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David Gray Lassiter
Supervisor: Dr. John L. Ivy
Energy drink consumption before exercise enhances
exercise performance (Ivy, 2009)
Energy drink consumption improves reaction time at rest (Howard & Marczinski, 2010)
Caffeine and carbohydrate consumption during exhaustive exercise improves information processing (Hogervorst, 2008)
Will energy drink consumption prior to shorter duration exercise improve performance on cognitive tests during and after exercise?
Background
Consumption of an energy drink will
1. Improve cycling performance on a 35-km time trial
2. Improved cognitive and psychomotor performance
A. At rest
B. After a time trial while still exercising at 70% of VO2MAX
C. After a time trial during cool down
Hypotheses
Design
Baseline mental acuity tests (Pre Drink, Pre Race)
Energy drink (ED) or placebo (PLA) consumption
After 40 minutes, more mental acuity tests (Post Drink, Pre Race)
35-km time trial
Expired gasses collected during time trial
After time trial, final mental acuity tests (Post Race)
Blood drawn throughout visit
Randomized crossover
Protocol
Dependent Variables
Exercise Measures
Time trial performance
Perceived exertion (RPE)
Cognitive/Psychomotor Measures
Decision making accuracy and speed
Psychomotor accuracy and speed
Physiological Measures
Heart rate
Respiratory
Blood analytes
Women VO2max ≥ 45 mL/kg/min
Men VO2max ≥ 55 mL/kg/min
Participants
Ingredients in the Energy Drink
2 servings distributed
-Includes 160 mg of caffeine and 54 g of carbohydrates in total
Statistical Analysis
Repeated measures ANOVA (Time*Treatment)
Greenhouse-Geisser correction was made when Mauchly’s W<.05
LSD for post-hoc analyses
α=.05
Results
Results- Differing Baseline Blood Caffeine Concentrations
Statistical Analysis Revisited
Categorized participants into 2 groups:
HI: baseline blood caffeine > 1000 ng/mL at both visits (N=5)
LO: everyone else (N=10)
Performed a 3-way ANOVA (Time*Treatment*Category)
Time and Treatment were WS factors
Category was BS factor
3-way ANOVA did not change any interpretations
Results- ED Enhanced Race Performance
Results- ED Led to Uncoupling of RPE from Exertion
Results- ED Increased VO2 Without Increasing RER
Results- ED Reduced Concentration of Substrates
Results- ED Increased Movement Speed on Simple Test Only
Results- Exercise Enhanced Reaction Time
Results- ED Negligibly Diminished Precision
Conclusions
This ED will enhance aerobic performance if taken before
exercise
Effect is regardless of baseline blood caffeine concentrations
Likely due to non-caffeine ingredients
At least 225 mg of caffeine must be taken with carbohydrate to enhance exercise performance greater than carbohydrate alone (Kovacs, 1998)
Studies utilizing controls in addition to PLA are recommended to elucidate the differential contributions of ingredients in this ED
Exercise Performance
This ED may enhance simple movement speed when
an athlete does not have to multi-task
This ED likely has no effects on reaction time, precision, or decision making (not shown)
Future studies ought to use whole-body reaction time to assess the ED’s effects since this is more ecologically relevant and caffeine alone has been shown to be effective (Duvnjak-Zaknich, 2011)
Cognitive and Psychomotor Performance