How do strength gains transfer to agility?

Strength coaches working with team sports athletes need to know which strength training exercises are best for improving agility, by enhancing its physical component, which is known as “change of direction” ability.

Change of direction ability is tested by maneuvers that involve a rapid series of whole-body movements while changing velocity. These maneuvers involve first decelerating, then changing direction, and finally accelerating, while maintaining balance at all times.

Even so, trying to identify which exercises are best by asking experts is a very challenging task, as many of them disagree vigorously with one another.

Fortunately, by looking at the factors that determine change of direction ability, we can identify the muscles that are used, and the types of strength that they need to display. Then we can work backwards from there to identify the best exercises.


What factors determine change of direction ability?

Unlike with sprinting, there are no studies comparing the muscle sizes of athletes who are good at changing direction with athletes who are not as accomplished at this skill.

Even so, by looking at studies using a range of other methods, we can see that change of direction ability is determined primarily by the deceleration phase, and only secondarily by the acceleration phase.

Additionally, we can see that both phases involve coordinated hip and knee flexion/extension.

Thus, the hip extensors (adductor magnus, hamstrings, and gluteus maximus) and knee extensors (quadriceps) first produce force while lengthening (to decelerate), and then while shortening (to accelerate). However, the quadriceps are the most important muscles in the deceleration phase, while the hip extensors are key for the acceleration phase.

While the hip abductors and adductors do play a role in “steering” the body, the engine that really drives the movement is the coordinated hip and knee extension action, even when the change of direction is very steep, or even lateral.

Let’s take a look at what the knee and hip extensors do during changes of direction.


#1. Knee extensors

When changing direction, the knee extensor muscles (quadriceps) produce force while the foot is in contact with the ground. This force is produced in two distinct phases.

Firstly, the quadriceps exert high levels of force while lengthening.

As the athlete plants their foot to stop themselves traveling forwards, the kinetic energy of their body must be absorbed. This is achieved by allowing the knee to bend (flex), while exerting force with the quadriceps to keep this knee movement as small as possible. Thus, the quadriceps undergo an “eccentric” contraction, in which forces can be far higher than can be achieved in any normal strength training exercise, regardless of the weight used or the velocity.

Secondly, the quadriceps produce force at a high velocity while shortening.

As the athlete reaches the point of maximum knee flexion, which is usually when the knee is moderately flexed (such that the quadriceps are at a moderately-long muscle length), the quadriceps stop producing force while lengthening, and start exerting force as quickly as possible while shortening. This then accelerates the athlete in the new direction.

Strength gains are very specific to (1) the contraction type (lengthening or shortening), (2) the velocity, and (3) the joint angle used in training.

When we carry out normal strength training with free weights or machines, we lift and lower the same weight. Since the force we produce is equivalent to gravity plus inertia in the lifting (concentric) phase, and gravity less inertia in the lowering (eccentric) phase, we actually produce less force in the lowering phase than in the lifting phase. Also, since we are 25–30% stronger in the lowering phase than in the lifting phase, lifting a weight that is 85% of our one repetition-maximum (1RM) is only 65% of our eccentric 1RM, when we come to lower it.

This means that unless we overload the quadriceps and make them lower a weight that they cannot lift, we will never be able to train them sufficiently for the critical deceleration phase of changing direction. This is why flywheel squats, squats with weight releasers, reverse Nordic hamstring curls, and even flywheel knee extension exercises are *indispensable* for improving change of direction ability, even though some traditional coaches dislike the idea of using exercises that work the knee extensors as a single-joint, and which are not performed while standing upright.

When we train using high-velocity exercises, like jump squats, we improve the ability to produce force at high velocities to a much greater extent than after training with heavy loads, which require low velocities. These superior high-velocity strength gains occur for several reasons, including a large increase in motor unit firing rate in the first 50ms of a contraction, and an increase in the contractile ability of the muscle fibers, which allows them to shorten faster.

When we do quarter, half, parallel or full squats, we improve the ability to produce force most at the joint angle near to the bottom of the movement, wherever that may occur in the variation being used. This happens because that is where peak muscle force is produced, since that is where inertia and the leverage of the barbell on the joints are greatest. Thus, when training coordinated hip and knee extension with a squat movement, optimal strength gains will occur at the joint angle corresponding to the start of the lifting phase.

Overall, this means that we should train the knee extensors (quadriceps) for change of direction ability in two very different ways. Firstly, we need to expose the muscle to lowering weights that they cannot lift, in order to improve lowering (eccentric) strength, because this is what helps with the deceleration phase. And secondly, we need to improve the ability to produce force at high velocities and moderately-long muscle lengths, such as with jump squats and hex bar jumps, perhaps with a slightly larger range of motion than would normally be chosen. This is what helps with the acceleration phase.


#2. Hip extensors

When changing direction, the hip extensor muscles (adductor magnus, gluteus maximus, and hamstrings) similarly produce force while the foot is in contact with the ground.

Again, this force is produced in two distinct phases, a lengthening phase while the athlete decelerates, and a shortening phase while the athlete accelerates. The hip extensors firstly have to produce a high level of force to prevent the thigh from rising too high, and the torso from tipping too far forwards when the front foot is planted. Secondly, they need to extend the hip from a position where the hip is moderately flexed (and the muscles are at moderately-long lengths) as quickly possible once the acceleration phase begins.

Consequently, the same logic applies to the hip extensor muscles as for the knee extensors, although with the opposite priority, since the hip extensors are more important in the acceleration phase than in the deceleration phase.

Firstly, we need to improve the ability of the hip extensors produce force at high velocities and moderately-long muscle lengths, such as with jump squats and hex bar jumps, perhaps with a slightly larger range of motion than would normally be chosen. This is what helps with the acceleration phase .Secondly, the hip extensors need to be exposed to lowering weights that they cannot lift in order to improve lowering (eccentric) strength, such as by using flywheel squats, squats with weight releasers, and eccentric-only or eccentric-overload single-leg hip thrusts. This is what helps with the deceleration phase.

(Note: elongating the lowering phase by using a slower tempo is *not* the same as using a heavier weight).


What is the takeaway?

For improving change of direction ability, we want to train the knee extensors (quadriceps) and hip extensors (adductor magnus, gluteus maximus, and hamstrings) using lowering (eccentric) exercises with weights that are too heavy to lift. For the hip and knee extensors together, we can use flywheel squats or squats with weight releasers. For the knee extensors alone, we can use flywheel knee extensions or reverse Nordic curls. For the hip extensors alone, we can use eccentric-only or eccentric overload hip thrusts.

Additionally, we ideally want to do strength training exercises that work the hip and knee extensors using high-velocity exercises that load the muscles at moderately-long muscle lengths, like jump squats, hex bar jumps, and heavy kettlebell swings, perhaps with a slightly larger range of motion than would normally be chosen.

Finally, to enhance coordination, direction of force application, and the involvement of the “steering” muscles, we probably want to add exercises that involve similar movement patterns to change of direction maneuvers, such as lateral and diagonal lunges.