Final answer:
Restricted hip flexors can impair a person's squat depth by limiting the range of motion in the hip joint, which is crucial for achieving adequate depth in a squat.
Step-by-step explanation:
The depth of a person's squat can be significantly affected by various factors related to the body's biomechanics. Among the options provided, C) Restricted hip flexors can impair a person's squat depth. Restricted hip flexors limit the range of motion in the hip joint, which is essential for achieving adequate squat depth.
While excessive dorsiflexion and pronated feet can affect squat mechanics, they do not specifically limit squat depth. Overactive quadriceps are not typically responsible for limiting squat depth either; instead, they might lead to dominance in the movement pattern, affecting form rather than depth. To improve squat depth and overall form, a person can work on hip mobility exercises, ensure proper squat technique, and use suitable footwear that provides stability.