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:
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).
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.
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).
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
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:
- Hilfiker (2007) et al., Drop Jumps Warm Up
- Hewett (1999) Neuromuscular Training on Incidence of Knee Injury
- Hewett 05 – Neuromuscular Control – ACL; Neuromuscular Training in Female Athletes
- Paterno (2004) Neuromuscular Training