What to do to maintain muscle mass while doing triathlon training?

Adequate nutrition: Adequate nutrition is key to maintaining muscle mass. Since one burns many calories with triathalon training, getting enough calories through a health balance diet is suggested.

Good proteincalories: ...And smart training. Refuel in a 3:1 carb/protein ratio during long runs, swims and bikes to prevent your body from tapping into muscle for energy. Also post workout, eat within 1 hour to fill your muscle glycogen stores for the next workout. Lastly, tailored weight lifting can maximize muscle mass and prevent loss, though you don't want too much muscle mass for triathlons. Happy training.

Tough one: Due to the high level of cardio, you tend to lean out with triathlon. Better to compete this way. You must do exercises to try to maintain muscle mass -- weight training and diet. Squats, deadlifts, benchpress, military press -- have been suggested to keep mass. However, if these are new to you, see a trainer to learn how to do properly. Pushups, pullups, chinups, sprints all will help.