The Omega-3 Index measures how much of the Omega-3 fats EPA and DHA are built into red blood cell membranes. These fats are essential for health, but the body cannot make enough of them, so they must come from foods like oily fish or from supplements. The Index reflects long-term Omega-3 intake and is considered optimal at 8% or higher. Levels below this range have been linked with poorer cardiovascular health (Harris \& Von Schacky, 2004). . For athletes, Omega-3 research suggests they can help reduce inflammation, ease muscle soreness, and support immune function. Despite this, many elite athletes appear to have Omega-3 Index values around 4-5%, well below the recommended level of 8%. Therefore, the aim of this study is to investigate whether increasing the Omega-3 index has any recovery benefits post a bout of downhill running in athletes. Downhill running is commonly used as way to cause exercise-induced muscle damage and study recovery. The Omega-3 index will be increased with a daily fish oil supplement.
The proposed research will follow quantitative methods using a randomized independent-groups design. Participants will be allocated to one of two conditions: a placebo group or a fish oil supplementation group. All testing will take place in the St. Mary's University Performance Labs. Screening and Eligibility At the initial visit, participants will provide informed consent and complete a PAR-Q form. Eligibility screening will include confirmation that participants have an Omega-3 index ≤ 5%, assessed via a dried blood spot sample obtained from a capillary finger-prick. Samples are processed by OmegaQuant at their lab in Stirling, and results are typically returned within one week. Participants will also be excluded if they are currently consuming ≥1 g/day of fish-oil supplements. Randomisation and Blinding Eligible participants will be randomly assigned to one of the two experimental groups using a random number generator (https://www.random.org). The study will follow a double-blind design: participants will not know which supplement they receive, and the primary investigators involved in data collection will also remain blinded. Supplement distribution and any dose adjustments will be conducted by a separate member of the research team who is unblinded and not involved in testing of participants or data analysis. Screening Tests/familiarisation Once Omega-3 index results are available, eligible participants will return to the lab for physiological screening/familiarisation of the test battery and to receive their supplements. Screening/familiarisation procedures include: * An incremental treadmill ramp test, starting at 8 km·h-¹ and increasing by 1 km·h-¹ every 3 minutes until volitional exhaustion. During the test the below measures will be taken: * Capillary blood lactate sampling (finger or earlobe) every 3 minutes. * Continuous breath-by-breath respiratory analysis using the Vyntus online gas analyser. * Heart rate monitoring (Polar H10) and Rate of Perceived Exertion (RPE; Borg scale). The screening session also introduces participants to the test battery illustrated in Figure 3. Supplementation Phase (Part A) Participants will be asked to refrain from: * Alcohol for 48 hours before each testing session. * Caffeine for 12 hours before each testing session. Participants will consume their assigned supplements daily for four months. Investigators will contact participants approximately every four weeks to assess adherence and to distribute additional supplement supplies. At two months, a repeat dried blood spot sample will assess whether Omega-3 levels in the fish-oil group are increasing as expected. If required, supplementation will be adjusted using the OmegaQuant calculator (https://omegaquant.com/omega-3-index-calculator/). Adjustments will typically involve changes of approximately 0.5 g/day (EPA + DHA). To maintain double-blinding, placebo dosages will also be altered by ±0.5 g/day, ensuring both investigator and participant remain unaware of group allocation. After four months, participants will provide another dried blood sample. The aim is for the fish-oil group to reach an Omega-3 index ≥ 8%. Participants who do not meet their target will continue supplementation for an additional 2-4 weeks, followed by another blood test, until the required level is achieved. A cut-off point 6 additional weeks will be incorporated. Completion of this phase constitutes Part A: the supplementation phase. Exercise-Induced Muscle Damage Trial (Part B) Approximately one week before Part B, participants will return to the lab to complete a second treadmill ramp test to determine the appropriate speed for the downhill running protocol. Participants will then attend the laboratory on four consecutive days to complete pre- and post-exercise assessments associated with the exercise-induced muscle damage protocol. The proposed study requires participants to take fish oil supplementation in order to increase their Omega-3 index and investigate whether this produces performance or recovery benefits, beyond the well-established long-term health effects associated with approximately 3 g/day of EPA + DHA. Fish oil supplementation is widely used in both clinical and general health contexts and is considered safe at doses of up to 5 g/day, as recognised by the European Food Safety Authority. Participants will be recruited to complete the supplementation phase and take part in an exercise-induced muscle damage (EIMD) protocol. They will be randomly allocated to one of the two study groups (fish oil or placebo). Fish oil supplementation will be provided by OmegaQuant (https://parasolnutrition.com/product/omega-3-fish-oil/) , this supplement is commercially available Test battery: 1. Venous Blood Samples Venous blood samples will be collected to assess resting concentrations of inflammatory and muscle-damage biomarkers, including Interleukin-6 (IL-6), Interleukin-10 (IL-10), Tumor Necrosis Factor-α (TNF-α), myoglobin, lactate dehydrogenase (LDH), and creatine kinase (CK). Samples will be obtained by qualified phlebotomists at St Mary's University (Toby Helder, Prof. Charles Pedlar, and Dr Jessica Hill). All venous samples will be stored at -80°C and later analysed using enzyme-linked immunosorbent assays (ELISAs). Venous sampling will occur at all required testing timepoints. 2. FORD/FORT Capillary Blood Testing Fingertip capillary blood samples (50 µL and 20 µL, respectively) will be collected to assess oxidative stress using the Clini5 device (Callegari, Italy): * FORT: Free Oxygen Radical Test * FORD: Free Oxygen Radical Defence Test These provide an overall assessment of redox status. The device uses rapid, ready-prepared reagents requiring no cooling or manual preparation. Results are available within 6 minutes. 3. hs-CRP Capillary Blood Testing A 20 µL fingertip capillary sample will be collected to measure high-sensitivity C-reactive protein (hs-CRP), a marker of systemic inflammation. Analysis will be performed using the Eurolyser Cube S analyser (Eurolyser, Austria), with results available within 5 minutes. 4. Perceived Muscle Soreness Participants will report muscle soreness using two validated scales: * The Visual Analogue Scale (VAS) * The Borg CR-10 Scale These will be administered at all relevant timepoints. 5. Maximal Strength Testing (Cybex Dynamometer) Isokinetic Strength: Peak torque of the knee extensors will be measured at 60°·s-¹ using a Cybex isokinetic dynamometer. This will be completed at all testing timepoints. 6. Isometric Mid-Thigh Pull (IMTP) Peak force and rate of force development will be assessed using an isometric mid-thigh pull rig with standardised knee and hip angles. Force production will be recorded via VALD force plates. 7. Countermovement Jump (CMJ) Participants will perform countermovement jumps on VALD force plates to assess neuromuscular function. They will complete three warm-up jumps, followed by three recorded trials, with hands placed on the hips to minimise upper-body contribution. Downhill running protocol Participants will arrive in a fasted state either over night (for morning sessions) or a minimum of four hours fasted (mid-morning, afternoon and evening sessions). Participants will be familiarized with all equipment used and procedures before baseline measurements of height, weight and body composition are taken and pre-test venous blood sample taken. Participants will then complete a five-minute warm-up on a treadmill at 1% gradient at a self-selected speed. Following the warm-up, the treadmill will then be lowered to -10% gradient and participants will run for 45 minutes at 70% of their maximal aerobic capacity. \- Participants will be required to take their assigned supplements daily for a period of four months. During this phase, they will have brief check-ins approximately every four weeks to monitor wellbeing and adherence. At the midpoint of supplementation (two months), a short visit is required for a dried blood spot test (see Figure 1 for an overview of the study timeline). Although the overall study duration spans several months, data collection involves only nine in-person visits, most of which will last under one hour. Only the main exercise-testing sessions will be longer in duration. * The research will take part at St Mary's University in the performance Laboratories. * All testing equipment used is the property of St Mary's University Twickenham. All supplement will be provided by OmegaQuant. All testing procedures are as outlined by British Association of Sport and Exercise Science.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
OTHER
Masking
DOUBLE
Enrollment
46
We are providing fish oil supplementation with the aim to increase the omega 3 index (O3I) in red blood cells from a low amount (5-6%) to a high amount \>8%. The fish oil group will be provided a supplement with a dose of EPA and DHA which is designed for them to get to this level. The placebo group has a supplement which is not designed to increase the EPA + DHA in the blood. After 4 months, the O3I levels in the blood will be checked and if they have reached the appropriate level they will proceed to the next phase which is to complete a muscle damaging protocol specifically down hill running. They will then be assessed on their recovery directly post exercise, 24h, 48h, and 72h post exercise.
Plasma interleukin-6 (IL-6) concentration
Venous blood samples will be collected at baseline (pre-exercise) and during recovery at immediately post-exercise, 24 hours, 48 hours, and 72 hours post-exercise. Samples will be processed to obtain plasma and stored at -80°C in coded tubes to maintain participant confidentiality. After completion of sample collection for all participants, plasma IL-6 concentration will be quantified (e.g., via immunoassay) and reported as concentration at each time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Plasma interleukin-10 (IL-10) concentration
Venous blood samples will be collected at baseline (pre-exercise) and during recovery at immediately post-exercise, 24 hours, 48 hours, and 72 hours post-exercise. Samples will be processed to obtain plasma and stored at -80°C in coded tubes to maintain participant confidentiality. After completion of sample collection for all participants, plasma IL-10 concentration will be quantified (e.g., via immunoassay) and reported as concentration at each time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Plasma Tumor Necrosis Factor-α (TNF-α) concentration
Venous blood samples will be collected at baseline (pre-exercise) and during recovery at immediately post-exercise, 24 hours, 48 hours, and 72 hours post-exercise. Samples will be processed to obtain plasma and stored at -80°C in coded tubes to maintain participant confidentiality. After completion of sample collection for all participants, plasma TNF-α concentration will be quantified (e.g., via immunoassay) and reported as concentration at each time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Myoglobin concentration
Venous blood samples will be collected at baseline (pre-exercise) and during recovery at immediately post-exercise, 24 hours, 48 hours, and 72 hours post-exercise. Samples will be processed to obtain both plasma and serum and stored at -80°C in coded tubes to maintain participant confidentiality. After completion of sample collection for all participants, myoglobin concentration will be quantified (e.g., via immunoassay) and reported as concentration at each time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Serum Lactate dehydrogenase (LDH) concentration
Venous blood samples will be collected at baseline (pre-exercise) and during recovery at immediately post-exercise, 24 hours, 48 hours, and 72 hours post-exercise. Samples will be processed to obtain plasma and stored at -80°C in coded tubes to maintain participant confidentiality. After completion of sample collection for all participants, Serum LDH concentration will be quantified (e.g., via immunoassay) and reported as concentration at each time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Plasma creatine kinase (CK) concentration
Venous blood samples will be collected at baseline (pre-exercise) and during recovery at immediately post-exercise, 24 hours, 48 hours, and 72 hours post-exercise. Samples will be processed to obtain plasma and stored at -80°C in coded tubes to maintain participant confidentiality. After completion of sample collection for all participants, plasma CK concentration will be quantified (e.g., via immunoassay) and reported as concentration at each time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Plasma high sensitivity C-reactive Protein (hs-CRP) concentration
Venous blood samples will be collected at baseline (pre-exercise) and during recovery at immediately post-exercise, 24 hours, 48 hours, and 72 hours post-exercise. Samples will be processed to obtain plasma and stored at -80°C in coded tubes to maintain participant confidentiality. After completion of sample collection for all participants, plasma hs-CRP concentration will be quantified (e.g., via immunoassay) and reported as concentration at each time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Capillary Free Oxygen Radical Test (FORT) Concentration
Capillary whole blood samples (20 µL) will be collected at baseline (pre-exercise) and immediately post-exercise from the fingertip or earlobe using a single-use lancet. Oxidative stress will be assessed using the Free Oxygen Radicals Test (FORT) on the Callegari Clini5 analyser; analysis time is approximately 6 minutes. Results will be recorded at each time point and reported as the FORT value and change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Capillary Free Oxygen Radical Defence (FORD) Concentration
Capillary whole blood samples (50 µL) will be collected at baseline (pre-exercise) and immediately post-exercise from the fingertip or earlobe using a single-use lancet. Oxidative stress will be assessed using the Free Oxygen Radical Defence (FORD) on the Callegari Clini5 analyser; analysis time is approximately 6 minutes. Results will be recorded at each time point and reported as the FORT value and change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Muscle soreness (Visual Analogue Scale, VAS)
Participants will complete 5 bodyweight squats, then rate perceived leg muscle soreness using a visual analogue scale (VAS) by placing a mark on a 100-mm line anchored from "no soreness" to "worst soreness imaginable." The score will be recorded in mm (0-100) at each assessment time point and analysed as the VAS value and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Muscle soreness (Borg CR-10 Scale)
Participants will rate perceived exertion using the Borg Category-Ratio 10 (CR-10) scale at baseline (pre-exercise), immediately post-exercise, and during recovery at 24 hours, 48 hours, and 72 hours post-exercise (aligned with venous sampling time points). The CR-10 ranges from 0 ("nothing at all") to 10 ("maximal"), and participants will select the number that best represents their exertion. Scores will be recorded in CR-10 units at each time point and analysed as the value and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Knee extensor strength (isokinetic dynamometry: peak torque at 60°/s)
Peak torque of the knee extensors will be assessed using a Cybex isokinetic dynamometer at an angular velocity of 60°·s-¹. Testing will be performed at all study assessment time points (baseline and post-exercise recovery visits). Peak torque will be recorded in N·m for each assessment and analysed as the value at each time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Knee extensor isometric endurance (time to task failure at 50% peak torque)
Knee extensor isometric endurance will be assessed using the Cybex dynamometer. After determination of knee extensor peak torque, participants will perform a sustained isometric contraction at 50% of their isokinetic peak torque and will be instructed to hold the target force/torque for as long as possible. The test will be terminated when the participant can no longer maintain the target (time to task failure). Endurance will be recorded as time (seconds) at each assessment time point and analysed as the value and/or change from baseline.
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Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Isometric mid-thigh pull (IMTP): peak force and rate of force development
Peak force and rate of force development (RFD) will be assessed using an isometric mid-thigh pull (IMTP) rig. Participants will be positioned in a standardized pulling posture with consistent knee and hip angles across sessions and secured to a fixed bar/rig. After instruction and familiarisation, participants will perform maximal isometric pulls "as hard and as fast as possible" for a fixed duration, with trials separated by standardized rest periods. Ground reaction forces will be recorded using VALD force plates, and outcomes will be derived as peak force (N) and RFD (e.g., N·s-¹) at each testing time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.
Countermovement jump (CMJ): jump performance
Countermovement jump performance will be assessed using VALD force plates. Participants will perform standardized CMJs (e.g., hands on hips) from an upright standing position, completing a rapid downward countermovement followed immediately by a maximal vertical jump. Trials will be separated by standardized rest periods, and force-time data will be recorded for each jump. Outcomes will be derived from the force-plate data (e.g., jump height and/or peak power/peak force, as specified) at each testing time point and/or change from baseline.
Time frame: Participants will complete this once at baseline and then again after 4 months of supplementation.