Up to 50% of all injuries sustained by runners are at the knee (van Gent et al.,2007). Among the most common is patellofemoral pain syndrome, characterised by excessive inward collapse and internal rotation of the knee under load (termed dynamic knee valgus) (Taunton et al., 2002). Being a hinge joint, it is not surprising that such movements are injurious to the knee. The conventional therapy is strengthening of the gluteus medius to prevent internal collapse at the knee. This is ineffective (Willy and Davis, 2011) as the problem generally originates below the knee at an inflexible ankle and/or an unstable foot.
Poor ankle dorsi-flexion/mobility prevents bodyweight passing smoothly forward over the supporting foot, leading to compensatory movements upstream in the kinetic chain i.e. at the knee. A recent systematic review reported consistent associations between poor ankle dorsi-flexion range and dynamic knee valgus, recommending the assessment of ankle range in clinical settings as a risk factor for knee injury (Lima et al.,2018).
The deep squat should be considered the most functional assessment for ankle dorsi-flexion, as ankle mobility is the primary limiting factor to performing a flat-footed deep squat (Kasuyama, Sakamoto and Nakazawa, 2009).
As a fundamental human movement pattern, the deep squat is an excellent exercise to develop and maintain functional ankle dorsi-flexion range and leg strength for running.