Are knees really the problem for runners? by Christopher Connelly

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[Christopher Connelly earned his Masters Degree in Exercise Science and Nutrition from Sacred Heart University where he competed for the D-I Track & Field / Cross Country team. Chris is currently an Athletic Development Intern at Athletic Lab]

All runners have dealt with an injury at some point in their experience and for many this is putting it lightly. Many runners struggle with injuries for years and often it’s a reoccurring problem. Past research has investigated the injuries that plague runners and found that nearly half (42.1% of 2,002 runners) of runners examined at one point had a knee injury (Taunton, 2002).  Of the 2,002 runners in the study, 16.5% experienced patella femoral pain syndrome (PFPS), and 8.4% experienced Iliotibial band syndrome (ITBS). These two knee-related injuries are the two most common injuries in runners and coming in as the fourth most common is meniscal injuries. The next most common area of injury was the foot/ankle at 16.9% (Taunton, 2002). This is significant because in the world of running, the knee has always been considered to be the biggest problem with why runners get injured. But just because the most injuries occur in this area of the body, does not mean the problem is arising from the knee itself.

More recent research has suggested that the body is a kinetic chain and problems in one area can affect the areas around it. This can be supported with research investigating hip weakness and dysfunction in runners (Homan et al, 2012, Mascal et al, 2003, Snyder et al, 2008, Souza and Powers, 2009). There is support that programs designed to strengthen the hips and develop dynamic stability can reduce injury risk in runners, and particularly for PFPS and ITBS. But there are still cases where the hip is still not the main problem. This is where the ankle comes in. Over time, focus has shifted away from the ankle and towards the upper parts of the kinetic chain. Often times, when problems at the hip and knee are fixed, the ankle follows. But this is not always the case, which means the ankle is still important to have the highest running economy and avoid injury.

Many recent studies have come to the conclusion that running has no correlation to knee osteoarthritis (Lo et al, 2017, Miller, 2017). But through this research and other research, there has been evidence that there is less work being done at the knee than previously thought, and more work at the ankle. This means if the ankles are not strong or stable enough to support the volume or intensity of the running done, the runner will be at an increased risk for injury, potentially up the chain at the knee.

Petersen et al (2014) investigated the joint load at the knee and ankle during different speeds. They found that the load at the ankle significantly increased as the speed increased, and increased significantly more than the load at the knee. This means that as someone runs faster, the lower leg, ankle and foot are more vulnerable to injury do to the increased demand of force production, especially when compared to the knee. Similar results were found by Fuller et al (2016). They investigated the mechanical work at the knee and ankle during increased running speeds in minimalist shoes. They found a redistribution of work from the knee to the ankle as speed increased. Although they investigated minimalist shoe use, the results still apply for running in any shoes. So this means as someone runs faster, the ankle has to produce more of the force for them to have a successful step and push off during running. When using minimalist shoes, the level of force needed is higher than in conventional shoes so runners that would like to transition to minimalist shoes or switch to more minimalist shoes when racing could be at in increased risk of injury to the ankle or calf. But these runners may possibly be at a slightly reduced risk for knee injury.

Baltich et al (2014) investigated muscle activity at the ankle during running with conventional shoes and barefoot. They found that there was greater calf muscle activation in runners with weaker ankles.  This means that runners that have weaker ankles may be at higher risk of injury due to an overload on the calf muscles over time. Baltich et al (2015) investigated the effects of an ankle strengthening program on injury risk.  They found that isolated ankle strength training and functional balance training led to a stronger and more stable ankle. They also found that this training led to lower joint loads at the ankle and knee. This means that with a program designed to strengthen and dynamically stabilize the ankle not only helped the ankle be stronger and more efficient, but it made the task of running easier for the knee as well. This would be an example of fixing the kinetic chain in the opposite direction than is normally suggested. More research is starting to point in the direction of strengthening from the bottom-up (ankle focus) rather than the top-down (hip focus) when trying to combat running injuries(Nigg et al, 2017). This is because when the small muscles that support the ankle are weak, joint forces at the ankle as well as the knee and hip increase substantially. This is due to increased work at these joints to make up for less stability at the ankle (Nigg et al, 2017).

One more important piece of information is that running experience and volume are significant factors when looking at joint loads at the ankle. Verheul et al (2016) investigated the effect of running speed on neuromuscular adaptations during landing along with the effect of training volume. Their findings with speed were consistent with the other research where increased speed led to increased muscle activity and load at the ankle. But when looking at the training volume, they found that at each speed increase, higher mileage runners had lower muscle activation and higher initial knee stiffness. They also saw higher estimated elastic work at the ankle in higher mileage runners which would suggest higher motor control and neuromuscular efficiency in these runners.

With all this information we can start piecing everything together. As runners become stronger in the lower leg and build neuromuscular adaptations through continued training, they begin to rely more on the elastic qualities of their tendons and ligaments around the ankle because the muscle begins to act more like a spring. This effect is greater when the training volume is higher because running is more efficient with higher muscle stiffness from more elastic activity at the ankle. This is important to note with less trained runners, weaker runners, or runners who have missed a significant amount of time due to injury because they will be exposed to higher muscular demands during running. This means strengthening these muscles and teaching them how to use them to keep the ankle stable will help keep them healthy, more efficient, and allow them to accumulate more volume to hopefully adapt to have lower joint loads and more efficient muscular activity. On the other hand, the stronger, more trained runners still have something to worry about. Now that they are more reliant on the elastic qualities of their tendons and ligaments, they are at risk of overuse injuries in these structures. Over time it is possible that these structures can slowly become more lax and lose some of their elastic qualities. This causes an increase in dynamic instability, which when coupled with fatigue during training could lead to altered control of the knee and increasing risk for injury (Gribble et al, 2004). This would shift the emphasis back to the musculature to keep the ankle stable, making the strength of these muscles still highly important. So it is important to always be working on ankle strength and power, along with everything else when trying to stay healthy as a runner at training level.

The last point to be made is that age plays a strong role in how well runners maintain their running mechanics overtime. The area of the body that seems to be most affected by years of running and older age is the ankles. Research has found that as runners age and gain more years running, there are mechanical reductions at the ankle, but not at the hip or knee (Devita et al, 2015). These mechanical changes contribute to decreases in horizontal force production, stride length, and running speed. Research also found from around the age of 20 to 60 years old, there can be a 20-30% reduction in force production and power at the ankle. This is thought to come from a general decline in calf muscle strength, mitochondrial function, and number of motor neurons compared to other muscles (Karamanidis and Arampatzis, 2005). There has also been research to find reduced elasticity in the achilles tendon with age, which could contribute to the reduction in ankle power because of the lessened energy return from the tendon (Ruan et al, 2015, McKean et al, 2006). These pieces of information would support that with age and more running, the ankle muscles and tendons may not be able to withstand the rigors of running especially in individuals running more volume or frequency.

With all this being said there are plenty of ways to make sure the ankles get the attention they need. In some cases simple exercises such as calf raises with weight or eccentric calf raises off of a box or stair is enough to help the calf muscles stay strong or gain strength. A slow drop during both of these exercises is important to teach the muscle how to control movement while under a load which is the main function it will serve during running. The other aspect that needs to be trained is the powerful and reflexive activity that is required for running, especially at faster paces. This can be done with exercises such as jumping rope and single leg hopping drills. These exercises will help teach the ankle to stay stable and powerful while having to repetitively produce force. Other simple things that can be done to help ankle function in general is to not wear shoes when it isn’t necessary. The more time people can spend barefoot, the better the foot can sense its environment and know how it has to react to stay stable. When people wear shoes they mute the foot’s ability to do this and over time allows the foot to rely on the shoe for added stability.

As some take home messages, even though the knee is the most frequently injured area of the body in runners, the problem usually doesn’t originate at the knee. Often times the hip can be the cause but the ankle shouldn’t be overlooked, especially with high mileage runners and runners that are getting older, the ankle can be the main culprit. This supports the importance of strength training in runners, with some specific attention to the ankle and maintaining its level of force production and power. This will help the ankle provide the necessary propulsive forces, stability and economy needed to keep running and stay healthy. With such simple and quick exercises to add to a routine, it doesn’t take much extra effort to get a huge return in the form of ankle function and continued health while running happy.

References:

Baltich J, Lucas-Cuevas A, Enders H, Nigg B. Increased muscle activity during barefoot and shod running with weaker ankles. In: Footwear Biomechanics II: Muscle. Boston, MA; 2014. doi:http://dx.doi.org/10.13140/2.1.2276.4321.

Baltich J, Emery C, Stefanyshyn D, Nigg B. The influence of ankle strength exercise training on running injury risk factors. Footwear Sci. 2015;7(1):99-100.

Devita P, Fellin R, Seay J, Ip E, Stavro N, Messier S. The relationships between age and running biomechanics. Med Sci Sports Exerc. 2015;48(1):98-106.

Fuller J, Buckley J, Tsiros M, Brown N, Thewlis D. Redistribution of mechanical work at the knee and ankle joints during fast running in minimalist shoes. J Athl Train. 2016;51(10):806-812.

Gribble PA, Hertel J, Denegar C, Buckley W. The effects of fatigue and chronic ankle instability on dynamic postural control. J Athl Train. 2004;39(4):321-329.

Homan KJ, Norcross MF, Goerger BM, Prentice WE, Blackburn JT. The influence of hip strength on gluteal activity and lower extremity kinematics. J Electromyogr Kinesiol Off J Int Soc Electrophysiol Kinesiol. 2013;23(2):411-415. doi:10.1016/j.jelekin.2012.11.009.

Karamanidis K, Arampatzis A. Mechanical and morphological properties of different muscle-tendon units in the lower extremity and running mechanics: effect of aging and physical activity. J Exp Biol. 2005;208(20):3907-3923.

Lo GH, Driban JB, Kriska AM, et al. Is There an Association Between a History of Running and Symptomatic Knee Osteoarthritis? A Cross-Sectional Study From the Osteoarthritis Initiative. Arthritis Care Res. 2017;69(2):183-191. doi:10.1002/acr.22939.

Mascal CL, Landel R, Powers C. Management of patellofemoral pain targeting hip, pelvis, and trunk muscle function: 2 case reports. J Orthop Sports Phys Ther. 2003;33(11):647-660. doi:10.2519/jospt.2003.33.11.647.

McKean KA, Manson NA, Stanish WD. Musculoskeletal injury in the masters runners. Clin J Sport Med. 2006;16(2):149–54.

Miller R. Joint Loading in Runners Does Not Initiate Knee Osteoarthrit… : Exercise and Sport Sciences Reviews. Exerc Sport Sci Rev. January 2017. http://journals.lww.com/acsm-essr/Abstract/publishahead/Joint_Loading_in_Runners_Does_Not_Initiate_Knee.99822.aspx. Accessed February 21, 2017.

Nigg BM, Baltich J, Federolf P, Manz S, Nigg S. Functional relevance of the small muscles crossing the ankle joint: the bottom-up approach. Current issues in Sport Science. February 2017;(2):article 3.doi:10.15203/CISS_2017.003

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