Correlation Between Stretching & Isokinetic Strength

If you have ever attended a yoga class, you may have questioned how a slender girl with little definition can hold a pose for a sustained period of time while a bodybuilder struggles. This is explained by the length-force curve, which states that at optimal length a muscle will produce maximum force. In other words, if a muscle is worked out and not stretched or stretched to a hyper-elongated state, it cannot produce maximal force.

  1. Types of Muscle Contractions

    • Isotonic, isometric and isokinetic are the three types of muscle contractions. In an isometric muscle contraction, the joint and muscle fiber length is fixed. An example is when you hold a stretch or exercise for several seconds or minutes. An isotonic contraction involves a constant load through a certain range of motion -- for example, weight lifting. On the other hand, isokinetic contractions are performed at a constant angular velocity and rate of muscle fiber shortening. Exercise machines that regulate velocity are treadmills and ellipticals. In rehabilitation, physical therapists use machines like the KinCom, Cybex and Biodex.

    Stretch Duration for Maximal Strength

    • In an article published in the 2006 edition of the "Journal of Bodywork and Movement Therapies," researchers from Aristotle University of Thessaloniki, Greece, discussed the relationship between duration of stretch and isokinetic strength. They found that when stretches were practiced for two repetitions or more, isokinetic strength decreased. However, when stretches were held for 30 seconds and only performed once, isokinetic strength was not affected. This suggests that individuals should stretch before activity but that they should limit the length of the stretch to 30 seconds and complete one repetition.

    Myofascial Trigger Points and Stretching

    • Myofascial trigger points can either be muscle contractual knots or adhered fascia, the surround sheath around muscle fibers. If contractual knots are present within the muscle, the muscle fibers in the area of the knot will be shortened. If the myofascia, muscle and its surrounding fascia, is adhered then the muscle loses flexibility, muscle fiber length and range of motion. In both cases, the muscle experiences decreased isokinetic strength. Stretching is an effective way to treat myofascial trigger points. Therefore, it is important to stretch muscles to maintain optimal muscle length and generate maximal isokinetic force.

    How to Stretch Safely

    • A way to sustain muscle at the peak of the length-force curve is to stretch in a heated room. Stretching when your muscles are cold puts them and their associated tendons at risk for tears. By heating your muscles before you stretch or stretching in a heated room, you can secure muscle lengthening instead of stretching or tearing tendons and ligaments. Stretching tendons and ligaments can bring instability to your joints, also decreasing isokinetic strength. For maximal isokinetic strength, stretch your muscles when they are warm. Hold your stretches for up to 30 seconds and only perform them once.