Force Couple: Although we usually think of a joint's movement as being the action of one muscle, muscles are actually recruited as groups. Each muscle, because of its different attachment points (origins and insertions) and angle of pull, tends to pull the bone in a different direction. These divergent pulls, collectively, culminate in a certain joint action.
A force couple relationship can be defined as a pair of muscle forces that act together on a joint to produce rotation, and these forces may actually exert pulls in opposite directions. These muscles may be synergistic pairs, consisting of prime movers and groups of stabilizers, for instance, or agonist/antagonist pairs. Force couple, then, is actually another way of referring to muscle synergists or a synergistic action. For more on synergists see muscle roles.
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Force-velocity Relationship: A propery of skeletal muscle contraction in which the force capability of a given muscle contraction is dependent on the velocity of shortening of the muscle.
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Every once in a while you will hear someone calling the squat a simultaneous lift. You'll even hear people calling the deadlift a sequential lift. What does this mean, and is it correct?
Well, these terms come from the description and measurement of the coordination of human movement, a branch of biomechanics called kinematics. Movements, in this context, are looked at in terms of the movement of body segments, and this means also the action of the body's joints. You may have never given it a second thought, but during some movements the joints act "all at once" or simultaneously and in others they act one after the other in a sequence. Most movements, however, are not really so black and white and fall in a continuum between the two. Sometimes, for instance, a movement may look to be simultaneous, but upon close observation be sequential.
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Training for maximal strength is essentially training to exert maximum muscular force. So what is force? The easiest way to think of a force is as a simple push or pull. When you push or pull on a barbell or other implement you are exerting a force. The pull of the Earth's gravity on an object is a force. Friction is a force. To be more precise, then, a force is something that causes or tends to cause a change in the motion or the shape of an object.
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Speed-Strength: Speed training where there is relatively more contribution from acceleration than force. Speed-strength training uses lower intensities than power training or strength-speed training and has its greatest effect on rate of force development rather than maximum strength
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