Research offers insight into flexibility, function and the pros and cons of stretching prior to activity.
Flexibility is an essential fitness component that decreases with age and physical inactivity. Traditionally, stretching as a warm-up has long been recommended for individuals who engage in exercise for rehabilitation, injury prevention, health improvement and athletic performance enhancement (American College of Sports Medicine [ACSM] 2006, Kovacs 2006, Shrier 2004). The proposed goals of acute stretching prior to physical activity to enhance performance include improved coordination and proprioception, increased range of motion (ROM), reduced injury potential, improved circulation and decreased muscle viscosity, which leads to smoother muscle contractions (Fredette 2001). However, in recent years there has been growing concern about whether or not stretching should be included in the warm-up phase. Mounting evidence suggests that pre-exercise stretching plays a limited role in injury prevention and may unfavorably impact exercise performance.
Two recent reviews on the topic have suggested that, contrary to popular belief, there isn’t adequate evidence to support the notion that pre-exercise static stretching reduces injury. In one review (Pope et al. 2000), the authors reported no significant reductions in the incidence of lower-limb injuries in people who stretched prior to exercise compared with those who did not. The other review concluded that pre-exercise static stretching does not lower the risk of local muscle injury (Shrier 1999). There does appear to be some benefit in reduced injury risk if static stretching is performed at other times, including postexercise and in the evening (Shrier 2004).
In the 1980s and 1990s, scientific literature suggested that pre-exercise static stretching positively enhanced performance (Kovacs 2006). However, current research findings demonstrate that pre-exercise stretching is ineffective and may contribute to a decrement in performance. Recent studies clearly suggest that an acute bout of pre-exercise static stretching reduces explosive jumping and sprinting abilities and inhibits maximal strength and power during various muscle actions. Why do these poststretching deficits occur? The reasons proposed include decreases in muscle stiffness, in neuromuscular activation and in muscle reflex sensitivity (Evetovich et al. 2003, Marek et al. 2005, Shrier 2004).
The following review looks at current and past literature dealing with pre-exercise stretching and performance. From this examination, recommendations can be made regarding pre-exercise stretching in various populations, the overall timing of stretching (including when it provides the greatest benefit to overall performance) and directions for future research.
Before we review the effects of pre-exercise stretching on muscular-force development, we must first understand the physiology behind this phenomenon. Scientists theorize that stretching-induced force deficits involve mechanical factors and neural factors. Most authors agree that both factors interact and contribute to create a muscular-force deficit following stretching.
The mechanical factor most responsible for decreases in force and power production is the temporary loss of muscular stiffness following stretching (Kokkonen, Nelson & Cornwell 1998, Marek et al. 2005, Shrier 2004). This loss increases the length of sarcomeres within individual muscle fibers and decreases the contact between actin and myosin, thereby altering the length-tension relationship and decreasing force (Nelson et al. 2001). In addition, the muscle fibers must shorten over a longer distance to reach maximal contraction. This can pose a problem for explosive-power performance because the muscle can’t contract rapidly or generate maximal force. Decreased stiffness also affects eccentric force development and alters the stretch- shortening cycle, thus affecting power development during plyometrics or jumping (Young & Elliott 2001).
The neural factor most responsible for reductions in force and power production is decreased neuromuscular activation. Even though data support this theory, how the effect occurs is not well understood. The leading thought is that stretching induces a neuroinhibitory mechanism that affects neural input to the muscle (Marek et al. 2005). One study concluded that decreased muscle activation was at least partially responsible for a decrease in muscular force among subjects (Behm, Button & Butt 2001). Another study that looked at the influence of stretching and warm-up exercises on Achilles tendon reflex activity theorized that decreases in neural activation might also accompany decreased reflex activity in muscle (Rosenbaum & Henning 1995). Additionally, the neuroinhibitory mechanism changes the ability of muscle to handle eccentric loading during exercise and could potentially increase, rather than prevent, the risk of injury (Marek et al. 2005).
Static stretching is what fitness professionals most commonly advocate for the general population. This form of stretching is recommended over other types because it involves minimal risk of injury, is time-efficient, requires little assistance and is effective at improving joint ROM. The following research evaluated the ways that static stretching affects different aspects of performance.
Muscle Strength and Power. Deficits in strength and power measurements following static stretching have ranged from 5% to 30%, according to Young and Behm (2003). Other researchers who measured one-repetition maximum (1RM) performances for knee flexion and knee extension found reductions of 7.3% and 8.1%, respectively, following acute static stretching (Kokkonen, Nelson & Cornwell 1998). A third study showed decrements in 1RM scores for knee extension (-5.7%) and knee flexion (-3.6%) following an acute bout of static stretching in individuals who had also just finished a 10-week flexibility training program (Nelson, Kokkonen & Eldredge 2005).
Researchers reported reductions of 28% in maximal voluntary contraction (MVC) of the plantar flexors following static stretching (Fowles, Sale & MacDougall 2000). These investigators found that there were still decrements of 9% in MVC 60 minutes later. Marek et al. (2005) noted significant decreases in peak torque (rotational force) and mean power output (determined by isokinetic muscular testing) following static stretching. Peak torque and mean power output decreased by 2.8% and 3.2% respectively during slow and fast contraction speeds. This was one of the first studies to demonstrate that torque and power output values are reduced during faster, more explosive muscular contractions. Lastly, Behm, Button and Butt (2001) found significant decreases (-12.2 %) in isometric MVC of the quadriceps following a static-stretching protocol.
Jumping Performance. Numerous researchers have reported that jumping performance is impaired following an acute bout of static stretching. One study found that drop jump performance decreased by 6.9% in subjects who warmed up with a static-stretching routine compared with a group of controls who warmed up without stretching (Young & Elliot 2001). These authors concluded that static stretching reduced eccentric muscular-force development and thus decreased the muscles’ stretch-shortening cycle, which is crucial to maintaining jumping performance. Similarly, another study reported that vertical-jump performance decreased by 1.5% following an acute bout of pre-exercise static stretching (Church et al. 2001). Shrier (2004) has suggested that the average decrease in vertical-jump performance following static stretching is 2.5%.
Young and Behm (2003) compared jumping performance results following four different warm-up protocols: a 4-minute run; static stretching; a 4-minute run and static stretching; and a 4-minute run, static stretching and practice jumps. The data revealed significantly lower performance on jump height, peak force during jumping and rate of force development following static stretching alone. The greatest improvements were in the run and in the run, stretch and practice groups. Running and practice jumps appeared to influence jumping performance more than static stretching did. Conversely, one study found that stretching prior to competition did not negatively impact vertical-jump performance in trained women (Unick et al. 2005). Likewise, Burkett, Phillips & Ziuraitis (2005) reported that vertical-jump performance was unchanged following a warm-up that incorporated a bout of static stretching.
Running Speed. There have been equivocal findings on the effect of pre-event static stretching on running performance. Two studies reported an inhibitory effect on running speed after an acute bout of static stretching (Nelson et al. 2005; Siatras et al. 2003). However, a third study reported improved flying 20-meter (m) sprint times in professional soccer players following a warm-up that incorporated static stretching (Little & Williams 2006).
Conversely, investigators who studied the effects of different static-stretching protocols (active and passive) on 20 m sprint performance among 97 rugby players reported significant increases in sprint times following both protocols (Fletcher & Jones 2004). An increase in 20 m sprint time in 16 division-1 track athletes was also attributed to passive static stretching (Nelson et al. 2005). Static stretching of both legs or of either the left or right leg prior to sprinting led to a significant increase (0.04 seconds) in 20 m sprint time. At elite levels of athletic competition, this small increase could be the difference between winning and losing a race.
Another investigation found improved running economy following static stretching (Godges et al. 1989). However, individuals in this study had tight hip flexors or extensors prior to the study. Consequently, the potential beneficial effects of pre-exercise static stretching on running economy for the general population are still unclear.
Muscular Strength Endurance. One study investigated the effects of an acute bout of static stretching on knee-flexion muscle strength endurance in a group of males and females (Nelson, Kokkonen & Arnall 2005). Muscle strength endurance was 28% lower after the stretching bout than it was after no stretching. The authors’ recommendation: Avoid heavy static stretching prior to maximal muscle strength endurance exercises.
Collectively, present research findings suggest that there are no ergogenic benefits, and there are potentially detrimental effects, to incorporating static-stretching exercises into the warm-up routine. These findings are consistent among different populations and research designs (Shrier 2004). Accordingly, a choice to include static stretching in pre-exercise routines warrants careful examination, and may ultimately need revision. Table 1 provides a brief summary of the current research findings on the physiological effects associated with an acute bout of pre-exercise static stretching.
Since studies have not been supportive of static stretching prior to exercise, researchers have begun to study other types of stretching to identify whether any of them might enhance exercise performance. Proprioceptive neuromuscular facilitation (PNF), ballistic and dynamic stretching are all effective at increasing ROM; however, they differ in their effectiveness for improving exercise performance. Table 2 provides a summary of research findings from selected studies focused on these modalities.
PNF stretching uses a contract-relax technique to relax muscle through spinal reflex mechanisms (Heyward 2006). Typically, PNF involves having the client contract against resistance for approximately 5–6 seconds and then relax to accept an assisted static stretch for up to 30 seconds. For enhancing ROM, this method has proved to be superior to static and ballistic stretching (Heyward 2006).
Authors from two studies looked at the effects of pre-exercise PNF stretching on exercise performance. One examined the short-term effects of PNF stretching on ROM; peak torque and mean power output, determined by isokinetic strength testing; and EMG signal amplitude (Marek et al. 2005). Subjects performed four lower-body PNF stretches prior to muscle testing, holding each stretch for 30 seconds. Results showed significant decreases in peak torque, mean power output and EMG signal amplitude (decreased neural activation). These findings were observed during slow and fast muscular-contraction speeds during isokinetic testing. Overall, this study demonstrated that decreased neural activation will lead to decreases in muscular performance during slow and fast muscular-contraction speeds.
The other study compared the effects of different warm-up protocols on explosive-force production and jumping performance (Young & Elliot 2001). The warm-up trials consisted of 5 minutes of jogging followed by lower-body static or PNF stretching; exercise at 100% MVC; or rest (control group). Subjects held each stretch for 15 seconds and performed two vertical-jump tests after each warm-up trial. Investigators found no differences in jumping performance following the different warm-ups (including the rest protocol).
Ballistic stretching is performed by quickly bouncing through ROM to produce a stretch in the muscle. Although this has been shown to increase ROM, it is not recommended, owing to the risk of injury and muscle damage (ACSM 2006; Heyward 2006). Only one study has been designed to determine the acute effects of ballistic stretching on exercise performance. Nelson & Kokkonen (2001) studied the effects of ballistic stretching on lower-body maximal muscular strength determined by 1RM. Subjects performed maximal knee-extension and knee-flexion exercises following either 10 minutes of sitting or 20 minutes of lower-body ballistic stretching. The results demonstrated significant decreases in both maximal knee-extension (5.6%) and knee-flexion (7.5%) strength following ballistic stretching. These losses were attributed to the same factors associated with decreases in strength due to static stretching.
Dynamic stretching involves movements that mimic specific actions that will occur during exercise. The major advantage of this type of stretching is that it involves controlled movement and therefore enhances the overall warm-up. Dynamic stretching also provides a rehearsal effect that may increase coordination and provide specific benefit to involved muscles.
Fletcher and Jones (2004) compared the effects of static- and dynamic-stretching protocols on 20 m sprint performance. Subjects who performed dynamic stretching prior to sprint performance significantly improved (decreased) sprint time compared with those assigned to other warm-up protocols. Little and Williams (2006) examined the effects of static and dynamic stretching on acceleration, maximum speed, vertical jump and agility. Participants performed dynamic and static stretching for 6 minutes on the lower-body muscles involved in the performance tests. For vertical-jump performance, researchers observed no difference between static and dynamic stretching. Dynamic stretching produced significantly faster 10 m run times (acceleration) than no stretching and better zigzag run times (agility) than both static and no stretching. Dynamic and static stretching significantly improved flying 20 m run times (speed) over no stretching. Researchers attributed the results to the active warm-up associated with dynamic stretching, which included specific movements that mimicked later performance, enhanced blood flow and increased core temperature. Pre-exercise activation of the stretched muscles was another factor.
Overall, there is a lack of research involving other than static forms of stretching. Therefore, it is important to summarize and make recommendations with some degree of caution. Current findings suggest that warm-up routines incorporating ballistic and PNF stretching do not enhance performance. However, research involving dynamic stretching as part of a warm-up routine looks more promising. Studies on this topic have shown significant improvements in acceleration, speed and agility during exercise. Early recommendations by some authors to include dynamic stretching in the pre-exercise routine are indeed appropriate, based on limited research, but further studies are warranted.
It is clear from examining the current research that there are significant decrements in force and power during exercise following stretching. The greatest deficiencies in performance were observed following static stretching; however, losses were also observed after ballistic and PNF stretching. Research on the latter modalities is lacking. While the main purpose of this article has been to outline the effects of pre-exercise stretching on exercise performance, in no way can we make broad recommendations to completely remove static or PNF stretching from client programs. Therefore, decisions regarding pre-exercise stretching and its timing must be made in a context-specific manner (Marek et al. 2005).
Exercise professionals must weigh the advantages and disadvantages of stretching for clients at all levels of function, from athletes to the deconditioned. Again, the overall results must be applied in a context-specific manner. Where does pre-exercise stretching fit, if at all? For instance, postrehabilitation clients and others with limited ROM may benefit more if functional ROM is emphasized over strength or power development. In such cases, pre-exercise static or PNF stretching would be the most important priority. The opposite is true for clients engaging in strength or power training activities. According to research, pre-exercise stretching is detrimental for a client attempting to increase speed, jumping ability, acceleration and agility (Young & Elliott 2001).
Some authors also recommend considering a risk-benefit ratio when implementing pre-exercise stretching strategies (Marek et al. 2005). For example, individuals who have very limited ROM may benefit from stretching first in order to perform subsequent exercise. The enhanced ROM will augment exercise performance, but the cost of improvement may be an increased risk of injury (Shrier 2004). Other authors recommend pre-exercise stretching during warm-up only for individuals who perform movements through a potentially extreme ROM for aesthetic or scoring reasons (e.g., dancers, divers and gymnasts) (Knudson 1999). However, it is clear that benefits from ballistic stretching do not outweigh potential risks, and this practice is not recommended for use at this time (Nelson & Kokkonen 2001).
According to current but limited research findings, dynamic stretching appears to be the best method to employ prior to exercise for significantly improving exercise performance. This method is recommended over static and PNF stretching because it provides an active warm-up; uses specific movements that mimic training or competitive performance; increases blood flow and core temperature; and activates muscles that will be involved in the activity (Little & Williams 2006).
The overall goals a client has regarding flexibility and performance are greatly impacted by the timing of stretching in relation to exercise. Kovacs (2006) recommends no static stretching within an hour prior to exercise or competition for activities involving a force or power component. The sidebar “Sample Stretch” on this page outlines a typical routine for clients who engage in such activities. If a client’s goal is to improve ROM, then static or PNF stretching following exercise is best for maximizing flexibility without affecting performance.
Shrier (2004) outlined seven studies that demonstrated that regular, postactivity stretching had beneficial effects on muscular force and power during exercise. When ROM increases, the muscle may be able to use the stretch-shortening cycle to a greater degree for increased power development, owing to increased loading prior to contraction. Regular stretching over time can elicit a stretching-induced hypertrophy that may lead to greater force and power output in the muscle. Shrier (2004) reported that stretching muscle as little as 20% beyond its resting length can cause damage, resulting in decreases in force. Repeated over time, this cycle of damage and repair may lead to muscle fiber hypertrophy and thus greater power and force output.
Interestingly, regular stretching was not associated with increases in running economy. This was because decreased muscular stiffness lowers the amount of energy needed to contract muscle. Therefore, practical suggestions for clients who engage in endurance running may include pre-exercise (dynamic, static or PNF) stretching to enhance running economy.
There remain a host of unanswered questions regarding stretching modalities and their effects on exercise performance. Areas that future studies may address include molecular mechanisms behind stretching-induced force and power declines; the effects of regular stretching and performance; and the effects of stretching on performance during an injured state. Such studies will continue to shed light on this important topic and its relationship to exercise performance.