Injury Prevention

The most common injuries associated with with team sports are hamstring strains and anterior cruciate ligament (ACL) injuries, accounting for between 8-27% of all injuries depending upon the sport (Hawkins et al., 2001; Gabbett and Domrow, 2005; Gabbe et al., 2006). In some sports such as rugby and NFL, these may not be preventable due to the high number of tackles and collisions during play, but there can be preventative measures in place (through appropriate conditioning) to decrease the number of non-contact lower limb injuries seen in sports such as soccer where there is less contact between bodies.

Common Causes of Non-Contact ACL & Hamstring Injuries:

Muscle Imbalance

The hamstring:quadricep ratio is commonly used to describe the muscle strength properties about the knee, assessed through isokinetic testing. Recent research has shown that the ratio of eccentric hamstring:concentric quadricep strength as a functional test and associated with detecting risk of musculoskeltal injury (Aagaard et al., 1998). A value of <0.7 is the recommended minimum level (Aagaard et al., 1998; Coombs and Garbutt, 2002), but the type of athlete must be taken into consideration when analysing results. For example, kicking athletes may have differences limb-to-limb, a right footed kicker’s left leg may be stronger (ECC) in his left leg, due to it producing force and stability, whereas the right leg will be the dominant velocity production leg (more CON).

Poor Neuromuscular Control
This can be broken down into several components such as the stretch-shorten cycle (SSC), mobility, stability, and proprioceptive awareness. Anatomical differences in pelvic structure and lower extremity alignment may account for differences in injury rates between males and females, but training the muscles that stabilise the knee may decrease the relative injury incidence in females. Many athletic movements, such as running, jumping, COD are inherently unstable and often unpredictable, requiring NM control to maintain stability and attain the desired body position to perform the required movement, at the right time, at the right speed. Dynamic knee valgus, landing from jumps with an extended knee, deceleration with an extended knee + valgus collapse, poor hip and trunk control (lateral & excessive anterior tilt) are commonly seen during landing, deceleration, and COD tasks. Athletes require the appropriate motor programming (technique) to perform these tasks safely and coordinated in order for the muscles to function most effectively, with minimal joint loading.

High Velocity Eccentric Loading
There is a high incidence of injuries in rugby and soccer resulting from high speed running and during stretching movements carried out by extreme range of motion, resulting in high velocity eccentric loading. (Cameron et al., 2003; Hewett et al., 2005). The strain is most likely to occur during 2 stages of the running cycle; late forward swing and toe off (Stanton, 1989) as, at this stage, the hamstrings decelerate hip flexion and knee extension (Hoskins and Pollard, 2005) resulting in large eccentric loads (Comfort, 2011). The hamstrings must be conditioned through eccentric muscle actions such as Nordics and Razor Curls, not only RDL’s, which have shown to decrease the risk of hamstring injury, increase strength, and improve the Q:H ratio (Askling et al., 2003; Mjolsnes et al., 2004).

Prevention

Concentric Strengthening
There are plenty of exercises to concentrically strengthen the hamstrings, but two I’ve selected are probably the most common – RDL and good mornings. These lifts strengthen the hamstring across both hip and knee, with unilateral versions possible to perform, as seen below. In a recent post, the glute-ham raise/”nordic curl” showed highest concentric activity of the hamstrings, even though most people train it as an eccentric exercise.

RDL

Good Morning

Eccentric Strengthening
As mentioned above about the hamstring activity study, highest eccentric activation was actually seen in the RDL, not the glute-ham raise. Some common eccentric hamstring exercises are the razor curl and nordic hamstring curl. the razor curl has shown maximum activation of the hamstrings musculature to reach up to 220%, and nordics have shown to increase strength and improve muscle balance through gradual progressions in soccer players (Mjolsnes et al., 2004).

Razor Curl

Nordic Hamstring Curl

High Velocity Eccentric Training
Eccentrics can be gradually progressed to higher velocity eccentric exercises such as jump landings, plyometrics, and deceleration/change of direction drills. Drills can move from technique focus (stationary), to a linear/lateral/multi-directional component, and bilateral to unilateral once adequate technique and neuromuscular control is mastered. Jump landings will focus on the eccentric stretch component of the SSC, teaching athletes to accept loads in preparation to overcome and generate positive forces when progressing to more reactive/plyometric drills. When progressing to plyometrics the rate of stretch is more important than the magnitude, with the athlete looking to use the storage of elastic energy (having trained solely eccentric phase landing), and re-use that energy during the concentric phase – improving the efficiency of neuromuscular performance. This can be progressed even further to “sports specific” plyometrics in terms of closed-skill practice, open-skill practice, to open-skill random practice. See Training for ACL Prevention and Jump Video.

High velocity eccentric control is crucial to change of direction performance. Athletes need to move efficiently (base of support, low COM, neutral spine, control to minimise energy leaks), but also need the relative strength to cause the desired movement. If athletes aren’t strong enough to control their own bodyweight, then once the load is increased (in the weight room, or on the field by increasing approach speed for example), we are only getting closer and closer to messing them up, it is far better to do something slower and controlled and progressing. Here are some very simple drills to incorporate in your programmes, and notice how the technique has to adjust when the drills move from closed to open and more reactive with a partner, obviously it’s harder for the person who has to react.

Closed – usually cone-cone to focus on technique and give a visual target to work to

Mirror Drills – more reactive, adds increased cognitive aspect too

Integration
Increase frequency = increased control. With drills like these repetition really is the mother of learning. These exercises can be added to warm ups very easily, there is plenty of research out there as using these types of exercises during intervention programmes resulting in the below, more so than rehabilitation style training (swiss ball, bosu ball, airex pad, stability pad led programmes). The majority of these programmes take 1 hour during training, and time is limited with athletes, it is about the coach being creative and inventive in how they can get the biggest return using the most bang for your buck exercises given the circumstances, an example is the Herrington programme which takes no longer than 15 minutes and significantly decreased knee valgus and improved performance in basketball players in as little as 4 weeks.

  • Decreased knee valgus
  • Increased Q:H ratio
  • Increased jump height
  • Enhanced neuromuscular control
  • Reduced incidence of lower limb injuries

Here are a few research papers to look at:

CT

Teaching the Olympic Lifts

This will be the first post in a series aimed at showing examples of exercises targeted to improve technique and efficiency when teaching and performing the Olympic lifts (clean & jerk and snatch). There are many ways to teach the lifts, but most coaches adopt one of two methods: top down or ground up, with the use of partial movements (using boxes, power racks). Personally, I prefer to coach from the top down, as in the early stages of development I like to emphasise movements performed from the mid-thigh position, as it’s a more natural position for someone to feel accustomed to (same position as when jumping), but I’m just as happy stating from the ground as well, just my preference.

Start PositionClean Start

  • Bar over metatarsals with the feet hip – shoulder width apart
  • Pronated claw or hook grip slightly < than shoulder width
  • Hips higher than the knees
  • Shoulders in front of the bar
  • Braced thoracic area with normal lumbar curve
  • Shoulder blades retracted, chest elevated
  • Head neutral, eyes looking forward

Common mistakes:

  • Bar doesn’t start close to the body, therefore when start to pull the spine will lose it’s neutral position
  • Hips start too high, or too low, affecting the trunk angle and will affect the position going into the first pull

First Pull to Hang PositionHang

  • Shoulders remain in front of the bar
  • Bar path is upwards and backwards in a controlled manner
  • Arms remain straight
  • Weight towards the heel
  • Back to floor angle remains the same as start position

Common mistakes:

  • Speed is too fast – must be controlled
  • Bar doesn’t remain close to the body – these two points are important as poor trajectory and control in the first pull can affect force production during the second pull (where most force can be produced)
  • Back angle becomes more upright too early or rounded = poor transfer of forces
  • The lifter wants to be balanced with a strong relationship between the lifter and the bar & the base of support at the feet by keeping the knees back, weight on the heels, and shoulders over the bar
  • Support muscles such as spinal erectors, abdominals, and hamstrings play a big part in maintaining balance

Transition Phase
Start Mid-thigh

  • Knees flex and move under the bar
  • Bar continues to move upwards
  • Weight moves towards the mid foot
  • Shoulders move directly above the bar

Common mistakes:

  • Lack of knee flexion (affects the SSC aspect of the transition)
  • Weight still on the heels, so don’t achieve full triple extension
  • Lack of transition/double knee bend and therefore start the second pull too early (causing a reduction of force produced during the second pull) – this will cause less transfer over to dynamic activities

Mid-Thigh Position and Second Pull
End Mid-thigh

  • Bar has to be at mid-thigh
  • Knees and hips flexed
  • Shoulders directly above the bar
  • Hip, knees and ankles extend vigorously, with a powerful shoulder shrug
  • Weight acts through the centre of the foot
  • Bar remains close to the body and continues in an upward direction
  • Arms remain straight

Common mistakes:

  • Bar starts below mid-thigh (more of a hang position) – will probably start the second pull too early
  • Shoulders are behind the bar meaning the weight is towards the heel, this will affect the range of hip extension the body can go through
  • Don’t achieve full triple extension and fail to shrug – the bar won’t displace vertically as much and will affect the chance of performing the catch
  • Bar bounces off the thigh forcing the bar path in front of the body, this will affect the ability to catch the bar on the front shoulders and get the elbows up high
  • Arm bend and row the bar upwards rather than using the legs to generate speed – poor transfer of forces usually caused by not achieving the correct mid-thigh position

Catch Position
Catch Clean

  • At the end of the second pull, the elbows bend and rotate rapidly under the bar
  • Simultaneous triple flexion at the hip, knee and ankle
  • Feet usually jump out > than shoulder width
  • Bar caught across the front shoulders in front squat position with elbows high in an upright posture

Common mistakes:

  • Not dropping quick enough to catch in a full front squat – could be due to a poor second pull, not enough speed on the pull
  • Catching in a power clean position will produce reduced triple flexion, decreasing eccentric loading
  • Feet externally rotating too much, putting stress on the knee joint, but may allow people who have restricted hip and ankle mobility to actually get into the squat position to catch the bar.
  • Elbows not high – very common in males who have to use the wrists rather than the front shoulders.

Recovery:

  • As in the ascent of a squat
  • Continue to drive the elbows high
  • Maintenance of neutral spine

Just some thoughts on coaching points, and some common errors I see, hopefully in the next few weeks I’ll get to video different variations and go through some ways to correct errors identified above.

Here’s the finished product, Niall is a second year Undergraduate student at the University of Salford and performed an 80kg clean on Friday after only just over two months of learning the variations. You can find out more on his Twitter Athletic Fitness.

And in slow motion

Resistance Training Considerations

Training should replicate the coordinative, biomechanical, and bioenergetics demands of the sport, and whilst we can’t prepare for everything due to to unknown nature of sporting events, but if we see things repeatedly happen on the field during play, then we need to prepare as best we can for them.  I believe that strength training should be planned, but as a coach, I think we can use research, monitoring, our own experiences, and the athlete’s experiences to guess how the athletes will adapt to stress, this is something you can read more about in Stuart McMillan’s blog post ‘just a dumb coach‘.

Kinetic variables (e.g. RFD, power, SSC, impulse and reactive ability) , which I believe are trainable in the weight room through effective planning and programming, as opposed to kinematic variables (base of support, centre of mass), which I would classify as coachable as they relate to the motion of a body. This will be covered in more detail in another post.

Photo 17-12-2012 14 09 12Rate of Force Development is an important variable in sporting actions. We want strong, powerful athletes who can produce large forces and power outputs, but the rate at which this can be expressed is just as important. Most dynamic movements in sport occur <200ms and can be classed as:
Short response
Ground contact time (GCT) during maximal sprinting during field drills, e.g. absolute speed days, as GCT during acceleration will be slightly longer due to overcoming inertia. The body is unloaded and to run faster athletes must generate high vertical forces, generate vertical impulse faster, and this is built through maximal strength and power training in the weight room, with exercises  like squat variations, deadlift variations, Olympic lifts can increase force production, and jumps and hops performed in plyometric/movement sessions, with a vertical emphasis will work on short GCT, bridging the gap between the weight room and the actual event so to speak.
Depth jumps [depending on the drop height] – could be one of the most beneficial plyometric exercises, but I don’t see it being used as effectively as it could be. I think the reason is because the majority of athletes  aren’t able to utilise the storage of elastic energy as efficiently to absorb the landing forces, and re-utilise the energy for the concentric component. This is evident in weaker athletes where I believe the majority should perform more drop landings to work on eccentric control, rather than the concentric component such as squat jumps and countermovement/box jumps. When we progress into continuous jumps, hops, and bounds the landing/decelerating mechanics are very poor, and are therefore just reinforcing bad mechanics repetition after repetition. It is far more effective, and safe to focus on single landings/jumps on the spot, rather than trying to add a linear/horizontal component before adequate technique has been mastered on the spot. However, with the stronger athletes, you can increase the intensity of the drills by increasing the eccentric component by holding dumbbells for the drop, get them to drop the DB’s on landing, and therefore perform the concentric ‘unloaded’  Other examples include increasing the height of the drop, or decreasing the height of the drop but increase the height of the concentric jump attempt.
Mini hurdle jumps – these can be performed out on the field, especially bilateral, and can be classed as short response. These will work on short ground contact time, so there is little hip, knee and ankle flexion (rate of stretch is short and fast) so the system is more stiff, but won’t produce high forces due to the magnitude of stretch being so short enough that high forces can’t be produced). So this exercise might not be classed as a ‘power exercise’, as I believe there are more beneficial exercises to produce maximal power, but can be used in the warm up or on a lower intensity day depending whether the emphasis is vertical or horizontal.

Long response >200ms – greater angles at the hip, knee, and ankle
Acceleration
phase requires longer ground contact, and stride length increases from short to long, so the focus is on producing high horizontal force and impulse, this can be done through the resisted sprints/pulls we performed on the field, or broad jumps for example. See the following paper for more information Kawamori N, Nosaka K, and Newton RU. Relationships between ground reaction impulse and sprint acceleration performance in team sport athletes. J Strength Cond Res 27: 568-573, 2013
Single leg hops – I’ve seen a few coaches use this exercise, and it has a purpose as a long response plyometric, but also to increase eccentric loading. The GCT will be longer in duration as compared to a bi-lateral jump, and the higher/further the athlete jumps will determine landing forces to control.  I feel most athletes would benefit more from bounds (either double leg or opposite leg landing), than hops as most can’t control the landing efficiently, and again links to the mechanical efficiency of the drill being stable and safe when landing especially.
Jump squats – Big power based exercise, research has shown produces maximal power more than power clean and pulls from power position, squat jumps, and back squat in a variety of athletic populations. Peak power has been shown at 0% body weight, so effectively it’s a CMJ, land, reset, go again. I see lots of coaches using this exercise, but maybe it can be used  with a loaded bar at a certain % of 1-RM or an absolute value (40kg), so that the whole force-velocity curve is targeted depending on the phase of training. If it is used with additional load the landing mechanics must again be  correct as landing forces will increase significantly as compared to performing with no external resistance. If the additional load is going up too, the exercise can change from  jump squat to a squat jump (where squat down, pause 2-3s, then jump), this won’t result in as great a power output, but is still an effective exercise for concentric power, then it’s up to the coach to use different methods to incorporate the SSC into the training programme.
Photo 17-12-2012 14 07 07
Olympic lifts – the Olympic lifts can also be classed as long response plyometrics due to the activation of the SSC during the transition from the first pull (RDL position) to the second pull (Power position). Also the catch position involves eccentric loading through rapid triple flexion, and can be compared to performing a drop landing, as athletes must absorb the load on the bar, depending if catching in the power position, or in deep front/overhead squat). I like to see the athletes performing ALL variations (from the floor, hang, power position), usually peak power and peak force is seen during lifts from the power position, as you can lift more load and velocity is at its highest during the second pull (triple extension).
power6

Athletes must not only produce high forces, but be able to generate these in a short time. For example, an NFL athlete with a long training history, who trains for 4 weeks in the off season at a performance facility in the USA may not be able to significantly increase their force production through maximal strength training (due to their training history), but they may be able to increase their RFD, time to peak force, time to peak power, impulse, and force at 100ms for example (if the technology is there), moving their force-velocity curve up and to the right. It is not always the athlete that produces the highest force that wins, but rather the athlete who can utilise that force in a rapid manner during the dynamic movements (<200ms).
RFD differs from the weight room and the field. In the weight room, we load up the bar for maximal strength and power training, where you move a load with the intention to move it fast. During maximal strength training, the higher the load, the slower the speed, but as long as the intention is to move the load as quickly as possible, then RFD will improve. This will improve motor unit recruitment, neural firing frequency, neural activation, rate coding, and neuromuscular inhibition. Outside we use plyometrics to bridge the gap between the weight room and the field. So the athlete is now unloaded and using only body weight, where the velocity will be higher than in the weight room, but utilising the force interaction between the body and the ground. This is so that the force-velocity curve player is worked as a whole, because sporting actions require different qualities. If an NFL player requires maximal force and strength to hold off an opponent during play, they may also be required to accelerate 10-yds the next play, depending upon tactics and game situation, and these require 2 different strength/power qualities.

Impulse has also shown to be an important kinetic variable and can be calculated as change in momentum, or force x time. Greater impulse will be generated during the limited time and distance in which force is applied. Recent research by Rob Newton at Edith Cowan University in Australia has shown impulse to be a key factor in horizontal force production during acceleration in team sport athletes (see paper reference early in the post). Examples of exercises used to increase impulse could be sled pushes and resisted acceleration drills, where athletes have to produce more force during the first 10-yds, to set up good transition and absolute speed mechanics if the sport requires sprinting over these distances, most team field sport is between 10-20m.

The stretch shortening cycle (SSC) utilises the elastic properties of the muscle-tendon unit, during many sporting activities such as running, jumping and change of direction. This involves a rapid and forcibly lengthened pre-stretch of a muscle, followed by an immediate shortening in a reactive manner. SSC actions exploit the stretch reflex of the muscle-tendon unit, and it is important to decrease the “coupling time”, or the time from the end of the eccentric contraction, to the onset of the concentric contraction. Training the SSC can include plyometric methods (CMJ, depth jumps, hops, bounds, med ball throws), and heavy and ballistic resistance exercises (jump squats, and Olympic lifts), depending on the goals of the session, and/or phase of training. Med ball throws, and plyometrics are good power exercises due to the body working multi-planar, with proximal to distal sequencing and the action is explosive throughout the whole movement, so the load/implement is accelerated throughout a full range of motion, whereas in typical resistance training exercises (power cleans, squats), the load is accelerated, but then decelerates towards the end range of the movement (think the last 40%).

Resistance Training Part I & Part 2 (Plisk)