Calories Burned During Exercise: A Science-Based Guide to Energy Expenditure

The term "calorie" as used in nutrition is actually a kilocalorie (kcal) — the energy required to raise 1 kg of water by 1°C. During exercise, your body burns calories primarily through aerobic metabolism (using oxygen to break down carbohydrates and fats into ATP) and, at high intensities, anaerobic glycolysis (breaking down carbohydrates without oxygen).

Total daily energy expenditure (TDEE) has three components:

1. Basal Metabolic Rate (BMR): The energy burned at complete rest — 60–70% of TDEE for most sedentary adults. 2. Thermic Effect of Food (TEF): Energy used to digest and process food — approximately 10% of TDEE. 3. Physical Activity Energy Expenditure (PAEE): Energy burned through movement — including both structured exercise and non-exercise activity thermogenesis (NEAT, such as walking, fidgeting, and standing).

Exercise energy expenditure specifically refers to PAEE from structured activity. However, research by Westerterp (2013) in the *European Journal of Clinical Nutrition* highlights that total PAEE varies enormously between individuals — from less than 200 kcal/day in very sedentary people to over 1,000 kcal/day in highly active individuals.

The Metabolic Equivalent of Task (MET) is the scientific unit used to express the energy cost of physical activities. One MET = the energy cost of sitting quietly, approximately 1 kcal per hour per kilogram of body weight (kcal/hr/kg).

The formula for calculating calories burned using METs is:

Calories burned (kcal) = MET × body weight (kg) × duration (hours)

For example, a 70 kg person walking briskly (MET ≈ 3.5) for 1 hour burns: 3.5 × 70 × 1 = 245 kcal

The Compendium of Physical Activities, published by Ainsworth et al. (2011) in *Medicine & Science in Sports & Exercise*, is the gold-standard reference listing MET values for over 800 activities. Key MET values include:

| Activity | MET value | Kcal/hr (70 kg person) | |----------|----------|----------------------| | Walking (brisk, 5.6 km/h) | 3.5 | 245 | | Jogging (8 km/h) | 7.0 | 490 | | Running (10 km/h) | 9.8 | 686 | | Cycling (moderate, 16–19 km/h) | 8.0 | 560 | | Swimming (freestyle, moderate) | 5.8 | 406 | | Resistance training | 3.5–5.0 | 245–350 | | Yoga (Hatha) | 2.5 | 175 | | HIIT | 8.0–12.0 | 560–840 |

Using the MET formula, here are calorie estimates for a 70 kg person over 30 minutes:

Walking: - Slow stroll (3 km/h, MET 2.0): ~70 kcal - Brisk walk (5.6 km/h, MET 3.5): ~123 kcal - Fast walk (6.5 km/h, MET 4.3): ~151 kcal

Running: - Light jog (8 km/h, MET 7.0): ~245 kcal - Moderate run (10 km/h, MET 9.8): ~343 kcal - Fast run (13 km/h, MET 12.5): ~438 kcal

Cycling: - Leisure cycling (14 km/h, MET 4.0): ~140 kcal - Moderate cycling (19 km/h, MET 8.0): ~280 kcal - Vigorous cycling (25+ km/h, MET 12.0): ~420 kcal

Strength training: 30 minutes burns approximately 90–175 kcal directly during the session — but resistance training also elevates resting metabolic rate for 24–72 hours post-workout through muscle protein synthesis, adding an additional 50–100 kcal to the total energy cost.

Steps: The relationship between steps and calories is approximately 0.03–0.05 kcal per step for most adults. 10,000 steps burns roughly 300–500 kcal depending on pace, body weight, and terrain.

The MET formula is an estimate for an "average" person. Individual calorie burn varies significantly due to:

Body weight and composition: Heavier individuals burn more calories for the same activity because more mass must be moved. A 90 kg person running at 10 km/h burns approximately 47% more than a 60 kg person.

Fitness level: More fit individuals are metabolically more efficient — their bodies perform the same work using less energy. This is an adaptation that reduces calorie burn per mile over time.

Age and sex: Muscle mass decreases with age, reducing BMR and exercise calorie burn. Men generally burn more calories at the same absolute workload due to greater average muscle mass.

Terrain and conditions: Walking on sand burns approximately 2.5× more calories than walking on flat pavement. Running in heat also increases energy expenditure due to thermoregulatory demands.

Fitness tracker accuracy: Consumer wrist-worn devices are generally inaccurate for calorie estimation — studies have found errors of 20–93% compared to metabolic cart measurements. They are more useful for relative comparisons (is today more active than yesterday?) than absolute calorie counting.

For practical self-monitoring, a combination of approaches works best:

1. Use MET-based calculations as a baseline estimate, adjusted for your body weight. 2. Record exercise type, duration, and intensity in a fitness app — HealthKoins logs your exercise sessions and awards coins based on time and type, providing a consistent daily record. 3. Track steps as the single most accessible indicator of non-exercise activity, which contributes significantly to TDEE. 4. Calibrate over weeks: Tracking calories burned alongside calorie intake allows you to observe actual weight trends and adjust. If weight is stable, your estimated TDEE is approximately correct. 5. Use heart rate for intensity: Heart-rate-based calorie estimates are more accurate than speed-only estimates, particularly at variable intensities. Polar's metabolic-cost algorithm (used in several sports watches) has been independently validated to within 10–15% of laboratory measures.

- Calories burned during exercise are calculated using METs: Kcal = MET × body weight (kg) × duration (hours). - Brisk walking burns ~245 kcal/hour for a 70 kg person; running at 10 km/h burns ~686 kcal/hour. - Body weight is the largest variable — heavier individuals burn proportionally more calories. - Fitness trackers have calorie accuracy errors of 20–93%; use them for trends and relative comparisons, not precise calorie accounting. - Steps (0.03–0.05 kcal/step) and non-exercise movement (NEAT) contribute substantially to daily calorie burn — often more than structured workouts for sedentary people.