Research says ...
Study title: The effect of a high carbohydrate meal on endurance running capacity
Authors: C. Chryssanthopoulos, C. Williams, A. Nowitz, C. Kosiopoulou and V. Vleck (2002)
Source: International Journal of Sport Nutrition and Exercise Metabolism, 12,157-171
Athletes who compete after an overnight fast may fatigue prematurely because fasting reduces liver glycogen stores. Therefore, athletes should avoid prolonged fasting and ingest a high carbohydrate meal which is low in fat, protein and fibre about three to four hours before exercise. However, other evidence suggests a pre-exercise carbohydrate meal does not always improve exercise performance. This is particularly evident when the amount of pre-exercise carbohydrate ingested is less than about two grams of carbohydrate per kg body mass (BM).
To determine whether a moderate amount of carbohydrate food, ingested three hours before exercise, improves endurance running capacity when compared to running without the meal and ingesting only water during the exercise.
Ten men performed three treadmill runs at 70 per cent of VO2max to exhaustion after consuming (i) a carbohydrate meal three hours before exercise and a carbohydrate-electrolyte solution during exercise (M+C); or (ii) the carbohydrate meal 3 hours before exercise and water during exercise (M+W); or (iii) a liquid placebo 3 hours before exercise and water during exercise (P+W). Douglas bags samples and blood samples were taken during each run.
Exercise time was longer in M+C compared with M+W and both were longer when compared with P+W. Serum insulin concentrations at the start of exercise and carbohydrate oxidation rates during the first hour of exercise were higher in M+C and M+W.
An athlete should never fast before training or competition. A high carbohydrate meal should be consumed three hours before training or running in an endurance based race. Ingesting a high carbohydrate meal of about two grams of carbohydrate per kg body mass (BM) will improve an athlete's endurance running capacity by nine percent before fatigue compared to no food consumption before exercise. In addition, an athlete who drinks a carbohydrate-electrolyte solution like Lucozade during training or in a race lasting approximately over 60 minutes will increase their endurance capacity by another 12 per cent before fatigue to approximately 22 per cent longer than if they ate nothing before training/competition. Knowledge of these findings may require the coach to consider their session times or educating the athlete/athlete’s parents as to suitable meal times and meal types to ensure enough carbohydrate is consumed dependent on the athlete's BM. This will ensure each athlete attends each training session with maximal glycogen stores to safely push their body to the limits and maximise their training.
Bartlett
Study title: Effects of different sodium concentrations in replacement fluids during prolonged exercise in women
Authors: R. Twerenbold, B. Knechtle, T. H. Kakebeeke, P. Eser, G. Miiller, P. Arx and H. Knecht (2003)
Source: British Journal of Sports Medicine, 37, 300-303
Adequate fluid replacement during exercise is important to replace sweat loss because exercise capacity is maintained by avoiding dehydration and a decline in thermoregulation. There is also increasing evidence that hyponatraemia (sodium deficiency) is one of the most common and most serious complications during prolonged exercise. There are two theories on the cause of exercise induced hyponatraemia: it is suggested that there is massive un-replaced sodium losses in sweat associated with dehydration. Alternatively, the proposal is that hyponatraemia develops from fluid overload in athletes who drink excessively. This causes dilutional hyponatraemia and prevents weight loss or even causes weight gain in hyponatraemic athletes immediately after long races.
To investigate the effect of different sodium concentrations in replacement fluids on haematological variables and endurance performance during prolonged exercise.
Thirteen female endurance athletes completed three four hour runs on a 400m track. Environmental conditions differed between the three trials: 5.3"C and snow (trial I), 19.O"C and sunny weather (trial 2), 13.X and precipitation (trial 3). They consumed 1 litre of fluid an hour during the trials with randomised intake of fluids: one trial (H) with high sodium concentration (680mg/l), one trial (L) with low sodium concentration (410mg/l), and one trial with only water (W). Weight and blood samples were taken before and after the trials.
The mean (SD) decrease in [Na+] plasma over the whole trial was significantly less in trial H compared to trial W. Mild hyponatraemia was observed in only six women (46 per cent) in trial H compared with nine (69 per cent) in trial L, and 12 (92 per cent) in trial W. Two subjects (17 per cent) in trial W developed severe hyponatraemia. No significant differences were found in performance or haematological variables with the three different fluids. There was no significant correlation between [Na+] plasma after the run and performance. There was a significant correlation between changes in [Na+] plasma and changes in body weight.
There was no indication of improved performance over the four hour trials by using sodium concentration replacement fluids. However, exercise induced hyponatraemia (sodium deficiency) in women is likely to be developed from fluid overload during prolonged exercise. This can be minimised by the use of replacement fluids of high sodium concentration. The study recommended sodium replacement of at least 680mg/h is required for women in a state of fluid overload during endurance exercise of four hours. Most commercially available sports drinks (Gatorade, Lucozade Sport, Isostar) contain 20-25 mmol/l sodium which works out at consuming approximately 1.3 litres of these sports drinks an hour during exercise to ensure adequate sodium replacement and prevent hyponatraemia.
Bartlett
Study title: The influence of post-exercise macronutrient intake on energy balance and protein metabolism in active females participating in endurance training
Authors: B. D. Roy, K. Luttmer, M. Bosman and M. A. Tarnopolsky (2002)
Source: International Journal of Sport Nutrition and Exercise Metabolism, 12,172-188
The importance of adequate carbohydrate (CHO) and energy intake to optimise endurance exercise performance has been a focus of investigation for many years. Historically, a high carbohydrate diet, which maximises muscle glycogen content, was established as improving endurance exercise performance. There is also evidence to suggest that the timing of macro-nutrient intake can also influence exercise metabolism, maximising the rate of muscle glycogen re-synthesis, increasing whole body protein synthesis and potentially increasing in muscle protein synthesis.
To determine the effects of the timing of macronutrient intake on indices of protein metabolism, energy balance, and endurance exercise performance in recreationally trained females exposed to a significant increase in training load (metabolic stress).
Ten healthy young female endurance athletes performed four 60-min bouts of cycle ergometry at -65 per cent of VO2peak on four days (day one, three, four and six) during two separate one-week periods. On day seven participants performed a ride to exhaustion at -75 per cent of VO2peak. One of the seven-day periods served as a control condition, where a placebo beverage was consumed following exercise bouts on days one, three, four and six (CON). During the other seven-day protocol (POST), participants consumed a predefined formula beverage with added carbohydrate following the exercise bouts on days one, three, four and six. Energy intake and macro-nutrients proportions were the same between the two trials; the only difference was the timing at which the macro-nutrients were consumed.
Glucose and insulin concentrations were significantly higher following exercise during POST as compared to CON. Time to exhaustion during exercise on day seven was longer during POST as compared to CON. POST resulted in maintenance of body weight during the seven-day protocol, while there was a significant weight reduction with CON.
This knowledge requires an education process of the athlete/athlete's parents into the importance of consuming a substantial meal filled with macronutrients as soon as it is possible after training or finishing a warm-down after a race, especially in heavy competition schedules of several events of heats, semi-finals and finals. Traveling and food preparation time are usually the biggest delays for athlete's trying to eat as soon as they can. Where possible have an appropriate meal ready to eat on arrival at home from training. In between the time it takes to get home consuming a snack cereal bar and fruit along with adequate fluid are good options to start replenishing the energy stores which have just been depleted.
Bartlett
Study title: Effect of high and low rates of fluid intake of post-exercise re-hydration
Authors: E. Kovacs, R. M. Schmahl, 1. Senden, and F. Brouns (2002)
Source: International Journal of Sport Nutrition and Exercise Metabolism, 12,14-23
Athletes who have lost a substantial amount of fluid are generally advised to re-hydrate as soon as possible after stopping exercise. However, there is research to suggest a high rate of fluid consumption during the first two hours of post-exercise rehydration is known to increase plasma volume (PV) significantly and result in substantial urine production. Therefore, it is hypothesized that ingestion of an equal fluid quantity but at a more moderate rate will lessen these effects and thus improve fluid retention and therefore hydration.
To investigate the effects of a high or a low rate of ingestion of a carbohydrate-electrolyte solution on plasma volume and fluid balance restoration.
Eight well trained cyclists were dehydrated at three per cent of body weight (BW) by cycling at 28°C. During the recovery period, they ingested a carbohydrate-electrolyte solution in a volume equivalent to 120 per cent of BW loss. Randomly, they ingested 60 per cent, 40 per cent and 20 per cent in the first, second and third hours of the recovery period, respectively (H), or 24 per cent - h-1 during five hours (L).
BW loss was similar for both trials and resulted in a total drink intake of 2.6 ffl 0.1 kg. Urine output in H exceeded significantly that of L in the second and third hours. This was reversed in the fifth and sixth hours. Plasma volume and fluid balance increased more rapidly in H compared to L. After six hours this difference disappeared.
Coaches should always educate and ensure where possible that their athlete's replace all fluid lost during exercise whether it is quickly or slowly. However, a high and forced rate of intake of a well-composed solution is of priority when repeated bouts of exercise like a busy athletics competition schedule of heats, semis and finals are being performed in order to maintain exercise capacity and performance and minimise possible health risks due to exercising in a dehydrated state. The solutions recommend and available to the athlete are the marketed Isotonic drinks with carbohydrate levels between six and eight per cent - e.g. High Five, SiS Go, Boots Isotonic, Lucozade Sport. However, if the recovery time to the next race or training session is substantial, fluid replacement can be met by a lower drink intake over a prolonged time period.
Bartlett
Study title: Effect of oral creatine supplementation on jumping and running performance
Authors: C. Bosco, J. Tihanyi, J. Pucspk, I. Kovacs, A. Gabossy R. Colli, G. Pulvirenti, C. Tranquilli, C. Forti, M. Viru, A. Viru (1997)
Source: International Journal of Sports Medicine, 18,369-372
Creatine (Cr) has an essential role on skeletal muscle energy metabolism. During short-time high intensity exercises the ATP turnover increases a hundred times in working muscles compared to resting conditions. The fastest way to re-synthesize ATP is the degradation of Phosphocreatine (PCr). This reaction leads to an accumulation of Cr which is rephosphorylated back to PCr during recovery time. It has been shown that daily ingestion of 20-30g Cr for several days leads to approximately 20 per cent increase in the total Cr content of human skeletal muscle of which about 30 per cent is in the form of PCr.
To investigate the effect of Cr supplementation on exercise performance as measured by changes over time in power output during maximal jumping and changes in maximal exercise duration in intensive all-out treadmill running.
Fourteen qualified male athletes (eight sprinters and six jumpers) were divided into either the experimental group who consumed 4x5g/day Cr monohydrate (HZO) for five consecutive days – Cr was supplemented and mixed with an equal amount of glucose - or the placebo group who received daily 4x5g/day of glucose in a double-blind design. All subjects were examined two days before and after the period of Cr or glucose administration. On day one, mechanical power output was monitored during continuous jumping exercises and day two a treadmill test for maximal duration of anaerobic running to exhaustion was performed. Peak lactate concentrations were determined from blood samples.
Cr supplementation led to a significant enhancement of performance capacity in the jumping test by seven per cent during the first 15 seconds and by 12 per cent during the second 15 seconds. The positive effect of Cr supplementation was not observed in the last third of the continuous jumping exercise, when the contribution of anaerobic metabolism was decreasing. The time of intensive running up to exhaustion improved by 13 per cent.
The study identifies Creatine and its supplementary benefits to the Alactic and Lactic energy system in the first 30 seconds of maximal exercise output. For a coach, the athletes who would benefit most from creatine supplementation would be lOOm to 400m track athletes. Although explosive field athletes and track athletes using a variation of the energy systems, for example a 1500m runner, would also gain benefits when a sprint finish is required using the Lactic energy system. The report does not identify amounts, timing and duration of a creatine supplement programme to obtain optimum performance. Therefore, the coach should seek professional nutrition advise or refer to relevant literature before letting their athlete's start such a programme. Finally, it must be certain that the supplement is legal and is not on the banned doping list for the sport and purchased/obtained from a reputable company, ideally recommended by the sports governing body.
Bartlett
Dr Sharon Dixon is a lecturer in sports biomechanics at the University of Exeter.
David Bartlett recently graduated from the University of Bath (BA Coach Education and Sports Development). He has been a successful junior international swimmer for Great Britain and while training at the University of Bath's High Performance Centre achieved his senior international debut in 2002. His ambition is to represent his country at a major Games or Championships.
______________________________________________________________________________
| Title |
Research says... |
| Author |
Dixon, Sharon; Denison, Jim |
| Source |
The Coach (Peterborough, England) |
| Publisher |
Descartes Publishing Ltd. |
| /Issue |
32 |
Date |
Winter 2006 |
| SIRC Article # |
S-1017072 |
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