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166 Injury and Skeletal Biomechanics

**Author details** 

J. Mizrahi and D. Daily

**Acknowledgement** 

**8. References** 

We have addressed a major fatigue-related factor taking part in exposing the shank to stress fractures risk: the decline in end tidal carbon dioxide pressure, the latter expressing metabolic fatigue [31,58]. The mechanical consequence of fatigue in long-distance running is two-fold: enhanced impact acceleration due to global fatigue and muscle activity imbalance due to local fatigue before and during foot contact, resulting in the development of excessive

While departing from the stiffness constancy concept, the model revealed that a correct and sufficient variability of the joint stiffness is a two-region piece-wise constant stiffness indicating that a higher order of non-linearity is not necessary. This result should be considered meaningful in those problems where the constant stiffness representation is not sufficient and in cases where the system's representation has to be improved. Joint stiffness is dominated by muscular activation [59-60] and as the joints stiffen, they undergo smaller angular displacements during the ground-contact phase, also resulting in smaller excursion of the hip and higher leg stiffness. Thus, since stiffness is related to muscle activation, the piece-wise constant stiffness obtained solution also provides, through the obtained stiffness

The fact that the simple model of a piece-wise constant stiffness can predict major features of the running exercise makes it an effective tool for future designing of artificial legs and

profiles, an insight into the patterns of the muscular activation in the legs' joints.

*Department of Biomedical Engineering, Technion, Israel Institute of Technology, Haifa, Israel* 

Institute of Technology, under the joint supervision of JM and Prof. Yacov Ben-Haim.

This Chapter is partly based on an MSc Thesis of second author DD, carried out in JM's Biomechatronics Laboratory, Department of Biomedical Engineering, Technion – Israel

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**Section 4** 

**Quantitative Biomechanics** 

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