ForceLength Relationships in Fatigued Hindlimb Suspended Rat Gastrocnemius Muscle - PowerPoint PPT Presentation

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ForceLength Relationships in Fatigued Hindlimb Suspended Rat Gastrocnemius Muscle

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Consequences of Disuse & Inactivity on the Size & Contractile Properties of. Skeletal Muscle ... selective loss of contractile proteins ... – PowerPoint PPT presentation

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Title: ForceLength Relationships in Fatigued Hindlimb Suspended Rat Gastrocnemius Muscle


1
Force-Length Relationships in Fatigued Hindlimb
Suspended Rat Gastrocnemius Muscle
  • Lacy D. Bradley
  • Markin-Flanagan Studentship Award Recipient
  • Faculty of Kinesiology
  • University of Calgary

2
  • Space-Flight
  • Causes Atrophy and Greater Fatigue
  • Could the greater fatigue be due to increased
    compliance of the connective tissue?

3
Consequences of Disuse Inactivity on the Size
Contractile Properties of Skeletal Muscle
  • Structural Changes
  • muscle atrophy
  • fiber type transitions
  • selective loss of contractile proteins
  • decreased protein synthesis increased rate of
    degradation
  • loss of integrity of connective tissue
  • Contractile Changes
  • decline in peak force
  • reduced peak power
  • increased maximal shortening velocity
  • increased fatigability (due to altered
    metabolism)
  • altered force-length force-frequency
    relationships?

4
Overview
  • Pilot Study Purpose
  • Hindlimb Suspension Apparatus
  • Materials methods
  • Experimental procedure
  • Pilot Study Hypothesis
  • Results Discussion
  • Force-length relationship
  • Conclusion Future Investigations

5
Hindlimb Suspension Pilot Study
  • Why hindlimb suspension?
  • Practical, effective method for studying physical
    inactivity
  • What is the purpose of this pilot study?
  • Preliminary observations is it worth pursuing
    study of changes to connective tissue and impact
    on length-tension relation?
  • Research limited or non-existent

6
Hindlimb Suspension Apparatus
  • Materials
  • Apparatus Preparation
  • Elastoplast tape
  • Plastic tab paper clip
  • Animal Preparation
  • Restrain animal
  • Clean tail
  • Adhere Elastoplast to tail
  • Secure with filament tape
  • Mark tape position

7
Hindlimb Suspension Apparatus
  • Suspension of the Animal
  • Attach hook to swivel
  • Adjustments
  • Adjust height 30
  • Rat unable to touch floor/sides of cage
  • Nylon chew bone
  • Observation Procedures
  • Weight
  • Appearance activity
  • Tail apparatus

8
Experimental Protocol
  • Set Optimal length
  • Force-length measurements
  • Double pulse tetanic contractions (200 Hz) at
    different lengths
  • Force-frequency measurements
  • Isometric contractions (200ms) at 20, 40, 60 80,
    100, 200 Hz
  • Fatigue recovery
  • Intermittent stimulation (50 Hz, 300 ms, 1 per s)
    for 5 minutes followed by 45 minutes of recovery
  • Post-fatigue force-length
  • Post-fatigue force-frequency
  • Re-check optimal length reset (if necessary)
  • Force-frequency (post-fatigue, post length
    change)

9
Research Question
  • What happens to the force-length relation as a
    result of hindlimb suspension?
  • Sustained stretch following repetitive
    contractions
  • Increased compliance
  • If this is true… we hypothesize
  • Shift in the force-length relationship in
    suspended animals (compared to control)
  • Shift exaggerated after fatigue

Hypothesis
10
Results Discussion
  • Force-Length Relationship

11
Pre-Fatigue Control vs. Suspended
  • Suspended Greater force generation at longer
    lengths
  • Why? Connective tissue compliance and/or
    stretch
  • Or more sarcomeres in series

12
Control Group Pre-fatigue vs. Post-fatigue
  • Post-fatigue Greater force generation at longer
    lengths
  • Why? Connective tissue more compliant

13
Suspended Group Pre-fatigue vs. Post-fatigue
  • Post-fatigue Optimal length shifted down to
    the right
  • Why? Incomplete recovery and over-stretched
    CT

14
Post-Fatigue Control vs. Suspended
  • Suspended Optimal length shifted down to the
    right
  • Why? Incomplete recovery, increased
    compliance, over-stretched CT

15
Future Investigations
  • Directions for future hindlimb suspension studies
  • Force-length relations in fatigued conditions
  • Fatigability the potential mechanisms involved
  • The role of aerobic metabolism in rates of
    recovery
  • Force-frequency relationships and the mechanisms
    responsible for any alterations
  • Conclusions (evidence for)
  • Hindlimb suspension causes greater compliance of
    connective tissue, and/or increased of
    sarcomeres
  • Repetitive stimulation causes sustained decrease
    in active force, and possibly greater stretch of
    connective tissue
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