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Potential Effects of Dynamic Stretching on Injury Incidence of Athletes: A Narrative Review of Risk Factors

Behm, D.G., Alizadeh, S., Daneshjoo, A. and Konrad, A., 2023. Potential Effects of Dynamic Stretching on Injury Incidence of Athletes: A Narrative Review of Risk Factors. Sports Medicine, pp.1-15.

In today’s letter

• Overview of dynamic stretching effects on injury prevention

• Rapid Results = There is no clear cut conclusion, but a quick session of dynamic stretching can help muscles feel looser, reduce tension, and improve mood. These benefits can boost focus and get players mentally and physically ready for games or competitions

• 3 Reads to check out to further you knowledge about dynamic stretching

• Meme: Don’t skip your warm ups boys and girls 😄 

Aim of the study

• This narrative review aimed to examine existing research on injury rates when dynamic stretching or dynamic activities are included in a warm-up routine before sport

Additionally, the authors looked at potential factors such as:

• Range of motion

• Strength

• Balance

• Proprioception

• Muscle structure

• Psychophysiological responses

After the dynamic warm up which could influence injury rates

Did you know?

• It has been widely suggested that static stretching reduces performance in the targeted muscles and the opposing, non-stretched muscles.

• However, more recent Research show that static stretching has minimal impact on performance if it is limited to 60 seconds or less per muscle group and integrated into a warm-up routine.

This routine should include prior aerobic activity, dynamic stretching, and sport-specific movements.

• Dynamic stretching focuses on controlled movements through the active range of motion (ROM), it involves repetitive cycles of muscle tension at the end of the ROM and relaxation during mid-ROM.

• While some studies suggest static stretching can be more effective than dynamic stretching for improving ROM in a single session, research findings on this comparison are inconsistent.

• Dynamic stretching is often seen as beneficial because it doesn’t usually cause performance declines and may even enhance performance.

This positive effects could be due to several factors, such as:

1. Improved muscle reflex

2. Increased nerve and spinal cord activity

3. Better muscle temperature regulation

4. Increased muscle stiffness during movement.

• Research on dynamic stretching immediate effects is mixed, with some studies showing performance improvements, others finding no change, and a few reporting decreased performance.

• Long-term effects of dynamic stretching are also unclear; for example, ten sessions over three weeks showed no significant improvement in hamstring strength or jumping distance.

• Overall, evidence is inconsistent on whether dynamic stretching is better than static stretching for improving range of motion or performance.

Range Of Motion

• Dynamic stretching generally improves flexibility and range of motion by engaging muscles through controlled movements. Studies have shown significant increases in ROM after consistent routines, such as a 15% improvement in knee extension after 10 sets of 30-second hip extensor stretches. However, the benefits depend on the volume and duration.

• There’s debate about whether impaired flexibility increases injury risk. Some studies suggest reduced range might predict injuries, while others find no clear link. Despite this, improving range of motion with dynamic stretching is considered beneficial, especially for sports requiring a wide motion, such as sprinting and tennis.

• The amount of dynamic stretching performed is important. For instance, a single set of dynamic stretching might not change flexibility, but multiple sets (e.g., 4 or more) have shown measurable range improvements. High volumes of dynamic stretching can also lead to minor improvements or even impaired performance if overdone.

• Dynamic stretching may change the properties of soft tissues like muscles and fascia, reducing resistance to movement. It can also improve stretch tolerance, likely due to neural responses like increased muscle spindle activity, though these effects are transient and may not last beyond the activity.

• A warm-up effect is a likely contributor to improved range of motion after dynamic stretching. Dynamic movements enhance fluid dynamics in tissues, reducing stiffness and making movements smoother. This effect has been observed even after activities like a 15-minute run at moderate intensity.

• Static stretching often shows greater chronic range of motion improvements than dynamic stretching. However, ballistic movements better prepares muscles for activities involving rapid, repetitive movements, making it more practical for warm-ups in sports.

Movement

• It's important to examine how dynamic stretching affects body movements (kinematics) because previous studies have linked kinematics to the risk of injuries, especially in the lower limbs.

• While most studies primarily focus on how dynamic stretching impacts flexibility and ROM, a handful of research projects have looked into how dynamic stretching affects the way the lower limbs move during football instep kicks and landings.

• Some evidence suggests that dynamic stretching can potentially alter how the knee moves during landings, specifically by reducing knee abduction (sideways movement) and internal rotation (inward twisting).

• This change in knee kinematics can reduce the risk of injury

• However, there is no complete understanding of the underlying mechanisms. Even though these findings show a generally positive impact of dynamic stretching on joint movements, more research is needed in various dynamic tasks to reinforce these conclusions

Effects of Dynamic Stretching on Performance

• Increasing the muscle-tendon complex's ability to handle forces, especially when muscles are stretched (which is where most muscle-tendon injuries occur), could reduce the risk of injuries.

• A meta-analysis found that a single session of dynamic stretching had a positive impact on performance in activities like jumping, sprinting, agility, and strength tests in 20 studies, with small or greater improvements.

• However, it had trivial effects in 21 studies and even impairments in 7 studies. On average, these improvements were small, totaling about 1.3%.

The improved performance seen after dynamic stretching in some studies can be attributed to several factors:

1. Increased muscle and body temperature, which enhances energy production

2. Improved neuromuscular function due to dynamic stretching effect on spindle reflexes and motor neurons

3. Stimulation of the nervous system

4. Reduced inhibition of antagonist muscles.

Additionally, post-activation potentiation may enhance the rate of muscle contractions.

• Interestingly, many of these factors can also be achieved with the more limited range of motion. This raises questions about whether performing dynamic movements throughout a full range (as seen in dynamic stretching) is necessary to reap these benefit

Balance & Proprioception

• It's well-established that impaired balance and proprioception are among the various factors linked to the risk of injuries.

• In two studies (1 & 2) where participants did a single session of dynamic stretching, minor improvements in balance were observed. These improvements were seen when participants stretched the quadriceps, hip flexors, gastrocnemius, and hamstrings, and then underwent balance tests such as the Y-balance test and Star Excursion Test.

• When a separate study applied acute dynamic stretching to both upper and lower limb muscles, there was no significant impact on participants' balance. This test used a stability platform, which restricts the balance assessment to a single plane of motion.

• Another study focusing on the quadriceps, hamstrings, and gastrocnemius muscles also found no balance improvement when evaluating centre of pressure during a demi-pointe pose.

• The results for the immediate effects of dynamic stretching on balance and proprioception appear conflicting. Since there are no studies that have looked into the long-term effects on balance and proprioception, this remains a significant research question for future studies

Tissue Change

• Dynamic stretching may have potential benefits in reducing the risk of injuries, possibly by decreasing muscle-tendon junction (MTJ) stiffness. This change in MTJ stiffness can occur due to muscles and tendons becoming more flexible.

• When the MTJ becomes more flexible or less stiff, it can better absorb energy during sport, potentially reducing the severity of muscle soreness.

• Some researchers have suggested that the increase in joint range following a single session of dynamic stretching is primarily due to improved stretch or pain tolerance rather than a reduction in soft tissue stiffness.

• In cases of chronic dynamic stretching training, reported increases in MTJ compliance can alter the angle-torque relationship. This change allows for greater relative force production at longer muscle lengths, which could contribute to injury prevention by enhancing dynamic joint stability.

• Since many injuries occur when muscles are in lengthened positions where force is naturally reduced, this shift towards greater force outputs with elongated muscles may give protection against muscle strains.

• Once again, there is conflicting evidence regarding how dynamic stretching affects MTJ stiffness, both in the short term and with chronic training.

• In various studies, dynamic stretching has resulted in decreased stiffness, no change, or even increased stiffness in muscles/MTUs.

• Consequently, based on the available evidence, it's challenging to draw a definitive conclusion about whether dynamic stretching-induced alterations (or the absence of alterations) in MTJ stiffness and compliance can prevent injuries.

Persons Psychology

• Dynamic stretching might have mental benefits for athletes

• The possible positive impact on psychosocial stressors and influences on emotional states, lead to potential improvements in psychophysiological aspects like reduced muscle tension, enhanced concentration or focus, and better mental readiness for games and competitions.

3 resources to check out

And further you knowledge on dynamic stretching

1. Dynamic warm up example - (PDF) - LINK 🏃‍♀️

2. Calf complex strengthening - (article) - LINK 🤸‍♀️

3. Dynamic stretching VS Static stretching

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