Bushman, Barbara A. Ph.D., FACSM

Q: What is the value of stretching? Does stretching impact subsequent performance and, in particular, performance related to muscle strength and power?

A: The American College of Sports Medicine (ACSM) states, “For most adults, an exercise program including aerobic, resistance, flexibility, and neuromotor exercise training is indispensable to improve and maintain physical fitness and health” (¹). Health and fitness benefits are well documented for cardiorespiratory endurance and resistance training (^1,5,16). As a result, both aerobic fitness and muscular fitness exercises are included within the goals for Healthy People 2020. Target goals are for 47.9% of U.S. adults to be engaging in recommended amounts of aerobic activity and 24.1% to be engaging in muscular-strengthening activities (¹⁷). As a country, the most current report is encouraging, with targeted goals having been attained in these two areas (¹⁷).

Although a goal related to flexibility exercises was included in the prior Healthy People 2010 objectives, the objective 22-5 related to flexibility (i.e., “Increase the proportion of adults who perform physical activities that enhance and maintain flexibility”) has been “archived” (i.e., no longer included in 2020 Healthy People) (¹⁸). However, this is not to imply that flexibility exercises are not valued. The 2008 Physical Activity Guidelines for Americans states “Flexibility is an important part of physical fitness…Stretching exercises are effective in increasing flexibility, and thereby can allow people to more easily do activities that require greater flexibility. For this reason, flexibility activities are an appropriate part of a physical activity program, even though they have no known health benefits and it is unclear whether they reduce risk of injury. Time spent doing flexibility activities by themselves does not count toward meeting the aerobic or muscle-strengthening guidelines” (¹⁶). Although flexibility may not impact health indicators as shown with aerobic or muscular fitness, stretching exercises should be considered as a valuable component of a complete exercise program.

FLEXIBILITY EXERCISE RECOMMENDATIONS AND CONSIDERATIONS

ACSM provides this simple definition of flexibility: “Flexibility is the ability to move a joint through its complete ROM [range of motion]” (¹). Many factors impact ROM, including distensibility of the joint capsule, adequate warm-up, muscle viscosity, and tightness of ligaments and tendons (¹). The ability to fully use one’s ROM plays a role in day-to-day activities (e.g., reaching, bending, turning) as well as athletic endeavors. The value of flexibility may be brought to full attention when a loss of range of motion occurs. Consider the impact of restricting ROM with poor posture, picturing the forward rounding of the shoulders of an office worker constantly hunched over a computer screen. Similarly, aging results in a loss of flexibility (⁵). Neglecting to spend time focused on flexibility can result in an avoidable loss of ROM. Instead, flexibility exercises should be included as part of an overall exercise program as a proactive way to maintain, or even improve, ROM.

Flexibility exercises used to improve ROM can take a number of forms, including the following (¹):

• static stretching (stretch and then hold the final position for a given time)
• ○ active static stretching (holding position by contraction of agonist muscle(s))
• ○ passive static stretching (holding position with no involvement of agonist muscles, may use partner or stretching aid)
• dynamic stretching (stretch with slow movement; progressively increase the range of motion through repeated movements)
• proprioceptive neuromuscular facilitation (isometric contraction is followed by a static stretch)

ACSM guidelines point out the acute improvement in ROM around a joint after engaging in flexibility exercise and suggest chronic, or long-term, improvement can be realized with regular stretching for 3 to 4 weeks (¹). Box 1 includes ACSM recommendations related to flexibility for adults (¹). Box 2 includes some background information related to the impact of proprioceptors on the muscles’ response to stretching (⁷).

The general recommendations for flexibility exercises seem rather simple and straightforward, but there are aspects related to the specifics of a stretching routine worthy of consideration. In particular, questions have surfaced regarding the impact that the type of stretching, and timing of stretching, may have on performance. ACSM guidelines note that “Stretching exercises may result in an immediate, short-term decrease in muscle strength, power, and sports performance after stretching, with the negative effect particularly apparent when strength and power is important to performance” (¹). Acknowledging that this is an area of ongoing research, ACSM suggests including flexibility exercises as a stand-alone activity or at the end of a training session (aerobic or resistance training) especially for exercises and sports in which strength and power are key elements (¹). This recommendation reflects the positive chronic impact of stretching on ROM while recognizing concerns related to the acute changes in the muscles in the short term that may impact performance. The following section will explore some of the recent research and reviews on this topic that may be useful in developing individual stretching routines.

FLEXIBILITY AND PERFORMANCE

Increases in joint ROM seen with static stretching are associated with neural and viscoelastic aspects. Specifically, there are decreases in neural activity (motor neuron excitability decreases) and decreases in muscle stiffness (or conversely, increases in muscle compliance) (¹⁰). These result in greater ROM and freer movement, both desired outcomes of stretching. However, because of these changes, stretching may induce acute strength loss, with some suggesting this likely is due to neural aspects (¹⁰), whereas others note decreases in stiffness of the muscle-tendon unit (^11,14).

Research in this area is diverse and difficult to summarize. Moving from controlled laboratory protocols into the reality of a performance environment introduces a number of potentially confounding variables. Challenges arise in understanding how, and to what extent, stretching activities impact performance. A small decrement in performance may not be an issue for a recreational exerciser whereas the same minor change may greatly impact outcomes for an elite competitor (³). Many factors come into play when looking at research studies, including type of stretch, total duration of stretching, hold time of individual stretches, how strength is measured (and at what muscle length), and the timeframe between stretching and strength measures. To extend findings from controlled research settings into actual athletic endeavors adds even more questions. For example, stretching activities usually are not done in isolation but typically are combined with other warm-up activities and sport-specific drills (¹⁰).

A small selection of studies are included in Box 3. This is by no means a comprehensive list, but it is intended to demonstrate how individual studies each add to the body of knowledge. These insights ultimately must be considered within the bigger picture, including other research. A number of summary articles and research reviews have been published. Some highlights from these review articles follow.

Recent reviews have noted acute reductions in muscle performance including maximal strength, power, speed-dependent performance (⁹), maximal muscle strength, and explosive performance (¹⁴) because of static stretching. However, stretch duration seemed to play a role. One review noted the smallest negative impact when stretch durations were less than 45 seconds (but still a negative effect) (¹⁴), whereas another review found that no decrements in performance occurred when total duration of static stretches was less than 45 seconds, and moderate effects were found for durations of more than a minute (⁹). A more recent review confirmed moderate performance impairment (less than 5%) when stretching is done within minutes before measurement and noted the dose-response relationship with longer-duration static stretches (60 seconds or more) having greater effects than shorter-duration stretches (³). Even though the impairment is moderate, authors point out that for competitive endeavors, this might be “practically relevant” (³). For the recreational exerciser, these mild alterations likely are not meaningful.

With an awareness of potential concerns related to static stretching, many athletes turned to dynamic stretching. Once again, pros and cons need to be considered. A recent review reported an overall 1.3% improvement in performance with dynamic stretching, proposing that benefits observed may be because of warming up of the muscles (elevation of core temperature), similarity of movement between the dynamic stretching and the exercise performance, and increase in central drive (neural mechanism) (³). This supports a prior review in which dynamic stretching did not seem to have a negative acute impact on performance, and half the studies reported improvements (⁸). The researchers did point out that the benefits in ROM improvements with dynamic stretching must be balanced with the potential of such activities causing fatigue (⁸).

Proprioceptive neuromuscular facilitation (PNF) is another method of stretching, but may be less common in many settings because of the need for a partner, the uncomfortable nature of the method, and potential for greater muscle damage when muscles contract when in a highly stretched position (³). In general, PNF results in small-to-moderate reductions in performance immediately after stretching, which, as noted with static stretching, may be of limited practical importance for the recreational exercisers whereas being worthy of consideration for competitive athletes (³).

With the potential negative acute effect of stretching on strength and performance, one might question the value of flexibility exercises. With regard to acute effects, stretching is reported to improve economy of motion (¹³) as well as potential injury reduction in sports with sprint running (as opposed to overuse injuries as reported with endurance running activity and military training) (³). One research review noted the chronic effects of stretching, increasing ROM through time, as a benefit to performance involving stretch-shortening cycles (e.g., sprints, vertical jump, jump length, running tasks) (⁸). In another summary article, the benefits of regular stretching through time include increases in force and power (ranging from 2% to 5%) as evidenced in isometric contractions, isokinetic torque, and jump height as well as improvements in sprint running (¹³).

One additional consideration is the impact of preactivity stretching on subsequent risk of injury. The research is not definitive with regard to the potential of stretching to impact injury risk. Study design is a challenge when trying to identify the influence of stretching, rather than other aspects of warm-up or training, on muscle strains (¹⁰). Risk factors that add to the difficulty in determining the role of stretching in preventing muscle strains are age, prior injury, and muscle weakness (¹⁰). Some studies show the benefits of stretching whereas others show no impact; however, no studies examined in a recent review found stretching to increase acute injury risk (³).

Examination of review articles (see reference list at the end of this article) can be very helpful in gaining insights, but, ultimately, the decision to include flexibility exercises before exercise must be made on an individual basis. Some factors include one’s level of flexibility, type of activity (e.g., power, speed, strength), ROM requirements for the activity, and performance aspects. If limited ROM impacts one’s ability to carry out the movements required in the target exercise, mild impairments in strength/power might be outweighed by the benefits to be gained by an increased ROM achieved with stretching. Conversely, if ROM is already sufficient, and the activity requires force and power, then shifting flexibility exercises postactivity or in a separate training session may be preferred. Consider these examples in which the decision regarding use of preactivity stretching differs (¹³):

• An elite athlete with an established excellent level of flexibility whose sport requires quick movements and force development (e.g., soccer player) → likely would not recommend stretching before activity to avoid any potential reduction in force development.
• A recreational competitor with poor flexibility whose sport requires full ROM (e.g., martial arts, dance) → stretching before activity would be recommended to improve performance (an ongoing stretching program may result in improvements in flexibility, at which time whether to stretch before competition may need to be reexamined).

For an individual engaging in a general exercise program to improve health and fitness, considerations include current flexibility, how ROM impacts the planned activity, and potential benefits (e.g., injury reduction). Because this is still an active and evolving area of research, ACSM Guidelines state, “…it is reasonable based on the available evidence to recommend when feasible, individuals engaging in a general fitness program perform flexibility exercises after cardiorespiratory or resistance exercise — or alternatively — as a stand-alone program” (¹).

CONCLUSIONS

Flexibility exercises are recommended as part of a complete exercise program along with cardiorespiratory exercise, resistance training, and neuromotor exercise training. Although chronic improvements in ROM are possible with a regular stretching program, concerns have been raised related to the acute impact of stretching on subsequent strength and power performance. Although far from definitive, shifting stretching exercises from preactivity to postactivity may be an option to consider, or including flexibility exercises as a stand-alone program to reap the benefits of chronic adaptations.

References