Get some exercise

You flex your bicep into the size of an unnaturally hard bowling ball.

Sophie: "Unf! This is one hawt bod. I gotta get you some exercise!"

You give a little loving smootch to your bicep, feeling your vein throbbing under your lips. But what could you possibly exercise with, besides masturbation? Solid steel melds to your moves like pudding.

Longingly you rest your arms and head on the cellar's window sill and look at the masses of pedestrians idly going by.

Sophie: "Ohh... if only there was an equally strong hunk who I could screw all day long, not having to worry about draining his stamina or crushing his member into a hair's width..."

As you fantasize out loud, every man on the streets subtly begins to gain muscle. Confusion and mild panic spread as people's outfits are ripped into shreds under their bulging muscles. The streets suddenly run rampant with the precum of these meatlockers, who've suddenly become uncontrollably horny. Some of them crack holes into the asphalt while blowing their loads, others shoot directly through cars - the smallest of slivers being enough to pierce an engine block.

Sophie: "That's it! They're mine, all of them are mine!"

You tear through your basement brick wall and climb onto the street, straddling the first man you encounter. Wresting his hands away from stroking his cock, you pin him to the ground and eagerly ride him. Your butt pounding against his hips shakes the entire neighbourhood and cracks the sidewalk, and yet he seems only delighted from your iniative. Just like you wanted, his physique is capable of handling your industrial crusher muscles.

His girth seems to thicken after every thrust. If you weren't about as strong as continental drift, this might even slow you down. You pay it no mind however, and gingerly hammer him for a good twenty seconds until he cums, which is honestly an impressive duration considering how hot you look. His load is so thick that at first it feels like getting stuffed with a warm, moist blanket.

As you get up to move over to the next Mr. Universe wannabe, you realise why this guy's cock felt so thick: he now has seven of them. Those definitely weren't there before!

Sophie: "Oh! So I can do that too, huh? Fuck yea! I wonder how far I can take this?"

You experiment while fucking your way through every man who dares to walk past your house. Some of them you endow with multiple, some with extremely large cocks. Some of them you give testicles the size of bean bag chairs, so they'll cum geysers into you. Before long word spreads and there's a whole line of men and women alike waiting to receive their 'treatment'.

You've not had that much experience with lesbian sex before. Only a few very drunken encounters in college, and you were told that you weren't that good at it. Well now things are different because you're a muscle Goddess and can literally make g-spots grow wherever your tongue lands! Cunnilingus from you makes women go rabid with pleasure, as you leave them burning with neverending waves of orgasms from their jungle of two dozen clits.

Some women you decide to grow cocks and extra boobs for. Biologically, the penis is just an engorged and specialised clitoris, after all. To balance things out, you also try giving enormous gym ball-sized boobs for men. All in good fun, you think!

But even after rigorously fucking about five dozen people into exhaustion in the span of an hour, you're no closer to having broken a sweat. It's like your body is powered solely by cumming. As you are the Goddess of Fleshly Delights, this assessment is indeed wholly correct. You clearly need to try actual physical activities instead of just sex.