The Effect of Playing Surfaces and Footwear on the Biomechanical Response of Soccer Players
Low, Daniel Craig
Date: 6 January 2010
Thesis or dissertation
University of Exeter
PhD in Sport and Health Sciences
This thesis describes three studies investigating biomechanical responses to changes in shoe-surface combinations in soccer. In the first study, six male participants (21.7 [S.D. 2.2] yrs, 74.0 [S.D. 6.9] kg [March], 74.6 [S.D. 6.9] kg (May), footwear size 10 -11) performed running and turning movements on natural and third generation ...
This thesis describes three studies investigating biomechanical responses to changes in shoe-surface combinations in soccer. In the first study, six male participants (21.7 [S.D. 2.2] yrs, 74.0 [S.D. 6.9] kg [March], 74.6 [S.D. 6.9] kg (May), footwear size 10 -11) performed running and turning movements on natural and third generation artificial surfaces whilst wearing different soccer specific footwear. This was performed at two times of the year where contrasting weather conditions were experienced. It was observed that there were significant differences when the natural and third generation artificial turf surfaces were compared. These differences however, were dependent on the type of movement, time of year and biomechanical measurement used. Each surface was also compared between the two test occasions. The main finding was that for both running and turning peak pressures and peak pressure loading rates were significantly greater in May (when the surfaces were mechanically hard) compared with the same surface in March. It was concluded that comparisons of third generation surfaces with natural turf are dependent on the specific properties of the surfaces and cannot be generalized for all such surfaces. A critical design feature of third generation surfaces that will influence biomechanical comparisons with other playing surfaces is the shock pad layer. In the second experimental chapter, ten male participants (20.9 yrs [S.D. 2.5], 83.2 kg [S.D. 7.1], footwear size 10 -11) were used to assess the effect of two different shock pad densities (55g and 65g) (Arpro® Expanded polypropylene BF2455W, 24mm S.D. 0.5mm thick, Brock International) on the lower extremity loading. These participants were also used to assess the biomechanical adaptations that occur with the inclusion of a 10 mm Sorbothane® heel insert or a Sorbothane® cushioning insole (Sorbo products division, Lancashire, UK), which have been associated with reducing overuse injury including that to the Achilles tendon. The footwear was also assessed for the risk of sustaining lateral ankle ligament damage. It was shown that whilst turning, peak impact force (taken using in-shoe pressure system) was significantly lower on the more cushioned shock pad as was peak pressure at the first metatarsal. Likewise, the time to peak impact force was significantly longer with the heel insert. However, despite the association between the heel insert and reduced dorsi-flexion, no significant differences were observed for this measurement between the footwear conditions. Peak plantar flexion was significantly greater with the heel insert whilst turning suggesting an increased loading of the lateral ankle ligaments, although rearfoot inversion was not significantly different. This study demonstrated the potential role of shock pad cushioning in providing protection from impact related injury in soccer, whilst cushioning inserts were not found to provide a protective effect. For heel inserts, the possibility of a negative influence on rearfoot stability was highlighted. It was suggested that the estimation of internal loads may reveal more regarding the specific role of cushioning interfaces and heel inserts in protecting from injury. In the final research chapter, nine male soccer players (83.4 kg [S.D. 5.8], 23 yrs [S.D. 3.7]) performed running and turning movements for the same conditions described in study two. The peak plantar flexion moment, Achilles tendon force and average loading rate of these measurements, were used to assess Achilles tendon loading. Likewise, peak dorsi-flexion and eversion moments were collected to assess the lateral ankle loading. Group analysis did not reveal any significant differences in these variables. Individual data showed that the response to heel insert intervention was specific to the participant. Some participants exhibited a reduced Achilles tendon force or average loading rate, suggesting a reduced risk of injury with the heel insert. However, it was observed that eversion and dorsi-flexion moment and average loading rates increased in some participants, suggesting that these participants were at an increased risk of lateral ankle ligament injury with the heel insert. Likewise, one participant experienced significantly greater peak Achilles tendon force, also indicating a greater risk of injury to this structure. The overall conclusions gained from these studies are that the design of the footwear and playing surfaces are worth considering in the quest to reduce injury risk. It was also highlighted that the choice of shock pad density for a third generation artificial surface can be influential in the protection of the athlete even when the surface is new, particularly when turning. Finally, although the use of heel inserts has proven successful in the reduction the Achilles tendon injury, the lack of significant differences for group comparisons suggests that the mechanisms behind the success is still unclear. However, although heel inserts may prove useful in the reduction of Achilles tendon injury, the observation that significant increases in the measurements associated with acute ankle ligament damage and chronic Achilles tendon injury, suggests that heel lift may not be suitable for some individuals.
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