S2 Lecture 2- Physiology of strength and power Flashcards
(24 cards)
What are the two components of muscle performance?
Neural activation (controller of the movement) and muscle-tendon unit force (executioner of the movement).
What typew of motor neurons coordinate our inputs?
Alpha motor neurons in the spinal cord
Describe reflexive actions:
They usually result from the activation of certain receptors in the peripheral nervous system and have a very short latency. The result of the action happens within approximately 50-100ms.
What is the stretch reflex?
The changing of length of muscle abruptly
Role of the Golgi-tendon organ?
Responds to changes in tension, and protects us from excessive forces, mainly protecting the tendons.
Explain the process of the final common pathway:
All of our signals converge onto our alpha motor neuron. If the summation results in depolarisation our muscles will be activated.
Explain innovation ratios:
The number of motor neurons attached to the muscle fibre. Muscles like the quadriceps would have a large innovation ratio. The muscles around the eye would have a very small innovation ratio (usually 1:1). Muscles used for sports usually have higher innovation ratios. Fibres are typically activated in groups not individually.
What is the size principal
Increasing forces increases the number of action potentials generated. Those action potentials generated later also tend to be greater.
Explain contractile properties:
Having multiple action potentials in a single motor unit close together creates a smooth summation force profile. Explosive actions allow us to generate the most motor units at once.
What is post-activation potentiation?
Performing a previous outcome will increase the output of that muscle over a short period of time. It increases performance by creating maximum contractions.
Explain the control of muscle force:
To lift something heavier we have 2 options:
1. We recruit new motor units, and more fibres are then activated.
2. We increase the rate of action potential generation in the same unit (rate coding).
Most muscles used in exercise are more similar to the biceps brachii and recruit more motor units.
What is rate coding?
The onion skin phenomenon: The unit recruited first usually has the greatest increase in discharge rate, and the last one recruited has the smallest change in discharge rate. This is because the first has the lowest threshold unit and the last has the highest threshold unit.
Motor unit vs muscle fibre:
Motor unit type, Muscle fibre type:
1. Slow-twitch=Slow-twitch, oxidative, Type 1
2. Fast-twitch, fatigue resistance= Fast-twitch, oxidative glycolytic, Type 2a
3. Fast-twitch, fatigable=Fast-twitch, glycolytic, Type 2x
Explain how muscle fibres and motor units are interlinked?
Motor units involve a motor neuron, the muscle fibre then uses that motor neuron.
Explain muscle mechanical properties using the Hill muscle model:
CE- Contractile element: The muscle fibre itself. Characterised for a specific force-length/force-velocity relationship.
SE- Serial elastic component: The elasticity of any structure that allows us to transfer force to the skeleton.
PE- Parallel elastic component: Transmitter of force to the skeleton
Explain the force-length relationship:
A short lever arm allows a reasonable torque in the whole range of motion. A longer lever arm allows a greater peak torque over a shorter range of motion. There is a somewhat parabolic relationship between sarcomere length and force percentage. The optimal length of a sarcomere is approximately 2.5-2.8 micrometres. This is where the most force in the muscle will be produced.
Explain the force-velocity relationship:
A lower required velocity means a greater force can be produced and vice versa. We are typically stronger in eccentric contractions than concentric contractions. In multi-joint actions the force-velocity relationship is linear. Maximal power will be a result of about half the maximal velocity and half the maximal force.
Explain why a warm-up is important:
Peak power comes at about a third of maximum velocity at 25.6 degrees celsius compared to maximal power at 37.1 degrees celsius.
What are the 2 types of input to the CNS?
Reflexive or voluntary
What is a motor unit?
The basic functional property of the neuromuscular system that transforms the activation signal and transduces it into contractile muscle activity.
Describe how a single action potential leads to a motor unit twitch:
Most contractions are achieved by a series of action potentials that result in overlapping twitches which summate to produce a tetanus.
How are mechanical muscle properties characterised
Distinct force-length and force-velocity relationships at the level of single fibre and whole muscle; these are different from relationships observed during “real-life” joint actions.
What is the stretch-shortening cycle?
A combination of eccentric, isometric and concentric contractions.
How is a force produced by a muscle influenced?
Contractile properties of muscle fibres, the arrangement of these fibres within the muscle, and the attachment sites of these muscles.
