Effectiveness of a wireless Sensor Insole in measuring vertically directed ground reaction force (GRF) during the sprinting action: The availability of a device to accurately measure the amount and direction of force applied to the ground with each step during the sprinting action would be major breakthrough. The specific training programs and exercises that increase GRF, decrease ground contact time (GCT), and improve speed in short sprints could then be accurately identified. The technology to develop these sensors is available and researchers are now experimenting with various devices and protocols. An abstract of a study by Nagahara and Morin (2018), who tested one type of shoe insole sensor, follows.
Temporal variables and vertical ground reaction force have been used as measures characterizing sprinting. A recently developed wireless pressure sensor insole (sensor insole) could be useful for monitoring sprinting in terms of temporal variables and vertical ground reaction force during training sessions. The purpose of this study was to examine the concurrent validity of the sensor insole for measuring temporal and vertical force variables during sprinting. One athlete performed five 50-m sprints, and the step-to-step vertical ground reaction force and plantar pressure were simultaneously measured by a long-force platform system (reference device) and the sensor insole, respectively. The temporal and vertical ground reaction force variables were calculated using signals from both devices, and a comparison was made between values obtained with both devices for 125 steps analyzed. The percentage bias, 95% limits of agreement, and Bland–Altman plots showed low agreement with the reference device for all variables except for step frequency. For the vertical ground reaction force variables, the sensor insole underestimated the values (−18.9 to −48.3%) compared to the force platform. While support time and time to maximal vertical force from the foot strike were overestimated by the sensor insole (54.6 ± 8.0% and 94.2 ± 23.2%), flight time was underestimated (−48.2 ± 15.0%). Moreover, t-test revealed the significant difference in all variables between the sensor insole and force platform, except for step frequency. The bias for step frequency (0.4 ± 7.5%) was small. However, there was heteroscedasticity for all variables. The results from this study demonstrate that a wireless pressure sensor insole is generally not valid to measure the temporal and vertical force variables during sprinting. Thus, using the examined sensor insole for monitoring sprinting characteristics is not recommended at this time.
Coaching Application. Although findings of the above study indicate that a wireless shoe sensor did not accurately measure temporal and vertical ground reaction forces, it is a first step toward the development of a low cost device that is as accurate or more accurate than the costly force plate technology currently available. Developing a low cost, accurate device is a challenge, however, the tremendous importance of finding ways to increase GRF and decrease GCT during the start, acceleration, and maximum speed phase of a short sprint, encourages researchers to continue their pursuit in this area of interest.
Reference: Ryu Nagahara and Jean-Benoit Morin. 2018. Sensor insole for measuring temporal variables and vertical force during sprinting. Proceedings of the Institution of Mechanical Engineers. Part P: Journal of Sports Engineering and Technology. First Published January 19, 2018.