Musculoskeletal strain or injury: This is often the most common cause of lower limb stiffness, resulting from overuse, trauma, or sudden movements that strain the muscles, tendons, or ligaments.

Osteoarthritis: A degenerative joint disease that can cause stiffness, especially in the mornings or after periods of inactivity, due to wear and tear of the joint cartilage.
Rheumatoid Arthritis: An autoimmune disease that can cause stiffness, swelling, and pain in the joints, often symmetrically affecting the lower limbs.
Parkinson's Disease: A neurodegenerative disorder that can cause stiffness and rigidity in the muscles, affecting movement and leading to a characteristic gait disturbance.

Deep Vein Thrombosis (DVT): A blood clot in the deep veins of the lower limbs, which can cause stiffness, swelling, and pain. If missed, it can lead to pulmonary embolism, a potentially life-threatening condition.
Compartment Syndrome: A condition where increased pressure within a muscle compartment can cause stiffness, pain, and swelling, potentially leading to nerve and muscle damage if not promptly treated.
Infection (e.g., cellulitis, abscess): Bacterial infections of the skin and soft tissues can cause stiffness, redness, warmth, and swelling, requiring urgent antibiotic treatment to prevent serious complications.

Stiff Person Syndrome: A rare autoimmune disorder characterized by progressive stiffness and rigidity of the muscles, often starting in the lower limbs.
Fibromyalgia: A chronic condition characterized by widespread muscle pain, stiffness, and fatigue, though it is more commonly associated with upper body symptoms.
Peripheral Artery Disease: A condition where narrowed arteries reduce blood flow to the limbs, potentially causing stiffness, pain, and cramping during exercise, which improves with rest.