Date of Award


Document Type

Honors Thesis

Degree Name

Bachelor of Arts



Advisor/Committee Chair

John D. Polk


During sprinting and hopping, the lower limbs act as a mechanical spring as it compresses and recoils to store and release elastic potential energy during each step. This is important because for individuals such as high performing sprinters, the stiffer the spring acting limb is, the more efficient it will be for the sprinter to maintain maximal velocity and optimal performance. The basis of this experiment lies in the fact that the mechanics of the lower limbs are modeled using to the mechanics of a spring, therefore, to calculate an approximate limb stiffness, Hooke’s Law can be used. Hooke’s Law (k=F/L), where k is the spring constant, F is maximum ground force that is produce when the limb makes contact with the ground and L is the change in hip height between the middle of stance phase and initial contact. The purpose of this study is to investigate whether the knee or ankle contributes more to limb stiffness and the limb length change. The subjects of this study were 10 high performing track athletes that attended the University of Illinois. All subjects are asked to jump in place, on a force plate at 2,3, and 4 Hz. Sprinting data were collected from a single ground contact near the end of a 60m sprint. All kinematic data such as the knee angle, ankle angle, and hip height was all captured using an optical motion capture system (Motion Analysis Corp.) and the reaction forces was recorded on an AMTI force plate. Data was analyzed using MATLAB and Microsoft Excel. Our results suggested that limb stiffness was dependent on the hopping frequencies, stiffness increases with the increasing in frequencies. With the addition of sprints, we also found that limb stiffness increases with increasing 1/Contact Time. At the same time, ankle and knee angles decrease with the increase in hopping frequencies, which is how stiffness is attained. However, for sprinting, knee and ankle angles increase. These results also suggest that dominant compliancy lies with the ankle.

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.