Reference values of intrinsic muscle strength of the hand of adolescents and young adults

Study Design: A cross-sectional clinical measurement study. Introduction: Measuring intrinsic hand muscle strength helps evaluate hand function or therapeutic outcomes. However, there are no established normative values in adolescents and young adults between 13 and 20 years of age. Purpose of the Study: To measure hand intrinsic muscle strength and identify associated factors that may influence such in adolescents and young adults through use of the Rotterdam intrinsic hand myometer. Methods: A total of 131 participants (male: 63; female: 68) between 13 and 20 years of age completed the strength measurements of abductor pollicis brevis, first dorsal interosseus (FDI), deep head of FDI and lumbrical of second digit, flexor pollicis brevis (FPB), and abductor digiti minimi. Two trials of the measurements of each muscle were averaged for analyses. Self-reported demographic data were used to examine the influences of age, sex, and body mass index (BMI) on intrinsic hand muscle strength. Results: Normative values of intrinsic hand muscle strength were presented by age groups (13, 14, 15-16, 17-18, 19-20 year olds) for each sex category (male, female). A main effect of sex, but not age, on all the muscles on both the dominant (FPB: P =.02, others: P <.001) and non-dominant (FDI: P =.005, FPB: P =.01, others: P <.001) sides was found. A significant effect of BMI was found on dominant (P =.009) and non-dominant abductor pollicis brevis (P =.002). In addition, FDI (P =.005) and FPB (P =.002) were stronger on the dominant side than the non-dominant side. Discussion: Intrinsic hand muscle strength may be influenced by different factors including sex, BMI, and hand dominance. A larger sample is needed to rigorously investigate the influence of age on intrinsic strength in male and female adolescents and young adults. Conclusion: The results provide reference values and suggest factors to be considered when evaluating hand function and therapeutic outcomes in both clinical and research settings. Further study is recommended. Level of Evidence: VI.