I still have my velodrome bikes, as well as one antique olympic bike. It's been a LONG time since I've been on the boards of a velodrome, but velodrome cycling is a cycling sport unlike most others in that, for others, a light, wiry rider has a marked performance advantage over a big, muscular rider. I was in the latter form, so on the boards, my muscle mass allowed me to outperform riders who were much lighter, and the reasons are mostly simple:
Velodrome racing is done on a fixed-gear cycle. They cannot 'coast', and you don't get to use a variety of gear ratios to get up to a given speed, or account for changes in load. You start in the only ratio you have, and it is a rather high ratio. To accellerate, it takes substantially more torque than you'd put into a road or criterium-race frame.
To further complicate matters, velodrome tracks have a very, very steep bank. IF you're on that bank, and not going fast enough, you WILL strike your uphill-side pedal. To prevent pedal-strikes, we run shorter crankarms. The added effect here, is that big heavy leg muscles are running a smaller circle, thus the accelleration from TDC to BDC and back, occurs at a lower G-force, so it takes less energy to 'spin faster', which is the essence of upper velocity limit for a velodrome cycle.
The problem, however, is that the amount of force necessary to do all this, is considerably higher than what's necessary to function in a road race, time trial, or criterium race environment.
When I was velodrome racing, we had aluminum handlebars and stems on EVERY road, criterium, and time-trial frame, but on the boards, it was steel bars and stem, or nothing. Why? Because many of the velodrome sprinters were pushing 260lbs or more... over 100lbs heavier than a criterium/road/time trialer. The forces in sprinting are 80% through handlebar reaction- When pushing down with right leg, you're pulling up hard with right hand, and pushing down with left. This puts phenominal force on the stem, and flexes the bottom bracket HARD.
I've broken steel bars and stems. I've broken crankarms, and bottom bracket axles and cups. I've cracked steel frames right at the bottom bracket, at the head tube, and bent two dozen axles.
The only technological difference between what I did 35 years ago, and what they do today, is aerodynamics, and materials technology. They've re-shaped handlebars to get the frontal area way down... that wasn't allowed when I raced, nor was running disc wheels... and carbon-fiber frames didn't exist. (Read about Graeme Obree for details there)
Handlebars, though, still flex under load. Bottom brackets flex, albeit not as much... but crankarms and pedal axles still break, bottom bracket spindles and rear axles still break, but not as often.
The fortunate part here, is that when that stem broke, he didn't land on the sharp edges with his throat. Velodrome crashes are bad, in that it is very easy to fall onto something very sharp, and one never falls 'pleasantly'.