Muscle Generated Heat

1
Muscle Generated Heat

• Primary sources of liberated heat energy from
  skeletal muscle due to chemical processes
• Maintenance (Resting) - Slowly liberated
  background heat, unrelated to muscle contraction.
• Recovery - Heat generated at the end of muscle
  contraction, related mainly to chemical reactions
  associated with energy production.
• Initial - Liberated immediately after stimulation
  and throughout muscle contraction (tension).

2
Initial Heat

• Isometric Contractions - Activation Heat
• Constant Length - No External Work
• Isotonic Contractions - Shortening Heat
• Constant Force (Load) - External Work
• Tension-Time Heat

3
Initial Heat - Isometric

• Two components
• Activation - Brief burst, immediately after
  stimulation.
• Slower rate of heat production associated with
  the development of increasing tension.
• DE A Wi (Activation Heat Internal Work)
• DE Q - W

4
Initial Heat - Isotonic

• In addition to external work (muscle shortening
  while lifting a constant load), additional heat
  is liberated due to the shortening process
  itself.
• Note This so called shortening heat is
  function of the shortening distance, but
  independent of the load. Although the amount of
  heat production is independent of the load, the
  rate of heat production decreases as the load
  increases.

5
Isotonic - Shortening Heat

• Shortening Heat ax
• a is muscle specific (units of force)
• x is the shortening distance
• DE A We ax
• A is Activation Heat
• We is External Work
• ax is Shortening Heat
• DE Q Px
• Heat (A ax) Work (Px)

6
Tension-Time Heat

• Note Early work of Hill (1930s) was refined in
  the 1960s with the advent of more precise
  measurements of heat.
• Activation Heat was found to not be a constant
  for isometric contractions at various loads, but
  rather is proportional to the developed tension.
• Shortening Heat however is a function of the
  load.

7
Tension-Time Heat continued

• Isometric
• DE A Wi f(P, t)
• Isotonic
• DE A We ax f(P, t)
• Where f(p, t) represents the heat liberated as a
  function of both the muscle tension P and
  thetime duration t that the tension is exerted.

8
Hills EquationCharacteristic Equation of
Muscle

• Extra Energy
• Let muscle lift a load P through a distance x.
• The energy generated as work W Px
• The energy generated as Shortening Heat ax
• Activation Heat A is omitted (not related to
  contraction)
• f(P, t) omitted for simplicity
• Extra Energy Px ax (P a) x
• Represents the total amount of extra energy
  liberated by a muscle contracting under isotonic
  conditions.

9
Extra Energy

• Extra Energy Liberation (P a) xRate of Extra
  Energy Liberation (P a) dx/dt
• For an isometrically contracting muscle P
  P0and the Rate 0 since there is no Work (x
  0)nor is there any Shortening Heat (isometric).
• For an unloaded freely shortening muscle (P
  0)the rate of energy release is a maximum.

10
Extra Energy - continued

• There is a direct linear proportionality for
• Rate of Extra Energy Released and the
• Difference between Max Load (P0) and
• the Actual Load (P), i.e. E (P0 - P)
• That is to say, the smaller the load, the greater
  the rate of energy released.
• (P a) v (P0 - P) b

11
Extra Energy - continued

• (P a) v (P0 - P) b
• P v a v P0 b - P b
• P v a v P b a b P0 b a b
• (P a) v (P a) b (P0 a) b

12
Hills Equation

• (P a) v (P a) b (P0 a) b