A few weeks ago a study was published in the Journal of Sports Sciences that investigated the effects of intensified training on sleep quantity and quality (1). Sleep is an important part of recovery and this is recognised by athletes and coaches. There is also some evidence that improving sleep can also improve performance. On the other hand, research has demonstrated that exercise can enhance sleep quality, but overtraining or excessive exercise might be associated with sleep disturbances.
Dr Sophie Killer led a study at Loughborough University in which 13 trained cyclists performed extremely hard training for 9 days. Essentially the training volume was doubled and the intensity of training increased at the same time. This protocol was used in several previous studies and consistently resulted in decreases in performance and other symptoms of overreaching in all participants. Such training periods are not too dissimilar to training camps that athletes often participate in early in the season. All cyclists performed the 9-day training periods twice: once with a carbohydrate supplemented diet and once with a normal diet. During the carbohydrate supplemented diet the cyclists received carbohydrates before during and after exercise according to recommendations, with the control diet they continued their habitual diet. All training was either supervised or monitored using powermeters (SRM). All training was carefully analyzed using TrainingPeaks.
Participants were wearing an actiwatch before the start of the training period for 5 days to obtain baseline sleep scores. An actiwatch is a relatively simple and non-invasive device that provides numerous measures of sleep quality. The cyclists continued to wear the actiwatch each night for the duration of the study. Mood state was monitored as well during the study.
Sleep and mood state changes
The cyclists increased the time they spent in bed during the intensified training period, suggesting that they were exhibiting symptoms of fatigue. This increased time in bed, however, did not result in an increase in actual sleep time. Sleep efficiency was reduced and there was an increase in the number of wake bouts throughout the night and a more fragmented sleep overall. In addition, the cyclists experienced significant disruptions to mood state, reporting increased tension, anger, fatigue, confusion, depression and increased feelings and symptoms of stress.
Sleep efficiency was reduced and there was an increase in the number of wake bouts throughout the night
Therefore, the main findings of this study were that 9 days of intensified training in highly-trained cyclists resulted in significant and progressive declines in sleep quality, mood state and maximal exercise performance.
Diet affects symptoms of overreaching
During the intensive training period the cyclists consumed fewer calories on the control diet compared with the carbohydrate supplemented diet. This is comparable to what we observed earlier in a study with cyclists who underwent similar training and received similar diets (2, 3). The carbohydrate supplementation reduced some, but not all of the detrimental effects of the intensified training. This is also consistent with a conclusion we drew based on previous studies: symptoms of overreaching may be reduced by feeding more carbohydrate but it cannot completely prevent them.
Symptoms of overreaching may be reduced by feeding more carbohydrate but it cannot completely prevent them
It is important to consider sleep when planning training camps and put strategies in place to optimize sleep in order to break the vicious circle and downward spiral of decreased sleep, decreased recovery, decreased exercise tolerance and so on..