And this, is why you do "straight knee broad jumps"
DID YOU KNOW? Scientific literature on the biomechanics of the vertical jump sheds light on the role of the ankle in weightlifting. It explains why active extension at the ankle during weightlifting is not a mere style preference nor executed just to add last-second height to the bar. Just as in maximal weightlifting, maximal vertical jumping depends on creating maximal vertical velocity of the center of mass at the proper time. Decades of undisputed biomechanical research tell us that active extension at the ankle (characterized by concentric contraction of the gastrocnemius and soleus, extension/downward rotation of the foot, and increased vertical distance between the hips and the toes) is the only known way to maintain vertical velocity of the hips and achieve peak vertical acceleration of the center of mass up until the hips reach full extension (i.e. are at their greatest vertical distance from the toes). In weightlifting, just as in jumping, without properly-timed and active extension at the ankle, the vertical velocity of the hips already starts slowing down well before the hips reach full extension. Because of this, those who eliminate active ankle extension may be giving away up to 30% of their peak vertical power potential.
See e.g. Bobbert MF, van Ingen Schenau GJ., Coordination in Vertical Jumping., J Biomechanics; 21(3):249-62. 1988; Bobbert, M.F., and A.J. Knowk Van Soest. Why Do People Jump the Way They Do? Exerc. Sport Sci. Rev., Vol. 29, No. 3, pp 95-102, 2001; Luhtanen, Segmental Contribution to Forces in Vertical Jump, European Journal of Applied Physiology and Occupational Physiology, 15. IV. Volume 38, Issue 3, pp 181-188, 1978; Pandy and Zajac Optimal Muscular Coordination Strategies for Jumping, J. Biomechanics, 24(1) 1-10, 1991.
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