"Calling on her thrice-weekly pilates training, she constricted her core muscles, her glutes flexing so she could grip him tight, like a fist, as he slid inside her."
Followed later by:
"The angle change meant the length of his cock now slid against her G-spot, that electrified, pleasure-charged sensor sending tight, tingling spirals of pleasure up, higher and higher in her belly."
A SEAL's Seduction -- Tawny Weber