How hard is the Tour de France? Ask our spandexed scribe.

About half way up the "Col de Grosse Pierre" (Big Stone Pass), sweat stinging my eyes and my thigh muscles screaming, it occurred to me that the big stone in question was not some ancient landmark but attached to my bicycle.

Or possibly located between my ears. What on earth did I think I was doing, cycling up a mountainside in eastern France until my lungs burst or my heart gave out, whichever came first? And ludicrously dressed in highly unflattering Spandex, to add insult to injury.

Blame it on my editor. Perhaps tired of reading my annual description of the Tour de France bicycle race (now ending its first week with Lance Armstrong, again, wearing the leader's yellow jersey) as the toughest physical challenge in world sport, he assigned me to answer a simple question: How hard is it really?

I am on the wrong side of 50, fully enjoy the gastronomic pleasures of France, and have not seriously exercised for several years. In no manner do I resemble the muscled young athletes at the peak of their form who are currently pedaling round France on a 2,255-mile race to glory.

But I thought it would be instructive to ride a little bit of their route, which is why I found myself a few days ago in this picturesque town in the Vosges mountains, listening carefully while bike-shop owner Marie Agnes Picart explained to me the finer points of 21-gear racing machines.

After taking an experimental spin around Ms. Picart's forecourt, I set off.

I didn't attract much attention as I wobbled down Gérardmer's main street - cycling is a popular sport in these parts - and I was soon at the edge of town starting my first climb into the pine-forested hills.

Almost immediately I was in trouble. I was having difficulty changing gears, I was breathing loudly, and I could feel my heart pounding. My greatest fear: I would not make it to the top even of this introductory slope, not steep enough to warrant any kind of classification on the Tour de France itinerary.

After a while, however, I found my rhythm, using the middle of the three chain-wheels so as to give myself room to maneuver when things got harder, and climbing at a steady seven miles per hour. My satisfaction overrode my realization that when the Tour riders come this way on Sunday they will treat this little hill as a speed bump.

At the top I stopped for a while to congratulate myself, and to study the road ahead which rose alarmingly out of rolling pasture up into the pine trees. This was not much of a challenge by Tour standards - a mere category 3 climb on a descending scale of four - but it looked serious enough to me.

Less than 500 yards from the bottom, I was already in the easiest gear, out of breath and badly flustered. I was left with only one option, to pedal more slowly, and little by little I recovered my nerve. I was doing five miles per hour, which may have been three times slower than the pros take a hill like this, but was not so tortoise-like as to fulfill my second greatest fear - that I would go so slowly I would tip over.

I didn't exactly feel the wind in my hair, however. At five miles per hour I should have had a chance to enjoy the scenery; in fact I found myself fixating on the tarmac, sucking air as I fought to turn the pedals. Looking up gave me a crick in my neck, and a dispiriting view of the continuing hill ahead.

The Col de Grosse Pierre, which lasts for two miles, has an average gradient of 6.4 percent. In a car, you would probably take it in third gear, changing down to second at the hairpin bends. On a bike, however, imperceptible changes in gradient make themselves painfully felt in your legs. And I had no gears left to change up to.

I was pouring sweat, my lungs were burning, my thighs straining, and my buttocks aching from the discomfort of racing saddle. "This is me against myself," I thought. That wasn't sufficient motivation. "OK, this is me against my editor."

Then slowly, miraculously, the slope seemed to ease. I allowed myself to hope, and raised my eyes. And there it was, a hundred yards ahead, the little black road sign "Col de Grosse Pierre" that marked the summit. My face broke into a big grin.

Then, of course, came the fun part, though I kept my hands on the brakes all the way down the other side of the mountain, nervous of going too fast on the steepest stretches. Freewheeling the whole of the three-mile descent, I was whooping and laughing with glee at the thrill, deafened by the wind rushing past my ears.

When I hit 30 miles per hour, I frightened myself and slowed down. Later that afternoon, on flat ground elsewhere in France, Tour de France riders averaged more than 35 mph over more than an hour of racing in a time trial.

By the time I reached the village of la Bresse, at the bottom of the hill, I did not even feel ridiculous in my Spandex as I rolled up the street. I had climbed a mountain and raced down the other side, and reckoned I knew what I was doing.

Which proved to be not entirely the case. I set off on my second ascent, an eight mile - but gentler - climb in high spirits, if a little sore. I discovered that though the average gradient was only 3.1 percent, that figure masked some nasty little walls.

Coming up on one of them, and getting my gear-change wrong again, I stalled and tipped over. With my feet strapped to the pedals I was helpless, and hit the road hard on my elbow. As I lay there entangled in my bike, my Spandex-enhanced paunch in the air, I was glad of the mountain solitude: On Sunday several thousand fans will line this route, but nobody was there to see me being undignified.

In the end I made it to the top without getting off, mainly by taking it slowly. Not counting stops for swigs of energy drink at the top and bottom of each climb it had taken me about two hours to do the two mountains - a 16 mile ride. It will probably take the Tour de France pack little more than half an hour.

I had a ten mile cruise back to my hotel, and was so exhausted the next day I fell asleep mid-afternoon. The Tour riders will have another 91 miles to go on Sunday, and another four mountains to climb before they can get out of their saddles. And then the Alps. And then the Pyrenees.

Case proven, I think, Mr. Editor. The Tour de France is the toughest competition in sports.