Easy.

Get a blazer
Men's blazers | jackets, coats and blazers | ASOS

Blazer will reinforce your body shape and as you work out you will have a good posture..A blazer /smart jacket will reflect this

Smart Jeans/ Tshirt with blazer is a great blend of Smart/Casual

I look bloody shag able in my blazer/chinos and toms/hightops!