Human Movement & Balance Laboratory

Swanson School of Engineering

Human Movement & Balance Laboratory

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Swanson School of Engineering

Human Movement & Balance Laboratory

Technical details on our methods:

As researchers, we have spent years pursuing our curiosities about how people slip and how we can measure footwear to evaluate its slipping risk. This research can be broadly characterized into our research on human slipping, the development of our friction test methods, and the validation of our test methods against human slipping.

Biomechanics of slips

In our gait lab, we measure human motion and human slipping events. In these experiments, participants are harnessed for safety and exposed to dry and slippery floor surfaces. Our test methods ensure that we capture an authentic and unexpected slip event to resemble real-world slips. We use a combination of experimental equipment including motion capture and force plates to measure the state of the shoe at the moment that it begins to slip. These metrics include the angle of the shoe, the force beneath the shoe, the speed at which it is moving, and the amount of time it is on the ground before slipping. These are the critical conditions that inform our test methods.

How do we conduct our tests?

Based on our understanding of the biomechanics of slipping, we conduct research test methods at a shoe-floor angle of 17°, a force of 250 N, and a sliding speed of 0.5 m/s. Our tests also ensure that the shoe is moving the entire time from contact with the floor through the friction measurement. The key differences between our test methods and other common methods is that we use a higher angle, a lower force, and we keep the shoe sliding. Our research has demonstrated that these better reflect the biomechanics of human slipping and thus leads to a valid friction measurement that is relevant to a shoe’s risk in the real world.

Validation of test methods

The validity of our lab’s test methods has been assessed using over 200 participants. During this process, our test methods have consistently been found to be predictive of whether a person experiences a slip. We validate our test methods using a metric called area under the receiver operating characteristic curve. This method of validation is consistent with how diagnostic tools are commonly evaluated and provides a value between 0.5 (no predictive value) and 1.0 (makes perfect predictions). Our test methods have consistently led to values between 0.78 and 0.86 ([1-3]) whereas another common test method received a value of 0.70 [4].

Citations:

  1. Beschorner, K.E., et al., Validating the ability of a portable shoe-floor friction testing device, NextSTEPS, to predict human slips. Applied Ergonomics, 2023. 106: p. 103854.
  2. Iraqi, A., et al., Coefficient of friction testing parameters influence the prediction of human slips. Applied Ergonomics, 2018. 70: p. 118-126.
  3. Sundaram, V., et al., Worn Region Size of Shoe Soles Impacts Human Slips: Testing a Mechanistic Model. Journal of Biomechanics, 2020: p. 109797.
  4. Beschorner, K.E., et al., Predicting slips based on the STM 603 whole-footwear tribometer under different coefficient of friction testing conditions. Ergonomics, 2019. 62(5): p. 668-681.

Other Papers Supporting Our Test Methods

  1. Albert, D.L., et al., Three-dimensional shoe kinematics during unexpected slips: Implications for shoe-floor friction testing. IIE: Transactions on Occupational Ergonomics and Human Factors, 2017. 5(1): p. 1-11.
  2. Beschorner, K.E., et al., Validating the ability of a portable shoe-floor friction testing device, NextSTEPS, to predict human slips. Applied Ergonomics, 2023. 106: p. 103854.
  3. Beschorner, K.E., et al., Predicting slips based on the STM 603 whole-footwear tribometer under different coefficient of friction testing conditions. Ergonomics, 2019. 62(5): p. 668-681.
  4. Beschorner, K.E., et al., Influence of averaging time-interval on shoe-floor-contaminant available coefficient of friction measurements. Applied Ergonomics, 2020. 82: p. 102959.
  5. Beschorner, K.E., et al., Effects of slip testing parameters on measured coefficient of friction. Applied Ergonomics, 2007. 38(6): p. 773-780.
  6. Iraqi, A., et al., Coefficient of friction testing parameters influence the prediction of human slips. Applied Ergonomics, 2018. 70: p. 118-126.
  7. Iraqi, A., et al., Kinematics and Kinetics of the Shoe during Human Slips. Journal of Biomechanics, 2018. 74: p. 57-63.
  8. Singh, G. and K.E. Beschorner, A Method for Measuring Fluid Pressures in the Shoe-Floor-Fluid Interface: Application to Shoe Tread Evaluation. IIE Transactions on Occupational Ergonomics and Human Factors, 2014. 2(2): p. 53-59.
  9. Sundaram, V., et al., Worn Region Size of Shoe Soles Impacts Human Slips: Testing a Mechanistic Model. Journal of Biomechanics, 2020: p. 109797.
  10. Beschorner, K.E., et al., Prospective validity assessment of a friction prediction model based on tread outsole features of slip-resistant shoes. Applied Ergonomics, 2024. 114: p. 104110.