The aim of the study was to investigate the manifestation of potentiation and fatigue as well as the coexistence of these phenomena at different muscle lengths during a 24-hour period after a sprint cycling for 30 s.
Material and methods: Twelve healthy untrained men (mean age 23.6+/-1.7 years) took part in the experiment. The contractility of quadriceps muscle was studied before (Initial) and 2, 5, 30, 60 min and 24 h after exercise via the electrically evoked contractions at 1, 15, 50 Hz and maximal voluntary contractions at short and long muscle length.
Results: 1) In early, fast-recovery phase (within the first 5 min), muscle force evoked by electrical stimulation of 1, 15, 50 Hz was restored at short muscle length, conversely at long length (Initial vs. 5 min: 15 Hz and 50 Hz, both P<0.05), whereas maximal voluntary contraction force was still suppressed at both muscle lengths; 2) in the second phase (from 5 min to 30-60 min), muscle force decreased at low- and high-frequency stimulations and was more expressed at low-frequency stimulation and at short muscle length than that at long length, but the maximum voluntary contraction force recovered to initial; 3) in long-lasting phase (within 24 hours), 15 Hz force was still suppressed at both muscle lengths.
Conclusion: A bimodal recovery of contractility of the quadriceps following sprint cycling for 30 s is determined by the concomitant complex interaction of mechanisms enhancing (potentiation) and suppressing (fatigue) contractile potential of the muscle.