Running Shoe Characteristics and Injury

The growing popularity of recreational running has resulted in an increase in associated injuries to lower extremities (Latter, 1981) and according to most reports 60% of these runners will experience injuries that limit their activity levels (Brody, 1982). Statistics have revealed that injury rate is higher in novice runners than their elite counter parts (Cook et al. 1990), this may be due to both biomechanical and physiological variables.

The impact period of the running stance phase is often called the heel strike, most runners make ground contact with the lateral aspect of the shoe sole at the heel. During the mid-support component, the foot rolls into a pronated position with both forefoot and rearfoot in contact with the ground. Control of this motion is affected by three muscle, tibialis posterior, flexor digitorium longus and flexor hallucius longus. Upon repetitive use, these muscle can become inflamed and produce conditions such as shin splits (Clement et al. 1981). The final component of the stance phase is  the push off, when the shoe should control the position of the foot with respect to the leg in order to maintain stability (Nigg et al., 1987).

Over pronation is not desirable; various running injuries have been reported to be associated with excessive foot pronation (Cook et al., 1990). However, the combined movement of eversion, abduction and dorsiflexion allows for surface adaptation and shock absorption and so is a necessary aspect to running gait (Perry & Lafortune, 1995). Nevertheless over pronation during the midstance phase results in a hyper flexible and unstable foot (Cheug et al., 2006). ‘Motion control’ training shoes attempt to negate these effects, either by realigning the foot or by a direct cushioning effect. Right leg foot positions and rear foot angles.

In order for a shoe to resist excessive or unwanted motion of the foot and ankle shoes can employ various characteristics such as a heel flare, medial posting and dual high density cushioning materials. Each intended to lessen the amount of rear foot movement experienced by an athlete. An increased medial heel flare has been shown to decrease rear foot movement (Clarke et al, 1983; Nigg & Morlock, 1987). Whilst a reduction in lateral heel flare reduces ankle leverage, therefore reducing rear foot movement (Nigg and Morlock, 1987).
The use of medial posting and dual high-density materials has also been found to reduce rear foot movement (Cheung & Nigg, 2007). Such motion control shoes have been shown to reduce rear foot angle by 4°. Although it has been found that pronation is of particular importance in the first 10% of stance (Duffey et al., 2000), as a reduction in rear foot movement at this time makes for a more rigid landing. Thereby increasing the impact shock to the lower extremity and contributing to overuse injury.

Alternatively, it has been suggested by Lieberman et al. (2010) that running shoes cause heel striking and that barefoot running would make for a flat/forefoot strike. It was thought that this forefoot strike would negate the impact peak of the heel strike that was linked to injury and thus this style of running would not subject athletes to the same types of impact loading. Ultimately, leading to the conclusion that running shoes cause an impact shock and accommodate higher injury susceptibility. Perhaps a key result of this study was the introduction of minimalist training shoes such as Nike Free and Vibram Five Fingers, such training shoes seek to emulate barefoot running since it was postulated that running shoe cushioning and heel lift were not beneficial. However, both running barefoot and with minimalist training shoes result in higher impact force magnitude and loading rates compared to traditional shod running (Squadrone & Gallozi, 2009). Both variables arguably possess a similar risk of injury as impact shock, thus highlighting flaws in the ‘safe’ and ‘gentle’ natural of running barefoot.

However, it has been shown that the impact force acts as an external input to our system, allowing us to detect the nature of the surface and adjust our muscle activation accordingly (Nigg + Wakeling, 2001). Contradicting the notion that impact peak is associated with injury (Zadpoort +Nikoofan, 2011) and instead providing a means for runners to efficiently adapt to different terrains. As opposed to examining ground reaction force data it has been suggested that the study of pressure variable would be more appropriate. This would allow for the identification of the area of the foot that first comes into contact with the ground, providing more detail of what foot contact style is being adopted for different conditions (Nunns et al., 2012).

Barefoot running is therefore not the miracle practice frequently speculated in the media, making athletes more efficient and injury free. Instead, it causes individuals to load the associated joints in a different manner through an alteration in stride type, the effects of which can be equally as injury inducing as traditional shod running. The notion that barefoot running also results in greater running economy can also be seen as a myth, although it rids the exerciser of the added mass from trainers (which increase oxygen consumption by 1% per 100g), it does not account for the need of greater proprioception. Overall leading to gait alterations that would have already been of optimal measures.

Overall, literature evidence is equivocal as to whether different footwear types truly can negate injury for runners. Although variations in heel flare may reduce rearfoot movement it is important to maintain a certain level of pronation (8-10°) for shock absorption and terrain adaptation.  This pronation is of particular significance during the first 10% of stance and so should not be eliminated. Whilst barefoot running/minimalist shoes have been shown to alter stride types, distributing impact forces differently and not necessarily preventing injury. It is important that coaches adopt a holistic assessment of their athlete when screening for injury risk. Taking into account training and physiological variables that may provide a clearer picture of injury, this may include strength of the surrounding skeletal muscles and the variance of the training programme.