The aim of the study was to define the influence of small-molecule proteins originating from the degradation of troponin T and intensity of fluorescence spectra on the tenderness of the Semitendinosus (ST) and Infraspinatus (IS) muscles, and determining their interdependence with instrumentally measured Warner-Bratzler Shear Force (WBSF). The examined muscles, sampled from Limousin × Holstein-Friesian beef crossbreds differed to a statistically significant extent (p<0.05) in the length of the sarcomeres, content of protein, fat, and total collagen. An increase in the activity of proteins originating from the process of degradation of troponin T was highly correlated with the WBSF both in the case of the ST (r2=0.851) and IS (r²=0.765) muscle. The 305÷400 nm emission spectrum, recorded with front-face fluorescence spectroscopy made it possible to calculate the intensity of fluorescence of tryptophan residues. The studies proved a relationship between the WBSF and intensity of tryptophan residues fluorescence on the level of r²=0.682 (ST) and r²=0.714 (IS). [ABSTRACT FROM AUTHOR]