Changes in functional magnetic resonance imaging cortical activation with cross education to an immobilized limb.
Farthing JP, Krentz JR, Magnus CR, Barss TS, Lanovaz JL, Cummine J, Esopenko C, Sarty GE, Borowsky R. Med Sci Sports Exerc. 2011 Aug;43(8):1394-405.
It has been well established that strength training one limb can lead to increases of strength in the opposite untrained limb. A few studies have also indicated that this cross education of strength may be useful in attenuating the loss of strength and muscle mass associated with immobilization. While there is agreement that neural mechanisms are responsible for the cross education the precise mechanisms are still unclear. To clarify possible mechanisms Farthing et al used functional magnetic resonance imaging (fMRI) to assess cortical activation associated with the cross-education effect to an immobilized limb. Fourteen healthy, young, right-handed individuals with little previous resistance training experienced volunteered to have their nondominant (left) forearm casted for 3 weeks. The casts were similar to a short arm cast but also included the thumb and proximal interphalangeal joints of the other fingers. The first 7 participants performed progressive strength training of the dominate arm (isometric handgrip contractions 5 days/week) while the last 7 participants were controls and did not strength train. Isometric maximal handgrip strength, muscle thickness, electromyography of wrist flexors and extensors (muscle activation during handgrip strength assessment), as well as fMRI (during handgrip contractions) were assessed for both arms before and immediately after the 3 weeks of immobilization. Handgrip strength in the immobilized arm was maintained among participants that completed the strength training but control participants lost strength in the immobilized arm. Muscle thickness decreased over time in both groups. The wrist flexor muscle activation (flexor carpi ulnaris) increased over time among the strength training participants but decreased over time among the controls (regardless of arm). Among the control participants there was no change over time in cortical activation but among the strength training group there was an increase in contralateral (left) motor cortex activation after training. The authors concluded that contralateral handgrip strength training could attenuate strength losses during forearm immobilization and that these outcomes may be associated with increased motor cortex activation.
This study is exciting because in a small cohort it demonstrates the clinical benefit of handgrip strength training the contralateral limb during immobilization and a possible mechanism for the clinical benefit. The authors acknowledge that their findings were limited by not measuring muscle activation of the immobilized forearm during strength training activities. Therefore, the study cannot conclusively rule out that the immobilized muscle were contracting during the contralateral strength training. The authors also note that their findings in healthy patients may not be applicable to an injured population. It will be interesting to see a randomized controlled trial of casted patients doing handgrip strength training compared to normal treatment protocols. Regardless, the risks associated with handgrip strength training of the contralateral arm during immobilization are low and it would seem prudent to advise our patients to do these easy exercises. How many of you are already using contralateral strength training with your injured patients?
Written by: Jeffrey Driban
Reviewed by: Stephen Thomas
Being an undergraduate junior athletic training student I'm still learning about therapeutic exercises/techniques and the physiology behind it all. This article caught my attention because I did not know you could strength train one limb and see results in the opposite limb. Our bodies amaze me every day! Whenever I perform rehabilitation exercises with athletes I always make them do the exercises bilaterally because in my mind I'm "evening everything out" (unless the injured limb is immobilized). I agree with the author, it would have strengthened the study if this was performed on athletes with an injury to the forearm, but it definitely opens up the doors of rehabilitation possibilities when working with upper extremity injuries. I will most certainly propose this technique to my preceptor and discuss it with her to see if we can incorporate it into a rehab program with an athlete suffering from an upper extremity injury, even if they are not immobilized. It will be interesting to see if the athlete senses a difference or if we objectively notice a difference in the athlete’s strength. It would be harder for us to determine muscle thickness and cortex activation without proper lab equipment/applied knowledge, but just keeping this information in the back of our minds as athletic training students and ATC's will provide us with more tactile knowledge up our sleeves!
It is interesting that the motor cortex helps to maintain strength in the injured limb but is it the most effective manner. would it not be more effective to use a electrical modality to work the injured limb such as russian stim or NMES?
NMES on the injured side would be appropriate if it is is not contraindicated. In cases where you'd prefer to avoid contracting the muscles on the limb with an injury this study supports the notion that you could strengthen the contralateral limb and get benefits in both extremities.
During a period where I was unable to weight train due to subacromial issues in my right arm I decided to train my nondominate arm for two weeks. I did not focus on executing one isolation / isometric exercise each day. I was working with compound movement and still training my non dominate arm at sub maximal intensities (ie: lower than 6 reps per set). The exercises comprised of chest pressed, pull downs, military presses, etc. I found after two weeks that I was not only able to return to submaximal intensities with my dominate arm but the strength loss was much less than I anticipated. My 1, 3, and 5 rep maxes for most exercises stayed the same.
I am curious to know how the effects of not only doing isometric grip work but also wrist flexion, extension, pronation, supination, Rdeviation, Udeviation would affect the bilateral side of the body.
This study was interesting and the outcome and conclusion was shocking to me personally. This is a great idea when it comes to treating an individual who is immobilized, the great thing about this is that it still gives the injured athlete something to do and a purpose while immobilized. If athletes are immobilized and do not have rehab or other things to do it can strongly affect them emotionally and physcologically not only is this study a break through with immobilization techniques and findings, but it is also is a huge benefit towards athletes physcological status I feel as well.
I am just posting to confirm. This post is a saying that an individual can strengthen his/her uninjured limb to help maintain strength in the injured limb? And how would the motor cortex be able to help maintain strength to the injured limb if not being used?
Joey: Yes, training the contralateral (uninjured) limb can strengthen the injured limb. Remember with exercises there's muscle and neural adaptation. The precise mechanism of the crossover effect is still being evaluated.
I find this study to be very interesting. I am amazed that strengthening the uninjured limb can benefit the injured, immobilized limb. Seeing as this study focused on the forearm, I am curious as to whether this bilateral transfer of strength could be applied to the lower extremity. I wonder if this could possibly be used for individuals with ACL injuries in order to limit atrophy of the quadriceps on the injured limb. Can't hurt to try, right?
Michele – This concept can be applied to the lower extremity. For example: https://www.ncbi.nlm.nih.gov/pubmed/10921652
I thought this article and its findings were remarkable. I would however love to see some of numbers to emphasize the positive benefits of training the contralateral limb during injury. I am also curious about the amount of training, total weight and/or reps, that the individuals would perform during this time period. Is there a “sweet spot” where muscle and neural adaptations benefit the without creating an overload? For instance, handgrip contractions can be done at varying degrees of resistance. Does this resistance change depending upon the individual’s strength, such as 60% of maximum strength, or is there a universal resistance that everyone can positively adapt to? And how is this applied to other extremities?
Leslie, you raise some great questions that I think should be addressed. A set of good research studies for anyone looking for project ideas 🙂
The small cohort study is very interesting to me, in that I never thought that by training a contralateral limb to an immobilized limb that the immobilized limb can maintain muscle strengthening. A possible future direct of study that I may consider when I look into graduate school is can this procedure be reproduced with the same results if you immobilize the ankle joint of a patient/athlete.
Sam, I think that would be a great project. I suspect you'll find that the cross-over effect will emerge there as well. It would be a good contribution to our clinical practice.
I think that application of this concept in the athletic training setting could have very positive effects for injured athletes. If it can be proven that contralateral limb strengthening does in fact cause some strength improvements in the injured limb, this would be a very useful tool for individuals who have an immobilized limb. I feel other than strength improvements, this concept, if proven, can be used to educate the athlete and give them incentive to strengthen the uninjured limb while the injured is immobilized. This has the potential to shorten an athlete's return to play time period which is a positive for everyone on the sports medicine team.
Matt, great points. The strength coach who taught me always reminded us that an injured athlete should always keep doing their weight training. Just because one limb is hurt doesn't mean the other three get time off. This type of data just provides more support for why they need to keep strengthening the other limb.
I agree with the post in that they had some limitations to this study. I think it is a good start off study, but they can't exactly say anything for sure. They have results, but I don't believe they are 100% accurate since there were many things that were not put into thought previously. I think that now knowing the activation of the muscles in the immobilized arm is a big key, as well as knowing how this could help patients that were actually injured. Being an athletic training student, you want to know what the best possible way is to heal an injury, and knowing all the facts is the best way of figuring out how to set up rehab for the athlete. I think the idea of strength training is very important, but I think this needs to be looked into further. For me to base my ideas off of a study, I need to know that everything was taken into account and the results were the best they could be. I think this was a very good start out study in showing how important strength training is, but I think it would be interesting to see how it would be in athletes that were injured and how that effects the treatment.
Jenn- Great points. It will be nice to see this work followed up by randomized clinical trials. We've seen several studies now demonstrate that the effect is real but we need to start testing its efficacy. Knowing if the muscle on the injured limb are activating may be important but I suspect that will help us better understand why it is working (which is still a bit of a mystery). If the muscles of the injured limb are contracting and not hurting the patient then it would still be worth taking advantage of the cross-over effect. By understanding the mechanisms though we could hopefully optimize the efficacy of this technique. Regardless of this study though we should be encouraging our patients to continue their strength training with the rest of their body (granted the injured limb should be rested). This study (and those preceding it) hint at another reason for why this might be a good idea.
This is definitely an interesting start that could open up the gates for new research potential. I am interested in looking into future research on the effects this could have on the lower extremity as well as other ways that this could be used. I am curious as to how the results will be different on injured athletes. I am also curious as to how this could be utilized by athletes who are going to be immobilized over a long period of time.
This post was very interesting and I am definitely curious to read more into the study and seeing if they went further into it. As Michele had said, I would also like to see if it would have an effect on the lower extremity and how much of an effect it would have on the legs. This study is beneficial because athletes become upset when they are injured because they think they will lose muscle and it may take awhile to regain muscle mass and strength. This study proves that working the uninjured arm helps the injured arm and can help convince athletes that it is not useless. Most athletes are skeptical about working out just one arm, especially the uninjured one, so this could help encourage and convince the athlete that the exercises are benefical and will help them get back to playing even quicker.
I found this particular article extremely interesting because, as a student in therapeutic exercise now, I have put very little thought in doing exercise to strengthen a limb with the contralateral side. With that being said, this article has given me a new perspective on thinking about possible rehabilitation programs for athletes. The article states that by educating the muscles on the contralateral side of the immobilized injury, one can prevent loss of strength and muscle mass. This study supported these findings in the case 14 participants with their not dominant forearm. These participants were solely immobilized for the purpose of this study, none of them were actually injured. I would be interested to see how an injured limb would be effected by this theory. For the purpose of this study, the forearm was used, I would also be interested to see how a study like this would play out in the lower extremity.
I think that this article is very interesting. It is good to know that one can train the mobilized arm, and they patient will not atrophy in the immobilized arm. One would assume that this would be true for all extremities in the body. So if one has a cast on their lower leg, they can train the other leg to speed up the time to full recovery. As a future athletic trainer, this was a very enlightening article. I know that I could potentially get an athlete to return quicker by exercising the opposite limb. That will save the athlete time because they will not have to regain all the strength that will normally be lost. I will really look to utilize what I learned here in the future.
I think this is a great article! My ACI has been telling me about this over the past few weeks. He has recently read articles pertaining to cross training the contralateral limb when the other is immobilized. A lacrosse player under his care severely sprained his ankle about 3 weeks ago and he has been using this technique on the athlete. I would definitely like to read more material on exactly how the muscles on the injured limb are contracting without causing in pain or discomfort to the patient. Is there a physiological reason, or is it a case of mind over matter- if an athlete believes they are getting better then they will, despite modalities, therapeutic interventions or rehab.