Static and proprioceptive neuromuscular facilitation (PNF) stretching tend to provide greater flexibility than dynamic stretching. Flexibility training adaptations can persist for 3–8 weeks with either reduced (once a week) or minimal stretching and activity. This persistent flexibility adaptations may be partially ascribed to neural adaptations such as an intrinsic disfacilitation of spindle afferent discharge. There is evidence, with human flexibility training, for alterations in muscle pennation angles, viscoelastic properties, and stretch tolerance.