Biggest birthday gift is fitness as 56-year-old walks a mile for every year.

The T-shirt Sandra Johnson wore last Friday was no April Fool’s joke.

As she walked on Arrow Highway as though her life depended on it, she proudly displayed the shirt, which proclaimed: “56 miles to celebrate 56 years, April 1, 1988.”

The long trek was Johnson’s way of celebrating her 56th birthday.

The temperature was in the 80s in the early afternoon as she approached the San Dimas city line from La Verne, not even sweating as she hit the 45-mile point in her journey.

She started from her South Pasadena home at 3 a.m. and reached the home of one of her sons in Upland at about 11:30 a.m. She concluded her journey at 6:37 p.m. in West Covina at the home of another son, who had invited 30 guests for her birthday party.

“There are a lot more scenic places I could have walked,” she said, “but I wanted a birthday party, so in choosing a route I ended up at the home of one son. That was the only way I was going to get it!”

A physical fitness buff, Johnson averaged about 4 m.p.h.

She had figured the mileage by driving the route, which took her east along Huntington Drive and Foothill Boulevard and west along Arrow Highway.

“I had thought Upland would be the end, but it wasn’t far enough, so I figured if I continued to my other son’s home, it would come out to 56 miles. It was 54, so I added two miles,” she said.

When she finally finished, Johnson said, her feet hurt. Otherwise, she felt fine.

Johnson was accompanied by a support car carrying essentials such as water, bananas, oranges and extra shoes and socks. The driver, Tony Bashoor, would stop a half-mile to a mile ahead and wait. But he said it never took very long for Johnson to catch up, yelling for food and water.

Another friend, Judy Stewart, joined her in San Dimas and ran alongside for 1 1/2 hours.

“Arrow Highway didn’t give me much trouble, although in a few places there was a lot of traffic,” Johnson said. “And I had to stay in the street because race walkers can’t go up and down curbs. I stretched when I had to wait for a stop light.”

Johnson is a fashion and image consultant who also teaches fashion design at Woodbury University.

“My first love is hiking and mountaineering, so I can get away from the city,” she said.

But she didn’t start formal exercise until she was 35 and began gaining weight. First came a stretching routine. Eventually she began swimming, weight-lifting and bicycling. She works out at a gym every day but didn’t take up walking as an exercise until last Thanksgiving.

“I competed in a 5-K combination walk and run,” she said. “I came in second, and the winner was 27 years old. So I decided to learn race walking and joined the Southern California Walkers club. You use your entire body in race walking, and that’s why I didn’t tire on my walk.”

Johnson isn’t sure she will spend her next birthday the same way. “But if I do, I’ll choose a different route.”