Flexibility, Stability & Core Strength

No matter what the specific goal, physical training should include considerations of flexibility, stability and developing core strength.


If flexibility and stability can be said to be the foundations of exercise, then the core can be said to be the foundation of all limb movement. All three of the aforementioned components are interrelated, but let’s start with a look at the body’s core. As the name suggests, the core is the body’s center. It is comprised of all of the muscles of the torso including those of the back, the abdominals, and the shoulders and hips. It is what keeps the body in a straight, upright position. The body’s overall musculoskeletal performance can be thought to radiate from the core outward. If the core is weak, the extremities cannot function properly. This causes muscle imbalances in the kinetic chain. As a person ages, balance and stability become compromised. If balance and stability deficiencies are not addressed, they will continue to degrade. This is one reason why falls are more common among the elderly.

The muscles of the core are used for both stabilization and for movement. Having a strong stabilization system enables us to use our strength and power in other parts of the body more efficiently and effectively. Training the core has been demonstrated to reduce injuries across a wide range of activities, from the everyday to the athletic. Core training also prevents injury, improves posture, and in general lends a tighter overall look. Many back and hip injuries are related to weak core muscles. There are many small muscles in the core that the general population knows little about, nor addresses, during exercise.

Pictures obtained from Magnetic Resonance Imaging (MRI) often show atrophy in such small muscles in most spinal injuries. These smaller muscles also need to be trained in order to maintain a healthy spine.

Flexibility is argued by some to be the most important component of a training program. Unfortunately it is often overlooked by many, including some trainers. Lack of flexibility is the root of many kinds of movement related accidents. When a muscle is tight, its ability to contract properly is compromised, leading to inefficient movements. Muscles that are tight are more likely to become injured and cause the opposing muscle to contract improperly. Without flexibility, the body’s movements become limited and tangible results are difficult to achieve.

Stability is related to core strength, and stability exercises should be implemented into every exercise program. Stability is critical for us all. Without it, even the strongest person couldn’t effectively propel a force. Stability training starts with an efficient core routine. A weak core contributes to poor stability and inhibits proper limb movements.

Some Exercise Selection Considerations

Training for core strength involves more than just the rote performance of sit ups and hyper-extensions. A more efficient (and informed) core routine consists of dynamic movements that challenge the center of gravity and isometric exercises. Exercising with free weights and challenged environments promotes balance and stability. Medicine balls, balance boards and physio balls are great tools for core training and can be integrated into just about every program. Training primarily with machines without integrating free weights into a program is inefficient because the client is moving resistance along a fixed axis and not free in space. A weak core contributes to poor stability and inhibits proper limb movements. Without it, even the strongest person can’t effectively propel a force. Stability training starts with an efficient core routine.

When the goal is lean muscle maintenance and loss of body fat, circuit training is typically a recommended choice. Circuit training is geared towards increasing the heart rate while using some type of resistance or environmental challenge. For the general population, the benefits of this type of training exceed those of the more traditional style, single body-part sessions. It is also recommended not to try to isolate muscles, but instead try to involve as many body parts as possible while adhering to strict form. In this way, a very efficient and balanced session can be ensured. When circuit training, it is crucial to keep moving and maintain a target heart rate. Muscles become stronger when they are challenged.

Because training should involve the entire body, all major muscle groups should be addressed during strength training. Regardless of the specific exercise goal, functional training that relates to everyday activities and focuses on core stability will lead to noticeable improvements in a person’s quality of life.


1. Brumitt, Jason. Core assessment and training. Human Kinetics, 2010.

2. Akuthota, Venu, and Scott F. Nadler. “Core strengthening.” Archives of physical medicine and rehabilitation 85 (2004): 86-92

3. Willardson JM. Core stability training: applications to sports conditioning programs. J Strength Condition Res. 2007;21(3):979-985


These resources are for the purpose of personal trainer growth and development through Continuing Education which advances the knowledge of fitness professionals. This article is written for NFPT Certified Personal Trainers to receive Continuing Education Credit (CEC). Please contact NFPT at 800.729.6378 or [email protected] with questions or for more information.