# Handgrip Strength as an Indicator of Overall Strength and Functional Performance--Systematic Review
## 3 Results
### Dependence Between Hand Grip Strength and the Values of the Moments of Muscle Forces in Upper limbs
#### 3.3.2 Tests in Isometric Conditions  
The dependences between hand grip strength and the moments of muscle forces in the knee joint during an isometric contraction were searched for also by [PERSON] [40], [PERSON] et al. [41], [PERSON] et al. [25], [PERSON] et al. [8], [PERSON] et al. [42], [PERSON] et al. [43], [PERSON] [26] and [PERSON] et al. [44]. The above-mentioned authors studied hand grip strength in a sitting position with the elbow flexed [8; 26; 40; 41; 44], and also in a standing position with the limb hanging on the side of the body [25; 42; 43]. In each of the analyzed articles, the study group consisted of elderly individuals [8; 26; 40; 41; 42; 43; 44]. Only in three articles were young participants also additionally tested [25; 41; 44]. The majority of the authors decided to search for the Pearson linear correlation. [PERSON] [40] determined the range of correlation values between hand grip strength and the moments of forces of extensors and flexors in the knee joint measured in isometric conditions at the level of 0.56-0.68; all correlations were statistically significant (below \(p<0.001\)). On the basis of the results, the authors came to the conclusion that hand grip strength may be used as an alternative to the muscle strength of lower limbs. Also, [PERSON] et al. [41] obtained high coefficients of the linear correlation between hand grip strength and the moments of forces of knee joint extensors, in the range of 0.772 to 0.805 (\(p<0.001\)), in the group of healthy adults. However, despite such a high correlation, they found that the differences in the activities requiring hand grip strength and knee extension exclude widespread support to use them interchangeably. [PERSON] et al. [25] performed tests in six different places, and thanks to that, several large study groups were created, i.e., two groups of young individuals and five groups of elderly people. On the basis of the conducted analyses, it was ascertained that in the study group of young individuals linear correlation coefficients between hand grip strength and the moments of forces of knee joint extensors fell into the range from 0.36 to 0.45 (\(p<0.05\)), whereas in the study group of the elderly, from 0.35 to 0.67 (\(p<0.05\)). The researchers observed that the dependence between hand grip strength and the force of the knee extension differed at an individual level. Due to this fact, the application of the measurement of only one group of muscles as an indicator of general strength seems to be unjustified. [PERSON] et al. [8] performed tests on a small group of 13 elderly individuals with an average age of 87 years. Value r of the Pearson correlation between hand grip strength (dominant and non-dominant) and the moments of forces of knee extensors fell into the range of 0.47-0.68 (statistically significant). The main conclusion reached by [PERSON] et al. [8] was that the force of the knee extension constitutes a repeatable and appropriate evaluation method in the screening tests of lower limbs. However, they did not address the dependence between hand grip strength and the force of the knee extensors. Neither did they define whether the hand grip strength itself was sufficient for the assessment of general strength. [PERSON] et al. [42] developed models based on the analysis of linear regression in order to investigate the relationship between hand grip strength and the moments of muscle forces in the knee joint, taking into considerations aspects such as age and gender, as well as physical and psychological features. The researchers came to the conclusion that health features are more related to the knee extension force than hand grip strength. [PERSON] et al. [43] conducted studies in a large group of 764 individuals (243 men, 521 women), each participant was above 75 years of age. In the first phase of the analyses, the results were normalized using square root transformation followed by standardization into Z scores, whereas the dependence itself was determined by means of linear regression.