Effect of Acidosis on Skeletal Muscle Contractions At Physiological Temperatures

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Effect of Acidosis on Skeletal Muscle
Contractions At Physiological Temperatures

• Leslie Chin
• Supervised by Dr. Brian R. MacIntosh
• Faculty of Kinesiology
• University of Calgary
• January 12th, 2005.

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Acidosis Controversy

• Does acidosis effect fatigue?
• Yes textbooks, lactic acid
• No Westerblad, Allen, temperature

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What is Fatigue?

• Many definitions in literature
• a response that is less than the expected or
  anticipated contractile response, for a given
  stimulation

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Where Do ProtonsCome From?

• Traditional view lactic acid
• Robergs et al. (2004)
• No evidence that lactic acid is source
• Protons are from ATP hydrolysis

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Acidosis and Fatigue

• Textbook Enzymes (e.g. PFK)
• Correlation between pH and force(r 0.77)
• Experiments reduced force output, shortening
  velocity, relaxation time

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So Acidosis Causes Fatigue, Right?

• So far the evidence is unconvincing
• New experiments use physiological temperatures
  instead of subphysiological temperatures
• The results

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Temperature Is Important!

• Westerblad et al. (1997)
• 32C
• Found that force and shortening velocity were not
  significantly affected by acidosis
• Concluded that acidosis does not directly inhibit
  force at physiological temperatures

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Purpose

• Determine whether acidosis effects skeletal
  muscle fatigue during repetitive tetanic
  stimulation over an extended period at
  physiological temperatures

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Protocol Differences

• Typical fatigue studies use short-duration
  stimulation, not representative of physiological
  conditions (i.e. acidosis treatment)
• This study uses long-duration stimulation, mimics
  acid generation

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Methods

• Adult Swiss-Webster mice
• Flexor digitorum brevis (FDB) muscle bundles

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Methods

• Two groups Non-acidosis (n5) and acidosis
  treatment (n4)
• Neutral gas 5CO2/95O2(7.35 pHo)
• Acidic gas 10CO2/90O2(7.00 pHo)
• Solution heated to 28-31C

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Methods
Adjustable Hook
Strain Gauge Transducer
Data Acquisition
Gas
Stimulator
Heater
Inflow Solution Bath
Outflow Solution Bath
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Methods
Force-freq (5 min)
Repetitive stimulation 150 Hz (14 mins)
Time
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Methods
Force-freq (5 min)
Force-freq (30 sec)
Repetitive stimulation 150 Hz (14 mins)
Time
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Methods
Force-freq (5 min)
Force-freq (30 sec)
Repetitive stimulation 150 Hz (14 mins)
Time
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Methods
Repetitive stimulation 150 Hz (14 mins)
Force-freq (5 min)
Force-freq (30 sec)
Repetitive stimulation 150 Hz (14 mins)
Force-freq (30 sec)
Time
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Methods
Repetitive stimulation 150 Hz (14 mins)
Recovery (15 mins)
Force-freq (5 min)
Force-freq (30 sec)
Repetitive stimulation 150 Hz (14 mins)
Force-freq (5 min)
Force-freq (30 sec)
Time
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Methods
Repetitive stimulation 150 Hz (14 mins)
Recovery (15 mins)
Force-freq (5 min)
Force-freq (30 sec)
Repetitive stimulation 150 Hz (14 mins)
Force-freq (5 min)
Force-freq (30 sec)
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Results
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Results
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Results
Before Invention
After Invention
After Recovery
not significant, p0.159 ? significant,
p0.03 and p0.009 Student t-test
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Protocol
Repetitive stimulation 150 Hz (14 mins)
Force-freq (5 min)
Force-freq (30 sec)
Recovery
Repetitive stimulation 150 Hz (14 mins)
Force-freq (5 min)
Force-freq (30 sec)
Time
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Results
Control Before Invention
Acidosis Before Invention
Control After Invention
Acidosis After Invention

• 5 min Force-frequency 1 minute between
  contractions
• 20, 40, 60, 80, 100, 150 Hz

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Results
Control After Invention
Control Before Invention
Acidosis Before Invention
Acidosis After Invention

• 30 second Force-frequency 5 seconds between
  contractions
• 20, 40, 60, 80, 100, 150 Hz

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Results
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Conclusions

• Acidosis caused significant declines in tetanic
  force
• Acidosis seems to effect fatigue by a long-term
  mechanism that delays recovery

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So What Do We Know?

• Difference between short-duration and
  long-duration stimulation
• Temperature dependence
• Acidosis effects fatigue by a long-term
  mechanism, delaying recovery

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Acknowledgments

• Dr. Brian MacIntosh
• Dr. Allan Markin and Jackie Flanagan
• USRP Review Committee
• Dr. Aaron Tubman

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