What is the hardest physical challenge you've ever done? For me, the toughest days are a toss-up between running a long way uphill and cycling a long way uphill.
I am upping the ante this week in Hawaii: cycling from sea level to the summit of the Haleakala volcano. To say that this is a very big hill would be a rank understatement.
Haleakala is simultaneously the longest paved continuous climb in the world as well as the shortest ascent from sea level to 10,000 feet in the world; with an elevation gain of 3048m over just 40 miles, that's the equivalent of riding to the top of Carrauntoohil three times in a row while cycling from Killarney to Dingle.
It will be a test of both my fitness and ability to deal with the physical and psychological challenge of cycling uphill for nearly five hours.
A recent scientific study, using tests with iced water to determine how well athletes can withstand pain, showed that triathletes have a higher pain threshold than non-athletes (and I suspect the same finding would apply to runners and cyclists).
Surprisingly, the researchers suggested that pain tolerance was perhaps an inherited trait for such athletes, meaning that they have become athletes because of an innate ability to withstand pain.
My immediate interpretation of the results is that the more you train, the better your ability – both mentally and physically – to tolerate and overcome discomfort (and indeed, it's that pure grit, or ability to squeeze out the last drop of speed when things really get tough that separates great athletes from the merely talented). So, athletes can bear discomfort (be it iced water, burning quads or searing lungs) much better than the average non-athlete. Uphill we go.
When taking on any new challenge (whether your first 5k or moving up distance from, say, a sprint to Olympic distance triathlon), the mental preparation is as important as the physical.
Recognising that you can push yourself to a point beyond which you have gone before (with the appropriate preparation), and preparing yourself mentally to reach that new milestone is an important part of breaking through to a new level of performance, whether it be distance or speed.
The ability to cope with new physical challenges translates into resilience and perseverance in other parts of life, so it's worth sometimes increasing the stakes and fighting that fear again.
You remember that episode of Friends where Monica goes to Hawaii and has hilarious hair frizz? Now add a Lycra cycle kit and a pint of sweat and you've got the picture. It's close to 30°C and 90pc humidity in Maui and I am as slick as a pound of butter left in the sun too long.
I've been nervously anticipating the ride up Haleakala all week and on Thursday three of us set off with a support car. The first two hours are intensely hot and I am raining all over my bike. The distance we are covering is relatively short so I break down the milestones by elevation gain rather than distance, gaining around 500ft every half hour.
As we get higher and the air gets thinner, my legs are working hard but I am emboldened by the steady progress into the National Park and towards the summit. Someone has thoughtfully painted 'Breathe' on the road, as well as 'Feed the Monster', which makes us smile as we jam energy bars into our mouths.
At last, four hours and 40 minutes of riding later, I struggle through a stiff wind and a final steep ascent to hit the top. Gravity 0, Deirdre 1.