I’ve discovered you can “swim” on the foam roller and make gains through improving shoulder/spine posture - noticeably.
Let’s start with what is slow: Kyphotic and Lordotic Curvatures.
Also known as: Forward head, hunched shoulders and upper back, curved spine, sway back and forward pelvic tilt.
Also known as: Me 
A kayak or canoe has a nice straight keel. It you warp the boat’s bottom it will be a slug. This is one big reason why kids are naturally faster in the water than adults - they have undistorted and better posture out of the box.
So me & my team of PT’s went to work on Lordotic stuff. Year long project and it was great! But now I’m turning my attention to the Kyphotic curvature. This is equally as important.
A kyphotic curve will raise your center of buoyancy, drop your elbows & the rest of your torso.It will also make your head track lower & harder to breathe.
To correct I have been lying on the foam roller to pressure the area between my shoulder blades, opening up the chest. Also you can run your arms from streamline through the full stroke, trying to keep your elbows grazing the floor( hard to do). I use the roller placed in-line with the spine.
I believe that when it comes to the spine, it’s a game of mm. So even small gains in alignment will pay dividends in the water.