Walking Metrics Formulas & Equations
Mathematical foundations of walking analytics – scientifically validated equations for intensity, energy, and performance
This page presents scientifically validated formulas used in walking analytics. All equations are cited with research references and validated accuracy ranges.
1. Cadence to METs Conversion
Moore et al. (2021) Cadence-Based Metabolic Equation
Cadence to METs
METs = 0.0219 × Cadence (steps/min) + 0.72
Why this formula is important: This equation is 23-35% more accurate than traditional ACSM speed-based equations for walking. It works because cadence directly reflects movement frequency and energy expenditure, whereas speed depends on variable stride length.
Examples:
Walking at 100 spm:
METs = 0.0219 × 100 + 0.72 = 2.19 + 0.72 = 2.91 METs
≈ 3 METs = Moderate intensity threshold ✓
Walking at 110 spm:
METs = 0.0219 × 110 + 0.72 = 2.409 + 0.72 = 3.13 METs
Solid moderate intensity
Walking at 120 spm:
METs = 0.0219 × 120 + 0.72 = 2.628 + 0.72 = 3.35 METs
Moderate-vigorous intensity
Walking at 130 spm:
METs = 0.0219 × 130 + 0.72 = 2.847 + 0.72 = 3.57 METs
Vigorous intensity threshold (6 METs by CADENCE-Adults direct measurement)
Note: The CADENCE-Adults study directly measured that 130 spm = 6 METs in controlled lab conditions. The Moore equation is designed for the 80-130 spm range and may underestimate at very high cadences.
Validation Data:
- Sample: 76 adults aged 21-40
- Method: Indirect calorimetry (gold standard)
- R² value: 0.87 (excellent correlation)
- Mean absolute error: 0.47 METs
- Applicable range: 80-130 steps/min
2. ACSM VO₂ Equations for Walking
ACSM Metabolic Calculations
Level Walking (0% grade)
VO₂ (mL/kg/min) = 0.1 × Speed (m/min) + 3.5
Speed in meters per minute (multiply km/h by 16.67 or mph by 26.82)
Walking with Grade (incline/decline)
VO₂ = 0.1(Speed) + 1.8(Speed)(Grade) + 3.5
Grade expressed as decimal (e.g., 5% = 0.05)
Examples:
Walking 5 km/h (83.3 m/min) on level ground:
VO₂ = 0.1 × 83.3 + 3.5 = 8.33 + 3.5 = 11.83 mL/kg/min
Convert to METs: 11.83 / 3.5 = 3.38 METs
Walking 5 km/h on 5% incline:
VO₂ = 0.1(83.3) + 1.8(83.3)(0.05) + 3.5
= 8.33 + 7.497 + 3.5 = 19.33 mL/kg/min
= 19.33 / 3.5 = 5.52 METs
Incline increases intensity by ~64%!
Speed Conversions:
- km/h to m/min: multiply by 16.67
- mph to m/min: multiply by 26.82
- m/s to m/min: multiply by 60
3. Energy Expenditure & Calorie Burn
Accurate Calorie Calculation
Calories per Minute
Cal/min = (METs × 3.5 × Body Weight kg) / 200
Total Calories for Session
Total Calories = Cal/min × Duration (minutes)
Examples:
70 kg person walking 100 spm (3 METs) for 45 minutes:
Cal/min = (3 × 3.5 × 70) / 200 = 735 / 200 = 3.675 cal/min
Total = 3.675 × 45 = 165.4 calories
85 kg person walking 120 spm (5 METs) for 30 minutes:
Cal/min = (5 × 3.5 × 85) / 200 = 1487.5 / 200 = 7.44 cal/min
Total = 7.44 × 30 = 223.2 calories
Why This Formula?
This equation comes from the definition of MET (Metabolic Equivalent of Task):
- 1 MET = 3.5 mL O₂/kg/min (resting metabolic rate)
- 1 liter of O₂ consumed ≈ 5 kcal burned
- Converting: (METs × 3.5 × kg × 5) / 1000 = (METs × 3.5 × kg) / 200
Net Calorie Burn (Exercise Only)
Net Calories (excluding resting)
Net Cal/min = [(METs - 1) × 3.5 × Body Weight] / 200
Subtracts 1 MET to exclude calories you'd burn anyway at rest
70 kg, 3 METs, 45 min – Net calories:
Net = [(3 - 1) × 3.5 × 70] / 200 × 45 = 2.45 × 45 = 110.3 net calories
vs 165.4 total calories (55 calories would've been burned at rest)
4. Gait Symmetry Index (GSI)
Quantifying Left-Right Asymmetry
Gait Symmetry Index
GSI (%) = |Right - Left| / [0.5 × (Right + Left)] × 100
Can be applied to stride length, step time, or contact time
Interpretation:
- <2-3%: Normal, symmetric gait
- 3-5%: Mild asymmetry
- 5-10%: Moderate asymmetry, monitor
- >10%: Clinically significant, assess professionally
Examples:
Step times: Right = 520 ms, Left = 480 ms
GSI = |520 - 480| / [0.5 × (520 + 480)] × 100
= 40 / [0.5 × 1000] × 100 = 40 / 500 × 100 = 8% asymmetry
Moderate asymmetry – consider strengthening weaker side
Stride lengths: Right = 1.42 m, Left = 1.38 m
GSI = |1.42 - 1.38| / [0.5 × (1.42 + 1.38)] × 100
= 0.04 / 1.4 × 100 = 2.86% asymmetry
Normal, healthy range ✓
Clinical Note: Apple HealthKit's Walking Asymmetry uses a slightly different calculation (simple percentage difference between step times) but the interpretation thresholds are similar.
5. WALK Score (Walk Analytics Proprietary Metric)
Walking Efficiency Score
WALK Score
WALK Score = Time (seconds) + Steps per 100 meters
Lower score = better efficiency (like SWOLF for swimming)
How It Works:
WALK Score combines time and step count to quantify walking efficiency. A walker who covers 100m in 75 seconds with 140 steps has a WALK Score of 215. Improving either speed OR stride efficiency lowers the score.
Examples:
100m in 80 seconds, 120 steps:
WALK Score = 80 + 120 = 200
100m in 70 seconds, 110 steps:
WALK Score = 70 + 110 = 180
Better efficiency through improved speed + stride
100m in 60 seconds, 130 steps (race walking):
WALK Score = 60 + 130 = 190
Fast but shorter strides
Typical Ranges:
- >250: Slow/inefficient gait, possible mobility issues
- 200-250: Casual walker, average efficiency
- 170-200: Fitness walker, good efficiency
- 150-170: Advanced walker, excellent efficiency
- <150: Elite/race walking level
Training with WALK Score: Track your score on the same 100m course weekly. Improvements show enhanced neuromuscular coordination, strength, and walking economy.
6. Basic Gait Metrics
Fundamental Calculations
Walking Speed
Speed (m/s) = Distance (m) / Time (s)
Cadence from Total Steps
Cadence (spm) = Total Steps / Time (minutes)
Stride Length
Stride Length (m) = Distance (m) / (Steps / 2)
Divide steps by 2 because one stride = two steps
Step Length
Step Length (m) = Distance (m) / Steps
Speed from Cadence & Stride Length
Speed = Stride Length × (Cadence / 2) / 60
Or: Speed (m/s) = Step Length × Cadence / 60
Example Workflow:
Walk 1000m in 12 minutes with 1320 steps:
Speed: 1000m / 720s = 1.39 m/s
Cadence: 1320 steps / 12 min = 110 spm
Stride Length: 1000m / (1320/2) = 1000 / 660 = 1.52 m
Step Length: 1000m / 1320 = 0.76 m
7. Heart Rate Zone Calculations
Traditional HR Zone Method
Maximum Heart Rate Estimation
Max HR = 220 - Age
Simple but ±10-15 bpm individual variation
Alternative: Tanaka Formula (more accurate)
Max HR = 208 - (0.7 × Age)
Zone Range Calculation
Zone = Max HR × (Lower%, Upper%)
Example: 40-year-old
Traditional: Max HR = 220 - 40 = 180 bpm
Tanaka: Max HR = 208 - (0.7 × 40) = 208 - 28 = 180 bpm
Zone 2 (60-70%): 180 × 0.60 = 108 bpm to 180 × 0.70 = 126 bpm
Note: While HR zones are useful, cadence-based zones are more accurate and practical for walking (see Walking Zones guide).
8. Cost of Transport & Walking Economy
Energy Cost of Walking
Cost of Transport (C)
C = Energy Expended / (Body Mass × Distance)
Units: J/kg/m or mL O₂/kg/m
U-Shaped Curve: Walking economy follows a U-shaped curve. There's an optimal speed (typically 1.2-1.4 m/s or 4.3-5.0 km/h) where cost of transport is minimized. Walking slower OR faster than this increases energy cost per distance traveled.
Factors Affecting Cost of Transport:
- Speed: U-shaped relationship (optimal around 1.3 m/s)
- Gradient: Uphill significantly increases cost; downhill increases eccentric cost
- Body mass: Heavier individuals have higher absolute but similar relative cost
- Stride mechanics: Optimal stride length minimizes cost
- Terrain: Uneven surfaces increase cost vs smooth pavement
Grade-Adjusted Cost
Cost multiplier = 1 + (Grade × 10)
Rough approximation: +10% cost per 1% grade
Example:
Walking on 5% incline:
Cost multiplier = 1 + (0.05 × 10) = 1.5×
50% increase in energy cost compared to level ground
9. Training Load & Stress Score
Walking Stress Score (WSS)
Zone-Based WSS
WSS = Σ (Minutes in Zone × Zone Factor)
Zone 1: ×1.0 | Zone 2: ×2.0 | Zone 3: ×3.0 | Zone 4: ×4.0 | Zone 5: ×5.0
Example: 60-minute walk
10 min Zone 1 × 1 = 10 points
40 min Zone 2 × 2 = 80 points
10 min Zone 3 × 3 = 30 points
Total WSS = 120
Weekly Training Load
Weekly Load
Weekly Load = Σ Daily WSS (7 days)
Progressive Overload
Next Week = Current Week × 1.05-1.10
Increase 5-10% per week maximum
Recovery Week
Recovery Week = Current × 0.50-0.70
Every 3-4 weeks, reduce to 50-70%
Typical Weekly Loads:
- Beginner health walker: 200-400 WSS/week
- Regular fitness walker: 400-700 WSS/week
- Serious fitness walker: 700-1000 WSS/week
- Competitive race walker: 1000-1500+ WSS/week
10. Predictive Equations
6-Minute Walk Test (6MWT) Distance Prediction
Predicted 6MWT Distance (Enright & Sherrill)
Men: (7.57 × Height cm) - (5.02 × Age) - (1.76 × Weight kg) - 309
Women: (2.11 × Height cm) - (5.78 × Age) - (2.29 × Weight kg) + 667
Predicts distance in meters for healthy adults
Example: 40-year-old man, 175 cm, 75 kg
6MWT = (7.57 × 175) - (5.02 × 40) - (1.76 × 75) - 309
= 1324.75 - 200.8 - 132 - 309 = 682.95 meters
Good functional capacity for age
Clinical Use: The 6MWT is used to assess functional exercise capacity in cardiopulmonary patients, pre/post-surgery evaluation, and general fitness in older adults.
11. Unit Conversions
Common Walking Metric Conversions
| From | To | Formula |
|---|---|---|
| km/h | m/s | km/h ÷ 3.6 |
| mph | m/s | mph × 0.447 |
| m/s | km/h | m/s × 3.6 |
| m/s | mph | m/s × 2.237 |
| km/h | m/min | km/h × 16.67 |
| mph | m/min | mph × 26.82 |
| METs | mL/kg/min | METs × 3.5 |
| mL/kg/min | METs | VO₂ ÷ 3.5 |
Quick Reference:
- 1.0 m/s = 3.6 km/h = 2.24 mph (typical healthy adult walking speed)
- 1.4 m/s = 5.0 km/h = 3.1 mph (brisk walking)
- 1 MET = 3.5 mL O₂/kg/min (resting metabolism)
- 3 METs = 10.5 mL O₂/kg/min (moderate intensity threshold)
- 6 METs = 21 mL O₂/kg/min (vigorous intensity threshold)