Leg Spring Stiffness is a measure of how well a runner recycles the energy applied to the
ground. LSS has been shown to be correlated with running performance. Think of your leg
as a spring upon which your body “bounces.” The stiffer the spring, the less energy you
must produce to propel yourself forward with each step. This metric measures the
stiffness of the muscles and tendons in your leg. Increases in LSS can indicate economy
improvement over time. What is a “good” LSS value? LSS is individual and cannot easily
be compared across different runners and should be standardized for body weight in
your own comparisons over time. For this reason, trends in LSS/kg for specific speeds
should be the focus of the analysis. Dynamic mobility and biomechanics drills along with
strength training and hill repeat workouts have been shown to improve leg stiffness
and running economy. All that said, LSS for most athletes ranges from 6 to 14 kN/M.
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