As much fun as it is simply to get out for a casual run, bike, paddle or swim with friends — suck in fresh air, get the heart pumping and muscles moving — sometimes it's worth bringing an edge to the workout, pushing the envelope into the discomfort zone.

And so we pick up the pace, take an extra lap, steer for uncharted waters, or set up challenges and complexities that demand sharpened focus, higher energy. Sure, this ratchets up the stress but then the ultimate rewards are much more gratifying.

This evidently contributed to bicyclist Kevin Clark's reasoning a few years ago when he gazed from the Connecticut shoreline and realized that Block Island and Long Island, both primo cycling destinations, really weren't that far apart. The wheels started churning, and then came the epiphany: Ferry boats.

He raced home, pulled out maps, checked boat schedules and came up with a madcap but elegant itinerary: Pedal from his home in Stonington to Point Judith, R.I.; board a ferry with his bike to Block Island; ride around the perimeter; then hop on another ferry to Montauk Point on New York's Long Island; bike to the Hamptons; then veer off to Sag Harbor; take another ferry to Shelter Island; ride across Shelter Island; take another ferry to Greenport; then sprint to Orient Point; board yet another ferry to New London and finally cycle back to Stonington. All in one day.

Buoyed with excitement he called a few pals to invite them to tag along.

"They all seemed to have other plans," Clark recalled the other day. No matter — he would go solo.

"And so that first year I went by myself," Clark said. "It was great!"

After that successful ride, Clark rhapsodized so extravagantly that he persuaded cycling buds Mary Georgetti and Steve Valach to join the fun the following year. Another triumph. I have to admit it is an excellent adventure — if you embrace the concept of pedaling like crazy for nearly 100 miles while casting frequent, nervous glances at your watch.

Still, at Clark's insistence the riders took the time for a hearty breakfast before setting out on Block Island and also briefly pulled over at a fruit stand for a short snack somewhere between the Hamptons and Sag Harbor. Other than breaks during ferry voyages, though, the pedaling was pretty much flat out.

"It is not a leisurely ride," Clark said. "No stops, except for a pee break. That's it."

Now the trio is planning a reprise sometime in the next couple of weeks.

"Has to be on a Sunday" because of the ferry schedule, Clark said. The trip, which he calls a "doorstep adventure," also must take place in the summer to take advantage of longer daylight. There's little joy in pedaling from New London back to Stonington in the dark at the end of a long day.

"Gotta start by 5:45 a.m. to catch the 8:30 high-speed ferry to Block," he explained.

Connections to the other ferries, which run regularly, are less critical, but you can't afford to waste time sightseeing. You definitely don't want to miss the ferry from Orient back to New London.

I can respect that, having launched a few nutty outings in my time.

I remember once having to run the Boston Marathon in under 3 hours and 20 minutes so I wouldn't miss the train back to Mystic. I've also had to time various kayak voyages through Hell Gate on New York's East River, The Race off Fishers Island, and Plum Gut off Orient Point — all with D-Day-like precision to avoid maelstrom-like currents and confused seas during peak tides.

There's nothing like a little added incentive to stay on schedule.

Sometimes, though, you have to bow to immutable forces.

While kayaking back from Groton to New London with Carl Astor and Dan Bendor a few years ago, we noticed a Navy patrol boat heading up the Thames River just as we prepared to cross.

"Must be a submarine coming," I said.

Sure enough, a moment later we could see the conning tower.

Dan, a psychiatrist who was scheduled to see a patient that morning, checked his watch.

"Can't wait," he said, and began to sprint ahead.

"Dan!" Carl and I shouted, but it was too late. He made a beeline for Ballard Beach and had gone maybe 10 yards before the patrol boat swerved and goosed it in our direction.

"Hold it!" an armed man on the bow shouted.

We stopped. Dan started to plead his case that he was late for an appointment, but by that time the sub was only 50 yards or so away.

Carl is a rabbi, and I was tempted to borrow a line from "The Blues Brothers" movie: "We're on a mission from God!" but wisely held my tongue. We all watched the giant vessel slowly and silently slip by. Some of the crew stood ramrod still on deck and stared.

As soon as the fantail passed, Dan took off. I learned later he got to his office in the nick of time.

Anyway, I hope the bike riders don't have any such close calls.

Good luck, guys! I'll keep readers posted on this year's ride.