“Cognitive performance is negatively affected by time-since-waking and by sleep loss; therefore sports performance with a substantial cognitive component will be affected by both of these factors as well as by a circadian component parallel to body temperature” (Reilly and Waterhouse, 2008) 1. Introduction Circadian rhythms refer to the many biological changes in cycles that occur over a 24 hour period. The circadian rhythm of core temperature depends upon several interacting rhythms, endogenous and exogenous. Humans are considered to be diurnal creatures that adapt to changing environmental factors.
They can control body temperature despite vast changes in ambient temperature, (Reilly et al, 1997). The circadian “clock” is located in the suprachiasmatic nucleus (SCN), a distinct group of cells located in the hypothalamus. These cells are associated with thermoregulation, regulation and release of hormones (Reilly and Waterhouse, 2005). Temperature is often used as a marker rhythm due to its location and large endogenous component (Reilly et al., 2004). Many human performance measures follow closely to rectal temperature circadian rhythm (Reilly et al., 2000).
Many studies have shown that performance, both physiological and gross motor performance show a time of day effect. Flexibility has been found to be lower in the morning and higher in the evening. Lowest flexibility has been recorded between 05:00h and 09:00h in the morning and highest between 18:00h and 21:00h. (Atkinson, 1994; cited in Drust et al., 2005). It has also been found that stiffness in the knee joint is similar to that of body temperature, with the highest values being recorded in the evening (Wright et al.,; cited in Drust et al., 2005)
Conversely, fine motor skills such as balance, hand-steadiness and co-ordination appeared better in the morning (Reilly, 1997). Reilly (2000) concluded that the reason for this is due to low arousal levels, lower than the diurnal peak, and closer to optimal level of performance, According to Carrier and Monk; cited in Edwards et al., (2000) it is also due to less fatigue because of the decreased amount of time spent awake.
Optimal time of day for exercise is determined by endogenous rhythms, as well as the nature and intensity of exercise, the population concerned, environmental conditions, and individual phase types. Exogenous influences on circadian rhythm include environmental factors, light, heat, air ionization, eating patterns and social activities (Reilly 1990). The biological circadian rhythm that synchronises with the day-night cycle is termed as a diurnal rhythm.
Rhythm disturbances such as jet lag or shift work can be a major influential factor. Individuals traveling from one time zone to another, show a slow adjustment of the body clock due to the change into the new time, using new zeitgebers (Drust et al., 2005). Shift work has the same effect as transmeridian travel although they are not chronobiologically identical. An individual’s adjustment to nocturnal work is never fully complete, since the natural light-dark cycle remains unchanged despite changes in zeitgebers (Reilly and Waterhouse, 2005).
As with other biological components, individual differences should be considered. Between subjects components such as gender can affect results. The acrophase of larks (morning types) occur earlier than that of owls (evening types) (Reilly et al., 2004). Only 5% of the whole populations are classed as definite owls or larks. These differences can occur due to individual responses to the zeitgebers and the free running of the body clock (Reilly et al., 1997). By depriving individuals of light and other external time cues, also known as zeitgebers, it has been found that most biological clocks work on a 25-hour cycle rather than 24-hours. Zeitgebers allow synchronicity of the body (Reilly and Waterhouse, 2005). However, as sunlight or other bright lights can reset the SCN, biological cycles normally follow the 24-hour cycle of the sun.
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 ï¿½ SD for subjects that took part were height 1.75m ï¿½ 0.11 and body mass 72.61 kg ï¿½ 11.20. Subjects usually slept 8.09 ï¿½ 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).