Fatigue induced by a cross-country skiing KO sprint

The aims of the present study were 1) to analyze whether the KO sprint simulation induced a phenomenon of fatigue of upper and lower limbs and 2) if there was any fatigue, to determine its origin.

Seven elite male skiers were tested before and after a simulation of KO sprints consisting of three 1200-m laps separated by 12 min of recovery. Surface electromyographic activity and force obtained under voluntary and electrically evoked contractions (single twitch) on knee-extensor muscles were analyzed to distinguish neural adaptations from contractile changes. A maximal power output test of the upper limbs was also performed.

During the last lap, the final sprint velocity was significantly lower than during the first lap. After the KO sprint, knee-extensor voluntary (-9.8 +/- 9.5%) and evoked (-16.2 +/- 11.9%) isometric force and upper-limb power output (-11.0 +/- 9.3%) and force (-11.3 +/- 8.7%) significantly decreased, whereas the blood lactate concentration increased to 11.6 mM. On the other hand, no changes were seen in RMS measurement during maximal voluntary contractions, RMS normalized by M-wave amplitude, or M-wave characteristics.

Changes in performance, lactate concentration, knee-extensor strength, and upper-limb power indicated that the KO sprint test led the skiers to a state of fatigue. On lower-limb muscles, the decrease of knee-extensor strength was exclusively caused by peripheral fatigue, which was at least in part attributable to a failure of the excitation-contraction coupling.