Every time we exercise, our muscles contract and lengthen from short to long positions and back.
There are three types of muscle contraction:
Concentric – the shortening of a muscle
Eccentric – the lengthening of a muscle
Isometric – when a muscle is tense but there’s no movement in the joint action
During a training session, a personal trainer will balance a client’s exercise programme to vary the range of movement and the contraction of muscles, to give an all-round work out.
How does this relate to specific exercises?
The position of the body during movement will affect the internal stress on the muscle fibres.
Example 1: Leg extension
At the start of a leg extension, the muscle will be in the ‘long’ position, which is the outer range of motion. As the client moves through the exercise, the muscle will move through the ‘middle’ position until it reaches the ‘short’ position, the inner range of motion.
Example 2: Leg press
When carrying out a leg press, the client will follow a movement that targets a range of motion within the outer and middle length of the muscle. As this exercise does not result in the knee fully extended to give high tension within the quad, the muscle does not reach the short contraction range.
Example 3: Bicep curl
An exercise like the bicep curl takes the client through initial movement, holding the position and then returning through the same path. This means that the muscle will experience a concentric, an isometric and an eccentric contraction. As the client brings their arm up for the bicep curl, there is a concentric contraction, where the bicep muscle becomes shortened. The next stage is holding the arm in position for an isometric contraction. Finally, as the client lowers their arm, the bicep muscle lengthens into an eccentric contraction.
What are agonists and antagonists?
Agonists and antagonists are muscles that work in pairs, with one shortening as the other lengthens.
Again using the bicep curl as an example, the bicep muscle will contract as the arm is lifted, but this action can only occur because the antagonist muscle, in this case the triceps, relaxes and lengthens. In this first stage of the exercise, the bicep is working concentrically as the agonist, while the triceps is operating eccentrically as the antagonist. This process is known as reciprocal inhibition.
There is more power in a muscle that is lengthening than one that is shortening, which is one of the reasons why it’s easier to lower a weight than to raise it.
How does muscular contraction impact metabolic rate?
An exercise that focuses more on eccentric contraction in the outer range of motion is generally less metabolic than one that requires a concentric contraction through the inner range of motion.
Because of this, it can help a client if a personal trainer orders their workout with movements that require short muscular contractions at the start of the session, followed by those that require eccentric movements towards the end of the session, as they will be easier to achieve than concentric movements when the client is fatigued.
Example 1: leg extension and leg press
In this series of exercises, the leg extension would be carried out first, as it targets the inner range of motion of the quad. The leg press would follow as it works the middle and outer range of motion of the quad.
Example 2: bent over row, pull down and deadlift
All three exercises target the latissimus dorsi muscle, but the best option is to start with the bent over row and/or the pull down, both of which target the lats concentrically in a short range of motion. They would then be followed later in the work out by a deadlift, which focuses on the lats in an isometric or lengthened position.
Carrying out exercises in this order can increase the effectiveness of training and reduce DOMS (delayed onset of muscle soreness).