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Hi, it is Tom here from Running Physio. Today, I want to talk to you about how we can potentially create lasting changes in flexibility, particularly in muscle flexibility in runners and athletes that we see in clinic. And I'm going to touch on some research, and also show you some of the parameters that you might choose to use for these particular types of approaches. And a video example of me using particular exercise I like for this.

Now, first up, we might want to think, why would we want to increase flexibility? How important is it? And that is a fair question. It's not necessarily going to be the limiting factor for every athlete we see in clinic.

I think it's fair to say things like strength or often more as a priority tolerance of their goal activity is often more of a priority. But there are some circumstances where improving flexibility. Can be important for an individual. I think perhaps one of the most clear examples is with hamstring muscle injury, and in particular, if we can increase the fascicle length of the muscle, that seems to help with injury.

Now, there's some nice research from Timmins et al in this. In their study, they found that for every 0.5 centimeter increase in biceps femoris long head fascicle length, the risk of hamstring strain injury was reduced by 73.9%. So it does seem that this is particularly important in preventing perhaps treating hamstring muscle injury. It may be important too, if someone has a muscle contracture and they've got long-term loss of length that we might want to address, or if their lack of flexibility is impairing their function, their ability to do things, it may well do if their goal activity involves needing to be flexible.

Think of a hurdler needing to have the hamstring flexibility to clear a hurdle or a gymnast for example, lots of flexibility needed there. Or even sometimes in a runner, if they've got a chronically very tight calf that's limiting their dorsiflexion range, that may lead to them altering their running gait to compensate.

So there can be situations where we would want to actually try and improve flexibility for an individual when it's relevant to their pain.

Now for a long time of course, the main thing for improving flexibility was static stretches. We used to recommend them to everyone. They were given out pre sport. We used to feel that they would help to prevent injury, but actually recent research shows that doesn't appear to be the case.

That static stretching even before or after sport, doesn't seem to significantly reduce injury risk. From what I understand, the changes in flexibility from static stretches are pretty short term. They might last as little as 20 to 30 minutes, and then we go back to where we were. But there's a downside.

So if we use static stretches for flexibility, immediately afterwards, we can see a loss in strength and power, which is not what we want when we're trying to perform something like running or a sport that requires us to produce force quickly, that requires us to be powerful. So what's the alternative then?

What can we use to create more lasting increases in flexibility for people we see? We think the answer lies in eccentric loading. So loading the muscle through an eccentrically biased activity that can build both strength and length within the muscle. Now if we think about the muscle a little bit like a spring, in that it needs to be able to manage load, it needs to be able to bounce us along, if you like.

If we are doing a static stretch, what we think we're doing is we are taking that spring and stretching it out so that yes, it's a little bit less stiff, it's a little bit more flexible for a short period of time, but because it's not quite so stiff, it's also not as able to produce power. And 20 minutes, half an hour later it goes back to where it was.

So we've not really gained much long term. What we think happens with our eccentrically biased strength work is rather than stretching the spring out, it's like adding extra coils on the bottom of the spring. So we are actually making the muscle longer, we think by increasing its fascicle length, and this is likely then perhaps to create more lasting changes in our flexibility, in our fascicle length, particularly if those exercises are maintained over time. Now, at the start, I said I'd touch on some new research. There's a systematic review by Diong et al that's looked into this. And this looked at 32 trials with over a thousand participants in total, and on average the interventions they used in there.

The eccentric loading programs lasted around about eight weeks, and they found that these programs did improve flexibility, especially in the lower limb. Although in the upper limb, the evidence was inconclusive. There weren't so many studies there. So we have reasonably recent or very recent evidence to show that potentially eccentric biased exercises can improve flexibility, they can improve fascicle length, and that may well help to reduce risk of things like hamstring muscle injury, perhaps improve range of movement after contracture .

Also it seems in the evidence that while eccentric loading is effective for doing this, concentric, only loading isn't, and one study even found that if we focused only on concentric muscle action, it may reduce fascicle length. So that's why there's this thought that we want to move more towards eccentric biased or eccentric only action. So what might this look like? It may well be exercises you are familiar with, like the Nordic hamstring curl, that is very much an eccentric exercise.

And the parameters we can use. Credit here to Steven Duhig who's done a lot of research in this area and discussed this with me to come up with some of these potential parameters that you could use. So we do want an eccentric only action. That's where maybe your Nordics come in, especially useful because it really biases that eccentric action.

Because we think if we bring the concentric action in as well, it may lessen effect. We are going to go for heavier load. Now in some of these studies, they've been suggesting people do four to six reps of maximal effort. So perhaps we are looking at gradually building towards somewhere around four to six rep max, although that's going to vary massively depending on the patient, their pain, their needs, their ability, et cetera.

We do want to work that muscle through into its lengthened position. So if you are doing a Nordic curl, we want to take people as far through range as we can, really aiming to get to perhaps 10 to 20 degrees shy of knee extension perhaps with that Nordic hamstring curl. And we can potentially include an isometric hold at the end, perhaps three or four seconds of working in that lengthened position to really bias loading this muscle in its lengthened state.

Now in terms of our volume, perhaps we start with four to five sets of four to six reps, and that's going to be about three times a week. And we maybe have an intervention period of perhaps six to eight weeks focusing on doing this to increase the eccentric strength and to increase the fascicle length and flexibility.

Now what they've found in the research is that there's then a fairly rapid detraining of fascicle length and flexibility in as little as two weeks. So in order to create lasting changes in flexibility, you would maintain these exercises perhaps at a low volume. So maybe two to four sets of four to six reps once or twice per week.

And there is some evidence to suggest that will help. So we could look at having that intervention period and then using a lower dose maintenance period perhaps to maintain the flexibility. And this is really a win-win using these exercises because we are going to get both strength and length at the same time. That may have a knock on effect in terms of injury prevention, particularly around the hamstring. Now, I like the Nordics, they're well supported in terms of evidence, but they are hard for people to do. And I think when you look at the studies, we're often looking at quite able athletes that are able to do Nordics.

A lot of people will just cramp up. An alternative I like to use is a supine leg curl. This is a supine leg curl. You bridge, you roll the skateboard out. We've got to hold at the end in that lengthened position. The hips drop down, and then the concentric phase is really easy. So we get the eccentric phase as the board rolls away, isometric pause at the end, drop the hips to the floor and then roll back and keep it nice and easy.

Now this is surprisingly tough, single leg. But I could progress this potentially by taking away the arm support and then by adding load across my abdomen to really take it to that kind of challenging, near maximal level for four to six reps. So supine leg curl, quite a nice option. Some good research out there showing that it actually really does effectively work the whole hamstring complex.

If you look at things like Zebet et al.'s work, but I must admit there's not a lot showing yet that it can improve fascicle length, but it should in theory because it fits the bill. It's eccentrically biased. We can load it up enough, we can have a hold at the end position. But unlike the Nordic curl, you don't need a partner. It's one that you can do on your own. If you treat yourself to a skateboard.

Okay, so we asked this question, how do we create lasting increases in flexibility? And in short, we believe from recent evidence, from Diong et al. In 2022 that eccentric loading can potentially help us to create lasting changes in flexibility particularly if we work with perhaps the heavier loads two or three times a week initially, and we use a maintenance dose afterwards to maintain the flexibility and the increase in fascicle length that we've got. Nordic curls are often the go-to option for this, but think about other options like the supine leg curl that we looked at there. Often people can start two legs with that progress to single leg then add load to really work and build that strength and flexibility.

Now, as I said there's a link to our free video series. Do check those out. We've got lots of great videos available in there.

I will also put in the comments a link to this recent systematic review. And I look forward to hearing your thoughts on the topic. Thanks again for listening. Bye for now.