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Frequency of strengthening activity: Number of units


STRONGFNO is a 4-digit-numeric variable.

995: Extreme value (2020-forward)
996: Unable to do this activity
9996: NIU
9997: Unknown-refused
9998: Unknown-not ascertained
9999: Unknown-don't know


STRONGFNO reports the frequency, in number of units, with which sample adults engaged in strengthening leisure-time physical activities. It must be interpreted in conjunction with the variable STRONGFTP, which reports the time period (e.g., per day, week, month, or year) corresponding to the number of units in STRONGFNO. For example, a respondent who lifts weights once a day would have a STRONGFNO value of 1 (to indicate 1 time) and a STRONGFTP value of 2 (which is the code for "day").

STRONGFWK, a recoded variable created by the staff at the National Center for Health Statistics, draws upon the information in STRONGFTP and STRONGFNO and reports the frequency of strengthening leisure-time physical activities in terms of a single time unit, times per week.


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 Manual provides 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.

Data Collection 

According to the Field Representative's Manuals for 2001-2018, the maximum frequency of each broad category of physical activity (moderate activity, vigorous activity, strengthening activities, and stretching activities) was topcoded at 4 times per day (or its equivalent in some other time unit) or higher. Beginning in 2020, individuals with values of 4 times per day (or its equivalent) or higher were coded as "995 - Extreme value."

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 further discussion of data collection on leisure-time physical activity in general for 1997 forward, see VIG10FNO (Frequency of vigorous activity 10+ minutes: Number of units).


The question wording for STRONGFNO changed slightly in 2004.


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.

A second minor change to the survey question was instituted in 1999, when the form added the following instruction to interviewers: "If necessary, prompt with: How many times per day, per week, per month, or per year do you do these activities?" This prompt gave explicit directions to interviewers on how to proceed if respondents gave a vague answer such as "quite often," "once in a while," or "hardly ever."


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?'"

Finally, major questionnaire changes introduced in 2019 may affect comparability with earlier years. The NHIS questionnaire was substantially redesigned in 2019 to introduce a different data collection structure and new content. For more information on changes in terminology, universes, and data collection methods beginning in 2019, please see the user note.


  • 1997-2013; 2014 2015 2016 2017 2018: Sample adults age 18+.
  • 2020: Sample adults age 18+.


  • 1997-2018, 2020