Text and Data Mining valid from 2019-02-05
First Online: 5 February 2019
Change Date: 21 February 2019
Change Type: Correction
Change Details: “As ACL injury may alter intracortical facilitation  and depressed intracortical inhibition is correlated with decreased quadriceps voluntary activation capability , external focus training may provide a means to restore quadriceps muscle activity via increasing intracortical inhibition.
Compliance with Ethical Standards
: No sources of funding were used to assist in the preparation of this article.
: Alli Gokeler, Dorothee Neuhaus, Anne Benjaminse, Dustin Grooms, and Jochen Baumeister declare that they have no potential conflicts of interests relevant to the content of this manuscript.
: Informed consent was obtained from all individual participants for whom identifying information is included in this article.