Understanding Muscles: The Engines of Human Movement
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 17, 2026
Muscles are soft tissues made of thousands of woven fibers that move your body, support your organs, and store and release energy. You have more than 600 of them, in three types: skeletal, cardiac, and smooth [1].
Quick Answer: What are muscles?
Muscles are pieces of soft tissue made of thousands of small fibers that move the body and its organs. There are more than 600, grouped into skeletal, cardiac and smooth types. Minor strains are common and often managed with rest, ice, compression and elevation, but pain lasting over a week needs checking, and trouble breathing or swallowing needs emergency care. [1]
What the research says
Strength training lowered sports injuries; stretching alone did not. In a meta-analysis of 25 randomized trials (26,610 participants, 3,464 injuries), strength training cut injury risk to less than a third (RR 0.315, 95% CI 0.207 to 0.480), while stretching alone showed no clear effect (RR 0.963, 95% CI 0.846 to 1.095) (Lauersen et al., Br J Sports Med, 2014).
Strength training changes the muscle itself. In a meta-analysis of 10 randomized trials in healthy adults, eccentric hamstring training increased fascicle length (mean difference 1.97, 95% CI 1.48 to 2.46) and raised eccentric hamstring strength compared with usual activity (standardized mean difference 2.72, 95% CI 1.68 to 3.77); the authors rated the evidence as limited to moderate for muscle structure and conflicted to moderate for strength (Gérard et al., J Athl Train, 2020).
What are the three types of muscle tissue?
Healthcare providers organize muscles by tissue type, based on where they are and what they do. Each type has a distinct job in keeping you moving and alive [1].
Muscle Type | Control Type | Primary Function | Location |
Skeletal | Voluntary | Supports your weight and moves your bones. | Attached to bones by tendons. |
Cardiac | Involuntary | Squeezes and relaxes to pump blood through the cardiovascular system. | Middle layers of the heart (myocardium). |
Smooth | Involuntary | Moves food and waste through the intestines and controls the width of the airways in the lungs. | Lining the inside of some organs, such as the intestines and lungs. |
Some skeletal muscle fibers contract quickly and use short bursts of energy (fast-twitch muscles), while others move slowly, like the back muscles that help with posture [1].
What are the main functions of the muscular system?
Muscles perform two kinds of movement. Voluntary movements are actions you choose to make, controlled through your nervous system, such as sprinting around a track or flicking your thumb to scroll on your phone. Involuntary movements happen automatically to keep you alive, such as your heart beating and the muscles in your chest and back moving your ribs when you breathe [1].
Beyond movement, muscles work with nearly every body system. They help with vision and hearing, breathing, speaking, and swallowing, digesting food and getting rid of waste, standing and sitting upright, pumping blood, and giving birth. Muscles also store and release energy as part of your metabolism [1].
What are common muscle conditions and their symptoms?
Because you have so many muscles, injuries and health conditions that affect them are common. Muscle strains, or pulled muscles, are the most common injury: muscle fibers are stretched beyond their limit and tear. Many health conditions can also affect muscles, including fibromyalgia, myopathies, myositis and polymyositis, infections such as the flu and COVID-19, amyotrophic lateral sclerosis (ALS), and cardiovascular disease [1].
Recognizing Warning Signs
It is normal to feel sore now and then, but long-term pain or weakness can signal something more serious. Common signs of a muscle injury or condition include [1]:
Muscle pain that lasts or keeps coming back.
Muscle weakness or stiffness.
Muscle spasms or cramps.
Swelling, bruising, or skin discoloration.
Diagnostic Approaches
If symptoms last, a healthcare provider may use blood tests (for example, to check markers of inflammation), electromyography (EMG) to assess the electrical activity of your muscles, imaging such as MRI or ultrasound to look at the tissue, or a muscle biopsy [1].
How can you care for muscles, prevent injury and recover?
Stretching and warming up before exercise are commonly recommended to prevent muscle injuries, because more flexible muscles have more room to stretch before fibers begin to tear. Increase your activity level gradually instead of suddenly ramping up intensity or frequency [1]. The research above adds a useful detail: in injury-prevention trials, strength training had the strongest effect while stretching on its own showed no clear benefit, so combining a warm-up with gradual, progressive strength work is consistent with the evidence.
For minor injuries, you can often manage symptoms at home with the RICE method [1]:
Rest: Avoid the activity that caused the injury and try not to use the injured area while it heals.
Ice: Apply a cold compress for about 15 minutes at a time, a few times a day. Wrap ice packs in a towel or thin cloth so they do not touch your skin directly.
Compression: Wrap an elastic bandage around the injured muscle to help reduce swelling.
Elevation: Keep the injured muscle above the level of your heart as often as you can.
When should you get medical help for problems with your muscles?
See a healthcare provider if muscle pain does not improve within a week of rest and home care, or if you are having trouble moving. Go to the emergency room if you have any of the following [1]:
Sudden chest pain or other heart attack symptoms.
Trouble breathing or swallowing.
Severe pain, muscle spasms, or muscle weakness.
Loss of balance.
Suddenly worse vision.
Problems controlling your bladder or bowels.
What is the bottom line on muscle health?
The muscular system is a vast network that powers nearly everything your body does, from the voluntary movements you choose to the involuntary ones that keep you alive. Warming up, building activity gradually, and adding strength training can lower your risk of injury, and persistent pain, weakness, or sudden changes deserve a healthcare provider's attention [1].
What steps can you take to keep your muscles healthy?
Muscle wellness starts with warming up before exercise, building strength gradually, resting minor injuries with the RICE method and seeing a provider if muscle pain lasts more than a week.
Warm up first: Warm up and stretch before exercise to improve flexibility.
Build strength gradually: Increase intensity and frequency step by step; strength training had the strongest research support for preventing injuries.
Listen to your body: Do not ignore chronic soreness; rest and use the RICE method at the first sign of a minor injury.
Seek expert advice: See a healthcare provider if muscle pain lasts more than a week or if you notice sudden weakness.
Frequently Asked Questions
How many muscles are in the human body?
You have more than 600 muscles located almost everywhere in your body.
What are the three types of muscles?
The three types are skeletal, cardiac, and smooth muscle tissue.
What is the difference between voluntary and involuntary muscles?
Voluntary muscles move when you think about moving that part of your body, while involuntary muscles work automatically without your input.
What are tendons?
Tendons are tough tissues that attach skeletal muscles to bones.
What is a muscle strain?
A strain, or pulled muscle, happens when muscle fibers are stretched beyond their limit and tear. It is the most common muscle injury.
How does the heart muscle work?
Cardiac muscle (myocardium) makes up the middle layers of the heart. It squeezes and relaxes on its own to pump blood through the cardiovascular system.
What is the RICE method?
RICE stands for Rest, Ice, Compression, and Elevation. It is a way to manage many minor muscle injuries at home.
What are fast-twitch muscles?
Fast-twitch muscles are skeletal muscle fibers that contract quickly and use short bursts of energy.
When should I go to the ER for muscle pain?
Go to the emergency room for sudden chest pain or other heart attack symptoms, trouble breathing or swallowing, severe pain, spasms, or weakness, loss of balance, suddenly worse vision, or loss of bladder or bowel control.
How can I prevent muscle injuries?
Warming up, stretching, and increasing your activity level gradually are recommended. In a large meta-analysis of randomized trials, strength training lowered injury risk the most, while stretching alone showed no clear benefit.
Related Reading
Understanding Smooth Muscle: The Involuntary Powerhouse explains the muscle type that works automatically in organs and vessels.
Muscle Spasms and Muscle Cramps: Causes, Treatment and Prevention covers why muscles cramp and how to relieve and prevent cramps.
Rhabdomyolysis: Symptoms, Causes, and Emergency Care explains serious muscle breakdown and when it needs emergency care.
What Is Muscular Dystrophy? A Plain-Language Guide to the Group of Diseases That Weaken Muscles describes inherited diseases that weaken muscles over time.
References
Cleveland Clinic. Muscles. Cleveland Clinic. January 23, 2024. https://my.clevelandclinic.org/health/body/21887-muscle
Lauersen JB, Bertelsen DM, Andersen LB. The effectiveness of exercise interventions to prevent sports injuries: a systematic review and meta-analysis of randomised controlled trials. Br J Sports Med. 2014;48(11):871-877. PMID: 24100287. DOI: 10.1136/bjsports-2013-092538
Gérard R, Gojon L, Decleve P, et al. The effects of eccentric training on biceps femoris architecture and strength: a systematic review with meta-analysis. J Athl Train. 2020;55(5):501-514. PMID: 32216654. DOI: 10.4085/1062-6050-194-19
Medical disclaimer
The information provided in this article is for educational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified healthcare provider with any questions you may have regarding a medical condition.
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