Muscle Flashcards
Muscle
Only part of musculoskeletal system that can produce force
Actin and myosin molecules interact to form cross-bridges
Force related to number of cross-bridges
Additional force from the passive elastic structure in muscle-tendon unit
Eccentric Contraction
Force generated by muscle is less than external force and muscle fibres are lengthened by the external force
Essential element of controlling movement
When not controlled, it is dangerous to muscles
Failure of muscle
If muscle lengthening cannot be controlled, the muscle will be strained too much and will fail
Muscle damage occurs when the sarcomeres are lengthened too much
Muscles are said to be ‘unstable’ when operating on the descending limb of the force length curve
The only way to develop more force is to increase activation level but this does not happen instantly
Tearing usually occurs at muscle fascicle-aponeurosis junction
Activities where hamstring tear is most likely
Sprinting
Accelerating
Kicking
Why hamstrings tear
Muscle strain injuries occur due to high active strain of muscle (Lieber & Frieden, 1993)
Highest strain and activation occur at end of swing phase ( Yu et al., 2008; Thelen et al., 2005)
Risk factors for hamstring tear
Low hamstring strength
Short fascicle length
Sprinting technique
Prevention of hamstring tear
Many risk factors modifiable
Eccentric exercises increase hamstring strength and fascicle length
Healing of muscle
Good compared to tendon and ligament because blood supply is good
Inflammatory response follows injury:
- Influx of neutrophils to injury area
- Oxidative burst of neutrophils causes more damage to fascicles to remove damaged cells
Between 4 and 24 hrs post injury, an increase in the number of torn fascicles at injury site
Protein synthesis upregulated to replace removed tissue
Loading stimulates this process
