Caffeine increases exogenous carbohydrate oxidation during exercise

Caffeine and carbohydrate supplementation during exercise when in negative energy balance: effects on performance, metabolism, and salivary cortisol

The ingestion of carbohydrate (+CHO) and caffeine (+CAF) during exercise is a commonly used ergogenic practice. Investigations are typically conducted with subjects who are in a rested state after an overnight fast. However, this state of positive energy balance is not achieved during many work and exercise circumstances. The aim of this study was to evaluate the substrate use and performance effects of caffeine and carbohydrate consumed alone and in combination while participants were in negative energy balance. Male participants (n = 9; 23 ± 3 years; 74.1 ± 10.6 kg) completed 4 trials in random order: –CAF/–CHO, –CAF/+CHO, +CAF/–CHO, and +CAF/+CHO. Diet and exercise were prescribed for 2 days before each trial to ensure negative energy balance. For each trial, before and after 2 h of cycling at 50% of maximal watts, a saliva sample and a muscle biopsy (vastus lateralis) were obtained. A simulated 20 km time trial was then performed. The respiratory exchange ratio was higher (p < 0.05) in +CHO trials and lower (p < 0.05) in the +CAF/+CHO trial than in the –CAF/+CHO trial. Salivary cortisol response was higher (p < 0.05) in the +CAF/–CHO trial than in any of the other trials. Muscle glycogen and heart rates were similar in all trials. Performance in the 20 km time trial was better in the –CAF/+CHO trial than in the –CAF/–CHO trial (p < 0.05), but the +CAF/+CHO trial was no better than the +CAF/–CHO trial (p > 0.05), or any of the other trials. When co-ingested with carbohydrate, caffeine increased fat use and decreased nonmuscle glycogen carbohydrate use over carbohydrate alone when participants are in negative energy balance; however, caffeine had no effect on the 20 km cycling time trial performance.

Caffeine use in sports: considerations for the athlete

The ergogenic effects of caffeine on athletic performance have been shown in many studies, and its broad range of metabolic, hormonal, and physiologic effects has been recorded, as this review of the literature shows. However, few caffeine studies have been published to include cognitive and physiologic considerations for the athlete. The following practical recommendations consider the global effects of caffeine on the body: Lower doses can be as effective as higher doses during exercise performance without any negative coincidence; after a period of cessation, restarting caffeine intake at a low amount before performance can provide the same ergogenic effects as acute intake; caffeine can be taken gradually at low doses to avoid tolerance during the course of 3 or 4 days, just before intense training to sustain exercise intensity; and caffeine can improve cognitive aspects of performance, such as concentration, when an athlete has not slept well. Athletes and coaches also must consider how a person's body size, age, gender, previous use, level of tolerance, and the dose itself all influence the ergogenic effects of caffeine on sports performance.

High rates of muscle glycogen resynthesis after exhaustive exercise when carbohydrate is coingested with caffeine

We determined the effect of coingestion of caffeine (Caff) with carbohydrate (CHO) on rates of muscle glycogen resynthesis during recovery from exhaustive exercise in seven trained subjects who completed two experimental trials in a randomized, double-blind crossover design. The evening before an experiment subjects performed intermittent exhaustive cycling and then consumed a low-CHO meal. The next morning subjects rode until volitional fatigue. On completion of this ride subjects consumed either CHO [4 g/kg body mass (BM)] or the same amount of CHO + Caff (8 mg/kg BM) during 4 h of passive recovery. Muscle biopsies and blood samples were taken at regular intervals throughout recovery. Muscle glycogen levels were similar at exhaustion [ approximately 75 mmol/kg dry wt (dw)] and increased by a similar amount ( approximately 80%) after 1 h of recovery (133 +/- 37.8 vs. 149 +/- 48 mmol/kg dw for CHO and Caff, respectively). After 4 h of recovery Caff resulted in higher glycogen accumulation (313 +/- 69 vs. 234 +/- 50 mmol/kg dw, P < 0.001). Accordingly, the overall rate of resynthesis for the 4-h recovery period was 66% higher in Caff compared with CHO (57.7 +/- 18.5 vs. 38.0 +/- 7.7 mmol x kg dw(-1) x h(-1), P < 0.05). After 1 h of recovery plasma Caff levels had increased to 31 +/- 11 microM (P < 0.001) and at the end of the recovery reached 77 +/- 11 microM (P < 0.001) with Caff. Phosphorylation of CaMK(Thr286) was similar after exercise and after 1 h of recovery, but after 4 h CaMK(Thr286) phosphorylation was higher in Caff than CHO (P < 0.05). Phosphorylation of AMP-activated protein kinase (AMPK)(Thr172) and Akt(Ser473) was similar for both treatments at all time points. We provide the first evidence that in trained subjects coingestion of large amounts of Caff (8 mg/kg BM) with CHO has an additive effect on rates of postexercise muscle glycogen accumulation compared with consumption of CHO alone.

Legal nutritional supplements during a sporting event

Nutrition significantly influences sports performance; however, the efficacy of any nutritional supplement or strategy should be carefully considered in relation to the event and the sex, training and nutritional status of the participant. The causes of fatigue, mechanism of action, safety and legality of the supplement, together with the scientific evidence from studies with an appropriate experimental design, should all be taken into account before incorporating into the training and/or competition diet. The efficacy of ingesting nutritional supplements immediately before and/or during endurance exercise (duration 45-180 min) is reviewed in this chapter. The ingestion of CES (carbohydrate-electrolyte solutions) have been shown to improve both exercise capacity and performance, either due to the maintenance of euglycaemia throughout exercise or the sparing of muscle glycogen early on in exercise. The addition of caffeine to CES may improve endurance performance as a consequence of a reduced perception of effort. Research suggests that the addition of protein to CES may only be effective when a suboptimal amount of CHO (carbohydrate) is ingested during exercise (<60 g of CHO.h(-1)); however, recovery of performance may be enhanced due to a reduction in subsequent muscle soreness and the promotion of muscle protein synthesis after exercise. The findings from studies investigating the effects of ingesting MCTs (medium-chain triacylglycerols) and BCAAs (branched-chain amino acids), either on their own or in combination with CES, on endurance performance have been equivocal and therefore would not be recommended. Any nutritional strategy should be practised in training before being used during a competition.

Fat and carbohydrate for exercise

PURPOSE OF REVIEW

To examine the results of new investigations that look at the efficacy of nutrient/training strategies on metabolism and athletic performance.

RECENT FINDINGS

'Dietary periodization' involves the manipulation of macronutrient intake in association with changes in physical training. Such interventions have a major effect on altering patterns of fuel utilization during exercise; however, they often fail to enhance performance capacity. In contrast, the ingestion of a combination of different types of carbohydrate during exercise results in high rates of muscle glucose oxidation (1.5 g/min) and can improve intense, short-duration (approximately 60 min), and prolonged (>90 min) submaximal steady-state exercise, either by metabolic or neural mechanisms.

SUMMARY

Further investigation into the responses of specific nutrient/training strategies on metabolic and cellular signaling pathways is warranted to determine the underlying mechanisms by which such interventions exert their effect. Such studies, however, should be coupled with investigations that assess the outcomes of these responses on the 'real life' training adaptations in athletes.