I and Stepsis are Doing a Muscle Show

After looking at seminaked girls on the phone, I and my step-sister decided to do a "muscle show" for each other, starting with me doing gradually harder flexing, when stepsis enjoying my strength and muscles, admiring their firmness and resilience, and sometimes testing their strength and resistance to pressure (gentle squeezing), and attempted arm pull-downs, and other occasional strength tests. After this, she goes through the same sequence with me. We show our arms, shoulders, abdominal muscles and back in a playful manner.