Poses can range in length from several seconds to many hours. Short dynamic poses may be used for gesture drawing exercises, with the model striking a pose - which can include strenuous or precarious positions that could not be sustained for a longer pose - just long enough for the artist to quickly capture the essence of it. Active, gestural, or challenging standing poses are often scheduled at the beginning of a session when the models' energy level is highest. Short exercises in drawing classes typically run from 5 to 25 minutes. For extended poses in which the model will take one or more breaks, chalk marks and/or masking tape are often used to help the model resume the same pose. These breaks - during which the model usually wears a robe or puts on clothing - allow the model to stretch, relax and attend to other needs.