Viewing, Reporting and Exporting Data
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      Data Guide: Prevent iMG

      To download a PDF version of this Data Guide, please see here.

      What does the Prevent iMG measure?


      The Prevent iMG measures Head Acceleration Events (HAEs). A HAE is a six degree-of-freedom (6DOF) skull kinematic motion caused by direct head impact or inertial accelerations (running, jumping, shoulder-to-shoulder, etc.)


      When the iMG is (a) on-teeth and (b) exceeds the linear acceleration trigger value, a Head Acceleration Event will be recorded (see graph below left).


      The Prevent iMG then computes six degree-of-freedom kinematics, whether triggered by inertial motion or direct head contact. 

      Note: The Prevent iMG measures Head Acceleration Events, not contacts or collisions. In some situations, the iMG will measure multiple HAEs due to a single collision, because the acceleration trigger threshold is exceeded more than once. For example, in rugby union, the initial tackle contact, a second tackler, and then hitting the floor, may trigger three separate HAEs. 


      What metrics are available?


      The following metrics are available from the Prevent iMG.

      Peak Linear Acceleration (PLA, g): Maximum of the vector resultant of the linear acceleration time trace @ head center of gravity (CG). 

      Peak Angular Acceleration (PAA, rad/s2): Maximum of the vector resultant of the angular acceleration time trace. Computed as the derivative of the directly measured angular velocity.

      Peak Linear Velocity (PLV, m/s): Maximum of the vector resultant of the linear velocity time trace @ head CG. Computed as the integral of the linear acceleration.

      Peak Angular Velocity (PAV, rad/s): Maximum of the vector resultant of the angular velocity time trace. Directly measured.

      Direction/Location: Visual representation of the estimated applied force vector and application point on the skull during the instant PLA is computed.

      Work (J): Estimated sum of kinetic energy transfer due to linear and rotational motion, as a result of the HAE. 

      Workload (J): Cumulative Work from multiple HAEa. Computed as sum of individual Work estimates for each HAE.

      Time on Teeth: Summation of time, down to the second, that the iMG is recorded on the teeth

      For further guidance on how to view, report, and export data, please see here.


      Inertial vs Direct Contact HAEs:


      When worn on-teeth, and the linear acceleration trigger value is exceeded, the Prevent iMG will record Head Acceleration Events generated by inertial movement and/or direct contact to the head. 

      Inertial HAE:

      • Example: running, jumping, changing direction, body-to-body collision
      • Typically < 10g Peak Linear Acceleration and < 2J Work
      • Time-trace signal with steady-state response and less clearly defined peak value
      • If inertial movements accelerate the head less than the trigger threshold, the iMG will not record a HAE

      Direct Contact:

      • Example: direct contact to the head during a collision
      • Typically > 10g Peak Linear Acceleration and > 2J Work. Glancing contacts can generate HAE < 10g
      • Usually has a well-defined peak value in the time-trace signal, with haversine pulse shape



      Understanding Work and Workload:


      Work (J):       The summation of the head's estimated linear and rotational kinetic energy change due to a Head Acceleration Event. Quantified in Joules.

      Workload (J): The summation of Work for each Head Acceleration Event.


      Work can be analysed for a single HAE, and Workload can be analysed for an entire day, week, month, or season of HAEs. 

      The analysis of Work and Workload metrics is emerging as useful metrics to help performance staff longitudinally monitor the training and match head impact load for athletes.

      Work can also help to provide additional insight into the head impact characteristics beyond PLA alone. This is especially true when contrasting situations where the contacting surfaces are rigid versus softer. 

      HAEs with similar PLA can vary in Work depending on the type of direct contact (see graphs below). HAEs with higher Work occur when the head impacts objects of sizeable and softer mass (e.g., ground, shoulder, hip, thigh), resulting in a longer impact pulse duration [Head to Thigh, Tackle]. HAEs with lower Work often occur due to glancing or rigid contacts, resulting in a shorter pulse duration [Head to Elbow, Tackle]