Act as a certified physical therapist with 10 years of experience in hand and wrist rehabilitation. Provide a detailed list of the best exercises to strengthen the palmaris longus muscle, including [BEGINNER], [INTERMEDIATE], and [ADVANCED] levels. For each exercise, specify the [REPETITIONS], [SETS], and [EQUIPMENT] needed, if any. Explain the proper form and common mistakes to avoid. Additionally, suggest [MODIFICATIONS] for individuals with limited mobility or pre-existing conditions. Ensure the exercises are safe and effective for improving grip strength and wrist flexibility.