Tendon Flashcards
Muscle Tendon unit
Ratio of muscle fibre length to length of tendon varies depending on function of muscle
Long fibres and short tendon create large active range of motion at joints - hip, knee, shoulder, elbow
Shorter fibres and long tendon important for elastic energy storage and return - ankle
Stance phase of running
KE and PE decreases in early stance
KE and PE lower at midstance
Energy stored in spring like elements in limbs and trunk
Springs recoil in late stance to return elastic energy to kinetic and potential energy of COM
Reduces the amount of work muscles need to do to accelerate the body during each stride
Store and return of elastic energy
Energy stored in a spring
Elastic energy stored = 0.5 force x linear deformation
Therefore the more it deforms the more energy it will store
To store and return significant energy tendon strains must be high
Tendon stiffness
Stiffness (Nm-1) = Force (N) / Change in length (m)
Compliance = 1 / Stiffness
Young’s Modulus (Pa) = Stress / Strain
The stiffer a tendon:
The more force it can withstand/transmit
The less it will strain for a given force
The less energy it will store for a given force
Human ankle joint and achilles tendon
Sites of most elastic energy in human running
Energy stored in the Achilles tendon and ligaments of the foot
Achilles tendon is the longest tendon in the human body:
- free tendon of gastrocnemius and soleus
- strain during running 3-7%
- high injury incidence
Failure of tendon
Force and strain in tendon can be measured in vivo
Invasive methods:
- tendon buckle
- fibre optics
Non-invasive methods - ultrasound
Strain at which damage occurs - 5-12%
Strains measured during walking, running, hopping and jumping - 3-10%
Achilles tendon working very close to safety limits
Hysteresis
Tendon is not perfectly elastic
Approximately 7% of energy lost due to heat
Temperature in Achilles tendon during 30 min run ~41 degrees (Farris et al., 2009)
Therefore tendons heat up which may lead to damage
Healing of tendon
Similar to healing of ligament
If the failure of the structure is partial or the ends of the ruptured tissue are apposed, ligament/tendon will heal
If not, surgery required
Ultrasound (US)
High frequency sound wave
Sound differentially reflected or absorbed by tissues of different densities
Cheap and available machinery
Operator dependent - high skill level required
Soft tissues and bone surfaces
Difficult to get ‘general picture’ of the area
Very low risk
Tendinopathy
Chronic, repetitive strain injury
Tendon loaded to high strain in order to accomplish its function
High strains are close to failure limit of collagen fascicles
Loading cycle repeated thousands of times in an exercise bout
Fundamentally related to mechanical overload
Anatomical, biomechanical and molecular changes associated with tendinopathy occur due to attempt to remodel
Common sites of tendinopathy
Achilles tendon
Patella tendon
Tendon of origin of extensor carpi radialis brevis
- lateral epicondylitis
- tennis elbow
Risk factors for tendinopathy
Change in training
High stress placed on tissue due to sub-optimal technique
- Running - excessive pronation
- Tennis - single handed backhand
Inappropriate equipment
Inappropriate tendon stiffness
Tendinopathic tendon & healthy tendon
Tendinopathic tendons have lower stiffness and greater CSA leading to lower Young’s modulus (Arya & Kulig, 2009)
Very difficult to determine cause and effect from cross-sectional study
Tendinopathy prevention
Overload
If rest between loading sessions not adequate will result in tissue degradation rather than net synthesis (Magnusson et al., 2010)
