(02) NOVEL 3D FORCE SENSORS FOR A LIGHTWEIGHT PORTABLE AND DURABLE 3D FORCE PLATE

Three-dimensional force plates are important tools for biomechanics discovery and sport performance practice.

Purpose: However, currently available 3D force plates lack portability and are often cost-prohibitive. Thus, a recently discovered, novel 3D force sensor technology was used in the fabrication of a prototype force plate aimed at addressing these issues.

Methods: These 3D force sensors, constructed according to methods presented in detail in Miller et al,¹ are small, lightweight, natively waterproof, and very durable. Briefly, the sensors were 40 x 40 x 5 mm in size, and composed of a magnetic-silicone composite construct coupled with a 3-axis magnetometer. The force plate construction included one 3D force sensor bonded to each corner of a 24” x 18” x 0.75” rigid aluminum plate which served as the top plate. Another 24” x 18” x 0.25” plate was bonded to the under-side of the sensors, to sandwich the sensors between the two plates, as is typical for force plate construction. Thirteen subjects performed bodyweight and weighted lunges (24 repetitions per subject) and squats (15 repetitions per subject) on the prototype force plate and a standard 3D force plate positioned in series, to compare forces measured by both force plates to validate the technology (See Figure 1).

Results: In terms of absolute agreement intraclass correlation coefficients (ICC), for the lunges, there was excellent agreement in peak forces measured by the prototype force plate and the standard force plate in the X-, Y-, and Z-axes (r = 0.950 – 0.996, p < 0.001). For the squats, ICCs indicated there was excellent agreement in peak forces measured by the force plates in the Z-axis (r = 0.996, p < 0.001). Across movements, root mean square error (RMSE) of the full force-time data traces ranged from 1.17% to 2.51% for the X- and Y-axes, and ranged from 3.66% to 5.36% for the Z-axis between force plates. Mean bias in peak forces measured by the prototype force plate were quite minimal across axes and movements (-1.18 – 1.95 N) except for the Z-axis during lunges, where the prototype force plate tended to overestimate peak forces by 14.56 N (1.75%).

Conclusions: Although the current prototype force plate is limited in sampling rate (100 Hz), the low RMSEs and mean biases, and extremely high agreement in peak forces measured by the force plates provides confidence in the novel force sensors for use in force plates and potentially other implementations. PRACTICAL APPLICATION: Although future implementations should increase sampling frequency to > 1000 Hz, the sensors described in the current study can be used for constructing cost-effective and versatile 3D force plates, with potential for outdoor use due to being waterproof.

References:

1.         Miller, J. D., Cabarkapa, D., Hermes, M. J., Fry, A. C. & Berkland, C. J. Soft Magnetic Composites as Quantitative 3D Compression Sensors for Wearable Technology. Advanced Materials Technologies 7, 2100784 (2022).

Acknowledgements:

We gratefully acknowledge support from Honeywell Federal Manufacturing & Technologies as a part of Department of Energy Contract DE-NA-0002893.