August 26


Slave to our Rhythm: Insights into BRAC, Ultradian and Circadian cycles

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Look around and you’ll see many examples of rhythms and cycles in nature. The green buds of spring and the reds and oranges of autumn. The dawn chorus, then the hooting on the owl at night. High tides and low tide. The stages of the moon. Natural rhythms are also an intrinsic part of the human body. Just some are BRAC, the Ultradian and Circadian cycles.

Modern technology allows us to lead the lifestyles we choose. If you want to perform at your best when it really counts however, it would be wise to understand these basic rhythms.

The circadian rhythm is probably one of the most well known – the normal wake/sleep cycle associated with day and night. It’s also the most powerful and influences how we feel and behave. However, other shorter and longer rhythms also play their part. It’s important to realise that all these different rhythms are layered on top of one another. This means that there are times when their effects can be amplified. For example, the most alert phase of your daily cycle may line up with the alert phase of your 90-minute alertness cycle (more on this later). There can also be times when these cycles clash and may act against one another.

Remember though, these underlying rhythms are just that – a tendency towards a mental or physical condition.

Your environment and what’s going on around you can easily mask any underlying rhythm. For example, you’re less likely to feel drowsy and inattentive as you enter the room for a big job interview regardless of the time of day. There’s usually not a lot of room for negotiation to manipulate your natural cycles to suit your own circumstances.

But you can understand them better. You can alter your schedule and devise strategies to be at your best when it really counts.

Ultradian (short) rhythms

Ultradian rhythms are any of those that are less than 20 hours in length. For example, the 15-20 breaths per minute of your breathing pattern. Or the fraction of a second frequency of brain waves. Probably the most relevant to physical performance though is the 90-minute cycle of rest/activity discovered in the 1950s.

Dubbed Basic Rest Activity Cycles, or BRAC cycles, these 90-minute cycles affect us 24 hours a day.

During the day, they represent periods of alertness at the top of the cycle and increased drowsiness at the bottom. During sleep, they produce the periods of Rapid Eye Movement (REM) sleep when the brain is more active. These are interspersed with periods of deep sleep at the bottom of the cycle when the brain is less active.

How do BRAC cycles affect me?

The effect of BRAC on our daily routine is to produce short periods of mental and physical fatigue every 90 minutes. These are interspersed with longer spells of alertness.

During the periods of decreased alertness, you’re more likely to start daydreaming, lose concentration and feel sleepy. This is why it’s important to schedule regular breaks from demanding work tasks at least every 90 minutes or so. You may also find yourself less motivated to start exercising at these low points. It might also take longer to get going when you do.

BRAC also interact with the daily circadian cycle. These drops in mental and physical performance become more pronounced and prolonged during mid-afternoon. The good news is that the low points in these cycles tend to pass pretty quickly.

So, for instance, you’ve otherwise been OK but might happen to feel a bit sluggish when it’s time to hit the gym. The chances are you’ll feel more energised if you hang on another 10 minutes or so. Don’t duck out of your workout altogether.

By the same token, BRAC cycles will mean that in events or workouts lasting longer than 90 minutes, you should expect at least one performance dip. This is especially true if you’ll also require a lot of concentration and/or mental agility. It makes sense, therefore, to limit gym workouts to around an hour and 15 minutes tops. Any longer and you may well find that your form suffers and your effort drops.

BRAC Cycles and Food Intake

If you’ve ever been really hungry but didn’t have the opportunity to eat, you’ll almost certainly have experienced intense hunger pangs that pass, only to return about 90 minutes later.

That’s because BRAC also affect other body functions, like appetite and hunger. Studies have shown that this rhythmic desire to eat is not ‘all in the mind.’

Our stomachs are programmed to contract about every 90 minutes or so, enhancing feelings of hunger. If you’re following a calorie-restricted diet, you can use this knowledge to get yourself through the ‘urge to eat’ period. Simply delay your visit to the fridge or store cupboard for 15 minutes or so.

Alternatively try having a very low-calorie nibble, knowing that your desire to eat will soon diminish again, even if you don’t eat.

Circadian Rhythm

The circadian rhythm is undoubtedly the most important of our natural rhythms and cycles. Not least because it’s the most powerful. It’s the one around which we structure our daily routines. This rhythm governs our waking and sleeping patterns. Our daily fluctuations in body temperature. Our mental and physical performance.

At different times of the day you, quite literally, become a different person.

The most powerful rhythm is our sleep wake cycle - linked to our BRAC and circadian rhythm

The most powerful and perhaps most important of the lot is the wake/sleep cycle. After waking, most people experience a steady surge in mental alertness, which peaks around late morning. A dip follows in the early-mid afternoon. There’s then a second, if somewhat lesser, peak during the late afternoon/early evening.

Manual dexterity on the other hand peaks in the afternoon.

Meanwhile, physical and athletic performance seems to peak around early evening.

Our ability to tolerate discomfort is highest in the morning.

Performing complex intellectual tasks and committing information to long-term memory is easiest in the afternoon.

Our senses are sharpest in the early evening.

All that being said, these trends can differ significantly from person to person. Many appear to be related to whether you are a ‘morning’ or a ‘night’ person.

About the author

Paul Stokes

Paul Stokes BSc (Hons) is a Certified Personal Trainer, Accredited Sports Nutritionist, qualified Exercise to Music Instructor, Precision Nutrition coach, Massage Therapist and teaches 8 of the Les Mills Group Exercise programs.

He currently works in the Oil & Gas industry as a Wellness Coach, imparting his vast knowledge and experience to improve the quality of life of several hundred offshore workers.

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