Wilkinson, M., & Williams, A. (2003). Too much of a good thing? Why increased joint flexibility may damage your distance performance. Peak Performance, 175, 5-6.

This is a well presented review article that looks at the research covering stretching and its effect on running economy. A number of statements concerning beliefs and theories regarding flexibility are made.

• "There is little evidence to support the claim that non-pathological [naturally endowed] muscle tightness reduces running economy, so impairing performance" (p. 5).
• "There is a growing body of evidence to suggest . . . that a lack of flexibility in certain areas of the body may be linked with increased running economy. And it is interesting to note that studies of competitive distance runners have shown them to be less flexible than non-runners" (p. 5)
• Decreased flexibility in the trunk and hip prevented trunk rotation and hip turn-out while running, both restrictions improving running economy.
• Decreased flexibility in the ankle (tightness in the calf and soleus muscles), and the lower back/hamstrings were associated with better running economy.

One explanation why a lack of flexibility actually increases running performance is that it reduces energy expenditure by enhancing elastic energy storage and return in the Achilles tendon and calf muscles.

• "Previous work has suggested that elastic recoil of muscle and tendons can contribute 25-40% of the energy necessary for subsequent movements in a maximally stretched muscle [Cavagna,G. A., Saibene, F. P., & Margaria, R. (1964). Mechanical work in running. Journal of Applied Physiology, 19, 249-256; Cavagna, G. A., & Margaria, R. (1966). Mechanics of walking. Journal of Applied Physiology, 21, 271-278.] (p. 6).

• "It is reasonable to suggest that inflexibility around the ankle joint would result in a greater relative stretch of the tight muscles and tendons, storing more elastic energy for subsequent recoil and reducing the active work of the muscles" (p. 6).
• "Musculoskeletal tightness can also explain the beneficial effects of limited hip/trunk flexibility . . . Limited external hip rotation could enhance running economy by stabilizing the pelvic region at the time of foot impact. Since running occurs primarily in a forward direction, rotational motion is potentially energy-wasting as it does not contribute to forward movement" (p. 6) [Thus, actions in baseball that are aligned to produce forward momentum on a ball do not need to have above-natural flexibility. So exercises that stretch abdominal muscles laterally and forward and backward would only serve to reduce the elastic energy potential of a segmented action because other muscular contributions would be required to halt the "softened musculature" from moving.]
• "There is a cut-off point where inflexibility ceases to be tightness within a normal range of motion and becomes excessive to the point of increasing injury risk. Clinically, excessive muscle tightness is believed to be an important cause of such injuries as muscle strains and inflammation of tendons" (p. 6)

Implication. ". . . while general stretching, designed to maintain existing levels of flexibility and muscle function, should remain an important aspect of every runner's warm-up and cool-down routines, improving flexibility beyond levels normal [natural] for runners is likely to impair rather than improve performance" (p. 6)

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