Ustrasana
hold 20 s · intermediate · move in slowly, hold, come out the same way
Take care: Keep the hands on the lower back and the chin tucked if the neck or lower back complains; pad the knees, and skip it during pregnancy.
Ustrasana with blocks: kneeling with the knees hip-width and the tops of the feet on the mat, a block on its middle height standing outside each heel. The hips press forward over the knees while the chest lifts and the spine arches back about 45°, until the straight arms rest the hands on the blocks; the full pose takes the hands to the heels. The head follows the spine, gaze up and back.
Bodyweight: no weights. Joint demand below is your own body's weight in this position.
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.
Femur changes keep standing height fixed by shortening or lengthening the torso. Longer femurs force more forward lean in any squat.
Hold for 20 seconds: move into the pose slowly, breathe steadily, and come out the way you went in. Yoga is practised for control, balance and mobility, never to failure, so this does not change with your limits.
Level: intermediate. One round counts like light conditioning work: 67 legs points, 7 push points, 47 core points.
Spinal erectors, gluteus maximus, hamstrings; quadriceps, hip flexors, abdominals, pectoralis major and anterior deltoid stretched.
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.