Abstract: Notifications for instructing user behavior can be determined and presented when appropriate. Current fitness data are accessed. This data is used to determine whether a user fitness goal is likely to be achieved. If not, a notification may be determined and presented at a user device.

Abstract: A portable oxygen concentrator system weighing 4-20 pounds that is adapted to be readily transported by a user and deliver oxygen to the user includes a rechargeable energy source; a concentrator powered by said energy source and adapted to convert ambient air into concentrated oxygen gas for the user; an inspiration sensor that senses respiratory activity of the user, and produces a signal in response thereto; and a control unit that receives the signal in response to sensed respiratory activity, determines a breath rate based in part on the received signal in response to sensed respiratory activity and controls the portable oxygen concentrator system to deliver oxygen flow sufficient to meet oxygen demand of the user based at least in part on the determined breath rate.