Abstract
Lower and upper limb maximum muscular force development is an important indicator of physical capacity. Manual muscle testing, load cell coupled with a signal conditioner, and handheld dynamometry are three widely used techniques for measuring isometric muscle strength. Recently, there is a proliferation of low-cost tools that have potential to be used to measure muscle strength. This study examined both the criterion validity, inter-day reliability and intra-day reliability of a microcontroller-based load cell amplifier for quantifying muscle strength. To do so, a low-cost microcontroller-based load cell amplifier for measuring lower and upper limb maximal voluntary isometric muscular force was compared to a commercial grade signal conditioner and to a handheld dynamometer. The results showed that the microcontroller-based load cell amplifier correlated nearly perfectly (Pearson's R-values between 0.947 to 0.992) with the commercial signal conditioner and the handheld dynamometer, and showed good to excellent association when calculating ICC scores, with values of 0.9582 [95% C.I.: 0.9297–0.9752] for inter-day reliability and of 0.9269 [95% C.I.: 0.8909–0.9533] for session one, intra-day reliability. Such results may have implications for how the evaluation of muscle strength measurement is conducted in the future, particularly for offering a commercial-like grade quality, low cost, portable and flexible option.
Highlights
Muscle strength has been defined as the maximum force or torque developed during maximal voluntary contraction under a given set of conditions [1]
Validation results for both the HX711 microcontroller-based load cell compared to the laboratory based setup, and the HX711 microcontroller-based load cell compared to the handheld dynamometer, are found in scatterplots (Figures 2–5) with linear regression and mean difference plots (Figures 6–9)
Similar validity was demonstrated for the HX711 microcontroller-based load cell when compared to the standard laboratory setup and the handheld dynamometer, with Pearson's R values for the first session of 0.977 and 0.971 for the upper limb and of 0.987 and 0.971 for the lower limb
Summary
Muscle strength has been defined as the maximum force (in N) or torque (in Nm) developed during maximal voluntary contraction under a given set of conditions [1]. Depending on the interaction between the force developed by the muscle and the load on the muscle, the muscle will either shorten, remain at a fixed length, or be lengthened [3]. Without a change in muscle length is an isometric muscle action [4]; the muscle acts against an immovable resistance at a specific joint angle [2]. Tension development with changes in the length of the muscle, allowing for a complete range of motion, is an isotonic muscle action [2]. An isotonic-concentric action involves the development of tension during shortening of the muscle, whereas an isotonic-eccentric action occurs when there is development of tension during lengthening of the muscle [4]
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