BANGPLEE, Thailand — As my 30th birthday approached, my fear of becoming a middle-aged woman plagued with mystery ailments, huffing and puffing up flights of stairs, finally started to outweigh my exercise phobia.

So I decided to get in shape while learning Thailand's notorious national sport, muay thai, known in English as kickboxing. This was no small commitment: I attended a muay thai camp near Bangkok for 10 days, training for five hours a day.

Muay thai is performed with boxing gloves in Western-style boxing rings, but uses knees, elbows and legs, in addition to fists, as weapons. It is considered the most violent of all martial arts because of the damage an elbow can inflict on an opponent.

The two gyms that got the highest ratings online from kickboxers around the world were Fairtex, located in the Bangkok suburb of Bangplee, and another gym on the dazzling Thai island Phuket. Both offer one-on-one muay thai training.

I chose Fairtex.

Fairtex opened its doors to Westerners five years ago and has two gyms in California, one in San Francisco and one in Silicon Valley, in addition to gyms in Thailand and Japan. Foreign students temporarily adopt the lifestyle of professional Thai fighters, who live, eat, sleep and train at camp.

Grunts, whacks and thumps greeted me when I arrived. Students glistening with sweat duked it out with trainers in four outdoor boxing rings.

Training began at 6:30 a.m. with a half-hour of cardiovascular exercise in the air-conditioned gym.

My fantasies of becoming a female Rocky faded fast when I got to the gym and couldn't figure out how to use the treadmill. I frantically poked at the mystery buttons and knobs, trying to will the machine into action. Finally another student came over and turned it on for me.

As I jogged, I imagined everyone staring at my jiggling thighs and listening to my haggard breathing, thinking, "What is she doing here?"

Next, a barely pubescent-looking Thai kid came over and started wrapping my hands in the flashy pink hand-wraps I had picked out at the onsite shop the previous day. Sarun Inta was my trainer for the next 10 days.

Each morning after cardio, I met Inta in the ring where he showed me muay thai moves, mostly by pantomiming, as his English was limited. Then he held up pads and told me to kick, punch, and jab with knees and elbows until my arms felt like rubber and my kicks came out sloppy and in slow motion.

After training in the ring for five rounds of four minutes each, Inta sent me staggering over to the punching bags to practice my technique. I finished each session with 100 sit-ups.

And then I repeated the whole process in the afternoon.

My entire body, from head to toe, hurt for the first few days. My knees and shins were covered in blue and green bruises.

In between training sessions, I could do little more than sleep and eat. I was too exhausted to even string together complete sentences. This was my journal entry on day two: "Everything bruised. Hurts. Red curry for dinner. Pain. Must sleep now."

Fairtex is not the kind of place where a trainer will sit you down with a steaming mug of herbal tea and talk to you about your fitness goals. But if you smile nicely, you might get someone to punch you in the stomach while you do sit-ups, which a trainer did for me on my fourth day. Apparently, the punching helps abdominal muscles toughen up to prevent injury from the impact of punches and kicks.

Women were once barred from entering Thai boxing rings, as they were seen to bring bad luck to the competitors. But that tradition has changed. Four out of the 25 foreigners training at Fairtex were women.

Claire Louise Douglas, 25, traveled from Scotland to train at Fairtex. She started taking Thai boxing classes in Glasgow four years ago to build her self-esteem after ending a bad relationship.

"I remember always standing at the back of the class because I was slightly overweight and had no confidence, but after about four months I ended up at the front of the class," said Douglas.

Douglas, now a university student, manages to squeeze three two-hour training sessions a week into her schedule at home.

Inta, my trainer loved to tease me. Sometimes he would tell me to punch, but then pull the pads back so that I would stumble off balance. Then he'd kick me softly on my side and laugh.

But on my third day, I knocked him down. By then, he'd taught me how to block, so when he pulled his pads away this time, I rebalanced and threw up my knee to block his kick. He fell to the ground, then rolled around clutching his foot and laughing.

After that, I felt tougher. I kicked and punched harder than before.

Back in New York, instead of falling into my usual pattern of laziness, I woke up at 6 a.m. and went running in Central Park. For the first time I could remember, I enjoyed exercising. Perhaps muay thai camp was the first step in my permanent lifestyle change.