Previous research by Spiegel et al (1999) has shown that sleep deprivation can slow glucose metabolism by as much as 30 to 40%. In the same study cortisol levels became elevated which can impair recovery in athletes. Another study into sleep, footballers and match performance concluded that a greater sleep duration the night before a game, resulted in higher levels of alertness and ‘leg-quickness’ i.e. less mental and physical fatigue (Martinez and Coyle, 2007) These findings suggest that sleep deprivation will have a negative effect on performance.
The purpose of this study is to look at the effect circadian rhythms (measured by oral temperature) has on dart throwing ability. It will also look to see if partial sleep deprivation has an effect on the same task.
2. Methodology
2.1 Subjects and general protocol
Subjects were acquired from students undertaking the environmental physiology module, level 3. Subjects were asked to complete a questionnaire prior to tests to identify chronotype, languidity/vigorousness and flexibility/rigidity.
The study was conducted over 2 days of familiarisation to the study and 2 experimental days, each separated by at least three days. Subjects were asked to conduct testing during non-sporting activity days. 58 subjects (42 male and 16 female) were selected from a total of 71, 13 subjects were deleted due to incomplete data. The mean ± SD for subjects that took part were height 1.75m ± 0.11 and body mass 72.61 kg ± 11.20. Subjects usually slept 8.09 ± 1.03 hours each night.
Each subject either started with normal sleep (N) or sleep deprivation (SD) first, depending on what was stated on their data collection sheet, this was necessary to counterbalance the experimental sessions. All subjects were asked to undertake the experiment indoors and were required to measure a distance of 2.37m from the centre of the target accurately with a tape measure.
2.2 Detailed protocol and measurements made
Each subject completed two familiarisation days. Oral temperature, performance, tiredness and subjective alertness were recorded every 4 hours starting at 08:00h and ending at 20:00h for the first day, then again at 08:00h the following day. Familiarisation was conducted to withdraw the possibility of a learning effect.
After the familiarisation days were complete, subjects were asked to record: oral temperature, performance and subjective tiredness / alertness every 4 hours between 08:00h and 24:00h. Tiredness and alertness was measured on a visual analogue scale, a scale of 0-10, where 0 indicates not at all and 10 indicates a lot. The data sheets also indicted to subjects whether they should conduct the first day of the study after normal or deprived sleep. The evening prior to the N experimental day subjects were required to retire at 23:30h and awaken at 0730h. Prior to the SD day, subjects were required to stay awake until 03:30h and awaken at 07:30h. Before the tests, subjects completed a composite morningness questionnaire to assess chronotype; 3 participants were characterised as morning types, 4 were evening types, and 51 participants were intermediate. The languidity/vigorousness and flexibility/rigidity questionnaire revealed that 44 participants were characterised under languidity, 14 were vigorousness, 50 were flexible and 8 were characterised under rigidity.
For the performance test participants were instructed to complete 20 throws of a dart (Unicorn Precision darts, 24 g, Unicorn Products Ltd, England) at a standardized target (see figure 1)
Variables recorded were body temperature (oC) using a thermometer (Omron MC-63B, Matsusaka, Japan) performance (N/SD 4-17 and N/SD zero) and tiredness and alertness, These variables were recorded at the start of each session prior to undertaking the test. Before temperature was recorded the subjects were asked to sit quietly for 10 minutes without eating or drinking. The results were recorded on the data collection sheet (appendix 1).
2.3 Statistical analysis
The results were collated for the class and analysed. Data were analysed by using the Statistical Package for Social Sciences (SPSS) for Windows. A two way ANOVA with repeated measures was used to investigate if any significant differences were apparent between N/SD4-17 and N/SD zero for the 5 times of day. According to Mauchly’s test of sphericity, the degrees of freedom were corrected in the normal way, using Huynh-Feldt (>0.75) or Greenhouse geisser (<0.05). For analysis of performance variables the first and last three dart throws were not included.
3. Results
(See tables 1 & 2) Oral temperature showed a diurnal variation with lowest values in the morning between 08:00h- 12:00h and highest values in the evening between 16:00-20:00h; p>0.05 (see figure 2). Results for performance F 1, 58 = 24.485, p < 0.05 and for time; F 5, 290 = 16.494, p < 0.05 both indicate a significant difference. There was no significant interaction between performance and time F 5, 290 = 0.678 p > 0.05. Mean difference of performance between normal and deprived sleep was 7.516, p < 0.05 (see figure 2) thus showing that there is a significant difference between the two groups. N zero and SD zero results were also analysed (figure 3): performance F 1, 58 = 29.825, p < 0.05 and for time; F 5, 290 = 6.815, p < 0.05. This shows a significant difference.
4. Discussion and Conclusion.
The aim of this study was to explore changes occurring between performance and temperature over different times throughout the day. It also looked to see if sleep deprivation had an effect on performance. The graphs indicate that performance peaks in the evening, which for this type of performance variable would not be expected as it is a fine motor skill test. Hand steadiness is at an optimum level for performance due to arousal levels being at their lowest in the diurnal peak in the morning, which helps increase accuracy (Reilly et al., 1997).
Figure 2 shows no significant variation in temperature over the two experimental days (F=0.863) On both days temperature follows time of day differences peaking at 1600h (normal sleep at 36.2°C and deprived sleep at 36.1°C) Acrophase and amplitude of temperature remain unchanged during exercise. Acrophase in larks occur earlier than that of owls (Reilly et al., 2004). There was no significant correlation between temperature and chronotype (t57= -4.708, p < 0.05) (figures 15 and 16) The two separate conditions were not individually analysed for biorhythm and standard deviation, a mean was taken from both days, biorhythm and standard deviation for temperature can be found in Figure 6.
There were significant differences between N_4-17 and SD_4-17 (F= 25.485) and N_zero and SD_zero (F= 29.825), which was expected, as previous research had shown sleep deprivation to impair performance. Figures 3 and 4 show that performance means (4-17 and zero respectively) were affected by time of day differences on both days, showing that circadian rhythm affects performance. Figures 9-12 show mean, standard deviations and biorhythms for performance (4-17 and zero). A factor which should however be considered is that of motivational levels. Reilly et al., (2004) stated that, motivational levels affect performance levels (Reilly et al., 2004); this factor could affect this study as participants were asked to take part in a repetitive test. Another factor that should be taken into account with this type of study is the build up of ‘fatigue’ due to time awake (Carrier and Monk 2000). Obviously during the sleep deprived day participants would feel greater fatigue, but during the ‘normal’ day, fatigue due to time awake cannot be ignored. This could be one of the reasons why some of the data was seen as unreliable. Figures 21-24 show correlations between chronotype and the performance variables. There was no obvious correlation between chronotype and N_4-17 (t57 = -9.383, p < 0.05) and SD_4-17 (t57 = -6.067, p < 0.05).
Figure 5 shows time of day differences for tiredness and alertness scores. SD_tiredness scores were significantly higher then N_tiredness (F=61.211) and SD_alertness scores were significantly lower that N_alertness (F=43.122). Figures 7-10 show mean, standard deviations and biorhythm for tiredness and alertness variables. Figures 17-20 show the correlation of chronotype and the variables. Tiredness showed a significant negative correlation with chronotype (N_tiredness, t57 = 26.235, p > 0.05 and SD_tiredness, t57 = 25.702, p > 0.05) and alertness showed a significant positive correlation with chronotype (N_alerness, t57 = 31.420, p > 0.05 and SD_alertness, t57 = 33.467, p > 0.05). Reilly et al. (2004) suggests there is a rhythm in arousal and alertness, which means that even during wakefulness individuals are ready for different performance types. The hormone, melatonin synthesised by the pineal gland affects alertness, by the amount released at different times during the day. It’s been suggested that levels of hormones circulating the body can affect performance (Reilly et al., 2004). The change in alertness scores shows that sleep deprivation reduces alertness for the rest of the day, although time of day differences remain unchanged.
These findings suggest that partial sleep deprivation impairs cognitive performance. The conclusions drawn from this study are limited to fine motor skill performance, such as dart throwing and other activities which involve similar processes. However it would be interesting to do further research to see if these findings can be transferred to other activities which require explosive power (sprinting, long jump) or endurance (long distance running), to confirm the findings of Martinez and Coyle’s (2007) study into sleep duration and physical and mental fatigue.
In summary, it should, firstly, be noted that the data was found to be unreliable, this indicates that the results from the ANOVA’s may also not be accurate, however, it can still be stated that partial sleep deprivation is likely to impair cognitive performance.
5. References
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Figure 1. Target used for dart throwing exercise.
Table 1. Means for each of the variables.
Table 2. Mesor, amplitude, acrophase, % rhythm and p values for each of the variables
Figure 2. Mean temperature
Figure 3. Mean 4-17 Performance
Figure 4. Mean Zero Performance
Time of Day
Time of Day
Figure 5. Mean Tiredness and Alertness on both experimental days.
Figure 6 Mean, standard deviations and biorhythm for temperature
Figure 7/8 Mean, SD and Biorhythm for N / SD tiredness
Figure 9/10 Mean, SD and biorhythm for N / SD Alertness
Time of Day Time of Day
Figure 11/12 Mean , SD and biorhythm for N / SD 4-17
Time of Day Time of Day
Figure 13/14 Mean, SD , Biorhythm for N /SD zero
Figure 15/ 16. N and SD temperature against chronotype
Figure 17/18. N and SD tiredness against chronotype
Chronotype Chronotype
Figure 19/20. N and SD Alertness against chronotype
Figure 21/22 N and SD 4-17 scores against chronotype
Chronotype Chronotype
Figure 23/24 N and SD zero scores against chronotype
Appendix
Appendix one Morningness questionnaire.
