title: The Effects of Squat Depth on Lower Extremity Joint Kinetics, ACL Loading, PCL Loading, Tibiofemoral Compressive Forces and Activations of Eight Lower Extremity Muscles
Creators: name: Sievert, Zachary A.
Publisher: name: Old Dominion University
publisherIdentifier: https://ror.org/04zjtrb98
publisherIdentifierScheme: ROR
Year: 2014

description: Performing resistance training exercises are important in many facets oflife. Resistance training can be used from elite athletes preparing for the Olympics to the average person exercising for overall health. The squat is a common training exercise that can be utilized to improve lower extremity strength and performance. There has been much debate on the effects of squatting depth on lower extremity joint kinetics and kinematics. Therefore the purpose of this thesis is to examine the effects of depth and load on the muscle activation of eight lower extremity muscles and three-dimensional (30) joint moments about the right knee, hip and ankle. The study will also examine the effects of load (BW, 50% !RM and 80% !RM loads) on anterior cruciate ligament loading, posterior cruciate ligament loading, and tibiofemoral compressive forces during 90° knee flexion squats.

Twenty-one recreationally active volunteers were recruited but only seventeen were used for analysis due to failure to complete the protocol or data processing difficulties. Recreationally active was defined as participating in exercise three times a week for at least 30 minutes per session and performing at least one session of lower body resistance training per week. Subjects were asked to perform two days of testing. During the first day of testing subjects one repetition maximum ( I RM) was determined. On day two subjects performed five squats to knee flexion angles of 90° and 120° at loads of body weight, 50% I RM and 80% I RM while right leg muscle activity, kinematics and kinetics were recorded. 90° knee flexion squat were further analyzed with a musculoskeletal model to determine anterior and poster cruciate ligament loading as well as tibiofemoral contact forces.

It was found that PCL loading and tibiofemoral compressive forces had significant increases as external load increased during the 90° squats. During the testing all the muscles tested, the gluteus maximus, medial hamstring, lateral hamstring, rectus femoris, vastus medialis, vastus lateral is, medial gastrocnemius and tibialis anterior tested had increases in activation as external load increased from body weight to 50% 1 RM to 80% 1 RM. All muscles tested had increases in activations as condition changed expect for the medial hamstring and medial gastrocnemius from the 90° squat to the deep condition. All the reported moments, hip extension, hip external rotation, knee extension, knee external rotation, knee adduction, ankle plantarflexion and ankle inversion had significant increases as weight increased from body weight to 50% 1 RM to 80% I RM and as condition changed from the 90° squat to the deep condition.

Overall it may be suggested that participating in squat exercises can be beneficial. First, as load and depth increase muscle activation in the lower extremities increases which can increase strength and hypertrophy in those muscles. Along with the potential of increased muscle activation there seems to be no increased risk in damaging the ligaments, but the risk of cartilage damage remains unclear.