A new device to measure isometric strength in upper limbs: comparison between dominant and non-dominant limbs

Accurate assessment of the performance of the human muscular system has been the object of scientists and practitioners of physical medicine and rehabilitation for many years.1-3 Evaluation of muscle strength is a common practice carried out by professionals and researchers. Few medical professionals have accurate measuring instruments, and almost in its entirety, the muscle strength tests are carried out manually by physicians, physiotherapists, physical educators, among others. The concern about the lack of quantitative data based on tests carried out by hand strength resulted in the development of instrumental forms of muscle testing, such as Jamar®, Kratos® and computerized isokinetic dynamometer Biodex®. These instruments have earned wide acceptance in clinical research of muscular strength evaluation.4 Rabin and Post5 performed a comparison between the evaluation by manual methods and the instrumental evaluation of the flexor moment and external rotator of the shoulder before and after surgery. It was found that applying the manual method time was rated higher, however, this increase was not evident when using the instrumental evaluation. Hsu et al6 indicated that increased muscle strength improves the functionality of the patient and suggested that the methods of muscle strength measurement should be accurate and reliable. Therefore, it is important equipments that assist in the accurate assessment of muscle strength and an experimental analysis of engineering possibilities. This analysis refers to applications where measurement provided by an instrument is designed to be used as a post-measurement for the determination of some parameters, models and / or validation.7 Measurement devices extend the possibilities of physical examination, particularly in the case of complex musculoskeletal problems during rehabilitation of patients with muscular weakness or restricted range of motion.8 The grip strength refers to any process that seeks to measure the forces, thus, the dynamometer is a type of equipment that measures the behaviour of the load and strain deformation of structures.9 The use of dynamometers to measure muscle strength has increased in recent decades and various types of instruments have been improved and made available for researchers.10 In a review conducted by Jaric11 on strength tests most studies involving muscle strength evaluation are performed using the lower limbs, suggesting new studies involving the upper limbs. There is little information available regarding the functional connections of the shoulder and wrist and the factors involved in its strength.12 Given the necessity of obtaining quantitative data in Biomechanics, it is necessary the design and development of equipments to measure the forces that interact with the locomotor system. Thus, the aim of this study was to evaluate a new device from our laboratory capable of measuring the strength generated by the muscles of the upper limbs and to compare the muscle strength of shoulder between dominant and non-dominant upper limbs in healthy subjects.