Understanding Flexibility and its Effect on Performance and Injury Prevention by Kyle O’Toole CSCS, CES, CPT


[This is a guest post by Kyle O’Toole is a Certified Strength and Conditioning Specialist with National Strength and Conditioning Association and a Corrective Exercise Specialist and Certified Personal Trainer with National Academy of Sports Medicine. Kyle recently completed the Athletic Development Mentorship  at Athletic Lab and you can reach him on Instagram @beyourownbest4life.]

Even with no conclusive evidence on how flexibility relates to athletic performance, the pursuit of optimal flexibility remains a high priority for many strength and conditioning coaches. Flexibility can be defined as the range of motion (ROM) about a joint of the body. Multiple factors help contribute to a joint’s available ROM. Some of these factors include the integrity of the joint capsule, tendon and ligament structure, and muscle belly size, all of which will be discussed in more detail below.

Optimal Flexibility

Why is optimal flexibility important? Some professionals spend their entire careers delving into answering this question. I’ll provide a “cliff notes version” to save time. Flexibility affects how a person moves. There is an optimal ROM within every joint in the body, that should provide us with a window of pain-free movement. Efficiently moving within this window is vital for everybody, including athletes. Poor flexibility causes imbalances, which leads to potential instability and pain. Over time instability and pain can lead to muscle strains, chronic tendonitis, or worse.

As a coach it is important to emphasize to your athletes, just how important flexibility is to their long-term goals.

Viscoelastic Properties

When talking about flexibility, we want to understand the pivotal role that muscles and tendons play. Both muscles and tendons are viscoelastic. This means their mechanical behavior is highly dependent on the amount of mechanical stress that is placed upon them. They are more deformable, or less stiff, at lower levels of stress, and less deformable, or stiffer, at higher levels of stress. As their stiffness increases, their ability to transmit higher amounts of force also increases. It’s the viscous property within muscles and tendons that allows them to resist the mechanical stress, and the elastic property that allows them to return to their original length once that mechanical stress has been removed.

As a coach it is important to remember, decreasing the viscoelastic property of a muscle will decrease the stiffness of the tissue. Increasing the viscoelastic property of a muscle, will increase the stiffness of the tissue.

Joint Mobility and Symmetry

Joint mobility also plays a pivotal role in overall flexibility. Synovial joints within the body are surrounded by a joint capsule. This joint capsule is a thin, two-layered tissue that holds synovial fluid around the joint. The inside layer of the joint capsule is known as the synovial membrane. Its purpose is to secrete the synovial fluid and help each joints surface to move smoothly across another. The outside layer of the capsule contains fibrous connective tissue that helps maintain the structure of the joint by holding it in place. If either layer of the joint capsule is damaged, the integrity of the joint is in question and pain and discomfort ensue.

Joint mobility can adapt based on the sport the athlete is involved in. Overhead athletes tend to have decreased, internal ROM in their dominant shoulder compared to their non-dominant side.2,3 This decreased ROM causes asymmetries between the left and right side of the body. Does your baseball or tennis player need to possess symmetrical movement between their throwing and non-throwing, or serving and non-serving sides? This is not an easy question to answer, but asymmetries like this seem necessary for athletes to compete at higher levels of these sports.

When working with athletes who perform asymmetrical movements, (baseball players, golfers, tennis players, throwers, etc.) similar joint mobility between each side of the body could be a limiting factor.

Muscle Bulk

A significant amount of muscle bulk can inhibit a joint’s ROM.1,3-5 Just think how differently a bodybuilder moves compared to a sprinter. The demands of the sport dictate the ROM that is required of the athlete. Resistance training that is geared toward increasing muscle hypertrophy with limited ROM during each exercise can decrease the available ROM over time.4 To prevent a loss of ROM, make sure your athletes perform exercises that develop agonist and antagonist muscles, through the entire available ROM of the involved joints.5

As a coach think about the requirements of the sport. The need for full ROM about a joint may supersede the need for muscle hypertrophy. With this, keep in mind the potential negative effects that muscle bulk has as it relates to overall joint mobility.


  1. Church, JB, Wiggins, MS, Moode, FM, and Crist, R. Effect of warm-up and flexibility treatments on vertical jump performance. J Strength Cond Res 15:332-336, 2001.
  2. DeVries, HA, and Housh, TJ. Physiology of Exercise for Physical Education, Athletics and Exercise Science. 5th ed. Dubuque, IA: Brown, 1995.
  3. Joyce, D. High Performance Training for Sports. Champaign, IL: Human Kinetics, 2014
  4. Leighton, JR. A study of the effect of progressive weight training on flexibility. J Assoc Phys Ment Rehabil 18:101, 1964.
  5. 5. Shrier, I. Does stretching improve performance? A systematic and critical review of the literature. Clin J Sp Med, 14:267-273, 2004.

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