Muscle Contraction and Relaxation Flashcards
Isometric
There is no change in the joint angle or length of the muscle while the muscle contracts (e.g. clenching a fist).
Concentric
The muscle shortens while contracting; the joint MOVES (e.g., abdominal crunch up-phase). It is the harder phase of a repetition.
Eccentric
The muscle lengthens while contracting; the joint MOVES (e.g., abdominal crunch down-phase). It is the easier phase of the repetition.
Passive Shortening of Muscle
The muscle shortens with no contraction; the joint moves (e.g. a physiotherapist moves your elbow into flexion and the biceps muscle shortens, yet it is relaxed. Or, the triceps muscle shortens and relaxes during the down-phase of a biceps dumbbell arm curl.)
Passive Lengthening of Muscle
The muscle lengthens with no contraction; joint moves (e.g. a physiotherapist moves your elbow into extension and the biceps muscle lengthens yet is relaxed. Or, the biceps muscle relaxes and lengthens during the up-phase of a triceps kick-back exercise.)
Agonist
The primary mover muscle working at a joint during movement. It is the muscle one is trying to strengthen during a specific resistance training exercise (e.g. the biceps during a dumbbell arm curl).
Antagonist
The opposite muscle to the agonist of the same joint (e.g. triceps during a biceps arm curl). It relaxes while the agonist is contracting concentrically.
Synergist
A muscle that assists the agonist to perform a joint movement (e.g. anterior deltoid helps the pectoralis major perform a bench press). It also works to help control the movement at the joint so that the movement is stable and smooth.
Co-contractors
The agonist and antagonist contracting at the same time to stabilize a joint (e.g. pectoralis major and the latissimus dorsi during a dumbbell arm curl).
Stabilizer
A muscle that contracts and, although produces little to no movement, helps maintain a certain posture or joint angle when performing an exercise. For example:
o The abdominals stabilize the spine during a push-up.
o The erector spinae stabilize the spine during a bent-over row.
o The rotator cuff stabilizes the shoulder joint during an overhead shoulder press
A Motor Unit
A motor unit is defined as a motor neuron (a team coach) and all the muscle fibres (the team players) it innervates (excites/contracts).
Length-Tension Relationship
The amount of force a muscle can produce depends on how shortened or stretched it is at the time of the contraction. The length-tension relationship states that a fully shortened muscle or fully stretched muscle will produce less force than when the muscle is in its mid-range.
