Scott LaFee, Contributor

I'll rest when I'm dead. It's an old joke, but also true. Alive, your body remains in constant motion: heart and lungs pumping, eyes blinking, muscles twitching, 100 trillion cells moving at the speed of life.

Flesh and bones

The average speed of human sperm is eight inches per hour.

On average, it takes 72 seconds for a mature egg to be pushed out of the ovary.

Fingernails grow at 0.02 inches per week, four times faster than toenails. This translates to 0.0028 inches in a day or 0.000119 inches per hour. The middle fingernail grows fastest; the thumb slowest.

The fastest a human has run is 34.3 mph.

A knee jerk reflex takes about 30 milliseconds or 30 one-thousandths of a second.

An adult human spine compresses roughly 0.59 inches from morning to night.

Humans shed about 600,000 particles of skin per hour, about 1.5 pounds a year or 105 pounds of skin by the time they are 70 years old. This translates to an entirely new outer layer of skin cells every 27 days, almost 1,000 new skins in an average lifetime.

Head and shoulders

Particles ejected during a sneeze have been clocked at speeds of up to 103.6 mph.

A normal swallow takes eight to 12 seconds, from mouth to stomach.

The average yawn lasts six seconds.

Gums are renewed every one to two weeks.

The average life span of a human taste bud is seven to 10 days. By age 60, most people have lost half their taste buds.

The average mouth produces 1.8 pints of saliva daily.

The average duration of a single blink of the human eye is 0.3 seconds.

The average person blinks 25 times per minute or about 13,140,000 blinks per year.

In a foetal brain, nerve cells develop at an average rate of 250,000 per minute.

At least 100,000 chemical reactions occur in the brain every second.

After age 30, the brain begins to lose neurons at a rate of about 50,000 per day, shrinking one-quarter of one per cent in mass each year.

A normal breath takes five seconds: two to inhale, three to exhale.

In maximum ordinary breathing, the speed of air passing through the nose equals 10 feet per second or Force 2 on the Beaufort wind scale, for example, a light breeze.

When you laugh, you expel short bursts of air up to 70 mph.

Human adults breathe, on average, about 23,000 times a day.

Blood and guts

The human heart beats about 70 times per minute or approximately 36,792,000 beats per year or about three billion (give or take a few million) over an average lifetime. A woman's heart typically beats faster than a man's.

Blood travels at about 0.7 mph. It takes 60 seconds for a drop of blood to circulate through the body.

The body's bone marrow produces three million blood cells every second - and destroys the same number.

The stomach produces a new layer of protective mucus every two weeks.

Nerve impulses travel at speeds up to 200 mph. A prickling pain travels at 67 mph; a burning pain at four mph.

The average human on an average day secretes 2.5 quarts of sweat.

The average American goes to the toilet (for one reason or another) six times a day.

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