Wrist and hand postures when falling and description of the upper limb falling reflex

Abstract

Introduction: Falling studies, i.e. assessing what happens when an individual falls, have been conducted in controlled environments but not in field studies for ethical reasons; this potentially limits the validity and applicability of previous studies. We performed field studies on existing YouTube © videos of skateboarders falling. The aims of these studies were to measure the wrist angle at impact on videos of real unprotected falls and to study the dynamics of the upper limbs when falling.

Methods: Youtube © videos of skateboarders falling were studied assessing the direction of the fall, the positions of both upper limbs and especially the wrists on impact quantitatively and qualitatively. This study would not be ethical by other means.

Results: In study one (the more quantitative study) there were 48 men and 50 falls. The mean elbow flexion was 30⁰ (range 0⁰ to 80⁰) and the mean maximal wrist extension was 80⁰ (range 50⁰ to 110⁰). The second wrist extended less or the same in > 90%. The second wrist only once (of 31) extended > 90⁰ which should minimise the risk of toppling. Falls onto only one wrist gave significantly greater maximal wrist extension. In the second more qualitative study we observed the "upper limb falling reflex" where the response to falling is for the upper limb(s) to align the upper limb with the direction of falling of the body with the elbow mostly but not fully extended. Initially the wrists extend c. 40⁰-50⁰ with the fingers held mildly flexed. Immediately before impact the fingers hyper-extend with some compensatory wrist flexion to c. 30⁰ of extension. The fingertips impact the ground first followed by the hand.

Conclusion: These studies confirm wrist extension at impact around 80⁰ but the wrist(s) may hyper-extend risking toppling. Falls on both wrists minimise the risk of toppling. The "upper limb falling reflex" is defined; it is a rapid dynamic response leading to the fingers impacting the ground first on falling. Abnormalities with the upper limb falling reflex may indicate problems with development in young children and may increase the risk of injury in older people.

Keywords: YouTube©; fall; field study; finger; hyperextension; skateboard; upper limb falling reflex; wrist.