The Sit-to-Stand Manoeuvre

Technical Details

Recorded at 25 pictures per second (total duration 4.26 seconds), manually digitised and low-pass filtered at 3 Hz. Ground reaction forces halved (assuming symmetry). Anthropometry from New York study.

Raw data

Raw x-coordinates

Raw y-coordinates

Ground Reaction Forces

Ground Reaction Vector (butterfly diagram)

Kinematics + Ground Reaction Vector

Kinematics & Inverse Dynamics

Joint Angles, Moments & Powers

Segment Energies & Velocities + Ground Reaction Forces

Segment Powers & Power Flows

Angle-angle-angle (AAA) diagram

Moment-moment-moment (MMM) diagram

Questions

• How is standing initiated?
• When is trunk energy at its maximum?
• When is trunk velocity at its maximum? Same time as energy is max? If not, why not?
• Which muscles are mainly responsible for standing?
• Which muscle is more active standing up, and which sitting down?
• At what point in the movement is knee power generation and absorption at a maximum?
• When is ankle activity at a maximum?
• What is the difference between concentric & eccentric contraction?
• To which direction (forwards/backwards?) is the ground reaction vector directed?
• How valid are the inverse dynamics?

The effect of starting position

Following the suggestions made on the CGA list, two further analyses were made on a subject rising to standing from two different starting positions. This starting position can be defined in several ways:

• Position of buttocks on the chair
• Position of feet on the floor with respect to chair
• Ankle angle (degrees of initial dorsiflexion or plantarflexion)

• In these experiments the position of the feet was kept constant, and the subject was asked to sit either forwards or backwards in the chair (equivalent to a dorsiflexed or plantarflexed ankle, respectively).

Here are the movies:

Standing from a backward position in the chair

... and here are the analyses:

Kinetics from front of the chair

Energetics from front of the chair

Kinetics from back of the chair

Energetics from back of the chair

In summary, here is the work done by each joint:

From forward position in chair .... backward position in chair
```Duration ........ 2.32 s                   2.76 s

Ankle Work ...... 1 J                      1 J
Knee Work ...... 43 J                     16 J
Hip Work ....... 56 J                     88 J

Total Work .....100 J                    104 J```

Summary

Thus, it seems that when the subject sits back in the chair, more work is done by the hip extensors (glutei), but the less by the knee extensors (quadriceps).