Hey - I've marched both euph and contra for many years (DCI and DCA).
It's a moot point --- but it ultimately helps to have a horn. There's no better way to understand the weight distribution and getting comfortable enough to maneuver with the same level of proficiency as the other instruments. There's no exercise that really mirrors getting it from ground to "chop" -- or snapping from "chop" to playing position -- other than actually DOING it.
That said: it doesn't hurt to be in generally decent physical shape.
I'm no licensed trainer or anything (usual disclaimer applies: talk to a certified fitness instructor or a doctor before starting a new regimen), but below are some exercises or general workouts that have helped me. In general: you want to give as much attention to your core and back muscles as you do your arms.
- Yoga
Find a class and start doing it now ... it's great for strength/breathing/endurance/flexibility/learning to achieve specific body shapes -- all of that is completely relevant to drum corps
There are classes everywhere (community centers, fitness centers, colleges, etc)
If anyone makes fun of you for doing yoga, they are wrong and stupid
- Core-specific workouts
Planks
Crunches
Leg-lifts
- Body weight training
Regular pushups, tucked-elbow pushups, pull-ups or chin-ups ... that sort of thing
Some of my friends have recommended stuff on the body weight sub-Reddit
- Light-weights + heavy rep training
For example - Front dumbell raises with 5-15 lbs weights
Low cable row machine to work on upper-rear muscles
- Running
You're going to be doing a bunch of it in the summer anyway
Get good shoes, don't cheap out on them
Again: this is all stuff I've done over the years. Find what works for YOU and commit to a regular-enough schedule (aim for 3x a week).
One final note: every tuba manufacturer is different. Some have better weight distribution and ergonomic design considerations than others.
I've marched several seasons on Yamaha ... by far my favorite, from a weight distribution standpoint. It's the easiest to maneuver and toss around.
Jupiter is the opposite, in my opinion. They sound good, but are stupid heavy. Dumb design for the drum corps.
Played a little bit on an Adams horn last summer ... it wasn't too bad, but still not as effortless to move around as Yamaha.