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Kettlebell Russian twist

Sitting on the floor leaning back about 40°, knees bent and heels down, a 12 kg bell held by the horns in front of the chest; the shoulders turn from one side to the other and the bell travels with them.

-29°Ankle dorsiflexion
115°Knee flexion
104°Hip flexion
40°Trunk from vertical
14°Arm to trunk
110°Elbow flexion
32Ankle spacing, cm
9Hand spacing, cm
8Knee outside ankle, cm
–Knee cave, ° inside toe line
–Load left / right, %
0Pelvis drop, cm

Load and joint demand

Bodyweight exercise: the load slider has no effect here; body mass comes from your limits.

No gravity-based joint demand to show for this exercise.

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

Abs and core
100 pts

Effort and your quota

2/10 effort2fatigue per set

Your quota per set: 13 reps at bodyweight, stopping 2 reps short of failure.

One hard set earns 100 core points.

Prime movers

Obliques, rectus abdominis, hip flexors (holding).

What to look for

  • Turn the shoulders, not just the arms.
  • Chest tall; do not slump.
  • Lift the feet only when it gets easy.
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.