Changes in height of jump, maximal voluntary contraction force and low-frequency fatigue after 100 intermittent or continuous jumps with maximal intensity.

Healthy untrained males (age 25.4 +/- 1.7 years, n=12) gave their informed consent to take part in all experiments within the study. After 100 intermittent (every 20 s) drop jumps from the height of 0. 4 m, jumps with counter-movement to 90 degrees angle in the knee and immediate maximal rebound (eccentric-concentric exercise; E-C) and 100 continuous jumps (five bouts of 20 jumps with counter-movement to 90 degrees angle in the knee with 10 s between bouts) (maximal exercise; M) with maximal intensity, the height of vertical jump decreased in a similar way, and this decrease did not depend on the performance mode of jumps. After E-C and M jumping exercises, there was a significant (P < 0.001) decrease in maximal voluntary contraction force, as well in the force generated by electrical stimulation at all stimulation frequencies, and these values were not restored to the initial level even after 24 h. After the E-C exercise, however, the muscle contraction force generated at different stimulation frequencies and, especially, at low-stimulation frequencies (1-20 Hz) decreased to a significantly (P < 0.05-0.001) greater extent than after M exercise. Twenty minutes after the end of M exercise, there was still a greater increase in low-frequency fatigue (LFF) and it was no different from the LFF registered 20 min after the end of E-C exercise. Twenty-four hours after the M exercise, however, LFF was smaller than its respective value after E-C exercise. There was no significant relationship between the values of LFF after E-C and M exercises. This may indicate that there are differences in the origin of the LFF after the E-C and M exercises.