Before the home stretch

A no BS guide to DS.

Literally nobody: how should I warm up?

Me: Yes.

What is dynamic stretching?

Tennis is a combination of various athletic movements like jumping, throwing, accelerating, cutting, back-pedalling and a whole lot more. The nature of these activities is such that they have to be performed somewhat explosively. Dynamic stretching (DS) serves as a way to take your joints through a full range of motion (ROM) in an explosive albeit controlled manner.

There is no standardised definition of DS and the literature doesn’t do well to distinguish between DS, ballistic stretching (BS) and dynamic exercises. A wise man told me that discussions on semantics would yield more semantics and therefore, in an attempt to simplify the noise, I would define DS as any move that fulfils the following two conditions.

a) The movement is active - the subsequent contraction and relaxation of your muscles is what facilitates movement. This happens in a controlled fashion. b) The joint is progressively taken through its full ROM. This ROM is achieved without the help of pilates straps, a partner, a wall, blah-blah.

Let’s answer some questions.

Does DS increase body temperature?

As the name suggests, a warm-up is meant to increase your body temperature. We know the benefits of keeping warm. Read my first post if you need a reminder. Muscles produce heat when they contract. DS requires you to contract your muscles actively and repeatedly, and this increases temperature and heart rate. On the other hand, SS involves holding elongated positions for extended times, not increasing temperature in the process. When was the last time you broke a sweat static stretching? Probably never.

How does this help with flexibility?

Tennis can demand extreme ranges of motion and oftentimes we are forced into whacky positions. It helps to be able to access such positions volitionally. DS serves as a way to train these ranges in a more controlled environment. In other words, DS is good flexibility training and has been shown to improve ROM acutely. The increased muscle temperature causes decreased viscous resistance of muscles, allowing them to elongate further.

Is DS the only way to access such positions?

Not really. I don’t believe that players like Serena and Dimitrov can attain those crazy positions but for a couple of prior high-knees and butt-kicks. Is DS correlated with improved ROM? Sure. Is it the cause of it? No. Some players are more naturally flexible than others and it would be impossible to ascertain the degree to which stretching contributes. As per our definition, anything that constitutes active, full ROM movement can be construed as DS. Strength training especially with eccentrics, some forms of yoga, few martial arts practices, calisthenics, etc should be able to serve you just as well. In this study, the author found exactly that.

Flexibility can be improved as long as the muscles undergo elongation during a regular tennis warming up either by incorporating calisthenics in full ROM dynamic flexibility exercises or via muscle elongation in field specific-tennis movements.

But where DS has the upper hand is in simulating specific sporting movements. DS can’t replicate the intensity of a tennis match (nothing can) but it serves as a milder form of training these ROM requirements. The idea is that you’re preparing the body for what is to come. The reason SS isn’t performed is because SS has been shown to decrease muscle activation, and force production and power output as a result. DS shows no such performance decrements.

If the objective is to achieve chronic improvements in ROM, then static stretching should be instituted as a separate training program as its inclusion in the warm-up may be counterproductive to the ensuing performance. If the objective is acute improvements in ROM then dynamic stretching activities may provide a suitable alternative to static stretching within the warm-up. (Behm & Chaouachi, 2011)

Conclusion: If you’re concerned about ROM, then DS is not the only option out there. If you can’t attain any position wilfully, it’s unlikely you do so after DS. DS just tells your body to brace itself for activity that ensues. Experiment to see what works for you. However, the other purported benefits of DS might make it a bigger bang for your buck.

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Does it help to simulate sporting movements?

By being specific to the activity at hand, DS could (a very big could) improve coordination and proprioception. Coordination is a broad term that encompasses the ability to react quickly, ability to orient position, ability to maintain physical composure, ability to feel rhythm, etc. Coordination has an ethereal appeal to it. You know it when you see it. Suffice to say, good coordination could help you find the right stride frequency vis-a-vis stride length, or it could be the difference between shanking the ball and clean contact.

In a particular study on rugby players running a 20 metre sprint, it was found that Active dynamic stretching (ADS) was found to yield faster sprint times while the SS groups had slower times. Here’s what the authors posited:

The reason why the ADS group improved performance is less clear, but could be linked to the rehearsal of specific movement patterns, which may help increase coordination of subsequent movement. Rehearsal of specific movement patterns while walking allows the muscle to be excited faster and earlier, therefore producing more power.

I have a couple of issues with this study. Firstly, core body temperature wasn’t monitored and the test was carried out on a warm summers evening (not my words). Maybe, just maybe, the ADS group ran faster because they were warmer? Secondly, they talk about muscles being excited earlier. We know that a higher body temperature increases nerve conduction velocity and the sensitivity of nerve receptors. It’s not shocking that muscles were excited earlier. Thirdly, the authors show evidence that passive SS negatively affects coordination. Undermining SS does not bolster DS. Finally, “could be linked” sounds too vague and gets on my nerves (pun intended).

Conclusion: I see greater value in a specific warm-up improving coordination better than DS could. For a sprinter A-skips, hops and bounds might be as specific as it gets. For a tennis player, playing football, foot tennis, frisbee, basketball, etc trains similar motor patterns and athletic movements in a fun, competitive way.

DS while standing or walking?

DS while walking might be more effective than DS while standing. This is because walking and jogging are plyometric activities themselves that call for proprioception. Proprioception is the kinesthetic awareness of where your body parts are in space, and in relation to one another. Good proprioception would be the ability to voluntarily touch the top of your nose (or any part you fancy) with your eyes closed. Humans have three kinds of proprioceptors. Muscle spindles (stretch receptors) are proprioceptors that lie in muscle fibres and detect changes in muscle length. When a muscle is rapidly lengthened such as when we dynamically stretch it, the muscle spindle reflexively contracts it as a protective mechanism. This reflexive contraction called the stretch reflex produces force, and could explain the force augmentation as a result of DS. Further, as muscle temperature rises, so does the activity of nerve fibres that wrap around these muscle spindles. This implies faster messaging to your brain. In contrast, SS does the opposite. By holding the stretch, we desensitise the stretch receptors, which decreases the activity of the concurrent stretch reflex. While overriding this protective mechanism is good for improving flexibility, it isn’t helpful when trying to produce force.

In simple terms, by harnessing the power of a protective mechanism that helps produce force, DS while walking might be more effective. It is definitely better than SS just prior to activity.

What else could explain the slower speed?

Above, we saw SS led to slower sprint times. This could be explained by the length-tension relationship. Your muscles’ ability to produce force depends on its length, amongst other things. Without getting into the science, highest amounts of force can be produced at moderate lengths or at very long lengths (due to tension created by resisting stretch). Conversely, when a muscle is slightly shortened or lengthened its ability to produce force is impacted. When we SS, we create an unfavourable increase in length which deceases the muscles’ ability to produce tension or force.

How fast should I stretch?

Fletcher makes the case that faster dynamic stretching (100 bpm) results in better jump performance than slower (50 bpm) or no stretching. Isn’t that like saying your car’s engine will warm up better when you drive it as opposed to idling it? Also, ain’t nobody got time for a metronome. The real question to me would be whether you can maintain quality of movement as velocity goes up. Are the joints moving through their full range? Are muscles actively lengthening and shortening? Is it a pain free motion? Is the motion coming from the right joint or is the body taking the path of least resistance?

For example, let’s dissect the high knee. Are you able to lift the knee high enough? Can you do so without hyperextending your lower back? Is your pelvis levelled or does it shift to one side when you get one leg up? Are you able to keep your abs engaged? Can you get your legs straight up or do they move to the side? Do your hips pinch at the top? To be able to notice all this, you’d have to perform them slowly. Only when you check all the right boxes would you want to consider doing them faster.

Conclusion: Prioritise movement quality over speed.

How long should I stretch?

This doesn’t seem to be too obvious. Different studies use varied units like seconds, reps, metres, etc. Unlike SS where greater impairments are noticed with longer stretch durations, DS does not seem to be affected by duration. As long as you’re not fatiguing yourself, DS shows neutral or improved performance. Fatigue could undermine positive stretch-induced effects. I’m personally not a fan of longer warm-ups unless absolutely necessary. In my opinion, it suffices to have one good exercise that takes the joint through its full ROM. For joints that work in multiple planes (hips and shoulders for example), it helps to have an exercise that targets each plane. 

Let’s consider the hip joint. The hip can move in all three planes. A squat challenges the frontal plane, high knees or lunges challenge the sagittal plane, and a hip 90-90 switch (internal and external rotation) challenges the transverse plane. In Djokovic’s book Serve To Win, he outlines nine dynamic stretches that take around five minutes to complete. This is how much time I would care to devote before moving onto things more specific.

Conclusion: Keep it short. More is only better if it doesn’t fatigue you.

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How else might DS improve performance? A grey area.

DS might have a PAP effect. Post-activation potentiation is fancy scientific jargon that simply means your muscles’ ability to produce force transiently improves after a pre-contraction. For example, performing vertical jumps or sprints after a set of really heavy back squats is said to improve performance in these moves. PAP is linked to the degree of motor unit recruitment from the pre-contraction. A motor unit is the junction between your muscle fibres and their respective motor neurons, and each motor unit controls a certain area of the muscle. How many motor units are recruited depends on how much force is called for. For instance, pushing a wall requires much more force than pushing a person, and will call upon every single motor unit.

Likewise, it has been found that explosive activities like med ball throws, jump squats and other plyometric activities call upon all motor units and require a muscle to contract maximally. This could explain why faster and more intense DS that recruits all motor units might improve various performance measures like sprint speed, vertical jump height, change of direction (COD) ability, etc.

While all this sounds promising, research is limited and most of the evidence seems to hold good for ballistic stretching (BS) and not DS. BS given its explosive nature, more closely resembles plyometric training. It becomes very hard to determine at what point a stretch can be called an “exercise”, as any movement requires some muscles to stretch and others to contract. For example, when does sneezing start being called diaphragm training? Similarly, is plyometric training just dynamic stretching on steroids?

Conclusion: The topic calls for as much research, as calls for semantic homogeneity. Stretch to increase body temperature and leave it at that. Consider any PAP effects a happy coincidence.

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Takeaway: Dynamic stretching’s positive effects stem from its ability to increase muscle temperature and heart rate. DS has been shown to improve performance in tasks that require strength, power, speed and agility. When done before such tasks, it fares better than SS. When combined with SS, it seems to nullify SS’s unfavourable effects. There appears to be no consensus on stretch duration, intensity and velocity. Further, the variance in nomenclature makes it difficult to compare studies and extrapolate results of the same. I’m extremely curious to see how DS would stack up against a light strength training session. Movement patterns like the squat, hinge and lunge are the same regardless of where they’re performed, and I wouldn’t be surprised if a light strength training session increased muscle activation and improved ROM just as much, if not better than DS. You could argue that DS is more specific, but if you’re really concerned with specificity, then why not warm-up for tennis with tennis?