Recreational male runners participated in 12 weeks training and omega-3 supplementation programme. Before starting and at the end of the 12-week cycle, the runners performed an increasing intensity treadmill test where oxygen uptake and VO2 peak were assessed.

40 healthy, recreational male runners participated in 12 weeks training and supplementation programme. The training protocol was built based on undulatory load manipulation 3:1, which was suggested to be effective to prevent overtraining and stress due to oscillations between volume/intensity. Throughout the study all participants took 4 identical-looking capsules per day (2 in the morning and 2 in the evening) containing either omega-3 fatty acids or medium chain triglycerides as placebo in total amount of 4g of fat per day. Before starting and at the end of the 12-week cycle, the runners performed an increasing intensity treadmill test where oxygen uptake and VO2 peak were assessed. Additionally, blood was collected to determine the concentrations of selected proteins (including eNOS, irisin, adiponectin) that may be associated with potential changes in participants' oxygen uptake during the treadmill test.

Inclusion Criteria:

• non smoking
• no chronic diseases
• no supplements and medicines
• personal best in 10km run between 35 and 59 min at the turn of 2016 and 2020 y

Exclusion Criteria:

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