Journal Title (Medline/Pubmed accepted abbreviation): Eur J Appl Physiol
Page number: 2381-2386
doi : 10.1007/s00421-011-1865-8
Summary of background and research design:
Background: Although it is established that carbohydrate (CHO) supplementation can improve endurance during prolonged exercise by providing an exogenous source of energy and sparing glycogen stores, improvement has also been observed during short durations of exercise. Limited evidence suggests that CHO may act on the central nervous system (CNS) to modulate fatigue and/or motor control and can be influenced by CNS sensing of CHOs via a mouth rinse. Clinical evidence of improved exercise endurance from CHO mouth rinses has been mixed, and effects on muscle strength are unknown.
Hypothesis: CNS response to an oral CHO rinse may improve strength exercise performance.
Subjects: Twelve recreationally strength-trained (1 to 2 y experience) males (mean age, 24 ± 3 y; height, 178.9 ± 7 cm; weight, 79 ± 8 kg) participated in this study.
Experimental design: Randomized, double-blind, cross-over
Treatments Protocol: Athletes were randomized to 1 of 3 mouth rinses (25 mL) before a bench press exercise session; none (CON), placebo (PLA; aspartame), or CHO (6.4% dextrose). Each athlete completed all experimental conditions followed by an identical exercise session 96 hours apart. The exercise session consisted of maximum dynamic strength and strength endurance tests. The maximum dynamic strength test consisted of a warm-up (5-min treadmill run at 9 km/hr, light stretching, 8 bench press reps at 50% 1-repetition maximum [1-RM] with a 2-min rest interval, and 3 reps at 70% 1-RM with a 3-min rest) and single repetitions of progressively heavier loads separated by 3-minute rests (maximum was heaviest load lifted with proper technique and 5 attempts were allowed). Strength endurance testing consisted of a warm-up (8 reps at 50% 1-RM with a 2-min rest) and 6 sets of 3 repetitions at 70% 1-RM until failure separated by 2-minute rests. Drinks were rinsed in the mouth for 10 to 15 seconds before spitting out at each single attempt for dynamic strength and before each set for strength testing. Blood samples were collected before and 5 minutes after each test for lactate and glucose levels.
Summary of research findings:
- Maximum dynamic strength was not different between mouth-rinse conditions.
- There was a main effect for time; reduction in the number of repetitions throughout the exercise (P < .0001).
- Blood glucose levels remained unchanged in all conditions, with no interactions between conditions (P = .39 for dynamic strength and P = .64 for endurance).
- Blood lactate increased from baseline throughout all exercise tests (main effect for time; P < .0001).
- There were no interactions between conditions (P = .74 for dynamic strength and P = .38 for endurance.
Interpretation of findings/Key practice applications:
CHO mouth sensing did not promote improvement in maximum strength or strength endurance. Previous positive evidence for CHO mouth rinses focused on aerobic exercise performance and showed a small effect on endurance (1% to 3%). The tests used in this study may not have been sensitive enough to detect such a small difference. Future studies may need to assess strength by isokinetic dynameter or a strength gauge. Although thus study did not find a benefit, CHO mouth rinses may enhance strength performance in individuals undergoing an extensive amount of training and/or in resistance-trained athletes who are endurance oriented.