I demonstrate playing a C Major scale using forearm rotation for thumb crossings instead of the "train in the tunnel" crossing movement that many of us learned as beginning piano students.

The idea comes from these principles:

Prefer small tension in big muscles (e.g., your arm) over big tension in small muscles (e.g., your hand).

Prefer muscle tension that gravity demands to maintain hand structure in a relaxed position over tension that works against your own anatomy. Any position where your muscles are working against your anatomy instead of against gravity is a potential source of injury and is to be avoided.