Comparative Mechanical Testing of Newton Running shoes versus other popular running Shoes.

Less Impact

Peak "in shoe" impact force measured against distance run. Higher peak force shows greater impact at foot strike, resulting in increased stress on the runners joints, muscles and tendon and increased risk of injury.

Higher Energy Return

Energy returned by each shoe (as a percentage of energy imparted during foot strike) measured against distance run. Greater energy return results in higher push off force and greater efficiency (better running performance.)

Better Cushioning

Amount of deformation of each shoe for one foot strike cycle measured against the force experienced by the runner. Lower force and greater displacement shows greater cushioning.

TEST METHOD AND BACKGROUND

Testing was conducted by an independent and internationally certified mechanical test laboratory, Knight Mechanical Testing (KMT) in Fort Wayne, IN. KMT specializes in military, aerospace and medical testing and is has no ties to the running shoe industry.

KMT was contracted by Newton Running to develop a test protocol and computer controlled, machine actuated testing to simulate a 150 lb runner at 7 miles per hour (90 foot strikes per foot each minute). These tests use technologically advanced, machines that are controlled with extreme precision.

ASTM Test vs. KMT Test

The current ASTM (American Standard for Testing Materials) "Standard Test Method for Shock Attenuating Properties of Materials Systems for Athletic Footwear" [ASTM F 1614 - 99] (used by the Runner's World Shoe Lab) was used as one of the source documents in developing the KMT test. The ASTM test uses a 1.8 inch diameter metal cylinder dropped from 1.97 inches onto the heel of a shoe, and repeated 5 times.

ASTM F 1614 - 99 does not simulate foot shape, foot surface area, angle of impact, the driving force of the leg, leg speed, cadence, material degradation over time or precise, repeated testing. KMT developed test fixtures, actuator and motion control that takes into account and overcomes the inadequacies of the ASTM drop test. Unlike the ASTM test, the KMT test repeatedly and continuously impacts the shoe with real life forces at a representative speed and cadence to a regular runner. This test is conducted for a minimum of 500 equivalent miles for each shoe model, or approximately 386,000 impacts.

Discussion of Results

KMT ran endurance tests on several shoes and stopped at 1,000 miles since it is unlikely anyone will run this far on a single pair. Test results and analysis showed that the Newton Active Membrane technology does not degrade up to 1,000 miles, whereas all other shoe technologies (gel, foam, wave etc.) have rapid degradation up to about 100 miles.

The KMT test loads each shoe at the flex point (mid foot) at an angle calculated to coincide with the maximum load on the shoe between impact and push off. This is different from the initial forces experienced during foot strike, since the forces imparted by the foot move from the heel to the toe in three axis motion (up-down, front-to-back and side-to-side.)

Additional Information

Most people load the heel portion of a shoe at some point during their gait cycle, and depending on they running style and shoe geometry, this varies from negligible to severe impact. Regardless of the heel load, significant mid foot forces are generated by all runners as their center of mass moves over the foot before push off.

It is worth noting that the standard heel to toe drop on regular running shoes is 1/2 inch, which means it is difficult to avoid hitting the heel portion of a regular shoe. Newton Running shoes have a 1/6 to 1/5 inch drop, which allows a more mid foot strike (as if running in your natural bare foot state) reducing the shock loads associated with heel striking.