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. Author manuscript; available in PMC: 2020 Dec 1.
Published in final edited form as: Ann Biomed Eng. 2019 Jul 9;47(12):2416–2430. doi: 10.1007/s10439-019-02318-w

Fig. 8:

Fig. 8:

Peak ASF as a function of Q-H (light gray) and Q-G (dark gray] co-contraction indexes (CI) obtained by artificially increasing the activations of the antagonist muscles (see text and Figs. 6 and 7 for more details). An increase in Q-H CI produced a decrease in peak ASF due to the line of action of the hamstrings, which is directed posteriorly, whereas an increase in Q-G CI produced a substantial increase in peak ASF, since the quadriceps and gastrocnemius pull and push the tibia anteriorly, respectively. This data can be interpreted as a lower bound in ACL force during landing, as the ACL is the primary restrain for the anterior translation of the tibia, and the ligament also restrains secondary knee rotations as abduction and internal rotation.