# Handgrip Strength as an Indicator of Overall Strength and Functional Performance--Systematic Review
## 4 Discussion
The following muscles were tested: flexors and extensors of the hip joint, abductors and adductors of the hip joint, flexors and extensors of the knee joint, dorsal and plantar flexors of the tarsal joint, extensors and flexors of the trunk, external and internal rotators of the shoulder, and abductors and adductors of the shoulder blade. The greatest interest is aroused by the search for the dependence between hand grip strength and the moments of forces of extensors and flexors of the knee joint [8; 24; 25; 37; 38; 39; 40; 41; 42; 43; 44] (Figure 3). The methodological differences in testing, including different measuring equipment and different measuring positions of participants, can affect the correlation results analyzed. Hand grip strength dependences were most often correlated with the measured maximum moments of muscle forces. However, [PERSON] et al. [29] conducted research where they searched for the dependence between mean maximum moments and obtained lower values in comparison to other authors [23; 29; 30]. On the other hand, [PERSON] et al. [24] compared correlation values obtained for hand grip strength expressed in kgf and the moments of muscle forces expressed in Nm, or when they were normalized to body weight. [PERSON] et al. [29] and [PERSON] et al. [24] reported lower correlation values between hand grip strength and muscle moments when related to body weight compared to unnormalized results. On the basis of the literature review (performed on 22 scientific articles), it was found that 11 articles showed a statistically significant, strong, positive correlation between the value of hand grip strength and the values of moments of muscle forces in the trunk, as well as upper and lower limbs [11; 23; 29; 30; 34; 36; 37; 38; 40; 41; 42]; five articles [24; 32; 33; 35; 39] determined that such a dependence was small and advised adopting a cautious approach to it; four articles [25; 26; 31; 39] ascertained that there was no dependence, whereas two articles [8; 43] did not interpret the meaning of the result. Dependences between the value of hand grip strength and the values of moments of muscle forces in the trunk, as well as upper and lower limbs may be analyzed in age groups. Taking into consideration the conclusions described in the articles where the study group consisted of elderly individuals, i.e., 12 articles [8; 11; 24; 26; 34; 35; 37; 38; 39; 40; 42; 43], only 6 research teams ascertained that [11; 34; 37; 38; 40; 42] hand grip strength could be used as a prognostic coefficient; 2 articles informed on a weak dependence [24; 35]; whereas successive 2 articles reported the lack of dependence [26; 39]. In the group of young individuals, i.e., in the case of 4 articles [23; 29; 33; 36], a positive correlation was revealed in 3 groups [23; 29; 36], whereas, in the case of one group, caution was advised as per the prognosis of muscle strength on the basis of hand grip strength [33]. In the case of research which analyzed the results of correlation jointly for the group of adults and elderly individuals [25; 30; 31; 32; 41; 44], information on the occurrence of dependences was found in two publications in the scientific literature [30; 41]; two articles came to the conclusion that one should be cautious in such an assessment [32; 44], whereas two articles revealed no such dependences [25; 31]. Figure 3: Classification of the analyzed publications according to the type of movement of the body part. Dependences between the values of hand grip strength were also searched for with reference to the results of moments of muscle forces for particular parts of the body, i.e., the trunk, upper and lower limbs. Six articles assessed the dependence between hand grip strength and the moments of muscle forces in upper limbs [23; 29; 30; 31; 32; 33], including three articles [23; 29; 30] indicating a positive linear dependence; two articles informed about a weak correlation [32] or advised a cautious approach to the result [33]; one article indicated the lack of dependence [31].