# Handgrip Strength Time Profile and Frailty: An Exploratory Study
## 2 Materials and Methods  
### The Prototype System  
To measure the HGSt, the BodyGrip dynamometer developed in the Integrated System and Automation Processes Research Unit of the Institute of Mechanical Engineering of the Faculty of Engineering of the University of Porto was used.  
The smart multifunction device allows measuring the compressive or traction force and the estimation of the energy and power used by a particular body muscle or of a group of muscles by just adapting accessories. Together with a software application developed for a PC, the BodyGrip system permits performing different calculations from measuring data provided by the device to recording them in a local or remote database, to processing the data and offering digital monitoring of all features. The system also shows in real-time on the user interface the respective force-time profile. The test elapsed time duration can be adjusted through the user interface to the protocol defined for the study. The prototype device has been used for handgrip evaluation in different fields and was initially validated against the gold standard JAMAR [28].  
During its mechanical design, features, such as portability, good sensitivity, force range, and ergonomics, were considered. The device is small, light, and easily portable, although robust. The novel design of its mechanical sensing element (load cell), sensorized with electrical strain gauges, avoids the need for specially designed handles. The bending-type cells, both cantilevered from the center, receive the load on both free ends. This arrangement, and the load sensorization with strain gauges, contribute to the calculation of non-uniformly distributed loads applied to the handle and to provide the free end displacement for partial estimation of the muscle energy.  
Its electronics include strain sensors, signal conditioning, and basic processing, which incorporates an IMU for the identification of device orientation, offering Bluetooth connection and USB connection for battery charging.  
The BodyGrip system, presenting good sensitivity and resolution, offers a compact device with wireless communication with a software application (10 ms sampling rate) for data registration and monitoring.  
The prototype dimensions (114 mm \(\times\) 22 mm \(\times\) 45 mm) and weight (0.250 Kg) make it a pocket device for a clinical trial, convenient to the diverse functions presently open to its use, Figure 1.  
Adding to these features, the BodyGrip allows the measurement of low-level forces without handling effort, in a suitable size where the current large and heavy devices are no longer adequate, which makes it suitable for the elderly, children, and young adults. Further, it offers good characteristics in sensitivity and range.  
Currently, the software application runs on a PC or a mobile device. This application provides data monitoring and patient registration, with access to a local or cloud database. Other functionalities include the possibility to access other patient data, such as hand circumference, hand length. A current implementation under development is to provide frailty screening based on handgrip force-time data, building on the experience that this work describes.  
The current development is under a Technology Transfer process by the UPorto spin-off named GripWise ([[https://gripwisetech.com/](https://gripwisetech.com/)]([https://gripwisetech.com/](https://gripwisetech.com/)); accessed May 2021), and about 15 systems in a further development stage, named GripWise, are already being used in different health and health care institutions.  
Figure 1: BodyGrip prototype.