Anthony Shield Senior lecturer, School of Exercise and Nutrition Science Institute of Health and Biomedical Innovation Queensland University of Technology, Brisbane, Australia. - Is neuromuscular inhibition a risk factor for hamstring strain?

1. Is neuromuscular inhibition a risk factor for hamstring strain?
Tony Shield
School of Exercise & Nutrition Sciences
Institute of Health & Biomedical Innovation
Queensland University of Technology

2. Ryan Timmins, Morgan Williams, Matt Bourne, Dave Opar

3. Running & knee flexor strength
Greig (2008)
Eccentric strength loss with little or no concentric decline.
Suggests possibility of inhibition
Concentric Torque
Eccentric Torque

4. doi: 10.1111/sms.12171
The decline in Bfem sEMG ‘explains’ changes in eccentric knee flexor strength (r2=0.69, p<0.001)
1830m sprints

5. Prior hamstring injury  Persistent eccentric weakness
From Croisier & Crielaard 2000
Evident months to years after grade 2+ injury
Jönhagen et al 1994, Lee et al 2009
Opar et al 2013

6. Is rehabilitation sabotaged by neuromuscular inhibition?
6

7. Hamstring strain injury
Pain
Avoid long m lengths
 Activity
NMI
Atrophy
 Fascicle lengths
 Opt. m length
 Strength Ecc>Con, Long>Short
 Prop. m damage
 Re-injury risk

8. ‘Recovered hamstring’
Resume long m lengths
 Activity
NMI
Atrophy
 Fascicle lengths
 Opt. m length
 Strength
Ecc>Con, Long>Short
 Prop. m damage
 Re-injury risk
BFlh

9. Our model…
•Athletes with Hx of unilateral strain injury
–At least one grade 2-3 strain
–‘Conventional’ rehabilitation
–Returned to full training & competition

10. Evidence for inhibition
8-12% deficits
18-20% deficits
23(3):696-703

11. Reduced voluntary activation
Inhibition limited to eccentric actions
Twitch interpolation during maximal isokinetic contractions
Buhmann et al unpublished

12. Reduced muscle use (MRI)
0
10
20
30
40
Inj BFlh
Uninj BFlh
%  T2 relaxation
Limb
9 elite to sub-elite track athletes ~8.5 mo post injury
1040m sprints
p<0.05
Bourne et al unpublished

13. p<0.05
*
ST > BFlh, BFsh, SM
p<0.05
10 recreational to sub-elite
athletes, ~9.8 mo post injury
Reduced muscle use (MRI)
610 Nordics
Bourne et al unpublished

14. Timmins et al (2014) Med Sci Sports Exerc. [Epub ahead of print]

15. Hamstring strain injury
Pain
Avoid long m lengths
 Activity
NMI
Atrophy
 Fascicle lengths
 Opt. m length
 Strength Ecc>Con, Long>Short
 Prop. m damage
 Re-injury risk
Opar et al
Sole et al
Timmins et al
Silder et al
Sole et al
Opar et al
Jönhagen et al Lee et al

16. Return to play w/out inhibition
Rehabilitation
Retraining
Competing
Intensity of eccentric hamstring contractions
Time
16
 Eccentric strength  Voluntary activation  Muscle size  Fascicle lengths Altered collagen expression?  Damage resistance

17. Rehabilitation
Retraining
Competing
Intensity of eccentric
SM, ST & BFlh contractions
Time
With BF inhibition…
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18. •Croisier JL, & Crielaard JM. (2000) Isokin Exerc Sci, 8:175-180.
•Fyfe JJ, Opar DA, Williams MD, Shield AJ. (2013) J Electromyog Kinesiol, 23(3): 523-530.
•Greig, M. (2008) Am J Sports Med, 36(7):1403-1409.
•Jönhagen, S, Nemeth, G, & Eriksson, E. (1994) Am J Sports Med, 22(2):262-266.
•Lee MJ, Reid SL, Elliott BC, Lloyd DG. (2009) Med Sci Sports Exerc, 41(10):1942- 1951.
•Opar DA, Williams MD, Timmins RG, Dear NM, Shield, AJ. (2013) J Electromyog Kinesiol, 23(3):696-703.
•Opar DA, Williams MD, Timmins RG, Dear NM, Shield, AJ. (2013) Am J Sports Med, 41(1):116-125.
•Silder A, Heiderscheit BC, Thelen DG, Enright T, Tuite, MJ. (2008) Skeletal
•Radiology 37(12):1101-1109.
•Sole G, Milosavljevic S, Nicholson HD, Sullivan SJ. (2011) JOSPT, 41(5):354-363.
•Timmins RG, Opar DA, Williams MD, Schache AG, Dear NM, Shield AJ. (2014) Scand J Med Sci Sport. Jan 15. doi: 10.1111/sms.12171
•Timmins RG, Shield AJ, Williams MD, Lorenzen C, Opar DA. (2014) Med Sci Sports Exerc, Sep 9. [Epub ahead of print]
References
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