During a biceps curl the triceps play what role in contraction

Well during a bicep curl the triceps relax enough for the biceps to be able to curl to tense and contract in a curl. This is called antagonist which means “a muscle whose action counteracts that of specified muscle.”
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The person who utilize the progression principle will keep adding the difficulty of the exercise that he's doing, while the person who does not, will only stay stagnant.  the person that utilize progression principle, will get a stronger endurance because now his body is conditioned to do harsher routines.{the answer was already on verified)

"observation" would be the correct answer