Balancing Communication between Hamstrings and Quadriceps Case 1

Mary Bai, Case Studies of Muscle Function

Context: Loss of balance is a common issue in certain musculoskeletal disorders such as Parkinson’s Disease. The hamstrings and quadriceps are strong muscle groups that play a key role in lower body movement and stability. If these two opposing muscle groups are not working well independently or together, overall body instability can result from the lack of a solid foundation.

Objective: The goal of this study is to isolate and correct muscle function disturbances, and to retrain the muscle movement patterns to determine if more efficient communication between the hamstrings and quadriceps can improve balance in the body as a whole.

Study Design: A therapeutic practitioner will perform multiple medical massage sessions to find and remove scar tissue using cross fiber friction and other trigger point release modalities to restore the body to as close to its original function as possible. Attempts will then be made to regain communication between these large, opposing muscle groups through alternating action and rest patterns.

The case is based on an aggregate of people presenting with similar issues.

Theoretical Structure of Muscle Function 

How Muscles Work Together to Move Bones Around a Joint

Muscles attach to bones via tendons. Ligaments attach bones to bones. 

Muscles cross over joints and apply energy in a contraction to a specific attachment site near the joint. The shortening of the muscle pulls (not pushes) bones closer together around a joint to initiate movement. The concentric force of a muscle contraction is like a rope using a simple machine pulley, which in the body is the groove of the joint, to efficiently shift bones and move in the desired direction. 

Muscles work together in groups to create movement in the body. The action group contracts as a special team for a specific offensive movement pattern. There is an opposing muscle group, a defensive special team for that unique movement pattern, that stretches to allow ease of movement, or it might partially contract to slow down the movement of the action group, an eccentric contraction. If opposing muscle groups both fully contract at the same time, nothing moves. Ligaments are very strong and constrain the physical limits of the joint to protect its integrity, 

Every movement in the body has a unique set of offensive and defensive muscle components that form special teams selected based on the attachment location_location_location and requested direction of movement. Muscles can have multiple attachment sites on various bones, so sometimes only a portion of the muscle may be needed for a movement pattern, with other sections of the muscle taking on supporting roles such as anchoring the muscle to stabilize the action.

For example, to lift the lower leg from a 90 degree bend at the knee into a straightened knee extension, the quadriceps on top of the thigh contract, and the patellar tendon of the quads attached at the front of the upper tibia lifts the lower leg bone. The upper femur and hip quadricep attachments hold a strong, fixed position to leverage the torque of the movement. The hamstrings do knee flexion which is the opposing muscle action to knee extension. The hamstrings, located on the back of the leg, stretch to allow the front of the leg to straighten through the knee joint. The hamstrings can stretch, or partially apply resistance to the movement using an eccentric contraction to slow down the knee extension, which is often a technique used in lifting weights.

See Table 1 below for a list of attachment sites used in knee extension and flexion. Notice the attachment sites of a single muscle are divided by function, loosely correlative to origin and insertion points which are more generic terms, but not specific to movement directives.

Table 1 Knee Extension and Knee Flexion Movement and Anchor Muscle Attachment Sites

QuadricepsMovement AttachAnchor AttachNerve
Rectus FemorisTibia
Tibial tuberosity via patellar tendon
Anterior Inferior Iliac Spine
Femoral Nerve
Vastus LateralisTibia
Tibial tuberosity via patellar tendon
gluteal tuberosity and greater trochanter
Femoral Nerve
Vastus MedialisTibia
Tibial tuberosity via patellar tendon
linea aspera
Femoral Nerve
Vastus IntermediusTibia
Tibial tuberosity via patellar tendon
Femoral Nerve
HamstringsMovement AttachAnchor AttachNerve
Biceps Femoris
Long Head
Lateral side of head
Ischial Tuberosity
Sciatic Nerve
Tibial Division
Biceps Femoris
Short Head
Lateral side of head
Linea Aspira
Sciatic Nerve
Common Fibular Division
pes anserinus
Ischial Tuberosity
Sciatic Nerve
Tibial Division
medial condyle
Ischial Tuberosity
Sciatic Nerve
Tibial Division


Nerves are like the bundle of cables used to run the computer components. They might all look the same, but each cable has a unique function. If the power cable to the monitor is pinched, the monitor might flicker, or the monitor might flicker if the cable connecting it to the computer is loose, or the monitor might flicker if there is something wrong with the internal wiring of the machine. Muscles and nerves can have a similar variety of issues. The nerve supporting a muscle might be in trouble from the nerve root. The nerve pathway itself could be impinged somewhere along the way. The fibers of the muscle might not be able to receive a nerve signal.

As shown in Table 1, the femoral nerve supports the knee extension muscles, each of the quadriceps. The knee flexion muscles, the hamstrings, are supported by the sciatic nerve in the back of the leg. The femoral nerve signal to the action or agonist knee extension muscle group creates a concentric contraction shortening the muscle, pulling up the tibia. If the sciatic nerve were to send an action signal to the hamstrings at the same time, the two opposing groups would be in conflict for control of the action through the joint. For knee extension to work efficiently, the quadriceps contract, and the hamstrings must stretch. A muscle cell can both contract and stretch, but the cell must select a single function dependent on the job it is doing at the time. 

A single cell cannot move a body; coordination within and between muscle cells and groups is necessary for movement. Looking at the Nerve column in the Hamstring table, did you notice that the Short Head of the Biceps Femoris is innervated by a different division of the Sciatic Nerve? Is that significant? Yes. That section of the hamstrings receives signals from a nerve division that is different than the other hamstrings. Movement within an offensive special team of knee flexion follows along the line of the nerve. The Short Head of the Biceps Femoris should be considered a separate special team because it has a different offensive coordinator.

How does the communication between muscle groups take place? Once a group of action and opposing muscles has finished its task, there is a communication to the next movement plan like passing the baton in a relay race. How does that communication take place?

Fast Twitch vs Slow Twitch Muscles, CNS vs PNS

Opposing Muscle Group Communication Theory 

How does an opposing muscle group know when to stretch, especially since the nerve to the agonist or action group is different from the antagonist or opposing group of muscles?

Both muscles and tendons have motor and sensory components. In the 5 elements of Chinese Medicine, muscles and tendons belong to different elements: Muscle/Earth, Tendon/Wood, implying different pathways for purpose. When a muscle contracts using the motor component, force is applied to the tendon attachment of the targeted movement area. The tendon contains a Golgi tendon organ (GTO), a proprioceptive tool for directing change in physical position through strands of collagen. Fascia is primarily made up of collagen, which can receive intended direction from the coded messages of the GTO providing sensory nerve proprioceptive impulses to fascia. The fascia reacts to body movement to create a new position in space relative to gravity, and sends signals to the sensory fibers of opposing muscle groups to stretch in support the intent of the initial motor contraction (reciprocal inhibition). Eccentric contractions of opposing muscle groups are regulated by the tension of the sensory fascia slowing the speed of motor contractions to create safe boundaries of movement. Motor neurons in the agonist muscles contract. Sensory neurons in the antagonist muscles relax. Movement happens.

With so many intricate elements of movement, what could possibly go wrong?


When there is injury to a nerve, muscle, tendon or fascia, the communication within and between the motor and sensory systems is interrupted. Motor nerve weakness results in tired phasic or action muscles. Any muscle within a group can decline to participate in an action if there is a nerve line disturbance, much like a faulty bulb in a string can disable an entire section of lights. Sensory nerve weakness can result in muscles that lock down to hold posture in the event of a fuel shortage. That resulting tightness doesn’t respond to stretching. It’s stuck.

Nerves react to external forces such as weather, sleep position, diet, changes in activity patterns, or stress so they can react differently day to day frustrating the cause and effect evaluation of restricted muscle movement or pain. 

How to Feel Muscle Direction and Find a Knot

To help resolve injury in the body, it is important to understand which muscles have been impacted. Start by first understanding how to palpate muscles under the skin. See Pound Sand or Palpate Muscles. Muscles and tendons have a very clear linear fiber direction. Fascia or connective tissue, such as ligaments that attach bones to bones, is made of collagen fibers that criss cross in multiple directions to hold a strong form that both allows movement in various directions but also constrains motion past the capacity of safe boundaries needed to protect the body, especially joints and organs. 

What is a knot in a muscle? Tight muscles are often constricted when the fibers in the muscle are overworked and don’t move or stretch well. When a muscle is injured, it can tear, and scar tissue is sent to the site as glue to pull together the borders of the tear until the muscle can repair the damage After an acute injury or surgery, physical therapy works to mobilize and strengthen the injured area to encourage it to heal and to keep excess scar tissue from forming in the wrong place. A knot or trigger point can form when the excess scar tissue isn’t cleared and unfortunately binds muscle fibers or fascia together that is not necessary for healing the tear. If just the injury is healed from the scar tissue, normal function is restored. If excess scar tissue is present, function is not normal. A muscle that did not heal well may not move at all, and pinched nerves caught in excess scar tissue are often initially protected against pain by rerouting movement away from the area into a compensation plan. The place that hurts may not be the source of the issue.

The key to successfully reestablishing improved movement and decreased pain is to understand how overuse or injury can change the function of the body through limited range of motion and subsequent compensation patterns caused by the adhesions in muscles and fascia. It can be a very involved process to reverse engineer incorrect movement patterns in search of clues to identify the true source of pain. Remember that multiple muscles in special teams are involved in a single movement: action, opposition and ligaments that constrain movement. Many muscles attach to specific sites on a bone moving around a joint. Pain or range of motion limitation might be the first clue of many in the process of healing.

A trigger point can be found by tracking muscle direction and looking for disruptions or bumps in the line. A knot can be removed with techniques such as myofascial release, cross fiber friction, foam rolling, compression with tennis balls, and many other targeted methods by intentionally approaching, then wiggling and untangling the fibers, taking them back to their intended linear position. The adhesion is excess scar tissue, not the part of the healing scar that fixes the original injury. Sometimes releasing A knot might not be THE knot. Keep looking. Keep trying. 

Data Collection: Using the information provided in Table 1, perform In depth evaluation of the movement patterns involving the muscles targeted in the study to track potential restrictions. The client performs a specific movement. The practitioner palpates points in the target muscles starting with the attachment sites looking for the anticipated contraction to perform the movement. For example, in knee extension, contraction of the patellar tendon should be felt at the tibial tuberosity, in front of the lower knee. Each of the four quadriceps should be contracting in a direct line from the femur and hip attachments to the patellar tendon. The hamstring attachments should relax and allow a stretch. Note any restrictions in the quadriceps as well as deviations in movement patterns seen visually or felt in surrounding muscles that should not be contracting.

Take an in depth physical history of clients with written intake form and follow up questions about treatment goals, activities, accidents, pain, and any other information that may or may not seem initially relevant.

Client Intake Issues Related to Balance in Lower Body

Inability to slow down when walking down hill

Balance and stability issues when standing

Unusual gait waddling legs side to side without bending knees 

Shuffling feet

History of sciatic nerve pain

At night, if there are leg tremors, the client will perform a technique that is commonly used in sports medicine. How to Stop a Cramp.

Analysis: Compare anticipated movement patterns to those presenting in client. Can muscle restrictions found in muscle review be related to an element of the physical injury history? Does the restriction present with scar tissue itself or appear to be a compensation plan to protect an old injury?

Perform scar tissue manipulation to areas flagged in data collection to restore the correct fiber direction of the muscle or tendon.

Review movement patterns before and after scar tissue manipulation to determine if there is improved function to the target area and then to the subsequent broader patterns in the lower body related to balance.

Observation of Client

Hyper-contracted quadricep muscles

Neither the quadriceps nor the hamstrings fire separately. When asking the client to do knee flexion with the hamstrings while standing, the quadriceps and the hamstrings both engage. It is the same for knee extension.

When the client is lying face up and the posture system is disengaged, neither the quadriceps nor the hamstrings perform as expected.

Multiple adhesions located and released in both quadriceps and hamstrings

Key Findings:

The quadricep muscles are depleted, and fast twitch signals from the CNS are ineffective in contracting action muscles. The PNS stress or posture system is driving movement through the fascia. There is no muscle contraction from fuel inside the muscle, therefore, signals between the agonist and antagonist muscles are not being sent. Both muscles groups try to move the knee at the same time, the knee is stiff, and balance is off.

A history of sciatic nerve compression could contribute to a decreased motor nerve support system to the hamstrings.

Going downhill, the muscles cannot communicate an eccentric contraction request for the opposing muscle group to safely slow the motion down.

Stress override impact on body and communication fails between the motor and sensor nervous systems. The long term stress system needs to conserve fuel so it doesn’t want fast sugar burn to waste fuel. Long term stress endurance is in direct competition with muscles for fuel.

A leg tremor and a leg cramp could both be considered neurological disturbances as the communication between the motor and sensory nervous systems is not working efficiently.

To encourage better communication between opposing muscle groups, perform this simple exercise using reciprocal inhibition of the quadriceps and hamstrings.

Lay face up on the table. This negate the fascia from taking control of movement as there is no need for postural muscle activation in this position. Press the knee into the table to activate the hamstring muscles without moving the quadriceps. Often on the first try, the client will lift the quads to push the hamstrings into the table. Start over by asking that only 5% of the hamstring power be used to press the knee into the table. Ensure that the quadriceps do not move while the hamstrings are trying to contract. Do this 4-5 times or until the hamstrings gently contract and the quadriceps start to relax. Next, cross one leg on top of the other ankle or have someone hold the intended action leg static for an isometric contraction that does not change muscle length. Gently try to lift the lower leg against resitance to extend the quadricep muscles. The hamstrings should relax. Contract just the quadriceps for 4-5 times and then try to shift back and forth slowly between the hamstring and quadricep action to activate communication between the motor contraction of the action group, and the reciprocal inhibition of the opposing group, relaxing on cue. Once the muscles start taking turns in a controlled environment, it is much easier to apply the process to standing and walking in a much more stable and balanced mode.

The balance between the hamstrings and quadriceps in knee flexion and extension is just the one step in understanding how muscle dysfunction can alter stability. Fixing these big muscle group interactions can really make a difference in regaining confidence in standing and walking, one step at a time.