Experimental set-up.

The forearm was supported in pronation. The thumb interphalangeal joint and index finger distal interphalangeal joint were free to move. Clamps and straps were used to stabalise the hand and prevent concomitant movement of any other finger or hand joint. An electrogoniometer measured the angle at the thumb interphalangeal joint, and a load cell measured force under the index finger. Electromyographic activity of the anterior forearm muscles was measured with surface electrodes (not shown).