How STATURE Mechanics Works

The physics and biomechanics behind fair lift comparisons

1. Work Calculation

In physics, work is defined as force applied over a distance:

Work = Force × Distance

or W = F × d (measured in Joules)

For lifting, force is the weight being moved (mass × gravity), and distance is how far the bar travels. A taller person with longer limbs moves the bar further, doing more work for the same load.

Example:

Lifter A (5'7"): Squats 315 lbs, bar moves 0.58m → 825 J
Lifter B (6'3"): Squats 315 lbs, bar moves 0.68m → 969 J
Lifter B does 17% more work for the same weight!

Interactive Demo — Adjust Heights

Lifter A5'7"

Lifter B6'3"

77cm

1077 J

86cm

1210 J

B does 12.4% more work for the same 143kg load

2. Moment Arms Matter

It’s not just about how far you move the bar—it’s also about how hard it is to move it.

In a squat, your hip muscles must generate torque to extend your hips. The torque required depends on the moment arm: the horizontal distance from your hip joint to the bar.

Torque = Force × Moment Arm

Larger moment arm = more torque needed = harder lift

Longer femurs push your hips further back at depth, increasing the horizontal distance between your hip and the bar. This creates a larger moment arm and makes the lift harder.

Example:

Short femur lifter: Hip moment arm = 0.20m
Long femur lifter: Hip moment arm = 0.24m (20% larger)
Long femur lifter needs 20% more hip torque!

Interactive Demo — Adjust Femur Length

Femur49.7cmAverage

Moment Arm

37.2 cm

Hip Torque Required

510 N·m

Longer femurs push the hips further back, increasing the horizontal distance the hip extensors must work against.

3. The Bar-Over-Midfoot Constraint

To squat without falling over, the bar must stay balanced over your midfoot. This is called the equilibrium constraint.

STATURE Mechanics uses an iterative kinematic solver to estimate your body position at parallel depth while keeping the bar over midfoot. The solver:

Positions your ankle at the origin (midfoot)
Places your femur parallel to the ground (parallel depth)
Iterates through ankle angles to find a valid trunk angle (20-80°)
Solves an estimated position of knee, hip, shoulder, and bar

Result:

A constrained geometric model of your squat biomechanics, including estimated moment arms and bar displacement.

Auto-Play Demo — Kinematic Solver Steps

Place ankle at midfoot

Extend tibia upward

Iterate ankle angles

Resolve trunk angle

4. Calculating Equivalent Load

To fairly compare lifters, STATURE Mechanics calculates a demand factor that combines work and moment arms:

Demand ≈ Base Factor × (ROM / ROM_ref) × (Moment Arm / MA_ref)

Lift-specific normalization keeps scores comparable across setups

The equivalent load is then calculated by scaling the original load by the demand ratio:

Equivalent Load = Original Load × (Demand_A / Demand_B)

Example:

Lifter A squats 300 lbs with demand factor = 0.180
Lifter B has demand factor = 0.210 (17% higher)
Lifter A’s 300 lbs = Lifter B’s 257 lbs

Interactive Calculator — Try Your Numbers

Lifter A Height

Lifter B Height

A's Load (lbs)

A Demand

0.1445

ROM: 76.9cm

B Demand

0.1811

ROM: 86.1cm

A's 300 lbs = B's equivalent of

239 lbs

Based on biomechanical demands (A faces higher demand)

5. Known Limitations

STATURE Mechanics is a biomechanics model with known limitations:

2D model: Only considers sagittal plane (side view). Stance width is approximated with modifiers, but full 3D knee/hip tracking is not modeled.
Population averages: Segment ratios are based on Winter’s data. Individual variation exists (±1-2 SD per segment).
No tissue properties: Doesn’t model muscle leverage, tendon stiffness, or strength curves.
No technique factors: Assumes similar bar path and tempo between lifters.

Bottom line:

STATURE Mechanics provides biomechanical insight, not absolute truth. Use it to understand why lifts feel different, not as a definitive ranking system.

Try It Out

STATURE Mechanics

1. Work Calculation

In physics, work is defined as force applied over a distance:

Work = Force × Distance

or W = F × d (measured in Joules)

For lifting, force is the weight being moved (mass × gravity), and distance is how far the bar travels. A taller person with longer limbs moves the bar further, doing more work for the same load.

Example:

Lifter A (5'7"): Squats 315 lbs, bar moves 0.58m → 825 J
Lifter B (6'3"): Squats 315 lbs, bar moves 0.68m → 969 J
Lifter B does 17% more work for the same weight!

Interactive Demo — Adjust Heights

Lifter A5'7"

Lifter B6'3"

77cm

1077 J

86cm

1210 J

B does 12.4% more work for the same 143kg load

2. Moment Arms Matter

It’s not just about how far you move the bar—it’s also about how hard it is to move it.

In a squat, your hip muscles must generate torque to extend your hips. The torque required depends on the moment arm: the horizontal distance from your hip joint to the bar.

Torque = Force × Moment Arm

Larger moment arm = more torque needed = harder lift

Longer femurs push your hips further back at depth, increasing the horizontal distance between your hip and the bar. This creates a larger moment arm and makes the lift harder.

Example:

Short femur lifter: Hip moment arm = 0.20m
Long femur lifter: Hip moment arm = 0.24m (20% larger)
Long femur lifter needs 20% more hip torque!

Interactive Demo — Adjust Femur Length

Femur49.7cmAverage

Moment Arm

37.2 cm

Hip Torque Required

510 N·m

Longer femurs push the hips further back, increasing the horizontal distance the hip extensors must work against.

3. The Bar-Over-Midfoot Constraint

To squat without falling over, the bar must stay balanced over your midfoot. This is called the equilibrium constraint.

STATURE Mechanics uses an iterative kinematic solver to estimate your body position at parallel depth while keeping the bar over midfoot. The solver:

Positions your ankle at the origin (midfoot)
Places your femur parallel to the ground (parallel depth)
Iterates through ankle angles to find a valid trunk angle (20-80°)
Solves an estimated position of knee, hip, shoulder, and bar

Result:

A constrained geometric model of your squat biomechanics, including estimated moment arms and bar displacement.

Auto-Play Demo — Kinematic Solver Steps

Place ankle at midfoot

Extend tibia upward

Iterate ankle angles

Resolve trunk angle

4. Calculating Equivalent Load

To fairly compare lifters, STATURE Mechanics calculates a demand factor that combines work and moment arms:

Demand ≈ Base Factor × (ROM / ROM_ref) × (Moment Arm / MA_ref)

Lift-specific normalization keeps scores comparable across setups

The equivalent load is then calculated by scaling the original load by the demand ratio:

Equivalent Load = Original Load × (Demand_A / Demand_B)

Example:

Lifter A squats 300 lbs with demand factor = 0.180
Lifter B has demand factor = 0.210 (17% higher)
Lifter A’s 300 lbs = Lifter B’s 257 lbs

Interactive Calculator — Try Your Numbers

Lifter A Height

Lifter B Height

A's Load (lbs)

A Demand

0.1445

ROM: 76.9cm

B Demand

0.1811

ROM: 86.1cm

A's 300 lbs = B's equivalent of

239 lbs

Based on biomechanical demands (A faces higher demand)

5. Known Limitations

STATURE Mechanics is a biomechanics model with known limitations:

2D model: Only considers sagittal plane (side view). Stance width is approximated with modifiers, but full 3D knee/hip tracking is not modeled.
Population averages: Segment ratios are based on Winter’s data. Individual variation exists (±1-2 SD per segment).
No tissue properties: Doesn’t model muscle leverage, tendon stiffness, or strength curves.
No technique factors: Assumes similar bar path and tempo between lifters.

Bottom line:

STATURE Mechanics provides biomechanical insight, not absolute truth. Use it to understand why lifts feel different, not as a definitive ranking system.