I know you're in love with my curvy arse, especially the way my cheeks rise and fall in sequence with each revolution of the exercise bike pedals. The taut skin casts barely a ripple in the black yoga pants, save for the faint outline of my cotton knickers and the crease below each globe where their flawless contour joins my thighs. From your vantage point, sat at eye level with my peach, I know you long to touch, but I've made sure you can't. Naked and yearning, a scant few feet from the action, the rope chafes your wrists as you hopelessly struggle against the bonds holding you to the chair. I can sense your desperation and it makes me glow, adding to the heat of exertion.

I cast a sidelong glance at the Ikea pull-out sofa bed and furniture stacked with photo albums and books I ought to read one day. Other items of equipment are scattered about my makeshift gym: treadmill, fitness ball, and pink weights of various denominations. All might feature in my games, but lay dormant today in favour of the bike, its continuous, whizzing drone a form of mechanistic comfort. I focus forward out the window and press on, breathing heavily.

The spare room overlooks our little leafy slice of suburbia and I spot a Sunday jogger puffing past the driveway, red and probably ten minutes from heart failure. A wry smile creeps across my lips. People are approaching fitness the wrong way; goal oriented, not pleasure oriented. While Olympians in Rio strive to demonstrate their might in tests of strength, agility and stamina, my methods explore resilience, determination and asceticism.

My newfound regime is of course rooted in self-improvement. If this were a story on some sex site, I'd be a svelte nymphomaniac addicted to working out at a local gym packed with hunky men, each sporting a foot-long snake in their tight shorts. And I'd sample them all, singly and in groups, shoved up against lockers or bent over the benches that line the changing area as they had their filthy way with me in ever-more imaginative positions. In reality, nobody's that perfect. Not that I'd necessarily be above such antics – the fantasy of being treated like a health-obsessed whore under the control of muscular men certainly has its allure. But I'm mostly conscious of not losing shape, since the new job requires plenty of wining and dining clients. I'm also smart enough to recognise that, with the best of intentions, exercise for its own sake can become tedious when the impetus and commitment both wane. Hence your predicament, reduced to nothing but a ravenous spectator for now, so close yet agonisingly not close enough.

Featuring your fabulous body as part of my routine has so far stymied any onset of boredom. You're my prize for good behaviour. My plaything, obedient and willing to let me taunt you. To drive you wild with frustration. To bring you to the brink of your resolve because it pleases me. It excites me. Sharing my hard work makes all the pain worthwhile because I have the proverbial dangling carrot at the end of each ride for being a good girl, albeit a beautifully solid, veined, throbbing, eight-inch carrot, slamming into me from behind as you release every pent-up second of denial into my hungry pussy.

I'm not svelte like the girls in the stories, but in the heat of such moments you never complain about my curves. In fact, quite the opposite, yet I doubt you'd appreciate me any less if I were more toned. I plan to make sure there's still enough left to hold, it'll just be firmer. Tighter. Better to spank because, after all, even good girls deserve a little discipline.

Not that I'm good. Far from it. If anything, the adherence to a strict programme has awoken my inner bitch, the part of me that craves control, both giving and receiving. To my delight, you're beginning to realise that bad girls need a lot more discipline when they have their fun. Idle thoughts wonder if you'd be up for gathering a few friends from your badminton league and treating me to a night of unbridled sex after the game. Me as the centre of male attention, every orifice available and more than willing to demonstrate its elasticity. Maybe one day I'll ask, but not today. Today I have you all to myself. And I can barely fucking wait.

My nipples harden beneath the tight sports bra and loose-fitting black T-shirt. I'm wet, and not only from the exercise. I can feel it, a different viscosity to sweat, seeping into my underwear. The saddle is going to reek of my desire, a heady mixture of perspiration and pussy juices that I may decide you need to inhale. That'll turn you on immeasurably, which will translate into delivering a harder pounding inside me. I shiver in anticipation.

I love sharing my exercise plan with you. Thoughts of your straining cock jutting from your squirming body flash inside my head, filling me with need. I swear I can feel the heat of your hardness protruding from your lap. Perhaps it's the intensity of your stare burning into my backside. Either way, I want you, naughty hunger welling up from the depths of my body, threatening to swallow me whole. I know I could take a shortcut. Press a few buttons to make the path easier, then pounce on you sooner, but that would be cheating, denying us this exquisite tension, coiled to breaking point then unleashed in a frenzied blur of skin on skin. And I love the lack of control we both exhibit in that moment.

Pushing such thoughts to one side, I focus on the machine's display. The on-screen symbols flicker and update every second, indicating distance travelled, calories burned, and terrain profile; currently flat, though a hill is approaching. A dirty smile forms across my lips and I stand in the saddle, driving into the slope, fully aware of the effect it'll have on you.

I hear you whimper. It pleases me and I moisten a little more, but that's for me to know and you to find out. I'm the alpha right now and bark, "Shut up."

Your barely audible whisper is laden with want. "Please."

"When I'm ready. Now shut up and watch."

The last part of the command is strictly unnecessary as there's no way in hell you could tear your stare from my undulating bottom. I feel the glutes flexing beneath the fleshy layer packed inside the shimmering fabric. My calves tighten and I power into the incline as the pressure on the pedals ratchets up a notch. The tendons inside my legs scream but I ignore them, concentrating on the prize that awaits me the other side of the hill. Your hands sliding from my bare butt to curvy hips, yoga pants unceremoniously yanked to my knees, your girth stretching my insides. Filling me. Fucking me without restraint because you know I need it that way.

The hill profile steepens and I slow a little, panting hard. Bastard machine is making me work for my reward. I grit my teeth and focus on the thought of reversing into your body. Grinding against your turgid prick in my clothes, your pre-come depositing silver streaks upon their surface. The wetness pooling in my knickers from my own raging hormones. The lap dance from heaven culminating in the fuck of our lives.

I consider how I should allow you to take me. Free, so you can punish me for the torture, or on the chair, still restrained? Each has considerable merit. In the latter case I'd have to maul my own tits, pinching and rolling the hard caps atop their doughy peaks before slithering my fingers down clammy abdomen and digging them beneath my body to relieve the wet ache I find there. Circling my excited, proud button that longs for your tongue, wetness tumbling from the puffy entrance it guards, shaved bare for the first time as a treat after your last amazing performance inside me. I can only imagine how you'll react.

Scaling the incline I notice I'm within thirty long seconds of its summit. My legs are burning, their heat matched only by the fire in my loins at the torrid thoughts of what awaits me in the valley beyond. I think you realise this too as I hear you take a breath, desperate to grab my tight behind and plumb my depths with your delightfully thick manhood.

I can almost feel it inside me, thrusting, pulsing and firm, my clutching walls ravenous for more. My pedalling slows as the resistance increases once more, chest heaving, but I'm determined to beat the machine and claim my rock hard compensation, the short-term pain well worth the material gain.

Time and again my long legs extend and contract against the pedals, each three-sixty drawing the meat of my rear with it. My burnt oak ponytail swishes, hips in unison, swaying a hypnotic beat I know you’re following. Above the blood roaring past my ears to fuel the exertion, I hear you gasp at the sight then let out a low groan of need. Ten seconds remain and I can taste victory. Four hundred and forty-five calories burned, and many more to go as our bodies buck together in a sweaty ballet of lust.

I don't know which of us will come first. I'm close enough already, both from the endorphin rush of the workout and from watching you strip before me at my demand, at my pace, item by delicious item until your sculpted, statuesque beauty was revealed. Telling you to sit, then dropping to my knees directly in front of you thrilled every part of me. Reaching around your torso to bind your wrists to the chair so my breasts and carefully placed breaths could brush your bobbing shaft was the pièce de résistance. I made sure it took ages, desperate to draw your rising hardness into my hot mouth and lick and suck until you lost control. Somehow I held back.

Teasing you was such a turn on, a massive test of willpower not to stand, turn away from you, roll the yoga pants and sticky white knickers over my rump and sink onto your prick. Fuck, I love that sensation as it glides into my slick channel and our bodies meet at its full travel. That moment of euphoria just before the rhythm begins, the rippling of your flared head stimulating nerves deep inside that deliver wave after wave of pleasure to my already heightened senses.

The prospect of soon being able to touch you is palpable as I detect the pedal's resistance easing and glance at the readout, releasing a breath. The summit! Sitting back in the saddle I pick up speed again, traverse the peak and cruise into the valley, elated, ultimately bringing the whirring machine to a standstill when the incline is safely behind me.

Above my laboured breathing all I can hear are your strained, muted exhalations.

Your level of arousal is amply evident and I know how much you need me. The feeling is more than reciprocated. Swinging one tired leg from the saddle I dismount and turn to face you. You're a picture, the pleading in your brown eyes beneath that dark fringe making my pussy twitch. Not to mention the sight of your huge erection as I drag my gaze across every ripple of your sexy physique.

Inside I'm a tangle of desire but try to hold my composure as I step towards you and sink to my knees, placing one hot hand on each of your warm thighs. With a slowness that belies my racing thoughts I bring my face towards your vertical mast, feeling its heat, its danger as I open my mouth. You tense, the flared end jumping, expecting my lips to wrap around it and to sink inside my wet throat. But where would the fun be in that? Instead, I pause, breathing hotly against the pulsing mushroom, wanting to please you so much, but needing to torment you a little longer.

Maybe I can line up you and your badminton buddies, wrists tied behind tight bodies and tease you all in the same manner as I move from one proud member to the next, sampling the obvious testosterone on display. It would be so erotic, the manly smell of exertion and desire filling my nostrils as my mouth hovers across each engorged prick, lips and tongue occasionally encircling the drooling tips, knowing that each one would have its time ravaging some part of my body. The sheer sluttiness captures my imagination. Maybe I am a nymphomaniac at heart.

I flick my tongue, lashing the tiny knot where your circumcised head meets the concrete shaft, delighting at the way it bobs and your hips squirm as you exhale noisily. My lips graze the tip, nibbling just a millimetre or two then backing off, close enough to excite, far enough that you can't take advantage. I taste your pre-come, sweet and potent. Lifting my eyes to yours I slide my tongue out and drift it slowly towards the head of your pole, connecting with the slit, seeking more of your sweet arousal. It seeps onto my coaxing tongue and I shut my eyes as I take the droplets of clear liquid into my mouth and sigh. I'm unsure who holds the most power: me for elevating you to the threshold of your resilience with barely a touch, or you for making me slave to your trim physique and steel erection beneath its chamois sheath that I can no longer resist.

Snapping my eyes open I once again draw your gaze and drop to your twitching centrepiece, lips parted as I take the first half of its fullness into my wet mouth. I swirl my tongue and let out an involuntary moan as you tense again and I fear I've pushed you too far. I quickly back off, enchanted by the crazed look in your eyes as you struggle to retain your poise. The beautifully iridescent trunk catches the sunlight from the window, sparkling wetness making me hornier.

Standing, I begin to circle your bound form, lingering halfway to stoop and hover my fingers above the knots around your wrists. Bringing my mouth to your ear, close enough that it must tickle, I rasp:

"Do you want me?"

A rapid nod. You remember to stay silent.

"If I untie you, do you promise to satisfy me?"

From over your shoulder beyond chiselled jaw and its three days of growth, I see your straining, gleaming phallus answer for you, before another swift nod confirms.

My fingers brush yours on their way to rest against your bonds. "Are you sure you have what it takes to fuck my sweaty, dripping pussy into oblivion?"

Another nod, more decisive.

"You may speak."

Your gravelly tone is soaked with want. "Yes, mistress. I have what it takes."

I smile. With trembling fingers, I deftly undo the ropes and complete the circuit of your body to face away from you, palms on the saddle. I can't resist wiggling my rump as I hear the chair tip backwards and clatter to the floor moments before your hands are on me. They slide from my hips, up under the T-shirt and grope my soft tits. I roll my head in bliss, sparks flying from my nipples to my core when you tweak them. I reach down and peel off the T-shirt, glad to be free of the clammy material, just as your hands drop to the waistband and wrench downward to reveal my lacteal lower half.

With saturated underwear and trousers rolled to mid-thigh, there's no impediment to my sex, and no prelude required. You step in, aim and sink to the hilt, grabbing my hips and setting up a rough rhythm. This isn't about closeness and making love, it's fucking to fulfil a primal need, pure and simple.

I'm drenched and you glide back and forth with ease, each long stroke making me groan into the small room. With already elevated heart rate, my erratic panting and the slapping of our flesh fills the space around us. Your pace is frenetic, relentless, exactly what I need, my self-styled reward for sticking to the workout plan. My pussy hugs you with every thrust then releases in readiness for the next, over and over, rapidly building towards my orgasm.

I feel your hands slide north again, this time up my back, pushing me forwards over the saddle. Obediently I bend, happy to relinquish control now I have what I want slamming inside me. It affords you an unencumbered view of my naked arse and the smooth curves that lead to the hidden, shorn lips. You piston with renewed vigour, maybe recalling the recent time I let you penetrate my dark star. I'm unsure if you realise how manipulative I can be, making it seem as if something's for your benefit when the reality is very different. The truth is I wanted it, and made damn sure I got it. Just like now. Just like I'll get your friends to gangbang me at the sports centre.

As if in an attempt to tame my raunchy mind, a firm hand strikes my rear, the burning heat spreading to join the raging fire within. Another rings out on the other cheek, the stinging blow absorbed by my lust as I cry out into the room, begging for you to fill me so I can finish. Snaking a hand to slither between my thighs, connecting with my clit, you pause while roaming the unfamiliar terrain, a catch in your voice. "Wow, you shaved?"

I can barely reply, the saddle squeezing my lungs as your pounding resumes. "It's all for you. Fuck me now and you can lick every naked millimetre later."

You need no further incentive, settling your fingers across my wet nub and drawing exquisite circles while you continue to ravage me. Your rhythm becomes uncoordinated as you fight a losing battle to delay your own pleasure. I'm proud to have pushed you further than ever before, breaking down your self-control for my own devious gains. You've no idea how much that sense of power pleases me, but you're about to find out. The pressure inside me builds with each second and I start to gasp as my world closes in.

From a singular point deep inside my core, a knot forms like those with which I bound you, and I'm aware of nothing and everything as my body stiffens, toes scrunching in the gym shoes. Somewhere in the distance, beyond the howling of blood past my ears, I sense you losing control too, your hands flying to my hips and grabbing handfuls of flesh as you unleash a torrent of white hot desire into my spasming depths.

I somehow have the presence of mind to clutch for the handlebars of the bike to steady myself and groan deeply as I connect with them on the second attempt. A moment later and I wouldn't have been able, my senses consumed by an electrical storm that flashes from the central knot, every nerve untangling at once. The climax thunders outward through each oxygen-starved muscle, emerging at my skin and rolling across the landscape of my body in all directions, my mind alive.

The tingling is all-consuming at first, magical, taking an age to segue from rush to roil before gradually dissipating, permitting me to wallow in the afterglow, for quite how long I'm unsure. Being connected with you in this way, our shared journey towards a fitter, leaner me, fills me with more than the physical dimensions of your pulsing cock and its opalescent syrup that I begin to feel creeping down my thighs. It's the continuation of our fantastic relationship, exploring boundaries and occasionally crossing them in the pursuit of desire and the mutual knowledge of where our limits lie. The fact I've yet to find mine is equal parts scary as it is exhilarating.

As we step apart and the sensation of your massive cock slithering from me triggers a second mini tremor inside my worn body, I spin to face you. I realise too late that it's nothing more than another taunt, showing off the distended bare lips with a string of your come dangling that I catch inside my underwear as I roll them and the yoga pants home.

Snapping the waistband shut I look at you standing before me, naked and agape with faint red marks circling your wrists, and I smile, wondering if I can ever be truly sated. The next encounter when I smother you with my sexy slit and force you to eat my pussy before devouring all of your delicious hardness cannot come soon enough. But for now I need to replace some spent energy.

Heading for the kitchen, I pass you and catch the musky scent that I adore, radiating from your body. Pausing to trail my fingertips across your softening cock and off your hips, I bring the digits to my tongue, a salty sweet combination of our lust dancing on my palate. My pussy stirs as I step to the door and I'm unable to resist looking back at your wondrous body, glimmering with a sheen of perspiration, punctuated with that perfectly tight behind. I lick my lips, devilish thoughts of how to use you twisting my libido.

"Stay exactly where you are. I'll be right back."

As the door closes behind me I already know you'll patiently await my return no matter how long I take, because you love to please me. It's what you live for. And that is my favourite aphrodisiac.