Training-induced changes in structural and mechanical properties of the patellar tendon are related to muscle hypertrophy but not to strength gains

J Appl Physiol (1985). 2009 Aug;107(2):523-30. doi: 10.1152/japplphysiol.00213.2009. Epub 2009 May 28.

Abstract

To obtain a better understanding of the adaptations of human tendon to chronic overloading, we examined the relationships between these adaptations and the changes in muscle structure and function. Fifteen healthy male subjects (20+/-2 yr) underwent 9 wk of knee extension resistance training. Patellar tendon stiffness and modulus were assessed with ultrasonography, and cross-sectional area (CSA) was determined along the entire length of the tendon by using magnetic resonance imaging. In the quadriceps muscles, architecture and volume measurements were combined to obtain physiological CSA (PCSA), and maximal isometric force was recorded. Following training, muscle force and PCSA increased by 31% (P<0.0001) and 7% (P<0.01), respectively. Tendon CSA increased regionally at 20-30%, 60%, and 90-100% of tendon length (5-6%; P<0.05), and tendon stiffness and modulus increased by 24% (P<0.001) and 20% (P<0.01), respectively. Although none of the tendon adaptations were related to strength gains, we observed a positive correlation between the increase in quadriceps PCSA and the increases in tendon stiffness (r=0.68; P<0.01) and modulus (r=0.75; P<0.01). Unexpectedly, the increase in muscle PCSA was inversely related to the distal and the mean increases in tendon CSA (in both cases, r=-0.64; P<0.05). These data suggest that, following short-term resistance training, changes in tendon mechanical and material properties are more closely related to the overall loading history and that tendon hypertrophy is driven by other mechanisms than those eliciting tendon stiffening.

MeSH terms

  • Adaptation, Physiological
  • Adolescent
  • Biomechanical Phenomena
  • Elastic Modulus
  • Electromyography
  • Humans
  • Hypertrophy
  • Isometric Contraction*
  • Magnetic Resonance Imaging
  • Male
  • Muscle Strength Dynamometer
  • Muscle Strength*
  • Patellar Ligament / diagnostic imaging
  • Patellar Ligament / pathology*
  • Patellar Ligament / physiopathology*
  • Quadriceps Muscle / pathology*
  • Quadriceps Muscle / physiopathology*
  • Resistance Training*
  • Time Factors
  • Torque
  • Ultrasonography
  • Young Adult