Hippos can run and swim around 20-30 miles an hour. If you wanted to beat one in a triathlon, you'd need to be really prepared for the biking portion.

While hippoes are surprisingly agile in water and surprisingly fast runners, they are not known for their endurance.

Hippoes would probably have an advantage while swimming due to a body adapted to water.

Hippoes don't sweat and have a very thick skin, so they would overheat quickly when running. The same thing applies to cycling, but with a bike designed for their body, I'd think they'll do better cycling than running. Their hind legs are about 70cm long (according to ChatGPT), so not that short. Shorter crank arms are required. The hind legs are super strong, so that would be a significant advantage, especially when the bike is holding their body weight.