Purpose: Characteristics of localised tendon strain in vivo are largely unknown. The present study examines local tendon strain between the deep, middle and surface structures at the proximal and distal aspect of the patellar tendon during ramped isometric contractions.
Methods: Male subjects (aged 28.0 +/- 6.3) were examined for patellar tendon excursion (anterior, midsection, posterior) during ramped isometric voluntary contractions using real time B-mode ultrasonography and dynamometry. Regional tendon excursion measurements were compared using an automated pixel tracking method. Strain was determined from the tendon delta length normalised to initial/resting segment length.
Results: Strain increased from 10-100% force for all regions. Significantly greater mean strain was seen for the anterior proximal region compared to the posterior and mid layer of the tendon (7.5+/-1.1% vs. 3.7+/-0.5% vs. 5.5+/-1.0%; P<0.05). Similarly the distal posterior region showed greater mean strain compared to the mid and anterior regions (7.9+/-0.6% vs. 5.0+/-0.6% vs. 5.4+/-0.6%; P<0.05). Relative changes in strain differences from 50-100% force for proximal were greatest for the anterior to midline regions (4.6+/-0.6%, 5.6+/-0.6%) and for the distal were also greatest for the anterior to midline regions (4.4%+/-0.2%, 5.3+/-0.2%). The largest mean strain for the proximal region was at the anterior layer (7.5+/-1.1%), and at the posterior layer for the distal tendon (7.9+/-0.9%).
Conclusions: This study shows significant regional differences in strain during ramped isometric contractions for the patellar tendon. Lower proximal strains in the posterior tendon compared to the anterior region may be associated with the suggestion of 'stress shielding' as an aetiological factor in insertional tendinopathy.
(C) 2014 American College of Sports Medicine