Yes, horse riding can have an effect on your knees. When you are riding, the bouncing motion of the horse's gait can cause pressure on your joints and muscles in your lower body - including your knees. Additionally, if you do not use proper posture while riding or do not use a correctly fitted saddle, this can also strain your knee joints. Taking lessons from an experienced instructor to ensure you are using proper technique is essential to help prevent any long-term effects. To further protect yourself when riding, wear protective legwear such as padded breeches and leg wraps which provide additional cushioning for the knee area.