How do healthcare providers apply the concept of metabolic equivalents to give fitness recommendations to adults with no underlying medical conditions?

How Healthcare Providers Apply METs to Give Fitness Recommendations

Healthcare providers should use the MET system to classify exercise intensity and prescribe specific activity targets, with 1 MET defined as 3.5 mL O₂/kg/min, recommending adults achieve 150 minutes per week of moderate-intensity activity (3.0-5.9 METs) or 75 minutes of vigorous activity (≥6.0 METs) for meaningful health benefits. 1

Understanding the MET System

The metabolic equivalent (MET) represents resting oxygen consumption, with 1 MET conventionally defined as 3.5 mL of oxygen per kilogram of body weight per minute, allowing providers to express physical activity as a multiple of resting metabolic rate. 2

Key principle: One MET equals sitting/resting oxygen uptake, making it a simple procedure for expressing energy cost of physical activities as multiples of resting metabolic rate. 2

Classifying Exercise Intensity Using METs

Providers should categorize activities into three intensity levels based on MET values:

Light Intensity (1.5-3.0 METs)

• Activities include: Casual walking, cycling <8 km/h, stretching, light weight training 1
• Physiological marker: Aerobic activity that does not cause noticeable changes in breathing rate 1
• Examples: Slow walking at 1.7-2.0 mph (2.3-2.5 METs), bathing, incidental activities 2

Moderate Intensity (3.0-5.9 METs)

• Activities include: Brisk walking, cycling 8-15 km/h, low impact aerobics, weight training 1
• Physiological marker: Aerobic activity where conversation can be maintained 1
• Examples: Walking at 3.0 mph = 3.3 METs, walking at 3.75 mph = 3.9 METs 2, 1
• Clinical significance: This is the target intensity for the WHO-recommended 150 minutes per week 2, 1

Vigorous Intensity (≥6.0 METs)

• Activities include: Race walking, jogging, mountain climbing, high impact aerobics 1
• Physiological marker: Aerobic activity where conversation cannot be maintained 1
• Examples: Running, strenuous sports, climbing hills 2, 1
• Clinical significance: 75 minutes per week at this intensity provides equivalent health benefits to 150 minutes of moderate activity 1

Calculating MET Values for Specific Activities

Using Treadmill Parameters

Providers can estimate metabolic cost from speed and grade using standardized equations and tables. 2

Walking MET values by speed and grade: 2

• 2.0 mph, 0% grade = 2.5 METs
• 3.0 mph, 0% grade = 3.3 METs
• 3.75 mph, 0% grade = 3.9 METs
• 3.0 mph, 10% grade = 7.4 METs

Direct Calculation Method

To determine MET value, divide measured oxygen consumption by 3.5 mL/kg/min, or use standardized MET values from activity compendiums. 1

Setting Evidence-Based Exercise Targets

Weekly Volume Recommendations

The WHO recommends: 2, 1

• Moderate intensity: 150 minutes per week (3.0-5.9 METs)
• Vigorous intensity: 75 minutes per week (≥6.0 METs)
• Combined approach: Equivalent combinations achieving the same total energy expenditure

Calculating Total Exercise Volume

Multiply intensity (METs) × duration (minutes) × frequency to calculate total MET-minutes per week, with a target of >360 MET-minutes per week (>6 MET-hours) for a 26% reduction in death/hospitalization. 1

Example calculation:

• 30 minutes of brisk walking (4 METs) × 5 days/week = 600 MET-minutes/week
• This exceeds the minimum threshold and provides substantial health benefits 1

Age-Specific Considerations

Providers must adjust expectations based on age-related declines in maximal oxygen uptake. 2

Normal maximal MET values by age and sex: 2

• Men 20-29 years: 12 METs
• Men 50-59 years: 10 METs
• Men 70-79 years: 8 METs
• Women 20-29 years: 10 METs
• Women 50-59 years: 8 METs
• Women 70-79 years: 8 METs

Clinical Application Algorithm

Step 1: Assess Current Fitness Level

Determine the patient's maximal MET capacity through exercise testing or functional assessment. 2

Step 2: Set Intensity Targets

• For deconditioned patients: Start with light-to-moderate intensity (2.0-4.0 METs) 1
• For average fitness: Target moderate intensity (3.0-5.9 METs) 1
• For high fitness: Include vigorous intensity (≥6.0 METs) 1

Step 3: Prescribe Specific Activities

Provide concrete examples of activities at the target MET level using standardized tables. 2, 1

Step 4: Calculate Weekly Volume

Ensure total weekly volume reaches ≥360 MET-minutes (≥6 MET-hours) through the formula: METs × minutes × frequency. 1

Step 5: Monitor and Progress

Each 1-MET increase in exercise capacity confers an 8-17% reduction in mortality, so progressively increase intensity or duration over time. 1

Important Caveats

The standard 1-MET value (3.5 mL O₂/kg/min) overestimates actual resting oxygen consumption by approximately 35% in heterogeneous populations, particularly in obese individuals. 3 However, this does not affect the practical application of MET-based exercise prescription, as the relative intensity categories remain valid. 2, 1

For older adults ≥60 years: Consider using age-adjusted MET thresholds, as conventional thresholds may be 10-22% too high depending on fitness level. 4 Fitness-specific adjustments are particularly important, with approximately 69% higher MET thresholds appropriate for "good/superior" fitness compared to "very poor/fair" fitness in this age group. 4

Holding handrails during treadmill exercise decreases the metabolic cost of the work rate, leading to underestimation of true exercise capacity. 2 Discourage this practice during both testing and training.