A decade after my epic cycling trip through the Scottish Highlands, I’m on my exercise bike, pedaling furiously, with sweat dripping everywhere. I’m re-reading Gretchen Reynolds’ “The First Twenty Minutes,” one of the most lucid, engaging and compelling books on fitness that I’ve ever read (I will do a review of that book in a future blog).

As the miles began to accumulate, I’m shocked to read the thoughts of David Nieman, Ph.D., a professor at Appalachian State University, and an author of numerous books on exercise.

Nieman was a skeptic of caloric afterburn — which, in simple terms, is the energy your body expends after you’ve finished exercising. He was adamant that no such thing existed. I was perplexed. I had seen that first-hand that the opposite was true. My own experiences had testified to that.

So I continued reading. A few paragraphs later, Dr. Nieman had his colleagues begin testing volunteers (healthy young men in their early twenties and thirties) in a very expensive and advanced metabolic chamber. The result? Caloric afterburn is possible. But there’s a caveat: the workout has to be suitably intense.

As cited in Reynolds’ book, the volunteers were burning, on average, 519 calories per hour. This equated to 75 percent of each volunteer’s endurance capacity. The result? The volunteers burned an extra 190 calories after their session, without the benefit of any additional workouts.

How does this translate to the everyday experience of the typical gym-goer? I’ll answer that question with a brief anecdote…

Years ago, when I was a trainer at UCSF Mission Bay, one of the gym manager slapped my on the back, and (perhaps half-heartedly) asked “You know, Josh, there must be a better way to get people to reach their goals.”

We surveyed the gym floor, which had a fairly typical layout. In the middle of the floor was a collection of neatly aligned cardio machines. Off to the right was the free-weight area. And squeezed around the edges was the stretching and “functional fitness” area.

There was a fairly predictable hum and whirr from the cardio machines, interrupted periodically by grunting and shrieking from the free weight area. The gym had a rhythmic complacency: people had settled upon their routines, and were dutifully carrying them out.

Greg and I watched the fitness vignettes play out without commenting. Perhaps the rhythmic whirring of the machines had addled our senses.

After several minutes, I broke the silence.

“Maybe we should introduce large predatory cats into the gym.”

Greg gave me a blank look.

“It would completely break up the monotony of the gym. People would run like hell.”

Greg gave me a friendly slap on the back and nodded as if to say, “your input is duly noted and will never be sought again.”

Snarky scenario aside, a valid point remains: if people are going to the gym for fat loss, they’re not working out hard enough to achieve it. And that’s the ultimate conundrum of the gym — people think their mere presence at the gym justifies however many calories they intake post-workout.

But it doesn’t work that way. If you’re going to the gym for fat loss (which is a good goal, but by no means the only one), then texting your friends, chatting on the phone, or watching reruns of “Everyone Loves Raymond” probably isn’t going to cut it.

You need to work out hard in order to achieve the goal of burning fat. There are people at the gym who are bathed in sweat and breathing hard. They don’t look like they’re having a particularly pleasant time. They’re the ones who will experience the caloric afterburn long after their exercise session has concluded.

When I’m on the exercise bike, I try to aim for burning around 700 calories an hour. (When I’m cycling outside, it’s more about climbing hills and enjoying the scenery). The volunteers cited in “The First Twenty Minutes” burned an average of around 520 calories. So, perhaps those numbers can provide such benchmarks.

I’ll end this article with a quote from Dr. Nieman, as cited in “The First Twenty Minutes.”

“We’ve become a nation of exercise wimps,” he said. “Too many people don’t bother or are afraid of exercising hard. But intensity is probably the only way to lose weight (fat) with exercise.”