The present study assessed longitudinal changes in levels of PA and ST among 30 women undergoing RYGB and 40 appurtenant children from three months before through nine and 48 months after maternal surgery. Findings show that women undergoing RYGB do not change levels of PA or ST noteworthy, whereas appurtenant children significantly reduce levels of PA and increase ST from three months before to 48 months after maternal surgery. In addition, there is a trend towards progressively decreased levels of PA and increased ST in children from nine to 48 months after maternal RYGB. Furthermore, the prevalence of women undergoing RYGB meeting the PA guidelines is low three months before and nine and 48 months after maternal surgery, while 60% of appurtenant children met the PA guidelines before maternal RYGB and that number dropped to 35% after 48 months.
The present study presents, to our knowledge, the lengthiest follow-up time with objectively accelerometer measured PA and ST in women undergoing RYGB and appurtenant children. To date, objectively measured PA data is available up to three years after bariatric surgery . However, those data on PA relies on indirect measures of MVPA and ST derived from pedometers measuring step counts in one minute bouts. Research has shown poor correlation between pedometer and accelerometer assessed PA in a free-living condition in obese women . Hence, comparability between the present study and previous research with a two-year follow-up is somewhat limited. Previous research with one-year follow-up indicates that self-reported PA increases and time spent sedentary decreases among all family members when an adult family member undergoes bariatric surgery . Contrary, objectively measured PA and ST in women undergoing RYGB do not increase substantially, with a reduction in children’s levels of MVPA (−11 min/day) and increases in ST (+ 53.7 min/day) nine months after maternal surgery . This discrepancy between self-reported and objectively measured PA has previously been shown in individuals undergoing bariatric surgery, who report a greater disagreement between self-reported and objectively measured PA after compared with before surgery [22, 23].
One plausible explanation for the gradual decrease in PA and increase in ST among children, after maternal RYGB, may be attributed to the observed age dependent decrease in objectively measured PA, starting at five-years of age with a gradual decrease throughout childhood and adolescence .
Compared with previous studies assessing PA and ST in individuals undergoing bariatric surgery in the US, women in the present study spent more time in MVPA and less time sedentary both before and after surgery [14, 20]. Study population dissimilarities may account for these observed differences in levels of activity. For example, objective measures have shown that Swedish females on average engage in higher levels of MVPA compared with US females .
Twenty to 33% of women undergoing RYGB, in the present study, reached the recommended levels of PA  at all three measure points, whereas, more than half of the women accumulated more than 150 min of MVPA per week, at all three measure points, when total MVPA minutes, independent of bout length, were analyzed. However, the American College of Sports Medicine propose that at least 250 min of MVPA per week is required to prevent weight regain after substantial weight loss . Twelve percent of women in the present study reach these levels of PA, at all three measure points. In addition, researchers have proposed that objectively assessed MVPA, reporting the sum of accumulated moderate to vigorous intensity PA as the primary feedback, needs to be five- to seven-fold greater than the 150 min per week target . Only one woman in the present study, at all three measure points, reach these levels of PA when using this cut-off with at least 750 min of MVPA per week. The number of women meeting the recommended levels of PA, when analyzed as MVPA in 10 min bouts, increased somewhat from three months before to nine and then 48 months after RYGB. Conversely, total MVPA per week, independent of bout length, decreased progressively from three months before through nine and 48 months after RYGB. This may indicate that women to some extent engage in more structured PA, such as different forms of exercise, and less daily life MVPA, which has been show to decrease globally .
Major strengths of the present study lie in the longitudinal study design with three measure points over four years in both women undergoing RYGB and appurtenant children, and the objective measurements of PA, ST and anthropometrics that, by study design, enables control of effects that are constant (e.g. genetics) from before to after surgery. Anthropometrics, PA and ST were measured with standardized techniques and the same instruments at all three measure points. The Vm axis of the tri-axial accelerometer Actigraph GT3X+ used to measure levels of activity has been shown to accurately assess PA and ST in adults [11, 15] and children . Moreover, both the accelerometer wear-time and data processing protocols followed best practice . Although the accelerometer is unable to measure what types of activities are performed (e.g. bicycling and weight lifting), data has shown that activities are performed with similar occurrences before and after bariatric surgery .
Several limitations should be considered when interpreting the results. First, dissimilarities in hospital routines in identifying potential study participants made it impossible to gather information on individuals who declined to participate in the study. Second, participants were recruited from five hospitals with slightly different PA advices before and after surgery. Third, accelerometers may not fully capture all types movements, such as weight baring activities, thus, not provide an accurate assessment of total daily PA performed during free-living conditions . Fourth, data on cut-offs developed using tri-axial Vm axis accelerometer data is sparse [11, 15]. Furthermore, accelerometer output from the Vm axis is not directly comparable with the more commonly used Vt axis from uni-axial accelerometers . Hence, results from the present study assessing tri-axial Vm accelerometer data cannot be directly compared with data from older uni-axial accelerometers. Fifth, lack of statistical power due to few observations and large variation on several outcome variables makes the results sensitive to outliers. There is great individual variability in longitudinal changes of PA and ST among women undergoing RYGB and appurtenant children through three months before to nine and 48 months after maternal surgery. Thus, results from the present study on mean average differences in PA and ST across all three measure points should be interpreted with caution. Sixth, the present study did not have a control group, therefore the presented data is restricted to be descriptive. A control group would though have been hard to compare to since individuals with obesity that does not perform bariatric surgery and loose similar amounts of weight might differ substantially from our population. Seventh, the low prevalence of type 2 diabetes in our sample implies a healthier population compared to the typical RYGB patient. Last, the sample size in the present study is small; however, studies with similar design have used comparable or even smaller study populations and shorter follow-up time [9, 22].