Graeme Alexander, 24, has been crawling through the rhinos' mud wallow, practising pull-ups in the elephant house and heaving hay bales as he prepares for the event later this month.
The Blair Drummond Safari Park worker is taking part in the Tough Mudder event at Dalkeith Country Estate on June 15 to raise money for the charities Tusk and Help for Heroes.
His charges are normally out of the way when he trains, but have shown some interest in his antics.
Mr Alexander, an elephant and rhino keeper, said: "The rhinos were all inside due to the weather when I was in the wallow but when I went inside they were quite interested because I was covered head to toe in mud and they came over to have a look.
"It's good to train in the park because it has quite similar obstacles to what I will face on the course, going through the mud wallows and climbing up on stuff.
"I've never done the event before so it will be a challenge for me."
Tough Mudder is a 10km military-style assault course.
Mr Alexander aims to raise £400 for Tusk, which currently supports 52 field projects in 17 African countries.
As well as working to protect wildlife, it also helps to alleviate poverty through sustainable development and education among rural communities who live alongside the wildlife.
Blair Drummond Safari Park manager Gary Gilmour said: "It's great to see one of our keepers go the extra mile for a charity such as Tusk.
"To help Graeme prepare for his big race we temporarily turned our reserve into a training course and had him wade across the rhino's mud wallow."
An activity stall at the park this weekend will be offering fun activities, games and special events as a way to help Mr Alexander reach his target.