The development, validity, and reliability of a manual muscle testing device with integrated limb position sensors

Objective: To report the development and validation of a new hand-held muscle strength-testing device that is integrated with orientation sensors and designed to test the strength of major muscle groups at a given limb or joint position. Design: Design description and validation study. Setting: University-based human movement facility. Participants: Twenty-eight able-bodied, healthy subjects. Interventions: Not applicable. Main Outcome Measure: A device was developed based on a hand-held force dynamometer with integrated orientation sensors. The validity and reliability (interrater, intertrial) of 5 maximum isometric contractions of hip flexion, knee extension, and ankle plantarflexion and dorsiflexion were assessed. The results were compared with those from an isokinetic dynamometer (KinCom). Results: The new manual muscle tester was highly reliable and valid in estimating muscle strength of the lower limbs. The coefficient of variation between trials of all movements was low, with a mean less than 10% (range, 3.7%-8.9%). The only significant difference in muscle strength between the new device and the isokinetic dynamometer was found for hip flexion. Conclusions: The new hand-held muscle strength tester appears to be a reliable and valid clinical assessment tool that can be used to objectively assess muscle strength at particular limb positions and/or joint angles. This feature appears to represent a technical advance in portable muscle strength devices, providing comparable information to those obtained by isokinetic dynamometers at a fraction of the cost and size. However. the device needs to be validated in clinical populations, such as patients with spinal cord injury and stroke, in order to demonstrate its general clinical utility.