More pelvic floor muscle training

The next day you arrived again at the gym first thing in the morning. Mia was already there. She wore the same clothes, had the same stopwatch.

"Ready for round two?" she asked.

You nodded. "Okay, let's get you ready for another pelvic floor exercise, then", she said with a smile.

Mia led you to the gym mat and lined up your cock in front of her face. "This is just warm up", she said, "Just relax until I start the time."

She looked up from your cock and smiled again, licking her lips. She then popped your tip into her mouth and sucked on it for a few seconds. As your cock swelled, she popped it out again and licked the sides with her tongue.

"Okay, let's do this", she said.

She motioned you to lie down on the gym mat and unzipped her top in the front. "Same exercise, different position. Just focus on your pelvic floor muscles and resist the temptation to move your hips", she said while climbing on top of you, kneading her massive tits. She squatted over you and guided your cock between her labia. "Time starts... NOW!", she shouted and started the clock as she pushed you inside her vagina and started to ride you aggressively.

Your hands clasped her ass as you started thrusting into her. "Don't... move... FOCUS!", she said as she slapped you across the face. "It's just like last time. Don't let go. Don't let your hips move. Don't cum..." she said. You stopped thrusting with your hips and tried to focus only on you pelvic floor muscles. It was impossible as Mia's enormous boobs were swaying freely in front of your face as she rode you wildly. You closed your eyes but you could still hear them clapping against each other.

The clock hit the 2:00 mark and Mia called the time out loud. "Don't cum... Don't move... Work more on those muscles...", she whispered in your ear as she bent down. You could feel her breasts press against your chest. You felt Mia's hand move onto her crotch as she started rubbing her clit while humping you vigorously. "I think I can... cum... with you inside me... please... don't stop... I... challenge... you... to outlast me", she panted in your ear. You felt yourself about to cum at any moment. You bit your lip and tried not to think how the weight of Mia's enormous bust and her movements felt against you. You tried to focus on your pelvic floor muscles and resisted the urge to shoot your cum inside her. You wanted it to last as long as possible.

The clock clicked over to 3:00 and Mia was panting in your ear, "I'm close... keep... holding...", she said. You forgot you were supposed to stay still and started thrusting into her to make her orgasm. Mia grabbed your hand and started pulling it to her massive breasts. As soon as you touched her tit, she started cumming.You felt Mia's vagina starting to contract around your cock. Your balls started throbbing and you came too. You couldn't help it. Mia noticed your reactions and grabbed the stopwatch and stopped the time. "3:11", she said, "Looks like you won".

After a few moments, she got off of you. Cum squirted out of her vagina as she pulled off of you. "Don't forget to clean up after your workout. Gym etiquette!"