Science of Performance: Diurnal Variation in Swimmers

By Swimming World correspondent G. John Mullen of Swimming Science and COR, Creator of Swimmer's Shoulder System

SANTA CLARA, California. May 1. MAN! If he would have been in finals he would have won the event!

This old adage surrounds prelim/final meets throughout the year. I remember when I started obsessing about swimming times and results as a young lad in Dayton, Ohio, rushing home after practice to hit the refresh button on the online results. Nowadays, smart phones, live results, and streaming videos have replaced the hassles of waiting for the session to finish.

One case of a poor morning swim I'll never forget was Chris Kemp from the University of Texas. In 2002, Chris Kemp finished prelims in 9th place in the 200 free on the second day of NCAAs. Chris just missed the top 8, by 0.02 seconds. In finals, Chris came back and dropped more than 1.5 seconds from his preliminary time to win the consolation final in a time which would have won the event!

The difference between 9th and 1st place at NCAAs is 11 points. In 2002, Texas and Stanford were battling for the top position and many thought this miscalculated morning swim would cost Texas the meet. Luckily, for Chris, Texas still won the meet by 11 points.

This unique prelim flop is common at large prelim/final meets. This commonality may differentiate your team winning NCAAs or finishing out of the top 3! Optimal performance is mandatory for elite swimmers in the prelims session, especially those where the prelim session starts before noon, as is common in age group competitions. This obvious statement is known across pool decks, but many swimmers fail to perform up to their potential in prelims.

This multivariable question is typically associated with choking or poor preparation. One physiological reason is diurnal variation.

Diurnal Variation
Diurnal variation is the difference in behavior caused by activity during the day and sleeping at night. This common sleeping pattern causes fluctuations in hormone level, body temperature, cognitive faculties, eating and sleeping. Let's take a deeper look into these areas:

Hormone level
Hormones alter athletic outcome as they respond to external stress. However, these hormones have peak periods for excretion. Most often these hormones peak during midday to early evening. This is not ideal for morning swim sessions and often times leave swimmers groggy and tired at the start of prelims.

Melatonin is well-known by those traveling across the country. Light stimulates this hormone and regulated by the pineal gland. Unlike most hormones contributing to exercise (testosterone, adrenalin, etc.) melatonin peaks at night and remains elevated until the afternoon. This prevents levels of alertness and awareness.

One study (Gibertini 1999) determined melatonin peaks were strongly related with cicardian rhythm, finding 'morning people' have a more rapid decline in melatonin levels after the peak than do 'night people'.

This rapid decline prepares 'morning people' for their prelim session, but might prevent the 'night people' from optimal performance.

Body Temperature
Similar to hormones, body temperature fluctuates during the day. The body is warmest, once again, during midday to early evening. This difference in body temperature makes it difficult to wake up for early races and requires specific steps to increase blood flow. Once again, 'morning people' have been shown to have a higher daytime temperature with an earlier peak in body temperature than 'night people' (Horne & stberg 1976).

Body temperate is lowest halfway through the sleep cycle and then rise gradually throughout the day. If you're a night owl, your body temperature remains lower for longer periods, another potential hindrance to performance.

Cognitive Faculties
Cognitive function during a race is a debated and complex subject. Every coach provides detailed race strategies for their swimmers, with the intentions of improving performance. However, if the swimmer is consistently thinking about the race, are they turning off the reactive animal within? Great athletes often 'black out' during their races, only remembering bits and pieces.

Cognitive function is slightly more individual than the aforementioned variables, as some people are able to turn on cortical activity at different times. However, peak brain activity is believed to be in the morning for a 'morning person' and in the evening for an 'evening person'. However, the question remains, do you want to have high cognitive function for your race? This debate continues around this question, but it is better a question be debated, than never discussed.

Being a morning or evening put each individual at an advantage or disadvantage when it comes to prelim/final meets. Luckily, there are tools to prevent a poor morning swim, which will be discussed in the next installment.

G. John Mullen is the owner of of the Center of Optimal Restoration and creator of Swimming Science. He received his doctorate in Physical Therapy at the University of Southern California. G. John has been featured in Swimming World Magazine, Swimmer Magazine, and the International Society of Swim Coaches Journal.

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