The 21-year-old Calgary rider is classified as a quadruple amputee at the Paralympic Games in London. He was born with his arms and legs underdeveloped.
His races at the velodrome completed Friday, Milley now prepares for next week's time trial and 60-kilometre road race at Brands Hatch.
Without the hand power to squeeze a handlebar brake, Milley's road bike is equipped with a "bum brake." He's heard jokes aplenty about clenching buttocks to apply the brakes, but Milley simply shifts his weight back to activate them.
It's among the modifications and adaptations made to a Cervelo bike by his biomechanist and machinist so Milley can race it.
"The amazing thing about my bike is the braking system," Milley explains. "I have gripping motion, but not enough to brake. If we hit a bump I would fall right off, so we put the brake on the back of the saddle.
"It actually comes up off the seatpost in a T-bar behind the saddle. I push back with my bum."
Milley doesn't have a left forearm or hand. He doesn't have feet and lacks bones in his shins. Milley's right hand consists of a large and small finger, which he clamps on the handlebar.
He slides his upper left arm into a prosthetic attached to the handlebar. Milley doesn't wear cycling shoes on the bottom of his prosthetic racing legs. There are cleats built into them.
The youngest member of Canada's Paralympic cycling team was seventh in Friday's C1 pursuit, a day after he was 25th in the track time trial.
The C1-5 classification is athletes with an impairment affecting their legs, arms and/or trunk, but they race on a standard bicycle. C1 athletes are the most severely impaired.
Speed comes with the power muscles produce. Milley doesn't have calf muscles, so he relies on other means of power generation, including a quick leg turnover.
"The amazing thing about Paralympics is every athlete is different," he says. "I don't have the calf muscles. I have less muscles to use. I have to use what I have.
"I tend to have to have a higher cadence, which uses more your lungs and your heart because I don't have the muscles and the strength. I raced my heart out. I'm coughing and hacking up a lung. It's not because I'm sick. It's because I dug so deep."
Milley says he trains like an able-bodied cyclist, which means he spends a lot of time on a stationary trainer for road races. He goes to the weight room to develop power for the track.
He played able-bodied soccer as a teenager. When Milley broke his kneecap at 14, he was devastated to hear his doctor tell him to stop playing.
At that time, he was riding a tricycle nicknamed "The Tank". He and his six-year-old sister Brittany went to a nearby park and learned to ride a two-wheeler together.
"I was falling over. She was falling over," Milley recalls. "We learned at the same time."
He joined the national para-cycling team two years ago. Getting the athlete, prosthetics and bike modifications working in concert to produce a winning effort is a puzzle. The pieces change with new technology and also because the athlete matures.
The evolution of the bum brake is just one example of advances. Milley's current brake is lightweight titanium and half the heft of its previous incarnation.
"The technology keeps getting better and better," Milley says. "I don't know when the ceiling is going to happen. Maybe one day 50 years from now, maybe it will be like Star Wars with Luke Skywalker."
Milley's allies in bike adaptation are Pro Stergiou, a biomechanist at the Canadian Sport Centre Calgary, and University of Calgary machinist Dallas Morris.
Milley plans to spend a lot of time with Stergiou after these Games. He wants to contend for a medal at the 2016 Paralympics in Rio de Janeiro, Brazil.
"I'm still working on things. My position is not perfect now," Milley says. "The goal when I get home is to work on that positioning with a biomechanist and get it 100 per cent.
"The Paralympics is so competitive. You have to be perfect. So that's what we're going to go home and do."