Directly Measuring Basal or Resting Metabolic Rate

Resting Metabolic Rate (RMR) and Basal Metabolic Rate (BMR) are measures of resting energy expenditure, which can be helpful in assisting patients with weight loss. BMR and RMR represent the minimum amount of energy required to keep your body functioning, including your heart beating, lungs breathing, and maintaining normal body temperature. Although the terms BMR and RMR are sometimes used interchangeably, they are measured under different conditions and have slightly different interpretations.

Described below is the method for directly measuring resting metabolic rate. A less common method is to use direct calorimetry which measures the heat generated by the body in an enclosed space. See also some simple equations for estimating BMR and RMR.

Aim: to directly determine resting oxygen consumption as a measure of metabolic rate at rest.

Equipment required: O2 and CO2 gas analyzers, ventilation measurement by a pneumotach or turbine ventilometer (as used for VO2max measurement).

using a Cosmed K5 to measuring resting energy consumption using a Cosmed K5 to measuring resting energy consumption

Procedure: The difference between BMR and RMR is in the subject preparation. BMR measurements are typically taken in a darkened room upon waking after 8 hours of sleep with 12 hours of fasting to ensure that the digestive system is inactive, and with the subject resting in a reclining position. On the other hand RMR measurements are typically taken under less restricted conditions than BMR. For BMR you should avoid any exercise or stressful situations for at least two hours prior to the test, as well as eating a meal or ingesting caffeine or other stimulants in the previous 4 hours. Smoking should also be avoided during that time. During the test the subject should be seated or reclining comfortably in a quiet room set at a neutral temperature, and not speaking, reading or watching television so that they can fully relax. Rest the subject for at least 10 minutes in these conditions before starting the measurements.

Measurement: The apparatus measures the oxygen consumption of the body (VO2) and the carbon dioxide (CO2) produced. Measurements should be taken for at least 10-20 minutes or until the values have stabilized. The results can show if you have increased or decreased metabolism, and the respiratory exchange ratio can show whether your body primarily uses fats or carbohydrates for energy.

Disadvantages: this test requires expensive equipment and is labor intensive. There are alternative equations for calculating BMR and RMR.

Comments: metabolic rate measurements can change over time, and are affected by body weight, height and age.

Understanding BMR and RMR for Athletes

Research conducted by Sjödin and colleagues (1996) demonstrated that elite endurance athletes have significantly higher BMR than sedentary individuals matched for fat-free mass. The study found athletes' BMR was 13% higher when related to fat-free mass and 16% higher when related to both fat-free and fat mass, compared to non-athletic controls. This elevation persists even 39 hours after the last training session, suggesting that athletic training creates lasting metabolic adaptations.

For athletic populations, understanding BMR is crucial for several sport-specific applications. Endurance athletes typically have higher resting metabolic rates due to increased mitochondrial density and cardiovascular adaptations. Power athletes benefit from elevated BMR through greater muscle mass, as muscle tissue requires significantly more energy for maintenance than fat tissue. Team sport athletes experience seasonal variations in BMR that correspond to training phases, with higher rates during competition seasons and potentially lower rates during off-seasons.

Using BMR for Training Nutrition

Athletes should use their calculated BMR as the foundation for determining total daily energy expenditure (TDEE). According to research published in Training & Conditioning, most athletes require activity multipliers between 1.55 and 2.0, with elite athletes training over 3 hours daily potentially exceeding 2.0. For a 220-pound athlete training hard for three hours daily, this could mean adding 1,800+ calories to their BMR to maintain weight and performance.

When using BMR for weight management in athletes, it's critical to never drop calorie intake below BMR values. Doing so can lead to loss of lean muscle mass, decreased athletic performance, hormonal imbalances, and metabolic adaptation that makes future weight loss more difficult. Safe weight loss for competitive athletes typically ranges from 0.5-1 pound per week, achieved by maintaining calorie intake 300-500 calories below TDEE while preserving training intensity.

Sport-Specific BMR Considerations

Weight Class Sports

For athletes in weight class sports such as wrestling, boxing, judo, and Olympic weightlifting, BMR knowledge is essential for making weight safely. Knowing your BMR establishes the absolute minimum calories needed for health and basic function, preventing dangerous weight-cutting practices that can compromise performance and safety. Athletes should never attempt to maintain body weight at a level requiring calorie intake below BMR for extended periods.

Endurance Sports

Marathon runners, cyclists, triathletes, and other endurance athletes have unique metabolic profiles. While they may have lower body weight than power athletes, their BMR per kilogram of body weight is often elevated due to cardiovascular adaptations and increased mitochondrial density. These athletes must be particularly careful to match energy intake with the high demands of training volumes that can exceed 15-20 hours weekly.

Power and Strength Sports

Weightlifters, throwers, football players, and rugby athletes typically have higher absolute BMR values due to greater muscle mass. These athletes benefit from understanding that muscle tissue requires approximately 6 calories per pound per day for maintenance, while fat tissue requires only 2 calories per pound. This knowledge helps optimize body composition for strength-to-weight ratio in specific sports.

Frequently Asked Questions

What is the difference between BMR and RMR?

BMR (Basal Metabolic Rate) is measured under strictly controlled laboratory conditions requiring 12 hours of fasting, 8 hours of sleep, and complete rest in a darkened room. RMR (Resting Metabolic Rate) is measured under less restrictive conditions and includes energy expenditure for minimal activities like digestion. RMR is typically 5-10% higher than BMR and is more practical for everyday use in athletic settings. Both represent the minimum energy your body needs for vital functions.

How accurate are BMR calculator formulas for athletes?

The Mifflin-St Jeor equation is accurate within 10% for most individuals and was validated by the American Dietetic Association in 2005 as the most reliable predictive equation. However, for athletes, standard formulas may underestimate BMR by 13-16% according to research on elite athletes. The Katch-McArdle formula, which accounts for lean body mass, is generally more accurate for athletic populations. For precision within 5%, indirect calorimetry testing is recommended.

Do athletes have higher BMR than non-athletes?

Yes, research conclusively shows that athletes have elevated BMR compared to sedentary individuals. Studies by Sjödin and colleagues found that elite endurance athletes had 13% higher BMR than matched controls when accounting for fat-free mass, and 16% higher when including total body composition. This elevation is due to increased muscle mass, larger organ size (heart, kidneys, liver), enhanced mitochondrial density, and lingering effects of training that keep metabolism elevated for 24-48 hours post-exercise.

How should I use BMR to plan my training nutrition?

Start by calculating your TDEE (Total Daily Energy Expenditure) by multiplying BMR by your activity level multiplier (1.55-2.0 for most athletes). To maintain weight and performance, eat at your TDEE. For muscle gain, add 300-500 calories above TDEE with adequate protein (1.6-2.2g per kg body weight). For weight loss, subtract 300-500 calories from TDEE, but never drop below your BMR. Adjust macronutrient timing around training with higher carbohydrates on training days and adequate protein for recovery.

Which BMR formula is most accurate for athletes?

For general athletic populations, the Mifflin-St Jeor equation provides the most accurate baseline. When body fat percentage is known, the Katch-McArdle formula is superior as it's based on lean body mass rather than total weight. For professional endurance athletes, the Ten Haaf equation may be most appropriate. Using multiple formulas and averaging the results, as our calculator does, provides the best estimate. For competitive athletes requiring precision, indirect calorimetry testing remains the gold standard.

How often should I recalculate my BMR?

Recalculate BMR whenever you experience significant body composition changes (5+ pounds of muscle gain or loss), major transitions in training phases, or every 3-6 months as a general practice. BMR naturally decreases with age at approximately 2% per decade after reaching physical maturity. For weight class athletes, recalculation before each competition prep phase is advisable. If you notice unexpected changes in body weight despite consistent training and nutrition, recalculating BMR can help identify if metabolic adaptation has occurred.

Can understanding BMR help with weight cutting for competition?

Yes, BMR is essential for safe weight cutting in weight class sports. Knowing your BMR establishes the absolute minimum calories needed for health and basic metabolic function. Successful weight cuts maintain calorie intake above BMR while creating a modest deficit from TDEE (300-500 calories). Attempting to maintain weight below levels requiring sub-BMR calorie intake leads to muscle loss, performance decline, hormonal disruption, and potential health complications. Safe weight loss for athletes is 0.5-1 pound per week, with more aggressive cuts reserved for the final week before weigh-in.