Wednesday, March 13, 2013

Evidence for the Late Swing Phase

There is something about the biomechanics of running at high speed that increases the risk of a hamstring injury. This is something of a review, focusing on the late swing phase of the gait cycle with the intent that if we understand what is going on, we can structure our training programs better.

Better training = injury prevention/ reducing the risk of injury = better performance.

In keeping with the principles of training (specificity, progressive overload), programs would ideally incorporate aspects (e.g. postures, muscle lengths, contraction type) that are most similar to those conditions associated with injury. Only then would athletes optimize the gains in functional strength and minimize the risk of future injury.

THE STANCE PHASE:


Some researchers, however, propose that the hamstrings are most likely to be injured during the stance phase of the gait. This is mostly due to the the external loading on the limb that comes as a result of ground contact. Lateral and medial hamstrings and gluteus maximus showed similar activities with peak levels of EMG during foot-strike (Jonhagen S, et al., 1996).

Yu B, et al. (2008) included the following in their abstract: "The potential for hamstring muscle strain injury exists during the late stance phase as well as during the late swing phases of overground sprinting."

CAVEAT


Notwithstanding, a landmark article describing the work by Lieber and Friden (1993), though largely uncited, should be considered. It was entitled Muscle damage is not a function of muscle force but active muscle strain. (Journal of Applied Physiology. 1993;74:520–6.) They interpreted their findings to signify that "it is not high force per se that causes muscle damage after eccentric contraction but the magnitude of the active strain (i.e., strain during active lengthening)."

THE LATE SWING PHASE: FORM AND FUNCTION

Conceptually, hamstring lengths are primarily a function of the angles of flexion found at the hip and knees during running. For example, the hamstrings are lengthening during late swing when the hip is flexing and the knee is extending, as both of these motions contribute to hamstring stretch.

  •  However, the hip starts to extend prior to foot contact and continues to extend throughout stance (47); 
  • the knee flexes until mid-stance and then extends until toe-off. Therefore, if hamstring stretch is to occur during the second half of stance, the hamstring lengthening due to knee extension would have to exceed the hamstring shortening due to hip extension. 
  • Further because the hamstring moment arms at the hip are greater than at the knee (1347), the knee extension velocity would have to exceed the hip extension velocity. 
  • However, sagittal hip and knee angular velocities during stance tend to be of comparable magnitude (27), making it unlikely that substantial hamstring stretch is occurring during stance.
THE LATE SWING: STUDY EVIDENCE

Heiderscheit BC, et al. (2005) identified, based upon the earliest indications in marker trajectories, a 130 ms period during the late swing phase as the period of injury. The biceps femoris (BF) reached a peak musculotendon length up to 12% beyond the length seen in an upright posture and exceeded the normalized peak length of the medial hamstrings. "This case provides quantitative data suggesting that the biceps femoris muscle is susceptible to an lengthening contraction injury during the late swing phase of the running gait cycle."

In an interesting 2009 study, Schache A, et al. collected 10 normal sprinting trials for kinematic and GRF analysis, and compared them with one after a hamstring strain. "For the pre-injury trials, the right leg compared to the left displayed greater knee extension and hamstring muscle-tendon unit length during terminal swing, an increased vertical ground reaction force peak and loading rate, and an increased peak hip extensor torque and peak hip power generation during initial stance."

"For the injury trial, significant biomechanical reactions were evident in response to the right hamstring strain, most notably for the right leg during the proceeding swing phase after the onset of the injury. The earliest kinematic deviations in response to the injury were displayed by the trunk and pelvis during right mid-stance. Taking into account neuromuscular latencies and electromechanical delays, the stimulus for the injury must have occurred prior to right foot-strike during the swing phase of the sprinting cycle. It is concluded that hamstring strains during sprinting most likely occur during terminal swing as a consequence of an eccentric contraction." (Biomechanical response to hamstring muscle strain injury.)

Using 3-D videographic and EMG data from the maximal overground (as opposed to treadmill) sprinting efforts of 20 male runners, soccer and lacrosse players, Yu B, et al (2008) interpreted their findings as such; "The potential for hamstring muscle strain injury exists during the late stance phase as well as during the late swing phases of overground sprinting." (Hamstring muscle kinematics and activation during overground sprinting.)




OTHER POINTS TO CONSIDER

  • Repetition: The biarticular hamstrings undergo maximal stretching during the late swing phase of running gait and also present with a repetitive active stretch-shortening contraction. "When active stretch-shortening cycles are imposed on a musculotendon unit, the degree of strain taken up by the fibers can change with time, making the muscle potentially more susceptible to injury after repeated loading cycles" (Butterfield and Herzog, 2005). Basically, the more strides you take, the greater the likelihood for injury. (Ever notice how nobody pulls up straight out of the blocks?)
  • Negative work: When running at high speeds, the amount of negative/concentric work increases significantly and thus, the hamstrings may be susceptible to a late swing injury as a result of repetitive strides of high speed running. (Heiderscheit BC, et al., 2005 and Schache A, et al., 2009)
  • Biceps Femoris Observations: BF loading increases with speed during swing but not stance. (Chumanov et. al., presently reviewed paper.)


It is worth noting that this information derives from studies and observations when the hamstrings are involved in forward sprinting at a fairly constant speed as in track sprinters. The hamstring loads that occur during sudden directional turns and accelerations as in soccer are vastly different, and could certainly factor into injury risk.



Hope Solo


Defining the musculotendon demands during sprinting, with specific emphasis on which time injury is most likely to occur offer direction as to the type of resistance training may be useful for injury risk management. The examples above suggest that the late swing is the time the hamstrings are most susceptible to injury. with this evidence, the most effective resistance training would be when the hip is in flexion and the knee in extension, as in the swing phase. For example, deadlifts, good mornings, back extensions.

Pauline Nordin

This data also provides evidence for the use of eccentric contractions under inertial load in programming. This approach has already been shown to be efficacious as a prevention and rehabilitative tool. See my article, "The Best Exercises Soccer Players Are Not Doing" , for an eccentric focused training program, including progressions from rehab to sport-specific training.

REFERENCES

All references in this article, unless otherwise stated refer to

Chumanov E. S, Heiderscheit B. C, and Thelen D. G (2011). Hamstring Musculotendon Dynamics during Stance and Swing Phases of High Speed Running. Med Sci Sports Exerc. 43(3): 525–532.

Monday, March 4, 2013

Strengthening Is Not The Same As Rehabilitation

There is a huge misconception floating in fitness centers all over the place- that injury is the result of weakness. "My back hurts; it must be weak." "I keep rolling my ankle. What can I do to make my ankles stronger?" 

Not every injury results from weakness. In fact, noted physiotherapist and strength coach Gray Cook and his team at Functional Movement Systems looked at the data before and since developing the FMS. The three leading causes for injury, they have found, are:

  • Previous Injury
  • Asymmetries 
  • Motor control issues

CASE STUDIES

I met a young soccer player who had not played in a while, but was hoping to return to the game. He had stopped playing because of an ACL injury. He was not alone. I met two more athletes, promising, but also with fairly recent operations. One was a lacrosse player, the other had switched from baseball to slow pitch before hearing that dreaded "pop" sound. I talked to these guys individually, and even trained one of them for a couple of weeks. All three could be found on the leg press and leg extension machines when they came into. They all skipped the balance work they were given as homework by their physios. I tested them and was not surprised to find that they all scored poorly, even on the uninjured leg.

Rotation Movement That Causes ACL Injury


A regular gym-goer told me that his back and shoulder were hurting. "What do you think I should do?" He didn't seem like he would hang around long enough for me to get more information. I got his info, and since he had mentioned they only hurt when he did certain movements, I advised staying away from those movements and promised to send him a research paper that had some good information for back pain. I met the guy a week later.

"How's the pain," I asked. "Receded, I hope."

"It's not as painful now. I still have to do more strengthening work though," came the reply.

I mention this guy because its not just athletes who are in a hurry to get back to playing. Weekend warriors with gym memberships do this too. Think of the dads who 'come out of retirement' for their kid's Father-Son day game, or take part in a little sports day event.

The prevalent ignorance is not because people choose to be stupid. They just don't get it. They think they were weak to begin with, hence the injury. They think since they've had to sit out while recovering, their strength capacity is the only thing deconditioned.




A LITTLE SCIENCE

A medial knee position during the stance phase when running may affect the line of pull of the quadriceps and contribute to the etiology or exacerbation of overuse injuries such as patellofemoral pain.

Stefanyshyn et al., (2006) hypothesized that increased internal hip and knee abduction moment during running results in greater forces on the lateral facet of the patella. These faulty/altered biomechanics likely result in increased contributions from the vastus lateralis, extensions of the iliotibial band, or both. Greater force on the patella from these tissues may result in greater retropatellar stress and activation of nociceptive fibers in patellar subchondral bone or synovium. They concluded that increased knee abduction impulses should be deemed risk factors that play a role in the development of patellofemoral pain in runners.

THE EVIDENCE

One of the main culprits when athletes have altered mechanics is the hip. Studies have been conducted assessing the effectiveness of strengthening the joint in these situations. In one, females with patellofemoral pain (PFP) demonstrated significantly less peak hip adduction while running at the end of a 2‐week training program when they were given visual 3-D feedback of what the hip was actually doing while they ran. (Noehren B, Scholz J, Davis I., 2011). In another, a study including a 14‐week rehabilitation ‐program for PFP that also included visual feedback and hip strengthening exercises was also found to decrease pain and hip adduction angle during a single leg step down. (Mascal C, Landel R, Powers C., 2003). Finally, in a study by (Herman D, OƱate J, Padua D, et al., (2009) peak hip adduction and knee abduction angles during a drop jump activity decreased among subjects who received visual feedback for altering movement performance and strength training. Most importantly, subjects who received the strength training intervention alone did not experience these changes.


Decreases of 15% in internal hip abduction and a 23% knee abductor moments were reported by Earl et al following an 8‐week “proximal stability program” that included five weeks of training including attention to lower extremity alignment during exercises for patellofemoral pain.



Wouters, et al., (2012) found internal hip and knee abduction moments decreased by 23% and 29%, respectively. They also found that subjects demonstrated less knee abduction excursion and increased knee adduction excursion during the stance phase of running after the movement training program.

The relevance of these studies is that hip strengthening alone may not be an effective remedy for altered lower extremity running mechanics that may increase the risk of running related injury. Based on the available evidence, it seems programs should emphasize neuromuscular control ‐elements such as guided practice of movement performance and visual, verbal, and tactile feedback rather than hip strengthening alone.

Motor control, stability, mobility. These three things are very important. We can't see them when they're there but we are immediately drawn to them when they are absent. How often have we seen players walk off the field only to hear that they picked up a knock and were substituted at half time? I'm writing this because I'm hoping the thing that draws us to the absence of those three factors is injury. If it is, hopefully we won't skip over them in favor of speed work, some weights and plyometrics.

There ought to be a progressive approach to returning to play. Address mobility. Soccer players are notorious for skipping the warm up. Or they have one, but it is ridiculous. Why is it that the numbers reflecting non-contact ACL injuries continues to increase when FIFA has had a prevention program out for years?...

Related Articles

Mechanisms of Non-contact ACL Injury
F-MARC's 11+ Warm-up Program

Reference

Wouters, I., Almonroeder, T., DeJarlais, B., Laack, A., Willson, D. and Kernozek, TW. (2012). Effects of A Movement Training Program On Hip and Knee Joint Frontal Plane Running. Int J Sports Phys Ther. 7(6): 637–646.