Can the gender gap in leisure-time physical activity participation be closed by 2035? A system dynamics modelling study

Problem Statement
Despite global recognition of gender equity as a priority in physical activity promotion (e.g., via the Global Action Plan for Physical Activity), significant disparities persist, with women generally less active than men. While national strategies often embed gender objectives, the specific level of effort required to close these gaps remains uncertain. Traditional linear trend analyses are insufficient for predicting future trends because they fail to account for complex, non-linear system dynamics, saturation effects, and feedback loops inherent in behavioral change. This study addresses the uncertainty regarding whether the gender gap in leisure-time physical activity (LTPA) participation can be closed by 2035, specifically examining how these disparities evolve across different life stages.

Methodology
The authors developed a system dynamics simulation model using historical data (2004–2019) from New South Wales (NSW), Australia, as a case study. The model structure divides the adult population (18+ years) into compartments based on gender (men, women) and three age groups (young: 18–29; middle-aged: 30–64; older: 65+).

• System Structure: The model utilizes a stock-and-flow framework where "stocks" represent population segments at three LTPA levels (least active: 0–59 mins/week; low active: 60–149 mins/week; active: 150+ mins/week). "Flows" represent transition rates between these levels (progression to higher activity and reversion to lower activity).
• Population Dynamics: The model incorporates population aging chains, immigration, inflows of children turning 18, and mortality rates, ensuring the simulation reflects demographic shifts alongside behavioral changes.
• Parameterization: Transition probabilities were calibrated using NSW Population Health Survey data (2004–2019), excluding years with questionnaire changes (2006, 2012) and the pandemic period (post-2019) to establish a "Business-as-Usual" (BAU) trajectory.
• Scenario Analysis: Five hypothetical intervention scenarios were simulated starting in 2026 and running through 2035. In these scenarios, the probability of women transitioning to a higher LTPA level was increased relative to the BAU by 1%, 5%, 10%, 15%, and 20%. Men's probabilities and women's reversion probabilities remained constant at BAU levels.
• Validation: The model was validated against historical data using goodness-of-fit measures (MAPE, MSE, RMSE) and sensitivity analyses (varying probabilities by ±10%).

Key Results
The model successfully replicated historical LTPA trajectories from 2004 to 2019. Projections to 2035 reveal distinct patterns across age groups:

• Young Adults (18–29): Under the BAU scenario, the gender gap is projected to close and reverse, with 84% of women and 79% of men expected to be active by 2035.
• Middle-Aged Adults (30–64): A persistent gap is projected. Under BAU, 61% of women and 65% of men are expected to be active. Even in the most optimistic scenario (20% relative increase in women's progression probabilities), the gap narrows to 0.8 percentage points but does not fully close by 2035.
• Older Adults (65+): The gap remains moderate and persistent. Under BAU, 46% of women and 52% of men are expected to be active. Even with a 20% relative increase in women's progression probabilities, a gap of 1.8 percentage points remains in 2035.
• Long-term Projections: Extended analysis to 2050 suggests that under the most optimistic scenario, the gap for older adults might close by 2045, but not by 2035.

Key Contributions

• System Dynamics Approach: The study moves beyond linear trend analysis to model the complex, dynamic interactions between demographic shifts (aging, migration) and behavioral transitions in physical activity.
• Life-Course Disaggregation: By stratifying data by age and gender, the study highlights that the gender gap is not uniform; it is closing among young women but remains stubbornly persistent among middle-aged and older populations.
• Policy Benchmarking: The simulation provides evidence-based benchmarks, demonstrating that incremental improvements (e.g., 1–5% increases) are insufficient to achieve equity by 2035, and even highly optimistic interventions (20% relative increase) fall short for older cohorts within the decade.

Significance and Claims
The paper claims that achieving gender equity in LTPA participation by 2035 is unlikely for middle-aged and older adults in NSW, even under progressive policy scenarios that significantly boost women's progression probabilities. The authors argue that current policies are insufficient and that the persistence of these gaps is likely driven by systemic barriers—such as caregiving responsibilities, work demands, and health status in later life—rather than individual preferences alone.

The study concludes that closing the gender gap requires "urgent, targeted systemic actions" that specifically enable women to participate actively, particularly in midlife and older age. The authors position their work as a tool for informing evidence-based policy targets, emphasizing that without addressing the underlying system-level drivers, global health goals regarding physical activity and gender equity will remain unmet.