It’s logical to assume that if your clients’ sleep duration or quality is compromised, it will be detrimental to their health. Studies have shown that sleep loss hampers healing from injury, increases emotional volatility and decreases immune function. But does sleep impact endurance performance, and if so, what objective and subjective markers might be moving in the wrong direction? That’s what we’ll attempt to answer in this article.
Altering Lactate Threshold
I explored a fresh way of considering lactate’s role in performance, fatigue and fueling, how the best in the world take this into account, and what implications the new view of lactate has for your athletes’ training in a previous article. Now let’s look at how lactate levels might be linked with recovery. It probably won’t shock you if I say that getting inadequate sleep – whether that’s insufficient duration or quality – can negatively impact your clients’ athletic performance. In recent years, researchers have sought to understand which factors sleep deprivation affects and how these are interrelated.
Several studies have included lactate in their investigations of the relationship between sleep and physical output, and a few have focused on this exclusively. These have produced seemingly contradictory results. For example, a study published in the European Journal of Applied Physiology kept participants awake overnight and then tested various parameters during morning and afternoon workouts the next day. They found that lactate levels were not affected in either session.[i]
However, other trials have noted a connection between compromised sleep and lactate. A team of French physiologists manipulated the sleep-wake cycles of eight well-trained endurance athletes to see how this might impact their hormonal responses during a 30-minute cycling time trial. They concluded that “blood lactate was higher during submaximal exercise performed after both a delayed bedtime and an early awakening.”[ii] The key distinction is the exertion level. The authors of the first study were concerned with measuring maximal, peak and mean power. Whereas in the second, participants performed at 75% of their VO2 max.
These findings suggest that while red-line output may be unaffected by compromised sleep if your athletes try to do a moderate-intensity endurance workout lasting a half-hour or more, they might hit their lactate threshold sooner than usual. This may impact their pacing late in such a session, increase their overall finish time and lead to them running out of steam sooner than expected.
Impacting Heart and Lung Function
In addition to affecting your athletes’ lactate threshold, insufficient sleep might also take a toll on the output of their cardiovascular system. The number of hours your clients spend in bed isn’t the only indicator of how well or poorly they might perform. A team of Brazilian researchers asked 28 healthy men to subjectively assess their sleep duration (over or under seven hours) and the quality of their slumber using the Pittsburgh Sleep Quality Index. They then performed a ramp test that required them to incrementally increase their power output on a scale tailored to the activity levels they were used to.
Publishing their results in Physiology & Behavior, the co-authors concluded that “Participants reporting good sleep quality presented higher values of Wmax, VO2max and lower values of HRmax when compared to participants with altered sleep. Regarding sleep duration, only Wmax was influenced by the number of sleeping hours per night.”[iii] In other words, those subjects who slept well required a lower heart rate to produce maximal power and oxygen uptake. The fact that power output was impacted by sleep duration while VO2 max was increased and HR max decreased among those who reported high sleep quality suggests that if one must choose between longer but interrupted sleep versus a few hours of deep sleep, shorter uninterrupted sleep might be preferable.
In another study conducted in 2022, Italian and German exercise physiologists investigated possible correlations between self-reported sleep, fatigue, and motivation and objective cardiovascular performance. Their regression modeling of the results found that “sleep was a significant predictor of VO2peak in males accounting for 20% of the variance, whereas physical performance seems more affected by fatigue in females.” This led them to state that “chronic inadequate and self-reported sleep quality seems to be one of the factors compromising cardiovascular performance in males.”[iv] The authors didn’t comment on why there might have been a difference between the results among men and women, but it would be interesting to see future trials exploring this.
It’s also insightful to incorporate cardiovascular metrics into exercise intensity ratios that offer clues about how fatigued your athletes are. A study led by exercise scientists from Deakin University in Australia examined how getting normal, restricted, or extended sleep alters heart rate indices in an endurance time trial performed over four consecutive days. They discovered that “Intensity ratios incorporating mean HR seem sensitive to effects of sleep duration on athlete readiness to perform.”[v] When the participants were well rested, their mean power-to-heart rate ratio stayed consistent, but when sleep was restricted, this increased. The change in this external-to-internal load ratio mimicked the effects of the elevated physical stressors that pro cyclists experienced during Grand Tour races, as noted by another paper published in the Journal of Sports Sciences.[vi] This suggests that sleep deprivation accelerates the onset of fatigue and forces the heart to work harder than usual.
Increasing RPE and Reducing Time to Exhaustion
A decline in sleep duration and/or quality doesn’t just reduce oxygen uptake or increase the heart rate needed to sustain performance but might also limit how far your clients can go in a session, how fast they do so, and how difficult they find it. Some studies have looked at how sleep deprivation over an extended period – such as one to three days – with no shuteye – impacts these measures. But it’s more likely that your athletes will occasionally get less slumber than they need than struggling with a chronic issue.
With this in mind, a French and German research team wondered what the consequences of reducing sleep duration for just one night might be. So they compared the performance of 20 runners in a 12-minute self-paced test after they’d had eight hours of sleep versus when they only got four. With less sleep, they totaled lower distances, recorded slower speeds and experienced increased physical discomfort. There were also changes to minute ventilation, VO2 max and core temperature, indicating “the deterioration of physical performance and physiological responses after PSD [partial sleep deprivation].”[vii]
Bruce J. Martin from Indiana University has been studying the connections between sleep and exercise for over 40 years. Like the co-authors of the 12-minute running test study, he has found that sleep loss reduces the body’s tolerance to exercise, particularly at moderate to high intensities. In one of his smaller studies, he asked eight participants to walk on a treadmill at 80% of their VO2 max. Those who were sleepless reduced their time to exhaustion by an average of 11%. Martin also noted that “sleep loss resulted in significantly greater perceived exertion,” which was supported by the Australian authors’ finding that the RPE to heart rate intensity ratio increased after sleep deprivation.[viii]
This observation brings up an important point. As significant as the impact of sleep deprivation on physiological markers may be, the psychological ramifications might be even greater. If one of your clients feels tired and this sensation intensifies during training, they’re more likely to slow down or stop earlier than usual. Plus, the knowledge that they didn’t sleep well the night before might lead to a self-limiting belief about how the workout will go.
Asking your clients to log their rate of perceived exertion (RPE) in TrainingPeaks might allow you to do a little detective work. If you notice a trend indicating that they’re finding a tempo run, lactate threshold ride or any other session harder than usual, it’s a signal to ask more questions. If objective data show their paces slipping or intensity dropping as well, poor sleep could be the culprit. This allows you to provide further education on the need for adequate rest and tips on sleep hygiene that could remedy the issue.
Resources
[i] Nizar Souissi et al., “Effects of One Night’s Sleep Deprivation on Anaerobic Performance the Following Day,” European Journal of Applied Physiology, May 2003, available online at https://pubmed.ncbi.nlm.nih.gov/12736846.
[ii] F Mougin et al., “Hormonal Responses to Exercise After Partial Sleep Deprivation and After a Hypnotic Drug-Induced Sleep,” Journal of Sports Sciences, February 2001, available online at https://pubmed.ncbi.nlm.nih.gov/11217014.
[iii] BM Antunes et al., “Sleep Quality and Duration are Associated with Performance in Maximal Incremental Test,” Physiology & Behavior, August 2017, available online at https://pubmed.ncbi.nlm.nih.gov/28502838.
[iv] Lucia Castelli et al., “Effect of Sleep and Fatigue on Cardiovascular Performance in Young, Healthy Subjects,” Physiology & Behavior, November 2022, available online at https://pubmed.ncbi.nlm.nih.gov/36108801.
[v] Spencer SH Roberts et al., “Monitoring Effects of Sleep Extension and Restriction on Endurance Performance Using Heart Rate Indices,” The Journal of Strength and Conditioning Research, December 2022, available online at https://journals.lww.com/nsca-jscr/Fulltext/2022/12000/Monitoring_Effects_of_Sleep_Extension_and.15.aspx.
[vi] Dajo Sanders et al., “Analysing a Cycling Grand Tour: Can We Monitor Fatigue with Intensity or Load Ratios?” Journal of Sports Sciences, June 2018, available online at https://pubmed.ncbi.nlm.nih.gov/29016241.
[vii] Wajdi Souissi, “Partial Sleep Deprivation Affects Endurance Performance and Psychophysiological Responses During 12-Minute Self-Paced Running Exercise,” Physiology & Behavior, December 2020, available online at https://pubmed.ncbi.nlm.nih.gov/32891607.
[viii] Bruce J Martin, “Effect of Sleep Deprivation on Tolerance of Prolonged Exercise,” European Journal of Applied Physiology and Occupational Physiology, December 1981, available online at https://link.springer.com/article/10.1007/BF02332962.
