Strengthening activities are described in the survey question itself as activities "specifically designed to strengthen your muscles such as lifting weights or doing calisthenics." The Field Representative's Manualprovides other examples of strengthening activities, although these examples were not routinely shared with respondents. These examples include "activities that require strenuous muscle contractions," such as resistance training, push-ups, and sit-ups.

Interviewers asked about the frequency of strengthening leisure-time physical activities after collecting information about vigorous and light or moderate leisure-time physical activities. They directed respondents to "include all such [strengthening] activities, even if you have mentioned them before." Strengthening activities could be done at either a "moderate" or a "vigorous" pace, and the time spent doing strengthening leisure-time activities was thus already incorporated in the duration variables for moderate and/or vigorous leisure-time physical activity. Accordingly, interviewers did not ask about the amount of time respondents spent doing strengthening activities.

For all years from 1997 forward, the survey section on physical activity began with the statement, "The next questions are about physical activities (exercise, sports, physically active hobbies ...) that you may do in your leisure time." Beginning in 2004, the question about the frequency of strengthening activities reiterated the point that respondents were only to report leisure-time activities. From 1997 through 2003, interviewers asked, "How often do you do physical activities specifically designed to strengthen your muscles ..."; for 2004 forward, they asked, "How often do you do leisure-time physical activities specifically designed to strengthen your muscles ..." Thus, beginning in 2004, the question wording made explicit what had previously been implicit and had been specified in the introductory statement only.

However, while these directions were missing from the survey questionnaire before 1999, they were included in the Field Representative's Manuals for 1997-2000, which directed, "Prompt with 'How many times per day, per week, per month, or per year do you do these activities?'" Furthermore, the 1997-2000 Manuals stated, "Always probe for an exact number. If the Sample Adult reports a range or interval, assist the Sample Adult in making an estimate by probing. For example, you might ask 'Could you give me a more exact number?'"