Think about the last time you got out of a low car. Or up off a soft couch. Did your hands do some of the work?

That push off the armrest creeps in so slowly you barely notice it. But it's your legs asking for help...

You can't buy leg strength in a bottle. But the produce aisle sells something close, for a few dollars a bag. And the proof started with a joke that turned out not to be a joke.

Let me explain...

On March 26, 1937, the spinach growers of Crystal City, Texas, put up a painted statue of a cartoon sailor. You know the one. Pop a can, squeeze it down, and the arms swell up. The town called itself the World Spinach Capital. In the hard years of the 1930s, its canneries turned out about 10,000 cans a day.

Growers gave the sailor a lot of the credit. Kids who hated the green stuff ate it anyway. Of course, grown-ups laughed. Muscles from a leaf? The old story said it was the iron, and that part never held up well.

Spinach had been around long before the cartoon. It came out of old Persia, and Chinese cooks once called it the Persian vegetable. Home cooks in the West said it "builds the blood." Nobody had a clue it might build anything else.

So for decades, spinach-for-strength sat on the shelf with the other cartoon gags. Then, in 2012, a lab in Stockholm put out a news release with a cheeky title. It said, in effect: solved at last, why spinach makes us strong...

A top sleep expert from the University of Washington points to something that takes thirty seconds and one cherry.

Studies show it releases a sleep-regulating hormone: you fall asleep faster, stay asleep, and gain 84 minutes of total sleep — which science puts at ten times better than melatonin.

It is working for 36,498 people.

See the 30-second cherry trick

Here's how a muscle pulls. A nerve fires. The muscle fiber opens a little store of calcium. Calcium floods in, and the fiber squeezes. More calcium out means a harder pull.

Spinach carries a plain compound called nitrate. Leafy greens are loaded with it. You see, the Stockholm team gave mice a small amount of nitrate in their water for one week — a dose you could match with vegetables. Then they tested single muscle fibers.

The fast fibers changed. Those are the ones you use to stand up quick or push out of a chair. They let out more calcium with each spark and pulled harder. The slow fibers, built for long walks, didn't budge.

Mice aren't people. So hold that part as the likely "how," not the proof. The proof came from the other side of the world.

Edith Cowan University, Perth: 3,759 Australian adults were tracked for 12 years. People in the top third for nitrate, most of it from vegetables, had legs about 11% stronger than the bottom third — roughly 2.6 kilograms, or close to 6 pounds, more push on a knee-strength test.

Dr. Marc Sim and his team at Edith Cowan University used a long-running national health study. People filled out food forms three times across 12 years. Then, in 2011 and 2012, the team measured how hard each person could push with the front of the thigh.

The top group ate about 91 milligrams of nitrate a day. That's about what one cup of raw leafy greens gives you. The bottom group got about half that. And the top group was far less likely to test as weak.

Here's the part that surprised the team. The link held whether people were active or not. Active people and couch sitters both showed it. The team still said to keep moving, and so do I.

Now the fine print. This kind of study watches people. It can't prove the leaf did the work. People who eat lots of greens may differ in other ways, and food forms are only as good as memory. The group was also younger than you might think, about 49 on average at the start.

But an earlier study from the same Perth team looked at 1,420 women over 70. More nitrate went with a stronger grip. Two groups, two ages, one direction. That's worth a cup a day.

Nitrate can't do this job alone. Tiny bacteria on the back of your tongue change it first. You swallow the result, and your body turns it into the messenger the muscle uses.

Strong germ-killing mouthwash knocks those bacteria flat. In one small study of 19 healthy people, a week of a strong rinse cut the mouth's change-over by about 90%. So if you swish right after your salad, you may be washing away the part that counts.

If your dentist gave you a rinse, keep using it. Just ask about timing. Brushing and flossing are fine.

Nitrate melts into water. Boiling spinach can pull a quarter to half of it into the pot, and then down the drain. Steaming barely touches it. Eat it raw, wilt it into eggs at the last second, or keep the liquid in a soup.

Raw spinach keeps a few days in the fridge. Cooked spinach is different. Left sitting warm, or kept for days, some of its nitrate can turn into a form you'd rather not stockpile. Cook a pan, eat it, and chill any leftovers fast.

A cup of raw spinach holds more than a full day of vitamin K, which helps blood clot. If you take warfarin, don't stop the greens — keep the amount steady and tell your doctor. And spinach is high in oxalate, so anyone who has had kidney stones should ask before eating it daily.

That painted sailor still stands in Crystal City. The growers put him up to sell cans. None of them knew a quiet compound in the leaf was doing real work inside the muscle.

Skip the can and the cartoon arms. What you need is a cup of green on your plate, day after day, and the patience of a season.

Start this week. Then notice how you get up off the couch come Christmas.