Basically do any cardio you can so that when you do get back on the erg you’re not huffin and puffin. Maybe you could do a stagnant bike… or would that bug your ankle too?

Also, Just some basic calisthenics to keep your muscles up to par like pushups, situps, squats, leg lifts, supermans… ect.

also stretch as much as you can so that you’re not all tight when you start rowing again.

go for practices…ask your skipper to join you..it’ll be fun and motivating

Can you use a stationary bike? If you can use a stationary bike (or a normal bike), you should try that. Alternate biking as hard as you can with a rest period. You can basically set it up like you’re doing erg pieces, and use the RPMs on the bike the same way you’d use your splits on an erg (except instead of trying to keep your splits low for the harder parts, you’d try to get higher RPMs for the harder parts). Obviously you have to experiment to get the right numbers for your own body.

Also, the downside is, with an erg, you’re working your entire body, where as with the bike you’d be working mostly your legs and butt. It’s not going to be the same. You should try to work your upper body additionally, especially focusing on your core. You should try to get time in for your abs and lower back, if nothing else. Despite what everyone tries to say, crunches/sit-ups aren’t actually practical. Try this instead:

If you have access to a pull-up bar – hang from the pull-up bar, arms straight, so that your feet don’t touch the ground. Let yourself dangle, shoulders extended. Then tighten your armpits, like you’re shortening your arms. Don’t pull your body up, just kind of pull your shoulders back into the sockets. Then, keeping your legs straight, raise them up towards the pull up bar. If you are extremely flexible, you should raise your straight legs all the way up and touch your ankles to the bar over your head. If you are not flexible you might have to bend your knees. This is the best way to work your abs. Your shoulders might feel sore. But it builds practical ab strength without getting on the erg.

Without a personal trainer, I don’t have any other tips. The very best thing for you would be to train with kettlebells, but you would need a trainer.