Fit Bones

Circadian Rhythms govern how our body works and adjust throughout a 24-hour cycle with the sleep/wake cycle being the most important. So what exactly is happening to your body at any given time of the day (or night)?

9am till around noon

• Maximum cortisol levels

• Maximum alertness

You are probably on your morning ride out, had your coffee, and it's time to let your brain free-flow, reflect and chew the cud. The stress hormone cortisol reaches its natural peak giving our brains a boost of alertness. We tend to be most productive before lunch and tests show short-term memory is at its best. Stay alert, there's a big dip coming up.

Noon till around 3pm

• Biological siesta – dip in alertness

• Surge in road deaths

With a fully loaded burger or egg & bacon bap at lunchtime, there's a boost in gastric activity. This leads to the 'biological siesta' as alertness dips and affects riding ability. There's a noticeable rise in the number of deaths on the roads from 2pm, particularly in older people. It is also not a great time to drink alcohol as it can make you drowsier than at other times of the day.

3pm to 6pm

• Best lung & cardiovascular performance

• Core body temperature rising to its peak

Body temperature increases in the late afternoon like a natural warm-up, the heart and lungs work better, and muscles are 6% stronger than at their lowest point in the day. Some people have even tried using this 'athletic sweet spot' to increase their chances of breaking sporting world records. If there is any hard technical offroad stuff to do, record to break, or you are working on your fitness levels, go get a sweat on!

6pm to 9pm

• Poor time to eat a big meal

• Liver handles alcohol better

• Intuitive thinking is better

Hard day's riding, ready for dinner and maybe a drink? Well, you might not want to leave it too late. Emerging evidence suggests that the body changes the way it handles food as it gets closer to night-time. Eating big meals in the evening could increase the risk of obesity and diabetes. Although the liver is more able to deal with alcohol at this time if you fancy a tipple.

9pm to midnight

• Melatonin production building

• Core body temperature dropping

Bedtime is fast approaching and the pineal gland in the brain is churning out the hormone melatonin to help you nod off. Core body temperature is falling, and the internal body clock is saying it's time to swap the sofa for the bed. It'll happen earlier if you're a morning or 'lark' type person, before hitting the 'owls' a bit later. Unless you are taking part in a rally, best to stay off the bike and hunker down for the night.

Midnight to 3am

• Sleep hormone melatonin peaking

• Minimum levels of attention and vigilance

• Brain washes itself and consolidates memories

It is well and truly bedtime. Hormonal changes in the body say it is time to be asleep. The brain is washing away the waste toxins built up during a hard day's riding and the bowels are shut down for the night. If you're still awake be careful - levels of attention are at their lowest, making night riding or night shifts a risk.

3am to 6am

• Core body temperature at its lowest

• Severe asthma attacks more common

• Most natural births occur

It's the middle of the night and your body is still some way off from waking up and getting you out of bed. Sleep hormone melatonin levels are still high but start to glide down as dawn approaches. Your core body temperature is notably cooler than at any other time of the day as energy is diverted elsewhere, to be used for things like skin repair.

6am to 9am

• Men have their testosterone peak

• Heart attack danger zone

Your body is kicking into gear as sleep hormone melatonin production stops. Blood vessels are stiffer and more rigid (like some other 'obvious' body parts), the blood is thicker and stickier, and your blood pressure is at its peak. Be careful - this is the time of day your heart is at its most vulnerable.  It all adds up to the greatest risk of a heart attack in a 24-hour cycle. Best to avoid heavy exercise during this time.