22.1 Importance of Activity, Movement, and Alignment

Skeletal System

The skeletal system consists of bones, joints, and other structures that allow for movement and perform other critical functions in the human body. It supports the body, shields organs, makes blood cells, and provides space for minerals and fat. No activity or movement can occur without the skeletal system.

The primary component of the skeletal system is bone, which is a hard tissue composed primarily of calcium, with other minerals such as magnesium, fluoride, and sulfates mixed in. The adult human body has 206 bones divided into five types (Figure 22.2). Each type plays a different role in activity and movement.

• Long bones, such as the femur, provide leverage.
• Short bones provide stability and support and enable limited motion.
• Flat bones protect internal organs and provide surfaces to which muscles attach.
• Sesamoid bones function as shock absorbers for tendons.
• Irregular bones protect internal organs and provide support for movement.

Figure 22.2 Bones are classified by their shape: long, short, flat, sesamoid, or irregular. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Bone surfaces come into contact at a joint, often allowing for movement. At the joints, bones are separated by cartilage, a spongy, smooth surface that decreases friction and acts as a shock absorber between bones. A tough but flexible fibrous tissue, called a ligament, connects bones or hold joints together. A tendon is a tough, flexible band of connective tissue that attaches muscles to bones, facilitating the transmission of muscle contractions and allowing for joint movement. Injury to bones, joints, cartilage, ligaments, or tendons can make movement painful or even impair the body’s ability to move altogether.

Joints

The hyoid bone of the neck is the only bone in the human body not connected to other bones. All other bones articulate, or connect to each other, at joints. Joints can be classified by the amount and type of movement they allow between adjacent bones (Table 22.1).

Types of Joint Movement

A diarthrotic joint is most likely a synovial joint. Synovial joints are the most common joints in the body; they are movable and characterized by a fluid-filled cavity in the space where bones articulate. This fluid, called synovial fluid, allows bones to move against each other freely without causing pain or eroding from the friction. Friction in synovial joints is also diminished by articular cartilage, a thin, spongy layer of cartilage that covers the surface of bones where they articulate. There are six types of synovial joints, defined by the ways the bones articulate with and move against each other (Figure 22.3 and Table 22.2).

Figure 22.3 Synovial joints are classified based on the type of movement they allow. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Type of Synovial Joint	Characteristics	Example
Ball-and-socket joint	The round end of one bone fits into a large concave space in another—like a baseball fitting into a baseball glove.	Hips and shoulders
Condyloid joint	A shallow depression on one bone articulates with the rounded end of another, allowing for biaxial movement.	The joints located in the knuckles of the hands
Hinge joint	An outwardly rounded end of one bone articulates with the inwardly rounded end of another, allowing for bending and straightening.	Elbows, knees, certain parts of the ankles, and fingers
Pivot joint	The rounded end of one bone articulates within a ring of another bone and rotates within that ring.	Allows the turning of the neck
Plane joint	Articulating points slide against each other within a small range of movement bound by ligaments.	Joints of the wrist and in certain parts of the ankle
Saddle joint	Both bones are concave on one side and convex on the other and fit together like puzzle pieces, allowing biaxial movement.	What allows human thumbs to be opposable thumbs

Table 22.2 Types of Synovial Joints

Link to Learning

Joints can be complex to understand. Watch the Crash Course Anatomy & Physiology video to develop a better understanding of how joints work with bones to facilitate movement.

Muscular System

The human body contains three types of muscles, each performing different actions as they contract and relax. The heart is composed of cardiac muscle, which acts to pump blood through the heart. A smooth muscle makes up the internal surface of arteries and veins, internal organs, and other internal passageways. It acts by pushing substances through the system—for example, food down the esophagus or blood through the veins and arteries.

Cardiac and smooth muscle movements are entirely unconscious and almost totally outside of the control of the individual. In contrast, skeletal muscle attaches to bone and creates intentional movement as it contracts and relaxes. Skeletal muscles allow the human body to resist the force of gravity and help keep the skeletal system stable. Most importantly for the purposes of this chapter, people use these muscles to start and stop movement.

Skeletal muscle is called striated muscle because it appears striped. Figure 22.4 shows a microscopic image of skeletal muscle. Note how the muscle appears to be banded. When muscles contract and relax, those bands slide across each other as the muscle shortens (contracts) or lengthens (relaxes). In contraction, the muscle works, the bands slide toward each other and become more tightly woven, and the joint bends. In relaxation, the muscle no longer works, the bands return to their resting position, and the muscle lengthens back out.

Figure 22.4 This microscopic image of skeletal muscle shows the striations in the muscle, which appear as stripes or bands. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

A muscle’s strength is determined by the amount of work it gets. Muscle fibers and muscles grow and become stronger when they are worked; the more work they do, the stronger they become. Conversely, when muscles are worked less or not at all, they begin to atrophy, or shrink, losing both size and strength.

Relationship between Muscles, Joints, and Bones

There are more than 640 skeletal muscles in the body; some muscles perform only single movements, and others can move in multiple ways. However, there is always a main muscle, the prime mover. A muscle that helps the prime mover, providing assistance or stability to the movement, is considered a synergist. Because skeletal muscles work only when they contract, there are generally other muscles that contract in the opposite direction to a prime mover. A muscle that performs this function is known as an antagonist. Antagonists have two functions: they maintain the body’s alignment by keeping joints at their “normal” angle, and they return the body to its proper alignment when the work of the prime mover is completed.

Try this: hold your arm out straight with your palm facing up. Flex the forearm toward your head. Your biceps brachii muscle is the prime mover, contracting to shorten the angle at your elbow and pull the forearm toward your face. Your upper arm does not move. Now, straighten your arm back out. Your triceps brachii muscle is the antagonist, extending your arm back out and widening the angle at the bend of your elbow. The biceps and triceps brachii muscles attach to opposite sides of the humerus in the upper arm and to opposite sides of the lower arm, causing flexion and extension.

Body Movements

The body can make many movements, depending on the type of synovial joint and the muscles that attach on either side of the joint (Table 22.3). Most commonly, each movement in one direction also has an opposite movement. Movement can be understood by looking at the changes in the angles between the two bones when the muscles are at rest and when they have contracted, as well as the angles of the bones to the center of the body. All these movements combine to allow a person to run, dance, type, engage in hobbies, play sports, eat food, dress, and climb into bed at night.

Type of Movement	Characteristics	Example	Illustration
Flexion	Bending: a decrease in the angle between two bones	Bending the neck forward, backward, or to the side	(credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)
Extension	Straightening: an increase in the angle between two bones (usually up to 180 degrees, or a straight line)	Straightening the neck back to center
Abduction	Side-out: a movement away from the body’s midline or center	Moving arms or legs out to the side	(credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)
Adduction	Side-in: a movement toward the body’s midline or center	Moving arms or legs in toward the body
Circumduction	The combination of flexion, abduction, extension, and adduction at a joint in a circular motion	Moving wrists, ankles, or neck in a circular motion
Rotation	Movement of one bone around another at the articulation point	Turning the neck from side to side; making large circles at the shoulder or hip	(credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)
Supination	Movement of the forearm so the hand faces forward	These movements are specific to the hands and forearms.	(credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)
Pronation	Movement of the forearm so the hand faces backward
Dorsiflexion	Movement of the ankle joint so the top of the foot moves toward the front of the leg	These movements are specific to the ankles; they are the only movements of the ankle joints.	(credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)
Plantar flexion	Movement of the ankle joint so the toes are pointed as far away from the front of the leg as possible
Protraction	Forward movements of the shoulder blade or mandible	Throwing an object forward (causes the shoulder blade to move forward)	(credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)
Retraction	Backward movements of the shoulder blade or mandible	Squeezing the shoulder blades together causing them to move backward
Depression	Downward movement of the shoulder blade or mandible	These movements allow you to shrug your shoulders and open and close your mouth.	(credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)
Elevation	Upward movement of the shoulder blade or mandible

Table 22.3 Types of Body Movements

Nervous System

The nervous system is the human body’s computer hard drive. It controls most of the body—both voluntary and involuntary processes—through communication that happens (via nerves) between portions of the brain and specific organs (Figure 22.5).

• The brain and spinal cord, which comprise the central nervous system, are the processing centers. The brain is protected by the bones of the skull; the spinal cord is protected by the vertebrae that make up the spine.
• All nerves that run through the body are part of the peripheral nervous system (PNS). One of the many functions of the cranial nerves is to control the movement of skeletal muscles in the face. The movement of most other skeletal muscles, particularly those involved in skeletal movement, is controlled by spinal nerves attached to the spinal cord.
• The part of the peripheral nervous system that controls purposeful movement, recognition of the environment, and voluntary actions is the somatic nervous system. The somatic nervous system allows for interplay between sensory neurons, motor neurons, and conscious thought.

Figure 22.5 The nervous system, which includes both central and peripheral components, controls the movement of the skeletal muscles. (credit: ASCCC OERI/Flickr, CCBY 2.0)

The thirty-one spinal nerves extend from the spinal cord and run throughout the body, branching into smaller nerves as they move outward. A neuron stretches out throughout the system like a spiderweb and attach to muscles and other organs. Every nerve is composed of many neurons. Each spinal nerve receives information (for example, feelings of pain or hunger) through sensory neurons and sends information (for example, instructions to move or breathe) through motor neurons. The location where a motor neuron meets a muscle fiber is called a neuromuscular junction (NMJ). The motor neurons signal the muscle fibers (the muscle) to contract. Muscles stop contracting when they become fatigued or when the signal from the motor neurons stops.

Circulation

The continuous, controlled movement of blood throughout the body is called circulation and is facilitated by the heart, blood vessels, and blood. This process ensures the delivery of oxygen, nutrients, hormones, and other essential substances to various tissues and organs while removing waste products, promoting overall metabolic function, and maintaining homeostasis within the body. Regular physical activity promotes a healthy heart. For adults, there is strong evidence that activity helps to improve blood flow and levels of good cholesterol in the body (American Heart Association [AHA], 2017). Consequently, it lowers blood pressure and decreases the risks of hypertension and early death from heart disease (Carini et al., 2017). Individuals who are largely sedentary—who engage in minimal to no activity—have a substantially higher and earlier mortality rate than those who are active (Lane-Cordova et al., 2022).

Balance

Postural stability or equilibrium, or balance is the ability to maintain an alignment that prevents an individual from falling and allows them to catch themselves if they trip. It involves the work of the nervous system, muscles, bones, and joints, as previously discussed, as well as the inner ear and the eyes (Harvard Medical School, n.d.). It allows individuals to be physically active and can usually be improved by physical activity. Balance is critically important to preventing injury, particularly in older adults.

Many conditions and symptoms can cause balance difficulties. For example, patients who have suffered a stroke often struggle with balance related to changes in their ability to control one side of their body. Parkinson disease causes tremoring of the extremities, making it difficult to control balance. Muscle weakness, particularly in the core (abdomen and back) and upper legs, diminishes a body’s stability. Other issues impacting balance include multiple sclerosis, inner ear conditions, and nerve damage. Balance can also be impacted by medications (such as pain medication or sleeping pills), alcohol, and illicit drugs, all of which can impair the body’s ability to remain upright and protect itself from falling.

Coordination

While balance is the ability to maintain a position, coordination is the ability to change position effectively and intentionally. Coordination requires the synchronized efforts of the nervous system, muscles, and joints. Coordination must occur between the brain and the muscles and between groups of muscles to make movement happen. Think about answering a cell phone. The brain recognizes the need to answer the phone and alerts the various muscle groups. Then one arm and hand generally pick up the phone and hold it in the correct position, so that the other arm and hand can work the controls on the phone. This requires coordinated movement as muscles in both arms, hands, fingers, and shoulders all work together to answer the phone. Imagine the level of coordination that occurs on a daily basis.

Coordination can be impacted by many factors, including vision and vision changes, age-related changes (coordination tends to decline with age), and conditions of the central nervous system, such as stroke and Parkinson disease (Gonzalez-Usigli, 2022). Common symptoms of coordination disorders include the following:

• ataxia, or loss of coordination
• dysmetria, or the inability to control or judge the range needed for a motion
• dysarthria, or the slurring of speech or changing of vocal volume
• tremor, or uncontrolled shaking when attempting purposeful movement or resting

Posture

The key to alignment is posture; it is how an individual holds their body. There are two types of posture (Medline, 2017):

• The way an individual holds their body at rest is called static posture.
• The way an individual holds their body during movement is called dynamic posture.

Posture is dependent on the spine, which holds the body upright. Figure 22.6 shows three natural curves in the spine, which can be seen from side to side but not from front to back. These are natural curves and indicate correct posture: the head is naturally above the shoulders, and the tops of the shoulders are over the hips. Correct posture is the position that applies the least stress on each joint.

Figure 22.6 The three natural curves in the spine function as both positioners and shock absorbers. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Faulty posture is any position that increases stress on the joints and thus negatively affects health, such as slouching and slumping over (Figure 22.7). Over time, faulty posture may impact other body systems, including the digestive and respiratory systems (MedlinePlus, 2017). It can also cause serious issues with the musculoskeletal system, including the following:

• moving the spine out of alignment
• causing pain in the neck, shoulders, and back
• decreasing flexibility, the ability to move a joint effectively through its entire range of motion
• eroding vertebrae, causing spinal degeneration and arthritis
• decreasing balance and increasing the risk of falls
• incontinence for people with vaginas

Figure 22.7 (a) Scoliosis, (b) kyphosis, and (c) lordosis are common faulty postures that can be related to a variety of conditions, whether genetic, age-related, or temporary. (credit: modification of work from Anatomy and Physiology 2e. attribution: Copyright Rice University, OpenStax, under CC BY 4.0 license)

Safety in the Workplace

Proper ergonomics is crucial to healthcare workers, who are at high risk for musculoskeletal injuries because they regularly care for patients who may not be able to move themselves. Sprains and strains occur frequently in the workplace but can be prevented by using proper ergonomics and body positioning (Karwowski & Zhang, 2022). These disorders most often occur because of manual activities related to patient care, including heavy lifting and working in awkward positions. In health care, nurses’ bodies are in constant motion, and understanding how to protect themselves from injury is critically important. By studying ergonomics and how nurses interact with their environments, patients, and everything around them, researchers have developed evidence-based strategies to improve performance, patient outcomes, and safety while minimizing staff injuries (Karwowski & Zhang, 2022).

Assistive Devices

An assistive device is available in most facilities to facilitate SPHM ergonomics (Figure 22.8). These devices allow for safe movement of patients between locations—for example, from bed to stretcher or wheelchair, within a bed, or between a bed and bath—and even to assist with standing. Each of these devices is intended to decrease the risk of injury to patient or provider during care.

Figure 22.8 (a) Sliding sheets or boards are friction-reducing surfaces that can be inserted beneath a patient to allow for easier movement between surfaces. (b) Lifts can attach to ceilings or move on the floor; slings go under patients and then attach to lifts. They are used together to lift patients. (c) Mechanical beds often consist of distinct sections that can separately be adjusted. For example, their heads and feet can be raised or lowered, or they may tilt from side to side or convert into chairs. Some beds can even take a patient’s weight without the patient having to get up. (credit a: modification of work “Stretcher and slider board” by Glynda Rees Doyle and Jodie Anita McCutcheon, CC BY 4.0; credit b: modification of work “U.S. Navy Medical Team Integrates with Spokane Hospital 211017-A-KC249-1093” by Navy Medicine/Flickr, Public Domain; credit c: RDNE Stock project/Pexels, CC 0)

It is important never to use assistive devices without proper training; assistive personnel should also have been trained. Without proper training, the device could accidentally hurt patients or staff rather than help them (AORN, 2019; Veterans Health Administration, 2022).

Safe Patient Handling and Mobility

SPHM includes a variety of techniques designed to protect patients’ safety and dignity while also protecting staff’s safety (AORN, 2019). For patients, the techniques reduce patient falls and skin tears, increase satisfaction, and encourage mobility. For staff, they decrease the risk of acute and chronic musculoskeletal injuries, improve worker morale, and decrease worker fatigue.

Proper preparation for patient care or transfer is hugely important for the safety of patients and staff alike. With every patient-handling activity, take the time to complete the following steps before performing the activity.

1. Assess the patient’s needs and gather the assistive devices necessary to provide their care.
2. Ensure there are enough staff available to assist with care.
3. Ensure the environment has been properly prepared. For example, move bedside tables and chairs, and ensure that devices that should be locked are locked and those that should be unlocked are unlocked.
4. Make sure team members understand their roles.
5. Explain to the patient the plan, and coach them if they can assist.
6. Apply proper body mechanics—intentional movements and muscle use designed to maintain an individual’s posture and alignment—to decrease the chance of injury.

Once these preparations have been made, it is much easier to safely handle or transfer the patient, minimizing the injury risk for patients and staff.

Types of Exercise

There are several types of exercise, each of which is important for different body systems (Johnston, 2023). Each type impacts multiple systems as well as the body’s core, or lower torso (particularly the abdomen and lower back). The core controls lower body postural stabilization.

Stretching and Flexibility

A slow, steady exercise or movement called a stretch is designed to extend or lengthen specific muscles or muscle groups in the body (Figure 22.9). They should never be painful and should not be pushed to the point of pain. Flexibility describes the body’s ability to bend safely at its joints. Exercises that involve stretching and flexibility improve range of motion (the extent and direction of movement that a joint or a group of joints can achieve), muscle relaxation, and comfortable engagement in other activities (Johnston, 2023). They also improve balance and movement coordination and decrease fall risk (Riverra-Torres el., 2019) and are beneficial for treating and managing pain, particularly chronic pain such as in the lower back (Kim & Yim, 2020).

Figure 22.9 (a) An individual stretches the piriformis muscle that affects hip movement. (b) The hip flexor stretch stretches the hips and improves balance and coordination. (c) The child’s pose stretch stretches the hips, lower back, and upper body. (credit a: modification of work “Stretching Fitness Workout” by ThoroughlyReviewed/Flickr, CC BY 2.0; credit b: modification of work by FocusFitness, Public Domain; credit c: modification of work by FocusFitness, Public Domain)

Aerobic Exercise

A continuous physical activity called aerobic exercise increases the heart rate and improves the function of the cardiovascular system—thereby improving the body’s ability to take in oxygen, increasing the amount of blood the heart pumps (stroke volume), decreasing the heart’s workload at rest (resting heart rate), and improving both cardiac and overall mortality rates (Johnston, 2023). The key is to perform aerobic activity for at least several minutes at a time and accumulate enough active minutes over the course of a day to impact the cardiovascular system (Figure 22.10).

Figure 22.10 Aerobic activities include running, walking, dancing, and even vacuuming. (credit: “Aerobic exercise” by CDC/James Gathany/Wikimedia Commons, Public Domain)

Strength Training

Resistance training, sometimes referred to as strength training, involves contracting a muscle against a load, such as free weights, elastic bands, water, or one’s body weight (Riverra-Torres et al., 2019). In addition to improving muscle strength, endurance, and size, strength training improves cartilage health, bone strength, and the individual’s overall functional ability (Maestroni et al., 2020; Johnston, 2023). It can also be used to decrease pain; improve cardiovascular endurance, posture, and flexibility; improve sleep; and help mitigate the effects of metabolic diseases, such as type 2 diabetes, and mental health and neurocognitive disorders, such as dementia (Maestroni et al., 2020).

There are two basic types of strength training: isometric and isotonic (Figure 22.11). Exercise that involves contracting a muscle against an unmoving force (such as a floor or wall) is called isometric training. Thus, the muscle cannot shorten or lengthen. It becomes fatigued by the pressure applied against the unmoving object. On the other hand, isotonic training involves contracting a muscle against a force that moves (such as a barbell or a weight machine). Users may gradually increase the weight to further strengthen the muscle, but this need not be a priority of a training program.

Figure 22.11 (a) This individual is performing strength training with resistance bands. (b) The plank pose strengthens muscles in the shoulders, back, core, buttocks, and legs. (c) Exercises such as the bird dog strengthen the core. (credit a: “Personal training shoulder exercise” by Tyler Read/PTI Pioneer, CC BY 2.0; credit b: PX here, CC0; credit c: “Woman Doing Bird Dog Exercise To Strengthen Core”/FocusFitness, Public Domain)

Balance Training

An activity called balance training is specifically used to improve an individual’s ability to remain upright while stationary or moving and to decrease the chance of falling (Riverra-Torres et al., 2019). It has also been shown to improve mobility, reaction time, and strength and to assist with postural control, both static and dynamic (Lal, 2022). Balance training frequently occurs in physical therapy and rehabilitation settings where the focus is to retrain the body to maintain its own center of gravity by challenging the individual’s stability (Johnston, 2023). Common techniques include having patients stand on one leg or use balance beams or wobble boards to improve balance in unstable settings. Many poses in the practice of yoga are also excellent for balance training (Figure 22.12).

Figure 22.12 (a) These people are working on balance during a yoga class by practicing the pose called downward-facing dog. (b) Standing on one leg strengthens postural stability, balance, and ankle strength. (credit a: “Spouses practice the crescent pose during a yoga workshop” by Defense Visual Information Distribution Service/Nara & DVIDS Public Domain Archive, Public Domain; credit b: PX Here, CC0)

Life-Stage Context

At-Risk Populations and Activity

People in marginalized communities—such as people with low incomes, immigrants, and people experiencing homelessness—are much less likely to participate in physical activity. Regular struggles with barriers such as cost, transportation, childcare needs, time, and basic financial and housing insecurity negatively impact their ability to be physically active in a purposeful way, which can profoundly affect their cardiovascular, mental, and physical health. Developing individual or community-level strategies to improve the physical activity of marginalized groups can have substantial impacts. For example, it might be possible to organize walking or aerobics groups in the community or distribute walking or running shoes to patients who have lower incomes (Creagh et al., 2023).