Axial loading of the wrist results in carpal pronation, which loads the scapholunate ligament (SLL). ECRL and FCR are carpal supinators and ECU is a carpal pronator. In this study we aim to show differential activity in the ECRL and ECU as a protective mechanism for the SLL in simulated falls.

Eight healthy volunteers were recruited for a simulated fall situation. Surface EMG was used to record muscle activity in the six major muscles that control wrist movement (FCU, FCR, ECRL, ECU, APL, ECRB) in the right forearm. The forearm skin was prepared in a standard fashion and the electrodes placed following an established protocol. Recordings were made using zero wire (Noraxon) surface EMG equipment. The data was exported and analysed using MyoResearch XP. Recordings were rectified and mean value, peak value, area under the curve and frequency were compared. Recordings were divided into five time periods from rest to post-impact.

ECRL has the most predictable and consistent response to impact of the wrist on the ground. Immediately following impact there is inhibition of the extensors and no change in flexor activity. The next phase is characterised by a ‘spike’ in ECRL activity with a less marked increase in ECRB and minimal change in ECU activity. There is decrease activity in the flexors during the ECRL peak.

The pre-peak period lasts between 5 to 10 ms. The ECRL peak period lasts between 20 to 30 ms.

We have identified that ECRL is active post fall and this response takes less than 10 ms from the time of impact. The time response is in the order of a spinal proprioceptive reflex. We were unable to identify a stretch response in the flexors that could act to trigger the ECRL response.