There has always been this big divide between those that prefer a strength oriented approach to training and rehab and those that like to use a more movement (also called proprioceptive or motor control training) based approach.
For some reason human beings tend to gravitate into camps, tribes or teams, its just part of nature! Training and rehab seems to be no different.
So....which tribe do you belong to?
I could not help but think of the Frankie goes to Hollywood classic!
First thing we have to realise is that is very hard to completely divorce the two modalities.
Strength training does not mean that we have no proprioceptive input or motor pattern output. Any movement will create feed forward commands and feed back through the proprioceptive system up into the cortex. We may REDUCE the amount of feedback that comes from differing joint positions and variability of movement during strength training as the movement is often constrained by the increased load. We must remember however proprioception is also about force regulation and a fair amount of proprioceptive research is based on measures involving force rather than being just joint position based.
Equally ‘movement’ training can involve strength and joint loads generated by acceleration & deceleration, end range tension and joint stabilization. Less utilised joint angles may also need less added load to achieve an overload effect that would stimulate a need to increase strength. ‘Strength’ training is essentially adding load to any movement after all, although often specific ‘strength’ exercises are preferred.
We seem to be looking for a one type of training or rehab that encompasses everything. Both types of will individually increase capacity AND interact in relevant situations so need to be looked at concurrently as well.
Maybe it would be better to see strength and movement training as having mostly DIFFERING affects on humans. There will of course be crossover where strength affects movement and movement will affect strength but expecting movement training to increase strength and load tolerance in the same way strength training does maybe misguided. The same is true of strength training, why would it have a specific effect on a motor pattern in the same way practicing that motor pattern would?
The problem here is that this thought process does not fit the ‘tribe’ mentality.
I see this as being similar to the pain science debate and the criticism of the pendulum swinging to far from peripheral to central mechanisms (another tribal debate). Often the truth lies in the middle ground and being inclusive and aware of the impact of many types of rehab and training modalities.
So are strength and movement unrelated?
Now this does not mean that strength and movement are unrelated. This study *Here* (thanks to Nick Clark) found that quadriceps strength was significantly correlated with the function of the knee during walking gait after ACL reconstruction. This makes sense if the level of strength falls below that required for normal movement and this is likely to occur after a significant event such as an ACL injury. One caveat would be that kinematics and strength levels might both be related to pain levels and once pain subsides ‘normal’ motor behavior and strength levels may be restored rather than strength and movement being related to each other.
The relationship between strength and movement patterns after injury is less clear in running potentially because strength levels during or post injury do not fall enough to significantly impact on movement.
This paper *Here* looked at changes in knee biomechanics after a strength training program for the hip abductors in runners with Patellofemoral pain. Peak ‘genu valgum’ or increased hip add and the resulting knee valgus has been hypothesized to be associated (although still unclear!) with PFP. Although hip strengthening programs are designed to decrease peak hip add (and knee abd) this study found a strength training program DID increase strength and decrease pain but did NOT impact on the movement of the knee in terms of peak genu valgum (peak knee valgus) angle at post test compared to baseline. A caveat here is that the analysis of the knee was in 2D, looking at the hip adduction and shank abduction angles, and movement of the knee during running is 3 dimensional.
This study *Here* into the frontal plane kinematics of the knee in running, this time in healthy female subjects, looked at the relationship between hip abduction strength and hip adduction kinematics and found no relationship and this time they did use 3D analysis.
Another study *Here* found that a hip strengthening program did not alter running mechanics in a healthy female population. In fact ‘movement’ training in the form of a single leg squat did not alter running mechanics either but did have an effect on the single leg squat! So ‘movement’ training also displays a healthy relationship with the SAID principle (specific adaptation to imposed demand) and if you want to alter a specific movement you probably have to work on that specific movement.
Gait retraining, the SAID principle in action, is becoming more popular with running *Here* and seems to be effective in improving running kinematics and pain and function in the short term and we also see a crossover to less complex skills such as squatting. It seems running may have more to do with coordination and timing of muscular contraction within a motor pattern rather than the strength of contraction that can be generated.
So another question is does the complexity of a skill, such as running gait which is very complex, seem to play a part in whether strength training has an impact on movement?
This paper *Here* looked at different training programs to improve knee alignment during landing that has been associated with both ACL and PFP injuries of the knee. They had two groups, a strength group and a jump landing training group and looked at the functional tasks of the single leg squat, single leg landing and bilateral landing.
They found that a strength training program DID affect frontal plane projection angle (FPPA) during a single leg squat AND single leg landing but NOT during a bilateral drop jump as well as increasing strength. Of course the jump landing training group DID improve landing but did NOT improve strength.
The caveat here would be that the strength training program included a single leg squat which more than likely (IMO) creates some motor learning carryover to the FPPA in the single leg test and this was fully acknowledged by the authors.
It might also be that a simpler movement is affected more by changes in strength.
The authors also pointed out that a change in the single leg landing task also improved in the strength group even though they did not train this movement. The conclusion being therefore strength was a factor in the improvement of the FPPA. However we may also see a motor learning carryover between the single leg squat to a single leg landing as they are a reasonably similar movements which has been previously shown. This study also utilised a 2D analysis that has been cited as a limitation in studies that failed to show a link between changes in strength and change in movement.
The authors did come to the most sensible conclusion of incorporating both strength and movement training to decrease FPPA at the knee and also utilised a comprehensive approach to their training programs!
One argument is that strength training does not affect the movement representations in the cortex but why should we expect them to?
This study *Here*, and yes its not a human study, found that changes in the motor cortex were associated with skill rather than strength as coupled strength and skill training did not induce any more change than skill training alone.
This article *Here* finds that strength training and ‘movement’ training are associated with DIFFERING affects on the brain in terms of neuroplasticity after skill (movement) and strength training.
The strength training group, surprise surprise, increased strength but did not increase the neurophysiological parameters involved with skill training. The skill group improved their skill performance but not their strength. This fits very nicely with the principle of SAID.
Working on different biomotor components created different changes neurologically in terms of MEP (motor evoked potential) behavior at different times throughout the 4 week training program with skill training creating quicker changes than the slower changes associated with strength training.
*Here* we also see different cortical activity between control (movement) and strength tasks.
We may find that strength training is more about the creation of force through co-contraction and movement training is more about the coordination and timing of contraction in relation to a, potentially complex, specific functional skill.
All this does NOT mean increasing strength won’t affect performance or pain
A mistake often made by the ‘movement’ tribe is to reason that because strength does not seem to have a clear relationship with altering movement is that it is not beneficial. Strength, and its more functional relation power, are still bio-motor qualities associated with function and increasing their capacity will surely be beneficial.
This study *Here* found that maximal strength training over 8 weeks improved running economy and time to exhaustion in distance runners. There maybe a number of mechanisms involved in resistance training affecting distance running performance as seen in this paper. *Here*.
We see a strong correlation *Here* between maximal squat strength and sprint performance in elite soccer players.
If we go back to the article earlier in the piece that looked at strength and knee biomechanics we see that although the strength training program did not affect peak knee kinematics it DID have an effect on PAIN. We would need a control group with knee pain however, instead of just healthies, to allow for the basic healing effects of time to make a really strong link.
Although a causal relationship between decreased strength levels and injury and pain is extremely unclear at the present time, reducing strength inhibition in rehab POST pain is a key variable as we see clearly in the evidence base that pain has an effect on strength output.
This paper *Here* showed that both strength and power (during hop test) were affected in the UNINJURED leg as well after an ACL injury. This may suggest a central modulation of strength and power output after injury not just damage to a joint, muscle or connective tissue.
This systematic review *Here* found that resistance training was beneficial for chronic low back pain, chronic tendinopathy, knee osteoarthritis and post knee surgery potentially strength training being more beneficial for chronic pain. It is important to note the authors felt that high intensity (above 70% 1RM) was more effective than low intensity approaches and did not increase injury risk that seems to be a fear of some when using resistance training.
This study *Here* found that a periodised strength training had a positive influence on strength, pain and disability in active middle to older aged men with chronic back pain.
This paper *Here* looked at the dose response between resistance training and upper and lower back pain in office workers. They found training volume per session more important than the number of sessions attended to be correlated with pain. Interestingly however the specific resistance training group and the more general physical exercise group showed pretty similar reductions in pain.
Strength and movement training were both found to be effective for chronic low back pain in this systematic review compared to controls or other treatments *Here*. It might just be that moving is better than NOT moving for those with chronic lower back pain!
We do have to remember that you could perform an exercise designed to increase strength without ever actually increasing strength because the load, and therefore overload, used does not require an adaptation from the body in terms of strength. A ‘strength’ or ‘strengthening’ exercise on its own is not guaranteed to increase strength. This could be a criticism of papers that look at strength training vs more general programs that the levels of load used are not sufficient to change strength and/or the actual changes in strength are not reported.
We may see that here with a comparison of walking and strength training for chronic lower back pain *Here* with a walking programme as effective as a specific lower back ‘strengthening’ exercises. There were no measures of actual strength or increases in strength in this paper so we do not know if strength is a factor or not and this may fall neatly into what is discussed in the paragraph above.
With CLBP we see an unclear relationship with changes in physical function such as strength and clinical outcome *Here* This does NOT mean that strength training is not beneficial it just means potentially that the moving component may be more important than any increases in strength or other physical factors and the moving component is in the format of strength training.
I have previously discussed this here Strengthening the most overused term in therapy
Certainly putting your body under regular load through resistance training should increase your tolerance to putting your body under load if the loads are sufficient for adaptation!
For example if I am a runner it is very difficult to recreate the loads associated with running without doing MORE running. This may be the cause of a running injury in the first place. However we can manipulate the application of force on the body to elicit cellular mechanotransduction and positive expressions of compounds that alter muscular architecture and subsequent tolerances to load.
Although the loads applied may not be identical in terms of mass X acceleration it does not mean they are not beneficial and the lack of replication and alternative load might be just ‘what the doctor ordered'.
Strength and Injury Prevention
This often cited systematic review *Here* on injury prevention shows very positive effects of strength training on decreasing injuries. This highlights the positive effects of putting your body regularly under load but should not be confused with how strong you are decreasing your injury risk.
You could regularly put your body under load without ever significantly increasing your strength equally you could be pretty strong in comparison to someone else naturally but not put your body under regular load. It is physical activity that is being studied in this paper.
It is also important to note that movement training (proprioceptive) was also shown to have an significant effect on injury prevention and if we think about the body of ACL prevention research we see beneficial effects there.
This all seems nice and clear until we look at this recent paper *Here* on ACTUAL strength deficits in those that go on to injure their ACLs. Here we see predictive risk factors for isometric hip strength of external rotation being under 20.3% BW (percentage of body weight) or abduction strength under 35.4% BW.
What is unclear here is HOW this impacts on non contact ACL injuries. Although the rationale in this paper is that abnormal lower extremity movement is related to non contact ACL ruptures, lots of evidence on this, and that strength is then related to the abnormal movement. BUT the relationship between strength and movement is most certainly uncertain at the present time in my opinion (and this being my blog my opinion rules!) so as a modifiable risk factor we cannot ignore this data but the exact mechanism is still unclear.
Strength may be more important with relation to movement in those that require very high levels such as in multi planar athletic populations as it might also be important when strength levels do not meet the required level for ‘normal’ movement to occur such as post operatively.
So shock and surprise I hear you gasp, strength and movement training have different effects on human body.
If you want to move in more varied or ‘better’ ways and improve the bits of the body and brain involved with moving then movement training is perfect.
Want to increase strength and power and load tolerance then strength and resistance training is awesome.
Sometimes to be really effective we have to think about using a bit of both and adding load to a relevant movement to get the kind of crossover to ‘function’ that maybe required or desired.
Both will have an impact on different components associated with performance and both should help reduce injuries. We must remember though that performance is extremely hard to quantify as this is often subjective, research often test elements of performance which is quite different.
Probably the clever guys are doing a bit of both already in the fields of rehab and training/performance and realise that both movement and strength training have their part to play.....just on different aspects!