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Eccentric strength and change of direction speed
Agility is a multifaceted physical quality requiring both physical and cognitive qualities. Typically sports require cognitive input to respond to an opponent or other stimuli (AFL, rugby, soccer, tennis, etc.), whilst some sports simply require change of direction ability (such as a batsman turning to go for a 2nd run in cricket). Looking at the factors that contribute to agility (figure. 1), we can see that change of direction speed (C.O.D.S) encompasses the physical aspects, whilst the cognitive and perceptual factors affect how well we can utilise the physical qualities within chaotic sporting situations.
Stretch shortening cycle
A sharp change of direction utilises the stretch-shortening cycle (SSC). This is when we have an eccentric muscle action (deceleration/muscle lengthening) which stores elastic energy, followed by an amortisation phase (isometric) and finally a concentric muscle action (acceleration). The less time we spend in the SSC, the more we can utilise the elastic energy stored within the eccentric phase. High levels of eccentric strength assist in our force absorbing capabilities allowing athletes to decelerate at a faster rate which has a follow on effect to the subsequent acceleration (Chaabene, 2018) (2). This lays the foundation for the theory that incorporating eccentric focussed training methods into a strength and conditioning program can increase an athletes C.O.D.S.
Comparing the effect of contraction types
Exercises that accentuate the eccentric loading on muscles and tendons have been shown to improve SSC performance (Elmer et al., 2012) (3) and whilst studies comparing strength with C.O.D.S. have shown inconsistencies, we consistently see a strong correlation when studies focus on eccentric strength (2). In order to measure the effect of different types of strength on agility and C.O.D.S., Spiteri et al. (4) compared the correlation of eccentric, concentric, isometric and dynamic strength measures with performance in the 505
Practical implications
The research supports the inclusion of eccentric strength training to develop C.O.D.S., Chaabene et al. (2), modified the above diagram from Sheppard and Young to further describe the types of strength contributing to change of direction speed. This model (figure. 2) supports the use of dynamic balance, concentric strength and power, reactive strength and eccentric strength as part of a well-rounded program.
There are many methods a coach may use to emphasise eccentric loading:
2:1 method – lift with 2 limbs, lower on 1. This method can be used to overload the single limb as the weight is twice as heavy on the way down
Supramaximal method: With the assistance of a spotter, the athlete lifts 90-140% of their 1RM. Without
Submaximal method: Using a submaximal load (less than 100% 1RM), the athlete emphasises the eccentric portion of the lift by lowering the weight slowly, typically 8-12 seconds
When incorporating eccentrics into a performance program to improve C.O.D.S., coaches should look to incorporate movements focusing on the ankle, knee and hip joints as this is where the majority of deceleration occurs. Due to the increased muscle damage seen with eccentric training, coaches should be mindful of training volume and where eccentrics are placed within a training cycle.
References
1. Sheppard, J. M., & Young, W. B. (2006). Agility literature review: Classifications, training and testing. Journal of sports sciences, 24(9), 919-932.
2. Chaabene, H., Prieske, O., Negra, Y., & Granacher, U. (2018). Change of direction speed: Toward a strength training approach with accentuated eccentric muscle actions. Sports Medicine, 1-7.
3. Elmer, S., Hahn, S., McAllister, P., Leong, C., & Martin, J. (2012). Improvements in multi‐joint leg function following chronic eccentric exercise. Scandinavian journal of medicine & science in sports, 22(5), 653-661.
4. Spiteri, T., Nimphius, S., Hart, N. H., Specos, C., Sheppard, J. M., & Newton, R. U. (2014).