Randomized Crossover Trial

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To examine whether ingestion of a carbohydrate supplement with additional protein can attenuate evidence of exercise-induced muscle damage relative to the ingestion of the carbohydrate fraction alone.

• Healthy young men
• Highly trained with varying degrees of accustomedness to the exercise protocol.

Recruitment

Not described.

Design

• The study adopted a repeated-measures crossover design in which each participant completed two trials in randomized and counter-balanced order
• Each trial required participants to perform approximately 90 minutes of high-intensity exercise followed by a four-hour recovery period
• Throughout the exercise and acute recovery, participants ingested a solution of either carbohydrate alone or a mixture of carbohydrate and protein
• Trials were separated by approximately nine weeks.

Blinding Used

Single-blinded: Participants were blinded to the treatment. Pre-testing was conducted to ensure that solutions were successfully matched for taste, odor and consistency.

Intervention

• Throughout the exercise and recovery period, participants ingested a solution of either carbohydrate alone or a mixture of carbohydrate and protein. The solutions were provided in equal volumes (5.5±0.5 L), relative to each participant's body mass (BM).
• The carbohydrate cencentration of 9% provided 1.2g per kg^-1 BM per hour^-1 of carbohydrates under both treatments, which equates to a total carbohydrate intake of 492±44g
• The carbohydrate-protein mixture contained an additional 0.4g per kg^-1 BM per hour^-1 of whey protein isolate, providing 164±15g of protein (20% glutamine). The estimated amount of energy that the carbohydrate and carbohydrate-protein solutions made available for metabolism was 8,231±729kJ vs. 10,975±972kJ, respectively.
• Participants ingested the first volume of prescribed solution (7.0ml per kg^-1 BM) during the standardized warm-up. Immediately upon completion of the exercise protocol, participants were provided with the first of eight volumes of prescribed solution (6.7ml per kg^-1 BM), to be ingested over the four-hour recovery period (53.6ml per kg^-1 BM in total). Subsequent solutions were provied at 30-minute intervals. Participants were permitted 15 minutes to consume each volume.

Statistical Analysis

• Post-hoc analyses revealed that the sample size of 17 used in the study provided approximately a 99% power at P≤0.05
• Overall differences between experimental conditions were examined using a two-way (treatment x time) general linear model for repeated measures, with the Greenhouse-Geisser correction utilized for e<0.75 and the Huynh-Feldt correction adopted for less severe asphericity
• Where significant F-values were identified, the Holm-Bonferroni stepwise correct was applied to determine the location of variance.

Timing of Measurements

• Blood samples were obtained throughout and 24 hours after each trial to determine the systemic indices of muscle damage and inflammation
• Expired gas samples were were obtained throughout and 24 hours after each trial to determine substrate metabolism
• An isokinetic dynamometer was used to establish baseline measurements of peak isometric torque for knee flexors and extensors and hip flexors and extensors. Measurements were followed up at four, 24, 48 and 168 hours post-exercise.

Dependent Variables

• Peak isometric torque for knee flexors and extensors and hip flexors and extensors (isokinetic dynamometer)
• Serum myoglobin concentration (blood samples)
• Serum creatine kinase activity (blood samples)
• Serum lactate dehydrogenase activity (blood samples)
• Serum interleukin-6 concentration (blood samples)
• Serum interleukin-10 concentration (blood samples)
• Serum interleukin-1 concentration (blood samples)
• Serum C-reactive protein concentration (blood samples)
• Perceived muscle soreness (subjective ratings using a one-to-10-point scale)
• Serum insulin (blood samples)
• Serum cortisol (blood samples)
• Plasma urea (blood samples)
• Blood glucose (blood samples)
• Blood lactate (blood samples)
• Perceived exertion (subjective ratings).

Independent Variables

Participants ingested a solution of either carbohydrate alone or a mixture of carbohydrate and protein throughout the exercise and acute recovery period.

Control Variables

• Standardized exercise testing protocol
• Timing of measurements
• Hydration (urine samples were collected to ensure adequate hydration)
• Diet (participants adhered to their normal diet during the study).

• Initial N: 17 (17 males, no females)
• Attrition (final N): Seven
• Age: 26±5 years 
• Ethnicity: Not described.

Other Relevant Demographics

• VO_2max was 61±5ml per kg^-1 per minute^-1
• Eight of the total cohort were highly trained cyclists; nine of the total cohort were highly trained team-sport players, sampled from a variety of sports (i.e., basketball, rugby, field hockey and lacross). Accordingly, the overall cohort were well matched in terms of aerobic capacity and worked at similar relative exercise intensities during the study, but the degree to which they were accustomed to the type of activity performed during the exercise varied considerably.

Anthropometrics

Body mass: 74±6.6kg

Location
Bath, United Kingdom.

Key Findings

• Muscle function: There was no difference in peak isometric torque between the carbohydrate and carbohydrate-protein treatments in either the magnitude or the time-course of this effect for any muscle group tested. The absence of treatment effects was consistent in both the highest and lowest responders, as evidenced by the strong positive correlations between treatments 24 hours after exercise in knee flexors (R=0.77; P<0.001), knee extensors (R=0.72; P<0.001), hip flexors (R=0.75; P<0.001) and hip extensors (R=0.75; P=0.001).
• Muscle damage: There was no difference in serum myoglobin concentrations, serum creatine kinase activity and serum lactate dehyrogenase activity between the carbohydrate and carbohydrate-protein treatments at any time-point. The absence of treatment effects was consistent in both the highest and lowest responders for each variable, as evidenced by moderate to strong positive correlations between treatments for the post-exercise elevations in myoglobin (R=0.53; P=0.04) and lactate dehydrogenase (R=0.49; P=0.05) and for the 24-hour post-exercise peak in creatine kinase (R=0.69; P=0.004).
• Inflammation: There was no difference in serum concentrations of interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-1 (IL-1) and C-reative protein between the carbohydrate and carbohydrate protein treaments. The absence of treatment effects was evidenced by moderate to strong positive correlations between treatments for the post-exercise peaks in IL-6 (R=0.53; P=0.03) and IL-10 (R=0.70; P=0.02), the peaks in IL-1 receptor antagonist after two hours of recovery (R=0.69; P=0.004) and, although not significant, the 24-hour peaks in C-reactive protein (R=0.420; P=0.12).
• Muscle soreness: Participants' subjective ratings of perceived muscle soreness did not differ by more than a single point at any time-point and were not different between the carbohydrate and carbohydrate-protein treatments
• Metabolic data: Serum insulin and urea concentrations were significantly higher (P<0.02) while ingesting the carbohydrate-protein solution, both during the exercise protocol and throughout the acute four-hour recovery period.

Other Findings

• Participants' subjective ratings of perceived exertion were virtually identical between treatments 
• The total volume of urine produced during recovery was significantly greater when carbohydrate alone was ingested (2,190±125ml vs. 1,797±99ml; P=0.01).

Acute ingestion of carbohydrate with addiitonal whey protein isolate during and for four hours after strenuous exercise does not attenuate systemic indices of muscle damage and inflammation, nor does it restore muscle function more effectively than ingestion of a matched quantity of carbohydrate alone.

Industry:

GlaxoSmithKline Nutritional Healthcare Pharmaceutical/Dietary Supplement Company:

Heterogeneous sample chosen so that conclusions could be generalized more broadly.