Friday, April 8, 2016

Two Hours of Extra-Sleep Before Sleep Deprivation Minimize the Performance Decrements Due to 24h Sleep Deprivation

If you want to practice "vorschlafen" you may have to set your alarm-clock to tell you when to go to bed.
"Vorschlafen" is the German term for getting extra sleep the nights before an event of which you know that it will leave you sleep deprived. Sounds stupid? Well, there are studies which show that increasing sleep duration for around one week may influence cognitive performance during a subsequent sleep loss period, but aside from a study on the accuracy of tennis serves (Schwartz. 2015), their practical significance for athletes is obviously limited. Why? Since your ability to focus during cognitive tasks is - as important as it is - not a reliable marker of exercise performance... or at least a very unreliable one.

Against that background it's good that in a new study from the Universit√© de Lyon, Instead of testing cognitive performance markers such as the attention span of an individual, the researchers set out to "assess the effect of 6 nights of sleep extension on neuromuscular function and motor performance before and after [total sleep deprivation] TSD" (Arnal. 2016).
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So what did the scientists do? Well, the subjects, twelve healthy men (age: 32.2 ± 3.9 years, weight: 75.2 ± 6.2 kg, height: 176.9 ± 6.2 cm, body mass index: 23.7 ± 1.7 kg/m², physical activity: < 4 h per week) participated in two counterbalanced experimental conditions (cross-over design):
  • extended sleep aka EXT - mean (SE) h = 9.8 (0.1) time in bed and
  • habitual sleep aka HAB - mean (SE) h = 8.2 (0.1) time in bed.
The two conditions were seperated by a 6-week washout period. In each condition, subjects performed six nights of either EXT or HAB followed by two days in-laboratory.
Sleep Science Update: New Insights into the Effect of a Lack of Quality Sleep on Glucose Control and Diabesity Risk | more
"Two weeks before the first phase, a familiarization night was spent in the laboratory to avoid any first-night laboratory effects. Moreover, a control week where subjects spent 8 h in bed each night was realized before the first phase to avoid starting the experiment with the subjects in sleep debt. Time in bed during the control week was checked with actigraphy (Actiwatch TM, Cambridge Neurotechnology, Cambridgeshire, UK). The first phase consisted in 5 nights at home (N1 to N5) with sleep recorded by polysomnography. In HAB, subjects were instructed to maintain their habitual sleep time and spend at least 8 h in bed (bedtime between 22:30 and 23:00 and wake up at 07:00).

In EXT, they spent 10 h in bed between 21:00 and 07:00. In both conditions, volunteers maintained a wake time of 07:00 to accustom themselves to the waking time of 07:00 used during the second laboratory phase. Volunteers were allowed to maintain their usual lifestyles but needed to return the polysomnography equipment to the laboratory every morning" (Arnal. 2016).
The second phase was conducted in the laboratory and started at 17:00 after the 5th night at home
(standardized to be on Saturday for everyone for each condition). Subjects were familiarized
with the experimental protocol between 17:00 and 20:00. The day after was considered as the
baseline day during which neuromuscular testing was performed between 17:00 and 20:00 (D0).
Neuromuscular testing was repeated at the same time of day the following day, i.e. after 34-37 h
of continuous wakefulness (D1).
Figure 1: Overview of the two phases of the experimental protocol (Arnal. 2016).
With temperature and light control, abstinence exercise, caffeine, tobacco, alcohol and other psychoactive substances 48 hours before and during the laboratory phase and standardized meals and caloric intakes (2600 kcal/day), the scientists sought to limit confounding factors.
Figure 2: The fact that the effect size was individual should not surprise you and could be due to the fact that the extra 2h in bed may not have been spent sleeping in all subjects (Arnal. 2016).

Accordingly, they are quite confident to conclude that the small, but for some of the subjects highly significant inter-treatment difference they observed, namely...
  • a longer time to exhaustion in EXT compared to HAB (+3.9 ± 7.7% and +8.1 ± 12.3% at D0 and D1, respectively), as well as 
  • a lower rating of perceived exertion during exercise at D2 in the EXT compared to HAB (-7.2 ± 7.5%) group 
triggered these performance benefits, of which the scientists say that it was no induced by blunted central fatigue in response to total sleep deprivation (TSD), but rather a consequence of the beneficial effect the subjects' ratings of perceived exertion in the sleep deprived state.
Figure 3: Rates of perceived exertion before and after total sleep deprivation (Arnal. 2016).
Bottom line: "Vorschlafen" works - at least in some individuals. If you scrutinize the data in Figure 2 and take a look at the average rates of perceived exertion and their large error bars in Figure 3, you will have to admit, though, that a significant effect of sleeping 2h extra before being sleep deprived cannot be guaranteed.

Speaking of sleeping: Since the subjects simply spent 2h extra in bed, we don't know whether those who didn't respond (a) even got 2h extra sleep and whether (b) this extra sleep was quality sleep. Next to potentially existing inter-individual difference in the response to "vorschlafen", methodological shortcomings of the study may thus also explain the heterogeneity of the results | Comment on Facebook!
  • Arnal, et al. "Sleep Extension before Sleep Loss: Effects on Performance and Neuromuscular Function." Medicine & Science in Sports & Exercise (2016): Publish Ahead of Print - DOI: 10.1249/MSS.0000000000000925
  • Schwartz, Jennifer, and Richard D. Simon. "Sleep extension improves serving accuracy: A study with college varsity tennis players." Physiology & behavior 151 (2015): 541-544.