Cerebral Palsy (CP) is the most frequent cause of motor disability in children and adolescents, characterized by non-progressive disturbances in the developing fetal or infant brain that result in limitations in movement and posture (Begum et al., 2019). To standardize the assessment of these functional limitations, the Gross Motor Function Classification System (GMFCS) is utilized globally to categorize children into five levels, where Level I represents the highest functional independence and Level V represents total dependence for mobility and transfers. 1,2,3 While the neurological injury in CP is static, the lived experience of the caregiver is highly dynamic. Recent systematic reviews have established that parents of children with CP experience significantly higher rates of stress, burden, and burnout compared to parents of typically developing children (Testani et al., 2024). Furthermore, this parental stress has been shown to have a direct negative influence on the behavioral, physical, and occupational outcomes of the children themselves, creating a bidirectional cycle of distress (Testani et al., 2024).Previous studies have established a significant association between a child’s physical functional limitations and the resulting level of parenting stress, highlighting the physical toll of caregiving. 4 The Research Gap: The Growth Factor Despite the wealth of associational data, current literature frequently overlooks three critical factors: 1. The Growth Factor: While a child’s GMFCS level may remain stable over time, their physical mass increases. A GMFCS Level V child at age 4 is physically easier to manage than a GMFCS Level V child at age 14. This "load-capacity divergence" is rarely measured longitudinally. 2. Recall Bias: Traditional Caregiver Strain Index (CSI) scales rely on retrospective memory, which is subject to bias. 3. The Resilience Factor: There is a lack of data on "Positive Outliers"—caregivers who maintain low stress levels despite high physical demands (GMFCS IV-V). Objectives The purpose of this study was to: • Determine if the correlation between GMFCS level and caregiver strain strengthens as a function of the child’s height and weight (The Physica Load Factor). • Identify the "Crossing Point"—the specific developmental age where physical strain (CSI items 1– 3) begins to outweigh emotional strain (CSI items 8–10). • Assess the impact of "environmental accessibility" as a moderator between child GMFCS level and caregiver strain.

Study Design This study employed a 6-month longitudinal mixed-methods design utilizing Ecological Momentary Assessment (EMA) and objective physical metrics. Subjects • Sample Size: 50 caregiver-child dyads. • Recruitment: Participants were recruited from pediatric rehabilitation units. • Inclusion Criteria: Children aged 6 to 16 years (to capture pre-pubescent and adolescent growth spurts) with a confirmed diagnosis of CP. • Stratification: The sample was divided into three cohorts based on functional mobility: Group 1 (GMFCS I-II), Group 2 (GMFCS III), and Group 3 (GMFCS IV-V). Data Collection Tools 1. GMFCS-E&R: The Expanded and Revised version of the Gross Motor Function Classification System will be used to establish the functional baseline (Begum et al., 2019). 2. Modified Caregiver Strain Index (MCSI): Administered every 3 months to track longitudinal trends. 3. Ecological Momentary Assessment (EMA): A researcher will "ping “caregivers three times daily for one week every 3months asking three 1–10 scale questions to capture real-time "momentary" strain and fatigue. 4. Wearable Technology: Caregivers will utilize fitness trackers to objectively measure Sleep Quality (CSI Item 1) and Steps/Physical Activity (CSI Item 3). 5. The "Weight-to-Caregiver-Strength" Ratio: A novel clinical variable. Researchers will measure the child’s weight against the caregiver’ objective grip strength. Data Analysis The study moves beyond simple Pearson correlations, utilizing Multi-Level Modeling (MLM) to analyze: • The Velocity of Strain: Calculating the rate of increase in CSI scores relative to the child's growth. • The Mismatch Index: Identifying "Resilient Caregivers" (High GMFCS Load, Low CSI Score) for qualitative interviews to determine successful protective strategies.

A hierarchical multiple regression was conducted to determine if the relationship between GMF and MSCI is moderated by WT. In Step 1, the main effects of GMF and WT accounted for 91.5% of the variance in MSCI,F(2, 47) = 251.72, p < .001. In Step 2, the interaction term (GMF_CEN *WT_CEN)was added, explaining a significant additional 1.2% of the variance, this shows that GMF has a stronger impact on MSCI when WT is low, and its impact diminishes (the slope flattens) as WT_STR ratio increases .Delta R^2 = .012, F(1, 46) = 7.50, p = .009. The significant negative interaction (B = -2.08, \beta = -.14, p = .009) indicates that the effect of GMF on MSCI is moderated by WT_STR ratio. Table 1: Multiple Regression Analysis Model Summary Model R R Square Adjusted R Square Std. Error of the Estimate Change Statistics R Square Change F Change df1 1 2 956 963 915 927 911. 922 2.78319 2.60854 915.012 251.719 7.504 2 1 Model Change Statistics df2 Sig. F Change 1 47a .000 2 46b .009 Table 2: Coefficients Model Unstandardized Coefficients Standardized Coefficients t Sig. B Std. Error Beta 1 2 (Constant) GMF_CEN WT_CEN (Constant) GMF_CEN WT_CEN GMF_CEN *WT_CEN 21.458 .586 36.617 .000 601 .767 .086 .784 .437 20.830 23.416 2.217 901 1.035 9.394 25.984 .000 .000 2.156 916 310 2.353 023 24.852 2.545 1.235 9.766 .000 2.082 760 140 2.739 .009

The results of this study provide empirical support for the "Load-Capacity Divergence" hypothesis, demonstrating that caregiver strain is not merely a product of a child's functional diagnosis (GMFCS level), but is significantly moderated by the physical "Growth Factor"—specifically the child’s weight relative to the caregiver’s physical strength (WT_STR ratio). The Moderation Effect: Weight vs. Function The most striking finding from the hierarchical regression is the significant interaction between centered GMFCS levels and the Weight-to-Strength ratio(B = -2.08, p = .009). The data reveals that when a child is young or light (LowWT_STR), the child's functional mobility (GMFCS) is the primary predictor of caregiver strain. In these cases, a caregiver of a child at GMFCS Level Iexperiences significantly less strain than one at Level V. However, as the child grows and their physical mass increases relative to the caregiver's capacity (High WT_STR), the "slope flattens." This indicates a ceiling effect of physical labor: when a child becomes sufficiently heavy, the sheer physical demand of transfers, bathing, and positioning causes high levels of strain regardless of whether the child has some residual mobility or is totally dependent. Essentially, the "Growth Factor" acts as a great equalizer of burden; the physical "load" eventually begins to outweigh the clinical "level." As the physical load increases, caregivers often experience a decline in health-related quality of life and increased feelings of caregiving incompetence, which further fuels the bidirectional cycle of distress 5 Ecological Momentary Assessment (EMAI) vs. Longitudinal Strain (MSCI) The inclusion of the Ecological Momentary Assessment Index (EMAI) provided a real-time window into the "Velocity of Strain" that traditional retrospective scales (like the MSCI) often miss. There is a strong tracking between the longitudinal MSCI and the real-time EMAI. Momentary Fatigue: While the MSCI captures the general "atmosphere" of stress, the EMAI captured the "weather"—the acute spikes in fatigue. The EMA data suggests that caregivers in the High WT_STR group spend more time in a state of"momentary exhaustion," which likely contributes to the higher longitudinal burnout rates reported in literature 1 The data also highlighted "Positive Outliers." For instance, one caregiver of a GMFCS Level V child reported an MSCI of only 14 and an EMAI of 4.2, despite the child’s high GMFCS level. This "Mismatch Index"identifies resilient caregivers who may be utilizing adaptive equipment to bridge the Load-Capacity gap. This validates the study’s objective to move beyond simple correlations and identify successful protective strategies. Limitations • Our sample size was small; a larger sample size may be instrumental in providing greater insights • Our study was only for six months; longer duration studies may provide more actionable results. • Our Study was not matched for caregiver age and gender.

This study successfully validates that caregiver strain in Cerebral Palsy is a moving target. While GMFCS levels are static neurological markers, the caregiver’s lived experience is dictated by the widening divergence between the child's increasing physical mass and the caregiver’s finite physical strength.

1. Testani DA, Hatherly K, Csercsics A, Pajak S, Brunton L.Caregiver stress and impact on children with cerebral palsy: a systematic review [Preprint]. Authorea; 2024. 2. Begum MR, Hossain MA, Sultana S. Gross Motor Function Classification System (GMFCS) for children with cerebral palsy. Int J Physiother Res. 2019;7(6):3281-86. 3. Palisano R, Rosenbaum P, Walter S, Russell D, Wood E, Galuppi B. Development 4. and reliability of a system to classify gross motor function in children 5. with cerebral palsy. Dev Med Child Neurol. 1997;39(4):214-23. 6. Park MS, Chung CY, Lee KM, Sung KH, Choi IH, Kim TW. Parenting stress in 7. parents of children with cerebral palsy and its association with physical 8. function. J Pediatr Orthop B. 2012;21(5):452-6. 9. Wang HY, Jong YJ. Parental stress and related factors in parents of children 10. with cerebral palsy. Kaohsiung J Med Sci. 2004;20(7):334-40.