Biomechanics of muscle strains

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Biomechanics of muscle strains

• John Orchard, MBBS BA MD PhD FACSP FACSM FASMF
• April 2007
• www.injuryupdate.com.au

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When do muscles strain?

• Muscle strains are amongst the most common
  injuries in football players and sprint athletes
• Little is known about the risk factors for
  strains
• Strains can be recreated in the laboratory, but
  in vivo occur so rapidly that the forces
  resulting in strain are very hard to assess

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Clinical occurrence of strains
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Laboratory occurrence of strains

• Strain model simulated in lab by over-stretch of
  isolated rabbit muscle (i.e. not rabbit muscle
  during a running activity)
• Strain occurs at musculotendinous junction
• Major authors Garrett, Leiber, Best
• Presumably similar pathology, but in real life
  activities (e.g. sprinting) maximal range of
  motion of muscle groups is not reached

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When do muscles strain?

• In real life activities, greatest range of motion
  (stretch) generally occurs during swing phases
• However, greatest external joint moments
  generally occur during ground phases
• No one has a biomechanical formula for
  determining when a muscle will fail

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Forces on muscles and joints

• Change of movement of a joint is determined by a
  sum of net muscle moment and net external moment
• Mann (1981) muscle moments for knee flexion and
  hip extension were both highest in the early
  ground phase of sprinting
• He concluded that this is when hamstring strains
  occur (initial contact)

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Clinical paradigm

• Teaching of Garrett et al. suggests that 2-joint
  muscles strain when undergoing an eccentric
  contraction
• This suggests that hamstring muscles may strain
  in late swing phase (eccentric phase) rather than
  early ground contact (when already contracting
  concentrically)

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Forces responsible for strain

• Leiber et al. (1993, JAP) showed that in the
  laboratory strain model, muscle strain damage
  correlated with external force applied rather
  than over activity of the muscle.
• Suggests that Ralph Manns explanation of muscle
  strain pathogenesis was wrong.

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Wrong for right reasons?

• However, muscle force correlates strongly with
  degree of stretch (i.e. eccentric contractions
  are much stronger than concentric contractions)
• Therefore maximal net muscle moments probably
  coincide with maximal external moments in the
  other direction

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Eccentric or isometric?

• Kurokawa et al. (JAP, 2001) have shown that there
  is a phase after eccentric contraction where
  musculo-tendinous unit as a whole is isometric
• However, using realtime U/S of gastroc during
  jumping have shown that initially the muscle
  component contracts while the tendon component
  continues to lengthen

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Kurokawa et al. sequences
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Quadriceps strains?

• Anecdotal description of occurrence during ball
  contact
• But, this would clearly be when shortening
• Why wouldnt triceps strain when serving or
  spiking in volleyball if ball contact can strain
  a shortening muscle?
• Could quadriceps strain occur in back-swing or
  even ground contact?

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Type of kicks at risk

• Running kicks rather than standing kicks
• Rare on kicking out from goal, or kicking after a
  mark
• Very rare in punters in NFL (D. Bennett)
• Rare in goalkickers in rugby codes
• Related to speed of running rather than distance
  of kick

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Epidemiology of muscle strains

• Hamstring, quadriceps, calf and adductor strains
  are common in AFL
• All, except groin, usually have sudden onset, so
  related variables can be analysed

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AFL Injury Survey data 92-99
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Risks for hamstring injuries
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Risks for quadriceps injuries
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Risks for calf injuries
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Dominant kicking leg

• Quadriceps strains more common in dominant
  kicking leg (RR 2.13, 95 CI 1.59-28.6)
• Hamstring and calf fairly evenly distributed

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AFL muscle strain study

• Previous muscle strain injury is a strong risk
  factor for future strain injury to the same
  muscle group (and in some cases other muscles)
• Calf and hamstring (but not quadriceps) strains
  are more common in older players
• Quadriceps strains are often related to kicking
  and are more common in the dominant kicking leg

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Download further details

• Website www.injuryupdate.com.au
• This study in Am J Sports Med 2001, 29 (3)
  300-303, Intrinsic and extrinsic risk factors
  for muscle strains in Australian football

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Biomechanics calf strains

• Occur during push-off phase
• Presumably ground contact
• Video one calf strain available of Steve Waugh
  from StumpCam
• Occurs during second step of take-off towards end
  of ground contact cycle

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Before and after frames
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Biomechanics calf strains

• Occur during ground contact phase
• Occur during close to full range (increased
  stretch) but not maximal range
• Close to an isometric phase (moving from
  eccentric to concentric)
• Occur during push-off (acceleration) of second
  step

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Biomechanics hamstring

• Hamstring strains are likely to occur during
  overstriding when close to maximum speed and
  trying to maintain speed
• Again near maximum stretch but not at maximal
  length
• Again moving from eccentric to concentric
• ?Start of ground contact

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Hamstrings strain overstriding
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Biomechanics quadriceps strains

• Can occur when running
• Related to dry weather (?ground contact)
• Mechanism perhaps caused by under-striding of
  kicking leg during final step (when slowing down)
  before the kicking motion

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Timing during ground contact
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Older players

• Hamstring and calf strains have a relationship to
  age also share a common nerve supply (L5 and
  S1/sciatic nerve), whereas quadriceps strains are
  not related to age
• Suggests that L5 nerve root impingement may have
  a role in hamstring and calf strains (?by
  aberrant lumbosacral ligament)

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L5 and S1 injuries and age
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L2-L4 injuries and age
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Prevalence of L5/S1 disc pathology
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The science of return to play

• Clin J Sports Med 15(6) 436- at injuryupdate
  site
• If you cant train you cant play
• If you can train you might be able to play
• Its all about risk assessment

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Return to play from muscle strains
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Risk of hamstring re-strain in AFL
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Trends in AFL hamstrings
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Factors to take into account

• Low strength
• Reduced flexibility
• Large lesion MRI
• High risk player
• Early season
• Biceps fem strain
• History of breaking down or playing poorly

• Full strength
• Full ROM
• Small lesion MRI
• Low risk player
• Must-win game
• Semimemb strain
• History of successfully carrying injury