The present study examined the effect of additional speed endurance training (SET) during the season on muscle adaptations and performance of trained soccer players.Methods
Eighteen subelite soccer players performed one session with six to nine 30-s intervals at an intensity of 90%–95% of maximal intensity (SET) a week for 5 wk (SET intervention). Before and after the SET intervention, the players carried out the Yo-Yo intermittent recovery level 2 (Yo-Yo IR2) test, a sprint test (10 and 30 m), and an agility test. In addition, seven of the players had a resting muscle biopsy specimen taken and they carried out a running protocol on a motorized treadmill before and after the SET intervention.Results
After the SET intervention, the Yo-Yo IR2 test (n = 13) performance was 11% better (P < 0.05), whereas sprint (n = 15) and agility (n = 13) performances were unchanged. The expression of the monocarboxylate transporter 1 (n = 6) was 9% higher (P < 0.05). and the expression of the Na+/K+ pump subunit β1 (n = 6) was 13% lower (P < 0.05) after the SET intervention. The Na+/K+ pump subunits α1, α2, as well as the monocarboxylate transporter 4 and the Na+/H+ exchanger 1 (n = 6) were unchanged. After the SET intervention, the relative number of Type IIx fibers and oxygen consumption at 10 km·h−1 were lower (P < 0.05), whereas V˙O2max was unchanged.Conclusions
In conclusion, adding ∼30 min of SET once a week during the season for trained soccer players did lead to an improved ability to perform repeated high-intensity exercise, with a concomitant increase in the expression of monocarboxylate transporter 1 and an improved running economy.