Stretching's Role in Influencing Performance

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Understanding Stretching's Role in Influencing Performance
As noted above, static stretching causes several changes within muscle. It decreases stiffness of the muscle, increases compliance, and increases length by breaking chemical bonds. If these theories are true, then performance may be negatively affected by stretching. If a muscle has decreased stiffness, then there may be an increased time delay between initial contraction and force production that can be thought of as "taking up the slack" within a muscle. Additionally, altered neuromuscular control could result in lack of body control or coordination and lead to injury during high risk maneuvers. In contrast, previous research had also concluded that stretching is believed to improve performance during running and sprinting. Evidence suggests that static stretching (done prior to activity) does inhibit muscular strength as discussed in the previous section, but it is unclear if decreased strength equates to decreased performance. For purposes of this paper, performance was defined as vertical jump or other measures related to performance such as reaction time, movement time, and balance. Eight research studies met the inclusion criteria to be reviewed in this paper (See Table 4).

The debate amongst many professionals centers on the use of static stretching (one form of flexibility) prior to performance. There are many who have determined that static stretching negatively influences performance. In fact, research has shown decreases in balance, reaction times, movement times (19) , and a decrease in jump height. (20) However, there exist some contradictory studies which reveal that static stretching may increase lower-limb stiffness resulting in higher countermovement jumps (21) and potentially having no impact on vertical jump heights. (22) Of potential importance is the varied approach to the subject of pre-activity static stretching. Hunter presented a study that looked at the effects of static stretching over a duration of weeks (static stretching integrated into a 10-week program) versus the acute effects of static stretching on performance (done immediately following the stretching protocols). The acute effects may not equate to decreases in muscle stiffness and therefore the results may not match those of Young. Shrier found in his review of the literature that seven studies found beneficial effects from chronic or regular stretching programs (showing improved range of motion), with only two studies showing no effect (based on tests of running economy). (23) In fact, Shrier found clinical evidence which "strongly suggested that regular stretching increases isometric force production and velocity of contraction." (23) Kokkonen and colleagues found in their 2007 study that regular stretching protocols (40 minutes of static stretching per day, 3 times per week for 10 weeks) increased flexibility, strength (23.9%), endurance (29.5%), and power in the lower extremities. (24) These studies show that flexibility may have a beneficial influence on performance and performance measures when used on a regular basis. The influence of a regular stretching program may equate to increases in range of motion, potential increases in stretch-induced hypertrophy, and increases in power due to increases in muscle length (increased contractile velocities and forces generated at a given shortening velocity). (24) Gadjosik found significant increases in agility and walking tests after implementing a regular stretching intervention program (25) while Wilson found significant improvement in concentric and eccentric strength following an 8-week stretching regimen, finding a reduction in the stiffness of the series elastic components. (26)


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