A 2009 study found the breast traces a figure-of-eight path during the gait cycle, tracked by optical motion capture

A 2009 peer-reviewed study (Scurr, White & Hedger, Journal of Applied Biomechanics) reported that "during the gait cycle, the breast followed a figure-of-eight pattern with four movement phases." The measurement method was marker-based optical motion capture: "Fifteen D-cup participants had reflective markers attached to their nipples and trunk to monitor absolute and relative breast displacement during treadmill walking (5 kph) and running (10 kph)." Placing markers on the nipple and the trunk lets the system separate the breast's absolute motion in space from its motion relative to the torso — the distinction a sports bra is engineered to reduce.

This formalizes, with instrumentation, the problem the 1977 Jogbra prototype solved by intuition three decades earlier. The reflective-marker optical system used here belongs to the same hardware category (Vicon-class marker tracking) whose cross-domain genealogy is traced in claim-vicon-motion-capture-lineage-gait-lab-to-nasa — the same measurement principle serves bra design, clinical gait analysis, film VFX, and astronaut biomechanics.

A separate, louder quantitative claim from the same research community — that breast acceleration during running exceeds a Formula 1 car's g-force — appears only in secondary/press coverage and was flagged [unverified-quant] in the source capture; it is not asserted here and is routed to question-verify-breast-acceleration-exceeds-formula-1.