Using Metabolic Equivalents in Clinical Practice.

Area of Science:

• Exercise Physiology
• Cardiorespiratory Fitness Assessment

Background:

• Metabolic equivalents (METs) are widely used for exercise prescription and cardiorespiratory fitness (CRF) evaluation.
• The MET concept has inherent limitations and common misapplications, potentially leading to inaccurate estimations of physical activity capacity.
• The standard 1 MET = 3.5 mL O₂/kg/min conversion is questioned, particularly in specific populations like coronary patients or the obese.

Purpose of the Study:

• To critically evaluate the utility and limitations of the Metabolic Equivalent (MET) concept in exercise science.
• To discuss the implications of MET concept inaccuracies on assessing energy expenditure and fitness levels.
• To introduce alternative metrics like Personal Activity Intelligence (PAI) and reaffirm the benefits of physical activity.

Main Methods:

• Review and synthesis of existing literature on METs, cardiorespiratory fitness, and energy expenditure.
• Analysis of studies challenging the conventional 1 MET conversion factor.
• Discussion of factors influencing MET accuracy, such as age, gender, and medication use (e.g., β-blockers).

Main Results:

• The MET concept can lead to overestimation of CRF and underestimation of physical activity capacity.
• The 3.5 mL O₂/kg/min conversion overestimates resting energy expenditure in certain populations.
• Fitness thresholds for mortality risk may be misleading due to confounding factors.
• Heart rate-based Personal Activity Intelligence (PAI) offers a potential alternative metric.

Conclusions:

• Despite limitations, METs remain a valuable tool for quantifying CRF and guiding safe, therapeutic physical activity.
• For inactive adults, engaging in moderate-to-vigorous physical activity (≥3 METs) can enhance MET capacity.
• Increased physical activity is associated with a reduced risk of future cardiac events.