|
Tensile strength
|
The maximum force the tendon can withstand in tension before tear.
Achilles [104]
59 ± 18 MPa
Patellar [105]
58.7 ± 16.3 MPa |
-
(1)
collagen type I, III or IV abundance [106,107,108], collagen crosslinking or nonreducible AGE crosslinks [101,108,109]
-
(2)
MMP production [75]
-
(3)
extracellular water and PGs [108,110]
-
(4)
tendon cross-sectional area and length [63]
|
Human
consistent reduction with aging across multiple tendon types: Achilles tendon [104], patellar tendon [98], anterior tibialis [111] Animal
inconclusive could be attributed to differences in species, age, types and conditions of tendons studies generally include the flexor and tail tendon [63,109], Achilles tendon [96,112] and patellar tendon [79]
|
|
Stiffness
|
The extent of resistance to elastic deformation in response to the applied force.
Achilles [104]
685 ± 262 N/mm
Patellar [113]
4434 ± 562 N/mm |
-
(1)
collagen—provides elasticity through its high-entropy containing polypeptide chains in the relaxed state [107]
-
(2)
AGE crosslink deposits—increases in lysine glycation and inter-collagen bonding stiffen tendons [63,114]
-
(3)
elastin—extends but only becomes elastic when hydrated [107]
-
(4)
PGs and water influencing a tendon’s elastic recoil [107]
-
(5)
increasing fibril radius and tendon cross-section may affect tendon stiffness and functions contradictorily [63,106]
|
Human
inconclusive [97,103,115,116] aged human patellar tendon mainly showed no changes in stiffness [115] Animal
inconclusive [108,112,117] stiffness was increased in aged mouse flexor tendon [63] and tibialis anterior and plantaris tendons [118], which could be region dependent
|
|
Tensile modulus
|
The slope of the stress–strain curve in the elastic deformation region that measures stiffness [116].
Achilles [119]
822 ± 211 MPa
Patellar [98]
660 ± 266 MPa |
Similar contributing biological factors as mentioned with additional factors:
-
(1)
pyrrole collagen crosslinks—positive correlation with the elastic modulus [120]
-
(2)
MMP production increase—associated with tensile modulus reduction [75]
-
(3)
modulus change is independent of collagen fibril morphology or force-generating muscle capacity [75,117]
|
Human
Animal
inconclusive [96,112,121,122,123] Only aged mouse tibialis anterior tendon and flexor tendon have significant increases in the modulus [63,117] while the increase was substantially greater in the proximal region than in the rest of the tendon [117,118]
|
|
Viscoelasticity
|
Represented by tendons exhibiting viscous and elastic characteristics when undergoing deformation
Decreased dynamic modulus indicates less resistance to strain and a reduced ability to properly transfer force [41]. |
-
(1)
collagen type I [100], collagen type III [112], and collagen crosslinks [41]—correlate to a greater elastic modulus, fibril volume fraction and stiffness [100]
-
(2)
GAG chains have not been shown to directly influence viscoelastic properties [41,112], but the absence of decorin leads to a reduction in the dynamic modulus in aged tendons [41]
|
Human
Animal
|
