PURPOSE: Grip strength has been well documented to represent whole body strength. This study was performed to investigate whether absolute and relative grip strength is associated with thigh strength, and thigh-derived single muscle fiber contractile properties. METHODS: Twelve healthy young adults (mean age 27.42 years) received needle biopsy on vastus lateralis muscles. Chemically skinned muscle fibers (n=215) were used to analyze single muscle fiber contractile properties (cross sectional area, maximal force, specific force, maximal shortening velocity) and MHC isoform composition. Pearson correlation was tested to identify the relationship between dominant hand grip strength, thigh strength, and thigh-derived single muscle fiber contractile properties. RESULTS: The distribution of MHC I was higher in all the subjects compared to MHC II (type I: 57.2%, IIa: 37.2%, IIa/IIx: 2.3%, IIx: 3.3%). Specific force (8.2%) and maximal shortening velocity (74%) in MHC II were greater than those of MHC I. Absolute and relative grip strength normalized by height had a positive correlation with knee extensor isometric (r=.777, r=.75) and isokinetic (r=.632, r=.603) strength. In addition, the positive correlation of knee extensor isometric and isokinetic strength was observed against both CSA and Po in the thigh-derived single muscle fiber. Finally, Absolute and relative grip strength normalized by height were positively correlated with CSA (r=.279, r=.267) and Po (r=.373, r=.351) in MHC II, but not in MHC I. CONCLUSIONS: These data suggest that hand grip strength is highly associated with not only whole thigh muscle strength, but also thigh-derived fast single muscle fiber contractile properties (MHC II).