Muscle, tendon and neural contributions to flexibility Prof Anthony Blazevich Centre for Exercise and Sports Science Research (CESSR) Edith Cowan University, Australia
We KNOW we need flexibility…
…which is interesting, because we’re not clear exactly what it is… “Resistance to stretch” “Maximum range of motion” “Tolerance to Stretch velocity? joint movement” Muscles contracting or relaxed? Own volition or external force?
Lesson 1 Study outcomes are context specific … so research conclusions should be context specific
Aim: to improve “flexibility” in different populations (athletes, clinical populations) Requirement: understand neuromuscular factors that influence “flexibility” Historically… Aim: get muscles to stretch further Method: stretch them…and hold them stretched
Acute Effects of Muscle Stretch Stretch-and-hold of non-contracted muscles (passive, static stretching) transiently increases range of motion, reduces resistance to stretch Magnusson et al., 1995 (Scand J Sci Med Sports) Bandy & Irion, 1994 (Phys Ther)
Lesson 2 Is the study actually measuring what you think it is, or what matters? (is it ‘muscle’ lengthening?)
Same findings as in animal experiments (rabbit extensor digitorum) Taylor et al., 1990 (Am J Sports Med)
Can identify the cause of change in tissue resistance using ultrasonography and motion analysis Kay & Blazevich, 2010 (J Appl Physiol)
Muscle Typically associated with Pre decrease in muscle Post (fascicle) stiffness, but no change in tendon Tendon Morse et al., 2008 (J Physiol)
But, decrease in resistance to stretch is not always seen, or resolves very rapidly! • Muscle group tested • Intensity of stretch • Duration of stretch (calf vs. hamstrings) • Resolves quickly • Others… Morse et al., 2008 Magnusson et al., 1998 (J Physiol; rapid stretches) (In J Sports Med)
Improvement in ‘stretch tolerance’ (force or torque at point of decision to stop stretch) a major predictor of improved ROM… Weppler & Magnusson, 2010 (Phys Ther)
Unclear how this ‘stretch tolerance’ mechanism works… Passive Flexibility stretch exits here enters here
Muscle Activation Change? EMG during stretches negligible – Changes in flexibility not related to EMG during test: reductions in reflex activity unlikely to underpin changes in flexibility Magnusson et al., 1995 (Scand J Sci Med Sports)
Decrease in ‘spinal excitability’ during stretch…but lasts only seconds (Guissard et al., 2001; Nielsen et al., 1993) Guissard et al., 2001 (Exp Brain Res)
• Putting muscle in Joint Angle (°) 40 stretch increases 35 30 MEP (‘corticospinal 25 excitability’) 20 Joint Angle 15 • Repeated stretches 10 0 1 2 3 4 5 increase MEP for Stretch Time (min) <10 min Soleus MEP/Mmax 0.08 Soleus MEP Amplitude/Mmax 0.07 0.06 0.05 NEUTRAL 0.04 ( ‐ ) 15 DF 0.03 (+) 15 PF 0.02 0.01 0.00 PRE POST POST ‐ 10
A change in ‘decision’ to stop the stretch from increasing? – Change in sensory feedback from periphery – Change in processing of sensory feedback a) Frontomedian cortex, and b) left and right anterior ventral insula; for contrast of veto (give up) versus action trials (Brass & Haggard, 2007; J Neurosci)
But remember context specificity…
What happens if… Different stretch velocities? Nordez et al., 2008 (Eur J Appl Physiol)
What happens if… Different stretch velocities? Different ages? Gajdosik, 2006 (Eur J Appl Physiol)
What happens if… Different stretch velocities? Different ages? Different sexes? Hoge et al., 2010 (J Str Cond Res)
So there’s a lot we don’t know…in particular how to improve ‘flexibility’ in the many contexts in which it’s needed
Lesson 3 Studying something a lot doesn’t mean that something is the best or right or…
But… Lesson 4 Are we asking the right question? (here we want to know about ‘flexibility’, not just ‘stretching’)
A Better Way to Stretch?
What if we compare passive muscle stretching to PNF (contract-relax; CR) or isometric contractions? CR 2x more effective Kay et al., 2015 (Med Sci Sports Exerc)
Different tissues affected…different interventions for different reasons? CR influences both muscle and tendon Kay et al., 2015 (Med Sci Sports Exerc)
But ultimately, change in maximum ROM was related to tolerance of loading… Kay et al., 2015 (Med Sci Sports Exerc)
Can we manipulate tissue properties to stretch more effectively? – Muscle contraction ‘off stretch’ is just as effective! Kay et al., 2016 (Eur J Appl Physiol)
And the effects on muscle and tendon stiffness were the same… Kay et al., 2016 (Eur J Appl Physiol)
Kay et al., 2016 (Eur J Appl Physiol)
Lesson 5 Always need to validate the findings of other st�dies…one st�dy ≠ proof. (hint: someone needs to validate our findings)
What about the long term? Compare people of different flexibility vs. compare changes with long-term training
Range of motion related to muscle cross-sectional area? CSA (mm 2 ) Magnusson et al., 1997 (Scand J Sci Med Sports)
Further data In flexible individuals: Stretch tolerance greater MTU stiffness lesser Blazevich et al., 2012 (J Appl Physiol)
Further data In flexible individuals: Stretch tolerance greater MTU stiffness lesser Fascicle rotation greater Blazevich et al., 2012 (J Appl Physiol)
Further data In flexible individuals: Stretch tolerance greater MTU stiffness lesser Fascicle rotation greater EMG onset later joint angle Blazevich et al., 2012 (J Appl Physiol)
Further data In flexible individuals: Stretch tolerance greater MTU stiffness lesser Fascicle rotation greater EMG onset later joint angle Tendon stretch later in ROM Blazevich et al., 2012 (J Appl Physiol)
Great! We now know that the keys to flexibility are: – Increased stretch tolerance – Later onset of (reflex or voluntary) muscle activity – Greater fascicle rotation – Greater elongation of tendon at end point – Smaller muscle cross-sectional area
Lesson 6 Cross‐sectional studies don’t tell us what we need to change, only what’s different between populations
Three weeks of static stretching (calf): Increases ROM Increases stretch tolerance Blazevich et al., 2014 (J Appl Physiol)
Three weeks of static stretching (calf): Increases ROM Increases stretch tolerance Muscle less stiff Blazevich et al., 2014 (J Appl Physiol)
Three weeks of static stretching (calf): Increases ROM Increases stretch tolerance Muscle less stiff Fascicles less stiff Blazevich et al., 2014 (J Appl Physiol)
Compare the Paradigms Cross-sectional Longitudinal 1. Stretch tolerance 1. Stretch tolerance 2. Later onset of (reflex 2. No change in muscle or voluntary) muscle activity (or reflexes) activity 3. Greater fascicle 3. Greater muscle/ rotation fascicle elongation 4. Greater elongation of tendon at end point 5. Muscle CSA
A Better Way to Stretch? One final thought…is there a better way to increase flexibility in the long term?
Strength training in lengthened position: – improved ROM as much as stretching, but increased angle of peak torque and stretch tolerance more Aquino et al., 2010 (Man Ther)
Stretching of ‘active muscle’ significantly increases ROM (faster, more effective than passive stretching?) F dyn F mus F mus F dyn F dyn F mus Kay et al., 2016 (Med Sci Sports Exerc)
Stretching of ‘active muscle’ significantly increases ROM (faster, more effective than passive stretching?) Kay et al., 2016 (Med Sci Sports Exerc)
No change in overall passive stiffness… But increases in strength observed – broader benefits than passive stretching? Kay et al., 2016 (Med Sci Sports Exerc)
• Many ways to become flexible: passive muscle stretching may not be the best method • Active muscle stretching or contractions at long length may be most effective? • Yoga, pilates, mobility exercises The best way to stretch, is to contract?
Questions? If we can figure this out, hopefully we can be as good as these guys…
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