Brian Schiff’s Blog

As someone who works with high level athletes and those aspiring to take their performance to new levels, I think it is important to understand power development and the real “why” behind the exercises we choose.  I also come at this from the side of a sports physical therapist who is working to get athletes back to their peak performance.

To that end, I am always looking for the most effective ways to train the neuromuscular system.  Finding the most “specific” exercises for our clients is important.  I thought I would provide a brief summery of a new article in the November 2013 Journal of Strength and Conditioning Research that looked to compare the neuromuscular characteristics of two types of jumps: hurdle and drop jumps.  In addition, the authors wanted to examine three types of landing techniques:

1. Preferred – athlete instructed to jump with a technique that allows for jumping as quickly and high as possible
2. Flat foot
3. Forefoot (FORE)

The working hypothesis was that hurdle jumps would be more powerful than drop jumps (DJs) and that foot flat technique would decrease mechanical power.  The study included 25 subjects (male athletes) from Memorial University and during the jumps reaction forces, contact time, rate of force development (RFD) and lower limb EMG were measured.

All subjects did regular regular resistance training multiple plyometric drills with a typical volume of > 100 repetitions per session.  However, none of the subjects had done drop jumps before.  As such, this was the first test assessed to avoid fatigue.  Subjects stood on a force platform and were asked to perform a maximal CMJ.  Two trials were conducted with 1 minute of rest in between jumps.  The maximum CMJ height was used to establish the DJ and hurdle height.  The average flight time of the two trials was used to calculate jump height.

The order of DJ and hurdle jump tests was randomized with 5 minutes of rest between the jumps.  The athletes did a 10 minute warm-up of cycling at 75 W-60 RPM followed by 5 sets of 5 sub maximal hopping, 5 single submaximal CMJ and 2 maximal CMJ.  Only dynamic stretching was allowed during the warm-up to avoid any muscular power deficits created by static stretching.

Results

Contact time

• Hurdle jump had a 36.9% shorter contact time compared to DJ
• Preferred technique 29.1% shorter contact time than FLAT
• Preferred technique had 9.6% longer contact time than FORE
• FLAT 25.9% longer than FORE
• Jump and landing type interaction 23.8% shorter ground contact time for DJ FORE vs. FLAT

Vertical ground reaction forces (VGRF)

• Hurdle jump forces were 11% higher than DJ
• FLAT techniques revealed 30.8% less reaction force than preferred technique and 40.9% less than FORE
• DJ preferred technique had 14.9% more force than DJ FLAT
• DJ FLAT had lowest force level and was 25.9% less than DF FORE

Rate of force development

• Main effect of hurdle jump showed 46.3% higher RFD than DJ
• FORE technique 11.3% higher than preferred and 45% higher than FLAT
• Preferred technique 38% higher than FLAT
• DJ preferred 35% > DJ FLAT
• Hurdle jump preferred 40.9% higher than DJ preferred
• Hurdle jump FORE 43.6% higher than DJ preferred
• DJ FLAT was lowest for RFD

Leg stiffness

• Hurdle jumps were 64% stiffer than DJ
• Hurdle jump FORE had greatest stiffness
• DJ FLAT was the least stiff technique

EMG Activity

• Rectus femoris – HJ had 30% higher activity than DJ, eccentric phase highest, and FLAT higher than preferred and FORE
• Biceps femoris – HJ 68.8% more activity than DJ, concentric phase highest, and preferred higher than FLAT
• Tibialis anterior – FLAT had highest activity, eccentric phase highest
• Gastrocnemius – Preferred 26.3% > FLAT, FLAT 47% < FORE, and concentric phase highest

Key findings of the study

1. Preferred and FORE hurdle jumps were more powerful plyometric exercises than the DJ based on a shorter contact time, higher VGRF, RFD and leg stiffness
2. FORE and preferred landings produced the best results for all mechanical power variables

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ACL injuries continue to proliferate among female athletes.  I am passionate about preventing them, and part of my professional mission is to study and evolve in my rehab and prevention training approaches all the time to stay on top.  I wanted to pass along some new information on a new screening tool just unveiled in the Strength and Conditioning Journal this month.

Before I reveal the screening and training tool, I want to take a moment and review what Timothy Hewett refers to as modifiable risk factors that contribute to injury risk based on his work:

1. Ligament Dominance – defined as an imbalance b/w neuromuscular and ligamentous control  of dynamic knee stability and it is visualized by loss of frontal plane control with landing and cutting
2. Quadriceps Dominance – defined as an imbalance between quad and hamstring strength, recruitment and coordination
3. Leg Dominance – defined as an imbalance between the two legs with respect to strength, coordination and control
4. Trunk Dominance ‘Core’ Dysfunction – defined as an imbalance b/w the inertial demands on the trunk and its ability to resist or control/resist it

Previously, Hewett has identified that high knee abduction moments are related to high LOAD on the knee and a major risk factor for ACL injury.  He and his colleagues have done extensive motion analysis in their lab in Cincinnati, OH.  As such, a drop landing test has been used as one tool to observe landing mechanics and assign some risk value to athletes competing in cutting and jumping sports.

In the current article (click here for the abstract) Meyer, Brent, Ford and Hewett unveil a new screening tool involving the tuck jump.  They propose that this tool is easier for the S & C coaches to do on the field and not only assess risk factors by way of observing technical flaws, but also use the tool as a training maneuver.

The idea is the subject will perform tuck jumps for 10 seconds consecutively while the observer makes notes on the following pre, mid and post jumping:

1. Lower extremity valgus at landing
2. Thighs do not reach parallel (peak height of jump)
3. Thighs not equal side-to-side (during flight)
4. Foot placement not shoulder width apart
5. Foot placement not parallel (front to back)
6. Foot contact timing not equal
7. Excessive landing contact noise
8. Pause b/w jumps
9. Technique declines prior to 10 seconds
10. Does not land in same footprint (excessive in flight motion)

Factors 1-3 refer to knee and thigh motion, 4-7 refer to foot position during landing and 8-10 refer to plyometric technique.  Coaches are instructed to grade the flaws if seen with check marks during the phases they are seen and use this as a guide for correction.  They may also use cameras in the frontal and sagittal plane to assist them.

My thoughts on this are:

• There is sound science behind the rationale for the test and modifiable risk factors
• There is a need for basic no-cost screening tools coaches can apply in their settings
• The tuck jump assessment will provide instant feedback on form and identify technical flaws that may indicate higher risk for injury
• The tuck jump is a higher demand plyo drill so I fear poor form may be as much to blame on inexperience and unrefined motor patterns as it is to just dominance patterns so we need to keep plyo training experience in mind when analyzing the screen results especially for beginners
• The tuck jump assessment does not really consider fundamental movement restrictions that may bias the form on one side if an asymmetry is present
• I still wonder how much ankle pronation impacts landing and whether we will see more research on this – there was a study done at ECU where they used orthotics and saw a reduction in ACL tears in their collegiate athletes so I have to wonder about this crucial element of the kinetic chain

In the end, we still lack many answers.  According to data published in the Journal of Athletic Training in 2006, non targeted neuromuscular training programs need to be applied to 89 female athletes to prevent 1 ACL tear.  So, we need to keep studying and applying science to our training, all the while critically questioning science and looking at our athletes holistically to find the best prevention strategies for each one individually and for at risk athletes as a whole.

As I prepare to present at an ACL Symposium with some of my colleagues this weekend, I thought I would share some of the information I am presenting on injury prevention.

Research consistently shows that neuromuscular training is beneficial in reducing ACL injuries.  This type of training hinges on training our athletes to land, plant and cut on a bent knee while shifting the COM (center of mass) forward.  Too many times, I see female athletes land with stiff knees in an upright posture relying too heavily on their quads.

Emphasizing hip and knee flexion is vital in order to activate the posterior chain and provided a restraint to anterior tibial translation.  When it comes to landing and plyometrics, I feel strongly that we need to focus on repetitive drills that enhance power and teach ideal form.

These exercises should include single and double leg varieties, but more importantly they should challenge the body in the sagittal, coronal and transverse plane.  I have included a short video today that illustrates just a few exercises that I incorporate in my training sessions.

Stay tuned as I will share more details about prevention training in future posts.

Whenever I speak at fitness industry events, I always tell my fellow fitness comrades that they must do everything in their power to elevate the profession.  I live in both the “rehab” and “training” world daily.  I can tell you unequivocally that the words “personal trainer” do not garner tons of respect in the medical community in many cases.

I will share a personal story from my professional work experience this week that illustrates why.  Yesterday, I evaluated a new patient (45 y/o male) who just underwent an ACL allograft reconstruction and medial meniscectomy for  a medial meniscus tear.  See the image below for an illustration of an ACL tear.

When I asked the patient how his injury occurred he replied, “I tore my ACL doing a plyometric workout with the personal trainer at my work.”  Ouch!  Naturally I wanted to know more.  So, I pressed him for more information – things like:

• What kind of plyometrics
• How many
• Were they at the beginning or end of the session
• How long had you been doing them

Let me tell you that a lot of therapists would not have asked these questions.  They would have moved on in the evaluation, dismissing this trainer as an incompetent fitness pro in their mind.  The fact of the matter is that bad things do happen at times even when we are doping everything just right so I like to give people the benefit of the doubt in most cases.

However, some of his answers led me to believe this particular trainer needed further education.  My client said the entire 30-40 minute workout was plyometrics. He was doing single leg multi-directional hops, but actually tore the ACL during a broad jump.  He mentioned he had only done a handful of the workouts before getting injured.  The kicker was when I asked him if anyone else in the class had been injured, and he remarked that another man recently tore his Achilles tendon.

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