Stretching in sport
Apparently we stretch to 1) improve flexibility and 2) to reduce injury rates.
What limits flexibility?
- Viscoelastic muscle properties (viscosity and titin?)
- The nervous system (reflexes may limit the stretch we can experience)
- Joint structures (bones, capsules, ligaments…)
- Skin tightness? (only some joints)
The nervous system seems to play a role in limiting muscle extensibility. There are also some physical characteristics that seem to play a role. Of the factors listed above, only the first two are ideally trainable (although extreme forces may result in adaptations to joint capsules or ligaments resulting in laxity – not ideal for athletes!)
Short and long-term effects of stretching
- Decreased stiffness and viscosity
- Neural changes including decreased excitation of motor neurons and reduced stretch reflex
- Muscular changes including perhaps less x-bridge numbers and transient deformation of muscle proteins (titin?)
Adaptations to regular flexibility training have been relatively poorly investigated. This means we have some hypothesising to do about what’s actually going on!
- Neural changes include increased stretch tolerance (the most significant adaptation in the first three weeks!) and reduced tonic reflex activity
- Muscular adaptations include reduced connective tissue content, reduced collagen cross-links (?), increased in-series sarcomeres (?) and deformation of connective tissue (in muscle and tendon?)
- Perhaps some changes in the joint capsule?
Kubo et al (2002) have shown reduced resistance to stretch after 20 days of stretching twice a day 5x45s. These changes were not due to neural adaptations.
Effect of detraining
Guissard et al (2004) showed that 74% of the gains made in a 6 week stretching program were still evident after a month of detraining (no stretching performed) – not too bad!
- There’s little evidence regarding how hard to stretch. Stretch as far as possible and apply overload (stretch further) over time.
- Stretching >60s seems to result in no further gains in flexibility.
- Total volume (reps x duration)
- Method (static, PNF, ballistic, dynamic…)
- Static stretching is regularly encouraged over ballistic stretching although the evidence doesn’t support the superiority of either over the other. There are studies that show similar increases in ROM with use of each method (La Roche et al 2006, Sady et al 1982). Bounce-type stretches may have some functional specificity (applicability) to sports with similar tasks (eg kicking in AFL).
Are more flexible people less prone to injury?
Maybe. But probably not.
“The basic science literature supports the epidemiological evidence that stretching before exercise does not reduce the risk of injury.”
- Shrier et al., 1999
“Due to the paucity, heterogeneity and poor quality of the available studies no definitive conclusions
can be drawn as to the value of stretching for reducing the risk of exercise-related injury.”
- Weldon et al., 2003
“There is not sufficient evidence to endorse or discontinue routine stretching before or after exercise to prevent injury among competitive or recreational athletes”
- Thacker et al., 2004
“Does not meaningfully reduce lower extremity injury risk”
- Andersen et al., 2005
“There is no evidence in the literature for a preventive effect of stretching on the occurrence of athletic injuries.”
- Gremion et al., 2005
"...flexibility of the muscle groups included in the stretching program were not predictors of hamstring injury."
- Gabbe et al., 2006
"A general consensus is that stretching in addition to warm-up does not affect the incidence of overuse injuries."
- McHugh and Cosgrave, 2010
“Stretching before exercising does not seem to confer a practically useful reduction in the risk of injury”
- Herbert et al., 2012
“Our data do not support the use of stretching for injury prevention purposes, neither before or after exercise”
- Lauersen et al., 2014
“Static stretching had no clear effect on all-cause or overuse injuries.”
- Behm et al., 2016
“ The literature fails to demonstrate any clear relationship between low levels of spine flexibility with LBP.”
- Ruas et al., 2017
"Static stretching had no clear effect on all-cause or overuse injuries." (Thacker et al., 2004)
While there isn’t enough evidence to support the benefits of stretching, there is insufficient evidence to categorically state that it is not worthwhile. You abandon it at your peril! There’s evidence to suggest that activities could be divided into categories – those in which stretching does not influence injury risk and those in which it quite possibly does.
Are there negatives to stretching?
Moderate (2-5mins) and severe (30mins) doses of stretching have been shown to reduce strength and power including counter-movement jump height and balance. Although it’s important to note that these doses are probably more than most would do! It’s also important to note that there are other studies that have shown no decline in performance with stretching when performed by athletes (e.g., Unick et al., 2005).
Stretching mostly improves your tolerance to the stretch, with small physical changes occurring with high volumes of stretching at moderate to high intensities of effort. It may reduce your chance of injury, but if so, not by much (and it probably depends on the sport/activity).
Bottom line: don't stretch at the expense of more high-value activities (for example, strength training). But include it if you can.
How to stretch well
To stretch a muscle effectively you need to know what actions it has. You then need to do the opposite movements. If a muscle has 2 or 3 actions you need to oppose all of them. For example, the biceps brachii flexes the shoulder and elbow and supinates the wrist (turns the palm up). Therefore, to stretch it you would need to extend the elbow, extend the shoulder and pronate as far as possible. To stretch the TFL (and attached ITB) you will need to know that it flexes and abducts the hip. To stretch it you need to adduct and extend simultaneously.
When performing these and other stretches it is important to consider which muscles might be the limiting factors. Two joint muscles such as the gracilis can be limiting during adductor stretches with extended knees but are not when the adductors are stretched with flexed knees.
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