Altered squat jumping mechanics after specific exercise

This study examined squat jumping (SJ) mechanics following length restricted strength training regimens of the knee extensors and flexors. SJ from a 110 degrees knee joint angle starting position and isometric moment-knee angle relations of knee extensors and flexors were analysed in 16 athletes before and directly after 8 weeks of strength training regimens that were restricted to knee joint angles corresponding to long muscle-tendon unit (MTU) length for the knee extensors and flexors. SJ mechanics were studied using a two-dimensional kinematic model with three rigid bodies (upper leg, lower leg, foot) in combination with force plates measurements of ground reaction force in the right and left lower extremity. Centre of mass jumping height significantly (p<0.05) increased post training, but this was not explained by enhanced absolute power generation in the knee joint. However, post training small but significant (p<0.05) shifts to smaller knee joint angles occurred in the normalized [% Max.] knee joint angle dependent power generation in the right and left knee joint during SJ. The isometric moment-knee angle relation of the knee extensors was also significantly (p<0.05) shifted to longer MTU lengths of knee extensors. Length restricted strength training may alter the mechanical situation during both isometric contractions and dynamic athletic movements.