21. Length - tension diagram: working range and power of the muscle; heat production and muscle fatigue Flashcards
Isotonic conditions
Velocity/Tension Relationship (Power)
A direct relationship can be seen between velocity of
shortening and tension-parameters of muscle contraction.
If the tension is low (the less load the muscle has to lift), velocity becomes higher during musclework. Similarly if the load is heavy (higher tension is needed) lifting will be slow.
From velocity - tension curve we can calculate power as:
Velocity x Tension= Power
Velocity related to an actual tension is determined by the type of the muscle (e.g.phasic (fast) or tonic (slow)).
Phases of heat production
- In Resting: the maintenance of muscle tonicity generates heat – it creates
most of the BMR (Basal Metabolic Rate; see later).
- Initial Heat Production is related to the 4 phases of ElectroMechanical Coupling:
a) Activation Heat - connected to the first 2 phases (1, Ca2+ -release; 2, Myosin-activation).
b) Contraction Heat - last 2 phases
3, sliding filament mechanism; 4, Ca2+ repumping during relaxation)
Restitution Heat: characteristic mostly to phasic (fast,white, anaerob- glycolytic) muscles.
The huge O2-debt created during contraction must be replaced by ATP resynthesis during restitution, which generates heat.
Phases of Heat Production (picture)
Passively streched muscle (picture)
Afterload experiment
Isometric conditions
In this topic:
Length and Tension Diagram
Passively streched muscle
Isotonic conditions
Isometric conditions
Preload experiment
Afterload experiment
Working range of the muscle
Velocity/Tension Relationship (Power)
The power of the muscle
Heat production
Phases of Heat Production
Fatigue of the Muscle
Working range of the muscle
Muscles work in this range (physiologically). Animals adjust their muscle length in a way that during muscle work these conditions can be kept (remember how a cat collects its limbs before jumping)
Length and Tension Diagram
Each sceletal muscle is under a certain degree of stretch.
Length x Tension (load) = Work
Length-Tension curve can be obtained when one stimulates (with maximal single impulses) muscles, which are pasively streched with different loads. As a result of Isometric, Isotonic, Preload and Afterload experiments, we can construct the area, where muscles execute normal physical work.
Preload experiment
Working range of the muscle (cardiac and skeletal)
fatigue of the Muscle
Signs of Fatigue on Mechanogram:
a, decreased amplitude of contraction
b, prolonged contraction. (slow relax)
In Vitro Fatigue:
a) lack of O2 (muscle stimulation in N2 (nitrogen) rich environment: the result is unrecoverable fatigue)
b) lack of transmitter (occurs only in experimental conditions + in special diseases)
In Vivo Fatigue:
a) peripheral – decrease of energy sources - increase of metabolic by-products - lactic acid (direct blocking of contraction due to protein denaturation)
b) central fatigue - exhaustion of motor-unit (due to lack of vesiculum production of motoneuron)
exhaustion of myoneural junction
Subjective Feelings of Fatigue, due to:
- increased heat production - decrease of pH
- direct effect of Lactic Acid - dehydration
- general hypoglycaemia
Fatigue develops earlier in fast (glycolytic, phasic) fibres than in tonic (oxidative) muscles.
Heat production
Muscle produces heat during work:
during contraction: ATP breakdown
after contraction: synthetic processes create heat.
Phasic (fast,white) fibres produce more heat during restitution. (during contraction the energy is provided by anerob glicolysis – resulting in high O2 debt – which must be „repayed” during restitution (which means resynthesis of ATP in the presence of O2).
Tonic (slow,red) fibers: heat production mostly occurs during contraction.
(energy need is covered by oxidative metabolism - No O2-debt)
Length and Tension Diagram (picture)
