strong antioxidant that naturally occurs in salmon, shrimp, krill, crustaceans, or certain types of algae, giving krill its reddish color. Astaxanthin administration has been shown to reduce muscle damage [
In athletes, krill oil has been shown to improve postexercise immune function (2 g/d for six weeks) [
C2C12 myoblasts (ATCC; Manassas, Virginia) were plated at approximately 30% confluence and grown for 24 hours in 10% FBS high glucose DMEM with antibiotics (100
This study consisted of a randomized, double-blind protocol consisting of 2 groups of individuals given either 3 g of placebo (olive oil) or 3 g of krill (
Forty subjects were assessed for eligibility and of the twenty-one subjects enrolled 11 subjects received the placebo and 10 received krill oil. A total of 3 subjects were lost to follow-up by a lack of communication with the researcher (2 from the placebo and 1 from the krill oil group). A total of 18 subjects were analyzed, 9 from each condition (Figure
CONSORT chart.
Subject inclusion criteria were males 18 to 30 years of age, resistance training at least 2 times per week for the past six months, a minimum of 1 year of training experience active and currently resistance training, free of musculoskeletal, metabolic, and respiratory disorders, free of cardiovascular disease, no musculoskeletal injuries with the last six months, no history of smoking or drug use, no history of excessive alcohol consumption, not taking prescription medication, have not used a fish oil-, thermogenic-, protein-, amino acid-, or creatine supplement within the prior two months, and have not habitually used caffeine (e.g., more than 2 cups of coffee per day). Subjects were matched-paired by age, body mass, strength and resistance training, and physical activity background and then randomly placed into one of the two groups. Subjects were prohibited from consuming any nutritional supplements (including fish oil) for the duration of the study. Additionally, subjects were instructed to avoid consumption of all fish and fish byproducts. After an explanation of the procedures and associated risks, all volunteers completed written informed consent. All procedures were approved by the IntegReview Institutional Review Board, Austin, TX, USA (protocol #7952). This study was registered with the ISRCTN registry (ISRCTN11524409). Subject characteristic data are displayed in Table
Subject characteristic data.
Age (yrs) | Training age (yrs) | Body mass (kg) | Height (cm) | |
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Placebo |
22.0 ± 0.6 | 3.0 ± 0.2 | 79.9 ± 3.9 | 179.3 ± 3.1 |
Krill oil |
22.3 ± 0.4 | 3.1 ± 0.7 | 82.9 ± 5.0 | 178.8 ± 2.3 |
Resistance training occurred four days per week (programmed, nonlinear training split). The resistance training protocol was modified from Kraemer et al. [
Training Protocol.
Weekly Schedule | |||||
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Weight Training | Week | 1E | 2H | 3E | 4H |
Hypertrophy/endurance: | 3 sets/12 repetitions |
3 sets/8 repetitions |
3 sets/15 repetitions |
3 sets/10 repetitions | |
Strength: | 3–5 sets/5 repetitions |
3–5 sets/4 repetitions |
3–5 sets/3 repetitions |
3–5 sets/5 repetitions | |
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Hypertrophy/endurance: | 3 sets/12 repetitions |
3 sets/8 repetitions |
3 sets/15 repetitions |
3 sets/10 repetitions | |
Strength: | 3–5 sets/ 4 repetitions |
3–5 sets/4 repetitions |
3–5 sets/ 3 repetitions |
3–5 sets/ 3 repetitions | |
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Exercise Selection | |||||
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Monday | Tuesday | Wednesday | Thursday | Friday | Saturday |
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Leg press | Bench press | Squat | Bench press | ||
Squat | BB row | Deadlift | BB row | ||
Glute-ham raise | BB shoulder press | Leg press | BB shoulder press | ||
Pull-ups | Glute-ham raise | Pull-ups | |||
DB press | Seated leg curl | ||||
Incline DB press | Lying leg curl | ||||
Side lateral raise | Leg ext. | ||||
Preacher curl | Calf raise | ||||
Overhead tricep ext. | |||||
Cable fly | |||||
Hammer curl | |||||
Tricep pushdown | |||||
Cable press |
A whole-body dual-energy X-ray absorptiometry (DXA) (Hologic, Bedford, MA, USA) scan was utilized to measure body composition. Lean body mass (LBM) and fat mass (FM) were determined for the total body with the subject laying in a supine position with the knee extended and instructed not to move for the entire duration of the scan (∼5 minutes). Results from each scan were uploaded and accessed on a computer directly connected to the DXA device. All DXA scans were conducted prior to and after the completion of the study, and each subject was required to fast overnight (10 hours) prior to the DXA scan. Calibration of the DXA device was done against a phantom provided by the manufacturing company prior to testing.
One-repetition maximum (1 RM) was assessed on bench press and leg press at baseline and after 8 weeks. Loads were increased incrementally until maximal load or failure at a given load was reached. Briefly, subjects performed a general warmup and a specific warmup consisting of three sets. During the first set, subjects performed 10 repetitions with 50% of their predicted 1 RM. For the second set, they performed five repetitions with 70% of the predicted 1 RM. In the third set, subjects perform one repetition with 90% of their predicted 1 RM. After the completion of warmup sets, subjects rested for 3 minutes. Then, each subject had as many as five attempts to achieve their 1 RM load with 3–5 minutes rest between each attempt.
The perceptual measures were collected using a perceived recovery status scale. Ratings of perceived recovery were collected at the beginning and end of every week. The perceived recovery status scale consisted of a scalar representation numbering from 0 to 10. Visual descriptors of “very poorly recovered,” “adequately recovered,” and “very well recovered” for perceived recovery were presented at numbers 0, 5, and 10, respectively. Subjects were asked to identify their level of perceived recovery after warming up and before performing the training protocol.
The Stroop test is a psychological test of mental vitality and flexibility. The test consists of computerized presentation of the names of four colors (yellow, blue, green, and red), written in capital letters, Times New Roman font, size 24, in black. The order is semirandom, so that the same word never appears two consecutive times throughout the test. The subject’s task is to read each word as quickly as possible. This part of the test is intended to obtain a baseline to evaluate the reading ability and determine whether this ability is high enough so as not to hinder the interference effect. This is because the effect of color-word interference may be absent if the reading ability is lower than expected. Characterized by a series of colorized words, which themselves are colors, subjects were instructed to read the color of the word aloud and not the word itself. Correct answers and time to completion were recorded. “Congruent” indicates the number of correct responses out of five responses to the test with matching words and colors. “Incongruent” indicates the number of correct responses out of fifteen responses to the test with nonmatched words and colors.
Subjects donated approximately 10 mL of fasted, whole blood at the baseline and at the end of week 8. All blood samples were collected by a trained phlebotomist via venipuncture of an antecubital vein in the forearm using standard sterile procedures. Biomarkers comprising CMP, CBC, and lipid panels were assayed for data collection.
Before carrying out the parametric statistical analysis, dependent variables were examined for a normal distribution and outliers through investigation of boxplots and a normality test (i.e., Shapiro–Wilk). Normality tests revealed no outliers, and analysis was performed using the original data set. Repeated measures ANOVA were used to scrutinize the effects of supplementation on dependent variables assuming the group (placebo and krill oil) and time (pre- and posttest) as fixed factors (GraphPad Prism 7®, La Jolla, CA). Whenever an interaction or main effect was demonstrated, a Bonferroni post hoc test was performed to identify where the differences occurred. The significance level was previously set at
As shown in Figure
The effect of phosphatidylcholine on the activation of mTOR signaling. C2C12 myoblasts were stimulated for 20 minutes with vehicle (control), or 10–30
A significant main time effect was noted for lean mass (
Summary of the group lean mass values (a), individual lean mass response (b), and lean mass delta change (c) (∗significant within-group difference (
No between or within group differences were observed for fat mass (
Summary of group fat mass values (a), individual fat mass response (b), and fat mass delta change (c).
A significant main time effect was demonstrated whereby both conditions increased performance on bench press (
Summary of group bench-press performance (a), individual bench-press performance (b), and bench-press performance delta change (c) (∗significant time effect whereby each group increased from baseline (
Summary of group leg-press performance (a) and individual leg-press performance (b), and leg-press performance delta change (c) (∗significant time effect whereby each group increased from baseline (
A main time effect was demonstrated for perceived recovery (
Summary plot for perceived recovery scale weekly average (∗significantly higher than baseline,
A main time effect was demonstrated for the Stroop test completion time (
Stroop test results.
Placebo | Krill oil | |||
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Pre | Post | Pre | Post | |
Congruent | 5.0 ± 0.0 | 5.0 ± 0.0 | 5.0 ± 0.0 | 5.0 ± 0.0 |
Incongruent | 14.7 ± 0.2 | 14.8 ± 0.2 | 14.8 ± 0.2 | 14.8 ± 0.2 |
Completion time | 32.6 ± 6.7 | 17.2 ± 2.3 ^ | 33.8 ± 6.1 | 18.3 ± 2.1 ^ |
^Trend for within-group significant differences from pretest (
There were no within or between group differences for markers on the comprehensive metabolic panel (Table
Comprehensive metabolic panel.
Placebo | Krill oil |
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Pre | Post | Pre | Post | ||
Glucose (mg/dL) | 84 ± 2 | 86 ± 4 | 91 ± 3 | 90 ± 4 | 0.689 |
BUN (mg/dL) | 13 ± 1 | 13 ± 1 | 13 ± 2 | 15 ± 2 | 0.200 |
Creatinine (mg/dL) | 1.07 ± 0.1 | 1.05 ± 0.1 | 1.06 ± 0.1 | 1.00 ± 0.1 | 0.523 |
Total protein (g/dL) | 7.1 ± 0.1 | 7.1 ± 0.1 | 7.2 ± 0.1 | 7.0 ± 0.1 | 0.114 |
Albumin (g/dL) | 4.6 ± 0.1 | 4.5 ± 0.1 | 4.8 ± 0.1 | 4.6 ± 0.1 | 0.227 |
Total bilirubin (mg/dL) | 0.4 ± 0.1 | 0.3 ± 0.1 | 0.6 ± 0.3 | 0.5 ± 0.3 | 0.510 |
Sodium (mmol/L) | 141 ± 1 | 141 ± 1 | 142 ± 1 | 141 ± 1 | 0.339 |
Potassium (mmol/L) | 4.3 ± 0.1 | 4.2 ± 0.1 | 4.3 ± 0.1 | 4.3 ± 0.1 | 0.328 |
Chloride (mmol/L) | 100 ± 1 | 101 ± 1 | 101 ± 1 | 101 ± 1 | 0.939 |
CO2 (mmol/L) | 23 ± 1 | 22 ± 1 | 22 ± 1 | 22 ± 1 | 0.791 |
ALP (IU/L) | 73 ± 6 | 75 ± 6 | 75 ± 5 | 70 ± 6 | 0.075 |
AST (IU/L) | 24 ± 5 | 22 ± 2 | 20 ± 1 | 17 ± 1 | 0.827 |
ALT (IU/L) | 22 ± 5 | 19 ± 3 | 19 ± 1 | 17 ± 2 | 0.754 |
Values are reported as mean ± standard deviation; BUN, blood urea nitrogen; CO2, carbon dioxide; ALP, alkaline phosphatase; AST, aspartate aminotransferase; ALT, alanine transaminase.
Complete blood count panel
Placebo | Krill oil |
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Pre | Post | Pre | Post | ||
WBC (K/ |
5.6 ± 0.2 | 5.5 ± 0.2 | 5.7 ± 0.2 | 5.5 ± 0.3 | 0.586 |
RBC (M/ |
5.01 ± 0.14 | 5.12 ± 0.12 | 5.26 ± 0.08 | 5.08 ± 0.09 | 0.114 |
Hemoglobin (g/dL) | 15.1 ± 0.4 | 15.4 ± 0.2 | 14.7 ± 1.1 | 15.3 ± 0.3 | 0.785 |
Hematocrit (%) | 44.6 ± 1.2 | 45.3 ± 0.7 | 46.9 ± 0.9 | 45.7 ± 1.1 | 0.160 |
MVC (fL) | 89.1 ± 1.6 | 89.2 ± 1.1 | 88.8 ± 1.3 | 90.4 ± 1.2 | 0.414 |
MCH (pg) | 30.2 ± 0.7 | 29.9 ± 0.5 | 30.0 ± 0.6 | 30.0 ± 0.4 | 0.999 |
MCHC (g/dL) | 33.4 ± 0.2 | 33.2 ± 0.3 | 33.8 ± 0.3 | 33.3 ± 0.2 | 0.481 |
Platelets (K/ |
228 ± 10 | 221 ± 10 | 232 ± 11 | 219 ± 10 | 0.431 |
Neutrophils (K/ |
2.8 ± 0.2 | 2.9 ± 0.2 | 3.1 ± 0.2 | 2.8 ± 0.2 | 0.197 |
Lymphocytes (K/ |
2.1 ± 0.1 | 2.0 ± 0.1 | 2.0 ± 0.1 | 2.0 ± 0.1 | 0.999 |
Monocytes (K/ |
0.5 ± 0.1 | 0.5 ± 0.1 | 0.5 ± 0.1 | 0.5 ± 0.2 | 0.739 |
Eosinophils (K/ |
0.1 ± 0.1 | 0.2 ± 0.1 | 0.1 ± 0.1 | 0.1 ± 0.1 | 0.461 |
Basophils (K/ |
0.0 ± 0.0 | 0.0 ± 0.0 | 0.0 ± 0.0 | 0.0 ± 0.0 | 0.555 |
Values are reported as mean ± standard deviation; WBC, white blood cells; RBC, red blood cells; MVC, mean cell volume; MCH, mean cell hemoglobin; MCHC, mean cell hemoglobin concentration.
Previous studies have shown that soy-derived phosphatidic acid (PA), lyso-PA, or phosphatidylserine (PS) can stimulate a robust increase in mTOR signaling; however, soy-derived PC was not effective [
Phospholipids, including PC, PS, or PA, have previously been shown to improve athletic performance [
While lean body mass significantly increased in the krill oil group (+1.4 kg, +2.1%) we observed no statistically significant difference in comparison to the control group (+0.3 kg, +0.5%). The increase in lean body mass was matched by an increase in muscle strength in the krill oil group (bench press +4.3 kg (+4.4%); leg press: +48.9 kg (+15.8%)); however, the increase was no different from the control group (+3.4 kg (+3.3%); leg press: +44.2 kg (+14.6%)). Perceived recovery significantly increased in the krill oil group (+15%) at the end of the trial in comparison to baseline; however, the results were not statistically different from the control group (+14%). Perceived recovery was the lowest in both groups in week 6, and subjects seem to adapt to recovering to the training stimulus by the end of the study. While the training protocol was challenging enough to see significant increases in strength, the training stimulus or the recovery periods might not have been challenging enough to elicit differences in perceived recovery. Our results contrast with previous studies showing significant improvements of postexercise muscle soreness with omega-3 supplementation [
While long-chain omega-3 polyunsaturated fatty acid supplementation has been linked to improved cardiovascular health [
Krill oil activates mTOR signaling. Krill oil supplementation in athletes is safe, and while no significant effects on cognition and strength were observed, its effects on body composition in combination with resistance exercise deserves further research.
All procedures were approved by the IntegReview Institutional Review Board, Austin, TX, USA (protocol #7952). This study was registered with the ISRCTN registry (ISRCTN11524409).
Flint Harding, James H. Johnson, and David M. Peele are employees of Avoca, Inc., a manufacturer of Krill oil. Martin Purpura and Ralf Jäger are independent paid consultants to Avoca, Inc., and David M. Peele, Ralf Jäger, and Martin Purpura have been named as inventors for the patent PCT/US2016/048079. All other authors declare that they have no competing interests.
Cell culture tests were performed by Troy A. Hornberger at the University of Wisconsin-Madison. All human work was conducted at the Applied Science and Performance Institute by John Georges, Matthew H. Sharp, Ryan P. Lowery, and Jacob M. Wilson. Flint Harding, James H. Johnson, David M. Peele, Ralf Jäger, and Martin Purpura were involved in concept and design of the overall study, but not in the data collection or analysis of the results. The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.
The authors would like to thank a dedicated group of subjects, who kindly donated their time and effort to this study. This research was supported by Rimfrost USA (Merry Hill, NC) and by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health (NIH) under Award number AR057347.