Characterization of central activation and contractile properties of lumbar extensor muscles
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Characterization of Central Activation and Contractile Properties of Lumbar Extensor Muscles. Rachel Ruggeri, SPT. Ohio University Motor Control Lab Dr. David Russ Ph.D., P.T. Stephanie Gustwiller, SPT Dr. James Thomas, Ph.D., P.T.

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Characterization of central activation and contractile properties of lumbar extensor muscles

Characterization of Central Activation and Contractile Properties of Lumbar Extensor Muscles

Rachel Ruggeri, SPT

Ohio University Motor Control Lab

Dr. David Russ Ph.D., P.T. Stephanie Gustwiller, SPT Dr. James Thomas, Ph.D., P.T.


Characterization of skeletal muscle through electrical stimulation
Characterization of Skeletal Muscle Through Electrical Stimulation

  • Commonly reported measurements

    1. Central Activation

    2. Force Frequency Relationship


Central activation
Central Activation Stimulation

  • Ability of the CNS to activate a particular muscle ( )

  • One method to asses central activation:

    • Brief, supramaximal stimulation train delivered during MVC

    • Central Activation Ratio:

Stackhouse et. al, Muscle and Nerve 2000

MVIC Force

MVIC + stim force

Kent-Braun et. al, Muscle & Nerve 1996


Force frequency relationship
Force Frequency Relationship Stimulation

  • Alteration in muscle force with change in activation frequency of motor units ( )

    • Analogous to rate coding

  • Sigmoid relationship observed in single muscle fibers, single motor units, and entire muscle

    • Absolute number values will vary

Lee et al., Encyclopedia of Neuroscience, Binder, Hirokawa, Windhorst (Eds.) 2009.


Application of central activation and ffr
Application of Central Activation and FFR Stimulation

  • Changes in central activation and FFR occur with:

    • Aging - Disease

    • Disuse - Trauma

    • Fatigue

  • At present measurements have been reported within peripheral skeletal muscle only


Intent of present research
Intent of Present Research Stimulation

  • Develop a testing methodology within the back extensors to assess:

    • Central Activation

    • Force Frequency Relationship

  • Establish baseline normative values


Apparatus
Apparatus Stimulation


Methods
Methods Stimulation

  • Determining maximum stimulated force:

    • Stim intensity increased by 1 mA increments until force plateau achieved

    • This intensity used for all central activation trials

    • Intensity producing 50% of max stimulated force used for force frequency trials


Central activation1

80 Stimulation

70

60

50

40

30

20

10

0

1

2

3

4

5

6

Central Activation

  • Raw data demonstrating central activation impairment: CAR = 0.81

MCIV + stim

MVIC Force

(MVIC + stim Force)

CAR =

Force (lbs)

Time (sec)


Central activation2
Central Activation Stimulation

  • Back extensors:

    • Mean CAR = 0.95 (SD = 0.06)

  • CAR values of other young, healthy muscle groups:

    • Dorsiflexors: CAR = 0.96 (SD = 0.02)

    • Quadriceps: CAR = 0.98 (SD = 0.02)

    • UE? Biceps: CAR = 100 (SD = 0.3%)

(Kent – Braun, Muscle & Nerve 1996)

(Stevens et. al, Arch Phys Med Rehabil Vol 82, 2001)


Characterization of central activation and contractile properties of lumbar extensor muscles

Hill Equation Force Frequency Relationship Stimulation

  • Typical raw data from a single subject


Force frequency relationship1
Force Frequency Relationship Stimulation

  • Graph of our F50 vs other people’s F50

y = y0 + [(axb)/(cb + xb)]

y = peak F

x = frequency

Y0 = minimum peak

a = scaling factor

c = frequency at which 50% of max peak F is produced

b = slope


F 50 values
F Stimulation50 Values

  • Back extensor mean F50: 16.40 (SD = 3.15)

  • F50 values measured in other young, healthy muscle groups:

    • Dorsiflexors: 14 Hz (Mela et. al, Journal of Electromyography and Kinesiology, 2001)

    • Quads: 12-13 Hz (Allman et. al, Journal of Applied Physiology, 2004)

    • Biceps:

    • Hand intrinsics:


Adverse response to stimulation
Adverse Response to Stimulation Stimulation

  • Episodes of syncope in 2 subjects

  • Abnormal response to increased stimulation amplitude


Characterization of central activation and contractile properties of lumbar extensor muscles

F Stimulation50 Values

  • Mean F50: 16.40 (SD = 3.15)

  • Similar value to other lower

  • extremity muscle groups


Hill coefficient values
Hill Coefficient Values Stimulation

  • Mean Hill Coefficient: 2.21 (SD = 0.50)

  • Slope steepness corresponds to rate coding


Car data
CAR Data Stimulation

Mean CAR: 0.95 (SD = 0.06)


Future research opportunities
Future Research Opportunities Stimulation

  • Examine central activation and FFR among low back pain populations


Acknowledgements
Acknowledgements Stimulation