What is Good Functional Capacity in Adults with Underlying Health Conditions?
Good functional capacity is defined as 7-10 METs (metabolic equivalents), which corresponds to the ability to perform activities such as climbing multiple flights of stairs, walking briskly at 4 mph, performing heavy housework, or engaging in moderate-intensity sports without symptoms. 1, 2
MET Classification Framework
The American Heart Association and American College of Cardiology classify functional capacity into five standardized levels 1, 2:
- Excellent: >10 METs
- Good: 7-10 METs
- Moderate: 4-6 METs
- Poor: <4 METs
- Unknown: Cannot be determined
Clinical Significance of the 4 MET Threshold
The 4 MET threshold represents the most critical cutoff for risk stratification in adults with underlying health conditions. 1, 2 Patients unable to achieve 4 METs during normal daily activities face significantly increased perioperative cardiac risk and long-term cardiovascular complications 1.
Activities Below 4 METs (Poor Functional Capacity):
- Slow ballroom dancing 1, 2
- Golfing with a cart 1, 2
- Playing a musical instrument 1, 2
- Walking at 2-3 mph on level ground 1, 2
- Light housework and self-care activities 2
Activities at or Above 4 METs (Adequate Functional Capacity):
- Climbing one flight of stairs 1, 2
- Walking 4 blocks on level ground 1, 2
- Walking at 4 mph 1, 2
- Heavy housework or yardwork 1, 2
- Moderate cycling, climbing hills 1, 2
- Singles tennis, jogging 1
Practical Assessment Methods
Two-Question Screen
The European Society of Cardiology recommends a simple two-question assessment 2:
- Can you walk 4 blocks without stopping?
- Can you climb 2 flights of stairs without stopping?
Inability to perform either activity identifies poor functional capacity (<4 METs) and significantly increased risk of perioperative myocardial ischemia and cardiovascular events. 1, 2
Duke Activity Status Index (DASI)
The DASI assigns specific MET values to 12 activities with scores ranging from 0 to 58.2 2. A DASI score ≤34 represents clinically significant impairment, corresponding roughly to the 4 MET threshold and indicating increased risk of postoperative complications. 2
Physiological Basis
Functional capacity reflects maximal oxygen uptake (VO2max), which is the product of cardiac output and arteriovenous oxygen difference at physical exhaustion 1. One MET equals the resting oxygen consumption of a 70-kg, 40-year-old man (3.5 mL/kg/min) 1.
Age and Gender Considerations
- Aerobic capacity declines approximately 10% per decade in nonathletic adults 1
- The rate of decline accelerates with advancing age: 3-6% per decade in younger adults (20s-30s) versus 20% per decade in elderly (70s and older) 1
- At any age, VO2max in men is 10-20% greater than in women due to higher hemoglobin concentration, greater muscle mass, and larger stroke volume 1
Clinical Implications for Patients with Underlying Conditions
Patients with good functional capacity (≥4 METs) who are asymptomatic can typically proceed to surgery without further cardiovascular testing, as management is rarely changed by additional testing in this population. 1, 2 Conversely, patients with poor functional capacity (<4 METs) require additional risk stratification and potential optimization before intermediate- or high-risk procedures 2.
Important Caveat
Poor functional capacity has stronger prognostic value for thoracic surgery compared to other non-cardiac surgeries, reflecting the importance of pulmonary function in thoracic procedures 2.
Impact on Quality of Life and Outcomes
Functional status is a reliable predictor of perioperative and long-term cardiac events 1. Higher functional capacity protects against developing limitations in activities of daily living (ADL) and instrumental activities of daily living (IADL) 3. The likelihood of serious complications is inversely related to the number of blocks that can be walked (p=0.006) or flights of stairs that can be climbed (p=0.01) 1.