In 1993 McConnell et al. recognised a lack of human experimental
data for low speed impacts, which they defined as being those
delta-V.which resulted in a speed change (delta-V) for the target vehicle
of 12.9 km/h (8 mph) or less. From nine successful test collisions
between various types of vehicle they subjected male human volunteers
aged 45–56 to speed changes from 3.04 km/h (2 mph) to
8.06 km/h (5 mph). In accordance with kinetic energy being proportional
to the square of the velocity, they recorded a visible four
fold decrease in collision related energy when the speed change
was halved. They suggested a speed change of 6–8 km/h (4–5 mph)
as being probably at or near to the typical human threshold for very
mild, single event musculo skeletal cervical strain injury. A participating
physician considered a speed change of 4 km/h (2.5 mph) to
have been so very mild that a single exposure would be unlikely to
result in any symptomology.