Understanding Stretching's Role in Influencing Strength

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Table 3 - Summary of studies that met inclusion criteria for Flexibility and Strength

1. Fowles, J. R., D. G. Sale, and J. D. MacDougall. Reduced strength after passive stretch of the human plantarflexors. J Appl Physiol. 89:1179-1188, 2000. 2. Knudson, D. and G. Noffal. Time course of stretch-induced isometric strength deficits. Eur J Appl Physiol . 94:348-351, 2005. 3. Kokkonen, J., A. G. Nelson, and A. Cornwell. Acute muscle stretching inhibits maximal strength performance. Res Q Exerc Sport . 69:411-415, 1998.
4. Marek, S. M., J. T. Cramer, A. L. Fincher, L. L. Massey, S. M. Dangelmaier, S. Purkayastha, K. A. Fitz, and J. Y. Culbertson. Acute effects of static and proprioceptive neuromuscular facilitation stretching on muscle strength and power output. J Athl Training . 40:94-103, 2005. 5. Power, K., D. Behm, F. Cahill, M. Carroll, and W. Young. An acute bout of static stretching: effects on force and jumping performance. Med Sci Sports Exer . 36:1389-1396, 2004.

Understanding Stretching's Role in Influencing Strength

Recent literature has created controversy within the sports medicine community about the influence of stretching on muscular strength. These articles have concluded that stretching may negatively influence strength. This conclusion has started a debate among clinicians about the role of stretching before activity. A decrease in muscular strength may be detrimental to performance or increase the risk of injury during high demand athletic events. According to research, stretching causes several changes within the muscle. It decreases stiffness of the muscle, increases compliance, and may cause physiological damage. Stretching is believed to affect the muscle in one of two ways: (1) by affecting mechanical properties including stiffness or (2) by affecting the neuromuscular control of the muscle via control mechanisms. (14)

Static stretching has become commonplace in most exercise and performance activities, usually performed prior and post-exercise or sporting activity. Historically, clinicians have used static stretching to increase range of motion and decrease muscle stiffness which theoretically will prevent injury and enhance performance through optimal neuromuscular efficiency. However, given the changes that static stretching may create in a muscle, researchers have questioned the practice of using static stretching prior to a strength activity, hypothesizing that static stretching may negatively influence strength.

While the effects of static stretching on strength may still be up for debate amongst clinicians, a literature review of five relevant research studies (see Table 3) has concluded that static stretching negatively influences strength. Researchers point to decreases in motor unit activation post-stretch, decreasing maximal voluntary contractions. (15) Marek determined that static stretching reduced both muscle strength and power and in fact, altered the mechanical properties of the muscle (using EMG and MMG data). Her study showed decreased EMG activity and increased MMG activity - leading researchers to believe that static stretching may reduce activation of a muscle and decrease muscle stiffness. (14) In fact, whether assisted or self applied, a study performed by Kokkonen (1998) determined that even short bouts of static stretching (15 second holds with 15 second relaxation times) reduced strength approximately 7-8% in the muscles tested (hip, thigh, and calf). (16) Knudson's research concurred with these results showing that 40 seconds of static stretching (done in bouts of 10 seconds for four repetitions) decreased strength when tested on the wrist flexors. (17) Of great interest was the two studies performed by Fowles and Power (18) which tested the lasting effects of static stretching up for up to two hours. These studies found that static stretching not only affected strength immediately after but 60 to 120 minutes post-stretch. These strength deficits shown up to 120 minutes post-static stretch are significant in determining the viability of including static stretching into a warm-up. However, despite the research, there are a few factors to consider. Overall, research shows that static stretching done prior to strength activity decreases strength and may affect strength up to two hours post-stretch. Researchers have determined that static stretching should not be performed in a warm-up if an individual is going to participate in high-level strength activities. NASM concurs with the researchers, however, limits agreement to a few factors. One, if muscle imbalances exist, strength might also be limited by decreased range of motion and neuromuscular inefficiency (improper length-tension relationships altering force-couple relationships - leading to altered reciprocal inhibition). Given this - static stretching should be incorporated and addressed to areas where tight/overactive muscles are shown when tested using a movement assessment. Two, improper firing of synergists during an exercise (synergistic dominance) can lead to faulty movement patterns and in effect, limit strength. Incorporating static stretching to address areas that show altered reciprocal inhibition (in turn addressing synergistic dominance) may enhance strength by increasing neuromuscular efficiency (allowing for greater recruitment of motor units).

The acute effects of static stretching have led NASM to determine pre-activity flexibility should be limited to active-isolated and dynamic stretches unless muscle imbalances are present that may impede proper movement and limit range of motion. If static stretching is used to address these imbalances, it must be followed with muscle activation to the antagonist and dynamic stretching to increase neuromuscular efficiency and motor neuron excitability pre-activity. See Table 8 for application guidelines in implementing a flexibility program to enhance strength.


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