More gear to put on and test

With John's leash in hand once more, Anna made full use of her position. Holding her arm straight out forwards, she drew him in so he was only a little more than a foot away from her behind, then sashayed sexily towards the door.

With the posture collar keeping him facing forwards and the blinders restricting his vision, she dominated his entire line of sight. The only thing he could see besides Anna's amazing bubble butt, the back of her corset, and her legs, was a little window between her athletic thighs where he could see the door that they were approaching.

Combined with the unrelenting pressure from the leash on his member, John had very little room for coherent thought. He occasionally blanked out and forgot to keep walking forwards on his knees, the dramatic increase in pressure on his dick always reminding him again.

"Did I mention I love this job?" The girl who had held his leash earlier punctuated her question with a hearty slap to John's butt.

"That's because you hog all the fun parts," the other girl retorted. "I get to lead the next one." The second girl patted the top of John's head lightly as she spoke.

"Sure, Leah, whatever you say!" Evidently the more petite girl's name was Leah. John felt himself growing curious about the other girl's name, despite himself.

As they neared the door, the two girls moved ahead to open the door for Anna and John.

John's mistress led him into the room. From between her shapely thighs, he caught glimpses of the interior of the room. The walls were whitewashed, but the room was dimly lit. What looked a bit like a hospital bed was fitted prominently with various kinds of restraints. He saw cabinets with various tools of some kind in them, but was **** to turn away as he was led in a different direction, and positioned facing a wall. Anna stepped to one side, passing John's leash to the bustier girl, who stretched up on her toes to fit the end of it onto a hook high up on the wall, which he had to lean his entire torso backwards to see.

"We think you'll really enjoy this one, Anna. Let's just do a couple of tests so we can figure out safe limits," Leah explained, fitting a mask over John's mouth and nose which she then pulled tight around the back of his head.

Over the next few seconds, John felt little clips being attached to various parts of his neck, dick, and balls. The girls were careful to not put any part of themselves besides their hands in front of John, which were now fitted with rubber gloves, so he wasn't sure if Anna was helping, or if it was just the other two girls. Leaning forwards, he was able to see wires coming out of the clips on his crotch.

"There. Begin testing!"

John suddenly found himself unable to breathe. Attempting to inhale just pulled the mask tighter against his face. He stretched his jaw open to try to **** open the seal, but with the gag in his mouth, opening his jaw hardly shifted the mask at all.

"Elevated pulse, blood pressure normal, circulation normal," Leah read out calmly.

He tried to shake the mask off of his face, but the posture collar meant that he had to use his whole shoulders instead of his neck, making the effort pretty obviously futile.

"Here we go, oxygen levels looking a little bit low, let's turn it off for a bit."

Feeling the seal break, John gasped for air.

Three or four breaths later, he felt the mask suffocating him again.

"Whoops, that was a bit on the short side. Let's just see..."

After several long moments the seal was broken again. Anticipating another cutoff of air, John intentionally hyperventilated.

Half a dozen more cycles later, Leah broke the seal.

"Looks like we have resting limits of 60 seconds maximum denial, 5 seconds minimum of air at a time. Let's take a look at his active limits."

The second girl stepped directly in front of John her plentiful ass stretching the golden mini dress inches away from his face as she reached up to unhook the leash, which she passed back to Anna.

"Walk him over to the treadmill over there, would you, and put the leash on the hook in the middle there."

Even with the prospect of what was to come, John still found himself enjoying Anna's black leather bikini clad ass greatly as she walked him over. A few steps later, he felt himself knee-walking up onto a treadmill. Unlike the rest of the floor, which was carpeted thickly enough that his knees hadn't been tired out, the treadmill was just an ordinary exercise treadmill, rough against his knees just from kneeling on it. The only addition was a stainless steel mesh in the front. Anna hung his leash from a hook that was hung in between the highly unnecessary handlebars of the treadmill. With her sub secured in place on the treadmill, she stepped off to watch from the side (he figured it was the side, he couldn't see her now that she was no longer in front of him).

"Right then, let's get started!" Leah declared gleefully.