Jen Campbell

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Winter 2005 Student Seminar Markin-Flanagan
Undergraduate Student Research Program in Bone
and Joint Health
Mechanism of Fatigue in Rat Medial Gastrocnemius
Muscle

• Jen Campbell
• Faculty of Kinesiology
• Faculty Mentor Dr. Brian MacIntosh
• April 25, 2005 1230 pm

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Introduction

• Why study muscle fatigue?
• Active lifestyle, quality of life, mobility
• What populations might this affect?
• Elite athletes
• Diseased populations
• Muscular dystrophy, stroke, and multiple
  sclerosis
• Average population day to day activities

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Introduction

• Fatigue in skeletal muscle may be due to
• Impaired Ca2 release mechanism (RyR)
• Then no change in the extra force for a stimulus
  late in a train (like dantrolene)
• Or decreased availability of Ca2
• Then a decrease in the extra force for a stimulus
  late in a train
• With metabolic rate, PCr Cr and Pi
• Pi can precipitate with Ca2 in the SR

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Hypotheses

• Hypothesis 1 During repetitive stimulation Ca2
  is less available due to precipitation with Pi
• Extra force for a stimulus late in a train will
  be severely diminished
• Hypothesis 2 Ca2 becomes available within 5
  minutes of recovery
• Should recover in parallel with phosphocreatine
  resynthesis (within 5 minutes of recovery)

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Methods

• 12 female Sprague-Dawley rats weighing 207 247
  g
• Randomized (coin flip!!!)
• Fatigue or control treatment
• N5 per group

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Methods

• Rats anesthetized by IM injection (0.1ml of
  ketamine-xylazine/100 g body weight)
• Rats euthanized afterwards by overdose
• Left medial gastrocnemius muscle isolated (fast
  twitch, non-endurance type fibers)
• Medial gastrocnemius portion of the sciatic nerve
  preserved
• All other sciatic nerve branches cut

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Methods

• Rat in a prone position
• Femur stabilized with the insertion of drill bit
• Metal pin inserted into tibia
• Pocket of skin formed and filled with warmed
  paraffin oil
• Stimulating electrode was hooked onto the sciatic
  nerve
• Rectal and muscle temperature maintained (37
  0.5C).

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Methods
FF Summation Fatigue Recovery
Summation FF
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Methods

• Figure 1 10 and 11 pulse contractions
• Figure 2 Difference between 10 and 11 pulse
  contractions

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Results - Fatigue
Ratio decreased from 2.10.2 (meanSD) to
0.820.25 (plt0.05)
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Fatigue Contractions

• Figure 1- 10 and 11 pulse contractions during
  fatigue
• Figure 2 Difference between 10 and 11 pulse
  contactions

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Results Relative Recovery

• Relative recovery active force
• of pre-test contraction

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Results Recovery Ratio
NS

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Discussion and Conclusions

• Hypothesis 1 During repetitive stimulation Ca2
  is less available due to precipitation with Pi
• Observation Extra force per activation was
  reduced during repetitive stimulation
• Conclusion Hypothesis is supported.

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Discussion and Conclusions

• Hypothesis 2 Ca2 becomes available within 5
  minutes of recovery
• Observation Extra force per activation did not
  recover within 5 minutes
• Conclusion Hypothesis is not supported.

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Possible Explanations

• Perhaps calcium does not come out of
  precipitation with inorganic phosphate within the
  first 5 min of recovery
• Some other mechanism responsible for limiting
  calcium ion availability???

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Future Considerations?

• Measure transport of Pi
• Measure PCr concentration
• Emulate decreased Ca2 availability
• Consider other types of fatigue

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Thank-yous

• Funding Dr. Allan Markin and Jackie Flanagan
  and NSERC
• Dr. Aaron Tubman USRP Coordinator
• Miriam Kearnes USRP Assistant
• Dr. Syme Biological Sciences Lab
• Shane Esau Data Collection
• Meredith MacNaughton Surgery and Analysis
• And.
• Dr. Brian MacIntosh Faculty Mentor!!!

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Questions?