You know me. I'm a tiger when it comes to persuading, cajoling, begging you to exercise outside, especially in the summertime. Jump on your bike, mow the lawn, paddle a canoe, do any activity you like that gets your heart pumping and your juices flowing, and doesn't involve a cell phone.

But exercising hard in extreme heat is a no-no. Heat illness is the No. 1 weather related killer, about 700 deaths a year, according to the Centers for Disease Control and Prevention. Even if it doesn't kill you, exercising in the heat can make you very sick.

I've long known that intellectually, but I'd never seen it up close and personal until a few weeks ago. It happened very quickly, and it scared the sunlight out of me.

My friend Claire was visiting me in Greece, and naturally we headed for the beach. Her first mistake was to slather on the sunscreen and assume it protected her from the ill effects of the intense Mediterranean sun. Not true. Next, she lay on the sand hatless. Third, she was dehydrated and didn't know it. Finally, she was taking a heart medication and her doctor didn't warn her of possible complications from too much sun exposure.

We didn't know she'd had too much until we walked up a long hill to the house and she collapsed in the kitchen. Luckily, she made it to a chair. She felt fireworks in her brain. Her vision blurred, her head buzzed, her arm tingled. Most frightening? She was mentally disoriented. "I can't remember what I just thought," she said. We were on a small remote island, a day away from the nearest hospital. Sun stroke? A heart attack? We weren't sure what was happening.

Fortunately, we got her cool and calm and hydrated in minutes, and after a few days of home care — more rest, more fluid — and conversations with her doctors, she felt much better and was able to get on a plane and go home. Heat exhaustion was the general explanation. Her short-term memory is still a bit wobbly, but it's coming back, and Claire — a nurse! — feels she dodged a bullet and learned her lesson.

And so did I, which is why I decided to bow out of a long bike ride the other day when the temperature was 90-plus. Why risk it? Instead, I took myself inside for some yoga in a cool room with the fan blowing. Life is too short to pretend you're invincible.

And that's my plea to you, oh, active reader: Don't play around with exercising in high heat. Use your common sense. Don't overdo it. If you feel like walking, running, biking or just playing at the beach, do it in the early morning or late afternoon to avoid the sun's most intense rays.

No matter what time you're out, pay close attention to how you're feeling. If you're struggling to keep going, stop and cool off. Drink plenty of water. (But not too much because that causes problems, too.) And most important, learn the early warning signs of heat illness: cramps, limited sweating, dizziness, headaches, nausea and thirst. If you experience any of these, don't push on. And remember what happened to my friend Claire, with no early warning signs at all.

EAT THIS UP! ANYTHING GOES ON THE GRILL

Summer is the No. 1 season for outdoor cooking, but don't think you're limited to the usual high-fat favorites of steaks and brats, ribs and chops. Have you ever heard of grilled salad? You have now.

Romaine, endive, cabbage and radicchio are hearty lettuces that do well in high heat, if you don't let them cook too long. Separate the leaves, or cut the thicker species in half, brush lightly with oil and grill face down over medium heat.

Also yummy to grill: red peppers, zucchini, pineapple, watermelon (!!!) portobello mushrooms, artichokes (sliced through the middle) and — hold on now — avocado. Yes, grilled avocado. Makes the best guacamole in the taco-chip-eating world.

3 WAYS TO BURN 100 CALORIES: Grocery shop for 20 minutes carrying a basket instead of pushing a cart; dance around the house for 20 minutes; mop the floors for 25 minutes.

ENERGY EXPRESS-O! TODAY'S BELLY LAUGH

"Self delusion is pulling in your stomach when you step on the scale." — Paul Sweeney