The human body was designed for movement. Gait is arguably the most essential of human movements. Walking, jogging and running have always been fundamental activities of daily living, and today running and running-based activities form the bulk of recreational and competitive sports. Furthermore, there has been a significant emphasis placed on the importance of endurance running for general health. There is therefore an ever-increasing number of the lay public engaging in high volumes of endurance running . There has been an almost concert evolution of the running shoe. Despite this, the incidence of running related injuries has recently been reported to be as high as 90% [1, 2].
For most of history humans have either been barefoot or worn minimal footwear such as sandals or moccasins with flat soles and little cushioning, whereas the modern running shoe is characterised by elevated heels and increased cushioning beneath the arches of the foot. Such modifications to footwear are proposed to enhance rear foot control, increase foot stability and attenuate the impact forces encountered at the moment the foot strikes the ground (foot contact), thereby protecting against injury. However, there remains no clinical evidence to support that the design of modern running footwear is most favourable to promote long-term health in runners . This poses several questions. How did runners cope with the impact forces at foot contact before the invention of the modern running shoe? Has the design of the modern running shoe influenced natural (barefoot) running technique, and if so, in what manner?
Biomechanics of the Lower Limb during Running
Given that running is most injurious at the moment of foot contact, the way in which the foot contacts the ground is of importance. Foot contact generally occurs in two ways: a rear foot strike (RFS) in which the heel strikes first, and a forefoot strike (FFS) in which the ball of the foot lands before the heel drops . The tables below provide a comparison of the biomechanics of each technique.
Table 1: Lower limb mechanics during rear foot and forefoot strike running techniques .
|Rear Foot Strike||Forefoot Strike|
|Foot Contact||Ankle is dorsi-flexed (toes point up).
Land on the heel, just below the ankle joint.
As you land the ankle begins to plantar-flex (toes move towards the ground).
Arch of the foot remains unloaded.
|Ankle is plantar-flexed (toes point down) and inverted (sole pointing inwards).
Land on the forefoot, just below the fourth and fifth metatarsal heads.
As you land the ankle dorsi-flexes (heel moves towards the ground).
Arch of the foot begins to stretch and flatten (storage of elastic energy).
|Knee and hip flex, lowering the centre of mass.
The forefoot comes down as the ankle plantar-flexes.
|The heel comes down, stretching the calf muscles (storage of elastic energy).|
|Knee and hip continue to flex.
The ankle dorsi-flexes as the lower leg moves over the foot and the foot begins to evert.
Now the arch begins to stretch and flatten.
Combination of dorsi-flexion, eversion and arch flattening is called pronation.
|The arch continues to stretch and flatten.
Pronation occurs here too but in the opposite direction (forefoot to rear foot, not heel to toe).
|Ankle plantar-flexes, bringing the heel off the ground (calf muscles contract).
The arch recoils and toes flex.
These actions drive the body upwards and forwards into the next stride.
Effective mass: Includes the portion of the body that comes to a dead stop and the point of impact on the foot at the time of foot contact.
Impact force: Force generated by the body colliding with the ground.
Impact transient: High and short-lasting increase in the impact force seen during RFS running.
Table 2: The forces experienced during rear foot and forefoot strike running techniques .
|Rear Foot Strike||Forefoot Strike|
|Effective Mass at Impact||Foot and leg come to a dead stop while the rest of the body continues to fall above the knee.||Forefoot comes to a dead stop, but the heel and lower leg continue to fall. The ankle flexes.|
|Effective mass is the foot and lower leg which is approximately 6.8% of the body mass in runners .||Effective mass is the forefoot and some portion of the rear foot and leg, which is 1.7% of the body mass of runners .|
|Conversion of Vertical Momentum at Impact||Vertical momentum of the lower leg is mostly absorbed by the collision force.||Vertical momentum of the rear foot and lower leg is converted into rotational momentum (restoration of elastic energy of the calf muscles and arch of the foot).|
|Similar to dropping a beam straight on its end. It comes to a sudden stop.||Similar to dropping a beam at an angle. There is a sudden stop at one end while the rest of the beam falls.|
|Impact force||This collision creates a rapid and high impact force, known as an impact transient, equal about 1.5 to 3 times body weight.||This collision creates a slow rise in force with no impact transient.|
|Although running shoes make RFS comfortable, they do not eliminate this impact transient .||The impact forces here are approximately 7 times lower than RFS even with shoes .|
Historically, shoe design was rudimentary and only varied in material construction, not in fundamental purpose. In contrast, shoes are nowadays considered essential for running safely and comfortably, and shoe design is regarded as a key component of exercise and running performance. However, the modern running-sports shoe was only invented in the mid 1900’s. Much research has since been dedicated to comparing the effects of different types of shoes on the mechanics of the lower limb during running. Let’s have a look at what the research shows.
Divert et al.  examined mechanical and muscular differences between barefoot and shod running. The results of their study showed a reduced flight time, contact time and stride duration during barefoot running when compared to shod running. They also found that the impact forces during barefoot running were significantly lower than shod running, and that subjects achieved this by naturally changing to a FFS when barefoot. Later research showed that this mechanical change also affected the innate elastic properties of the body.
Bishop and colleagues  described the lower limb as a linear spring whereby elastic energy is stored and returned within the musculoskeletal system. During running or hopping, the ankle, knee and hip act to lower the body’s centre of mass (CoM) after the foot contacts the ground, representing compression of the spring and absorption of elastic energy (Figure 1). During push off the lower limb extends, representing restoration of the elastic energy and a recoil of the spring. Bishop et al.  showed that when running barefoot, subjects landed with a plantar-flexed ankle and then moved into dorsi-flexion as the heel dropped (compression of the spring). Whereas during shod running, subjects landed with a dorsi-flexed ankle in a RFS technique and moved through less dorsi-flexion after foot contact. This suggests that the FFS technique adopted during barefoot running utilises the natural stretch-shorten behaviour to generate energy during the push-off phase of running. In contrast, the RFS technique observed when running in shoes increased the stiffness of the ankle at foot contact, consequently diminishing the natural compression and recoil of the lower limb.
.”]Evidence also shows that a RFS increases the forces experienced at the knee and hip. Kerrigan et al.  found that running in shoes with elevated heels and increased cushioning under the arches of the foot increased knee flexion, knee varus and hip flexion torques by 36%, 38% and 54% respectively when compared to running barefoot. Therefore the RFS technique induced by running in cushioned shoes exposes the lower limb to larger joint forces, exposing a potential mechanism for joint injury .
Most recently, Lieberman et al.  found that habitually shod runners employ mostly RFS when running shod. These runners also adopt a RFS when barefoot, but adopt a flatter foot placement by dorsi-flexing the ankle less. In contrast, runners who grew up barefoot or changed to barefoot running predominantly used a FFS technique in both barefoot and shod conditions. They also found that the impact forces at foot contact for RFS runners were approximately three times lower in habitually barefoot runners who employ FFS. The collective findings of the available literature comparing the effects of barefoot and shod running may have significant implications in the development of footwear and in reducing the incidence of running-related injuries.
Habitually barefoot runners adopt a forefoot strike pattern characterised by a more plantar-flexed ankle and more ankle compliance at the time of foot contact. This method of running has been shown to generate impact forces up to seven times lower than a rear-foot strike (heel to toe) technique . A forefoot strike also permits the use of the body’s natural elastic properties, potentially enhancing running efficiency [7, 8, 11]. Despite the apparent benefits of using a natural forefoot strike technique, modern footwear is designed to elevate the heel and provide cushioning beneath the arches of the feet. Such designs elicit a RFS technique which exposes the body to significantly greater forces at the moment of foot contact. This may be a factor in the high incidence of running-related injuries.
Therefore, gradually transitioning to the natural forefoot strike technique may be more favourable towards long-term health while improving overall running efficiency. You need to unlearn and re-learn running, and you need to obtain footwear that permits natural foot and leg motion while providing meaningful protection against the environment.
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- Van Gent, R.N., et al., Incidence and determinants of lower extremity running injuries in long distance runners: A systematic review. Incidence and determinants of lower extremity running injuries in long distance runners: A systematic review, 2007. 40(4): p. 16-29.
- Richards, C.E., P.J. Magin, and R. Callister, Is your prescription of distance running shoes evidence-based? British Journal of Sports Medicine, 2009. 43(3): p. 159-162.
- Lieberman, D.E., et al., Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature, 2010. 463(7280): p. 531-5.
- Lieberman, D.E. Barefoot Running. 2010 [cited 2010; Available from: http://www.barefootrunning.fas.harvard.edu/index.html.
- De Cock, A., et al., Temporal characteristics of foot roll-over during barefoot jogging: Reference data for young adults. Gait and Posture, 2005. 21(4): p. 432-439.
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- Squadrone, R. and C. Gallozzi, Biomechanical and physiological comparison of barefoot and two shod conditions in experienced barefoot runners. Journal of Sports Medicine and Physical Fitness, 2009. 49(1): p. 6-13.
- Kerrigan, D.C., et al., The Effect of Running Shoes on Lower Extremity Joint Torques. PM and R, 2009. 1(12): p. 1058-1063.
- Divert, C., et al., Barefoot-shod running differences: Shoe or mass effect? International Journal of Sports Medicine, 2008. 29(6): p. 512-518.