Understanding The Science Behind Muscle

Understanding The Science Behind Muscle

Muscles power health in essential ways

There are more than 600 muscles in the body that help with performing a myriad of functions, from involuntary ones like breathing, circulation and digestion to voluntary ones such as walking or speaking.1 Within the body, there are three types of muscles: cardiac, skeletal, and smooth. Cardiac muscle makes up the walls of the heart, powering contraction and relaxation to enable circulation. Skeletal muscles connect with bones, tendons and ligaments to support movement of the body. Smooth muscle makes up the inside of organs such as the bladder, stomach and intestines and play an important role in involuntary functions such as the digestive and urinary systems. Optimal muscle performance is critical to health and well-being.


When muscles don’t perform optimally, the consequences may significantly impact quality of life. For instance, when the diaphragm, the muscle that supports movement of air in the lungs, is compromised, it may lead to difficulty breathing and potential respiratory failure.2 Similarly, for the heart to function well, it relies on the ability of the cardiac muscle to effectively contract and pump blood throughout the body. If the pumping function of the heart is compromised, it may cause fatigue, shortness of breath, dizziness and fluid buildup.3

Many diseases that affect muscle function—such as ALS and heart failure—result in muscle weakness either through diminished signaling between nerves and muscle or through other mechanisms, and this leads to limited performance of vital muscle systems. Increasing muscle function may help address the impact of these diseases, and may also improve a person’s prognosis or quality of life.

The Sarcomere

The Fundamental Unit of Muscle Contractility

The principal functionality of muscle is rooted in its ability to contract and relax. The foundation for muscle contraction is the sarcomere, found in all muscle cells. Sarcomeres contain a motor protein called myosin, which powers the muscle to contract by “grabbing” onto another protein called actin and “flexing.” When the myosin releases the actin, the muscle relaxes. This process is regulated by another protein called troponin.

Sarcomere malfunctions that cause decreased or increased contractility of the muscle play a central role in diseases like heart failure with reduced ejection fraction (HFrEF) and hypertrophic cardiomyopathy (HCM Disease), respectively.4,5 Therapies with the potential to modulate sarcomere function may improve the lives of patients suffering from these diseases.

Beyond muscle contractility

Just as muscle function is essential to life, so are metabolic processes that provide energy to drive muscle contraction. Through many biochemical pathways, our bodies convert the nutrition we consume into chemical energy (adenosine triphosphate or ATP) that powers contraction in all muscle types. Most ATP in muscle is made by mitochondria, organelles that serve as the engines that power movement, growth, and maintenance of other normal muscle functions. Muscle dysfunction can result from defects in the protein complexes directly involved in contraction, such as myosin and troponin, but can also arise from defects in metabolism or energy transduction resulting in too little ATP. Cytokinetics is expanding its drug discovery efforts to address defects in energy metabolism with new therapies. By doing so, we aim to address muscle dysfunction in a more wholistic and comprehensive manner.


  1. Muscle. Cleveland Clinic. Available at https://my.clevelandclinic.org/health/body/21887-muscle. Accessed March 22, 2019.
  2. Heart Failure | National Heart, Lung, and Blood Institute (NHLBI). Nhlbi.nih.gov. 2019. Available at: https://www.nhlbi.nih.gov/health-topics/heart-failure. Accessed March 22, 2019.
  3. Amyotrophic Lateral Sclerosis (ALS) Fact Sheet | National Institute of Neurological Disorders and Stroke. Ninds.nih.gov. 2019. Available at: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Amyotrophic-Lateral-Sclerosis-ALS-Fact-Sheet. Accessed March 22, 2019.
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