Assessing Muscle Length

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Introduction

Muscle length refers to the ability of a muscle crossing a joint to lengthen, allowing one or more joints to move through the full available range of motion. The lengthening of a muscle fiber be gins with the sarcomere, the basic unit of contraction in the muscle fiber. As the sarcomere contracts, the area of overlap between the thick and thin myofilaments increases. As it lengthens, this area of overlap decreases, allowing the muscle fiber to elongate. Maximal muscle length therefore is the greatest extensibility of the muscle-tendon junction.

Muscle Length Tests are are performed to determine whether the range of muscle length is normal, limited, or excessive and is used to identify if these changes in muscle extensibility may be contributing to movement impairment and/or symptoms. Muscle length testing consist of movements that increase the distance between origin and insertion, thereby lengthening muscles in directions opposite to the muscles actions, while assessing its resistance to passive lengthening.

Precise testing requires that one of the bony attachments of the muscle be in a fixed position while the other bony attachment is moved passively in the direction of lengthening the muscle. This means that to assess and measure the length of a muscle we need to passively stretch or lengthen the muscle across the joint or joints crossed by that muscle. For the best accuracy and precision, muscle length testing should be performed when the patient is not in acute pain in order to avoid pain inhibition and muscle guarding.

According to Kendall et al, for muscles that pass over one joint only, the range of motion and range of muscle length will measure the same but for muscles that pass over two or more joints, the normal range of the muscle will be less than the total range of motion of the joints over which the muscle passes. As such if the goal is to measure muscle length over two or more joints then it is important that the muscle be placed in an elongated position across all joints affected.

Factors Effecting Muscle Length

• Age
• Sex

Measurement Methods

Muscle length can be measured through two methods,

1. Composite Method, which measures the movement across more than one muscle or joint. e.g. sit and reach test, or apleys test. While these tests are commonly used research suggests that these composite tests do not provide accurate measurements of muscle length as they assess combinations of movements across several joints involving several muscles.
2. Alternative method is direct measurement between adjacent segments.

Measuring Muscle Length

Measurement of muscle length include can be competed through use of one or more of the following tools.

1. Goniometer; A goniometer is a device that measure an angle or allow an object to be rotated into a specific angular position.
2. Inclinometer; An inclinometer or clinometer is an instrument used for measuring angles of slope, elevation, or depression of an object with respect to gravity's direction
3. Tape Measure;

Principles of Measurement

Positioning

Ensure maximal lengthening of the muscle from origin to insertion.

One-Joint Muscle

To assess and measure the length of a muscle that crosses one joint, the joint crossed by the muscle is positioned so that the muscle is lengthened across the joint. The position of the joint is measured and this represents an indirect measure of the muscle length. The end feel will be firm.

Two-Joint Muscle

To assess and measure the length of a two-joint muscle, position one of the joints crossed by the muscle so as to lengthen the muscle across the joint. Then move the second joint through a passive range of motion until the muscle is placed on full stretch and prevents further joint motion. Assess and measure the final position of the second joint; the joint position represents an indirect measure of the muscle length.

Multi-joint Muscle

To assess and measure the length of a multi-joint muscle, position all but one of the joints crossed by the muscle so that the muscle is lengthened across the joints. Then move the one remaining joint crossed by the muscle through a passive range of motion, until the muscle is on full stretch and prevents further motion at the joint. Assess and measure the final position of the joint; the joint position represents an indirect measure of the muscle length.

Stabilisation

Firmly stabilise one end of the muscle, typically this is at the origin or proximal aspect of the muscle.

Speed of Movement

The elongation of the muscle should be performed slowly to avoid eliciting a quick stretch of the muscle spindle and subsequently inducing a twitch response and muscle contraction.

Determining End Feel

The most valuable clinical information is the muscular end feel and the location of the range of motion end feel. When the muscle is on full stretch, the end feel will be firm, and the patient will report a pulling sensation or pain in the region of the muscle.

Aligning Measurement Device

Documentation

Resources

References