Module 1 - Generating Movement; Measuring Movement/Power

• Stress = the impact, load, demand on the body
• Strain = the response of the body to stress
• Validity = if what is measured is the true value
• Reliability = how reproducible the measurement is
• Accessing acute & adaptive response to exercise:

  1. Means to stress body - usually in exercise, in which work measured
  2. Means to quantify physiological responses - often involves measuring energy usage
  3. Control or standardise factors that influence body's responses (eg environment, diet, meds, hydration etc)

  • Must be valid & reliable
• Within muscle = intrinsic

  • Is both passive & active
• Proprioceptive info = feedback of how muscle going
• Huge number of contractile proteins in a muscle structure
• Muscle cells are multinucleated; allows high protein production if stressed
• Satellite cells = keep ultimate number of nuclei & help cell repair
• Excitation-Contraction Coupling:

  1. AP travels down T-tubules & release Ca from SR
  2. Ca binds to troponin & causes position change of tropomyosin, exposing active sites of actin
  3. Binding bw/ actin & myosin - contraction occurs
  4. ATP binds to myosin head allows relaxation
• During contracting each stroke shortens muscle ~1%
• Neuromuscular junction also known as motor end plate
• Depolarisation of NMJ to initiate contraction
• The Size Principle = Motor neurons recruited by axon size, small to large
• Type 1 = slow twitch, low force & fatigue resistant
• Type 2a = fast twitch, moderate force & less fatigue resistant
• Type 2x = fast twitch, high force & fast fatigue
• 1 motor unit stimulates multiple fibres of the same type
• 2 Major benefits of Size Principle:

  1. Use fatigue-resistant units longer
  2. Increase frequency gives force initially (summation), but diminishing effect w/ further increase frequency until tetanus
• Exercise begins & ends in the brain
• CNS receives feedback from muscles
• Fatigue = reduction in strength; can have peripheral & central components
• CNS limits motor output to prevent muscle being used too severely, BUT many potential limitations:

  • Motor cortex
  • Descending motor tracts
  • Spinal synapses
  • Electrical propagation in muscle
  • Neuromuscular junction
  • Chemical events in muscle
• Chemical events in muscle include:

  • Availability of substrate(s) - (energy source)
  • Enzyme activity
  • Local environment (pH, ionic conc's & T-tubules conductance)
• The Central Governor model - performance is set by subconscious brain specifically to ensure that the athlete reaches the finish whilst still in physiological homeostasis = Anticipatory behaviour regulation
• Will fatigue with no or little ATP depletion & some glycogen in muscles
• Metabolites & low fuel "sensors" (myokines) feedback to CNS
• Peripheral fatigue:

  • Muscle factors more involved in highly intensive (Type 2x fibres)
  • Vary with exercise duration
• Peripheral fatigue mechanisms:

  • Excitability (decrease Na/K pump) - T-tubules, Ca release
  • Oxidative (free recall) damage - Na/K pump, actin & myosin
  • H+ & Pi accumulation - decrease Ca release from SR, decrease binding of Ca to troponin, decrease x-bridge directly
  • Sarcomere damage - z line streaming (foggy = microtrauma), from eccentric & unaccustomed exercise
• Problems of uncontrolled force:

  • Muscle cramps - due to electrolyte depletion (guilt by association)
  • Now considered mostly due to NMJ (reflex) control
• Length-Tension Relationship:

  • Optimal length has most actin & myosin overlap, so active tension (force application)
  • Tension develops rapidly at longer muscle lengths
• Fibre length to Muscle length:

  1. Hamstrings

  • Longer muscle fibre/muscle, less CSA
  • Rapid shortening
  • Greater risk of tear

  1. Quadriceps

  • Shorter fibre/muscle, greater CSA
  • Greater force capacity
  • Lower risk of tear
• Force-Velocity Relationship:

  • Cross-bridges bw/ actin & myosin attach & detach at certain rates ("rate constants")
• Force-Velocity Relationship:

  • As velocity increases, the number of x-bridges decreases & less force generated
• Force-Velocity Relationship:

  • Force highest for eccentric > isometric > concentric
  • Eccentric contractions involve unaccustomed force frequently cause muscle damage (microtrauma, DOMS)
• Muscles act around joints, so force produced is measured as torque (Nm)

  • Power athletes generate more torque @ ALL velocities, compared w/ endurance athletes, but force decreases @ similar rate as velocity increases (in relative terms)
• Length-Tension-Velocity Relationship:

  • If velocity increases, force decreases, regardless of length
  • If velocity decreases, length is an important modulator
  • @ eccentric velocities, muscle velocity dominates length as the determinants of force
• Optimal Power = a tradeoff bw/ force & speed
• Power = work/time = force x time (Watt = J/sec)