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. 2025 Mar 20:13:e19123.
doi: 10.7717/peerj.19123. eCollection 2025.

Quantitative MRI reveals infrapatellar fat pad changes after running a marathon

Xiang Bo Zhao #  1   2 , Haifeng Zhao #  1   2 , Wen Juan Du  1   2 , Hao Zhang  2   3
Affiliations

Quantitative MRI reveals infrapatellar fat pad changes after running a marathon

Xiang Bo Zhao et al. PeerJ. .

Abstract

Background: Marathon running, while offering health benefits, is associated with a high incidence of knee injuries. The infrapatellar fat pad (IFP) plays a critical role in knee joint homeostasis and injury mitigation. This study investigated IFP adaptations to the acute stress of marathon running using quantitative magnetic resonance imaging (MRI).

Methods: Fourteen amateur marathon runners (12 male, two female) were prospectively enrolled and underwent 3.0T MRI (GE SIGNA Architect) one week before and after the marathon. Left knee imaging included MAGiC and IDEAL-IQ sequences. MAGiC sequences provide T1, T2, and proton density (PD) maps. IDEAL-IQ sequences yield fat fraction (FF), representing the relative amount of fat within the IFP, and the transverse relaxation rate (R2*) within the IFP. IFP volume and maximum cross-sectional area were quantified. Two experienced radiologists independently analyzed the images using dedicated software. Inter-observer reliability for quantitative MRI measurements was assessed using intraclass correlation coefficients (ICCs). Paired t-tests were used to compare pre- and post-marathon measurements of T1, T2, FF, R2* values, IFP volume and maximum cross-sectional area. Pearson correlation analysis explored relationships between changes in IFP parameter changes and participant characteristics. P < 0.05 was considered statistically significant for all analyses.

Results: Post-marathon, IFP FF significantly increased (p < 0.05), while IFP volume significantly decreased (p < 0.05), T1 and T2 values showed a decreasing trend. IFP appeared morphologically compressed post-marathon. A significant negative correlation was found between FF change and both body weight and body mass index (BMI) (p < 0.05).

Conclusions: This study provides novel evidence of robust IFP adaptation to marathon running, characterized by increased FF and potential fluid shifts, suggesting enhanced cushioning and load dissipation. These findings highlight the importance of considering individual biomechanics in understanding IFP function and injury susceptibility. Future research should clarify the clinical implications of these adaptations for runner injury prevention and rehabilitation.

Keywords: Infrapatellar fat pad; MAGiC; Magnetic resonance imaging; Marathon running; Sports medicine.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. Three-dimensional visualization of the IFP.
3D reconstruction of the IFP, segmented from MRI data, illustrating its complex morphology and volume.
Figure 2
Figure 2. Schematic diagram illustrating the region of interest (ROI) delineation on PD-FS images.
(A) Before the marathon, the maximum cross-sectional area of the IFP was 538 mm2. (B) After the marathon, the maximum cross-sectional area of the IFP was 507 mm2.
Figure 3
Figure 3. Quantitative maps of the IFP metrics from a male runner before (A) and after (B) the marathon.
(A1, B1) PD-FS images; (A2, B2) T1 (pre: 457.50 ms, post: 451.76 ms); (A3, B3) T2 (pre: 48.21 ms, post: 44.42 ms); (A4, B4) PD (pre: 23.43, post: 22.34); (A5, B5) FF (pre: 80.12%, post: 80.88%); (A6, B6) R2* (pre: 59.62 Hz, post: 57.64 Hz). Post-marathon imaging reveals a slight decrease in T1 and T2 values, a increase in FF and a flatter shape than before the marathon.
See this image and copyright information in PMC

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