Foot Strike Position Affects: Part 2
We have previously discussed the concepts of different types of foot strike positions in running.
- The foot strike position affects braking energy dissipation techniques.
- The angle a joint finds itself on receiving a force through the ground reaction force (GRF) dictates the direction in which the joint will want to move…
- and the muscle activity that will be required to control the motion.
When activated, muscles are able to absorb energy through their muscle-tendon buffering effect (1). In heel strikes, tibialis anterior dissipates the energy around the ankle through resistance of the ankle plantarflexion moment caused by the heel impacting the ground (Fig. 1A). In a forefoot strike, the GRF is in front of the ankle as contact is on the forefoot. In a forefoot strike, the muscle that resists the impact around the ankle is primarily the triceps surae (through the Achilles tendon). The muscles and Achilles have to dissipate energy through resisting the ankle dorsiflexion moment (Fig. 1B).
A flat foot strike known as a midfoot strike will tend to use the Achilles to dissipate energy as the ankle quickly dorsiflexes after loading, but the stresses on the Achilles will be less, and instead, other energy dissipation techniques such as those of the more proximal muscles around the knee and hip, will absorb more of the energy usually absorbed around the ankle.
Heel strikes cause the impact force known as the ground reaction force, to be directed behind the ankle so that the muscles in front of the ankle (mainly tibialis anterior) must control the ankle motion and help dissipate the impact energy (A). In forefoot strikes, the ground reaction force is in front of the ankle so the heel is forced downwards (dorsiflexion). This heel drop must be resisted by the calf muscles and tendons, primarily the triceps surae which is attached to the Achilles tendon.
Each strike position is on a continuum but has been classified by a ‘strike index’, which relates to the position of the initial ground reaction force generated on the foot (2). To be able to classify a runner you really need a force plate gait analysis system, but as this is unlikely to be available to most clinicians, then either an in-shoe pressure system such as the FScan or Pedar, or a pressure plate can be used through the initial centre of pressures location. If none of these are available, careful slow-motion video analysis in the sagittal plane can be used to spot the point of the first contact. Locations from the posterior heel to 33% along the foot indicate rearfoot strikes, from 34-67% along the foot midfoot strike, and 68-100% of length a forefoot strike (3).
Another option is to use the angle formed between the plantar aspect of the foot (or shoe) and the ground. This again can be captured reasonably well using slow-motion video by 2D motion capture, although 3D capture technology is the ideal choice. An angle of zero degrees or near to zero indicates a foot flat landing associated with a midfoot strike, a positive dorsiflexed angle means a heel strike and a negative plantarflexed angle, a forefoot strike. The greater the strike angles the higher the positive or negative strike positions will be (3,4).
Foot strike on a continuum with a large positive angle at heel strike (A), a low positive angle of a less extreme heel strike (B) and a high negative angle of a forefoot strike (C).
The faster the running speed the more likely the runner is to forefoot strike(4). Running speed has far more influence on the strike position than the presence or absence of running shoes. High powered activity such as fast running, requires lots of energy storage in the tendon for elastic recoil during acceleration to maintain higher speeds. When tendons dissipate energy, they also store some, which is released as the tendon recoils after being stretched. Certain tendons are better to load at high speed than others because they store more energy which can be used to help acceleration through elastic recoil. The Achilles tendon is a high energy storage tendon, whereas the tibialis anterior is a positional tendon and can not store a great amount of energy like the Achilles(5). Therefore to maintain high speed the energy stored and released in the Achilles will be more important than just the energy dissipation it provides, making forefoot running with its early Achilles loading a better option running at high speeds than rearfoot strikes (6,7).
It has been claimed that forefoot running reduces injury because rearfoot strikers are reported as having higher injury rates (8,9,10), although claims on reduced impact forces and reduced injury rates by changing rearfoot strike runners to forefoot striker are lacking (11). It appears that certain injuries are a greater risk in one foot-strike type than another. The Achilles tendon is loaded with higher stress in forefoot running (12), but long stride lengths associated with extreme heel strikes have been associated with an increase in the number of injuries lower limb injuries around the hip and shin (13).
So which is the best? The answer probably depends on the runner, and the distance and running pace of that runner. For shorter distance and speed running, forefoot running is probably best, but for long-distance where fatigue is a high risk, heel or midfoot strikes may be better. The key is to always avoid extremes of foot strike positions, as they are more likely to create problems. A long stride length is usually the cause so keep stride lengths short and encourage more steps to cover the ground.
- Konow N, Azizi E, Roberts TJ. (2012). Muscle power attenuation during energy dissipation. Proc Royal Soc. B: Bio Sci. 279: 1108-1113.
- Cavanagh PR, Lafortune MA. (1980). Ground reaction forces in distance running. Journal of Biomechanics. 13: 397-406.
- Forrester SE, Townend J. (2015). The effect of running velocity on foot strike angle-A curve-cluster approach. Gait Posture.41: 26-32.
- Altman AR, Davis IS (2012). A kinematic method of foot strike pattern detection in barefoot and shod running. Gait Posture. 35: 298-300.
- Thorpe CT, Udeze CP, Birch HL, Screen HRC. (2012). Specialization of tendon mechanical properties result from interfascicular differences. J Royal Soc. Interface. 9: 3108-3117.
- Roberts TJ, Azizi E. (2011). Flexible mechanisms: the diverse roles of biological springs in vertebrate movement. J Exp. Bio. 214: 353-361.
- Roberts T, Konow N. (2013). How tendons buffer energy dissipation by muscle. Ex Sport Sci Rev. 41: 186-193.
- Daoud AI, Geiler GJ, Wang F. (2012). Foot strike and injury rates in endurance runners: a retrospective study. Med Sci Sport Exerc. 44: 1325-1334.
- Diesel AR, Gregory R, Alita C, Gerber JP.l (2012). Forefoot running improves pain and disability associated with chronic exertion compartment syndrome. Am J Sports Med. 40: 1060-1067.
- Nunns M, House C, Fallowfield J, Allsopp A, Dixon S. (2013). Biomechanical characteristics of barefoot foot strike modalities. J Biomech. 46: 2603-2610.
- Hamill J, Gruber AH. (2017). Is changing foot strike patterns beneficial to runners? J Sport Health Sci. 6: 146-153.
- Kernozek TW, Knaus A, Rademaker T, Almonroeder TG. (2018). The effects of habitual foot strike patterns on the Achilles tendon in female runners. Gait Posture. 66: 283-287.
- Brahma C, Preece SJ, Gill N, Herrington L. (2018). Is there a pathological gait associated with common soft tissue running injuries. Am J Sport Med. 46: 3023-3031