Assessing the validity and reliability of a low-cost microcontroller-based load cell amplifier for measuring lower limb and upper limb muscular force

Manual muscle testing, load cell coupled with a signal conditioner, and handheld dynamometry are three widely used techniques for measuring isometric muscle strength. In this study, we examined both the criterion validity, inter-day reliability and intra-day reliability of a microcontroller-based load cell amplifier for quantifying muscle strength and we compared its results the other means of strength evaluation.

Before we start, let's get acquainted with these devices!

This is the HX711 load cell amplifier, it is used to get measurable data out from a load cell and strain gauge.

This is the Lafayette handheld dynamometer (formerly known as the Manual Muscle Tester), an ergonomic hand-held device for objectively quantifying muscle strength.

The objective of this study was to assess the criterion validity, inter-day reliability and intra-day reliability of a low-cost microcontroller-based load cell amplifier for measuring lower limb and upper limb maximal isometric muscular force development.

Statistical analysis of inter-day reliability was conducted using the intraclass correlation coefficients and their 95% confidence intervals to compare the strength measurements obtained in two separate sessions for each tool. All three tools had excellent ICC values (0.90–1) when based on a mean-rating, absolute-agreement, 2-way mixed-effects model.

Materials and Methods

To measure the upper limb strength, the load cell is fixed to the wall at one end to hold it in place, and at the other end it is attached to the participant's forearm, with a rigid band (Nite Ize, Sangle Camjam, Boulder, CO, USA) of 2.54 cm width. The handheld dynamometer is also attached to this band so that the participant can push against it. The band holding the instruments was placed six to eight centimeters proximal to the styloid process of the ulna on the anterior surface of the forearm. We can see it at the imgage below.

We also created table comparing between the three different instruments (Lafayette handheld dynamometer, the commercial signal conditioner and the HX711 microcontroller-based load cell amplifier) used for measuring strength. We compared which one is bigger, more expensive, more heavy, as you can see below.

Conclusion

The results of this study could have significant implications for the way in which the evaluation of muscle strength measurement is performed in the future. The quantification of muscle strength is an essential aspect of physical capacity assessment, and the use of the HX711 microcontroller-based load cell amplifier, as described in this study, could be a useful substitute to current methods.

The HX711 microcontroller-based load cell amplifier shows nearly perfect correlation with the standard laboratory setup and the handheld dynamometer, which demonstrates its validity, and shows a good association when calculating the inter-day and intra-day reliability score with the use of the ICC, which demonstrates its reliability. There are numerous possibilities in terms of practical implications for the microcontroller-based load cell amplifier and further studies should evaluate its use in laboratory settings and clinical settings. Having characteristics, including commercial-like grade quality at a low cost, as well as being small and portable, this device has the potential to be used in a wide range of settings.

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