Fitness Calculations: The Science Behind Your Workout

Understand the math behind one-rep max, calorie burn, heart rate zones, and other key fitness metrics.

7 min read read

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One Rep Max Calculator

One-Rep Max and Training Percentages

Your one-rep max (1RM) is the maximum weight you can lift for a single repetition of an exercise. It's the foundation of percentage-based strength training programs.

Rather than testing your actual 1RM (which can be dangerous), you can estimate it from a lighter weight lifted for multiple reps. The Epley formula (1RM = Weight × (1 + Reps/30)) is widely used and reasonably accurate for 1-10 reps.

Heart Rate Zones

Training in different heart rate zones targets different fitness goals. Zone 1 (50-60% max HR): Recovery. Zone 2 (60-70%): Fat burning and endurance. Zone 3 (70-80%): Aerobic fitness. Zone 4 (80-90%): Anaerobic threshold. Zone 5 (90-100%): Maximum effort.

Maximum heart rate is commonly estimated as 220 minus your age, though individual variation exists.

Calorie Burn and MET Values

MET (Metabolic Equivalent of Task) values quantify the energy cost of activities relative to rest. Walking is about 3.5 METs, jogging 7 METs, and sprinting 15+ METs.

To estimate calories burned: Calories = MET × weight (kg) × time (hours). This provides a reasonable estimate, though individual factors like fitness level and efficiency affect actual burn.

Questions people ask

How often should I test my 1RM?
Most programs recommend retesting every 4-8 weeks, or using rep-max estimates from your regular training. Actually testing a true 1RM should be done sparingly and with a spotter.