The aim of the research was to determine linear changes and relationship between spontaneous electrical activity and the activity of creatine kinase (CK) isoenzymes after skeletal muscle is physically fatigued. Methods: ten high class competitive male basketball players (23.6 ± 3.8 years) participated in the study. Functional capacity was measured during the exhausting cycloergometry. The maximally relaxed m. rectus femoris was investigated before and after exercise bout with electromyography, using concentric needle electrodes and 8 channel surface electrodes for spontaneous electrical activity. CK activity in blood was determined before and after exercise bout, too. Results: before the exercise bout spontaneous electrical activity in the maximally relaxed muscles was minimal. However, the potentials 24 hours after the exercise were noticed at 1.9 ± .3 ms length, 76.4±11.4 mkV amplitudes, 9.8±1.4 Hz frequency singlephase, dualphase 2.6 ± .5 ms, 84.3 ±13.8 mkV, 5.4± .6 Hz, and triphase 3.9 ± .6 ms, 98.4 ± 16.2 mkV, 3.8 ± 1.2 Hz. Long positive waves were registered in a few instances. After the exercise, paucity, spontaneous electrical activity was noticed 14.9± 4.6 ms, 86.2 ±15.9 mkV, 2.4 ± .9 Hz. Total CK activity 24 hours after the exercise bout was 619±185 U/l, CKMM 493 ±133 U/l, and CKMB 24±17 U/l. Conclusion: there was expressed spontaneous electrical activity and especially long positive waves and fasciculation, followed by increased CK isoenzymes activity in the fatigued muscle. These findings show the damage of muscular tissue. The signs of this damage are more expressed in the superficial layer of m. rectus femoris and this shows that fast twitch fibres are less resistant.