Ergonomics Archives - ISPGR

Slippery Business: Unexpected risks of flip-flop footwear

Blog Editor — Mon, 01 Mar 2021 02:45:17 +0000

By Liana Tennant

Common sense tells us that flip-flops should never be worn in the chemistry lab or when cutting the grass, but could flip-flops increase injury risk in less obvious situations? We were approached by a forensic engineering company who wanted to determine the role flip-flops might play in a slip and fall incident. In addition to evaluating slip dynamics on wet and dry tile, the firm also wanted to know how slips change when the foot is also wet, a scenario that might be encountered on a rainy day. We expected that with a wet foot, it might move around inside the flip-flop during a slip. A slip within a slip if you will.

To answer these questions, we invoked slips from a standing posture by pulling one ankle forward using a cable and pulley device (Figure 1). Although the slip speeds using this method were higher than those reported during walking, it allowed us to control some of the variables that can affect how slips occur and progress. We tracked the foot and flip-flop separately using a 3D motion capture system. We found that there was minimal relative motion between the foot and flip-flop during slips, so long as the flip-flop stayed on the foot; however, in several instances the flip-flop slid forward off the participant’s heel, which we called ‘decoupling.’ Decoupling occurs when the friction between the foot and flip-flop is insufficient to halt the forward momentum of the flip-flop caused by the initial pull at the ankle. Sometimes the flip-flop came off entirely (see video Figure 2 )! Decoupling happened in at least 1 of 27 slips for 12 of the 17 participants. We saw decoupling less often on wet tile with a dry foot, and more often when both the tile and foot were either dry or wet.

This study highlighted that friction between the foot and flip-flop matters. When flip-flops are worn, two different yet important slips may occur: 1) your flip-flop can slip along the ground or 2) your foot can slip inside the flip-flop. If you lose your flip-flop during a slip, you could injure your unprotected foot, or it might make it harder for you to catch yourself when falling. The results also have implications for flip-flop design. As consumers, we likely focus on how comfortable our footwear is, but the materials and the surface texture of the flip-flop footbed could also be important from a safety perspective. Future work evaluating real-life scenarios like walking or going downstairs is needed to see if decoupling occurs as frequently in these situations as what we saw when we invoked a slip.

Figure1. The experimental setup. The participant stood with their right foot on a tile mounted on a force plate. Their ankle was connected to a cable and pulley machine loaded with 25% of the participant’s body weight (weight stack was hidden from view). An active motion capture system was used to track the foot and flip-flop. The participant wore a harness tethered to the ceiling to protect them in the event of a fall.

Figure 2. This video shows an example of the decoupling phenomenon we observed during some of the slips. Playback is at 0.5x speed. The flip-flop is represented by the white planar surface.

Publication

Tennant, L.M., Fok, D.J., Kingston, D.C., Winberg, T.B., Parkinson, R.J., Laing, A.C., Callaghan, J.P., 2021. Analysis of invoked slips while wearing flip-flops in wet and dry conditions: Does alternative footwear alter slip kinematics? Applied Ergonomics 92, 103318. https://doi.org/10.1016/j.apergo.2020.103318

About the Author

Liana Tennant

Department of Kinesiology, University of Waterloo

Liana is a PhD student at the University of Waterloo. She enjoys working with industry partners on collaborative projects and her doctoral research focuses on the study of the biomechanics of shock transmission through the lumbar spine.

Copyright

© 2021 by the author. Except as otherwise noted, the ISPGR blog, including its text and figures, is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. To view a copy of this license, visit https://creativecommons.org/licenses/by-sa/4.0/legalcode.

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Standing up from the floor – A sensor based analysis

PodiumAdmin — Wed, 12 Oct 2016 17:45:14 +0000

Everyone is familiar with the horrific stories about older adults who are unable to get up after a fall. Getting up after a fall is indeed problematic for many older adults, which often leads them to remain incapacitated on the floor for a long time. It is a strong interest of clinicians and health-care providers to prevent these so-called “long-lies” as they can cause serious medical problems. A valuable approach to assist with the development of technologies to detect and prevent falls is to identify the act of standing up from a lying position. Kinematic analysis to objectively describe and assess standing up performance from inertial sensors is currently lacking. Hence, our main aim was to assess kinematic features during lie-to-stand transfers and describe age-related differences. In our study in Sensors, we present an easily deployable method to assess standing up based on inertial sensor signals.

Fourteen younger participants between 20 and 50 years of age, and 10 healthy older community dwellers aged 60 years and older, were asked to stand up from different initial lying postures on the floor (lying on their back, front, left and right sides). All participants were able to repeatedly stand up without help. The participants were asked to initiate the transfers voluntarily and to end the transfers in an erect standing position without considerable body movement. Kinematic data were recorded with Opal sensors (Figure 1, APDM, Portland, OR, USA) located on the sternum and lower back, which sampled 3D accelerations, angular velocity and magnetic fields at 128 Hz.

Figure 1: Lower-back tri-axial (anterior-posterior (AP), medio-lateral (ML) and superior-inferior (SI)) acceleration signal of a lie-to-stand transfer in a younger (A) and older adult (B). C and D show the correspondent vertical velocity traces, with the start and end points marking the main elevation events measured at the lower back.

Our results show that temporal and kinematic measures of transfer performance, such as duration, angular velocity, maximum vertical acceleration, maximum vertical velocity, smoothness, fluency, total rotation, were significantly different between younger and older participants. These results showed the feasibility of using body-worn sensors for the analysis of lie-to-stand movements and describe how younger and older adults stand up from the floor. This will help to better understand sensor signals of recovery after real world falls.

Understanding kinematics and different movement patterns underlying lie-to-stand transfers will help to develop autonomous technologies to detect long lies after falls and provide suitable exercise interventions for their prevention. Our results motivate further application of kinematic analysis on recovery patterns after real-world falls.

Publication:

L. Schwickert, R. Boos, J. Klenk, A. Bourke, C. Becker and W. Zijlstra (2016). Inertial Sensor Based Analysis of Lie-to-Stand Transfers in Younger and Older Adults. Sensors, online August 2016. http://www.mdpi.com/1424-8220/16/8/1277

About the Author

Lars Schwickert

Department of Clinical Gerontology at Robert-Bosch-Hospital, Stuttgart

Lars Schwickert is a research fellow at the Department of Clinical Gerontology at Robert-Bosch-Hospital in Stuttgart, Germany, working with Prof. Dr. Clemens Becker. He has a background in sports and exercise science with a medical focus, and he is currently in the final stage of his doctoral research at the Institute of Movement and Sport Gerontology of the German Sport University Cologne with Prof. Wiebren Zijlstra. His research focuses on the recovery after a fall measured with body-worn sensors.

Copyright

© 2018 by the author. Except as otherwise noted, the ISPGR blog, including its text and figures, is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. To view a copy of this license, visit https://creativecommons.org/licenses/by-sa/4.0/legalcode.

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Are you interested in writing a blog post for the ISPGR website? If so, please email the ISGPR Secretariat with the following information:

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