WHEN IS SLEEP MOST IMPORTANT? EXAMING SLEEP AND PERFORMANCE IN FEMALE COLLEGIATE CROSS COUNTRY RUNNERS

BACKGROUND: Sleep plays a paramount role in exercise recovery and may improve the tolerance of the physical demands typical of endurance training. While the distinction between the effects of sufficient and insufficient sleep on performance is known, there is a paucity of data evaluating when that sleep is most important prior to an endurance race event. PURPOSE: This study evaluated the relationship between sleep habits at multiple pre-race time points and performance in female collegiate cross country runners. METHODS: Mid-season sleep duration and race performance were assessed in 11 female collegiate cross country runners during the 2021 COVID-19-shortened season. Sleep duration was determined via use of a vetted wrist-worn heart rate and biometric monitor. Additionally, sleep duration was evaluated at multiple pre-race time points: 7-, 5-, 3-, and 1-day pre-race as well as mid-training (i.e., >7 days pre-race). Race performance was defined as the average time per kilometer (time/k) during race events. Repeated measures analysis of variance testing was utilized to evaluate differences in pre-race sleep, while Pearson correlations were used to assess the relationships between sleep and performance. RESULTS: There were 7 races (average distance: 5.8 ± 0.4 km) during the season. Average finish time was 21.6 ± 2.4 mins, equating to 3.7 ± 0.2 mins/km. Average sleep duration was the same at all pre-race time points (7.40 - 7.05 hrs; p > 0.05). Mid-training as well as 7- and 5-day pre-race sleep duration was significantly, negatively correlated with time/k (r = -0.71 - -0.56; all p < 0.05), with 7-day pre-race sleep exhibiting the strongest relationship and accounting for 50% of the variation in time/k. This relationship was not seen with 3- and 1-day pre-race sleep. CONCLUSIONS: Sleep duration did not change at any point pre-race in female collegiate cross country runners. However, mid-training as well as 7- and 5-day pre-race sleep exhibited a negative relationship with race performance (i.e., those who slept more ran faster), while 3- and 1-day pre-race sleep showed no relationship. These findings suggest that sleep habits are imperative to race day performance, and that the most emphasis on these habits should be placed farther out from race day (i.e., ~7 days pre-race).