How to Create Variables that Classify the Intensity of Each Minute in the Physical Activity Monitor Data

Once you have defined minutes of wear and non-wear, you can classify the intensity count for each minute as sedentary, light intensity, lifestyle moderate intensity, locomotor moderate intensity, or vigorous according to pre-defined criteria. (For more information see Troiano et al., Physical Activity in the United States Measured by Accelerometer1). For locomotor moderate and vigorous intensity, the criteria are age specific for ages 6 to 18 years. Lifestyle moderate intensity is defined only for adults. The criteria can be modified as desired by analysts by changing the values of variables in the following segment of SAS code for:

  • sedthresh (sedentary threshold)
  • lightthresh (light threshold)
  • lifethresh (lifestyle moderate threshold)
  • modthresh (moderate threshold)
  • vigthresh (vigorous threshold).

 

Sample Code

Recall: ridageyr = age in years

* sedentary threshold *;
  sedthresh=0 ;

* light threshold * ;
  lightthresh = 100 ;

* lifestyle moderate threshold is only defined for adults   ;
  if (ridageyr >= 18 ) then lifethresh = 760 ;
  else lifethresh=modthresh;

* moderate threshold *;
  if       ridageyr= 6   then modthresh= 1400 ;
  else if ridageyr= 7   then modthresh= 1515 ;
  else if ridageyr= 8   then modthresh= 1638 ;
  else if ridageyr= 9   then modthresh= 1770 ;
  else if ridageyr= 10 then modthresh= 1910 ;
  else if ridageyr= 11 then modthresh= 2059 ;
  else if ridageyr= 12 then modthresh= 2220 ;
  else if ridageyr= 13 then modthresh= 2393 ;
  else if ridageyr= 14 then modthresh= 2580 ;
  else if ridageyr= 15 then modthresh= 2781 ;
  else if ridageyr= 16 then modthresh= 3000 ;
  else if ridageyr= 17 then modthresh= 3239 ;
  else if ridageyr>= 18 then modthresh= 2020 ;

  * vigorous threshold *;
  if       ridageyr= 6   then vigthresh= 3758 ;
  else if ridageyr= 7   then vigthresh= 3947 ;
  else if ridageyr= 8   then vigthresh= 4147 ;
  else if ridageyr= 9   then vigthresh= 4360 ;
  else if ridageyr= 10 then vigthresh= 4588 ;
  else if ridageyr= 11 then vigthresh= 4832 ;
  else if ridageyr= 12 then vigthresh= 5094 ;
  else if ridageyr= 13 then vigthresh= 5375 ;
  else if ridageyr= 14 then vigthresh= 5679 ;
  else if ridageyr= 15 then vigthresh= 6007 ;
  else if ridageyr= 16 then vigthresh= 6363 ;
  else if ridageyr= 17 then vigthresh= 6751 ;
  else if ridageyr>= 18 then vigthresh= 5999 ;

References

  • Troiano R et al. Physical Activity in the United States Measured by Accelerometer. Med Sci Sports Exerc. 2008 Jan;40(1):181-8.

 

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