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.


PMB #408
2887 College Ave. #1
Berkeley, CA 94705
tel: 888.996.OPIS™

Please email us at or use the form at the bottom of the page.

The purpose of the Optimal Performance Index System (OPIS™) is to provide objective data, through laboratory shoe testing, and subjective data, through clinical observations, to the athletic footwear industry and medical community, with the goal of reducing injuries and improving athletic performance. OPIS™ will continue to remain an independent testing company and will accept neither contributions nor advertising compensation.

Advisory Board of OPIS™:

Mark A. Reiley, M.D.
Orthopedic Surgeon specializing in foot and ankle pathologies. Author of Guidelines for Prescribing Foot Orthotics. Medical consultant to OPIS™

Tony Tadin
CEO and Founder, Amfit, Inc.; Engineering consultant to OPIS™

Craig D. Norton, R.P.T.
President/CEO, Ortho-sport P.T., Inc.; Consultant, human biomechanics and physical therapy

Delanie K. Bach, M.S.P.T.
Consultant, human biomechanics and physical therapy

Matt Bell, M.S.
Kinesiologist; Consultant, biomechanics and statistics

Ben Aiken
Consultant, medical website media