I turned 55 today and celebrated with a 30-minute ab workout.

I had to: According to the National Institutes of Health, while 55 is when males generally start dropping weight (sorry gals, it doesn’t happen for you until around 65), I’m now more inclined to hang on to the weight I’m keeping — in the form of fat — around my midsection.

Some other interesting bits I learned from the NIH on getting older:

• Shrinking Coming into 55, I was worried I might start the geriatric shrinking process. Turns out I should have started worrying about that 15 years ago: According to the NIH, people generally shrink 0.4 inches every 10 years. After 70, your height can diminish by up to 3 inches over a decade. (That shrinkage, incidentally, is in the torso, not in the arms or legs.)
• Muscle and organ atrophy Muscles, liver, kidney and other organs start to lose cells. I’m not so worried about the liver and kidneys, but that loss of muscle can make them weaker, fatigue more easily and result in “reduced activity tolerance.” (Worried that might have happened overnight, I’ve also celebrated today with a 70-minute, 12-mile mountain bike ride at Lake Crabtree.)
• Slowed reflexes Did I mention that on the aforementioned mountain bike ride I reacted late to a tree root, hit the disc brakes and flew into, then over, the handlebars? This reduction is caused less by a slowing of nerve impulses and more by changes in the muscles and tendons.
• Dehydration A “change in body water” makes it easier for older people to get dehydrated. May be time to upgrade my Camelbak from a 70 ml bladder to 100.
• Stiff joints, less flexibility. Hips and knees, in particular, ankles less so. Seems the best way to keep them from stiffening up is to not let them stop moving.
• Wrinkly, sagging skin, gray hair, crow’s feet, less hair growing where I want it, more growing where I don’t … I’m ahead of the game on these counts, but who cares? Gray eyebrows don’t keep you from running a half marathon, droopy eyelids don’t keep you from riding a mountain bike.

So I’ll have a few more age-related challenges in the year ahead. All the more reason to be disciplined, and the best way I know to do that is to have goals. Thus, to mark the milestone of having turned 55 I’ve adopted the number 55 as my theme for the year ahead. That said, my goals (some of which are inspired by a book I’m starting to write on adventure sports in the Carolinas):

• Run 11 5Ks (11 x 5 = 55, for those of you who didn’t come here expecting math problems)
• Climb “The Mummy” at Linville Gorge, a 5.5-rated rock climb.
• Do a 55-mile backpacking trip.
• Do a 55-mile canoe trip.
• Do 55 straight push-ups. (I’ve been especially slack over the years on strength training; with my muscles atrophying staying strong becomes even more important.)
• 55: Total of my waist size (30) and BMI (25). I’m an inch or two away on the waist size, and while the body mass index is still woefully flawed, I’m still irked that my current rating of 26 makes me overweight in the government’s eyes.
• Resting heart rate of 55. Cheating a little on this one: Last time I checked my resting heart rate was 54.
• 55-mile mountain bike race. Still looking for a candidate for this one. Could come in a 6-hour endurance race, though the most miles I’ve racked up in one of those was 48. Yell if you know of any 55-mile mountain bike races.
• 55 miles on my mountain bike on my birthday. I cut this one short because I need to fetch kids from school starting a 2 p.m. Hopefully next week.
• Umstead 50-miler trail run. OK, so it’s five short. I’ll be dang lucky to make the 50. (Most runners in this race, btw, run 100 miles.)

As my 55th approached, I was asked a few times how I felt about turning 55. I gave the only answer that made sense: It beats not turning 55.

Besides, look at all the cool stuff I get to do!