 The complexity of gait arises from the need to adapt to expected and unexpected changes in the environment (e.g.  changes in walking surface or obstacles).
<fluency>  The complexity of gait arises from the need to adapt to expected and unexpected changes in the environment (e.g.  changes in walking surface or obstacles).
 The complexity of gait arises from the need to adapt to expected and unexpected changes in the environment (e.g. , changes in walking surface or obstacles).