BIOMECHANICS INJURY RISK

900 800 700 600 500 400 300 200 100 0

Studs Moulded Synthetic

surfaces such as concrete. In terms of performance, compliant (less stiff) surfaces appear to be able to improve performance through lower muscle moments and forces, and possibly by providing some rebound during ground contact. However, there may be an increased energy cost associated with a surface that is too compliant. Overall, a surface with suitable compliance appears to have the potential to reduce injury risk and improve performance.

Surface 1 Surface 2

Figure 5: Peak heel force for a compliant surface (surface 1) and a stiff surface (surface 2) for three footwear types. There is a significantly higher peak loading on the heel for the stiffer surface (*p<0.05) (from Dixon et al., 2008)

rather than below the running surface, and a pressure insole allows data to be collected specifically for the heel region, rather than providing a resultant force for the entire ground contacting surface. This recent evidence of higher heel loads for stiffer surfaces supports the suggestions of authors such as Hardin and colleagues (13) and Butler and colleagues (14) that stiffer surfaces will increase impact shock and thus injury risk.

SUMMARY AND CONCLUSIONS Based on the evidence presented in this article, responses to the questions posed at the start of this article are:

Q What changes occur in lower limb biomechanics with changes in running surface? A Adjustments in kinematics and joint moments to influence lower limb stiffness throughout ground contact Q What criteria govern the changes in biomechanics? Maintenance of consistent centre of gravity vertical displacement? Q What influence do these changes have on lower limb chronic injury and performance? A Stiffer surfaces can increase initial impact shock; and performance considerations dominate over injury concerns.

Thus, in terms of injury, there is

evidence that surfaces of high stiffness may increase injury risk, through increased impact loading. Although there is a lack of good scientific evidence regarding injury incidence for different surfaces to support this suggestion, caution seems to be advised when running on stiffer

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References 1. Farley CT, Houdijk HHP, van Strien C, Louie M. Mechanism of leg stiffness adjustment for hopping on surfaces of different stiffnesses. Journal of Applied Physiology 1998;85:1044–1055. 2. Ferris D, Liang K, Farley C. Runners adjust leg stiffness for their first step on a new running surface. Journal of Biomechanics 1999;32:787–794. 3. Dixon SJ, Collop AC, Batt ME. Compensatory adjustments on lower extremity kinematics in response to a reduced cushioning of the impact interface in heel–toe running. Sports Engineering 2005;8:47–56. 4. Stiles VH, Dixon SJ. The influence of different playing surfaces on the biomechanics of a tennis running forehand foot plant. Journal of Applied Physiology 2006;22:14–24. 5. Bobbert M, Yeadon M, Nigg BM. Mechanical analysis of the landing phase in heel-toe running. Journal of Biomechanics 1992;25:223–234. 6. Clarke TE, Frederick EC, Cooper LB. Biomechanical measurement of running shoe cushioning properties. In Nigg BM, Kerr BA, eds. Biomechanical aspects of sport shoes and playing surfaces. University of Calgary Press 1983. 7. Herzog W. The influence of running velocity and playing surface on the load on the locomotor system. Zurich ETH 1978.

8. Nunns M, Dixon S. The influence of running surface compliance on lower limb kinetic and kinmatic variables. BASES Biomechanics Interest Group Easter Meeting 2008. 9. Andreasson G, Olofsson B. Surface and shoe deformation in sports activities and injury. In Nigg BM, Kerr BA, eds. Biomechanical aspects of sports shoes and playing surfaces. University of Calgary Press 1983. 10. Meyers M, Barnhill B. Incidence, causes and severity of high school football injuries on fieldturf versus natural grass. American Journal of Sports Medicine 2004;32:1626–1638. 11. Cole G, Nigg BM, Fick GH. Internal loading of the foot and ankle during impact in running. Journal of Applied Biomechanics 1995;11:25–46. 12. Ferris D, Louie M, Farley C. Running in the real world: adjusting leg stiffness for different surfaces. Proceedings of the Royal Society of London 1998;265:989–994. 13. Hardin E, van den Bogert A, Hamill J. Kinematic adaptations during running: effects of footwear, surface and duration. Medicine and Science in Sports and Exercise 2004;36:838–844. 14. Butler R, Crowell H, McClay Davis I. Lower extremity stiffness: implications for performance and injury. Clinical Biomechanics 2003;18:511–517. 15. Kerdok AE, Biewener AA, McMahon TA, Weyand PG, Herr HM. Energetics and mechanics of human running on surfaces of different stiffness. Journal of Applied Physiology 2002;92:469–478. 16. Dixon S, et al. Influence of footwear and soil density variations on loading within the shoe and soil surface during running. Journal of Sports Engineering and Technology 2008;1:in press. 17. Dixon S, Stiles V. Shoe–surface interaction in tennis. Sports Engineering 2003;6:1-10. 18. Dixon S. Use of pressure insoles to compare in-shoe loading for modern running shoes. Ergonomics 2008; in press.

THE AUTHOR TH

Dr Sharon Dixon is a senior lecturer with the School of Sport and

(Loughborough

and Health Sciences at the University of Exeter, and has been a lecturer here since January 1999. Dr Dixon gained her Ph.D.

(Loughborough University) in 1996, investigating the influence of footwear interventions on Achilles tendon loading. In the period 1997-1998, she held postdoctoral research positions in the School of Civil Engineering, University of Nottingham (EPSRC Grant) and in the Human Performance Laboratory, University of Calgary. Dr Dixon’s research interests are in the increased understanding of lower extremity overuse injury mechanisms, the influence of footwear, shoe insert and surface manipulations on lower extremity biomechanics, and the application of pressure data to understanding foot function. Dr Dixon leads the Exeter Biomechanics Research Team, comprising fellow lecturers and research students. She has published in a range of international peer reviewed journals in the field of sports and exercise related biomechanics, sports medicine and sports engineering.

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