Author(s): MANRESA-ROCAMORA, A., GALVAN, V., GARCIA, E., GARCIA, G., MARTINEZ, M., GALLEGO, A., SANTANA, A., MORALES, D., FERNANDEZ, B., BOUSHEL, R., HALLEN, J., MARTIN, M., CALBET, J.A.L., Institution: LAS PALMAS DE GRAN CANARIA UNIVERSITY, Country: SPAIN, Abstract-ID: 2474

INTRODUCTION:
Previous studies have investigated the effect of short-term sprint interval training (SIT) on skeletal muscle lactate transporters (i.e., monocarboxylate transporter 1 [MCT1] and 4 [MCT4]). The studies lasted 4 to 6 weeks, and their findings were controversial. Cell-culture experiments indicate that lactate accumulation stimulates MCT1 and lactate receptor (i.e., G protein-coupled receptor 81 [GPR81]) protein expression. Besides, repeated myocardial ischaemia in rodents is accompanied by increased expression of MCT1 after 15 min reperfusion. No study has determined whether repeated periods of post-exercise ischaemia applied at the end of SIT may enhance MCT1 and MCT4 protein expression as adaptation mechanisms. In addition, only one study has studied GPR81 expression in human skeletal and reported no significant changes after resistance exercise or lactate infusion. However, the effect of SIT and ischaemia on GPR81 protein expression in human skeletal muscle remains unknown.
METHODS:
Thirteen physically active subjects (6M, 7F) performed a SIT programme (4-6 × 30-s isokinetic sprints with 4-min recovery periods, 3 d/w for 2 weeks). The circulation of one leg was immediately occluded (300 mmHg) after each sprint for 30-50 s, followed by unloaded pedalling without occlusion. Pre- and post-training (PRET and POSTT), each participant carried out a maximal incremental exercise test (IET), followed by a 90-min rest period, and a supramaximal exercise test (SET) (i.e., 6 × supramaximal bouts at 120% of VO2 max to exhaustion followed by 20-s recovery periods with occlusion of the two legs). Vastus lateralis muscle biopsies were obtained at rest, 90 min after IET (post-IET), and after SET (post-SET). MCTs and GPR81 protein expressions were determined by western blot in muscle biopsies. Analysis of variance and partial eta squared were used to carry out analyses.
RESULTS:
No significant changes in any of the analysed proteins were observed in MCTs and GPR81 with acute exercise neither before training (p > .050) nor after training in the leg trained without ischaemia. Similar results were observed in the leg trained with ischaemia (p > .050). SIT did not significantly modify the resting expression levels of MCTs or GPR81 in the leg trained with free circulation nor in the leg trained with ischaemia (p > .050).
CONCLUSION:
MCT1 and MCT4 protein expression in the sarcolemma may increase by 2-fold with 15 × 1 min knee extension exercise performed 4 d/w for 7-8 weeks. Our study shows that with a shorter duration training programme, despite a much higher exercise intensity and adding post-exercise ischaemia to stimulate lactate accumulation further, neither MCT1 nor MCT4 significantly increase. These findings may explain why peak lactate accumulation after short-term SIT does not increase in humans. As a novelty, we have shown that GPR81 protein expression does not seem responsive to short-term SIT in humans in human skeletal muscle.
GRANT: PID2021-125354OB-C21/C22.