what athletes should know about muscle spindle and Golgi tendon organ

Skeletal muscle contraction and relaxation plays an important role in maintaining posture and movement. by using skeletal muscles we are able to move and perform our daily tasks but how can we know we are not hurting ourselves when we are using them and to be more precise, how do we know if we are contracting or stretching them too much?
the answer is simple, with the help of proprioceptors named Golgi Tendon Organs and Muscle Spindles(cutaneous and joint receptors also help but not to that extent).
There are two structures involved in collecting sensory information from muscle in the somatic nervous system, muscle spindle and Golgi tendon organ.

muscle spindles and golgi tendon organs are a big factor in overall health and fitness and understanding them is essential in any type of sport and exercise since they help athletes prevent injuries and also helps you understand human anatomy and biology and promote mind muscle connection, especially in explosive types of training like plyometrics, power lifting, body building, cross fit and HIIT training(high intensity interval training),

what are proprioceptors?

Proprioception is the ability to move through a space without the need to see or feel every aspect of that movement.
For muscles to work properly, sensory feedback is necessary to provide feedback. Sensory receptors are very specialized, as different types of receptors are needed for each type of sensory feedback. touch receptors convey information about mechanical stimuli external to the body where as proprioceptors detect mechanical stimuli occurring within the body. Proprioception allows for awareness of limb position as well as perception of limb movement, which is referred to as kinesthesia.
Kinesthetic feedback is characterized by the sense of movement and strength in our limbs. The receiving organs that allow this sensation are the muscular spindles and Golgi tendon organs.
The proprioceptors involve both exteroceptors (which sense stimuli originating from outside of the body, including pain, touch, vibration, temperature, and sound) and mechanoreceptors (which respond to external stimuli such as touch, pressure, and vibration). Together, they deliver millions of signals to the brain which direct not only our movements but many of our reflexes.
Age, injury, inner ear problems, alcohol, or a diminished neurologic response are just some of the reasons why proprioception may be compromised.
Proprioception also relies upon a coordinated response from both the inner ear (which is central to balance, motion, and orientation). There are also reflex arcs in which one movement will compensate for another to prevent injury.
One such example is stepping on something sharp like a nail or piece of glass. While the pain reflex will cause the injured foot to pull away, the body will counteract by shifting the center of gravity to the other foot while stabilizing your position with your arms. The complex reaction is sometimes referred to as human antigravity reflex arc.
the fact that you can practice and learn to stand on one foot with your eyes shut(if you can’t right now of course!) suggests that proprioception can be improved. The same applies to any activity for which you may be less coordinated, such as catching a ball or playing tennis. With practice, your body can adapt and expand its proprioceptive response to specific tasks.
yoga, Alexander Technique, and T’ai chi can also help you improve your proprioception.

what is proprioceptive neuromuscular facilitation(PNF)?

PNF is a stretching practice that promotes the response of neuromuscular mechanisms through the stimulation of proprioceptors in an attempt to gain more stretch in a muscle. A practical example of this method is to produce a low-grade (50% of maximum force) contraction within a muscle for six to 15 seconds immediately before having a partner passively stretch the muscle. The pre-stretch contraction reduces muscle spindle activity within its associated muscle (the muscle that is about to be stretched) so that the brain more willingly accepts an increase in range of motion during the impending stretch.

what is Golgi Tendon Organ(GTO)?

tendons typically stretch about 5% at maximal isometric force. The golgi tendon organ or tendon spindle is a proprioceptor, sense organ that receives information from the tendon, that senses tension. The tendon-spindle is smaller than the muscle spindle and lies in only 10% of the cases within the tendon.
When the GTO is activated during stretching, it inhibits muscle spindle activity within the working muscle (agonist) so a deeper stretch can be achieved.
Golgi tendon organs are found within the collagen fibers of tendons and within joint capsules. When you lift weights, the golgi tendon organ is the sense organ that tells you how much tension the muscle is exerting. If there is too much muscle tension the golgi tendon organ will inhibit the muscle from creating any force (via a reflex arc), thus protecting the you from injuring itself.
When a GTO is stimulated, it causes its associated muscle to relax by interrupting its contraction. When a muscle is inhibited by a GTO, the process is called autogenic inhibition.
autogenic inhibition can be induced by contracting a muscle right before it is passively stretched(proprioceptive neuromuscular facilitation or PNF that we talked about).
cerebellum(a part of brain which is responsible for coordinating voluntary movements) receives input from muscle spindles and Golgi tendon organs as well as centers for vision, hearing, touch, and balance. When the cerebellum is damaged, muscle tone (the slight tension continually present in the muscles) is impaired.

what is muscle spindle?

The muscle spindle is a proprioceptor. a sense organ that receives information from muscle, that senses stretch and the speed of the stretch. When you stretch and feel the message that you are at the end point of your stretch the spindle is sending a reflex arc signal to your spinal column telling you not to stretch any further. This sense organ protects you from overstretching or stretching too fast and hurting yourself.
Gamma motor neurons activate muscle spindles during contraction to maintain that information flow.
Imagine a muscle spindle as if it were a thread twisted around muscle fibres near the muscle belly; as the muscle lengthens or stretches, it pulls on the spindle causing it to lose its spiral shape and also stretch. This signals the muscle to contract (after which, the spiral regains its shape), in turn protecting the muscle from being overstretched. This process is called the stretch reflex.