University of Groningen Grasping light Lok, Renske

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University of Groningen

Grasping light

Lok, Renske

DOI:

10.33612/diss.173352710

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Publication date:

2021

Link to publication in University of Groningen/UMCG research database

Citation for published version (APA):

Lok, R. (2021). Grasping light: Mental and physiological responses to illumination. University of Groningen.

https://doi.org/10.33612/diss.173352710

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CHAPTER 8

Renske Lok

1,2

_{, Giulia Zerbini}

3

_{, Marijke C.M. Gordijn}

4

_,

Domien G.M. Beersma

1

_{, Roelof A. Hut}

1

1_{University of Groningen, Chronobiology unit, Groningen Institute for}

Evolutionary Life Sciences, PO box 11103, 9700CC, Groningen, the Netherlands.

2_{University of Groningen, Campus Fryslân, Wirdumerdijk 34, 8911 CE,}

Leeuwarden, the Netherlands.

3_{University of Augsburg, Department of Medical Psychology and Sociology,}

Augsburg, Germany

4_{Chrono@Work B.V., Frieschestraatsweg 213, 9743 AD, Groningen, The}

Netherlands

Scientific Reports (2020), 10(1):16088

GOLD, SILVER OR BRONZE:

CIRCADIAN VARIATION

STRONGLY AFFECTS

PERFORMANCE IN

OLYMPIC ATHLETES.

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Gold, Silver or Bronze: Circadian variation strongly affects performance in Olympic athletes.

CHAPTER 8

Abstract.

The circadian system affects physiological, psychological, and molecular mechanisms in the body, resulting in varying physical performance over the day. The timing and relative size of these effects are important for optimizing sport performance. In this study, Olympic swim times (from 2004 to 2016) were used to determine time-of-day and circadian effects under maximal motivational conditions. Data of athletes who made it to the finals (N = 144, 72 female) were included and normalized on individual levels based on the average swim times over race types (heat, semifinal, and final) per individual for each stroke, distance and Olympic Venue. Normalized swim times were analyzed with a linear mixed model and a sine fitted model. Swim performance was better during finals as compared to semi-finals and heats. Performance was strongly affected by time-of-day, showing fastest swim times in the late afternoon around 17:12 h, indicating 0.32% improved performance relative to 08:00 h. This study reveals clear effects of time-of-day on physical performance in Olympic athletes. The time-of-day effect is large, and exceeds the time difference between gold and silver medal in 40%, silver and bronze medal in 64%, and bronze or no medal in 61% of the finals.

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8 Introduction.

Circadian rhythms, regulated by the Suprachiasmatic Nucleus (SCN), influence many aspects associated with physiological performance, such as muscle strength 402_{, and muscle flexibility}403_{, in addition to perceptual and cognitive}

aspects of performance 404_{. Strong correlations between physical performance}

and (circadian) variation in core body temperature (CBT) have been assessed, with optimal physical performance coinciding with the peak in CBT in the early evening

405–408_{. Passive heating of muscles improves physical performance, indicating that}

either thermoregulation409_{, muscle temperature}410,411_{or both influence physical}

performance, although other factors (such as insulin, cortisol, total and free testosterone, oxygen uptake, glucose, growth hormone, norepinephrine 412_{, and}

melatonin release 409_{) also play a role}413_{. Depending on the type of exercise (e.g.}

short-term or long-term, aerobic or anaerobic, individual sport or team sport), the involvement of psychological aspects (e.g. motivation, concentration), external conditions (e.g. cold vs. hot environments), and time-of-day effects on physical performance vary 409,414,415_{. Additionally, variations in chronotype (which describes}

an individual’s biological optimal timing for activity and sleep), relate to substantial variations in peak performance time 416,417_.

Studies investigating these effects on elite athletes during high-level competitions are scarce. The Olympic venues are leading international sporting events, with thousands of athletes from around the world. The country selected to host the Olympics, sometimes adjusts race times to accommodate prime-broadcasting times in other continents. As a result, athletes are often required to perform at different, and sometimes unusual, times of day. This variation can be used to analyze time-of-day effects on physical performance in professional, extremely motivated male and female athletes. The goal of this study was to determine if Olympic athletes are affected by circadian fluctuations in physical performance, by analyzing Olympic swim data from the Games of Athens (2004), Beijing (2008), London (2012) and Rio de Janeiro (2016). Swimming requires minimal aiding materials (such as bikes, shoes) that could induce variation within and between athletes, and water temperature is mandated to vary within 25 to 28 degrees Celsius (by the Fédération internationale de natation), which forces water temperatures to be within the same range between Olympic Venues. Swimming is therefore less likely to be influenced by confounding environmental effects (such as environmental temperature, humidity, wind etc), and, of all sports types, we therefore expect that Olympic swim performance may reveal a very clean signal of daily variation in physical (e.g. muscle) performance. Our results can lead to strategies to significantly improve individual swimming performance.

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CHAPTER 8

Materials and methods.

Data collection. All data concerning participating athletes, swim schedules and

pertinent finish times of Olympic venues of Athens, Beijing, London and Rio de Janeiro were obtained from https://www.olympic.org/ (publically accessible from official reports). Athens Olympic swim schedules were analyzed using Eastern Standard Time, Beijing swim schedules using China Standard Time, London swimming schedules using Greenwich Mean Time, and Rio de Janeiro using Brasilia Standard Time. Olympic swim contests exist of three race types: heats (varying number of competing athletes), from which the 16 fastest finish times can partake in semi-finals, after which the 8 highest ranked athletes participate in finals. To ensure a homogenous sample of athletes, only athletes that qualified for the finals were included, resulting in a total of 144 athletes (72 female) per Olympic venue. The breakdown of athletes per Olympic Venue can be found in Fig. S2. Data of all four Olympic venues consisted of four different strokes in two or three distances, resulting in nine different combinations: backstroke (100 and 200 m), breaststroke (100 and 200 m), butterfly (100 and 200 m), and freestyle (50, 100, and 200 m). Both at the Olympic venue of Athens and Beijing, one finalist was disqualified (at the 200 m breaststroke and 100 m freestyle respectively), resulting in inclusion of 1722 data points in total for the current analysis.

Data analysis (1): Effects of race type and time-of-day. To exclude effects

of novel training methods, techniques and equipment (e.g. shark suits used in Beijing418_{), data were normalized as follows: first the average swim time over race}

type (heats, semifinal and final), was calculated per individual, stroke, distance, and per Olympic venue; then the percentage difference between each race swim time (heat, semifinal and final) and the average swim time was calculated for each combination of stroke and distance. This normalization method allowed for inclusion of all available swim strokes and distances in a single linear mixed model. To assess differences between race type, normalized swim scores were plotted separately for heats, semi-finals and finals per Olympic venue.

Data analysis (2): Time-of-day. To accommodate differences in race timing (finals

in the morning in Beijing, whereas held in the evening in Athens and London), we compared swim times between all four Olympics venues in a linear model (R-studio, version 1.0.136), with swim time (as calculated (1)) as dependent variable and type of race (heat, semifinal or final), Olympic venue location, and time-of-day as independent variables. Subject identity was included as random effect, to control for between-subject variation. The data distribution was normal (the Shapiro-Wilk normality test (w=0.979, p

<

2.2e-16_{) justifying usage of the linear mixed}

model. To visualize time-of-day effects, the residual variation after subtraction of the components race type, Olympic venue, individual, and intercept of the linear mixed model from the normalized data was calculated. This residual variation was

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8

plotted against local time at Olympic venue (h) and the sine function that resulted

from the linear mixed model was plotted through the data.

Data analysis (3): Effect size. The relative magnitude of the time-of-day effect

was assessed by comparing it to the relative time difference between the first and the second place, which was calculated by dividing their time difference by second finishing time.

Results.

Effects of race type and time-of-day: Data analysis on within subject normalized

data revealed that race type significantly affected swim performance (Fig. 1). Heats were 0.5% slower than semi-finals, which in turn were 0.2% slower than finals, in females (F2,850=225.05, p

<

2·10-16) and males (F2,850=220.07, p

<

2·10-16). There was a

significant interaction between Olympic venue and race type (F9,850=4.71, p

<

1·10 -6_{) for females and males (F}

9,850=1.97, p=0.039), suggesting that performance

differences between race types varied between Olympic venue locations. The percentage difference in swim times between heats and finals in Beijing (0.60%, average of males and females) was much smaller than in Athens and in London (0.99% and 0.93% respectively). A major difference between those Games is that the finals in Beijing were held at about the time of the heats in London and Athens, while the heats in Beijing were held at about the time of the finals in London and Athens. This scheduling difference is an interesting opportunity to disentangle motivation (faster swim times in the finals) from possible time-of-day effects. In fact, if time-of-day did not play a role, one would expect the same percentage difference in swim times between heats and finals in Beijing as in Athens and London. To test for time-of-day effects we fitted a sine model.

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Gold, Silver or Bronze: Circadian variation strongly aﬀ ects performance in Olympic athletes.

CHAPTER 8

Figure 1: Normalized swim scores of Olympic venues in Athens (A,E), Beijing (B,F), London (C,G) and Rio de Janeiro (D,H). Data is plotted as mean ± standard error of the mean, with grey dots representing swim times collected during heats, and white and black dots representing swim data collected during semi-fi nals and fi nals, respectively. Top row (A-D) indicates male fi nish times, while bottom row (E-H) depicts fi nish times of female athletes.

The linear mixed model (in which normalized fi nish times were explained by race type, Game venue and time-of-day) indicated signifi cant eff ects of race type

(F2,1719=440.26, p

<

1·10-15), Olympic Venue (F3,1719=0.017, p=0.05), and time-of-day

(F2,1719=28.54, p

<

1·10-8).

The sine fi tted model (period=24 h; F2,1719=11.9393, p

<

1·10-5; Fig. 2) predicted that

swim performance would be worst in the early morning (5:12 h), and best in the late afternoon (17:12 h). There was no signifi cant diff erence depending on sex, therefore the same sine wave was plotted for both males and females (see Fig. S1 for the data plotted separately for males and females).

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8

Figure 2: Olympic swim performance depends on time-of-day. Residual variation of individually

normalized data of heats, semi-fi nals and fi nals (corrected for intercept, type of race, Olympic venue, and individual diff erences, as quantifi ed by a linear mixed model), was fi tted by a 24-h period sine function and plotted against local time at the Olympic venue location (h). Data represent mean ± SEM. (A) Data collected during heats (green), semi-fi nals (orange) and fi nals (red). (B) Black dots indicate average fi nish times in 3-h bins (B). Sine fi t (period=24 h, black curve) describing variation in swim performance over the day, indicates worst performance in the early morning and best performance in the late afternoon (dotted lines).

The relative magnitude of time-of-day eff ects: The amplitude range of the

fi tted sine wave representing the eff ects of time-of-day is 0.37% (peak-to-trough distance, Fig. 2). In 40% of the fi nals, this time-of-day eff ect was larger than the time diff erence between gold or silver medal fi nishing times (Table S1). Moreover, time-of-day eff ects exceed the time diff erence between the silver and bronze medal in 64% of the fi nals, and the time diff erence between bronze or fourth place in 61% of the fi nals (Table S2, S3).

Discussion.

The current analysis reveals that Olympic athletes always perform better in fi nals compared to semi-fi nals and heats (probably due to motivational diff erences) and that physical performance assessed in Olympic athletes was signifi cantly aff ected by time-of-day. Best performance was determined in the late afternoon. This indicates that, despite of elaborate training schedules ranging from morning to evening hours, time-of-day still aff ects professional athletes’ performance. Physical performance is therefore not determined by training only, but also by the

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CHAPTER 8

endogenous circadian system. Some studies indicate that physical performance at a specific time-of-day can improve after repeatedly training at that time-of-day, suggesting that the trough observed in morning performance can be partially counteracted 419_{. This time-of-day effect may depend on CBT levels. On one}

hand, cold water immersion in the afternoon decreases CBT levels to morning levels, as well as it decreases evening- to morning performance levels. On the other hand, passive increase (i.e. variation in environmental temperature) in CBT rescues impaired morning performance 409,413,420_{, similar to hot water immersion} 413_{and active warm-up}421,422_{, that also improve time-of-day related decrements in}

performance, by increasing CBT or muscle temperature levels.

Internal clock time also influences physical performance, causing early chronotypes to perform best around mid-day, intermediate chronotypes around mid-afternoon, and late chronotypes in the evening 417_{. It is therefore possible that}

morning races benefit early types, while evening races benefit later types. Swim training times are often scheduled in the early morning, therefore a selection bias towards earlier chronotypes can exist, as has been determined in other sports 423_.

Later chronotypes are also associated with more diurnal variation in performance, which might cause an additional selection pressure towards earlier chronotypes, particularly in Olympic athletes 417_{. The optimal performance peak in finish times}

analyzed here occurs relatively early compared to the peak in CBT timing 402,424,425_,

which may indicate an over-representation of early chronotypes (with earlier CBT peak times) among Olympic swimmers.

Various circadian rhythms in the body may contribute to time-of-day variation in physical performance. Limb movement speed and muscle strength depend on time-of-day 402_{, as well as muscle flexibility and grip strength}403_{. Improved performance}

coincides with lower levels of insulin, cortisol, total and free testosterone, and higher oxygen uptake, aerobic mechanical power output, metabolic rate and concentrations of glucose and growth hormone 412_{. Moreover, factors such as}

sleep duration, -quality and sleep inertia influence performance 426,427_{. Here we}

could not collect data on sleep in athletes prior and during the Olympics and we can therefore not disentangle between circadian and homeostatic effects. The optimum in physical performance might therefore depend on a complex combination of mental performance, time awake, circadian rhythm in muscle cells and mitochondrial oxygen consumption.

The current analysis only includes individuals who made it to the finals, which may have induced a bias to more successful athletes. Athletes that suffer more from time-of-day effects, might have been excluded because they did not reach the finals, resulting in an underestimation of the time-of-day effect. Shorter recovery time is also associated with impaired physical performance 428,429_{. In London and}

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8

in Beijing, recovery time after heats was 13.5 hours on average. Yet, differences

in performance between heats and semi-finals are smaller in Beijing compared to other Olympic venues, suggesting that time-of-day effects counteracted beneficial effects of longer recovery time, including a night sleep.

Our analysis concerns only swimmers and therefore generalization to other sports might be difficult. However, we chose to analyze specifically this sport because swimming requires minimal aiding materials (such as bikes or shoes) that could induce variation within and between athletes, while water temperature varies within a relatively narrow range, further minimizing confounding factors. In addition, swimming employs muscles in both arms and legs. Since there is no indication that muscle clocks differ over the body between arms and legs, we expect that this circadian effect on swim performance is actually reflecting a general variation over the day in muscle performance, and could therefore affect other sport performance in a similar manner.

In 40% of the races, the time-of-day effect is bigger than the difference between finishing first or second. Moreover, the time-of-day effect exceeds the time difference between silver and bronze in 64% of the finals, and the time difference between bronze or fourth place in 61% of the finals. In upcoming Olympic venues, swimmers and other athletes may have to perform at times of day that do not coincide with their circadian peak performance. Shifting peak performance to better match each race type is difficult, since heats and semi-finals for instance are often on the same day in the morning and in the afternoon/evening. Depending on one’s goal (reaching the semi-final or winning the final) athletes may consider to adjust their circadian system such that their peak performance better matches race timing accordingly.

Author contributions.

R.L and G.Z. performed data collection. R.L. analyzed data and drafted the original manuscript. G.Z.,

M.C.M.G., D.G.M.B., R.A.H. reviewed and edited the original

manuscript.

Funding.

This research was funded by the University of Groningen Campus Fryslân (Grant number 001110939; cofinanced by Philips Drachten and Provincie Fryslân)

Competing interests.

Dr. Gordijn reports receiving consultancy fees from Philips Consumer Lifestyle, not related to the submitted work. The other authors do not report any competing interests.

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CHAPTER 8

Data availability.

Original data is publically accessible at https://www.olympic.org/. Analyzed data and R codes can be accessed by contacting the corresponding author. The complete dataset (original and analyzed) and R codes are also available at the data repository of the University of Groningen.

Supplementary information

Figure S1. Swim performance as a function of time of day in male and female athletes. Residual

variation of individually normalized data of heats, semi-fi nals and fi nals (containing type of race, Olympic Game) plotted as percentage diff erence in fi nishing time, was fi tted by a 24-h period sine function and plotted against local time at the Olympic Game location (h). Data represent mean ± SEM. Data collected during heats (green), semi-fi nals (orange) and fi nals (red) in male (A) and female (B) athletes. Sine fi t (period=24 h, black curve) describing variation in swim performance over the day, indicates worst performance in the late morning and best performance in the late evening (dotted lines). Since normalized performance did not diff er in phase and amplitude between genders (F2,1719=0.84, p=0.53), the

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8

Figure S2: Breakdown of the represented countries at the Olympic Games of Athens, Beijing, London and Rio de Janeiro.

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CHAPTER 8

Table S1: Overview of first or second place finish times at the Olympic Games of Athens, Beijing, London and Rio de Janeiro. In 40% of the finals, the difference between finishing first or second is

smaller than the variance predicted by time of day (including one joint first place).

Stroke Distance Olympic

venue Gender First place finish time

(s)

Second place

finish time (s) Difference (%) Time of day

effect (0.369%) bigger?

Backstroke 100 Athens Female 60.37 60.50 0.215 Yes Backstroke 100 Beijing Female 58.96 59.19 0.389 No Backstroke 100 London Female 58.33 58.68 0.596 No Backstroke 100 Rio de

Janeiro Female 58.45 58.75 0.511 No Backstroke 100 Athens Male 54.06 54.35 0.534 No Backstroke 100 Beijing Male 52.54 53.11 1.073 No Backstroke 100 London Male 52.16 52.92 1.436 No Backstroke 100 Rio de

Janeiro Male 51.97 52.31 0.650 No Backstroke 200 Athens Female 129.19 129.72 0.409 No Backstroke 200 Beijing Female 125.24 126.23 0.784 No Backstroke 200 London Female 124.06 125.92 1.477 No Backstroke 200 Rio de

Janeiro Female 125.99 126.05 0.048 Yes Backstroke 200 Athens Male 114.95 117.35 2.045 No Backstroke 200 Beijing Male 113.94 114.33 0.341 Yes Backstroke 200 London Male 113.41 113.78 0.325 Yes Backstroke 200 Rio de

Janeiro Male 113.62 113.96 0.298 Yes Breaststroke 100 Athens Female 66.60 67.20 0.893 No Breaststroke 100 Beijing Female 65.17 66.73 2.338 No Breaststroke 100 London Female 65.47 65.55 0.122 Yes Breaststroke 100 Rio de

Janeiro Female 64.93 65.50 0.870 No Breaststroke 100 Athens Male 60.08 60.25 0.118 Yes Breaststroke 100 Beijing Male 58.91 59.20 0.490 No Breaststroke 100 London Male 58.46 58.93 0.454 No Breaststroke 100 Rio de

Janeiro Male 57.13 58.69 2.658 No Breaststroke 200 Athens Female 143.37 143.60 0.160 Yes Breaststroke 200 Beijing Female 140.22 142.05 1.288 No Breaststroke 200 London Female 139.59 140.72 0.803 No

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8

(s)

Second place

effect (0.369%) bigger?

Breaststroke 200 Rio de

Janeiro Female 140.30 141.97 1.176 No Breaststroke 200 Athens Male 129.44 130.88 2.658 No Breaststroke 200 Beijing Male 127.64 128.88 0.798 No Breaststroke 200 London Male 127.28 127.43 0.020 Yes Breaststroke 200 Rio de

Janeiro Male 127.46 127.53 0.055 Yes Butterfly 100 Athens Female 57.72 57.84 0.207 Yes Butterfly 100 Beijing Female 56.73 57.10 0.648 No Butterfly 100 London Female 55.98 56.87 1.565 No Butterfly 100 Rio de

Janeiro Female 55.48 56.46 1.736 No Butterfly 100 Athens Male 51.25 51.29 0.078 Yes Butterfly 100 Beijing Male 50.58 50.59 0.020 Yes Butterfly 100 London Male 51.21 51.44 0.447 No Butterfly 100 Rio de

Janeiro Male 50.39 51.14 1.467 No Butterfly 200 Athens Female 126.05 126.36 0.245 Yes Butterfly 200 Beijing Female 124.18 124.72 0.433 No Butterfly 200 London Female 124.06 125.25 0.950 No Butterfly 200 Rio de

Janeiro Female 124.85 124.88 0.024 Yes Butterfly 200 Athens Male 114.04 114.56 0.454 No Butterfly 200 Beijing Male 112.03 112.70 0.594 No Butterfly 200 London Male 112.96 113.01 0.044 Yes Butterfly 200 Rio de

Janeiro Male 113.36 113.40 0.035 Yes Freestyle 50 Athens Female 24.58 24.89 1.245 No Freestyle 50 Beijing Female 24.06 24.07 0.042 Yes Freestyle 50 London Female 24.05 24.28 0.947 No Freestyle 50 Rio de

Janeiro Female 24.07 24.09 0.083 Yes Freestyle 50 Athens Male 21.93 21.94 0.046 Yes Freestyle 50 Beijing Male 21.30 21.45 0.699 No Freestyle 50 London Male 21.34 21.54 0.929 No

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CHAPTER 8

(s)

Second place

effect (0.369%) bigger?

Freestyle 100 Athens Female 53.84 54.16 0.591 No Freestyle 100 Beijing Female 53.12 53.16 0.075 Yes Freestyle 100 London Female 53.00 53.38 0.712 No Freestyle 100 Rio de

Janeiro Female 52.70 52.70 0.000 Yes Freestyle 100 Athens Male 48.17 48.23 0.124 Yes Freestyle 100 Beijing Male 47.21 47.32 0.232 Yes Freestyle 100 London Male 47.52 47.53 0.021 Yes Freestyle 100 Rio de

Janeiro Male 47.58 47.80 0.460 No Freestyle 200 Athens Female 118.03 118.22 0.161 Yes Freestyle 200 Beijing Female 114.80 115.00 0.174 Yes Freestyle 200 London Female 113.61 115.58 1.704 No Freestyle 200 Rio de

Janeiro Female 113.73 114.08 0.307 Yes Freestyle 200 Athens Male 104.71 105.23 0.494 No Freestyle 200 Beijing Male 102.96 104.85 1.803 No Freestyle 200 London Male 103.14 104.93 1.706 No Freestyle 200 Rio de

Janeiro Male 104.65 105.20 0.523 No

Table S2: Overview of second (silver medal) or third place (bronze medal) finish times at the Olympic Games of Athens, Beijing, London and Rio de Janeiro. In 64% of the finals, the difference

between finishing second or third is smaller than the variance predicted by time of day (including three joint second places).

venue Gender Second place finish

time (s)

Third place

effect (0.369%) bigger?

Backstroke 100 Athens Female 60.50 60.88 0.624 No Backstroke 100 Beijing Female 59.19 59.34 0.253 Yes Backstroke 100 London Female 58.68 58.83 0.255 Yes Backstroke 100 Rio de

Janeiro Female 58.75 58.76 0.017 Yes Backstroke 100 Athens Male 54.35 54.36 0.018 Yes

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8

time (s)

Third place

effect (0.369%) bigger?

Backstroke 100 London Male 52.92 52.97 0.094 Yes Backstroke 100 Rio de

Janeiro Male 52.31 52.40 0.172 Yes Backstroke 200 Athens Female 129.72 129.88 0.123 Yes Backstroke 200 Beijing Female 126.23 127.13 0.708 No Backstroke 200 London Female 125.92 126.55 0.498 No Backstroke 200 Rio de

Janeiro Female 126.05 127.54 1.168 No Backstroke 200 Athens Male 117.35 117.56 0.179 Yes Backstroke 200 Beijing Male 114.33 114.93 0.522 No Backstroke 200 London Male 113.78 113.94 0.140 Yes Backstroke 200 Rio de

Janeiro Male 113.96 113.97 0.009 Yes Breaststroke 100 Athens Female 67.15 67.16 0.015 Yes Breaststroke 100 Beijing Female 66.73 67.34 0.906 No Breaststroke 100 London Female 65.55 66.46 1.369 No Breaststroke 100 Rio de

Janeiro Female 65.50 65.69 0.289 Yes Breaststroke 100 Athens Male 60.25 60.88 1.035 No Breaststroke 100 Beijing Male 59.20 59.37 0.286 Yes Breaststroke 100 London Male 58.93 59.49 0.941 No Breaststroke 100 Rio de

Janeiro Male 58.69 58.87 0.306 Yes Breaststroke 200 Athens Female 143.6 145.82 1.522 No Breaststroke 200 Beijing Female 142.05 143.02 0.678 No Breaststroke 200 London Female 140.72 140.92 0.142 Yes Breaststroke 200 Rio de

Janeiro Female 141.97 142.28 0.218 Yes Breaststroke 200 Athens Male 130.80 130.87 0.053 Yes Breaststroke 200 Beijing Male 128.88 128.94 0.047 Yes Breaststroke 200 London Male 127.43 128.29 0.670 No Breaststroke 200 Rio de

Janeiro Male 127.53 127.7 0.133 Yes Butterfly 100 Athens Female 57.84 57.99 0.259 Yes Butterfly 100 Beijing Female 57.10 57.25 0.262 Yes Butterfly 100 London Female 56.87 56.94 0.123 Yes Butterfly 100 Rio de

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CHAPTER 8

time (s)

Third place

effect (0.369%) bigger?

Butterfly 100 Beijing Male 50.59 51.12 1.037 No Butterfly 100 London Male 51.44 51.44 0.000 Yes Butterfly 100 Rio de

Janeiro Male 51.14 51.14 0.000 Yes Butterfly 200 Athens Female 126.36 128.04 1.312 No Butterfly 200 Beijing Female 124.70 126.26 1.236 No Butterfly 200 London Female 125.25 125.48 0.183 Yes Butterfly 200 Rio de

Janeiro Female 124.88 125.2 0.256 Yes Butterfly 200 Athens Male 114.56 115.52 0.831 No Butterfly 200 Beijing Male 112.70 112.97 0.239 Yes Butterfly 200 London Male 113.01 113.21 0.177 Yes Butterfly 200 Rio de

Janeiro Male 113.4 113.62 0.194 Yes Freestyle 50 Athens Female 24.89 24.91 0.080 Yes Freestyle 50 Beijing Female 24.07 24.17 0.414 No Freestyle 50 London Female 24.28 24.39 0.451 No Freestyle 50 Rio de

Janeiro Male 21.41 21.49 0.372 No Freestyle 100 Athens Female 54.16 54.4 0.441 No Freestyle 100 Beijing Female 53.16 53.39 0.431 No Freestyle 100 London Female 53.38 53.44 0.112 Yes Freestyle 100 Rio de

Janeiro Female 52.70 52.99 0.547 No Freestyle 100 Athens Male 48.23 48.56 0.680 No Freestyle 100 Beijing Male 47.32 47.67 0.734 No Freestyle 100 London Male 47.53 47.80 0.565 No Freestyle 100 Rio de

Janeiro Male 47.80 47.85 0.104 Yes Freestyle 200 Athens Female 118.22 118.45 0.194 Yes Freestyle 200 Beijing Female 114.97 115.04 0.061 Yes Freestyle 200 London Female 115.58 115.81 0.199 Yes

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8

time (s)

Third place

effect (0.369%) bigger?

Freestyle 200 Athens Male 105.23 105.32 0.085 Yes Freestyle 200 Beijing Male 104.85 105.14 0.276 Yes Freestyle 200 London Male 104.93 104.93 0.000 Yes Freestyle 200 Rio de

Janeiro Male 105.20 105.23 0.029 Yes

Table S3: Overview of third (bronze medal) or fourth place (no medal) finish times at the Olympic Games of Athens, Beijing, London and Rio de Janeiro. In 61% of the finals, the difference between

finishing third or fourth is smaller than the variance predicted by time of day (including five joint third places).

venue Gender Third place finish time

(s)

Fourth place finish time (s)

Difference

(%) Time of day effect

(0.369%) bigger?

Backstroke 100 Athens Female 60.88 61.05 0.278 Yes Backstroke 100 Beijing Female 59.34 59.38 0.067 Yes Backstroke 100 London Female 58.83 59.00 0.288 Yes Backstroke 100 Rio de

Janeiro Female 58.76 58.76 0.000 Yes Backstroke 100 Athens Male 54.36 54.38 0.037 Yes Backstroke 100 Beijing Male 53.18 53.18 0.000 Yes Backstroke 100 London Male 52.97 53.08 0.207 Yes Backstroke 100 Rio de

Janeiro Male 52.4 52.43 0.057 Yes Backstroke 200 Athens Female 129.88 129.88 0.000 Yes Backstroke 200 Beijing Female 127.13 127.88 0.586 No Backstroke 200 London Female 126.55 127.26 0.558 No Backstroke 200 Rio de

Janeiro Female 127.54 127.89 0.274 Yes Backstroke 200 Athens Male 117.56 117.76 0.170 Yes Backstroke 200 Beijing Male 114.93 115.49 0.485 No Backstroke 200 London Male 113.94 115.59 1.427 No Backstroke 200 Rio de

Janeiro Male 113.97 115.16 1.033 No Breaststroke 100 Athens Female 67.16 67.44 0.415 No Breaststroke 100 Beijing Female 67.34 67.43 0.133 Yes

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CHAPTER 8

(s)

Difference

(0.369%) bigger?

Breaststroke 100 London Female 66.46 66.93 0.702 No Breaststroke 100 Rio de

Janeiro Female 65.69 66.37 1.025 No Breaststroke 100 Athens Male 60.88 61.17 0.474 No Breaststroke 100 Beijing Male 59.37 59.57 0.336 Yes Breaststroke 100 London Male 59.49 59.53 0.067 Yes Breaststroke 100 Rio de

Janeiro Male 58.87 59.22 0.591 No Breaststroke 200 Athens Female 145.82 145.87 0.034 Yes Breaststroke 200 Beijing Female 143.02 143.24 0.154 Yes Breaststroke 200 London Female 140.92 141.65 0.515 No Breaststroke 200 Rio de

Janeiro Female 142.28 142.34 0.042 Yes Breaststroke 200 Athens Male 130.87 131.2 0.252 Yes Breaststroke 200 Beijing Male 128.94 129.03 0.070 Yes Breaststroke 200 London Male 128.29 128.35 0.047 Yes Breaststroke 200 Rio de

Janeiro Male 127.7 127.78 0.063 Yes Butterfly 100 Athens Female 57.99 58.22 0.395 No Butterfly 100 Beijing Female 57.25 57.84 1.020 No Butterfly 100 London Female 56.94 57.17 0.402 No Butterfly 100 Rio de

Janeiro Female 56.63 56.76 0.229 Yes Butterfly 100 Athens Male 51.36 52.27 1.741 No Butterfly 100 Beijing Male 51.12 51.13 0.020 Yes Butterfly 100 London Male 51.44 51.81 0.714 No Butterfly 100 Rio de

Janeiro Male 51.14 51.26 0.234 Yes Butterfly 200 Athens Female 128.04 128.18 0.109 Yes Butterfly 200 Beijing Female 126.26 127.02 0.598 No Butterfly 200 London Female 125.48 125.78 0.239 Yes Butterfly 200 Rio de

Janeiro Female 125.2 125.9 0.556 No Butterfly 200 Athens Male 115.52 116.00 0.414 No Butterfly 200 Beijing Male 112.97 114.35 1.207 No

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8

(s)

Difference

(0.369%) bigger?

Butterfly 200 London Male 113.21 114.35 0.997 No Butterfly 200 Rio de

Janeiro Male 113.62 114.06 0.386 No Freestyle 50 Athens Female 24.91 24.93 0.080 Yes Freestyle 50 Beijing Female 24.17 24.25 0.330 Yes Freestyle 50 London Female 24.39 24.46 0.286 Yes Freestyle 50 Rio de

Janeiro Female 24.11 24.13 0.083 Yes Freestyle 50 Athens Male 22.02 22.08 0.272 Yes Freestyle 50 Beijing Male 21.49 21.62 0.601 No Freestyle 50 London Male 21.59 21.61 0.093 Yes Freestyle 50 Rio de

Janeiro Male 21.49 21.68 0.876 No Freestyle 100 Athens Female 54.4 54.5 0.183 Yes Freestyle 100 Beijing Female 53.39 53.97 1.075 No Freestyle 100 London Female 53.44 53.47 0.056 Yes Freestyle 100 Rio de

Janeiro Male 47.85 47.88 0.063 Yes Freestyle 200 Athens Female 118.45 118.62 0.143 Yes Freestyle 200 Beijing Female 115.05 115.78 0.631 No Freestyle 200 London Female 115.81 115.82 0.009 Yes Freestyle 200 Rio de

Janeiro Female 114.92 115.18 0.226 Yes Freestyle 200 Athens Male 105.32 106.13 0.763 No Freestyle 200 Beijing Male 105.14 105.97 0.783 No Freestyle 200 London Male 104.93 105.04 0.105 Yes Freestyle 200 Rio de

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Gold, Silver or Bronze: Circadian variation strongly affects performance in Olympic athletes. CHAPTER 8 Table S4: Selected example

data explaining the concept of within subject normalization

as employed

in the current analysis.

The average swim time over

race type (heats, semifinal and final), was calculated per individual, stroke, distance, and per Olympic venue (Average over

all race types)

; then the percentage difference between each race swim time (heat, semifinal and final) and the average swim time was calculated for each combination of stroke and distance, resulting in the Individually normalized score column. A linear mixed model, with indiv idually normalized scores as dependent variable and type of race (heat, semifinal or final), Olympic venue, and start time (h) as independent variables, and subject identity as random effect was employed. The residuals of this model result in the column Model residuals . Subject identity Olympic venue Stroke Distance (m) Race type Start time (h) Finish time (s) Average over all race types Individually normalized score Model residuals 1 Athens Butterfly 100 heat 10.5 52.05 51.71667 1.006445 0.002024 1 Athens Butterfly 100 semi-final 21.3 51.74 51.71667 1.000451 0.001274 1 Athens Butterfly 100 final 22.6 51.36 51.71667 0.993103 -0.00327 2 Beijing Breaststroke 100 heat 20.1 59.41 59.25667 1.002588 -0.00184 2 Beijing Breaststroke 100 semi-final 10.0 59.16 59.25667 0.998369 -0.00082 2 Beijing Breaststroke 100 final 11.5 59.20 59.25667 0.999044 0.002661 2 Beijing Breaststroke 200 heat 21.3 128.68 129.21 0.995898 -0.00853 2 Beijing Breaststroke 200 semi-final 9.6 129.73 129.21 1.004024 0.004838 2 Beijing Breaststroke 200 final 10.8 129.22 129.21 1.000077 0.003695 3 London Backstroke 200 heat 11.5 116.36 115.2333 1.009777 0.005346 3 London Backstroke 200 semi-final 19.8 115.40 115.2333 1.001446 0.00226 3 London Backstroke 200 final 20.5 113.94 115.2333 0.988776 -0.00761 4 Rio de Janeiro Freestyle 50 heat 8.6 24.26 24.26667 0.999725 -0.00471 4 Rio de Janeiro Freestyle 50 semi-final 19.4 24.41 24.26667 1.005907 0.00672 4 Rio de Janeiro Freestyle 50 final 21.6 24.13 24.26667 0.994368 -0.00201 1 Rio de Janeiro Butterfly 100 heat 10.5 51.78 51.51667 1.005112 0.00068 1 Rio de Janeiro Butterfly 100 semi-final 20.8 51.51 51.51667 0.999871 0.000684 1 Rio de Janeiro Butterfly 100 final 22.4 51.26 51.51667 0.995018 -0.00136

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