Search Results

You are looking at 1 - 5 of 5 items for :

  • Author: Gordon L. Warren x
  • Physical Education and Coaching x
  • Refine by Access: All Content x
Clear All Modify Search
Restricted access

Does Caffeine Added to Carbohydrate Provide Additional Ergogenic Benefit for Endurance?

Scott A. Conger, Gordon L. Warren, Michelle A. Hardy, and Mindy L. Millard-Stafford

Context:

Carbohydrate (CHO) and caffeine (CAF) both improve endurance performance.

Purpose:

To determine by systematic literature review coupled with meta-analysis whether CAF ingested with CHO (CHO+CAF) improves endurance performance more than CHO alone.

Methods:

Databases were searched using the keywords caffeine, endurance, exercise, carbohydrate, and performance. Criteria for inclusion were studies that used human subjects performing an endurance-exercise performance task and included both a CHO and CHO+CAF condition. Effect sizes (ESs) were calculated as the standardized mean difference.

Results:

Twenty-one studies met the criteria for analysis. ESs for individual studies ranged from –0.08 (trivial effect favoring CHO) to 1.01 (large effect favoring CHO+CAF). The overall ES equaled 0.26 (95% CI 0.15–0.38, p < .001), indicating that CHO+CAF provides a small but significant performance benefit over CHO. ES was not significantly (p > .05) related to CAF dose, exercise duration, or performance-assessment method. To determine whether ES of CHO+CAF vs. CHO was different than CAF compared with water (placebo), a subgroup meta-analysis compared 36 CAF vs. placebo studies against the 21 CHO+CAF vs. CHO studies. The overall ES for the former group of studies (ES = 0.51, 95% CI 0.40–0.61) was nearly 2-fold greater than in CHO+CAF vs. CHO studies (p = .006).

Conclusions:

CHO+CAF ingestion provides a significant but small effect to improve endurance performance compared with CHO alone. However, the magnitude of the performance benefit that CAF provides is less when added to CHO than when added to placebo.

Restricted access

Caffeinated Sports Drink: Ergogenic Effects and Possible Mechanisms

Kirk J. Cureton, Gordon L. Warren, Mindy L. Millard-Stafford, Jonathan E. Wingo, Jennifer Trilk, and Maxime Buyckx

This double-blind experiment examined the effects of a caffeinated sports drink during prolonged cycling in a warm environment. Sixteen highly trained cyclists completed 3 trials: placebo, carbohydrate-electrolyte sports drink (CES), and caffeinated sports drink (CES+CAF). Subjects cycled for 135 min, alternating between 60% and 75% VO2max every 15 min for the first 120 min, followed by a 15-min performance ride. Maximal voluntary (MVC) and electrically evoked contractile properties of the knee extensors were measured before and after cycling. Work completed during the performance ride was 15–23% greater for CES+CAF than for the other beverages. Ratings of perceived exertion were lower with CES+CAF than with placebo and CES. After cycling, the MVC strength loss was two-thirds less for CES+CAF than for the other beverages (5% vs. 15%). Data from the interpolated-twitch technique indicated that attenuated strength loss with CES+CAF was explained by reduced intrinsic muscle fatigue.

Restricted access

Hydration during Exercise in Warm, Humid Conditions: Effect of a Caffeinated Sports Drink

Mindy L. Millard-Stafford, Kirk J. Cureton, Jonathan E. Wingo, Jennifer Trilk, Gordon L. Warren, and Maxime Buyckx

Caffeine is regarded as a diuretic despite evidence that hydration is not impaired with habitual ingestion. The purpose of this study was to determine whether a caffeinated sports drink impairs fluid delivery and hydration during exercise in warm, humid conditions (28.5 °C, 60% relative humidity). Sixteen cyclists completed 3 trials: placebo (P), carbohydrate-electrolyte (CE), and caffeinated (195 mg/L) sports drink (CAF+CE). Subjects cycled for 120 min at 60–75%VO2max followed by 15 min of maximal-effort cycling. Heart rate and rectal temperature were similar until the final 15 min, when these responses and exercise intensity were higher with CAF+CE than with CE and P. Sweat rate, urine output, plasma-volume losses, serum electrolytes, and blood deuterium-oxide accumulation were not different. Serum osmolality was higher with CAF+CE vs. P but not CE. The authors conclude that CAF+CE appears as rapidly in blood as CE and maintains hydration and sustains cardiovascular and thermoregulatory function as well as CE during exercise in a warm, humid environment.

Restricted access

Recovery from Run Training: Efficacy of a Carbohydrate-Protein Beverage?

Mindy Millard-Stafford, Gordon L. Warren, Leah Moore Thomas, J. Andrew Doyle, Teresa Snow, and Kristen Hitchcock

Post-exercise nutrition is critical to facilitate recovery from training. To determine if added protein (P) or increased carbohydrate (CHO) differentially improves recovery, eight runners ingested: 6% CHO (CHO6), 8% CHO + 2% protein (CHOP), and isocaloric 10% CHO (CHO10) following a 21-km run plus treadmill run to fatigue (RTF) at 90% VO2max. RTF was repeated after 2 h recovery. After 24 h, a 5 km time trial was performed. Insulin and blood glucose were higher (P < 0.05) following CHO10 compared to CHO-P and CHO6, but did not affect improvement from the first to second RTF (29.6% ± 6, 40.5% ± 8.8, 40.5% ± 14.5) or 5 km time (1100 ± 36.3, 1110 ± 37.3, 1118 ± 36.5 s). CK was not different, but perceived soreness with CHO-P (2.1 ± 0.5) was lower than CHO10 (5.2 ± 0.7). Additional calories from CHO or P above that provided in sports drinks does not improve subsequent performance after recovery; but less soreness suggests benefits with CHO-P.

Restricted access

Caffeine’s Beneficial Effect on Maximal Voluntary Strength and Activation in Uninjured but Not Injured Muscle

Nicole D. Park, Robert D. Maresca, Kimberly I. McKibans, D. Reid Morgan, Timothy S. Allen, and Gordon L. Warren

The study’s objective was to determine whether orally ingested caffeine could help overcome excitation-contraction-coupling failure, which has been suggested to explain part of the strength loss associated with eccentric-contraction-induced muscle injury. A sample of 13 college students (4 men and 9 women) was used in a double-blind, repeated-measures experimental design. Each participant performed 2 experimental trials, 1 with each leg, with each trial lasting 4 consecutive days. On a given day, each participant was randomly assigned to ingest a capsule containing 6 mg/kg of either caffeine or flour (placebo). On the day of and the first 2 days after a bout of 50 injurious eccentric contractions done by the knee extensors, the interpolated-twitch technique was used to assess electrically evoked strength, maximal voluntary isometric contraction (MVIC) strength, and percent muscle activation during MVIC both before and after capsule ingestion. These variables were also measured before and after capsule ingestion the day before the eccentric-contraction bout—when the muscle was uninjured. In injured muscle, caffeine had no effect on any variable. In uninjured muscle, caffeine also had no effect on electrically evoked strength but increased MVIC strength by 10.4% compared with placebo (p = .00002), and this was attributed to an increase in muscle activation (6.2%; p = .01). In conclusion, the data provide no evidence that caffeine ingestion can help overcome excitation-contraction-coupling failure, if it exists, in injured human muscle. The data do indicate that caffeine ingestion can increase MVIC strength and activation in uninjured muscle but not in injured muscle.