Conversation so far:
What is the marching technique?
Given that instrument-wielding members most often face toward the audience (for maximum sound projection), marching technique must not affect the rigidity of members' upper torsos.
How rigid is their upper torso supposed to be?
members of the battery, due to the nature of their equipment, must keep their entire bodies facing forward at all times.

Question: What is another factor of their technique?
Self-contained rewrite: What is another factor of Drum and bugle corps technique, aside from rigid upper bodies?