Repeated days of hard training typically result in an accumulation of fatigue, making it more and more difficult to complete the workouts, that would be no problem in a rested state. This is a very common scenario in a training camp. Even within 7 days athletes can develop symptoms of overreaching and it may take 2 weeks or longer to fully recover. For more information on overtraining see: Overtraining is it real? The symptoms of overtraining and Causes and prevention of overtraining.
The composition of the diet is one of the key factors that determines the recovery during such periods. In 1992 we developed a protocol to induce a state of overreaching in well-trained athletes and used this protocol successfully in a number of studies since then. We started to learn more about the symptoms and the time line in which performance reductions and other overtraining symptoms develop. An important practical question was: can this be altered (improved) by diet? Can we prevent the symptoms by feeding more carbohydrate for example?
In a study published in 2004 (Dr Juul Achten was the first author of the paper) we simulated a training camp situation in runners. For 7 days the runners trained extremely hard and performance seemed to deteriorate over time. Runners also developed various other symptoms of overreaching; most notably changes in mood state. Although some runners seemed a little more fatigue resistant then others, by the end of the week all runners displayed deterioration of performance and changes in mood state.
These runners performed the same intensified training period twice, with a 10-14 day period of rest separating them. In random order the runners received a normal carbohydrate diet containing 5.4 grams of carbohydrate per kilogram body weight per day (g/kg/day) or a higher carbohydrate diet. A diet of 5.4 g/kg/day is a very common carbohydrate intake for endurance and other athletes. The high carbohydrate condition consisted of 8.5 g/kg/day. This is a high, but not extreme carbohydrate intake (often carbohydrate intake recommendations exceed 10 g/kg).
It was obvious that the high carbohydrate diet improved the situation. Performance still decreased as training intensified but he runners’ performance did not decrease as much and their disturbances in mood state and feelings of fatigue were less severe when more carbohydrate was ingested.
We therefore concluded that a high carbohydrate diet cannot prevent the symptoms, but it can reduce them. It will allow athletes to train a little harder for a little longer and it may reduce the risks of becoming overtrained (more on overtraining can be found here)
Currently a lot is talked about low carbohydrate diets. Based on these findings and a number of other studies it is difficult to see how an athlete could survive the training load on a low carbohydrate diet. Very likely the training quality would decrease because even a normal carbohydrate intake resulted in a significant performance decrease.
Although there may be other benefits of training with a low carbohydrate diet (which I will discuss in future posts), the evidence currently suggests that during periods of hard training an adequate carbohydrate intake is essential to minimize the impact on performance and reduce symptoms of overtraining.
The performance figure was constructed from the data of the study. The baseline measurements were set at 100% and any performance change was expressed as a percentage change from that value. The performance results of two different tests used in the study were combined. On days 1,5,8 and 11 the runners completed an 8km (5 mile) time trial after 1 hour of submaximal running on a treadmill. On days 6,7,9 and 10 the runners completed a 16km (10 mile) run.
The intention of the graphs here is to illustrate the points made in the text. The text is usually to short to discuss the paper in much detail and the main purpose is to get messages across that reflect the evidence presented. I always include the actual link to the original papers so people can evaluate my interpretations of data.