Torsion Control Index (TCI): measurement of midfoot shoe stability, in inch-pound units (in.-lbs.). TCI is measured through actively twisting a shoe around the longitudinal axis of the shoe, from the heel to the area of the toes joints, simulating rotational forces of the foot, and measuring the shoe’s resistance to this motion.
Vertical Compression Index (VCI): measurement of hindfoot shoe stability, in millimeters (mm). VCI is measured through compression of the heel portion of the shoe under a fixed amount of pressure, thereby measuring how the structure of the shoe controls rearfoot motion.
Rebound Index (RI): indicator of energy return of shoe to the foot, in millimeters (mm). RI is measured through compression of the heel portion of the shoe under a fixed amount of pressure, and then determining how much force the shoe exerts on the foot.
Shoe Stability Index (SSI):
indicator of shoe stability, as an index. SSI is derived through mathematically combining the quantified measurements of midfoot stability (TCI) and hindfoot stability (VCI), indicating the shoe’s overall ability to control the motion of the foot.

OPIS at Work

It is widely recognized that proper footwear reduces injuries and enhances athletic performance by improving biomechanics. The purpose of OPIS is to help determine the best footwear for an individual, given his or her physical stature, physical activity, foot pattern and injury history.