ACL Non-Contact Injuries Part III (by guest contributor Anna Napolitano)

The third and final installment of the ACL Non-Contact injury series by Guest Contributor Anna Napolitano. Thanks Anna for a great series!

DANCERS AND RISK OF NON CONTACT ACL  INJURY:

Studies show volleyball and basketball female athletes are at increased risk of NCACL injury due to ankle, knee and hip joint kinematic/kinetic asymmetries during jump landings.  Therefore it should be safe to state ALL jumping activities can place the athlete at greater risk of NCACL injury.  However, this is not true with female dancers.  It has been reported dancers have a much lower incidence of NCACL injuries (0.009 NCACL injuries per 1000 exposures) compared with team sports like basketball and volleyball (0.07-0.31 NCACL injuries per 1000 exposures) (Orishimo, 2009).  This is a substantial difference in the injury rates considering both groups of athletes perform jump landing skills regularly.  Also, no clear gender difference has been identified within the dance population which is unique to this sport compared with other sports like basketball and volleyball (Orishimo, 2009).  Further investigation of the kinematics and kinetics of dancers during jump landings will help determine why NCACL risk is lower in this population.

Understanding the training background of dancers is important when trying to analyze jump landings.  Dancers are trained early “in highly specific jumping/landing techniques” (Orishimo, 2009).  They are trained to land with their lower extremities in full extension, their spine vertical and maximum plantar flexion occurring at the ankle joint during initial contact of the jump landing (Orishimo, 2009).  Previous research with basketball and volleyball female athletes has indicated the negative effects of landing with lower extremities in full extension.  However, dancers have been trained to land on their phalanges and metatarsal heads and then to rotate through their heels using eccentric control to achieve quiet landings (Orishimo, 2009).  This is contrary to female basketball and volleyball athletes who would increase knee flexion and hip flexion to achieve “softer” or quiet landings.  Dancers have also been able to exhibit the ability to control their patellar alignment (over the second ray of the foot) during jump landings (Orishimo, 2009).  Proper alignment of the patella protects the knee joint from unwanted forces acting on the joint and protects soft tissue structures from risk of injury.

Leg stiffness is another common variable seen among dancers.  Defined as “tissue compressibility and individual joint angular stiffness,” leg stiffness is dependent on kinematic and kinetic events occurring in the lower extremity (Kulig, 2010).  Ground reaction forces, joint reaction forces and sagittal/frontal plane kinematics are some variables affecting leg stiffness in dancers.  In Kulig et al, dancers were able to modify their joint angular stiffness during landings (2010).  This was also seen with volleyball and basketball athletes when they were instructed to land soft.  However, the vertical ground reaction forces were subconsciously modified with dancers.  As joint angular stiffness increased so does the ability of the dancer to use stored elastic energy “from the weight acceptance sub phase through the propulsion sub phase” (Kulig, 2010).  Therefore, increasing knee angular stiffness may be optimal for take-off phase and decreasing knee angular stiffness allows for protection of the joint during landing phase (Kulig, 2010).  Take off jump kinematics were not studied for basketball and volleyball athletes so no comparison can be made.

Leg stiffness can also be associated with neuromuscular training, a method of training allowing the body to more efficiently use sport like patterns and combine muscular strengthening with dynamic stabilization exercises.  The result would be the body being able to respond more efficiently to opposing forces as seen during athletic movements like jump landings.  Dancers learn specific jumping and landing techniques during their training.  They are able to activate their medial hamstrings early in the landing and lateral quadriceps and gastrocnemius later (Ambegaonkar, 2011).  Both aspects help represent the neuromuscular timing and cooperation of the hip and ankle joint during jump landings.  Female basketball and volleyball athletes have not demonstrated these neuromuscular timing and cooperation abilities in studies.  However, with the proper intervention program, basketball and volleyball athletes could decrease their NCACL risk by increasing their hip and ankle joint neuromuscular stability.  Orishimo et al determined a large peak hip abduction moment experienced during single jump landing may be due to the dancers’ ability to limit frontal plane hip range of motion through increased neuromuscular control of associated joints (2009).  This study highlights the technical training dancers receive and how it appears to help decrease their risk of NCACL injury.

The purpose of this paper was to examine the biomechanics of jump landings and determine why basketball and volleyball athletes and dancers differ in their risk for NCACL injury.  While effective intervention programs have been established, basketball and volleyball athletes are more prone to NCACL injury due to their technical training in jump landings, or lack of.  Dancers have been taught at an early age the proper technique and appearance of jump landings.  Minimal jump training programs exist for young athletes wanting to learn how to play basketball and volleyball.  Instead they are taught the fundamentals of the game and not the fundamentals of jump landings.  Dancers are trained more from a neuromuscular standpoint as well.  Meaning their training protocol involves dynamic strength and stabilization training.  Basketball and volleyball athletes may or may not even complete any type of strength training depending on the program and/or team they are associated with.  So much emphasis is placed on proper technique during dance for the pure purposes of appearance that it translates into better training methods overall.  Basketball and volleyball athletes are not encouraged to be “graceful” or “delicate” when they compete.  They are instructed to go after the ball in a manner according to which the sport they are playing demands it.  If female basketball and volleyball athletes were to be placed on a neuromuscular training program similar to the demands of their sport with the addition of more dynamic stabilization exercises at an earlier age, it would be interesting to see how much their NCACL injury risk would decrease (if at all).

 

ACL Non-Contact Injuries Part II (by guest contributor Anna Napolitano)

PROPER LANDING TECHNIQUES:

Much emphasis has been placed on proper landing techniques for female volleyball and basketball athletes.  Body position and alignment during jump landings along with proper joint angles and range of motion are important factors to investigate.  Studies have found that NCACL injury possibly occurs in all three planes of motion due to increased knee internal rotation, increased knee valgus and decreased knee flexion during jump landings (Laughlin et al, 2011).  Valgus collapse (knee valgus) may result due to poor timing of the activation of the gluteus medius.  Valgus collapse is also associated with increased ankle pronation and subtalar joint eversion especially during a jump landing.  Decreased knee flexion (most often seen with decreased hip flexion) leads to increased anterior shear forces or increased anterior translation of the tibia over the femur.  With minimal hip and knee flexion occurring, a greater force of the quadriceps occurs to absorb the momentum of the jump landing therefore pulling the tibia forward over the femur.  If the hamstrings are unable to counter this force, then a NCACL injury may occur.  Joseph et al. found increased frontal plane motion during a drop jump test occurring more in females than males and found female athletes exhibiting greater valgus angular velocity (2011).  Increased angular velocity generally occurs during sport specific drills forcing female athletes to adapt to ever changing environments at a quick pace.

Most studies have investigated basketball or volleyball landings separately.  Few studies have compared jump landings between the two sports at one time.  Lee Herrington (2011) investigated knee valgus angles during jump landings between volleyball and basketball athletes.  The results could help identify possible sport specific situations that would place females at greater NCACL risk.  The Herrrington study found no difference between single and bilateral jumping tasks in volleyball athletes (2011).  Basketball athletes showed a decrease in knee valgus angle during the unilateral jump tasks (2011).  A decrease in knee valgus shows greater dynamic hip and knee joint stability and strength.  During the unilateral jumping task volleyball athletes exhibited greater knee valgus than basketball athletes for both the left and right knees (2011).  In contrast the female basketball athletes displayed greater knee valgus angle control during the unilateral task (2011).  The differences here could be related to sport specific skills and demands found unique to that sport.  During volleyball, especially at the middle blocker position, knee, hip and ankle joints are placed at greater risk as the blocker moves across the net to defend the opposing attackers.  Often times when blockers move to the outside or right side of the net to block, their ensuing footwork requires the athlete to maintain stabilization and move quickly to their necessary target.  If there are any imbalances within the lower extremity muscle chain then the forces experienced by the athlete as they move across the net places he/she at possible higher risk of NCACL injury.

Kinematic asymmetries, although not desired, are common among athletes.  Single limb dominance is a common theme however strong research to support it does not exist.  Females could present with greater kinematic asymmetries than males when performing jump landing tasks explaining their “dominance” in NCACL injuries.  During forward jump landings, females displayed greater asymmetry than males in knee valgus and ankle abduction (Pappas and Carpes, 2011).  Ankle abduction increases stress along the medial aspect of the knee joint therefore possibly increasing the amount of knee valgus measured.  Also, the asymmetry presented could have been right limb vs. left limb dominance during landings.  Navicular drop and subtalar pronation are associated with ankle abduction (Pappas and Carpes, 2011).  Females displayed greater asymmetries than males with ankle joint kinematics in the frontal plane as well (Pappas and Carpes, 2011).  Ankle motion in the frontal plane is necessary for shock absorption.  Increased ankle movement leads to internal rotation of the tibia and preloading of the ACL (Pappas and Carpes, 2011).  If the ankle is unable to absorb the extra movements and forces the lower extremity experiences during jump landings, more stress will be placed on the knee and hip joints placing the ACL at greater risk for injury.

 

ACL non-contact injuries in female athletes: a three (3) part series

The following is a three part series devoted to the female athlete, specifically ACL injuries of the non-contact variety. Guest contributor Anna Napolitano explores some of the reasoning behind this frequent injury and the role of dance as a possible protection against such injuries. Anna is a 1998 graduate of the University of Michigan with a Bachelor of Science in Athletic Training and Movement Science and is licensed as an AT.  She has her CSCS from the NSCA and her PES-NASM through the National Academy of Sports Medicine.  Anna owns Innovative Training Solutions, LLC (www.mytrain-solutions.com) where she works with middle and high school athletes on sports performance training with her specialty being in ACL prevention and post ACL rehab.  I hope you enjoy this series.

PART I

INTRODUCTION:

 

Injuries are a possible outcome experienced by athletes participating in sports of all types with some athletes at a greater risk for injuries than others.  According to Hughes et al, women competing in the same sport as men are reported to be six to eight times more likely to experience a non-contact anterior cruciate ligament (NCACL) tear than men (Hughes, 2009).  Numerous studies have attempted to gain a better understanding of this phenomenon.  The majority of female NCACL injuries occur during jump landings as seen in the sports of basketball and volleyball (Pappas and Carpes, 2011).  Another study by Hootman et al found female basketball athletes and volleyball athletes experienced NCACL injuries but at different exposure rates (Herrington, 2011).  Many more studies have documented and investigated jump landing biomechanics of female basketball and volleyball athletes.  However, not all jump landing athletes are prone to NCACL injuries. 

Dancers may not be considered athletes as this form of physical activity is often classified under the “arts”.  However, their training protocol places them at risk for soft tissue joint injuries similar to those of traditionally defined athletes.  “Dancers may perform more than 200 jumping and landing activities throughout their daily training and practice.” (Orishimo, 2009).  Training at this caliber could place female dancers at increased risk of NCACL injury.  However, the incidence of NCACL injuries among female dancers is much lower than that of female basketball and volleyball athletes (Orishimo, 2009).  Biomechanics of jumping styles may play a role in the difference between female basketball and volleyball athletes and dancers.  The purpose of this report is to examine the biomechanics of jump landings and determine why basketball and volleyball athletes are a greater risk for NCACL injury than female dancers.

MECHANICS OF NON CONTACT ACL INJURIES:

Before evaluating the biomechanics of jump landings, a thorough understanding of the mechanics of NCACL injuries occur needs to be discussed.  Simply explained, NCACL injuries occur when there is too much stress on the ligament (i.e., anterior cruciate ligament, ACL) leading to failure of the tensile strength of the ligament (Hashemi et al, 2011).  Stress factors include the magnitude of the stress as well as the rate of loading of this stress.  NCACL injuries may occur during practices, games or competitions.  Research has identified not one but numerous risk factors associated with NCACL injuries.  Factors found to “affect both ACL strength and the loads applied to it” include anterior shear force, hyperextension, axial compressive loads, internal rotation of tibia, valgus collapse mechanism, combination of anterior and valgus shear forces, and combination of external tibia torque and valgus forces (Hashemi et al, 2011).  These factors can be found in sport movements especially jump landings.

BIOMECHANICS OF SPORT MOVEMENTS:

The biomechanics of a jump landing involves observation of the ankle, knee and hip joints and the kinetics/kinematics occurring at these structures.  At initial contact of the jump landing the body experiences forces from the ground absorbed through the lower extremities.  Gravity is pulling the athlete down and ground reaction forces are pushing back on the athlete as the athlete lands from the jump.  Great ground reaction forces during landing tasks result in an increase on the load of the passive structures (ACL) of the knee (Hughes, 2009).  The muscles of the hip and knee joint become a protective mechanism at this point.  Some studies have attempted to determine if a decrease in ground reaction forces can result by having female athletes perform “soft” landing or “stiff” landings.  “Soft” landings are defined as maximizing knee flexion and “stiff” landings are defined as minimizing knee flexion (Lauglin et al, 2011).  This same study determined that soft landings allowed the lower extremity to absorb the ground reaction forces experienced by the body.  The ability to absorb the ground reaction forces may be due to increased muscle activation during the jump landings and may be protective of the passive structures (i.e., ACL).  The “soft” landing may provide an increase in posterior shear force by the hamstrings to counter the anterior shear force created by the quadriceps and tibio femoral joint (Laughlin et al, 2011).  This counterbalance between the quadriceps and hamstrings protects the ACL from damage.  Hughes et al found an increase in ground reaction forces during the first 40% of landing phase and a decrease in ground reaction forces during the final 60% of the landing phase while observing females landing from volleyball block jumps (2009).  The higher absorption of the ground reaction forces at initial contact of landing phase coincide with the athlete’s proper body position and alignment as well as joint positions.  The majority of the ground reaction forces was absorbed initially and then subsided as the velocity of the jump decreased.    Coincidently, most NCACL tears occur immediately upon ground contact, as the athlete lands or makes a sudden change in direction.

 

Sock with a sole: training tool for foreward foot strike during running

Warning: Opinion only (albeit hopefully based on science and experience : )

Having examined much of the research on barefoot running, minimalist shoe running, foot strike patterns, and the relationship of these variables to injury risk and performance, I’ve come to two (2) conclusions: 1) Running is risky (over 50% of all runners will experience injury at some point in his/her career) and 2) Injury risk varies depending on foot strike running style.  All runners, regardless of foot strike pattern, are at risk of injury because running is a tremendous musculoskeletal stress.  Fortunately, the musculoskeletal system is quite adept at adapting to stress; if the runner properly “doses” the stresses to the body, the body will happily and effectively adapt. But if the runner over-doses these stresses, the body will react negatively (i.e., injuries), regardless of the foot strike landing style, shoe wear (or lack thereof), experience, etc.

In terms of injury risk, it appears that barefoot runners (and runners who land with a midfoot or forefoot strike) have lower risk of injury at the knee and hip, but perhaps an elevated risk of injury at the foot and Achilles tendon.  There remains insufficient evidence to verify this – I make this observation strictly based on biomechanical studies of landing forces.  Heel strike runners (most of us) place greater stresses on the knee and hip, compared with midfoot/forefoot strikers.  So, while each style “reduces” risk of injury, each style also comes with elevated risk of injury.  The key remains: Dosage!  But, there is a slowly growing body of evidence to suggest that forefoot/midfoot strike landing might, I repeat might, be perhaps a bit more safe than heel strike landing.  With that said, how might one transition to a forefoot/midfoot strike runner?  The key is likely foot wear.

There are dozens of “minimalist” running shoes on the market.  However, based on a few observational studies, even running in a minimalist shoe does not guarantee a foreward striking running style.  Heel striking continues to be observed in runners even when wearing minimalist shoes. I suspect part of the dilemma is the fact that even the most minimal of minimalist  “running shoes” remain too similar to their standard running shoe cousins: in general appearance (laces, heel counter, uppers, outer sole, etc.).  Anecdotally, running friends have told me they need to really “concentrate” on their running form, in order to land more forward on the foot, even when wearing their “minimalist” shoes. I have experienced similar when testing multiple different minimalist shoes.  That is, until I tried on a pair of what I would call “Socks with a sole” (Sockwa G3).

What is more minimal than a sock?  Given that a sock provides absolutely no support to the foot, and essentially no protection to the bottom of the foot, a sock is truly minimal.  The Sockwa is basically one slight upgrade over a sock in that it adds a protective sole to the bottom of the sock.  When I ran in the G3, I was actually forced to land with a foreward strike pattern – identical to how I run when barefoot.  I am not a barefoot runner, but of course I do run barefoot (to get the mail, to run home from the beach, etc.).  The Sockwa G3 is as close to running barefoot as I have experienced – and no comparison at all to the “minimalist” running shoes on the market. This is not to disparage minimalist running shoes but only to point out that a sock is about as close to barefoot running as a shoe can become.

I have successfully completed several runs now in the G3 and have had no difficulty at all maintaining a forward striking running style.  It happens naturally, without much thought.  This is quite different than my experiences with my “minimalist” shoes in which I have to consciously work on my stride to maintain a forward strike running style. Again, this is my own personal experience.  But I have found in a short time that the G3 is a better foot cover for running in terms of promoting a barefoot type running technique.

So, if your running goal includes transitioning to a foreward foot strike running style (like barefoot running) because you hope to change your risk of injury, I certainly recommend giving the G3 a try.  And as with all new stress, don’t over-dose.  Gradually add new running stresses – listening to your body as it reacts to these stressors.  If you are an experienced runner, but new to foreward strike landing, or new to a minimalist shoe, begin with shorter runs to give your Achilles tendon and your foot bones (the tarsals and metatarsals in particular) a chance to adapt to this new running form.  If you are new runner, ditto J  I cannot recommend a specific level of dosage – this is person dependent – but your body should be able to provide you with important feedback – so listen carefully to what it is telling you.

 

 

 

 

Foot-strike pattern and runners: advantage Barefoot runners?!

Fortunately for runners and running coaches, research continues to emerge that examines the role of “foot-strike” pattern on running, and how running barefoot or in minimalist type shoes contribute to this foot strike pattern.  Three studies published at the end of 2012 and beginning of 2013 provide more insights.

First, in a study ahead of print by Delgado et al (MSSE, 2012), the researchers found that forefoot strike (FFS) landing may not provide the protection against ‘shock absorbtion’ that has been promoted in other studies.  They found that rearfoot striking (RFS) attenuated ground reaction forces better than forefoot strike running, at least in the lumbar spine.  In this study subjects were instructed to  run with a rearfoot strike pattern as well as a forefoot strike pattern. It is not clear by the abstract whether these runners were experienced as FFS or RFS runners.

A study that has recevied quite the buzz on the internet (Twitter, Social Media, News outlets) is the study by Hatala et al (2013) who found that habitual barefoot runners in a group of northern Kenyan runners and found that the majority of these barefoot runners actually ran with a heel-strike pattern. This is quite contrary to the studies by Leiberman et al and others who have documented that habitual barefoot runners are midfoot or forefoot strikers.  But in actuality, the Hatala et al study finds similar foot strike pattern in these Kenyan runners as the speed of running increases.  When running at a comfortable endurance pace, a RFS pattern seems to work for these runners. But as they increase their running speed, they adopt a MFS or FFS pattern of landing, similar to the findings by Leiberman and others.

Similarly, in a recent ahead of  print study by Kasmer et al (2012), foot-strike landing was highly dependent on speed.  They examined the landing pattern of nearly 2000 runners at the 8.1km mark of a local marathon.  They found that 94% (yes 94%) of all runners landed with a heel-strike landing pattern!  BUT, they also found that elite performers (i.e., those running the fastest), were more likely to run with a MFS or FFS pattern.  Hence, running speed, regardless of foot wear, dictated landing style.  Faster running appears to be associated with a MFS or FFS running pattern, although runners of all speeds successfully run with RFS pattern as well.

What are the implications for barefoot runners and those who have switched to minimalist running shoes?  For the barefoot runner, these studies really don’t have much of an impact as they do not support nor challenge the practice of barefoot running.  But for the minimalist shoe runner, one take home message is to consider that simply switching to a minimalist shoe does not  guarantee a FFS or MFS running style.  Even runners in minimalist type shoes were observed to run with a RFS pattern.  To transition to a MFS or FFS running style, similar to the barefoot runner, requires more than a shoe change. It requires a conscious change in leg movement (shorter stride, focusing on landing on the midfoot or forefoot, a bit more knee flexion, higher cadence, etc.).  I will address some strategies for adopting a “barefoot” running style in a forthcoming column.

What the Sockwa?

Being quite new to “minimalist” running, I have tried to keep up on all the new research that continues to emerge on the topic of Barefoot (BF) running and Minimalist Shoe (MS) running.  I am a Traditional Shoe (TS) runner having run in stable, motion control shoes for 20+ years.  And during most of those years I’ve worn semi-rigid custom orthotics in my shoes. The original reaon for the orthotics was persistent hip and lateral knee pain when I first started running – and I just continued wearing the orthotics because they helped so well at the time.

I recently made the leap to MS (Minimal shoe) running, tossing my orthotics and stable, motion control shoes for the New Balance “Minimus” running shoe. I fell in love almost immediately – I loved the light weight shoe, and the fact that I could almost, almost, feel the ground beneath my feet.  But, I still felt like I was running like a TS runner – even with the minimal heel of the New Balance Minimalist – I continue to land with a heel strike running form. The good news was that I was able to run with minimal protection and without orthotics and without my old hip or knee pain.  I cannot attribute the minimal shoe or lack of orthotics to painfree running – it is just as likely that 20 years of running allowed me to positively adapt physically to running.

In any case I was also intrigued by the notion of barefoot running (BF running) and have the ambition to one day run “like” the barefoot runner.  But, I want sufficient protection to the bottom of my feet. As most now know, BF embraces a midfoot or forefoot landing style of the foot, rather than the traditional heel strike pattern. I will be writing more about what we know in the research literature about the pros/cons of midfoot/forefoot striking compared with heel striking, but suffice to say there is sufficient research to entice me to try to make this transition as a runner.

Knowing that “true” barefoot running would require that I learn to land on my midfoot and/or forefoot (at least for higher speed running), I knew I needed to learn how to transition from my heel striking ways to that of the midfoot striker.  Unfortunately, the Minimus shoe was a bit too close to the traditional shoe to help me  sufficiently with this transition.  And while I am sure the Vibram Five-Finger would likely do the trick, I am “toe-space” sensitive. I am quite sure I would not tolerate toe socks – I cannot tolerate a single “big toe thong” type sandle…so, something between each toe was not going to work.

And then I stumbled upon Sockwa – through Twitter.  Clever name (Sockwa = sock with attitude) – these “shoes” slip on almost like a crew cut sock but they have sufficient minimal rubber on the sole to offer protection to the bottom of the foot.  The Sockwa G3 (which is what I am wearing) are deigned to allow for running outdoors. And because they have absolutely no heel reinforcement, no heel thickness at all, the Sockwa encourages the runner to land softly on the midfoot or forefoot, essentially as if running barefoot.  As soon as I slipped on my Sockwa G3′s I knew I was in for a treat.  My feet felt almost naked…and I was excited to go for a short run.  Kind of reminded me of the moccasins I wore as  kid playing in the backyard.

My first run was a combination of concrete road surface, gravel road, and rock/dirt trail.  I kept the run short (about 3-miles) but right from the start I knew I was landing on my midfoot and not on my heels. Even when I tried to land on my heels I did not like the sensation and immediately resorted to midfoot landing. This naturally required a slightly higher cadence, a shorter stride, and a bit more “tall” running posture – but, well, that is actually the idea – and the basic requirement of BF running.  I only wish I had picked a route that also had some minor hills – I just felt like I wanted to surge – which is unusual for me as a runner.  What a total joy – and I am not one to gush about running.  I anxiously await to see how I feel tomorrow…and am looking foward to my next run.  The G3 is super comfortable and feels almost as if running without anything on my feet - about as close to BF running as I’ll get – but with the requisite protection.  Thank you Sockwa!!!!!

Follow up to Barefoot running and minimalist blog

A recent study by Goss and Gross (2012) (Relationship among self-reported shoe type, footstrike pattern, and injury incidence) reports that heel-strike runners (by self-report) also report 3.4 x greater likelihood of sustaining an injury compared with barefoot runners and/or minimalist runners who land on the midfoot or forefoot.  The authors are quick to point out that “landing” mechanics in this study was identified strictly by self-report, and unfortunately self-reported landing mechanics has been shown to be a very poor indicator of true landing style. In addition, “injury incidence” was also self-reported.  None the less, even with errors in self-report, this study certainly provides fuel for further investigation, and may be encouraging for those who are making that switch to the minimalist shoe and/or barefoot running.  Hopefully we’ll see a longitudinal study that follows runners of different landing mechanics and shoe wear (shod, minimal, barefoot)…and track injury incidence.  For now, one step at a time – proceed with caution.  Dosing is critical to success – as with any form of exercise/training program.