Background Adequate leg extensors preparation is highly important especially in volleyball which involve several jumping techniques. Values of developed force in the function of time generated during the isometric (static) muscle contraction, with it's own F-t curve characteristics are the fundamental data on contractile ability.

Objective Factor structure differences of indicators for evaluating isometric leg extensors explosive force (RFDLEGEXTISO) regarding different trained female population will be examined in this research.

Setting and participants Sample included 50 examinees: top level female volleyball players (Elite N=20), unspecific trained female athletes (Nonspec N=18) and untrained female (Control N=12).

Methods In order to assess characteristics of the F-t isometric leg extensors force, tensiometric probe and standardized ‘seating leg extension’ test were used. The measurement range was defined by 11 variables regarding the contractile characteristics of the leg extensors isometric muscle force at the level of 100, 50, 30, 50–100% of maximal force (FmaxLEGEXTISO): rate of force development (RFD) analysed from the aspect of absolute and relative (allometric) values – the indicators of basic (RFDBASICLEGEXTISO, RFDallomLEGEXTISO), specific (RFD50%LEGEXTISO, RFDallomLEGEXTISO50%), special (RFD30%LEGEXTISO, RFDallomLEGEXTISO30%), at 50–100% (RFD50–100%LEGEXTISO) level of RFD, Synergy Index as a criterion of relation between RFDLEGEXTISO and FmaxLEGEXTISO at the basic level of 100% – IndexSNGBASIC, specific level of 50% – IndexSNGSPEC and special level of 30% – IndexSNGSPECIJ.

Results Factor analysis set apart two factors in all the observed groups, which have explained 96.491% in Elite, 95.502% in Nonspec, 96.512% in Control of valid variance. The differences in structure and in number of parameters for separated factors were established especially between tested trained and untrained population. They can be explained with differences in muscle tissue and maximal nervous activation of muscles during the specific training, that is, adaptation to specific training.

Conclusions The obtained results can possibly be used as an indicator of potential of leg explosiveness and jumping performances in volleyball players selection.