Accuracy and Precision of a Novel Photogate System to Measure Toe Clearance on Stairs

Timmion K. Skervin, Neil M. Thomas, Andrew J. Schofield, Mark A. Hollands, Constantinos N. Maganaris, Thomas D. O’Brien, Vasilios Baltzopoulos, Richard J. Foster

Research output: Contribution to journalArticlepeer-review


Background: Toe clearance on stairs is typically measured using optoelectronic systems, though these are often constrained to the laboratory, due to their complex setups. Here we measured stair toe clearance through a novel prototype photogate setup and compared this to optoelectronic measurements. Methods: Twelve participants (age 22 ± 3 years) completed 25 stair ascent trials, each on a seven-step staircase. Toe clearance over the fifth step edge was measured using Vicon and the photogates. Twenty-two photogates were created in rows through laser diodes and phototransistors. The height of the lowest photogate broken at step-edge crossing was used to determine photogate toe clearance. A limits of agreement analysis and Pearson’s correlation coefficient compared the accuracy, precision and relationship between systems. Results: We found a mean difference of −1.5 mm (accuracy) between the two measurement systems, with upper and lower limits (precision) of 10.7 mm and −13.8 mm, respectively. A strong positive correlation was also found (r = 70, n = 12, p = 0.009) between the systems. Discussion: The results suggest that photogates could be an option for measuring real-world stair toe clearances, where optoelectronic systems are not routinely used. Improvements to the design and measurement factors may help to improve the precision of the photogates.
Original languageEnglish
Article number2429
Number of pages8
Issue number5
Early online date22 Feb 2023
Publication statusPublished - Mar 2023

Bibliographical note

Copyright © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (

Funding: This research was funded by a Liverpool John Moores University (UK) PhD scholarship.


  • optoelectronic
  • photogates
  • stair safety
  • toe clearance


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