Habitual Loading Yields Patella Tendon Hypertrophy

Abstract

The average stress (force/area) of a tendon is determined by the tendon cross-sectional area (CSA) and tendon force. Thus, a larger CSA will reduce the stress and maybe protect against injury. However, if habitual loading results in tendon hypertrophy is unknown, and existing human data are based on cross-sectional designs or short term training studies. PURPOSE: To examine bilateral patella tendon CSA in subjects with an existing strength difference (≥ 20 %) due to long standing sports specific loading. METHODS: Six young male elite fencers & badminton players (22±5 yrs, 73±6 Kg, 1.79±0.05 m) with ≥ 20 % difference in side-side isometric knee extension strength (237 Nm vs. 191 Nm, p<0.05) were included. All were healthy and without knee pathology. Axial plane MR images along the patella tendon were obtained (T1- weighted), and the mean of 3 blinded CSA (mm2) measurements at the proximal, middle and distal tendon region were carried out. Non-parametric statistics were employed. Results are reported as mean±SD. RESULTS:CSA (mm2)Table: Upregulated Genes in ODHPSC Versus NOsDistal CSA was greater than the middle and proximal tendon on both the strong and weak side (P<0.05). Distal and proximal CSA, but not middle CSA, was greater on the strong side compared to the weak side (P<0.05). For a given common force, stress at the proximal tendon was lower on the strong side (49±11 MPa) compared to the weak side (61±21 MPa)(P<0.05). Maximal stress at the middle tendon was similar for the strong (71±23 MPa) and weak side (71±21 MPa)(r2= 0.99). CONCLUSIONS: These data show a regional variation in CSA along the patellar tendon, which markedly influences the stress. The larger distal and proximal CSA on the strong side demonstrate that increased habitual loading results in a region specific tendon hypertrophy.