Cookee is right. I have a balance ball & a series of dumb bell weights I use almlost daily along with the addition of a rowing machine again used almost daily, but remember I am an old sod of 67+ yrs of age & ride 6 to 8 + hrs each time I take off with one of my sportbikes up here in the Cdn Rockie Mtn roads. Tack on a lot of knee injuries, broken left hip & such so I have to sort of try & keep myself in shape---well for an old fart of my age.
That means I grip the petrol tanks with my knees & put the abs into work. My back was damaged many yrs ago at home to some comp m/c events. So I can feel a bit of wanting to stretch my back around when riding, BUT worse is getting into my SUV & just driving to the gun range some 15 miles is real agony. I would not dare drive my SUV for an hour.
So a tip is to do a bit of stretching when you are going to ride & when fueling up do the same at the fuel station to where you might stop off at half-way point to when home---stretch a bit & in a while the problems will be gone.
Lastly I am 5'9" plus being around 170 lbs & I had a ball racing, on the circuit, a Yamaha TZR-250 with far more TZ racing parts then most bikes, to also screaming it around the hwys to, to & from work. That small bike was simply a ball to throw around.