Abstract: Few studies have differentiated the effects of total physical activity volume vs. physical activity frequency on health. Therefore, the purpose of this study was to examine whether daily frequency of moderate-to-vigorous physical activity (MVPA) throughout the week or overall weekly accumulation of MVPA is a greater predictor of systemic inflammation. Data from the 2003–2006 NHANES were used, which included 2330 adults (≥ 20 years). Participants wore an accelerometer for 7 days to assess physical activity, with C-reactive protein (CRP) measured from a blood sample. Only participants with 7 valid (10+ hours/day of monitoring) days of monitoring were included. Two physical activity variables were created: 1) total weekly accumulation of MVPA, and 2) the number of days per week participants engaged in ≥ 30 min/day of MVPA. After adjusting for age, gender, race–ethnicity, poverty level, comorbid illness, body mass index, sedentary behavior, and smoking status, participants engaging in more days of ≥ 30 min/day of MVPA had lower log-transformed CRP levels (β = − 0.01, P < .001), and in a separate multivariate model, total weekly MVPA volume (β = − 0.005, P = .002) was also inversely associated with log-transformed CRP levels. However, when both MVPA frequency and total weekly volume were entered into the model at the same time, MVPA frequency remained significant (β = − 0.01, P = .04), but total weekly MVPA volume was no longer significant (β = − 0.001, P = .82). In conclusion, MVPA frequency, compared to total weekly MVPA accumulation, is a stronger predictor of CRP among the U.S. adults. Clinicians are encouraged to advise their patients to engage in consistent physical activity throughout the week.
Alex’s Notes: The ACSM and CDC recommend that adults engage in at least 150 minutes of moderate-to-vigorous physical activity (MVPA) per week, but it is not entirely clear how this time should be distributed for health. Clearly there is a difference between engaging in 75 minutes twice per week compared to 30 minutes five days per week. As a result, the purpose of this study was to examine whether daily frequency of MVPA or weekly accumulation of MVPA was a stronger predictor of systemic inflammation [determined by C-reactive protein (CRP)] among the U.S. adults.
Data for 2,330 adults from the 2003-2006 NHANES survey was used for analysis. There are many more people in the NHANES dataset, but inclusion criteria restricted participants to those over 20 years of age who wore an accelerometer for at least 10 hours per day for seven consecutive days. All outcomes controlled for age, gender, race, ethnicity, poverty-to-income ratio (PIR), comorbid illness, BMI, sedentary behavior, and smoking status.
The average MVPA per day ranged from 21.8 to 24.1 minutes depending on the day of the week, with a levels being stable throughout the work week and showing a small decline on the weekends. On average, participants engaged in at least 30 min/day of MVPA for 2 of the 7 monitoring days. And indeed there was a clear inverse association between CRP concentrations and the number of days engaged in ≥30 min/day of MVPA. However, there was also an inverse association between total weekly MVPA and CRP. Thus, both variables were entered into a statistical equation with CRP, and together the significant inverse association remained only for CRP and frequency of MVPA.
Although there was an even split of men and women, the participants, on average, were 51.5 years of age and predominately non-Hispanic white (80.2%). Despite this limitation for generalizability, it appears that for reducing inflammation, it is better to be active consistently than to be active for longer less frequently. This pairs nicely with another study that found regularly active men (≥1000 kcal of per week on 3 or more days) had a 36% reduced risk of premature mortality, compared to only a 15% reduced risk for weekend warriors (≥1000 kcal of MVPA per week on 1 or 2 days). Hopefully future studies will add to this research by examining other inflammatory biomarkers such as TNF-α and the interleukins.