The impact of seasonality on changes in body weight and physical activity in Mexican-American women.

This 12-month, longitudinal panel study examined seasonal variability in body weight and physical activity in Mexican-American women. Fifty-nine women (20 to 63 years of age) were measured five times at intervals of three months between March 2010 and March 2011. Complete data were collected for all measures at all times on 36 women. Repeated measures multivariate analysis of variance with follow-up univariate repeated measures analysis of variance revealed that body weight increased on average by 1.36 kg (p < .01), with the greatest increase occurring during the fall (+0.80 kg). Changes in vigorous-intensity aerobic activity were statistically significant, with the greatest increase occurring in the spring (+51.99 min/week) and the greatest decline occurring in the fall (-30.11 min/week). Significant changes were observed in muscle-strengthening activity during the summer (-32.38 min/week). Moderate-intensity aerobic activity remained relatively stable. The decline in muscle-strengthening activity during the summer and subsequent decline in vigorous-intensity aerobic activity in the fall likely led to the observed increase in body weight during the fall. Thus, weight management interventions should consider the time of year when Mexican-American women's physical activity declines and include strategies specifically designed to prevent weight gain during the fall season.