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23 Dec 2025

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2 pages

Understanding Infradian and Ultradian Biological Rhythms

Erica

@erica4

Your body runs on several different biological clocks that control... Show more

Biopsychology
A01
Infradian rhythms
The menstrual cycle
BIOLOGICAL RHYTHMS: INFRADIAN AND ULTRADIAN RHYTHMS
Cycle refers to time between fir

Infradian Rhythms: Monthly and Seasonal Patterns

Infradian rhythms are biological cycles that last longer than 24 hours - think monthly or seasonal patterns that your body follows naturally. The most well-known example is the menstrual cycle, which runs roughly every 28 days from the start of one period to the day before the next.

What's fascinating is that whilst the menstrual cycle is controlled internally (endogenous), it can actually be influenced by external factors like other women's cycles. This menstrual synchrony might have evolutionary benefits - our ancestors who menstruated together could help care for each other's babies, improving survival rates.

Seasonal Affective Disorder (SAD) is another infradian rhythm that affects many people during winter months. When daylight hours shrink, some people develop depression because their internal clocks get disrupted by the prolonged darkness. The good news? Light therapy boxes can help reset your body clock, though they might cause headaches or eye strain.

Quick Tip: If you feel more depressed during winter months, you're not imagining it - it's a real biological rhythm that affects millions of people!

Ultradian Rhythms: Your Nightly Sleep Cycles

Ultradian rhythms are shorter than 24 hours, and the most important one happens whilst you're sleeping. Your brain cycles through five stages of sleep approximately every 90 minutes throughout the night, each with distinct brainwave patterns.

Stages 1 and 2 involve light sleep with high-frequency, short waves - this is when you might wake up easily. Stages 3 and 4 are deep sleep, characterised by slow, powerful brainwaves that help your body recover. Stage 5 is REM sleep (Rapid Eye Movement), where your body becomes paralysed but your brain acts like it's awake - this is when most vivid dreams occur.

Understanding these sleep stages has revealed why older people often struggle with sleep quality. Deep sleep stages (3 and 4) naturally decrease with age, explaining why your grandparents might wake up more frequently than you do.

Research shows massive individual differences in sleep patterns, making it difficult to define "normal sleep". Whilst sleep labs help scientists control variables, people attached to monitoring equipment rarely sleep as naturally as they would at home.

Remember: Your sleep cycles repeat every 90 minutes - that's why you sometimes wake up naturally feeling refreshed whilst other times you feel groggy, depending on which stage you're in!

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Psychology

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642

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23 Dec 2025

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2 pages

Understanding Infradian and Ultradian Biological Rhythms

Erica

@erica4

Your body runs on several different biological clocks that control everything from when you feel sleepy to when you're most alert. These rhythms, which last longer or shorter than 24 hours, play a massive role in your daily life and... Show more

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Infradian Rhythms: Monthly and Seasonal Patterns

Quick Tip: If you feel more depressed during winter months, you're not imagining it - it's a real biological rhythm that affects millions of people!

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Ultradian Rhythms: Your Nightly Sleep Cycles

Remember: Your sleep cycles repeat every 90 minutes - that's why you sometimes wake up naturally feeling refreshed whilst other times you feel groggy, depending on which stage you're in!