System determines impact of a helmet, comprising: accelerometer and processor, the accelerometer detecting acceleration of the helmet, the processor configured to process the signals from the accelerometer to determine impact of the helmet. System determines athletic performance, comprising: pressure sensor for sensing change in elevation; microprocessor for processing signals from the pressure sensor to determine vertical speed corresponding to the change in elevation; and display for reporting the vertical speed to a user. System assesses athletic performance, comprising: protective housing configured for attachment to a human-powered sport vehicle; GPS sensor configured with the housing for generating earth position signals; microprocessor configured with the housing for processing the signals to determine speed and distance traveled of the sport vehicle; and display configured with the housing for displaying one or both of the speed and distance traveled to a user of the human-powered sport vehicle.