Horizontal and Declined Squats in Healthy Individuals: A Study of Kinematic and Muscle Patterns

Squats are frequently incorporated in physiotherapy programmes and performed in different ways. Accordingly, muscle and kinematic patterns also differ. The objective was to compare the kinematics and EMG patterns of the major muscles of knee and ankle joints during different squat exercises on horizontal (HP) and 25° decline (DP) boards. Seventeen healthy individuals performed squats on HP and DP with bilateral support and restriction of trunk movements in the sagittal plane. The knee and ankle angular displacements in the sagittal plane and the EMG activities of the major muscles of the lower limb in four subphases of movement were recorded and analyzed. For the descending phase of the HP squats, the angular excursion, as well as the initial and final positions, was smaller for the knee ( ) but larger for the ankle ( ). For the ascending phase of the HP squats, the initial and final positions were larger for the ankle ( ) and the final position was smaller for the knee ( ). All muscles remained activated and showed similarity between the tasks ( ), except for the tibialis anterior in both squat exercises ( ). The HP and DP squats produced different kinematics (knee and ankle joints) but did not modify the EMG strategy for both movement phases. 1. Introduction Injuries of the knee joint account for numerous lesions that affect the lower extremities [1]. In any lesion involving the knee, a reflex inhibition of the quadriceps is observed, accompanied by hypotrophy [2, 3], which causes knee instability [4]. This instability contributes to chronic pain, increasing the inhibition process and weakening the quadriceps and, in turn, leading to dysfunctions of the extensor mechanism [5]. Under these circumstances, quadriceps strengthening is essential to stabilize and minimize or reverse the process of inhibition and muscle weakening; such strengthening is therefore the main challenge that confronts the rehabilitation process [4]. Several protocols have been suggested for recovering quadriceps force, but multijoint exercises are the preferred form of therapy for dysfunctions of the extensor mechanism [6, 7]. Multijoint exercises are regarded as advantageous because they simulate functional activities [6, 8], exert minimal stress on the patellofemoral joint during the functional range of movements [6], and enable muscle cocontraction, which contributes to joint stability [9]. An effective multijoint exercise extensively used in clinical practice by physiotherapists is the squat [7, 10]. Some studies have demonstrated the usefulness of performing squats during