Summary:

Though post-exercise stretching has been performed as a recovery modality for many decades, current research discredits this form of recovery almost entirely. It has been suggested that this practice is outdated, based on previous discredited theories, and with very little evidence to support its effectiveness. Furthermore, it has also been suggested that the research conducted in virtually all stretching-based investigations is very ambiguous, and lacks any real validity and/or reliability.

Keywords: pre-exercise, post-exercise, stretch tolerance, muscle soreness, range of movement.

Introduction

The practice of stretching after exercise (e.g. training and competition) is extremely common, and something that has been conducted for many decades. The concept of stretching post-exercise to reduce muscle soreness, re-establish ‘lost’, or pre-exercise range of motion, and thus promote recovery was perhaps first popularised after a particular research publication in the 1960’s (1). Since then, whilst the underpinning theory supporting the usefulness of post-exercise stretching has been discredited, the practice of this recovery modality still persists (2).

What is Stretching?

Stretching has been defined as…

“the application of force to musculotendinous structures in order to achieve a change in their length, usually for the purposes of improving joint range of motion (ROM), reducing stiffness or soreness, or preparing for (physical) activity.” (3).

Though there are many forms of stretching (Figure 1), static stretching appears to be the most common type prescribed in post-exercise cool-down routines. Stretching is also classified as either acute or chronic. Acute stretching typically refers to a single stretch usually lasting >30-seconds or less (4, 5). Chronic stretching refers to repeated stretches over a series of sets, days and even weeks (6).

Figure 1 - Types of Stretching stretching for recovery science for sport

What is Recovery?

Recovery is traditionally defined as a 1-stage model: that is, returning something that was lost (8), or a reestablishment of the initial stage (9). However, recovery in sport, or from exercise is seen as a 2-stage model: that is, returning what was lost (i.e. reducing fatigue), and adapting (i.e. supercompensating) to the imposed training demands (6). Given this, full recovery should not be considered complete until the athlete has achieved a level of fitness that is higher than pre-exercise levels (i.e. the supercompensation principle). This principle is simply displayed in Figure 2.

Figure 2 - Supercompensation Principle stretching for recovery science for sport

Does post-exercise stretching enhance recovery?

The primary objectives of post-exercise stretching are two-fold:

  1. Reduce the delayed-onset of muscle soreness (hereby referred to a muscle soreness)
  2. Reduce stiffness (i.e. enhance or re-establish pre-exercise ranges of motion).

Before we begin to discuss whether not stretching can improve recovery, just remember that other post-exercise modalities such as: Heat, cold, vibration, massage, hydrotherapy, anesthetics, and foam rolling have all been shown to reduce muscle soreness and enhance ROM; thus enhancing recovery (10-18).

Performing post-exercise static stretching to promote recovery has a relatively long, and somewhat confusing, history (6). This recovery modality was initially encouraged during the early 1960’s when a team of investigators thought that unaccustomed exercise caused muscle spasms (1). Muscle spasm was thought to reduce blood flow to the muscle, causing pain, and then further muscle spasm – a process therefore referred to as the ‘pain-spasm-pain cycle’.

As a result, stretching was believed to interrupt this cycle by improving blood flow to the muscle, thus leading to reduce muscle soreness and improved recovery rates. To further discredit this theory, other research has demonstrated that blood flow, capillary region oxygenation, and the velocity of red blood cells to the muscle decrease during stretching (19-21). So whilst the muscle-spasm theory has since been discredited by Bobbert and colleagues (22), the practice of post-exercise stretching to improve recovery still persists.

Muscle Soreness and Post-Exercise Stretching

Reducing muscle soreness post-exercise is an admirable goal for enhancing recovery. Though a large quantity of independent research has been conducted on the effects of stretching on muscle soreness, the quality of virtually all of these investigations have been reported as low-moderate (2). One extensive meta-analysis on this topic, including over 2,500 participants, concluded that post-exercise stretching for recovery only reduced the effects of muscle soreness by 1-4 points on a 100-point scale.

Despite this figure being statistically significant, the effect is very small and almost trivial. Unfortunately, despite its long history, and large popularity in the recovery strategies of many training programmes, post-exercise static stretching appears to have no worthwhile effect on muscle soreness.

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Range of Motion and Post-Exercise Stretching

Flexibility is usually referred to as the range of motion (ROM) around a joint, or a series of joints (e.g. the spine). Static or pre-contraction stretching techniques are perhaps most frequently used to develop, or increase, joint ROM – particularly after exercise.

It must be formally understood that there is a difference between ‘stretching’, commonly used to improve joint ROM, and ‘ROM exercises’, which can perhaps be referred to as ‘mobility exercises’ (23). Is the objective of post-exercise stretching to: 1) re-establish ‘normal’, or pre-exercise joint ROM; or 2) improve joint ROM? If it is the first answer (re-establish joint ROM), then it is recommended that dynamic, pain-free movements should be used (6). If the answer is number two (improve joint ROM), then perhaps static stretching is a more appropriate choice.

However, static stretching techniques generally require the athlete to endure ‘mild’ discomfort in order to place the muscle and tendon under tensile stress (6). This very concept of inducing pain (i.e. ‘mild discomfort’) post-exercise, in an attempt to reduce pain and promote recovery seems somewhat counterintuitive. Okay, so the idea behind this objective of static stretching is to develop or re-establish pre-exercise ROM, but recall previously, are not other recovery modalities just as useful for achieving such goals?

To our knowledge, no study has directly compared the effects of these modalities at improving ROM against each other. Even so, unless static stretching appears to be substantially superior to these other modalities, then its worthwhile is questionable. To add to this, though many investigations have observed increases in ROM after various weeks of static stretching, these improvements have been suggested to be the result of an increase in stretch tolerance (ability to withstand more stretching force), and not extensibility (increased muscle length) (24-27).

Our present knowledge after reviewing the current body of literature, would suggest that static post-exercise stretching is not very worthwhile. Instead, other recovery modalities that not only reduce muscle soreness, but also improve ROM in a pain-free manner are recommended (e.g. active recovery which includes dynamic, pain-free movements).

Issues with the current research on stretching

One key issue surrounding virtually all stretching-based research, is the current ability to appropriately quantify the intensity of stretching – i.e. how do you measure the intensity of a stretch? For example, how do you quantify, or determine, whether the stretch is slightly uncomfortable, moderately uncomfortable, or very uncomfortable during investigations as every individual has different tolerances to pain. To complicate things further, discomfort and pain may be exercise specific – suggesting that individuals may have higher stretch tolerances during certain exercises than others (12).

This also complicates things further when research is compared – as an athlete may have a higher pain tolerance for a quadriceps stretch, than for a hamstring stretch. Athletes are also often directed to perform a stretch that is pain-free, but the line between mere discomfort and pain is unclear (6). Furthermore, to the best of our knowledge, no single metric has ever been proposed which can reliably measure (i.e. quantify) the level, intensity, or magnitude of stretching. All in all, there is a wealth of issues surrounding the reliability of stretching-based investigations, this therefore makes comparing such research very problematic.

Future Research

Having discussed the potential limitations of stretching and its effects on recovery, in addition to highlighting a series of issues regarding the modality, the following topics are advisable for future research:

  • Direct comparisons between stretching and other recovery modalities and their abilities to improve ROM.
  • A metric for quantifying (i.e. measuring) the intensity of stretching.
  • Identifying pain tolerances between different stretches (e.g. quadriceps vs. hamstrings).

Practical Application (Take home messages)

The following provides clinical information, abstracted from this review, which can be applied to practical environments:

  • Post-exercise stretching appears to have a very little effect on reducing muscle soreness 1-7 days after exercise.
  • Though static stretching has been shown to improve ROM, this may be attributable to stretch tolerance and not an increase in muscle-tendon length.
  • Static stretching requires enduring mild discomfort to increase ROM, which may be conflicting to the very principle of aiding recovery (i.e. reducing soreness).
  • ROM/mobility exercises utilising dynamic, pain-free movements may be more appropriate for re-establishing any lost ROM after exercise.
  • Static stretching reduces blood flow, capillary region oxygenation, and the velocity of red blood cells to the muscle.
  • Thus, other recovery modalities such as active recovery and water immersion therapy (e.g. ice baths) may be more beneficial.

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