Fructose addition to a glucose supplement modifies perceived exertion during strength and endurance exercise
 
 
Journal Title (Medline/Pubmed accepted abbreviation): J Strength Cond Res
Year: 2010
Volume: 24
Number: 12
Page numbers: 3334-3342
doi (if applicable):

Summary of Background and Research Design

Background:It is well established that carbohydrate supplements improve exercise performance and perceived exertion (PE), particularly during long-endurance exercise. Glucose + fructose (GF), specifically, provides benefits in time to exhaustion and, therefore, in long-duration performance. However, information on how GF supplements affect endurance exercise (EE) or strength exercise (SE) when ingested immediately before (≤ 30 min) short-duration exercise is limited.

Hypothesis/purpose of study: Adding fructose to a glucose supplement would diminish perceived exertion and modify the postprandial response during short-duration EE or SE.

Subjects:20 men (mean age, 26.2 ± 1.1 yr; mean weight, 75.0 ± 2.4 kg) who had participated in physical training ≥ 4 days per week during the last year.

Experimental design: Randomized, crossover.

Treatments and protocol:Subjects followed a controlled diet for 2 weeks, after which they ingested an oral dose of glucose alone (G, 50 g glucose anhydride) or glucose + fructose (GF, 50 g glucose anhydride + 15 g fructose monosaccharide) 15 minutes before a 30-minute session of either SE (10 sets of 10 repetitions of half squat) or EE (cycling for 30 min). At 1-week intervals, each participant completed 4 protocols: G + SE, GF + SE, G + EE, and GF + SE. Perceived exertion (as measured by the Borg PE Scale) and heart rate were measured to gauge effort intensity, and the postprandial response was monitored with laboratory markers (plasma glucose, insulin, lactate, and urinary catecholamine). All evaluations were measured 15 minutes before exercise, mid-exercise (15 min; T15), at the end of the exercise (30 min; T30), and during acute recovery (60 min; T60).

Summary of research findings:
  •   PE was lower with GF than with G during SE (T15 effect size = 0.43, T30 effect size = 0.48; P < .05 for each) and EE (T15 effect size = 0.23, T30 effect size = 0.29; P < .05 for each).
  •   PE of the overall 30-minute session, performed at T60, was also lower with GF than with G for SE (effect size = 0.78; P < .05) and EE (effect size = 0.32; P < .05).
  • Glycemic peak with GF + SE was lower than with G + SE during exercise (P < .05); there was no difference in blood glucose levels between G and GF supplements during EE.
  • In only the EE group, heart rate, urinary adrenaline, and noradrenaline were lower with GF than with G, both during exercise and afterward (P < .05).

Interpretation of findings/Key practice applications:

Physical exertion is affected by a number of factors, including the interplay of muscular metabolism with the central and peripheral nervous systems. The beneficial effects of adding fructose to a glucose supplement observed here are possibly a result of improved carbohydrate availability that leads to improved energy flow in active tissues. The practical application is that GF supplementation may be a useful dietary strategy for helping to achieve higher training loads for both SE and EE. A key limitation to these findings, however, is that the 2 treatments were not isocaloric. As such, it is possible that the beneficial effects observed were simply due to the overall increase in carbohydrate in the GF versus G groups.
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