By Steven Scott Plisk
Steven Scott Plisk, MS, CSCS, is the Director of Sports Conditioning at Yale University.
Training & Conditioning, 10.6, September 2000, http://www.momentummedia.com/articles/tc/tc1006/agility.htm
We’ve all seen them: athletes with such great speed they make our jaws drop. Put these athletes in a dash and opponents are left in the dust. But, put that fast athlete on a football field and ask him to avoid a tackle and watch him get clobbered. How come?
Speed—the ability to achieve and maintain high running velocity—is one thing, and the sport literature is replete with sprint-training methods and techniques addressing this. Agility—the ability to explosively change speed and direction—is quite another thing, however, and is often more important than linear speed. The more advanced the athlete’s development, the more distinct these two entities become.
Most resources on the topic of agility offer plenty of drills and diagrams, but not much on underlying theory. Drills, however, must be individualized for each athlete’s needs. And, in order to design optimal drills for each athlete, it is essential to first understand the principles behind speed and agility. In this article, I discuss agility in terms of explosive movement mechanics, cover some of the other important attrib-utes that contribute to agility, and propose a classification scheme that can help when devising agility drills.
Agility development begins with a working knowledge of basic movement mechanics, especially with regard to the following three concepts: impulse production, reactive ability, and power. These concepts govern explosive force application, which results in speed of movement.
Impulse Production. Impulse is the change in momentum resulting from a force. The brief execution times of most athletic tasks require high rates of force development. Case in point: force is applied for 0.1 to 0.2 seconds during the ground support phase of running, whereas absolute maximum force production requires up to 0.6 to 0.8 seconds (such as during an act of brute strength).
Performance is usually determined by the ability to generate force quickly and thereby achieve a critical impulse output. Thus, a basic objective of agility training is to improve an athlete’s rate of force development, so that he or she is able to generate greater force in less time.
Reactive Ability. Many functional movements involve spring-like muscle-tendon actions and are ballistic in nature. The action begins with a preparatory countermovement where the involved muscles are rapidly and forcibly lengthened, or stretch loaded, then immediately shortened in a reactive or elastic manner. This eccentric-concentric coupling phenomenon (referred to as the stretch-shortening cycle, or SSC) is especially prevalent in sports involving running, jumping, and rapid changes in speed and direction. SSC actions exploit motoneural reflexes as well as intrinsic qualities of the muscle-tendon complex.
It is important to distinguish this concept of reactive ability from that of reaction time. The former is a characteristic of speed-strength that can be improved through reactive-explosive training. In contrast, the latter is a relatively untrainable quality that correlates poorly with movement action time or performance in many brief explosive events. For example, an elite sprinter’s auditory reaction time typically ranges from 0.12 to 0.18 seconds, but is not significantly related to the total time it takes to actually cover 100 meters. Other factors such as acceleration, speed-endurance, and, to a lesser extent, maximum speed are more closely associated with overall sprint times. Reaction time is, however, an important determinant of performance in quick-timing tasks (e.g., a batter hitting a baseball) and defensive stimulus-response actions (e.g., a goaltender making a save).
Power. Speed is often incorrectly thought to be independent from or incompatible with strength, when in fact there is a direct cause-and-effect relationship between the two. As discussed, agility involves accelerative as well as decelerative speed-strength—the ability to apply force rapidly during both concentric and eccentric actions. The peak levels of force and power absorbed by the tissues while actively lengthening can be much greater (up to 40%) than those produced while shortening. If not adequately addressed in training, this can be the mechanism of noncontact injury, technical inefficiency, or outright nonathleticism.
Thus, in addition to improving concentric power production capability, the demands of SSC movements dictate two other important training objectives:
• to develop the eccentric strength needed to tolerate extreme power absorption while explosively braking during the initial lengthening action; and
• to develop the reactive strength needed to rapidly recoil into the subsequent shortening action.
Breaking It Down
In terms of motor control and learning, agility is a synthesis of an athlete’s “coordinative abilities,” which include the following:
• balance: static and dynamic equilibrium
• differentiation: accurate, economical adjustment of body movements and mechanics
• orientation: spatial and temporal control of body movements
• reactiveness: quick, well-directed response to stimuli
• rhythm: observation and implementation of dynamic motion pattern, timing, and variation
• adaptive ability: modification of action sequence upon observing or anticipating new or changing conditions and situations
• combinatory ability: coordination of body movements into a given action.
These abilities are the elements of specific technical skills, which, in turn, are simply solutions to particular motor tasks. They should be considered prerequisites for achieving one’s athletic potential. While all training must be approached with respect to specific tasks, some general guidelines can be recommended for training agility on the basis of these coordinative abilities:
1. Exercises should be specialized, individualized, and task-specific (see “Dynamic Correspon-dence,” below).
2. Coordinative abilities interact, to varying degrees, when performing different motor tasks, and, while they cannot be isolated, training activities can be selected according to their dominant requirements.
3. Optimal arousal, focused attention, and motivation are required for tasks to be learned correctly and executed precisely.
4. Tasks should be aimed at integrating information processes; motor program acquisition, stabilization, and automation; and movement behavior evaluation.
5. Learning and training effects are augmented by progressive application of novel tasks; distribution, randomization, and variation of practice; and extrinsic feedback that is informative, motivational, and reinforcing.
A single principle guides all training programs: Training tasks should be selected and prioritized according to their dynamic correspondence with the demands of the activity. This concept is commonly referred to as task specificity or transfer of training effect, but is sometimes simplistically interpreted to mean “skill simulation.” What it really means is that the basic biomechanics—but not necessarily outward appearance—of the exercises should be specific to those occurring in competition. The rate and time of peak force production (impulse) and dynamics of effort (power) are especially important criteria in explosive athletic movements. Other practical considerations include amplitude and direction of movement, accentuated region of force application, and regime of muscular work (SSC versus pure concentric or eccentric).
This guiding principle should be used to gauge the usefulness of any training exercise, including those performed in the weight room. In fact, the reason that movements like Olympic-style lifts, plyometrics, and medicine-ball drills are so effective is that there’s no way to perform them without high power production, rapid force application, and acceleration—which is precisely why they dynamically correspond with so many athletic activities and deserve high priority in training.
Also keep in mind that inherently impulsive movements are not the only way to develop speed-strength. The “brief maximal efforts” and “submaximal accelerative efforts” methods can be applied to basic strength-training exercises (such as the squat) as a complement to reactive-ballistic actions. These methods improve an athlete’s rate of force development and his or her ability to accelerate heavy loads, including the athlete’s own body mass.
Given that most student-athletes’ developmental needs are fairly basic, a rule of thumb is to balance your emphasis by drawing from each of these training methods. In my experience, a general increase in power output is usually required, and there is such a range of abilities to shore up—and so much intermediate ground to cover—that training tactics don’t need to be too advanced or specialized. In any case, disregard what the exercises or training methods are called, and instead think in terms of what they do and how to complement or contrast them with each other. For the best results, make use of all available tactics, focus on training effect rather than strength demonstration, and do some strategic planning to most effectively mix your training components to exploit their cumulative and interactive effects.
The exercises and their progression must also be designed with the criterion of requisite ability in mind. Similar to the guidelines underlying plyometric training, the athlete must master one level before moving onto the next. Perhaps most importantly, the capability to decelerate from a given velocity is a prerequisite to changing directions—just as the athlete must be able to land safely and efficiently from a given drop height before attempting depth/rebound jumps from it. An example of how to progressively develop and evaluate this capability is as follows:
• The athlete is instructed to achieve second gear (1/2 speed) upon hearing a first whistle, and to decelerate and stop within three steps upon hearing a second whistle.
• Once the athlete can satisfactorily execute this drill, a five-step braking action from third gear (3/4 speed) can be introduced.
• Finally, a seven-step braking action from fourth gear (full speed) can be implemented, if appropriate.
A similar approach can also be used in backward and lateral movements. While the choice of velocities and braking distances is somewhat arbitrary, it is imperative to establish an athlete’s decelerative ability at different speeds before attempting to explosively redirect.
Three general schemes for classifying motor behavior can be applied to agility: general/special, closed/open, and continuous/discrete/serial. These schemes should not be considered mutually exclusive, and in fact all of them are useful when evaluating performance and selecting or prioritizing training methods.
General vs. Special. This concept is based on the motor learning principle of practice specificity (analogous to the dynamic correspondence principle mentioned previously). General drills are aimed at developing one or more of the athlete’s basic coordinative abilities, whereas special drills unify them in a skill-specific manner. In addition to modeling training drills on coordinative and biomechanical demands of competition, other practical considerations include the type, number, and combination of horizontal (backward, forward, lateral), vertical (falling, jumping, tumbling), and two-point vs. four-point (bipedal vs. quadrupedal) movement patterns.
Closed vs. Open. This does not refer to closed-chain vs. open-chain exercises, but rather to the perceptual attributes of the tasks. Closed skills are those with programmed assignments or predictable environments, where the training objective is to optimize motor patterns and achieve consistent, stable performances. Examples include tasks such as the “pro-agility drill” or “T-drill.” Open skills are those with nonprogrammed assignments or unpredictable environments, where the training objective is to rapidly respond and adapt to new or unforeseen situations. Examples include tasks with no predetermined structure where movements cannot be effectively preplanned, such as open-field dodging in team games. Some tasks are performed in semi-predictable circumstances (the assignment or environment is variable, but can be anticipated with experience and practice), and may be classified at an intermediate point on the continuum.
Continuous vs. Dis-crete vs. Serial. Finally, agility tasks can be classified according to their continuous, discrete, or serial qualities. Continuous tasks have no identifiable start or finish, with activity beginning and ending arbitrarily. They are usually performed at low or intermediate speeds due to their ongoing, cyclical nature. From a motor control standpoint, premovement planning tends to be limited, and performance is heavily influenced by feedback and error detection/correction.
In contrast, discrete tasks have a definite start and finish. Their brief, acyclical nature often—but not always—allows them to be performed at high speeds, and motor programs tend to play a more dominant role.
Serial tasks comprise discrete movements performed in sequence, with the overall outcome determined by successful execution of each subtask in order. Most athletic skills are serial in nature, whereas strict examples of the former two are rare (for example, “continuous cyclic” events such as a marathon, while prolonged, usually have a clearly defined beginning and end; “discrete acyclic” activities such as a 100 m sprint, although brief, often consist of multiple subtasks in series).
When performing the types of open skills and unpredictable movements occurring in many sports, there are a few basic, technical considerations to keep in mind. Since running is a common means of locomotion, an understanding of its basic mechanics—especially the sprint-drive technique—combined with practical experience allows some useful guidelines to be proposed. (The sprint drive is a technique addressing starting/acceleration push-off action during the first 20 to 30 m. Emphasis is placed on horizontal thrust with low body position, a piked trunk, powerful arm action, full-range leg driving action, and exaggerated knee lift.) Creativity and imagination are the only limits to how they might be adapted to actual agility drills.
Movement variations occurring in competition involve both simply sprinting straight ahead and a wide variety of transitions, turns, and redirection maneuvers. Furthermore, in comparison with linear sprinting, dynamic agility involves greater emphasis on deceleration, as well as reactively coupling it with subsequent acceleration in tasks with a SSC character. Finally, it must be kept in mind that changes in direction and speed can be executed at a variety of velocities. Agility should, therefore, be viewed in a larger context than simple stop-and-go types of tasks.
Visual Focus. The role of visual focus while sprinting has important implications for agility tasks. In general, the athlete’s head should be in a neutral position with eyes focused directly ahead regardless of movement direction. When running forward or backward, the athlete should focus on the point he or she is moving toward or away from; whereas peripheral vision can be used during lateral movements. Exceptions to this guideline can be made when the athlete must focus on a projectile, teammate, opponent, or other visual target, or for tactical reasons, such as using the eyes for deception when “looking off” an opponent.
Furthermore, directional changes (such as cutting left or right) and transitions (such as a turn-and-run maneuver from a backpedal into a forward sprint in the same direction) should be initiated by getting the head around quickly and finding a new point of focus. Examples of coaching points that reinforce this are to “open up from the top down” and “let the hips and shoulders follow the eyes.” Errors may occur when such actions are initiated by turning the shoulders or hips first and the eyes and head afterward, which can result in rounding off a turn or weaving outside of a desired movement path, with subsequent loss of time and efficiency.
Arm Action. The role of arm action during the sprint start and acceleration has fundamental importance in agility tasks. The athlete must rapidly accelerate into a new movement pattern when redirecting or performing transitions and turns. As is the case when driving out of the sprint start, powerful arm action should be used to facilitate push-off and knee lift, and, in turn, reacquire high stride rate and length. Examples of coaching points that reinforce this are to “punch off the line/out of the corner” (such as when executing the transition from a backpedal into a forward sprint in the opposite direction, or vice-versa) and “punch through the turn” (such as during the turn-and-run maneuver mentioned above). Inadequate or improper arm action may likewise result in a loss of speed and efficiency.
Agility is the essence of athleticism for many sports. It can be thought of as a synthesis of explosive strength, coordination, and technical skill. Each of these elements is trainable, and they must be trained collectively. While natural ability will always play its part in making one athlete more agile than another, properly designed drills can assist in closing the agility gap.