When someone mentions posture, you probably immediately think of static posture. Static posture is the alignment of your body while you are still. More importantly, static posture refers to the length-tension relationships of your muscles and the corresponding alignment of your joints. You may first notice posture problems when you or someone else observes obvious issues with your static posture.
Dynamic posture is the alignment of your body during movement. The length-tension relationships between working and opposing muscles are especially important to dynamic posture. Poor dynamic posture can influence static posture and vice versa. Since many exercises are repetitive movements, it is important to keep your dynamic posture in mind.