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No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living populationIt is often suggested that coffee causes dehydration and its consumption should be avoided or significantly reduced to maintain fluid balance. The aim of this study was to directly compare the effects of coffee consumption against water ingestion across a range of validated hydration assessment techniques. In a counterbalanced cross-over design, 50 male coffee drinkers (habitually consuming 3-6 cups per day) participated in two trials, each lasting three consecutive days. In addition to controlled physical activity, food and fluid intake, participants consumed either 4X200 mL of coffee containing 4 mg/kg caffeine (C) or water (W). Total body water (TBW) was calculated pre- and post-trial via ingestion of Deuterium Oxide. Urinary and haematological hydration markers were recorded daily in addition to nude body mass measurement (BM). Plasma was analysed for caffeine to confirm compliance. There were no significant changes in TBW from beginning to end of either trial and no differences between trials (51.5±1.4 vs. 51.4±1.3 kg, for C and W, respectively). No differences were observed between trials across any haematological markers or in 24 h urine volume (2409±660 vs. 2428±669 mL, for C and W, respectively), USG, osmolality or creatinine. Mean urinary Na+ excretion was higher in C than W (p = 0.02). No significant differences in BM were found between conditions, although a small progressive daily fall was observed within both trials (0.4±0.5 kg; p<0.05). Our data show that there were no significant differences across a wide range of haematological and urinary markers of hydration status between trials. These data suggest that coffee, when consumed in moderation by caffeine habituated males provides similar hydrating qualities to water. © 2014 Killer et al.
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Impact of intensified training and carbohydrate supplementation on immunity and markers of overreaching in highly trained cyclistsPurpose: To determine effects of intensified training (IT) and carbohydrate supplementation on overreaching and immunity. Methods: In a randomized, double-blind, crossover design, 13 male cyclists (age 25 ± 6 years, (Formula presented.) 72 ± 5 ml/kg/min) completed two 8-day periods of IT. On one occasion, participants ingested 2 % carbohydrate (L-CHO) beverages before, during and after training sessions. On the second occasion, 6 % carbohydrate (H-CHO) solutions were ingested before, during and after training, with the addition of 20 g of protein in the post-exercise beverage. Blood samples were collected before and immediately after incremental exercise to fatigue on days 1 and 9. Results: In both trials, IT resulted in decreased peak power (375 ± 37 vs. 391 ± 37 W, P < 0.001), maximal heart rate (179 ± 8 vs. 190 ± 10 bpm, P < 0.001) and haematocrit (39 ± 2 vs. 42 ± 2 %, P < 0.001), and increased plasma volume (P < 0.001). Resting plasma cortisol increased while plasma ACTH decreased following IT (P < 0.05), with no between-trial differences. Following IT, antigen-stimulated whole blood culture production of IL-1α was higher in L-CHO than H-CHO (0.70 (95 % CI 0.52–0.95) pg/ml versus 0.33 (0.24–0.45) pg/ml, P < 0.01), as was production of IL-1β (9.3 (95 % CI 7–10.4) pg/ml versus 6.0 (5.0–7.8) pg/ml, P < 0.05). Circulating total leukocytes (P < 0.05) and neutrophils (P < 0.01) at rest increased following IT, as did neutrophil:lymphocyte ratio and percentage CD4+ lymphocytes (P < 0.05), with no between-trial differences. Conclusion: IT resulted in symptoms consistent with overreaching, although immunological changes were modest. Higher carbohydrate intake was not able to alleviate physiological/immunological disturbances.
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Fueling for the field: nutrition for jumps, throws, and combined eventsAthletes participating in the athletics (track and field) events of jumps, throws, and combined events (CEs; seven-event heptathlon and 10-event decathlon) engage in training and competition that emphasize speed and explosive movements, requiring optimal power-weight ratios. While these athletes represent a wide range of somatotypes, they share an emphasis on Type IIa and IIx muscle fiber typing. In general, athletes competing in jumps tend to have a lower body mass and may benefit from a higher protein (1.5-1.8 g PRO·kg−1·day−1) and lower carbohydrate (3-6 g CHO·kg−1·day−1) diet. Throwers tend to have a higher body mass, but with considerable differences between events. Their intense, whole-body training program suggests higher PRO requirements (1.5-2.2 g PRO·kg−1·day−1), while CHO needs (per kg) are similar to jumpers. The CE athletes must strike a balance between strength and muscle mass for throws and sprints, while maintaining a low enough body mass to maximize performance in jumps and middle-distance events. CE athletes may benefit from a higher PRO (1.5-2 g PRO·kg−1·day−1) and moderate CHO (5-8 g CHO·kg−1·day−1) diet with good energy availability to support multiple daily training sessions. Since they compete over 2 days, well-rehearsed competition-day fueling and recovery strategies are imperative for CE athletes. Depending on their events' bioenergetic demands, athletes in throws, jumps, and CE may benefit from the periodized use of ergogenic aids, including creatine, caffeine, and/or beta-alanine. The diverse training demands, physiques, and competitive environments of jumpers, throwers, and CE athletes necessitate nutrition interventions that are periodized throughout the season and tailored to the individual needs of the athlete.
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Prolonged cycling exercise alters neural control strategy, irrespective of carbohydrate dose ingestedThe interactions between CHO dosage and neuromuscular regulation following fatiguing endurance exercise are not well understood. Fifteen well‐trained male cyclists completed 4 experimental trials of 120‐min submaximal cycling (95% lactate threshold) during which water (0 g CHO·h−1) or CHO beverages (20, 39, or 64 g CHO·h−1) were consumed every 15 minutes, at a rate of 1 L·h−1, followed by a work‐matched time trial ~30 minutes. Maximal voluntary contraction (MVC), M‐wave twitch potentiation and torque, motor unit recruitment and firing rate were recorded pre‐ and post‐cycling. Time trial performance improved following 39 and 64 versus 0 and 20 g CHO·h−1, with no effect of CHO dose on any pre‐ to post‐neuromuscular function measures. Pre‐ to post‐cycling exercise: (1) MVC, and M‐wave amplitude and duration declined by −21.5 Nm, and −4.9 mV and −7.1 ms, respectively; (2) peak evoked torque remained unchanged; (3) Firing rate of early‐ and mid‐recruited motor units increased by 0.93 pps and 0.74 pps, respectively, with no change in later‐recruited motor units. Thus, central drive to early‐ and mid‐recruited motor units increases as a result of endurance cycling, due to a likely fatigue compensatory mechanism. However, CHO availability does not appear to influence increased neuromuscular drive.
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Metabolic responses to carbohydrate ingestion during exercise: associations between carbohydrate dose and endurance performanceCarbohydrate (CHO) ingestion during exercise lasting less than three hours improves endurance exercise performance but there is still debate about the optimal dose. We utilised stable isotopes and blood metabolite profiles to further examine metabolic responses to CHO (glucose only) ingestion in the 20–64 g·h−1 range, and to determine the association with performance outcome. In a double-blind, randomized cross-over design, male cyclists (n = 20, mean ± SD, age 34 ± 10 years, mass 75.8 ± 9 kg, peak power output 394 ± 36 W, VO2max 62 ± 9 mL·kg−1·min−1) completed four main experimental trials. Each trial involved a two-hour constant load ride (185 ± 25 W) followed by a time trial, where one of three CHO beverages, or a control (water), were administered every 15 min, providing 0, 20, 39 or 64 g CHO·h−1. Dual glucose tracer techniques, indirect calorimetry and blood analyses were used to determine glucose kinetics, exogenous CHO oxidation (EXO), endogenous CHO and fat oxidation; and metabolite responses. Regression analysis revealed that total exogenous CHO oxidised in the second hour of exercise, and suppression of serum NEFA concentration provided the best prediction model of performance outcome. However, the model could only explain ~19% of the variance in performance outcome. The present data demonstrate that consuming ~40 g·h−1 of CHO appears to be the minimum ingestion rate required to induce metabolic effects that are sufficient to impact upon performance outcome. These data highlight a lack of performance benefit and few changes in metabolic outcomes beyond an ingestion rate of 39 g·h−1. Further work is required to explore dose-response effects of CHO feeding and associations between multiple metabolic parameters and subsequent performance outcome.
