Consequence of the muscle load on muscle shortening:
Force-velocity relationship: More force (heavier load) = _____ velocity. Less force (lighter load) = _____ velocity
If you try to push something so heavy that it doesn’t move, your velocity = _____. This is an _____ _____ which produces the _____ _____.
Power = _____ × _____
Too heavy = _____ force but _____ speed
Too light = _____ speed but _____ force
Best power happens when the _____ and _____ are _____.
Consequence of the muscle load on muscle shortening:
Force-velocity relationship: More force (heavier load) = lower velocity. Less force (lighter load) = higher velocity
If you try to push something so heavy that it doesn’t move, your velocity = 0. This is an isometric contraction which produces the maximum force.
Power = force × velocity
Too heavy = high force but low speed
Too light = high speed but low force
Best power happens when the load and speed are balanced.
Isometric contraction:
Muscle contracts but stays the _____ _____ (no movement).
It includes two types:
Concentric: muscle _____ (_____ a weight)
Eccentric: muscle _____ (_____ a weight)
iso = _____
tonic = _____
metric = _____
Henneman’s size principle:
Motor units are recruited _____ based on _____ from _____ to _____, depending on how much _____ is needed.
Isometric contraction:
Muscle contracts but stays the same length (no movement).
It includes two types:
Concentric: muscle shortens (lifting a weight)
Eccentric: muscle lengthens (lowering a weight)
iso = same
tonic = tension
metric = length
Henneman’s size principle:
Motor units are recruited automatically based on size from smallest to largest, depending on how much force is needed.
Isotonic and Isometric contractions:
Muscle tension: The force the _____ _____.
Load: The Force the _____ puts on the _____
Whether a muscle gets shorter or longer depends on which force is stronger: the _____’s _____ or the _____ (_____).
If muscle tension is stronger than the load, the muscle _____.
If the load is stronger than the muscle tension, the muscle _____.
Isotonic and Isometric contractions:
Muscle tension: The force the muscle produces.
Load: The Force the object puts on the muscle
Whether a muscle gets shorter or longer depends on which force is stronger: the muscle’s tension or the weight (load).
If muscle tension is stronger than the load, the muscle shortens.
If the load is stronger than the muscle tension, the muscle lengthens.
Importance of initial muscle length:
Optimal length = _____ _____. Actin and myosin optimally overlap, allowing the _____ cross-bridges to form, so the muscle produces _____ _____.
Muscle too stretched = _____ force. Actin and myosin _____ overlap, resulting in _____ cross-bridges that can _____ = _____ contraction.
Muscle too shortened = _____ force. Actin overlap too much. Myosin can’t _____ properly = _____ _____ cross-bridges.
Importance of initial muscle length:
Optimal length = maximum force. Actin and myosin optimally overlap, allowing the most cross-bridges to form, so the muscle produces maximum tension.
Muscle too stretched = less force. Actin and myosin barely overlap, resulting in fewer cross-bridges that can form = weaker contraction.
Muscle too shortened = less force. Actin overlap too much. Myosin can’t grab properly = fewer effective cross-bridges.
Twitch vs. summation:
One action potential = one _____ (a _____, _____ contraction).
_____ _____ = summation.
Temporal summation = fibre receives another _____ _____ before it fully _____, the second contraction _____ to the first, resulting in _____ _____.
Tetanus:
If fibre is stimulated _____ without _____, the contractions _____ into a _____, _____ contraction.
Central nervous system:
The central nervous system can control muscle force through two key mechanisms
_____ _____ _____ - through _____’s size _____
_____ _____ _____ _____ - Change how _____ each motor unit _____.
Twitch vs. summation:
One action potential = one twitch (a small, brief contraction).
Repeated stimulation = summation.
Temporal summation = fibre receives another action potential before it fully relaxes, the second contraction adds to the first, resulting in greater tension.
Tetanus:
If fibre is stimulated repeatedly without relaxing, the contractions fuse into a smooth, sustained contraction.
Central nervous system:
The central nervous system can control muscle force through two key mechanisms
Motor unit recruitment - through Henneman’s size principle
Motor unit activation rate - Change how fast each motor unit fires.
Muscle tension - depends on two main things:
_____ of fibres _____ - This is controlled by motor unit recruitment (how many motor units are activated).
Tension produced by each fibre - This depends on how _____ each motor unit is activated (the rate of _____ _____).
Other factors affecting muscle tension:
Frequency of _____, faster _____ = more _____.
Fibre length at start of contraction, optimal length = _____ _____.
Fatigue, tired fibres produce _____ force.
Fibre _____, more _____/_____ = stronger contraction.
Muscle tension - depends on two main things:
Number of fibres contracting - This is controlled by motor unit recruitment (how many motor units are activated).
Tension produced by each fibre - This depends on how frequently each motor unit is activated (the rate of action potentials).
Other factors affecting muscle tension:
Frequency of stimulation, faster firing = more tension.
Fibre length at start of contraction, optimal length = maximum tension.
Fatigue, tired fibres produce less force.
Fibre thickness, more myofibrils/sarcomeres = stronger contraction.
Type I:
Structure: _____ fibre diameter, _____ motor units per muscle, _____ _____ sarcoplasmic reticulum.
Function: _____ contraction and relaxation, _____ force, _____ fatigue-resistant, _____ sensitive to recruitment.
Metabolism: _____ _____ colour, _____ myosin-ATPase activity.
Type II (FTa/FOG & FTx/FG – _____-twitch, _____-glycolytic & _____):
Structure: _____ fibre diameter, _____ motor units, SR development _____ (FTa) to _____ (FTx).
Function: _____ contraction and relaxation, _____ (FTa) to _____ (FTx) force, more _____ fatigued (FTa _____, FTx most _____), sensitivity to recruitment _____ (FTa) to _____ (FTx)
Metabolism: _____ (FTa) to _____ (FTx), myosin-ATPase activity _____ (FTa) to _____ (FTx).
Type I:
Structure: Small fibre diameter, more motor units per muscle, poorly developed sarcoplasmic reticulum.
Function: Slow contraction and relaxation, low force, highly fatigue-resistant, highly sensitive to recruitment.
Metabolism: Dark red colour, low myosin-ATPase activity.
Type II (FTa/FOG & FTx/FG – fast-twitch, oxidative-glycolytic & glycolytic):
Structure: Large fibre diameter, fewer motor units, SR development intermediate to high.
Function: Fast contraction and relaxation, intermediate to high force, more easily fatigued (FTa intermediate, FTx most fatigable), sensitivity to recruitment intermediate to high
Metabolism: Dark (FTa) to pale (FTx), myosin-ATPase activity intermediate to high.
Muscle fibre types
Type I fibres (_____-twitch): _____-resistant, good for _____, and control _____ movements
Type II fibres (_____-twitch): Fatigue _____, good for _____ or _____ movements (e.g., sprinting, lifting).
Type IIA (_____-twitch, more fatigue-_____)
Type IIX (_____-twitch, strongest but fatigues _____)
They differ in their:
_____ (size, number of mitochondria, myoglobin, etc.)
_____ (speed of contraction, force)
_____ (how they make ATP—using oxygen or not)
During weak/moderate exercise, the body recruits Type _____ fibres because they are _____ to fatigue. As intensity increases, Type _____ fibres are recruited.
Muscle fibre types
Type I fibres (slow-twitch): Fatigue-resistant, good for endurance, and control fine movements
Type II fibres (fast-twitch): Fatigue faster, good for quick or strong movements (e.g., sprinting, lifting).
Type IIA (fast-twitch, more fatigue-resistant)
Type IIX (fast-twitch, strongest but fatigues fastest)
They differ in their:
Structure (size, number of mitochondria, myoglobin, etc.)
Function (speed of contraction, force)
Metabolism (how they make ATP—using oxygen or not)
During weak/moderate exercise, the body recruits Type I fibres because they are resistant to fatigue. As intensity increases, Type II fibres are recruited.
Motor units:
1 _____ _____ + all the _____ _____ it controls = Motor unit
When a motor neuron is activated, all fibres in its motor unit contract _____.
Different muscles have motor units of different _____ depending on their _____.
When a motor neuron is activated, it sends a signal down the _____, which _____ and connects to multiple _____ at their _____ _____.
Fewer fibres per motor unit = _____ control of _____ movements
More fibres per motor unit = _____ control of _____ movements
Asynchronous recruitment:
“Asynchronous” = not all motor units are _____ at the _____ time.
The nervous system _____ between different motor units during sustained activity to prevent _____.
Motor units:
1 motor neuron + all the muscle fibres it controls = Motor unit
When a motor neuron is activated, all fibres in its motor unit contract together.
Different muscles have motor units of different sizes depending on their function.
When a motor neuron is activated, it sends a signal down the axon, which branches and connects to multiple fibres at their neuromuscular junctions.
Fewer fibres per motor unit = greater control of fine movements
More fibres per motor unit = less control of fine movements
Asynchronous recruitment:
“Asynchronous” = not all motor units are active at the same time.
The nervous system switches between different motor units during sustained activity to prevent fatigue.
Muscle twitch:
A response of a muscle fibre to an _____ _____, which includes the _____ _____, _____, and _____.
Contraction time:
Time from the start of _____ _____ to _____ _____.
How fast the muscle _____ once the _____-_____ start _____.
Relaxation time:
Time from _____ _____ back down to _____ (muscle _____).
It depends on how quickly _____ is pumped back into the _____ _____.
Skeletal muscle mechanics: Contraction of the whole muscle:
An _____ _____ in a muscle fibre only causes a small, brief contraction called a _____ (too small to move a muscle)
Muscles can _____ the _____ they _____ by controlling the number of _____ _____ and the _____ of each _____ (how strongly each fibre contracts, e.g., by firing more rapidly - adds up the action potential)
Muscle twitch:
A response of a muscle fibre to an action potential, which includes the latent period, contraction, and relaxation.
Contraction time:
Time from the start of tension development to peak tension.
How fast the muscle contracts once the cross-bridges start pulling.
Relaxation time:
Time from peak tension back down to baseline (muscle relaxes).
It depends on how quickly calcium is pumped back into the sarcoplasmic reticulum.
Skeletal muscle mechanics: Contraction of the whole muscle:
An action potential in a muscle fibre only causes a small, brief contraction called a twitch (too small to move a muscle)
Muscles can change the force they generate by controlling the number of fibres activated and the tension of each fibre (how strongly each fibre contracts, e.g., by firing more rapidly - adds up the action potential)
Skeletal muscle contractile activity:
An action potential lasts _____-_____ msec.
Muscle contraction begins after the action potential has _____. The mechanical part of a muscle twitch (_____ + _____ + _____) lasts about _____ms
Latent period:
The _____ between the start of the _____ _____ and the start of _____ is called the _____ _____.
Includes the release of _____ from the _____ _____ to bind to _____, which moves _____ off _____ so _____ heads _____ and begin cycling
Skeletal muscle contractile activity:
An action potential lasts 1-2 msec.
Muscle contraction begins after the action potential has ended. The mechanical part of a muscle twitch (tension + contraction + relaxation) lasts about 100ms
Latent period:
The gap between the start of the electrical event and the start of contraction is called the latent period.
Includes the release of calcium from the sarcoplasmic reticulum to bind to Troponin, which moves tropomyosin off actin so myosin heads attach and begin cycling
