Dominic Stone
Measuring muscle length is an important tool for understanding the mechanics and energetics of locomotion and informing models of motor control. Muscle length testing involves elongating the muscle in the direction opposite of its action while assessing its resistance to passive lengthening. There are several methods for measuring muscle length, including sonomicrometry, fluoromicrometry, magnetomicrometry, and ultrasound. The most suitable method depends on the specific muscle being tested and the goals of the test. For example, to measure the length of the flexor digitorum superficialis muscle, the patient is positioned sitting with their forearm in pronation on a table, and the wrist is passively extended. This measurement can be taken using a universal goniometer, an inclinometer, or a linear form of measurement such as a tape measure.
| Characteristics | Values |
|---|---|
| Measurement tools | Universal goniometer, Inclinometer, Tape measure, Magnetic resonance imaging (MRI), Sonomicrometry, Fluoromicrometry, Magnetomicrometry, Ultrasound, DXA scan, InBody device |
| Muscle length testing | Elongating the muscle in the direction opposite of its action while assessing its resistance to passive lengthening |
| Patient position | Sitting with their forearm in pronation on a table, supine |
| Muscle movement | All but one of the joints are positioned with the tested muscle in a lengthened position |
| Muscle resistance | 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 |
| Patient pain | Muscle length testing should be performed when the patient is not in acute pain to avoid pain inhibition and muscle guarding |
| Muscle location | Lower limb, multi-joint muscles, hip, knee joint, finger flexors |
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What You'll Learn
Direct measurement methods
Sonomicrometry
This technique involves using sound waves to measure muscle length. It offers a non-invasive way to assess muscle length and function.
Fluoromicrometry
Fluoromicrometry is a method that uses fluorescent markers to track muscle length changes. It is a valuable tool for understanding muscle mechanics and movement.
Magnetomicrometry
This technique, developed more recently, involves tracking the locations of implanted magnetic spheres using an array of magnetometers. It provides accurate and low-latency measurements of muscle length.
Ultrasound
Ultrasound technology has become increasingly popular in biomechanics due to its affordability, portability, and ability to measure dynamic changes in muscle architecture during contractions. It was first used in the mid-1990s to assess muscle-tendon architecture in humans, both at rest and during contraction.
Goniometry
Goniometry is a method that uses a goniometer to measure the range of motion of a joint. It is particularly useful for assessing muscle length in the lower limb.
Inclinometry
Inclinometry, or clinometry, measures the angles of slope, elevation, or depression of an object. It is another tool used to assess muscle length.
Manual Muscle Testing
This involves manually testing the length of a muscle by positioning the patient and moving the relevant joints to assess the muscle's length and flexibility. For example, when measuring the length of the flexor digitorum superficialis, the patient is positioned sitting with their forearm in pronation on a table, and the clinician moves the elbow, wrist, and finger joints into extension to determine the length of the muscle.
Clinical Assessment Tools
Clinicians use specific tests, such as the modified Thomas test, to assess muscle length and identify muscle imbalances. These tests involve specific patient positioning and movements to evaluate particular muscles.
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Elongating muscle fibres
Muscle length can be measured using a few different methods, including sonomicrometry, fluoromicrometry, magnetomicrometry, and ultrasound. The universal goniometer, inclinometer, and linear forms of measurement, such as a tape measure, are also used.
Muscles can only contract and release, and they cannot grow longer or expand in length. However, if muscles are held in a shortened position, stretching and a full range of motion can help release tight muscles, allowing the muscle tissue to reach its full natural length.
Pilates, for example, can help release tight muscles and allow them to reach their full natural length. It involves slow, controlled exercises that provide a full range of motion without putting the body under heavy loads or explosive movements. This type of exercise taps into the slow-twitch muscle fibres, which are thinner and longer than fast-twitch fibres. Slow-twitch fibres are endurance muscles, which means they don't have much power capacity, but they can sustain activity for a long time.
To elongate muscle fibres, a hypertrophic stimulus is required. This can cause an increase in the diameter of singly innervated muscles, such as the soleus and gracilis posterior, or the elongation of intrafascicularly terminating fibres in multiply innervated muscles like the gracilis posterior. This elongation increases the overall diameter of the muscle. To facilitate this process, the relationship between neighbouring fibres must change, involving the breaking of old connections and the formation of new junctions.
To achieve significant muscle growth, or hypertrophy, exercises that create metabolic stress and a moderate degree of muscle tension are required. Concentric (shortening) movements performed at fast-to-moderate speeds for 1-3 seconds, followed by eccentric (elongating) movements at slower speeds (2-4 seconds), are highly effective. For example, in a bicep curl, raising the weight to your shoulder is a concentric movement, while lowering it back down is eccentric.
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Passive insufficiency
There are various methods and tools for measuring muscle length. The most accurate way to calculate muscle mass percentage is to use magnetic resonance imaging (MRI). An MRI uses strong magnets to take an image of your muscles. When you’re placed in an MRI machine, the magnetic field briefly rearranges your body’s hydrogen atoms. This releases energy, which the machine uses to determine your muscle mass. However, this method is very expensive. Other methods include sonomicrometry, fluoromicrometry, magnetomicrometry, and ultrasound. Tools used to measure muscle length include the universal goniometer and its variants, the inclinometer and its variants, and linear forms of measurement such as a tape measure.
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Muscle tightness
There are several treatments for muscle stiffness, including home remedies and medical treatments. Home remedies include stretching, exercising more frequently, improving posture, and increasing hydration. Alternating hot and cold therapy, massages, and over-the-counter pain relievers can also help relieve muscle stiffness.
If home remedies do not provide relief, a healthcare provider may recommend physical therapy or additional medical treatments. A physical therapist can prescribe exercises to increase mobility and strength and reduce pain. In some cases, muscle stiffness may be a symptom of an underlying infection or chronic condition, so it is important to seek medical advice if stiffness is prolonged or frequent.
To prevent muscle stiffness, it is essential to warm up before exercising and to gradually increase the intensity and duration of workouts. Maintaining proper hydration and electrolyte balance is also crucial, as imbalances can contribute to muscle stiffness. Additionally, ensuring adequate recovery time between workouts can help prevent overuse of muscles and reduce the risk of muscle stiffness.
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In vivo measurement
One approach to measuring muscle length in vivo is through the use of myographs, which are devices designed to measure muscle contraction. Current myograph devices have limitations in accurately determining the optimum muscle length due to their variable reproducibility and inability to maintain precise conditions during examinations. However, recent advancements have led to the development of a new myograph with three key elements: an element for adjusting the axle and the physiological axis of muscle contraction; an element to accurately position and reposition the muscle extremity; and an element for progressive pre-stretching and isometric locking of the target muscle. This new myograph enables the examination of individual in vivo muscles at specific pre-stretched positions, maintaining constant muscle-length conditions.
Another method for in vivo muscle length measurement involves the use of needle electrode placement. This technique requires stability in electrode placement to ensure consistent and reliable data. Taping the leads to the motor prior to insertion helps minimize electrode movement during contraction. Additionally, proper hair removal is vital for accurate needle electrode insertion and visualizing the knee joint to ensure correct clamping.
Aurora Scientific's 1300A/1305A Whole Animal Systems provide a valuable tool for characterizing complete muscle function using three powerful assays. This system allows researchers to measure ankle torsion of the animal's hind limb and perform a range of functional assays to test different aspects of muscle function. The in vivo assay is less invasive and offers a low barrier to entry, not requiring complicated surgery or special handling of the animal.
Furthermore, recent advancements in technology have expanded the methods available for in vivo muscle length measurement. Videofluoroscopy, for instance, utilizes implanted radiopaque markers that can be tracked in three dimensions to measure muscle length changes. Additionally, magnetomicrometry tracks the locations of implanted magnetic spheres using an array of magnetometers to determine muscle length.
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Frequently asked questions
Muscle length testing involves elongating the muscle in the direction opposite of its action while assessing its resistance to passive lengthening. One of the bony attachments of the muscle should be in a fixed position while the other is moved in the direction of lengthening the muscle.
There are several tools that can be used to measure muscle length, including the universal goniometer, the inclinometer, and linear forms of measurement such as a tape measure. Other methods include sonomicrometry, fluoromicrometry, magnetomicrometry, and ultrasound.
To measure the length of a multi-joint muscle, all but one of the joints are positioned with the tested muscle in a lengthened position. Then, the remaining joint crossed by the muscle is moved passively until the muscle is on a full stretch and prevents further motion at the joint. The final position of this joint is then assessed to determine muscle length.
To measure the length of the flexor digitorum superficialis, position the patient in a sitting position with their forearm in pronation on a table and their hand resting over the edge of the table. Then, move the elbow and finger joints into extension and then passively extend the wrist. The amount of wrist extension will determine the length of the flexor digitorum superficialis.
