Squatting is a fundamental human movement, but it places significant mechanical demand on the knee joint. As the knee moves into deep flexion, the forces acting upon the joint surfaces increase substantially, involving both compressive and shear stress. This repetitive, high-load movement frequently exposes underlying issues, making knee pain during a squat a common complaint. The location and quality of the pain can often indicate which anatomical structure is irritated or damaged.
Understanding Patellofemoral Pain
Patellofemoral pain syndrome (PFPS) is a frequent diagnosis for pain experienced around or behind the kneecap, often aggravated by deep knee bending activities like squatting. This condition is primarily related to how the kneecap, or patella, moves within the trochlear groove of the femur. Ideally, the patella tracks smoothly along this groove as the knee flexes and extends, but poor alignment or muscle imbalance can cause improper tracking.
When the patella shifts or rubs, the increased friction can irritate sensitive tissue and lead to inflammation. This misaligned movement increases compressive forces on the articular cartilage that lines the back of the kneecap. The pain often intensifies when the knee reaches 60 to 90 degrees of flexion, a common depth reached during a squat. Chronic irritation can eventually contribute to the softening or breakdown of the cartilage, a condition known as chondromalacia patellae.
Damage to Meniscus and Joint Cartilage
Pain originating from the menisci or the main joint cartilage indicates a structural issue deep within the knee joint, distinct from kneecap tracking problems. The menisci are two C-shaped pieces of fibrocartilage that sit between the thigh bone and shin bone, acting as shock absorbers and contributing to joint stability. Squatting, especially deep flexion or squatting under load, places high compression and shear force on these structures.
A tear or fraying of the meniscus causes sharp pain felt deep inside the joint, often accompanied by mechanical symptoms like clicking, popping, or locking. Generalized deep joint pain that worsens with weight-bearing flexion may point to osteoarthritis. Osteoarthritis involves the gradual wear and tear of the articular cartilage covering the ends of the femur and tibia. As this protective layer breaks down, bone-on-bone friction increases, which is aggravated by the high compressive forces of a squat.
Tendon Strain and Inflammation
Pain localized above or below the kneecap suggests a tendinopathy, involving the strain and inflammation of a tendon. The patellar tendon connects the kneecap to the shin bone; its inflammation, known as patellar tendinitis or “Jumper’s Knee,” causes pain just below the patella. Conversely, quadriceps tendinitis affects the tendon just above the kneecap, where the thigh muscle attaches.
Both conditions are overuse injuries resulting from repetitive loading, which causes microscopic tears and structural changes within the tendon tissue. The squat movement requires the quadriceps muscle group and its associated tendons to manage high eccentric and concentric forces. When the knee bends, the tendon is stretched under tension, and the pain is exacerbated as the load increases. Repetitive squatting prevents the tendon from adequately recovering, perpetuating the cycle of strain and inflammation.
Biomechanical Factors Affecting Squat Form
Knee pain during squatting often stems not from a primary injury within the knee, but from movement patterns originating elsewhere in the lower body. One common issue is an inward collapse of the knees during the squat descent, known as knee valgus. This movement places undue rotational and shear stress on the knee joint, suggesting the hip and gluteal muscles are not adequately stabilizing the leg. Weakness in the hip muscles, particularly the gluteus medius, can fail to control the thigh bone’s rotation, forcing the knee into an unsafe alignment.
Another biomechanical factor is limited ankle dorsiflexion, which is the ability of the shin to move forward over the foot. If the ankle joint lacks sufficient mobility, the body compensates by shifting the center of mass, often forcing the knee to travel excessively far forward past the toes. This compensation increases the load and stress placed on the patellofemoral joint, contributing to anterior knee pain. Adjusting the angle of the trunk and tibia inclination can alter the distribution of forces, determining whether the load is primarily absorbed by the hips or the knees.