For individuals starting to lift weights, motor units are important for muscle movement. Can building more motor units help build strength and maintain muscle mass?
Motor Units
Motor units control the skeletal muscles and are the force behind every body movement. (C J. Heckman, Roger M. Enoka 2012)
This includes voluntary movements like lifting weights and involuntary movements like breathing. When lifting objects and weights, the body adapts to motor unit needs, meaning that individuals must consistently increase the weight to progress.
Lifting weights regularly trains the body to generate more motor units and force.
General guidelines recommend lifting weights for all muscle groups two to three non-consecutive days a week.
Consistency helps maintain muscle mass.
Regular progression increases the risk of plateauing.
What They Are
Exercise increases the body’s muscle strength, while sedentariness and inactivity weaken them. A motor unit is a single nerve cell/neuron that supplies the nerves to innervate a group of skeletal muscles. The neuron receives signals from the brain that stimulate all the muscle fibers in that particular motor unit to generate movement.
Muscles comprise different fiber types.
They are attached to the bones with connective tissue, which is stronger than the muscle.
Multiple motor units are dispersed throughout the muscle.
The motor units help ensure muscle contraction force is evenly spread throughout the muscle.
Motor units are different sizes and operate differently depending on where and what they do.
Small motor units might only innervate five or ten fibers. For example, to blink or sniff.
Large motor units can comprise hundreds of muscle fibers for swinging or jumping movements.
How They Work
The number of units activated depends on the task. Stronger muscle contractions require more. However, fewer units are needed to accomplish the movement for individuals expending less effort.
Contraction
Once a unit receives a signal from the brain, the muscle fibers contract simultaneously.
The force generated depends on how many units are required to accomplish the task. (Purves D. et al., 2001)
For example, picking up small objects like a pen and paper requires only a few units to generate the force needed.
If picking up a heavy barbell, the body needs more units because more force is needed to lift the heavier load.
The body can generate more force with stronger muscles.
This happens when lifting weights on a regular basis and overloading the muscles with more weight than they can handle.
This process is known as adaptation.
Adaptation
The purpose of lifting weights is to challenge the muscles so they adapt to the new challenge and grow in strength and mass. Motor units are a major part of the adaptation process. (Dr. Erin Nitschke. American Council on Exercise. 2017)
As individuals continue working out, their ability to generate more force increases and units activate more rapidly.
This makes movements more efficient.
Individuals can increase motor unit recruitment by consistently increasing the weight challenge to their muscles.
The development creates movement memory.
A relationship between the brain, muscles, and motor units is established even if the individual stops working out. The pathways are still there no matter how long the individual takes off.
When returning to training, the body will remember how to ride a bike, do a bicep curl, or squat.
However, the muscles will not have the same strength as the strength needs to be built back along with endurance that may have been lost.
It is the movement memory that remains.
Military Training and Chiropractic Care: Maximizing Performance
References
Heckman, C. J., & Enoka, R. M. (2012). Motor unit. Comprehensive Physiology, 2(4), 2629–2682. doi.org/10.1002/cphy.c100087
Purves D, Augustine GJ, Fitzpatrick D, et al., editors. (2001). Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. The Motor Unit. Available from: www.ncbi.nlm.nih.gov/books/NBK10874/
Nerves control muscle fibers. Muscle twitching is an involuntary contraction of the muscle fibers. When individuals play sports/work out vigorously or for a long time, they may experience muscle twitching and can often see and/or feel the twitches happening. The most worked-out muscles are likely to twitch, which includes the biceps, thighs, and calves, but twitches can occur in any muscle. Chiropractic care, massage therapy, and functional medicine can help relax the muscles, improve circulation, restore function, and train individuals to prevent future episodes.
Muscle Twitching
A muscle twitch often occurs after intense physical activity or a hard workout because the muscle or muscles have been overworked, and there is hyper-excitability of the nerve/s that makes the muscle/s continue to contract.
A muscle twitch that can be seen is called fasciculation.
A muscle twitch that cannot be seen is called fibrillation.
If there is pain or the twitching is prolonged, it is a muscle spasm.
Causes
The most common causes include the following:
Intense exercise and rigorous physical activity build up lactic acid in the muscles.
Dehydration is a very common factor for shaky muscles.
Vitamin D and calcium deficiencies could cause muscle spasms in the hand, calves, and eyelids.
Using caffeinated products to increase physical performance.
Not enough or a lack of healthy sleep.
Anxiety or stress.
Certain medications like estrogen and corticosteroids.
Nicotine and tobacco use.
Physical Activity/Exercise
Intense exercise and physical activity can cause muscle fatigue.
Muscle fatigue triggers twitching and cramping in overworked muscle fibers.
Electrolytes play a role in muscle contraction.
Electrolyte loss and imbalances within muscle fibers through sweating can lead to twitching.
Dehydration
Muscle mass comprises 75% water.
Water carries nutrients and minerals to muscles to support function.
Not being properly hydrated can cause twitching and cramping.
Vitamin D Deficiency
Nerves need vitamin D to relay messages to and from the brain to the body’s muscles.
A vitamin D deficiency can cause muscle weakness and twitching.
Lack of sleep can affect neurotransmitter function.
A common site of fasciculation tiredness occurs in the eyelids.
Anxiety and Stress
Experiencing psychological stress or high anxiety levels can cause excess muscle tension.
This can lead to muscle twitching.
Muscle fasciculation caused by stress can occur anywhere in the body.
Certain Medications
Certain medications can lead to involuntary muscle twitching.
The reaction can be a side effect due to interactions with other medications.
Individuals should discuss side effects and medication interactions with their doctor when taking a new medication.
Chiropractic Care
Chiropractors are experts on the musculoskeletal system and have many techniques to treat muscle fasciculation and spasms. It often depends on the cause/s, and specific treatment varies on a case-by-case basis. Common chiropractic treatments include:
Massage therapy
Heat and ice therapy
Manual manipulation
Joint adjustments
Ultrasound
Stretches to keep the muscles flexible
Exercises to strengthen the muscles
Nutritional recommendations
Fasciculation
References
Bergeron, Michael F.. Muscle Cramps during Exercise-Is It Fatigue or Electrolyte Deficit?. Current Sports Medicine Reports July 2008 – Volume 7 – Issue 4 – p S50-S55 doi: 10.1249/JSR.0b013e31817f476a
Gragossian A, Bashir K, Friede R. Hypomagnesemia. [Updated 2022 May 15]. In: StatPearls [Internet]. Treasure Island (F.L.): StatPearls Publishing; 2022 Jan-. Available from: www.ncbi.nlm.nih.gov/books/NBK500003/
Küçükali, Cem Ismail, et al. “Peripheral nerve hyperexcitability syndromes.” Reviews in the neurosciences vol. 26,2 (2015): 239-51. doi:10.1515/revneuro-2014-0066
Maughan, Ronald J, and Susan M Shirreffs. “Muscle Cramping During Exercise: Causes, Solutions, and Questions Remaining.” Sports medicine (Auckland, N.Z.) vol. 49, Suppl 2 (2019): 115-124. doi:10.1007/s40279-019-01162-1
Miller, Kevin C et al. “Exercise-associated muscle cramps: causes, treatment, and prevention.” Sports health vol. 2,4 (2010): 279-83. doi:10.1177/1941738109357299
Riebl, Shaun K, and Brenda M Davy. “The Hydration Equation: Update on Water Balance and Cognitive Performance.” ACSM’s health & fitness journal vol. 17,6 (2013): 21-28. doi:10.1249/FIT.0b013e3182a9570f
Muscle knots are common and can occur anywhere on the body. They can cause aching and pain in the muscles and joints. When examining a muscle knot also known as myofascial trigger points, it can feel swollen, tense, or like a bump. A particular area where these knots present is in the low back. This happens from excessive wear-and-tear on the lower spine from work, school, daily tasks, and chores. This causes the muscle fibers to tear, and with restricted or no time to rest the area and let it heal properly leads to the fibers bunching/clumping together forming a painful knot.
Muscle Knots In The Lower Back
A muscle knot in the lower back causes aching, soreness, and full-on pain. They tighten and contract even when the muscle is resting. The affected area often becomes inflamed or swollen causing pain and aches to radiate/spread to the gluteal muscles, as well.
Development
These knots develop when the tissue fibers pull apart and bunch up together. They start to stick together and with time the area becomes thicker. This results in the muscle knot. They can be caused by:
Stress
Tension
Poor posture
Muscle overuse
Muscle strain
Sedentary habits
Body dehydration and an unhealthy diet can also contribute to muscle knots. They look like a small bump under the skin. The bump can be red and is usually tender/sore when touched. However, not all muscle knots are visible, but when touched there is soreness and/or pain.
Do They Go Away?
They can go away on their own, but this comes from proper rest and recovery time. However, muscle knots should not be ignored, as even the smallest knot can compress surrounding nerves and muscle tissues. This can cause irritation and weakness. Larger muscle knots could cause movement/mobility issues.
Therapies
Stretching
Stretching will help stretch out and release tight muscle knots. Stretching loosens the muscle fibers and prevents them from becoming attached. Stretches to release a muscle knot include:
Start with these simple stretches/exercises and slowly work up to more vigorous ones.
Chiropractic Care
Chiropractic care can break down muscle knots through various adjustments. They are experts on the musculoskeletal system and understand where the problem is occurring along with the connected muscles.
A chiropractor will palpate the spot where the most pain presents and the surrounding area.
They will begin with a soft massage. This warms up the area getting the blood circulating. The blood circulation helps prevent pain making the adjustment/s far more effective.
Then pressing on nearby joints that the muscle knot is connected to breaks up the tight fibers.
Then the section/area is stretched out. This extends the fibers and prevents them from winding back into a knot.
They will recommend stretches and exercises
Therapeutic Massage
A massage helps to release tension and encourages muscle knots to loosen up and break down. A massage therapist will perform a deep tissue massage or a Swedish massage. Massage helps to release endorphins, which are the body’s natural painkiller. These calm the body and reduce pain. They will also recommend simple massages at home. These can include:
Rolling a massage ball/roller on the muscle knot
Self-massage using the fingers in circular motions on the affected area
Heat and Ice
Hot and cold therapy can calm and prevent inflammation. Heating pads are best if the area has stiffness or is painful. The heat relaxes tight muscles and increases blood flow. Cold therapy stops the swelling. If the muscle knot gets bigger or begins turning red, icing the area is recommended. Alternating between the two can eliminate symptoms and assist with quicker healing.
Body Composition
Building Functional Strength
There are exercises to improve functional strength. Functional training targets specific areas:
Then lift the outside leg up as high as possible and hold for 10 seconds
Repeat on the other side
Do 6-10 repetitions on each side
This exercise builds shoulder, arm, and hip strength. It engages the core and abdominal muscles and improves flexibility in the shoulders, back, and hips.
Disclaimer
The information herein is not intended to replace a one-on-one relationship with a qualified health care professional, licensed physician, and is not medical advice. We encourage you to make your own health care decisions based on your research and partnership with a qualified health care professional. Our information scope is limited to chiropractic, musculoskeletal, physical medicines, wellness, sensitive health issues, functional medicine articles, topics, and discussions. We provide and present clinical collaboration with specialists from a wide array of disciplines. Each specialist is governed by their professional scope of practice and their jurisdiction of licensure. We use functional health & wellness protocols to treat and support care for the musculoskeletal system’s injuries or disorders. Our videos, posts, topics, subjects, and insights cover clinical matters, issues, and topics that relate to and support, directly or indirectly, our clinical scope of practice.* Our office has made a reasonable attempt to provide supportive citations and has identified the relevant research study or studies supporting our posts. We provide copies of supporting research studies available to regulatory boards and the public upon request. We understand that we cover matters that require an additional explanation of how it may assist in a particular care plan or treatment protocol; therefore, to further discuss the subject matter above, please feel free to ask Dr. Alex Jimenez or contact us at 915-850-0900.
Dr. Alex Jimenez DC, MSACP, CCST, IFMCP*, CIFM*, CTG*
email: coach@elpasofunctionalmedicine.com
phone: 915-850-0900
Licensed in Texas & New Mexico
References
Cramer, Holger et al. “Postural awareness and its relation to pain: validation of an innovative instrument measuring awareness of body posture in patients with chronic pain.” BMC musculoskeletal disorders vol. 19,1 109. 6 Apr. 2018, doi:10.1186/s12891-018-2031-9
Malanga, Gerard A et al. “Mechanisms and efficacy of heat and cold therapies for musculoskeletal injury.” Postgraduate medicine vol. 127,1 (2015): 57-65. doi:10.1080/00325481.2015.992719
El Paso, TX. Chiropractor, Dr. Alexander Jimenez continues the discussion on the anatomy of nerve fibers, receptors, spinal tracts and brain pathway/s. As the spinal nerve nears the spinal cord, it splits into the dorsal and ventral roots. The dorsal root only contains the axons of sensory neurons. While the ventral roots contain only the axons of motor neurons. Some of the branches synapse with local neurons in the dorsal root ganglion, posterior (dorsal) horn, and even the anterior (ventral) horn, at the spine where they enter.
Other branches travel short distances up or down the spine to interact with neurons at other levels of the spinal cord. A branch can also turn into the posterior (dorsal) column white matter to connect with the brain. Spinal nerve systems that connect to the brain are contralateral, in that the right side of the body is connected to the left side of the brain and the left side of the body is connected to the right side of the brain.
Cranial nerves convey specific sense information from the head and neck directly to the brain. Whereas spinal information is contralateral, cranial nerve systems are for the most part�ipsilateral, meaning that a cranial nerve on the right side of the head is connected to the right side of the brain. Some cranial nerves contain only sensory axons. Other cranial nerves have both sensory and motor axons, including the trigeminal, facial and glossopharyngeal. General senses of somatosensation for the face travel through the trigeminal system.
PATHWAYS
THE POSTERIOR COLUMN� MEDIAL LEMNISCUS SYSTEM CONVEYS INFORMATION ABOUT TOUCH AND LIMB POSITION
POSTERIOR COLUMN MEDIAL LEMNISCAL PATHWAY
The term posterior column refers to the entire contents of a posterior funiculus, exclusive of its share of the propriospinal tract. The posterior columns consist mainly of ascending collaterals of large myelinated primary afferents carrying impulses from various kinds of mechanoreceptors (although substantial numbers of second-order fibers and unmyelinated fibers are also included). This has traditionally been considered the major pathway by which information from low-threshold cutaneous, joint, and muscle receptors reaches the cerebral cortex.
2-Minute Neuroscience: Touch & The Dorsal Columns-Medial Lemniscus
DAMAGE TO THE POSTERIOR COLUMN�MEDIAL LEMNISCUS SYSTEM CAUSES IMPAIRMENT OF PROPRIOCEPTION AND DISCRIMINATIVE TACTILE FUNCTIONS
�As might be expected from the types of afferents contained in the posterior columns, this pathway carries information important for the conscious appreciation of touch, pressure, and vibration and of joint position and movement. However, because input from cutaneous receptors also reaches the cortex by other routes, damage to the posterior columns causes impairment, but not abolition, of tactile perception. Complex discrimination tasks are more severely affected than is the simple detection of stimuli. Other functions, such as proprioception and kinesthesia, are classically considered to be totally lost after posterior column destruction. The result is a distinctive type of ataxia (incoordination of movement); the brain is unable to direct motor activity properly without sensory feedback about the current position of parts of the body. This ataxia is particularly pronounced when the patient�s eyes are closed, preventing visual compensation.�
Given the role of the posterior column, the patient should be screened for any abnormalities regarding their sense of fine touch, vibration, barognosis, graphesthesia, stereognosis, kinaesthesia, two-point discrimination and conscious proprioception:
A common way of testing for fine touch is to ask the patient to recognize common objects placed within a cloth using their touch.
Vibration sense can be tested using a low pitched C128 tuning fork placed along a bony prominence of the desired corresponding spinal level(s) to be tested.
Barognosis refers to the ability to determine the approximate weight of an object.
Graphesthesia refers to the ability to recognize writing on the skin by touch. The practitioner can draw out a letter on the patients skin as a way of testing.
Kinaesthesia refers to ones own sense of body motion (excluding equilibrium which is controlled in part by the inner ear) and is commonly tested using the subject�s ability to detect an externally imposed passive movement, or the ability to reposition a joint to a predetermined position.
Proprioception is often assessed using the Rombergs test. This examination is based on the notion that a person requires at least two of the three following senses to maintain balance while standing: proprioception; vestibular function and vision. A patient who has a defect within their proprioceptive mechanism can still maintain balance by using vestibular function and vision. In the Romberg test, the patient is stood up and asked to close their eyes. A loss of balance is interpreted as a positive Romberg sign.
THE SPINOTHALAMIC TRACT CONVEYS INFORMATION ABOUT PAIN AND TEMPERATURE
A GOOD BRAIN CAN MODULATE PAIN
SPINOTHALAMIC TRACT
Pain is a complex sensation, in that a noxious stimulus leads not only to the perception of where it occurred but also to things such as a rapid increase in level of attention, emotional reactions, autonomic responses, and a greater likelihood that the event and its circumstances will be remembered. Corresponding to this complexity, multiple pathways convey nociceptive information rostrally from the spinal cord. One of them (the spinothalamic tract) is analogous to the posterior column�medial lemniscus pathway.
SPINOTHALAMIC TRACTS
Two main parts of the Spinothalamic Tract (STT)
Lateral Spinothalamic Tract
Transmission of pain and temperature
Anterior Spinothalamic Tract
Transmission of crude touch and firm pressure
DAMAGE TO THE ANTEROLATERAL SYSTEM CAUSES DIMINUTION OF PAIN AND TEMPERATURE SENSATIONS
Examination:
Given the role of the spinothalamic tract, the patient should be screened for any abnormalities regarding their sense of touch, pain, temperature, and pressure sensation.
Screening for such abnormalities is commonly done using gentle pin pricks and cotton wool, to contrast between sharp and soft, following cutaneous sensory nerve root distributions. Hot and cold discrimination can be ascertained using the cold metal arm of a tuning fork, and a warm palm or heated object.
2 Minute Neuroscience: Pain & The Anterolateral System
HAUSER ET AL. FIBROMYALGIA, 2015
�Pain processing and its modulation: Activation of peripheral pain receptors (also called nociceptors) by noxious stimuli generates signals that travel to the dorsal horn of the spinal cord via the dorsal root ganglion. From the dorsal horn, the signals are carried along the ascending pain pathway or the spinothalamic tract to the thalamus and the cortex. Pain can be controlled by nociception- inhibiting and nociception-facilitating neurons. Descending signals originating in the supraspinal centers can modulate activity in the dorsal horn by controlling spinal pain transmission. CNS, central nervous system.�
SPINAL INFORMATION REACHES THE CEREBELLUM BOTH DIRECTLY AND INDIRECTLY
The spinal cord is an important source of information used by the cerebellum in the coordination of movement. This information reaches the cerebellar cortex and nuclei both directly, by way of spinocerebellar tracts, and indirectly, by way of relays in brainstem nuclei. A number of spinocerebellar tracts have been described, some representing the upper extremity and others the lower extremity. Only three have been well characterized.
Ascending Tracts | Spinocerebellar Tract
DESCENDING PATHWAYS INFLUENCE THE ACTIVITY OF LOWER MOTOR NEURONS
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The term posterior column refers to the entire contents of a posterior funiculus, exclusive of its share of the propriospinal tract. The posterior columns consist mainly of ascending collaterals of large myelinated primary afferents carrying impulses from various kinds of mechanoreceptors (although substantial numbers of second-order fibers and unmyelinated fibers are also included). This has traditionally been considered the major pathway by which information from low-threshold cutaneous, joint, and muscle receptors reaches the cerebral cortex.
