Sleep is generally regarded as a valuable resource for psychological and physiological well-being. Although the effects of sleep on athletic performance have been acknowledged in sport science, few studies have investigated the prevalence of sleep problems and their effects on elite athletes before a sport event. In this study, 632 German athletes from various sports were asked about their sleep habits during the night(s) before an important competition or game. The findings indicate that 65.8% of the athletes experienced poor sleep in the night(s) before a sports event at least once in their lives and a similarly high percentage (62.3%) had this experience at least once during the previous 12 months. Athletes of individual sports reported more sleep difficulties than athletes of team sports. The main sleep problem was not being able to fall asleep. Internal factors such as nervousness and thoughts about the competition were rated highest for causing sleep problems. Most athletes stated that disturbed sleep had no influence on their athletic performance; however, athletes also reported effects such as a bad mood the following day, increased daytime sleepiness, and worse performance in the competition or game. The differences between individual and team sports indicate that athletes in some sports need more help than those in other sports in managing sleep problems.

In recent years, muscle oxygen saturation (${\mathrm{SmO}}_2$) measured via near-infrared spectroscopy (NIRS) has developed into an affordable and readily available technology. The application of this technology in athletic settings is expanding, as fundamental questions are being addressed.¹ One of the major concerns in the application of NIRS in athletic settings is that common limitations of NIRS are not well understood and need to be properly addressed, while still allowing the technology to be utilized for its clear advantages.^2,3

The body of research that reports the relevance of sleep in high-performance sports is growing steadily. While the identification of sleep cycles and diagnosis of sleep disorders is limited to lab-based assessment via polysomnography, the development of activity-based devices estimating sleep patterns provides greater insight into the sleep behaviour of athletes in ecological settings. Overall, small sleep quantity and/or poor quality appears to exist in many athletic populations, though this may be related to training and competition context. Typical sleep-affecting factors are the scheduling of training sessions and competitions as well as impaired sleep-onset as a result of increased arousal prior to competition or due to the use of electronic devices before bedtime. Further challenges are travel demands which may be accompanied by jet-lag symptoms and disruption of sleep habits. Promotion of sleep may be approached via behavioural strategies, such as sleep hygiene, extending night-time sleep or daytim...