Curl upBalanced over midfoot, bar 5.8 cm behind
Side view
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Behind-the-back wrist curl

Standing with a 40 kg bar held behind the thighs, palms facing back, arms straight. Only the wrists move: the bar rolls up and back about 40° and down again.

6°Ankle dorsiflexion
2°Knee flexion
4°Hip flexion
6°Trunk from vertical
8°Arm to trunk
2°Elbow flexion
28Ankle spacing, cm
49Hand spacing, cm
-3Knee outside ankle, cm
–Knee cave, ° inside toe line
50 / 50Load left / right, %
0Pelvis drop, cm

Load and joint demand

Load in the model: 40 kg. Balance and joint demand re-solve as you change it.

Lower back
21 / 38
Hip flexors
7 / 15
Knee flexors
13 / 13
Calves
43 / 43
Shoulder, per side
30 / 41
Elbow, per side
13 / 24

N·m now / peak over the rep.

Faults

Faults grow with knee bend and apply to lifts standing on the floor. The fault check flags a knee caving more than 10° inside the line of the toes and a load split beyond 60/40. Knee cave shows best in the front camera.

Body

Femur changes keep standing height fixed by shortening or lengthening the torso. Longer femurs force more forward lean in any squat.

Muscles worked

Forearms and grip
100 pts

Effort and your quota

1/10 effort1fatigue per set

Your quota per set: 10 reps at 40 kg, stopping 2 reps short of failure.

One hard set earns 50 arms points.

Prime movers

Wrist flexors, forearm.

What to look for

  • Arms straight; only the wrists move.
  • Let the bar roll to the fingers at the bottom.
  • Squeeze at the top.
How the model works, and its limits

One 3D skeleton drives both views. Segment lengths and widths are Winter's anthropometric ratios of height; segment masses and centre-of-mass positions follow Dempster's data. For free-standing lifts the whole-body angle is found numerically so the combined centre of mass of lifter and load sits over the middle of the foot. Arms and legs use two-link inverse kinematics with a pole direction. Rep timing follows a minimum-jerk profile.

Balance is quasi-static, so ballistic lifts are shown slowed down. Cable pull and pad support forces are not modelled. The spine is one rigid segment and joints have no range-of-motion limits or muscle forces.