Caffeine Effects Short-Term Performance during Heat Prolonged Exercise

Last Updated on November 18, 2011 by Jimson Lee

During my College years, I was known for drinking a Dunkin Donuts thermos of coffee before my 100 meter dashes. I wasn’t a great starter, and my ability to react to the gun was average, not great like Armin Hary.

Basically, I would consume coffee for caffeine to help my “alertness” while it also provided a diuretic experience. Of course, there are no bathrooms or restrooms in the Control Area, so always remember to take care of personal matters before checking in!

Caffeine, plus competing in extremely hot and humid weather, intensified the diuretic effects.

Looking back, was this dangerous or plain stupid? What are the effects of caffeine and heat for a sprinter, jumper, or thrower? Hydration plays a crucial role in endurance events, so I’ll leave them out of the equation.

Check out below this month’s entry in the American College of Sports Medicine, and I’ll let you decide what’s right or wrong:

Caffeine Effects on Short-Term Performance during Prolonged Exercise in the Heat.
The American College of Sports Medicine
Medicine & Science in Sports & Exercise. 40(4):744-751, April 2008

Abstract

Purpose: To determine the effect of water, carbohydrate, and caffeine ingestion on fatigue during prolonged exercise in the heat.

Methods: Seven endurance-trained cyclists (V[spacing dot above]O2max = 61 +/- 8 mL[middle dot]kg-1[middle dot]min-1) pedaled for 120 min at 63% VO2max in a hot-dry environment (36[degrees]C; 29% humidity), ingesting either no fluid (NF), water (WAT) to replace 97% fluid losses, the same volume of a 6% carbohydrate-electrolyte solution (CES), or each of these treatments along with ingestion of 6 mg of caffeine per kilogram of body weight (NF + CAFF, WAT + CAFF, and CES + CAFF). At regular intervals during exercise, maximal cycling power (PMAX) was measured. Before and after exercise, maximal voluntary contraction (MVC), voluntary activation (VA), and electrically evoked contractile properties of the quadriceps were determined.

Results: Without fluid replacement (NF and NF + CAFF), subjects were dehydrated by 3.8 +/- 0.3%, and rectal temperature reached 39.4 +/- 0.3[degrees]C, while it was maintained at 38.7 +/- 0.3[degrees]C in trials with rehydration (P < 0.05). Trials with caffeine ingestion increased PMAX by 3% above trials without caffeine (P < 0.05). MVC reductions after exercise were larger with NF (-11 +/- 5%) than for the rest of the trials (P < 0.05). MVC was reduced in WAT compared with CES + CAFF (-6 +/- 4 vs 2 +/- 4%; P < 0.05). However, NF + CAFF maintained MVC at the level of the CES trial. VA showed the same treatment response pattern as MVC. There were no differences in electrically evoked contractile properties among trials.
Conclusion: During prolonged exercise in the heat, caffeine ingestion (6 mg[middle dot]kg-1 body weight) maintains MVC and increases PMAX despite dehydration and hyperthermia. When combined with water and carbohydrate, caffeine ingestion increases maximal leg force by increasing VA (i.e., reducing central fatigue).