One of those active during strenuous exercise was tangled in knots (5,5)

I believe the answer is:

sweat gland

I'm a little stuck... Click here to teach me more about this clue!

'one of those active during strenuous exercise' is the definition.
I can't tell whether this defines the answer.

'was tangled in knots' is the wordplay.
'in knots' indicates anagramming the letters (I've seen this in other clues).
'was'+'tangled'='wastangled'
'wastangled' with letters rearranged gives 'SWEAT GLAND'.

Can you help me to learn more?

(Another definition for sweat gland that I've seen is " Perspirer".)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.