Thank you for your query at DoctorSpring.com
I understand your concern.
If there has been no increase in size, then usually it can be ignored. Sometimes, certain lymph nodes can be present due to a previous infection or reactive lymphadenitis. If the size does not increase, or there is no pain, it can be ignored.
Since you're active and fit, you should not worry.
The only way to find the exact cause is a biopsy from the lymph nodes, but it not required without symptoms.
Feel free to discuss further,