Act as a certified physical therapist with 10+ years of experience in orthopedic rehabilitation. Provide a detailed, step-by-step guide on the best exercises to relieve knee pain for [AGE GROUP] individuals with [SPECIFIC CONDITION, e.g., arthritis, ligament injury, or general wear-and-tear]. Include modifications for [FITNESS LEVEL, e.g., beginners, athletes, or seniors] and explain the biomechanics of each exercise to ensure proper form and avoid further injury. Recommend the optimal frequency, duration, and progression for each exercise, as well as any complementary therapies (e.g., ice, heat, or stretching) that may enhance recovery. Highlight any warning signs to stop immediately and consult a medical professional.