I suggest the idiom go against someone's grain:

to not seem right or natural to someone.

It goes against his grain to question the boss's judgment.

[Merriam-Webster]

On a side note, are you sure working out is the sort of thing that is against your instincts? Everyone does "work out" every once in a while if I may say so, right? Apart from that, the suggested idiom seems to cover your question very well.

I suggest the idiom go against someone's grain:

to not seem right or natural to someone.

It goes against his grain to question the boss's judgment.

[Merriam-Webster]

On a side note, are you sure working out is the sort of thing that goes aainst your instincts? Everyone does "work out" every once in a while if I may say so, right? Apart from that, the suggested idiom seems to cover your question very well.

I suggest the idiom go against someone's grain:

to not seem right or natural to someone.

It goes against his grain to question the boss's judgment.

[Merriam-Webster]

I suggest the idiom go against someone's grain:

to not seem right or natural to someone.

It goes against his grain to question the boss's judgment.

[Merriam-Webster]

On a side note, are you sure working out is the sort of thing that is against your instincts? Everyone does "work out" every once in a while if I may say so, right? Apart from that, the suggested idiom seems to cover your question very well.