Abstract This study assessed how mechanical forces, altered by postnatal Sciatic Nerve Resection (SNR), impact the structural and material development of energy-storing tendons (Achilles) versus positional tendons (Plantaris).

SNR was performed on the left hindlimb of Col1a1-CFP reporter mice on postnatal day 1 (P1) to unload the distal limb. Tendons were harvested, and properties were quantified using Fluorescent imaging (cross-sectional area/CSA, Col1a1 expression) and Scanning Electron Microscopy (SEM) (collagen fibril diameter). SNR limbs were compared to contralateral limbs over time. Reduced mechanical loading impaired overall tendon growth. Both Achilles and Plantaris tendons showed reduced collagen fibril diameters and decreased CSA compared to controls, indicating stunted development. Crucially, SNR demonstrated differential effects on the two tendon types. The Achilles tendon (energy-storing) displayed greater CSA reductions and a significant reduction in Col1a1 expression (collagen synthesis) over time, indicating a greater dependence on mechanical loading. In contrast, the Plantaris tendon (positional) showed no detectable change in Col1a1 expression and exhibited more minor, more variable CFP changes.