Isometric, concentric, and eccentric contractions refer to different ways muscles generate force; each type plays a distinct role in movement and exercise.
Concentric Muscle Contraction
During a concentric contraction, a muscle shortens while generating force, typically when it overcomes an external resistance. This type of contraction is key for movements that involve lifting or pulling.
For example, when performing a bicep curl, the biceps brachii muscle contracts concentrically as it shortens to lift the weight towards your shoulder. This shortening of the muscle fibres results in the arm flexing at the elbow.
The Squat illustration above demonstrates that the concentric phase of the lift involves standing up. The concentric contraction happens in the quadriceps as you ascend and the quadriceps shorten.
Concentric contractions are crucial for developing strength and power, as they are involved in the positive phase of any movement. Concentric contractions occur when muscles shorten while contracting to move, making them essential for various physical activities, from everyday tasks to athletic performance.
Eccentric Muscle Contraction (Negatives)
Eccentric contractions, or eccentric muscle actions, occur when a muscle lengthens under tension. This contraction typically happens when a muscle actively resists a force while elongating. Eccentric contractions are crucial for various movements and play a significant role in muscle development, injury prevention, and rehabilitation.
From the illustration below, eccentric squats occur when a lifter squats down, causing the quadriceps and gluteus maximus muscles to lengthen and contract eccentrically during the descent phase of the movement. The illustration below shows the eccentric portion of a bicep curl, also known as Negative Training, whereby the focus is on lowering the weight to a 3-6 second count, putting your biceps under more tension and thus influencing muscle growth.
In practical terms, eccentric contractions are often observed during activities such as lowering weights or descending. Research has shown that eccentric-focused Resistance training can have favourable strength and hypertrophic adaptions. However, the research is still mixed; I always recommend bodybuilders implement Eccentric Training in their programs in phases, maybe when adaptions have plateaued, or training has stagnated and got boring, and something new is needed. But I don't recommend this as a form of training to perform consistently week-in-week-out as research is still limited and conflicting on its benefits.
Isometric Muscle Contraction (Holds)
Isometric contraction is a muscle contraction that generates tension without changing its length; it does not shorten or lengthen. During an isometric contraction, the muscle fibres engage and produce force, but there is no visible movement of the joint or the muscle itself. This occurs because the resistance or load is constant, preventing the muscle from shortening or lengthening.
Isometric contractions are commonly utilised in various exercises and physical activities. For example, when you hold a weight in a fixed position, such as during a plank or wall sit, your muscles contract isometrically to maintain that position. These contractions are crucial for building muscle endurance and stability. In bodybuilding literature, isometric contractions are referred to as static Repetitions (Static reps), Isometric holds, or Static holds and are when the lifter keeps a muscle flexed and contracted in a fixed position for an extended period that can range from 7-12 seconds or more depending on the exercise.
Below, one can see that the isometric contraction for the squat is at the bottom of the lift, where there is no movement at the joint angle. In addition, one can see the illustration of an Isometric Hammer Curl Hold, whereby the elbow is bent at 90 degrees flexion, the elbow joint is fixed and not moving, and the muscle is not shortening or lengthening.
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