Figure 4. Fatigue index in percent per jump of P20, P100 and P20/P100 ratio during SSE (mean ± SD). P20 and P100 - muscle contraction force evoked by stimulating quadriceps muscle at 20 Hz and 100 Hz frequencies. SSE - stretch-shortening exercise (100 drop jumps performed from 0.5 m with counter-movement to 90 degrees in the knee with immediate maximal rebound, with 30 s interval between jumps).