Flexibility relates to the ability to move a joint through its full range of motion. Developing a complete fitness program requires taking time to emphasize this component by stretching. Unfortunately, as the American Council on Exercise (ACSM) indicates that most people neglect flexibility training. which limits freedom of movement, physical and mental relaxation, release of muscle tension and soreness. In addition, reduced mobility of joints increases the risk of injury during an exercise routine, as well as the risk of occasional and chronic back pain.
Types of Flexibility
Flexibility is classified into two types: static and dynamic.
- Static flexibility: This type of flexibility is a measure of the limits of a joint’s overall range of motion. It is measured by stretching and holding a joint in the position of its maximum range while using a measuring instrument to quantify that range. To achieve the maximum range, passive forces, the force generated from an external source, are required.
- Dynamic Flexibility: This type of flexibility is a measure of overall joint stiffness during movement. Unlike static flexibility, dynamic flexibility requires active force production, or your own muscles contracting. Because quantifying “stiffness,” is difficult, dynamic flexibility is measured more subjectively. Assessment is based on how easy or difficult it is to perform certain tasks, such as swinging a tennis racket, climbing steps, or getting in and out of a car.
The aim of any good stretching program is to improve both static and dynamic flexibility so that full range of motion can be achieved.
Benefits of Flexibility Training
Regular stretching provides many benefits, the most important of which is simple: flexibility provides freedom of movement and the ability to complete activities with greater ease.
Healthy Joints and Pain Management
As many as 26% of all adults report pain and stiffness in joints. That number increases dramatically with age, and women are more likely to develop joint symptoms. For adults, arthritis is one of the most common conditions, with 54% of people 75 years and older having been diagnosed with arthritis. Regular exercise, including regular stretching, is essential for people with arthritis to maintain function and manage joint pain. Even for those not affected by joint conditions, stretching increases joint mobility and function, and decreases joint stiffness and pain.
Imbalances in the muscles can cause discomfort and pain. For example, if the front of a person’s thighs and hips gets too tight from a lack of flexibility, the tension will pull on the hips, where the muscles are attached. The result is the pelvis may be pulled forward and cause greater sway in your lower back. This affects posture and can eventually lead to pain and stiffness in the neck, shoulders, and lower back. Stretching all major muscle groups and joint areas regularly promotes good alignment and balance.
Muscle Relaxation and Stress Relief
Staying in one position for long periods of time, repetitive movements, and other every day stressors can result in stiff muscles. Regular stretching decreases anxiety, blood pressure, and breathing rate, which help to relax muscles and aches and pains related to neuromuscular tension (stress).
- Increased blood flow: Blood carries vital nutrients and oxygen to muscles and tissues. Stretching increases blood flow to the muscles being stretched, which helps them recover faster following exercise.
- Flexibility and aging: For many college students, maintaining long-term flexibility is not a concern. For young adults, bending over to tie their shoes is painless. Walking around campus with a backpack requires minimal effort. However, range of motion declines with age. Simple activities like rotating the head and neck to glance over the shoulders, getting in and out of a vehicle, or carrying groceries can become painful. Therefore, flexibility is critical in maintaining a high quality of life throughout the aging process.
- The inactivity-mobility cycle: When the joints’ range of motion becomes restricted by arthritis or other injuries, activity declines. As activity declines, the range of motion continues to diminish as a result of inactivity, and a vicious cycle ensues. A simple stretching program can help alleviate this problem and break the cycle.
Improving Range of Motion
Joint range of motion results from a combination of factors, which are classified as either internal or external. Internal structures relate to the physical structures of body materials and tissue. External factors are non-structural and include gender, age, excess fat mass, muscle mass, environmental temperature, and restrictions in clothing or equipment.
Internal factors include joint structure/joint mechanics and the connective and soft tissue surrounding the joint. Because muscular actions, such as muscular contractions and stretching, are controlled by the nervous system, another internal factor can be attributed to the neuromuscular system and how the stretching and tension is managed.
A joint is defined as a location on the skeletal system where two or more bones intersect and interact. For example, the humerus (upper arm) intersects with the radius and ulna (lower arm) at the point of the elbow. The bony formation of each joint structurally limits its range of motion. For example, the shoulder joint, which is structurally a ball-in-socket joint, can rotate in multiple directions, giving it a wide range of motion. However, the knee joint is a modified hinge joint, which is limited to essentially a forward-backward direction of movement.
Additionally, range of motion may be limited by excessive fat mass or even large muscle mass surrounding a particular joint. Although the amount of muscle mass and fat mass surrounding a joint can be altered by diet and activity levels, joint structure is permanent. As a result, little can be done to improve flexibility in this area.
Not only is range of motion related to the joint structure, but flexibility exercises are joint-specific. Stretching the hamstring will not improve flexibility in the shoulders. Likewise, flexibility in the shoulders may be excellent while fingers or ankles remain “stiff.” As such, a complete and effective stretching program includes multiple stretches for various joints.
Connective and Muscle Tissue
Joints are surrounded and connected by muscles, tendons, ligaments, and skin. The head of the humerus fits into a small cavity to create the shoulder joint. However, those bones cannot remain in that position without the muscles, tendons, and ligaments that keep the joint tight and hold it in place. In addition, muscle tissue is surrounded with connective tissue, primarily collagen and elastin. As a joint moves through its normal range of motion, all of this soft tissue must stretch to accommodate the movement. Therefore, static and dynamic flexibility is probably most limited by the flexibility of the surrounding soft tissue, specifically the connective tissue.
Improvements in flexibility is related to the elastic and plastic properties of the connective tissue. Elasticity is defined as the ability to return to resting length after passive stretching (i.e., elastic recoil). Like a spring, soft tissues stretch and then recoil to their resting position. Plasticity is the tendency to assume a greater length after passive stretching (i.e., plastic deformation). Stretching that spring composed of soft tissues will change its resting position to a new longer length. The goal of a flexibility program is to repeatedly overload the elastic properties of the muscle to elicit plastic deformation over time. Experts suggest that a slow, sustained stretch for 30–90 seconds is necessary to produce chronic plastic deformation.
Modern cars come equipped with a central computer and sensors to troubleshoot problems with the vehicle. Sensors in the engine monitor temperature. Sensors on the wheels gauge tire pressure while sensors in the gas tank alert the driver when fuel is low. Much like a car, our bodies are equipped with sensors, called proprioceptors, that help us manage movement and prevent injury. Muscles have two specific types of proprioceptors that determine the length and tension of the muscle. These proprioceptors are called muscle spindles and Golgi tendon organs (GTOs).
Muscle spindles lie parallel to the regular muscle and help determine the length of muscles when they are being stretched. When a muscle is stretched, it sends signals to the central nervous system causing the stretched muscle to contract. This resistance to the stretch, called the myotatic or stretch reflex is generated by the nervous system’s reflexive stimulus sent to the stretching muscle. That same signal also causes the antagonist, or opposing muscle to relax, called reciprocal inhibition. As such, when the upper thigh muscles (quadriceps) are stretched, the hamstrings (antagonist to the quadriceps) relax.
The GTOs are located near the musculotendon junction, the end points of the muscle, and relay messages to the central nervous system regarding muscle lengthening and tension of the muscle. When activated, these signals will override the stretch reflex causing a sudden relaxation of the stretching muscle. This is called autogenic inhibition or the inverse myotatic reflex. This inhibitory reflex can only occur after the muscle has been stretched for 5 seconds or longer. This is why, to effectively stretch, movements must be sustained for long, slow increments of time. Otherwise, the resistance encountered from the stretch reflex will not be overridden and lengthening cannot occur. Whether signaling the muscles to contract or relax, the neuromuscular system manipulates the stretched muscle, presumably as a protective mechanism to prevent injury.
Creating an Effective Flexibility Training Program
To create an effective flexibility training program you must first evaluate your current flexibility status by assessing various joints’ range of motion. Once you determine which of your joints are the most and least flexible, you can set some realistic goals to improve or maintain your range of motion. Be specific when you set goals. Instead of just saying, “I want to increase my flexibility,” identify the specific area of the body you intend to improve. You will also want to make sure your goal can be measured. A better way to state your goal is, “I will improve my sit-and-reach score by 4 cm by the end of the semester.” Notice this goal, as stated, includes a specific area, is measurable, and includes a deadline. By stating your goal properly, you will increase the likelihood of achieving it. When designing a flexibility program use the FITT Principle (frequency, intensity, time and type). Your flexibility program should include multiple stretching exercises that target all major joints, including the neck, shoulders, elbows, wrists, trunk, hips, knees, and ankles.
After selecting your exercises, follow the recommendations below when performing your routine:
- Frequency: Stretch a minimum of 2-3 days per week, ideally 5-7 days per week.
- Intensity: Stretch to the point of tightness or mild discomfort.
- Time (duration of each stretch): Stretch for a minimum of 10 seconds for very tight muscles with an emphasis on progressing to 30-90 seconds. Complete two to four repetitions of each stretch.
- Type (mode): Select the technique that best suits your circumstances: static, dynamic, or proprioceptive neuromuscular facilitation.
When to Stretch
Although stretching can be done any time, ACSM traditionally recommends that flexibility training be incorporated into the warm-up and cool-down phase of an exercise session. Recent studies suggests that static stretching before an exercise session will compromise the force-producing capabilities of muscles and should be avoided and that dynamic stretching is most beneficial. Static stretching should be restricted to after the warm-up or workout, when the temperature of the body and muscles has increased. Additional evidence pertaining to this concept shows that applying heat packs for 20 minutes to increase muscle temperature can increase hamstring flexibility more so than 30 seconds of static stretching. These findings confirm that temperature also plays a significant role in muscle range of motion.
In addition to warming up your muscles before performing stretching exercises, additional precautions can be taken to ensure the safety of your routine. When muscles are stretched quickly and forcefully, the stretch reflex can be activated. This creates significant tension because the muscle fibers will not only be stretching but also attempting to contract. To avoid this, stretch slowly and in a controlled fashion while holding the stretch for 10 seconds or more.
Dawn Markell & Diane Peterson, Health and Fitness for Life. MHCC Library Press. Sept 4, 2019. https://mhcc.pressbooks.pub/hpe295
North Carolina State University Department of Health and Exercise Studies. Health and Exercise Wellbeing (8th.ed.). Plymouth, MI: Hayden McNeil.