but Lieberman noted that there is correlation between the foot-landing style and exposure to shoes. In some individuals, the gait pattern is largely unchanged – the leg position and foot position are identical in barefoot and shoe running – but the wedge shape of the padding moves the point of impact back from the forefoot to the mid-foot. In other cases, it is believed that the padding of the heel softens the impact and results in runners modifying their gait to move the point of contact further back in the foot. A 2012 study involving Harvard University runners found that those who "habitually rear-foot strike had approximately twice the rate of repetitive stress injuries than individuals who habitually forefoot strike". This was the first study that investigated the link between foot strike and injury rates. However, earlier studies have shown that smaller collision forces were generated when running forefoot strike compared to rear-foot strike. This may protect the ankle joints and lower limbs from some of the impact-related injuries experienced by rear-foot strikers. In a 2017 article called "Foot Strike Pattern in Children During Shod-Unshod Running", over 700 children aged 6–16 were observed using multiple video recording devices, to study their foot strike patterns and neutral support. Rear foot strike was most common, in both shod and unshod running, and in both boys and girls. There was a significant reduction in rear foot strike from shod to unshod: boys shod - 83.95% RFS, boys unshod - 62.65% RFS; girls shod - 87.85% RFS, girls unshod - 62.70% RFS. As-of 2021 there was a very low level of evidence to suggest a relationship between foot strike pattern and runner injury. Studies used retrospective designs, low sample size and potentially inaccurate self-reporting. Control of gait by the nervous system The central nervous system regulates gait in a highly ordered fashion through a combination of voluntary and automatic processes. The basic locomotor pattern is an automatic process that results from rhythmic reciprocal bursts of flexor and extensor activity. This rhythmic firing is the result of Central Pattern Generators (CPGs), which operate regardless of whether a motion is voluntary or not. CPGs do not require sensory input to be sustained. However, studies have identified that gait patterns in deafferented or immobilized animals are more simplistic than in neurologically intact animals. (Deafferentation and immobilization are experimental preparations of animals to study neural control. Deafferentation involves