Introduction: Agility Is Not Just Quick Feet

When discussing agility, the temptation is always the same: to think that everything depends on foot quickness, explosive strength, or the ability to push harder.

In reality, in open-skill sports, elite agility is a much more complex quality. An athlete must accelerate, brake, absorb high forces, control their body in space, react to external stimuli, and re-accelerate in the new direction in the shortest possible time.

For this reason, agility cannot be reduced to a sequence of exercises involving cones, agility ladders, or footwork drills. It is the result of the integration of strength, coordination, motor control, perceptual-cognitive ability, and biomechanics.

The true competitive advantage does not stem solely from force production, but from the ability to manage energy and momentum: absorbing them, dissipating them when necessary, redirecting them, and transforming them into useful movement.

This is where biomechanics becomes fundamental.

Training agility means understanding at least two dimensions of movement:

• the vertical component, linked to the stretch-shortening cycle (SSC) and elastic energy restitution;
• the horizontal component, linked to braking, deceleration, and change of direction.

The Stretch-Shortening Cycle: A Spring, But Not a Passive One

The stretch-shortening cycle, or SSC, is one of the most important mechanisms in athletic performance.

It occurs when an active eccentric contraction—where the muscle lengthens while producing tension—is rapidly followed by a concentric contraction, where the muscle shortens to produce movement.

A simple example is the countermovement before a jump. Before jumping upward, the athlete drops down quickly, loading the musculo-tendon system, and then utilizes that preparatory phase to produce a more effective push.

It is often said that the body works “like a spring.” While the image is useful, it needs clarification: the musculo-tendon system is not a passive spring. It is an active-passive system in which elastic energy, eccentric muscle work, neuromuscular coordination, and reflex contributions combine to achieve the final performance.

Therefore, the eccentric phase is not a simple stretch. It is an active, controlled phase in which the athlete must know how to absorb force while maintaining an efficient structure. The transition, or amortization phase, must be rapid enough to avoid excessive energy dissipation. The final concentric phase returns part of the stored energy and adds the force actively produced by the neuromuscular system.

The key point is that being strong is not enough. You must be able to apply force within the correct timeframe.

If the transition between the eccentric and concentric phases is too slow, a portion of the energy is dissipated. If, on the other hand, the athlete is able to maintain short ground contact times, good joint control, and adequate functional stiffness, the system becomes far more efficient.

Tendons, Stiffness, and Elasticity: Why Being More “Compliant” Isn’t Always Better

One of the most nuanced topics in the biomechanics of the SSC concerns the role of the tendons.

In common language, one might think that a more “compliant” structure is always more effective because it allows for a greater pre-stretch. In reality, this concept must be treated with caution.

In rapid actions, especially when ground contact times are short, good tendon stiffness is generally a positive factor. An overly compliant tendon can increase energy dissipation and reduce the ability to rapidly transfer force to the ground.

This does not mean the system must be rigid in an absolute sense. The more correct concept is that of controlled elasticity: the musculo-tendon system must deform just enough to store energy, but it must also be stiff enough to return it quickly and effectively.

Performance in the SSC, therefore, depends on a balance: not pure stiffness, not pure compliance, but the capacity for reversible elastic deformation, coordinated with muscle action and the timing of the athletic movement.

In a countermovement jump, this balance allows for better utilization of the pre-load. In a change of direction, the problem becomes even more complex, because the force must not only be returned upwards but often must be reoriented horizontally.

The difference between an athlete who is simply strong and one who is truly agile lies right here: in the ability to orient force.

Changing Direction Is a Physics Problem, Not Just a Muscular One

Every athlete in motion possesses momentum. Momentum is expressed by the formula:

p = m × v

where m is the athlete’s mass and v is the velocity.

This value is not just “how much movement” the athlete possesses: it is a vector. This means it has a magnitude, but also a direction. In a change of direction, the direction is decisive.

When an athlete brakes or turns, they must change their momentum. To do this, they must produce an impulse, which is a force applied over a certain time interval:

F × Δt = Δp

The greater the required change in momentum, the greater the necessary impulse.

Here, another quantity also comes into play: kinetic energy, which is expressed as:

KE = ½mv²

The distinction is important. Momentum grows linearly with velocity. Kinetic energy, however, grows with the square of the velocity. This means that increasing the entry speed makes the braking task much more demanding.

A heavier and faster athlete doesn’t just have to “push harder.” They must also brake, dissipate, and redirect greater forces, often in very short periods.

For this reason, deceleration is a fundamental athletic quality.

Deceleration: The Often-Overlooked Side of Performance

A fast athlete is not automatically an agile athlete.

The higher the entry speed into a change of direction, the greater the momentum that needs to be changed and the more kinetic energy there is to manage. Consequently, the athlete must be able to apply high braking forces, correctly oriented and distributed over timeframes compatible with the athletic movement.

This is not a true physical paradox, but a direct mechanical consequence: to change direction quickly, you first need to know how to lose speed in the right way.

This is particularly evident in 180° changes of direction, where the athlete must drastically reduce or cancel out their velocity in the initial direction before re-accelerating in the opposite one.

Concentric force is needed to re-accelerate. But even before that, a great eccentric capacity is required to brake.

In the biomechanics of deceleration, it is useful to distinguish between different components of the ground reaction force. The antero-posterior component primarily contributes to braking and subsequent re-acceleration. The medio-lateral component, on the other hand, becomes central in lateral cuts and changes of trajectory. In an effective change of direction, the athlete must be able to modulate both: braking in the direction they are coming from and producing force in the direction they want to go.

Another important element is the ground contact time. Shorter contact times can lead to faster performance, but they also require the ability to express high forces in very short time windows. This is where part of the trade-off between performance and safety arises: the faster and more aggressive the movement, the greater the mechanical demands on muscles, tendons, and joints.

This is why athletic preparation should not be limited to sprints, jumps, and acceleration work. It must also include specific drills for deceleration: progressive braking, controlled landings, eccentric work, inertial overload exercises, changes of direction at different angles, and progressions that gradually increase entry speed.

In other words: the athlete must learn to brake hard, but without losing control.

The Role of the PFC: The Penultimate Foot Contact Prepares the Change of Direction

In a change of direction, attention is often focused on the final foot plant, the foot that “plants” on the ground to brake and push off. However, the phase immediately preceding it is just as important.

The PFC, or penultimate foot contact, is a key phase because it prepares the braking action, helps to lower the center of mass, and allows for better load distribution before the final plant.

An athlete who arrives too high, too long, or too fast on the final plant will be forced to manage a huge amount of force in a very short time. Conversely, an effective PFC allows the deceleration to begin before the final plant, making the change of direction smoother, faster, and potentially safer.

From a practical standpoint, this means one should not only observe “the foot that changes direction” but also the preceding step. Often, the quality of the cut is decided before the final plant.

Training the PFC means teaching the athlete to prepare their body: lowering the center of mass, shortening or modulating the stride, orienting the trunk, and creating the conditions to produce effective horizontal force.

Why the Stopwatch Can Be Deceiving

Many traditional agility tests are based solely on the final time. The problem is that the stopwatch measures the result, but it doesn’t explain how that result was achieved.

A lighter or slower athlete may achieve a good time not necessarily because they have superior mechanics, but because they have less momentum to change and less kinetic energy to manage.

Similarly, a very fast athlete may be penalized in a change of direction test if they enter the cut at high speed but lack sufficient braking ability to control it.

For this reason, the concept of the Change of Direction Deficit, or COD deficit, has become widespread in the literature. The idea is simple: to separate, as much as possible, the linear sprint component from the actual ability to change direction. The total time of a test like the 505 can be influenced by linear speed; the COD deficit, however, attempts to better isolate the specific cost of the change of direction.

This does not mean the stopwatch is useless. It means that on its own, it is not enough.

Today, even a simple video camera or a smartphone can provide valuable information. Recording a test allows for the observation of:

• Which foot is used for the primary braking action;
• How the PFC (penultimate foot contact) is managed;
• The width of the base of support;
• The position of the trunk and head;
• The relationship between the center of mass and the supporting foot;
• The number of corrective steps before re-acceleration;
• The ground contact time;
• The actual direction of the force applied to the ground.

The time tells you “how much.” The video helps you understand “how.”

Gemini ha risposto

A frequent mistake is the so-called “reaching”: the athlete reaches for the line, cone, or marker by excessively overextending their outside leg.

At first glance, it may seem like an advantageous strategy because it allows the athlete to reach the target sooner. In reality, it often reduces braking efficiency.

The problem is not simply that the force “points upwards”. The problem is more complex: a foot plant too far from the body can increase ground contact time, worsen the ability to produce horizontal braking force, increase joint moments, and force the athlete to take corrective steps before re-accelerating.

In a change of direction, arriving at the line first does not necessarily mean exiting the line better.

True quality is seen in the ability to brake, rotate, and push off with the fewest possible adjustments.

60° and 90° Cuts: Plant-and-Cut, Faking, and Managing Risk

In 60° and 90° cuts, the dynamics are different compared to a 180° change of direction.

Here, the athlete does not have to completely reverse their direction, but rather modify their trajectory while maintaining a portion of their speed. In this case, the outside foot often plays a determining role in the plant-and-cut or side-step cut phase.

In some sports, the athlete can use a fake, a preparatory step, or a deceptive movement to shift the defender and create a new trajectory. The biomechanical principle is the creation of effective separation between the center of mass and the base of support, transforming entry speed into a horizontal projection in the new direction.

This strategy can be highly effective for performance, but it must be trained carefully.

A pronounced separation between the center of mass and the supporting foot, if associated with poor knee control, dynamic valgus, uncontrolled rotations, or poor trunk positioning, can increase knee loads and contribute to situations of higher risk for the anterior cruciate ligament (ACL).

This concept is known in recent literature as the performance-injury conflict or performance-injury trade-off: some mechanical strategies that favor the speed of a change of direction can, if left uncontrolled, also increase joint loads.

It is not enough to change direction faster. It must be done with sustainable mechanics.

The ideal technique is not the one that always minimizes every load, because in sports, the athlete must still produce force and win high-intensity situations. The goal is to create a balance: maximize performance without unnecessarily exposing the musculoskeletal system to avoidable stress.

How to Truly Train Agility

Training agility in a modern way means integrating physiology, physics, technique, and sports context.

Physiologically, the goal is to develop eccentric strength, functional stiffness, and the ability to utilize the stretch-shortening cycle within timeframes compatible with the sport.

Physically, it is necessary to understand that mass, velocity, momentum, and kinetic energy dictate every change of direction. A fast athlete must not only accelerate hard: they must also decelerate hard.

Technically, one must build effective mechanics: a lower center of mass when needed, well-oriented foot plants, a controlled trunk, a reduction of corrective steps, and the ability to produce horizontal braking and re-acceleration forces.

Practically, training must progress from generic exercises to targeted progressions.

Here are some operational guidelines:

1. Train Eccentric Strength

Incorporate exercises such as split squats, controlled lunges, step-downs, eccentric-emphasized squats, Nordic hamstrings, calf exercises, and inertial overload work. The goal is not just “producing force,” but learning how to absorb force.

1. Use Flywheel Training for Eccentric Overload

Exercises with an inertial flywheel, or flywheel training, can be particularly useful because they allow for an emphasis on the eccentric phase. Unlike many traditional exercises, the inertial system can generate a high braking demand during the return phase, stimulating the athlete’s ability to absorb and control force.
This makes it highly relevant for preparing for changes of direction, where the ability to decelerate rapidly is decisive.

1. Train Deceleration Progressively

Start with low-speed linear braking, then progressively increase entry speed, stopping distance, exit angle, and task complexity.
The progression must consider both the antero-posterior component (braking and re-acceleration) and the medio-lateral component (controlling lateral forces in cuts).

1. Use Vertical and Horizontal Plyometrics

Vertical jumps are useful, but changing direction also requires more specific exercises in the horizontal plane: bounding, broad jumps, lateral bounds, lateral hops, and controlled single-leg landings.
Horizontal and lateral plyometrics help the athlete better manage the forces that actually occur during changes of direction on the pitch.

1. Work on Different Angles

45°, 60°, 90°, and 180° changes of direction require different strategies. It makes no sense to train them all the same way.
A 60° cut requires a different management of speed compared to a 180° stop. The foot plants, the role of the PFC (penultimate foot contact), the direction of the force, and the ratio between braking and re-acceleration all change.

1. Evaluate Mechanics, Not Just Time

Use video to observe foot plants, the trunk, knee position, the center of mass-base of support relationship, the number of corrective steps, ground contact time, and the quality of the re-acceleration.
The technology can be simple: even a smartphone, if used wisely, can provide useful information. The difference is made by the coach’s ability to know what to look for.

1. Integrate Perception and Decision-making

Sport-specific agility is not just pre-planned change of direction. In a match, the athlete must react to the ball, opponents, teammates, and space.
For this reason, following the technical phase, reactive and open-skill drills are necessary. The goal is not just to change direction well, but to change direction well at the exact right moment.

1. Manage Joint Risk

In high-intensity cuts, especially lateral ones, it is essential to train knee control, trunk positioning, and foot plant quality.
Performance must not be separated from prevention. The coach must understand the performance-injury conflict and build progressions that increase the athlete’s capacity to tolerate high loads without losing mechanical quality.

From Speed to Movement Quality

Elite agility is not just about going fast.

It is about knowing how to lose speed when necessary, maintaining control, orienting the body, and producing a new acceleration in the correct direction.

A truly agile athlete is not the one who moves their feet the fastest in absolute terms, but the one who can transform force, energy, and momentum into useful movement with the least possible waste.

For this reason, athletic preparation must transcend the concept of simple “quickness work” and focus on what actually happens in the body: tendons storing and returning energy, muscles braking, foot plants orienting force, the center of mass separating from the base of support, and vectors determining the trajectory.

Biomechanics is not theory distant from the field. It is what allows us to understand why an athlete brakes better, changes direction more effectively, and pushes off with greater power.

Conclusion

The new paradigm of agility integrates physiology, physics, and practice.

• Physiology explains how the musculo-tendon system produces, absorbs, and returns energy.
• Physics explains why mass, velocity, momentum, and kinetic energy make deceleration so demanding.
• Biomechanics explains how the center of mass, base of support, PFC (penultimate foot contact), ground contact time, and the direction of ground reaction forces influence the quality of the change of direction.
• On-field practice transforms these principles into concrete exercises, progressions, and assessments.

Therefore, training agility means training the ability to control movement, not just to produce it.

For S&C coaches, personal trainers, and performance centers, this approach opens a more precise path: fewer generic tests, more technical observation; less reliance on the stopwatch as the sole judge, more movement analysis; fewer random drills, more progressions built on the real mechanics of the sport.

Because in a change of direction, as in any high-level athletic movement, it is not just the one who pushes the hardest who wins.

It is the one who knows how to use force better.

References

• Komi, P. V. (2000). Stretch-shortening cycle: a powerful model to study normal and fatigued muscle. Journal of Biomechanics, 33(10), 1197–1206. DOI: 10.1016/S0021-9290(00)00064-6.
• Kubo, K., Kanehisa, H., Kawakami, Y., & Fukunaga, T. (1999). Influence of elastic properties of tendon structures on jump performance in humans. Journal of Applied Physiology, 87(6), 2090–2096. DOI: 10.1152/jappl.1999.87.6.2090.
• Sheppard, J. M., & Young, W. B. (2006). Agility literature review: classifications, training and testing. Journal of Sports Sciences, 24(9), 919–932. DOI: 10.1080/02640410500457109.
• Nimphius, S., Callaghan, S. J., Bezodis, N. E., & Lockie, R. G. (2018). Change of direction and agility tests: challenging our current measures of performance. Strength and Conditioning Journal, 40(1), 26–38. DOI: 10.1519/SSC.0000000000000309.
• Dos’Santos, T., Thomas, C., Jones, P. A., & Comfort, P. (2017). Mechanical determinants of faster change of direction speed performance in male athletes. Journal of Strength and Conditioning Research, 31(3), 696–705.
• Dos’Santos, T., Thomas, C., Comfort, P., & Jones, P. A. (2018). The effect of angle and velocity on change of direction biomechanics: an angle-velocity trade-off. Sports Medicine, 48(10), 2235–2253.
• Dos’Santos, T., Thomas, C., Comfort, P., & Jones, P. A. (2019). Role of the penultimate foot contact during change of direction: implications on performance and risk of injury. Strength and Conditioning Journal, 41(1), 87–104.
• Dos’Santos, T., Thomas, C., McBurnie, A., Comfort, P., & Jones, P. A. (2021). Biomechanical determinants of performance and injury risk during cutting: a performance-injury conflict? Sports Medicine, 51(9), 1983–1998.
• McBurnie, A. J., Harper, D. J., Jones, P. A., & Dos’Santos, T. (2022). Deceleration training in team sports: another potential “vaccine” for sports-related injury? Sports Medicine, 52(1), 1–12. DOI: 10.1007/s40279-021-01583-x.
• Donelon, T. A., Dos’Santos, T., Pitchers, G., Brown, M., & Jones, P. A. (2020). Biomechanical determinants of knee joint loads associated with increased anterior cruciate ligament loading during cutting: a systematic review and technical framework. Sports Medicine – Open, 6, Article 53. DOI: 10.1186/s40798-020-00276-5.