Change of direction (COD) and agility are much debated topics among strength and conditioning professionals both in academia and the applied setting. Agility is defined as ‘a rapid whole body movement with change of velocity or direction in response to a stimulus’ (15) while COD is a closed skill, with pre- determined planned movements (17). Much debate exists over the most effective way to train agility as the task involves both physical and conceptual components (18). While the nature of agility means that athletes must be masterful at both a change of direction movement as well as a perceptual decision making ability the purpose of this article is to investigate how best to train the physical aspects of COD ability from a strength and movement stand point and in particular the benefits of eccentric training.

Speed training in team sports is undergoing a paradigm shift by which, the emphasis is moving away from traditional straight line acceleration and top speed drills and starting to include more change of directional drills (17). Research indicates that the ability to change direction quickly and performance in agility tests are independent skills and as such training should be specific to the given task. Studies indicate that elite athletes have demonstrated superior ability over sub elite athletes in agility tasks however, there were no difference between elite and sub elite athletes in COD tests (8; 10; 4). This goes some way to supporting the definition that agility is heavily dependent on perceptual abilities, however, improving COD kinematics may go some way towards improving overall agility (14).

Another researched topic in the ongoing pursuit of improving COD performance is the effects of strength training. If the definition for agility is broken down then it becomes apparent that a change in velocity is one of the key components, this also holds true for COD tasks as the plant leg (PL) makes contact with the ground and results in a rapid deceleration (6). For example, when an athlete demonstrates a cutting action (side- step) to the right, the athlete will plant the left leg to decelerate and propel or push themselves onto the right leg or push off leg (POL) to accelerate in this new direction (6). This rapid deceleration is dependent on high levels of strength in order to cope with the high eccentric forces acting on the PL (6). Not only does the athlete need to demonstrate an ability to cope with the eccentric braking forces, they also need to demonstrate efficient stretch shortening cycle (SSC) as they decelerate and then quickly accelerate again onto the POL (6). Decelerating is in effect a landing task, the importance of strength training in COD ability is highlighted by the fact that low levels of strength result in poor landing mechanics (11). McCurdy et al. (2012) suggests that during landing tasks low strength levels results in decreased knee and hip flexion as well as increased knee valgus which are also patterns associated with anterior cruciate ligament (ACL) injuries. Alongside this, an upright landing posture associated with decreased knee and hip flexion results in increased ground reaction forces (GRF), which will result in increased demand placed on the PL in a cutting task (1). This suggests that not only can COD ability be improved by adequate strength training but improved efficiency and safer landing as well as COD mechanics are also supported (11).

As previously stated, improving SSC efficiency is important when aiming to train and improve COD performance. Strength training has been shown to have positive effects on tendon and connective tissue which are essential components in the SSC (3). Tendon stiffness has positive effects on the series elastic component involved in the SSC and therefore plays a role in improving rate of force development (RFD) (12). Increasing RFD may result in a decrease in ground contact time (GCT) during cutting tasks and therefore improve the time taken to change direction. While these generic adaptations to strength training are important in COD tasks, recent research has tended to focus on eccentric training when investigating improvements in COD tasks (2; 7; 6).

Kristianslund and Krosshaug, demonstrated that eccentric forces acting on the hamstrings and the horizontal and transverse forces acting on the knee may result in the knee collapsing into a dangerous valgus position. Therefore, programme design should focus on how best to ensure athletes adapt in order to cope with the eccentric forces as well as the need to produce force in a horizontal and vertical direction when performing a COD task. While eccentric training also involves concentric actions the eccentric portion of the lift is overloaded more than the concentric and so more emphasis is placed on the decelerating of weight.  Spiteri et al. (16) found that faster athletes display shorter braking, propulsive and GCT than slower athletes, again supporting the theory that the ability to decelerate quickly is an important factor for COD performance. Furthermore, the sharper the angle the athlete is changing direction in the greater the braking requirements (2). This further supports the need to incorporate eccentric training into an athletes training programme in order to prepare them for the forces experienced during COD tasks. De Hoyo et al. (2) state that eccentric training reduces GCT as well as increasing vertical ground reaction forces (VGRF), which may again suggest that eccentric training is beneficial in COD performance. These trainable physical qualities may ensure that COD technique is as efficient from a neurological and morphological point of view as possible, by enabling the athlete to negotiate large forces at high speeds in a safe manner (7).

Technical coaching alongside strength training may result in increased efficiency in COD tasks which may result in improved agility following specific agility based training (14). The benefits of strength training are well researched from a physical needs approach to COD tasks, it is important for practitioners to understand how strength can assist the coaching of COD in a way that goes beyond kinematic analysis. Contact times of the PL and POL as well as the time to decelerate and re- accelerate are all key performance indicators (KPI’s) of COD performance. The above review highlights how strength training and in particular eccentric training has the potential to improve all of these KPI’s and it is the role of the strength and conditioning coach to programme it in a logical and progressive way. Keiner, Sander, Wirth & Schmidtbleicher (9) conducted a study in which 112 elite youth soccer athletes were selected for a 2 year periodized strength training programme where correlations between 1 repetition maximum (1RM) and COD performance were investigated. The athletes were divided into two groups with one group performing strength training in addition to their regular soccer training (STG) with the control group only performing soccer training (CG). Furthermore, the COD performance of 34 professional Soccer players were measured as a standard level for high COD performance. The STG group showed significantly faster COD times than the CG over a 2- year period as well as up to 10% better speed times over a 10- meter distance. This study highlights the practicality of strength training and how it compares to purely sport specific training with respect to improving COD performance.

From the above review the benefits for strength training include reduced GCT, increased GRF and the ability decelerate at higher velocities with improved postures which seem to result in an improved COD ability. Strength training offers both neural and morphological adaptations which appear to assist in COD tasks, appropriate loading strategies over an extensive period of time offer benefits not observed by non- strength training groups.

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