Impact of a Carbohydrate Mouth Rinse on Corticomotor Excitability after Mental Fatigue.

Abstract

Mental Fatigue (MF) has been associated with reduced physical performance. Carbohydrate (CHO) mouth rinse (MR) has been shown to be effective at increasing corticomotor excitability. PURPOSE: The purpose of this study was to determine if CHO MR positively impacts corticomotor excitability and cognitive function after MF. METHODS: Nine subjects (6 females, 3 males; Age= 23±1 years; Height=170±3 cm; Weight=68±4 kg) completed 2 experimental sessions under different MR conditions (Placebo (PLAC), 6.4% glucose (CHO)) each separated by at least 48 hours and applied in a random fashion. Motor-evoked potential (MEP) of the left first dorsal interosseous (FDI) was determined at rest by transcranial magnetic stimulation (TMS) before and immediately after completion of a task designed to cause MF. The MF task required the subjects to complete six blocks (448 trials each) of the Stroop Color Word Test (SCWT). MR was applied between each SCWT block and held in the mouth for 20 sec. Perceived MF was recorded before and after the MF task using a 100 mm VAS. RESULTS: Perceived MF increased from pre (PLAC=16±6 mm; CHO=19±7 mm) to post (PLAC=41±5 mm; CHO=46±4 mm) in both conditions (p<0.001) but no differences were seen between the groups. Overall reaction time during SCWT was better (p=0.03) in CHO (698±10 ms) compared to PLAC (738±16 ms), but correct response rate was not different between the groups (PLAC=97.5±0.4; CHO=98.1±0.2). MEP improved (33±9%) (p=0.03) after the MF task in CHO (Pre=2241±633 μV; Post=2704±606 μV) and declined (-28±6%) (p=0.02) after the MF task in PLAC (Pre=1810±389 μV; Post=1208±244 μV). CONCLUSIONS: CHO MR was successful at preventing a reduction in corticomotor excitability subsequent to MF. CHO MR also had a positive impact on some measures of cognitive performance during the MF task. CHO MR did not impact perceived MF. These results suggest that CHO MR may be a valuable tool at combating the negative consequences of MF.