GENERATION ANO TRANSMISSION OF HEEL STRIKE IMPACTS IN CHILDREN RUNNING, FOOTWEAR ANO SEX INFLUENCE.
AbstractINTRODUCTION: Heel strike impacts have been correlated with degenerative joint diseases, stress fractures and low back pain (Folman et al, 1986; Robbins,1993).As a result, a new trend in adult sport footwear design including shock absorbing systems has centered the attention of the main sport footwear manufacturers. Children's sport footwear is In most cases designed according to adults' criteria and it is widely accepted that children sport footwear must provides as much shock absorption as in' (Fredericks, 1993). The literatures with on children running, but little attention has been paid to heel strike impacts. This paper presents a pilot study to better understanding shock absorption and transmission in children running. RESULTS: Eight healthy children (4 girls and 4 boys) aged 7-14 years were selected. Each child ran across a 10metres walk away stepping with the right foot on a force plate. The ground reaction force and the acceleration on the tibia were recorded simultaneously. Each subject performed 5 valid trials running barefoot, with 2 types of sport footwear and with 2 types of casual footwear. Maximum vertical impact force (Fzi), rate of load at impact (RFzi), maximum acceleration on tibia (Atib), rate of acceleration on tibia (Ratib) and the ratio AtiblFzi (SF) were computed. In the present work it has been shown that impact forces do occur in children running, and that they do give rise to transient stress waves travelling through the body. Girls present higher shock transmission and tibia1 acceleration than boys. There were statistically significant differences for all the study parameters between shod and unshod conditions. The type of footwear used influenced shock absorption and transmission. Sportsfootwear gave rise to higher Fzi (similar to barefoot), Atib and RFzi than casual footwear. CONCLUSIONS: When considered from adult footwear design criteria, the above results will give rise to protective footwear for children similar to the adult sportfootwear. However, the skeletal and neuromuscular systems of children are not yet consolidated, the negative effects of the impacts observed in adults may not be present in children, and osteogenic and stimulating effects of impacts must not be neglected. So, detailed understanding of the effects of impact on the child body is needed before design criteria for children footwear are established. The results with sport footwear support this since it is normally regarded as more shock absorbing than casual footwear. These results could be explained either as a consequence of a bad footwear design, or due to a bad perception of impact with the sport footwear according to Robbins' feedback model for impact attenuation behaviour (1 991). Amore detailed study with more children would help to better understand impact perception and adaptation in children. REFERENCES: Folman Y.; Wosk J.;Voloshin A.; Liberty S. (1986) Cyclicimpacts on heel strike: A possible biomechanical factor in the etiology of degenerative disease of the human locomotor system. Arch. Orthop. TraumaSurg. 104, 363-365.Robbins S.E., Gouw G.J. (1991) Athleticfootwear: Unsafe Due to PerceptuaI llusions. Med. Sci. Sports Exer., 23(2): 217-224.Fredericks, E.C. (1993) Shoe design and children's running. NlKE ResearchNewsletter
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