Brian Schiff’s Blog
Injury Prevention, Sports Rehab & Performance Training Expert
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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:
- Preferred – athlete instructed to jump with a technique that allows for jumping as quickly and high as possible
- Flat foot
- 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
- 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
- FORE and preferred landings produced the best results for all mechanical power variables
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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