What is the Harris-Benedict Equation and how can you use it to master your nutrition?

Keeping fit and lean isn’t rocket science, is it? It’s the simple equation of calories consumed vs calories burnt. You want to lose weight? Make sure you’re in a calorie deficit. Want to gain wait and build muscle while working out? Consume those calories so you’re in a surplus. Easy-peasy right? Well, how do you know how many calories you should either be burning or consuming? That’s where the Harris-Benedict equation comes in.

The Harris-Benedict equation is one of the oldest and most widely used methods to estimate BMR, which is the amount of energy expended while at rest in a neutrally temperate environment, in a post-absorptive state (meaning that the digestive system is inactive, which requires about 12 hours of fasting in humans).

The original equation, developed in 1919, was later revised in 1984 to improve accuracy. For the mathematicians out there interested in the equation, here it is:

For Men:

BMR=88.362+(13.397×weight in kg)+(4.799×height in cm)−(5.677×age in years)

For Women:

BMR=447.593+(9.247×weight in kg)+(3.098×height in cm)−(4.330×age in years

How the Harris-Benedict Equation Works

Both equations are used to calculate BMR, which represents the number of calories your body needs to maintain basic physiological functions like breathing, circulation, and cell production while at rest. Once you have your BMR, you can adjust it based on your level of physical activity to estimate your Total Daily Energy Expenditure (TDEE). So how can we use the Harris-Benedict equation to understand how many calories we burn during prolonged activities such as rucking?

The number of calories burned while rucking (walking or hiking with a weighted backpack) for an hour depends on several factors, including your weight, the weight of the ruck, the terrain, and your pace. Here's a rough estimate based on some of these variables:

General Estimates:

Moderate Pace (3.5 mph) with a Light Ruck (20 lbs):

• A 150-pound person might burn approximately 430-500 calories per hour.
• A 200-pound person might burn approximately 550-650 calories per hour.

Faster Pace (4 mph) with a Moderate Ruck (30-40 lbs):

• A 150-pound person might burn approximately 500-600 calories per hour.
• A 200-pound person might burn approximately 650-750 calories per hour.

Challenging Terrain (hills, trails) with a Heavy Ruck (50+ lbs):

• A 150-pound person might burn 600-700+ calories per hour.
• A 200-pound person might burn 750-850+ calories per hour.

Factors Affecting Calorie Burn:

• Body Weight: Heavier individuals burn more calories.
• Ruck Weight: The heavier the ruck, the more calories you'll burn.
• Pace: Faster walking increases calorie expenditure.
• Terrain: Rougher, hillier terrain requires more energy.
• Fitness Level: More fit individuals might burn slightly fewer calories because their bodies are more efficient.

Let's say you're 180 pounds and rucking with a 30-pound pack at a moderate pace on flat terrain. You might burn roughly 550-650 calories in an hour. Either way, rucking is proved to be a highly effective calorie-burning activity, especially when compared to other activities of the same duration.

The Harris-Benedict equation can be a great way to understand how many calories we burn idly. Your body will passively burn calories by simply keeping our body temperatures optimal, brain activity and through other micro movements. It can be quite surprising! But the great thing is that once we know what this number is, we can easily set a goal for either losing or gaining weight through this method.

The Harris-Benedict Equation for Rucking

How can we use the Harris-Benedict Equation when rucking? If you’re an avid rucker, you’ve most likely got a steps counter, heart rate monitor and calorie counter tracking your session. All you need to do is use an online calculator like the OMNI calculator to input your age, weight, gender and height, giving you your base calorie burn. Then simply track your calories throughout the day, depending on whether you want to lose weight, pushing you into a deficit, or maintain, by keeping a balance between calories consumed and burned.