Muscle Group Balancing through Tendon Alignment Part 1: How Muscles Work Together

Muscles work together in groups to create movement in the body. Muscles attach to bones via tendons, and applied energy near a specific attachment site moves a bone around a joint. Muscles pull (not push) when they contract. The change in the force of movement is started by muscles contracting as ropes using a simple machine pulley, the groove of the joint, to efficiently lift and move bones in the desired direction. The opposing muscle group stretches to allow ease of movement, or it might partially contract to slow down the movement of the action group.

For example, to lift the lower leg from 90 degrees of flexion into a straightened knee extension, the quadriceps contract, and the patellar tendon attached to the front of the upper tibia lifts the lower leg bone. The quadriceps attachments to the upper leg and hip hold a strong, fixed position to leverage the force of the movement. The hamstrings do knee flexion, which is the opposing muscle force to knee extension. The hamstring attachments are located on either side of the posterior knee, and stretch to allow the leg to straighten through the top of knee joint. The hamstrings can fully stretch, or partially resist using an eccentric contraction to slow down the knee extension. See Table 1 below for attachment sites.

The femoral nerve supports the knee extension muscles, 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 between muscle cells and groups is necessary for movement.

The central nervous system sends the action signal to the muscles. The fuel already stored inside the muscle cell reacts to the nerve signal creating intense kinetic energy for a fast twitch muscle response. There is a 3 second burn of ATP in the cell and then an 8-10 second anaerobic reaction of Creatine Phosphate, an amino acid naturally synthesized in the liver. The phosphate releases from the Creatine to activate ATP, the main energy supply for the muscles. The activation of the glycogen stored inside the muscle cell is the next reaction set in motion and can fuel the muscle for 60-90 seconds without an external oxygen supply, This anaerobic fast twitch energy burn in a high fuel, high speed, high output reaction.

Each of the 5 elements of Chinese Medicine: Water, Wood, Fire, Earth, Metal, have unique properties assigned to them. A muscle belongs to Earth; a tendon or ligament is part of Wood. The generating cycle of the 5 elements is a process by which energy is created in the body. Using Creatine as an example, Water/Kidney filters Creatine from the body and sends it to Wood/Liver to be synthesized into Creatine Phosphate. It then passes through Fire/Heart blood stream to Earth/Spleen to replenish the muscle fuel. Metal/Lungs and Large Intestine recycle excess or dispose of waste, and the kidney filters the Creatine to be used again and again.

After the initial fast twitch response, the remainder of glycogen inside the muscle cells and glucose in the blood supply continue to burn over the next 20 minutes with access to oxygen from the red blood cells. It is important to note that fuel must be inside the muscle cells before the ATP can be activated for movement. Carb loading by an endurance athlete is a recovery process replacing expended muscle fuel. Creatine and glucose are delivered to resting muscle cells through the blood system and insulin stores the fuel inside the muscle cells to prepare for the next adventure. The 20 minutes of fast twitch sugar burn allows time for the cardio fat burn to ramp up production of slow twitch energy, named for the amount of processing time to perform the many steps required to convert fat into ATP.

Once the fuel inside the muscle cells is depleted, slow twitch process starts to take over energy production. The pancreas emits the hormone, glucagon, to pull stored glycogen directly from the liver, and corticosteroids from the adrenal glands start hunting for fat and protein supplies to break down into glucose. This low grade stress response to a shortage of glucose shifts the body into a conservative low fuel, high output fat burn that allows for long-term endurance of high performance activity such as running long distance to hunt food or migrating to the next food supply. The muscle cells are depleted, and the fascia of the muscles likely takes over the majority of movement supported by the delivery of the systemic fuel supplied by the deep storage locations of fat in the lymphatic system such as belly fat, and vascular system fuel provided by the liver and scavenger corticosteroid in bio fuel conversions of fats and proteins to glucose.

The fast twitch motor action directed by the central nervous system fuels a muscle through the contraction fibers of a muscle spindle. 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? Here is a theory.

The cerebellum in the brain receives sensory system information. Sensory neurons in the skin sense and transmit heat, pain and other sensations to communicate perceived problems to the Central Nervous System CNS. The fascia in the body also has sensory proprioceptive qualities.

Both muscles and tendons have motor and sensory components. In Chinese Medicine, muscles and tendons belong to different elements: muscle/Earth, tendon/Wood, implying different pathways for generation of energy. 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 in the GTO. Fascia is primarily made up of collagen, which can receive signals from the GTO. Fascia tissues in the body are innervated by sensory nerve endings controlled by the peripheral nervous system PNS. The sensory component in the fascia of muscles regulates posture, balance, coordination, equilibrium and muscle tone. Muscle tone is what is left in the muscle after a contraction takes place to hold the form of the human being.

Then is no definitive list of which muscles are phasic, providing action, and which provide posture. Most likely, the list can only be made in a snapshot of a single point in time. Posture muscles are actually fascia-based elements in the muscles holding the body upright, and phasic muscles are engaged in motor contraction giving direction of movement through the GTO of the tendon providing sensory nerve proprioceptive impulses to fascia. The fascia reacts to body movement to create proprioceptive position in space relative to gravity, and sends signals to opposing muscle groups to stretch in support the intent of the initial motor contraction. Eccentric contractions of opposing muscle groups are regulated by the tension of the sensory fascia slowing the speed of motor contractions.

The motor component of muscles is managed by a separate fuel and neurological system than the sensory component. The muscles in action activate motor neurons through the CNS and are fueled by fast twitch glucose fuel inside the muscle. The opposing muscle group muscles managed by the peripheral nervous system PNS activate the stretch or sensory neurons in the fascia and the spindles of the muscle cells and are fueled by the systemic slow twitch fuel in the lymphatic and vascular systems intricately embedded in fascia.

The communication from the initial action to the opposing muscle groups is passed from the motor system to the sensory system through the GTO of the muscle tendon.

When there is injury to a muscle, tendon or fascia, the communication between the motor and sensory systems is interrupted.

Future blogs:

Muscle Group Balancing through Tendon Alignment

Part 2: Communication Breakdown

Part 3: How to Fix It




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


QuadricepsKnee Extension MovementKnee Extension AnchorNerve
Rectus FemorisTibia: tibial tuberosity, upper anteriorIlium: Anterior Inferior Iliac SpineFemoral Nerve

L2-4 Posterior Division of Lumbar Plexus

Vastus LateralisTibia: tibial tuberosity, upper anteriorFemur: gluteal tuberosity and greater trochanterFemoral Nerve
Vastus MedialisTibia: tibial tuberosity, upper anteriorFemur: linea asperaFemoral Nerve
Vastus IntermediusTibia: tibial tuberosity, upper anteriorFemur: shaftFemoral Nerve


HamstringsKnee Flexion MovementKnee Flexion AnchorNerve
Biceps FemorisFibula: HeadIchium: ischial tuberosityTibial Part of Sciatic Nerve

L4- S3 Sacral Plexus

Biceps FemorisFibula: HeadFemur: linea aspiraCommon Fibular Nerve
SemitendinosusTibia: pes anserinusIchium: ischial tuberosityTibial Part of Sciatic Nerve
SemimembranosisTibia: medial condyleIchium: ischial tuberosityTibial Part of Sciatic Nerve