# Handgrip Strength Time Profile and Frailty: An Exploratory Study
## 1 Introduction
HGS offers numerous advantages over other nutritional, functional, and health indicators as it is simply evaluated based on dynamometry, an inexpensive, easy, quick, and reliable method, exhibiting low intra- and between-variability and does not require specialized professionals [23]. In most studies found in the literature, handgrip strength is defined as the maximum value of strength, typically assessed using an isometric test with a handgrip dynamometer, according to a given protocol. With the availability of a few dynamometers capable of measuring the exerted force during a test time interval continuously, other force parameters related to muscle condition have been studied and proposed, such as the rate of force development and sustainability of maximum force. Such parameters depend on the ability to produce energy at the mitochondrial level, which is crucial to several daily tasks that require repetition or a continuous hold [24; 25; 26; 27]. The hand dynamometer most frequently reported and accepted as the gold standard is the JAMAR (from Patterson Medical). The original design of JAMAR using a hydraulic system is only able to measure the maximum value of handgrip strength. The JAMAR(r) Smart Hand Dynamometer uses a load cell and electronics for wireless communications, with a mobile app that allows accessing other handgrip strength vs. time parameters. Although these new functionalities are quite helpful, accessing the raw data and implementing other data processes is not possible. Moreover, the test time intervals are quite short, nor selectable, and therefore not suitable for the investigations, such as the one here described. Similar limitations arise when considering the use of other commercialized handgrip dynamometers, such as the one from Biometrics and the one from JTECH Medical(tm) Commander Echo Grip and software (USA). The proprietary nature of the communications and available software for these devices limit their use if other test configurations and data analysis are required. In this work, measurements of handgrip strength time profile were performed using BodyGrip, a patented digital system based on a novel dynamometer [28], allowing the exploitation of the raw data coming from the recorded handgrip test, also permitting the suitable time interval to be defined and adjusted. Adding to its new functionalities, the device is very light, a great advantage for testing among the elderly. Very little research has focused on the relationship between frailty and the parameters obtained from the force _vs._ time profile, such as rate of force development and sustainability of maximum force, etc. Furthermore, universal definitions of these parameters are not found in the literature. The present study aims at exploring HGSt data obtained from an isometric handgrip test and to match it with a frailty state based on the TFI score. A universal set of descriptors is proposed inspired by the response of a first-order system to a step stimulus. In fact, this type of response is similar to that obtained when an individual is incited to apply a sudden maximum grip force to the handgrip and sustain it for a given time period. In this exploratory work, the BodyGrip system was used to measure the dominant handgrip strength profile during a ten-second duration test performed in a group of community-dwelling elderly women. The TFI questionnaire data were also collected. Different sets of descriptors from the force vs. time curves were applied to train ANN models to match the TFI test results. This approach envisages ultimately configuring the handgrip prototype system [23] as a tool for supporting frailty screening that can be utilized in ambulatory care, with the test conducted and results obtained in a short time, and performed by any health care professional, such as occupational therapists, after an informed short training.