# Toward a Symbolic AI Approach to the WHO/ACSM Physical Activity & Sedentary Behavior Guidelines
## 2 Materials and Methods
### Symbolic AI Approach: From Analysis to Design
#### 2.3.4 Conceptualization and Formalization
\\ \hline Adults should do at least 150–300 min of moderate-intensity aerobic physical activity; or at least 75–150 min of vigorous-intensity aerobic physical activity; or an equivalent combination of moderate- and vigorous-intensity activity  
throughout the week, for substantial health benefits. \\ \hline \hline
**Older adults (aged 65 years and older)** \\ \hline Older adults should do at least 150—300 min of moderate-intensity aerobic  
physical activity; or at least 75–150 min of vigorous-intensity aerobic  
physical activity; or an equivalent combination of moderate- and vigorous intensity  
activity throughout the week, for substantial health benefits. \\ \hline Older adults may increase moderate intensity aerobic physical activity to  
more than 300 min; or do more than 150 min of vigorous-intensity  
aerobic physical activity; or an equivalent combination of moderate- and vigorous  
intensity activity throughout the week, for additional health benefits. \\ \hline To help reduce the detrimental effects of high levels of sedentary behavior on health,  
older adults should aim to do more than the recommended levels of moderate to  
vigorous-intensity physical activity. \\ \hline \hline
**Pregnant and postpartum women** \\ \hline All pregnant and postpartum women without contraindication should do at least 150 min  
of moderate-intensity aerobic physical activity throughout the week for  
substantial health benefits. \\ \hline All pregnant and postpartum women without contraindication should incorporate  
a variety of aerobic and muscle-strengthening activities. Adding gentle stretching  
may also be beneficial  
Pregnant and postpartum women should limit the amount of time spent being  
sedentary. Replacing sedentary time with physical activity of any intensity  
(including light intensity) provides health benefits. \\ \hline \hline
**Peak to compute the intensity of a physical activity:** The intensity of a physical activity is related to how hard our body works while doing a specific physical activity [51]. There are four levels of the physical activity intensity: _High, Vigorous, Moderate_, and _Sedentary_ and they are measured and estimated by one of the variables: Heart rate reserve (\(HRR\)), rate reserve max (\(HR_{max}\)), metabolic equivalents (\(MET\)), maximal oxygen consumption (\(VO_{2 max}\)), and steps count. In Table 3, we present the different rules to estimate the physical activity intensity. The WHO and ACSM guidelines are structured for four main categories of users: (i) children and adolescents (aged 5-17 yeas old); (ii) adults (aged 18-64); (iii) older adults (aged 64 years and older), and (iv) pregnant women. HeLiFit-Rule implements 137 rules to cover all the above users. In the paper, we describe a few of them and leave the rest in the Appendix A. Figure 8 below models the case of a physical activity with low intensity that is classified as Sedentary. 3. **Rule to issue WHO/ACSM recommendations**: Rules are triggered according to the user's age, the frequency, the modality, the duration (typically a week), and the intensity of the physical activity. While frequency, modality, and duration are given explicitly, intensity needs to be calculated. Once we have computed the intensity of all the physical activities that a user has performed over a specific time window, using the above rule, we aggregate them and, based on the results, one or more recommendations are triggered. As an example, we show the rule that codifies the following WHO guideline: **WHO Recommendation**: _Adults(18-64 years) should also do muscle-strengthening activities at moderate or greater intensity that involve all major muscle groups on 2 or more days a week, as these provide additional health benefits._ The user, assumed to be between 18 and 65 years, will get this recommendation in two cases:  
Figure 8: Rule to classify the user as sedentary.