Progressive muscle weakness is the hallmark of ALS. Evaluating muscle strength is therefore an important way to monitor disease progression in clinical trials. This is usually done in the hospital by means of a ‘hand-held dynamometer’. Using this method, the strength of various muscle groups is measured. New research from the Netherlands ALS Centre now shows that the reliability and sensitivity of muscle strength testing can be improved using a portable fixed dynamometer.
A portable, fixed dynamometer
While the hand-held dynamometer (Figure 1a) is very user-friendly, it is not without limitations. For instance, its reliability depends on the technique and strength of the examiner. This can lead to ceiling effects in strong muscle groups – the strength can no longer be measured if it exceeds that of the examiner. In addition, if muscle strength is evaluated by different examiners over time, this can introduce unwanted variability in measurements. By fixating the dynamometer in a rigid structure, muscle strength can be measured in a very standardised way, independent of an examiner that has to give counter pressure. Current systems that use fixed dynamometry are, however, bulky and expensive. Research performed by the Netherlands ALS Centre has now led to the development of a portable fixed dynamometer (Figure 1b). This new dynamometer measures strength of the quadriceps (a muscle group in the upper leg).
Improving muscle strength measurements
Muscle strength measurements with the portable fixed dynamometer were compared with the hand-held dynamometer in45 people living with either Amyotrophic Lateral Sclerosis, Progressive Muscular Atrophy or Primary Lateral Sclerosis and by 43 healthy controls. The results showed that the portable fixed dynamometer not only reliably measures muscle strength, but also and decreased the ceiling effect caused by the examiner using a hand-held dynamometer.
The portable design of the portable fixed dynamometer provides a future opportunity for remote muscle strength measurements, independent of an examiner. Home based measurement of muscle strength can help to reduce the number of hospital visits and the burden to participate in clinical trials. In addition, the portable fixed dynamometer allows more frequent measurements in a standardised way, therefore contributing to improvement of the evaluation of new therapies for ALS.
Bakers, J.N.E., van den Berg, L.H., Ajeks, T.G. et al. Portable fixed dynamometry: towards remote muscle strength measurements in patients with motor neuron disease. J Neurol (2020). https://doi.org/10.1007/s00415-020-10366-9