Final answer:
When the force exerted by a muscle is greater than the opposing load, without producing movement, it is called an isometric contraction. This type of muscle contraction is distinguished from isotonic contractions, where muscle length changes as it moves a load either by shortening (concentric) or by lengthening under tension (eccentric).
Step-by-step explanation:
When the load is greater than the force of the muscle, we refer to muscle contraction as isometric contraction. Muscle contractions are fundamentally of two types, which are isotonic contractions and isometric contractions. Isometric contractions occur when the muscle exerts force without changing length, effectively causing no movement of the load despite muscle tension.
In contrast, isotonic contractions involve the shortening of the muscle and can be further categorized into concentric and eccentric contractions. Concentric contractions happen when the muscle shortens as it exerts force, moving a load effectively as in lifting a weight, while eccentric contractions take place when the muscle lengthens under tension, for instance, when lowering a weight.
A muscle contraction is triggered by a nervous impulse leading to an increase in muscle tension or a decrease in muscle length. The sliding filament model describes the process of muscle contraction, where action potentials initiate the cross-bridge cycling between actin and myosin within the muscle fibers, powered by ATP.
The resulting contraction depends on the number and timing of motor unit activations controlled by the nervous system, which can alternatively allow variation in muscle tension or produce tetanus when successive stimuli result in a continuous contraction.