# Handgrip Strength as an Indicator of Overall Strength and Functional Performance--Systematic Review
## 4 Discussion  
The aim of the systematic review of the literature was to verify whether hand grip strength can be used as an indicator of overall strength and functional performance. This task required ordering the existing knowledge and results obtained in scientific research on the dependences between hand grip strength and muscle strength/moments of forces in the joint muscles. Selected articles were subjected to the impact of methodological quality assessment (risk of bias). The score for all articles was above 75%, with an average score for all articles of 85.61%, SD = 6.73. This shows a correct selection of articles of high scientific quality. Based on the systematic review of the literature, only half of the studies analyzed showed a relationship between hand grip strength and muscle force moments in the trunk, upper and lower limbs. No definitive conclusions can be drawn about the existence of these relationships in different age groups or for specific parts of the body. On the basis of the conducted literature review, it was observed that in the search of dependences between the moments of muscle forces and hand grip strength, the majority of authors decided to seek correlations by limiting the study group to the group consisting only of elderly individuals: 12 articles [8; 11; 24; 26; 34; 35; 37; 38; 39; 40; 42; 43]. Only four articles were found where the dependences were looked for in the group of young subjects [23; 29; 33; 36], and one paper described the dependences in the group of adults at an average age of 52 years [30]. Five research papers attempted to determine such dependences both in the group of young and elderly individuals [25; 31; 32; 41; 44]. The analyzed articles encompassed the total number of 2965 elderly individuals and additionally 112 elderly individuals with coexisting conditions [40], 752 healthy adults, 30 physically active subjects and 120 ill patients after stroke [30], or spinal cord injury [33]. In two publications [31; 41], the results were analyzed jointly in the group of young and elderly individuals. Despite the clinical heterogeneity of the study groups, the focus of the study was to determine the relationship between hand grip strength and muscle force moments. The correlation coefficients analyzed, rather than the experimental results from the different groups, determined whether hand grip strength could be used as an indicator of overall strength and functional performance. In the analyzed articles, the measurement of hand grip strength was performed most frequently according to the recommendations of the American Society of Hand Therapy, i.e., in a sitting position, with the elbow flexed at an angle of 90\({}^{0}\). Also, measurements carried out in other positions could be found, such as with the limb extended (straight limb) [31], in a standing position [25; 29; 32; 42; 43], e.g., with the limb hanging by the body side [29; 32; 42]. The most popular device used for the measurement of hand grip strength is a dynamometer manufactured by Jamar company (Sammons Preston, Illinois, USA) [23; 24; 25; 26; 30; 31; 34; 35; 37; 38; 40; 41; 42; 43]; however, other types are also applied: Lafayette [29], E-Link [11], Vetek [32], TKK 5101 Grip-D [8], TSD121C Biopac System [39], Saehan Corporation [33], Cites type CT3001 [36], Good Strength dynamometer [25] and Biometrics Data Link software [44]. The Biodex system is most often used for the measurements of the moments of muscle forces [11; 23; 24; 26; 30; 32; 33; 34; 37; 38; 39]. The studies analyzed were characterized by methodological heterogeneity due to different measurement equipment. The measurement results were presented in the same unit of measurement (Tables 3-5). However, the relationship analyzed was demonstrated by the value of the correlation coefficients. Researchers performed measurements of the moments of muscle forces in isokinetic or isometric conditions in various angular positions.