Ready? Set! Know!

Putting your body through its paces is like driving a manual: it's much easier to master if you understand exactly how a car zips from zero to 80. I know how my body feels when I'm gunning hard during a workout or a race (can you say, "shoot me now"?), but I have no clue what's really making it go. So I dialled up some leading fitness experts to find out, blow by painful blow, exactly what was happening to my body during my most recent triathlon.

Apply their tips to your next workout, whether it's a killer strength session, a spin class or a day on the slopes, and you'll get a new appreciation for what your hardworking body can do - and a killer performance boost to go with it.

Fuelling up

4:45AM
It's two hours before the race starts.
I force down two slices of wholegrain toast with peanut butter and a sliced banana on top.

WHAT'S GOING ON
Eating is the last thing I want to do, but I have to nosh now because my stomach needs time - two hours to be exact - to digest complex carbs. Once I'm in motion, digestion will all but stop, so my belly will get no love from my body's oxygen-rich blood, which it needs for digestion. "The nervous system directs blood to where it's needed most," says Dr Carol L Otis, co-author of The Athletic Woman's Survival Guide. During a hard physical effort, the muscles that move my body crave oxygen and demand nearly 85 per cent of my blood flow. The O² combines with glycogen (a byproduct of carbs) to produce adenosine triphosphate, aka ATP. That's the fuel that makes the body go.

Revving and (sort of) willing

6:35AM
The starting gun goes off in 10 minutes. Even though pre-race jitters make me want to hurl, I suck down an energy gel, sip some water and wade into the water for a quick warm-up.

WHAT'S GOING ON
The blood can hold about 420 kilojoules worth of easy-to-access glycogen, and I want my tank at full capacity. Eating a simple carb, like a banana or an energy gel, within 30 minutes of a tough workout tops it off. As for that pukey feeling: anticipation has my heart beating fast - my nervous system is primed for action. "It's like waving a leash in front of a dog," says Matt Fitzgerald, author of Brain Training for Runners. "The dog knows it's going for a walk and gets excited."

A 10-minute warm-up gets blood flowing to my muscles and away from other organs, revs my heart rate, starts working my lungs, lubes my joints and reacquaints my nervous system with how my muscles fire. In a race, skipping a warm-up means a breathless, achy start.

High gear

6:45AM
The starting gun fires. I dive in for the 1500-metre swim. Breathing is a struggle and my arms and legs protest.

WHAT'S GOING ON
As picky as a diesel-powered 4WD, my body runs on only one fuel: ATP. At the beginning of a hard effort, the body makes this muscle food using creatine, an acid it produces naturally. "This ATP is created in a flash," Katz says, "and is gone just as quickly." At the start of a workout, my cells have just under 10 seconds' worth of this fuel. Then a process called anaerobic glycolysis kicks in. For the next one to three minutes, I can produce ATP without oxygen (right now I'm using all I've got to breathe). The trade-off: I cringe as my muscles start to burn.

Now my system switches to the lowest-maintenance method of making ATP: aerobic glycolysis. Here, a combo of oxygen, glycogen (from my breakfast and last night's pasta), lactic acid, and fat stores feed my muscles. The body can run this way for hours; in fact, it uses this form of ATP for 99 per cent of all activity.

Meanwhile, my adrenal glands release epinephrine (aka adrenaline), raising my heart rate and lowering my perception of pain. "Epinephrine is the cavalry swooping in for a fight, which is how your body sees this race," says exercise physiologist Dr Tommy Boone. My nervous system doesn't know if I'm being chased by competitors or a great white. Either way, its message is the same: go fast and hard.

Cruise control

6:57AM
My arms and legs stop hurting and I no longer feel like I'm about to hyperventilate.

WHAT'S GOING ON
My muscles are now using about 20 times as much energy as they would if I was watching a race on TV. My heart rate rises to around 160 beats per minute (compared with about 70 at rest) and increases the amount of blood it pumps per beat. That blood swooshes through the thousands of adrenaline-widened capillaries in my muscles.

Because I've done endurance sports for most of my life, my heart, like any muscle, has grown stronger through regular sweat sessions. My left ventricle, the piston that pushes blood through my body, is larger than an untrained female's, so it's able to distribute a steady stream of blood over long physical efforts. My lungs, however, will never change size. Their job is to suck oxygen from the air, and they're programmed to keep up with my body's oxygen demand and with how fast my heart shuttles the oxygen-spiked blood to my muscles.

Feeling the heat

7:53AM
I've conquered the swim and now, halfway through the 42km bike portion of the race, the relentless sun gets to me. I'm thirsty, sweating and need energy - but the heat has killed my appetite. I grab a sports drink at an aid station.

WHAT'S GOING ON
As I gulp it down, the electrolyte-filled liquid flows through my stomach and into my small intestine, which converts the sugars into glucose to be deposited into the bloodstream. The process takes roughly 20 minutes. Had I forced down a protein bar, I probably would have paid for it: "During exercise, muscular demand is greater than digestive demand, so any food in your stomach just sits there," Dr Otis says. That's why your stomach protests if you munch right before or during a tough workout. As for the buckets of sweat pouring off my skin, that's my body keeping me cool. Those wide-open capillaries in my muscles are transferring warm blood to sweat glands in my skin. Like itty-bitty air conditioners, these glands siphon off water and chemicals like sodium and potassium from the blood and spit it out through my pores. The sweat evaporates on my skin; I cool down. The more I sweat, the longer my body temperature stays low and the harder and longer I can go - as long as I keep replenishing my fluids. If I don't, then dehydration sets in. If that happens, my blood will thicken, my heart rate will rise and every motion will become harder.

I'm sweating profusely. But when I dismount my bike, I see that I've finished only about a third of a 700ml bottle of the sports drink. Uh-oh.

Running on empty

9:20AM
I'm about a third of the way into the 10km run and my legs are officially made of lead. Negative thoughts flood my mind: It's too hot, I'm too slow, I didn't train enough. I don't have the physical energy or the mental discipline to slog through. So I settle into a run/walk pattern that I keep up for the rest of the race.

WHAT'S GOING ON
Physically, I'm toast. If the swim, bike and run weren't enough to accelerate muscle mutiny, suffering in 32-degree-plus temps are. My brain doesn't recruit muscles to work as effectively as it does in cooler weather. It switches to overprotective mode. "Your brain's primary job during exercise is to prevent you from harming yourself," Fitzgerald says. When your core temperature goes up, your brain makes you feel like crap to slow you down.

Afterburn

9:42AM
Two hours, 56 minutes and 30 seconds after I dove into the water, I kick it across the finish line, awash in sweat and endorphins. After catching my breath, I beeline for the post-race spread of bananas and sambos.

WHAT'S GOING ON
The race may be over, but my body is still busy replacing its glycogen stores, removing lactic acid, lowering my heart and breathing rates, and shutting down the capillaries to my muscles as the ones to my stomach reopen. Mentally, I'm flying. "Exercise produces an opium-like substance in the brain that gives you a natural high," Dr Ruby says.

Over and ouch!

Working my engine at a greater intensity than usual makes my muscles decidedly annoyed with me the following day.

WHAT'S GOING ON
Although no one's sure about the exact cause of delayed-onset muscle soreness, or DOMS, the breakdown of muscles is probably to blame. In fact, the number of white blood cells, which aid ailing muscles, increases after strenuous activity. Mine are in serious overdrive. And surprisingly, research shows that ibuprofen and massage don't soothe them that much. But sitting in an ice bath for eight to 15 minutes within a few hours of a tough workout does lessen damage. Elite marathon runners and sporting teams swear by it.

A few days later, once the post-race suffer-fest has passed, all I remember is the endorphin-fuelled high at the finish. Sign me up for more! With everything I know now, next time I'll be kicking arse more than ever.

This is your body on strength training - click here.

This is your body on yoga - click here.