Carbohydrate Mouth Rinsing Does Not Alter Skeletal Muscle Contractile Properties Following Fatigue

Abstract

Carbohydrate (CHO) mouth rinsing without ingestion of the solution has been shown to improve endurance exercise performance and to attenuate the decline of muscular strength following fatiguing exercise. However it is unclear whether central or peripheral factors are responsible for the attenuated force decline. PURPOSE: The purpose of this study was to determine the effect a of CHO mouth rinse on electrically evoke skeletal muscle contractile properties following fatiguing exercise. METHODS: Ten recreationally trained adults (3 males, 7 females) participated in a double-blind, cross-over study. Maximal twitch torque (TT), time-to-peak-tension (TTP), half-relaxation time (HRT), rate of torque development (RTD), and rate of torque relaxation (RTR) were determined via electrical stimulation in the dominant knee extensors. Participants then performed an isometric contraction at 50% of MVC until volitional fatigue. This was immediately followed by a 20s mouth rinse of a 25ml solution of 8% maltodextrin (CARB) or placebo (PLA) solution. TT was then re-assessed 3 times, each separated by 10 seconds. Five minutes of rest was provided and TT was again re-assessed 3 times. RESULTS: Evoked twitch torque (TT) did not differ between CARB and PLA conditions (70.2±22.3 vs. 71.4±19.8 Nm; p≥0.51), but was reduced (~28%; p=0.003) following fatiguing exercise with all post-fatigue values differing from pre-fatigue values (p≤0.024). TTP (121.6±11.6 vs. 125.6±7.8 ms) and RTD (584±211 vs. 565±141 Nm/sec) did not differ between conditions, but both decreased (slowed) following fatigue (~20%; p≤0.02) and returned to near pre levels following 5 minutes of recovery. Similarly, HRT (67.2±10.2 vs, 67.3± 32.0) and RTR (538±199 vs. 602±262 Nm/sec) were also slowed following fatigue (~60%; p≤0.001), but did not recover to baseline levels following 5 minutes of recovery (p≤0.04). CONCLUSIONS: A carbohydrate mouth-rinse had no effect on electrically evoked torque and skeletal muscle contractile properties following fatiguing exercise. This finding suggests any effect of carbohydrate mouth rinsing is likely mediated by “central” mechanisms rather than a direct effect on skeletal muscle.