The mornings I don't have a surf session I feel a little off. A touch of lethargy follows me around throughout the day. I'm a little more anxious and little less grateful. Even the 'not-so-great' surf sessions set me up for an all-around better day.

It's often cold and difficult to bring myself to paddle out, particularly when the waves aren't looking great. But I try to anyways. Why? What's in the water?

Factor 1: The Cold

I like the early morning sessions, but they do have their drawbacks. In the South African winter, when swell is consistent and winds are favorable, the cold water and air can be a challenge. In particular it's these liminal moments that chill me:

• After getting out of bed and before getting into my sweats.

• Between my sweats and my wetsuit.

• That first duck dive.

• The last 20 minutes of the session... waiting for just one more good wave I can be satisfied with taking in.

• Then back at the car between my wetsuit and my sweats.

I find these all manageable, especially when the waves are good. But my hands and feet don't agree.

The Extremities:

Even a standard morning session can put my feet to the test. On those particularly cold mornings in the peak of winter my hands and feet go numb but become oddly sensitive to pain. A cobblestone path I wouldn't think twice about in warmer weather gives me pause. I'm often relieved to reach the cold water, getting my feet out of the even colder air. On these days a pebble can feel like a nail and a light breeze pokes my hands like needles.

This unintuitive flip of sensations is due to Differential Nerve Sensitivity: the nerves in our hands and feet contain different types of fibers responsible for transmitting various sensations, including touch, temperature, and pain. Two types explain this phenomenon:

• What I expect: Large, Myelinated Fibers (like A-beta): These fibers are responsible for transmitting light touch and pressure sensations quickly. They are relatively sensitive to cold and their conduction speed slows down significantly as tissues cool. This reduced activity contributes to the feeling of numbness and loss of fine tactile sensation.

• The real culprit: Small, Thinly Myelinated Fibers (A-delta): These fibers are involved in sensing cold temperatures and also transmit sharp, initial pain signals. While their conduction also slows in the cold, they can remain active and even become more excitable under certain cold conditions.

The first mental override of the day happens early, "it's okay feet, we're doing this for fun. I won't let you freeze... I promise".

On particularly cold days even a post-session hot shower is uncomfortable. My extremities, trying to adjust to the change in temperature burn, even under luke warm water.

The explanation of this phenomenon is vasoconstriction and dilation.

When your hands and feet become intensely cold, your body initiates a protective response called vasoconstriction.This narrows the blood vessels in your extremities, significantly reducing blood flow to these areas.This helps to conserve core body heat and protect vital organs. It's a survival mechanism.As a result, your hands and feet become numb and very cold due to the lack of warm blood circulating to them.

When you then expose your severely cold hands and feet to warm water, such as in a hot shower, a rapid rewarming occurs. This causes the constricted blood vessels to quickly widen (vasodilation), and blood rushes back into the capillaries of your extremities. It's this sudden influx of warm blood, combined with the "waking up" of nerves that were suppressed by the cold, which leads to the burning sensation.

A gradual re-warming is best, but usually not something I take the time to do. Instead, I start the day with nubs for hands and feet.

My Head:

Less common and shorter lived, but arguably more painful, is the ice cream headache - a physiological response triggered by the rapid cooling of the head and the body's reaction.

This shock to the system is remarkably similar to the "brain freeze" we're all familiar with from childhood; I got my first brain freeze at a 7-11 when taking down a cherry slurpee.

While similar in feeling, the physiology is a little different. There are 4 main factors for surfers:

1. Back Again, Our Friends: Vasoconstriction and Vasodilation: The initial contact with cold triggers a rapid constriction (narrowing) of blood vessels in the head as a protective measure to reduce heat loss in the body. As the body starts to rewarm these areas, vasodilation (widening) of these same blood vessels occurs. It's this rapid change in blood vessel size is a key contributor to the "ice cream" headache.

2. A New Player: Trigeminal Nerve Activation: The trigeminal nerve, the largest nerve in our head, is responsible for transmitting sensory information from the face and head to the brain. It has branches that extend to the palate, sinuses, and forehead. The sudden cooling and the subsequent changes in blood vessel size irritate its nerve endings.

3. Referred Pain: The brain interprets the signals from the stimulated trigeminal nerve as pain. However, because of how the nerve pathways are routed, the brain often perceives this pain as originating in the forehead, even though the initial stimulus was in the face (for the surfer) and the roof of the mouth (for the slurpee drinker). The pain is felt strongest in the forehead. This is known as referred pain.

4. Repeated Stimulation: For surfers, the act of repeatedly duck diving in cold water means this rapid cooling and rewarming cycle happens multiple times during a session, increasing the likelihood and potentially the intensity of the ice cream headache. This is why it usually doesn't happen after one or two duck dives mid session, but more likely on the initial paddle out or when getting stuck inside.

The Core:

Sometimes I get cold down to the core - "chilled to the bone" as my dad would say, which I always thought was a funny saying, but upon researching further is actually a little more viable than I initially gave credit.

Even after I get out of the water, take a warm shower, and put on warm clothes, several factors contribute to a persistent feeling of cold:

• Significant Peripheral Cooling: This sophisticated term for a rather simple concept, basically just means your extremities have become much colder than your core body temperature. This deep tissue cooling takes a long time to reverse.

• Slow Return of Blood Flow: While a warm shower helps initiate the rewarming process and causes some vasodilation, the blood flow to your extremities may not immediately return to normal levels. Your body might still be in a mode of conserving heat, or the blood vessels are slower to fully dilate and restore normal circulation.

• Tissue Temperature Lag: Even with warmer blood flowing back in, it takes time for the temperature of the muscles, skin, and other tissues in your extremities to increase significantly. These areas have been cooled for an extended period, and heat transfer throughout these tissues is a slow process. Note: this also contributes to more energy your body requires to return to homeostasis (more on energy expenditure later).

• Reduced Metabolic Heat Production in Extremities: Muscles generate heat through metabolic activity. When your extremities are very cold, muscle activity may be reduced, leading to less heat production in those areas compared to your core.

• "Afterdrop": When your core body temperature actually continues to drop slightly after you've come out of the water. It may be a combination of less body movement that was generating heat, plus the removal of a wetsuit, that colder blood from your extremities starts to circulate back towards your core.

Upon learning this, I realized why I would be cold all day long after a some sessions. After being chilled to the bone I'd get out and drink coffee - a vasoconstrictor - and sit down to start work.

Instead, I should drink warm water and do a little yoga try to get my blood flowing again before moving on with my day. Duly noted science!

Factor 2: Hunger & Thirst

My Stomach:

Onaka Peko Peko - a Japanese term used to express extreme hunger is literally translated as "stomach" "peko peko" where "peko peko" is used to describe the sound a stomach makes when it's hungry.

An hour in to my session I start thinking about my next meal. Two hours in my dreams turn from a healthy breakfast to burgers, burritos, and candy bars. Beyond two hours I'm elated to cram any source of calories.

Several factors contribute to the significant energy expenditure of surfing, going beyond just the physical effort of paddling and shredding.

Thermoregulation - One of the primary reasons is thermoregulation. Water conducts heat away from the body much more efficiently than air – about 25 times faster. In the water, particularly cold water, your body has to work considerably harder to prevent its core temperature from dropping. This metabolic effort running in the background is quietly draining energy reserves, building up an appetite.

Focus - Intense mental focus and concentration require significant energy from your brain. Your brain, although it only makes up about 2% of your body weight, can use up to 20% of your body's total energy when active. When you're surfing, you're not just physically paddling and balancing; you're constantly processing information – reading the waves, anticipating their movement, reacting to changing conditions, and making split-second decisions about positioning and maneuvers. This high level of cognitive activity demands a considerable amount of glucose, the brain's primary fuel.

My Throat:

Nodo Kara Kara - a Japanese term used to express extreme thirst, is literally translated to throat dry, where "nodo nodo" means dry or empty.

Then there is the thirst factor. It's an unusual type of thirst. It's not the same type of thirst I've experienced out on a hike in the desert or in the air conditioned gym... or the un-airconditioned gym in Indonesia where I recently got my work in. The discomfort of the land-based thirst is dominated by the dry mouth. It's a wonderful relief just to take a sip of water from a fountain to 'wet my whistle'. In these cases it feels like my body's desire for hydration is placated instantly... even though I know it will take more than this to properly rehydrate.

Being dehydrated in the ocean, surrounded by water, is more subtle and actually less annoying. You'd think it would be devastating to be thirsty with water all around you, none of which you can drink. In fact I rarely notice my thirst until I'm out of the water. Nonetheless, the ocean is particularly dehydrating.

Here's how surfing draws the water out of my body:

Sweating - Sweating is an odd one because I don't notice it at all when I'm in the water, but even on the cold days when I'm wearing a wetsuit, my body can go from freezing when I first get in, to overheating by the time I get to the lineup. Since I don't feel the sweat in the water, I'm less aware of the water leaving my body and the need to replace it.

Respiration - Respiratory water loss is the water vapor that your body loses when you breathe. This is going to happen all day and night as we breathe, but when I'm out in the water exerting myself through paddling or being beat up by by a few set waves, my respiration increases and so does the loss of water.

Osmosis - In comparison, this actually makes a very small contribution to dehydration, but it is interesting. Water tends to move from an area of lower solute concentration to an area of higher concentration to try and equalize the concentrations. In other words, low salt levels in skin cells and high salt levels in ocean water creates a tendency for water to move out of our skin cells into the surrounding salty water.

This is why our skin, particularly on our fingers and toes, gets prunie. The wrinkling is partly due to the keratin in the outer layer of your skin absorbing water and the osmotic effect of saltwater drawing water out of the deeper skin cells.

However, it's crucial to understand that while osmosis across the skin occurs, the outer layers of our skin provide a significant barrier. This prevents massive and rapid shifts in fluid balance through the skin alone.

The intestine is a different story.

Through the same process of osmosis, swallowing saltwater dehydrates us a bit more (depending on how much we take in of course). Saltwater in the body disrupts our internal balance and requires water from our blood to restore it.

Here's how it works:

1. Ocean saltwater has a much higher concentration of salt than the fluids inside our body's cells and bloodstream.  

2. When you swallow saltwater, it enters your stomach and intestines. The lining of your digestive tract acts like a semipermeable membrane. Due to the high salt concentration of the ingested saltwater, water is drawn out of the surrounding body tissues and into the digestive tract to try and dilute the saltwater and equalize the salt concentration. This means your body is losing water from its cells and bloodstream into your gut.  

3. As the saltwater is absorbed, the large amount of excess salt enters your bloodstream. Your kidneys are responsible for filtering waste products and excess salts from your blood and producing urine. To get rid of the large load of salt you've ingested, your kidneys need to use a significant amount of water to excrete it in the urine. Ah! This explains - at least partially - why I pee so much while surfing!

Finally, That Thirst feeling

Paradoxically, being in cold water can sometimes suppress our sensation of thirst, even though we're are losing fluids. This means we might not feel the need to drink while we're surfing, leading to a greater fluid deficit by the time we get out.

More self-evidently, when I'm focused on catching waves I'm less likely to be thinking about hydration. Although it is odd that I do think about hunger. I guess my stomach is louder than my throat.

Factor 3: The Humbling

It seems like I can never go a session without getting some sort of body check from the ocean.

Most often my humbling comes from a rogue set hammering me. I know I should never take the first wave of the set, but unless I'm the only one around, I rarely resist the temptation of that first wave.

Since the first wave of the set is generally a little bit smaller than the next few, that means even if I make it when I come out of the wave, I'm still going to be looking at a few slightly bigger waves that I need to battle through to make it back to the outside. This battle doesn't feel too bad after getting a nice ride, but in the case where I just barely miss the wave... I really end up paying my dues.

It's an awful feeling to be pushing as hard as possible to catch the first wave and just miss it knowing what awaits me behind it. I turn around and I'm too far inside to make it under the set waves that are coming. I know, no matter what I do, I'm going to get pummeled by all of them. My choice here is to stay inside, hope the oncoming wave breaks and dissipates a little of its energy before it gets to me... or, charge as hard as possible toward it and hope to god I can make it under with a clean duck dive. These are both low probability gambles.

More likely, I'm going to be in the worst possible position - the impact zone: where the lip of the wave meets the surface of the water as it breaks. The power of the wave at this point is like a perfectly timed karate punch.

Usually, sets come in 3 to 4 waves, sometimes 6 or more depending on the swell. This means two things:

1. There's a good chance I'm going to be in the worst possible position on at least one of these as I try to battle through the set.

2. I'm going to be more and more tired after each one reducing my chances of making it past the following wave.

At a minimum, I'll be exhausted from the battle, more likely I'm going to get thrashed.

I think it's these short intense thrashing and hold-downs that make my entire body feels sore after a surf session. I would expect my shoulders and back to be sore from all the paddling. Maybe my legs a bit if I'm on a particularly long wave. But the post-surf soreness often runs from my fingers to my toes. It's a unique soreness I've never been able to replicate outside of the water.

My theory is, it's a result of flexing all of the muscles in my body in short, intense bursts... mostly when I'm being worked by a wave not from the actual surfing of it.

When a powerful wave hits me during a duck dive, if I don't time it just right, it can feel like I'm riding a bull. I'm pulled and pushed with amazing force from the left to the right and up and down... without any ability to predict where the next blow will come from. I'm hanging on to my board for dear life because I know it's the only thing that's going to guide me back up to surface, eventually... and out of pride I refuse to be seen ditching my board.

Although only a few seconds at most, during the thrashing my entire body is braced for impact - every muscle flexed. The death grip of my hands sometimes creates pressure dents in my board along the rails of the deck. This probably explains why my my fingers get sore on bigger days.

But even small waves will humble me.

A Simple Humbling

On the small days I thoroughly enjoy taking out the log and messing around on little waves. Part of the fun is experimenting with the timing of the longboard, which is so different from the quick responsiveness of a thruster. The other part is harnessing the power that comes in even a knee high wave in shallow water.

I can get super stoked on a knee high day, flying down the line on a longboard or trying to hang ten right off the takeoff. The low pressure playful feel on small days is a different kind of fun and somehow it always leads me to forget that one small mistake can be punishing, even at this size.

All it takes is a slight misplacement of the foot, digging a rail, sending me flying out into the shallows; an unexpected section breaking a little bit quicker than I thought causing me to Pearl and ejecting me over the falls. I've had some of my worst wipeouts in small waves. Standing upright, cruising on the longboard, feeling relaxed, thinking I'm looking cool, then hitting a bump unexpectedly and flying out onto the flats, flatbacked or whiplashed. Part of the pain surely comes from my sore ego after so abruptly transitioning from super cool to super kook.

The Recalibration

What does it all mean?

After almost every early morning session, I'm lighter and happier.

It only takes a small bit of exposure to the elements before I'm returning home grateful for what I took for granted just a few hours earlier. After being humbled by the ocean, a warm shower, pair of Rainbows, and a PB & J make for a wonderful day.