Reactivity is a component of fitness that we use daily, mostly without even realizing it. In the broadest sense, reactivity involves taking in sensory input from the outside world and producing an appropriate physical response. 

Beyond the obvious input we get through the five senses (touching, smelling, seeing, tasting and hearing), we use proprioception to continually monitor and adjust our position and motion. Proprioception, from the Latin proprius, meaning “one’s own” or “individual,” and capio/capere, which means to take or grasp, is the awareness of the position and movement of the body and is controlled by the hypothalamus in the brain.

Like all fitness components, reactivity is trainable. Repeated exposure to exercises or movements solidifies learning in such a way that the speed of the nervous system signals increases. The result is an enhanced ability to respond to a proprioceptive challenge as the body’s “processing speed” improves.

How to Train for Reactivity

Reactivity, with respect to balance training, can be challenged in two main ways. Proactive balance training is an anticipatory and self-initiated approach of performing strength and balance exercises to improve balance for the prevention of falls. Reactive balance training, on the other hand, is the practice of responding to unexpected perturbations that cause losses of balance.

Proactive balance training is typically more common due to its ease of use, lower perceived safety threat and greater acceptance by participants. However, falls generally occur due to inadequate reactive responses to external perturbations. This makes sense because reactive responses are often caused by unexpected stimuli or stimuli of miscalculated strength. Given its real-life application, interest in reactive balance training is growing and research suggests that it produces more effective, long-term results than proactive training. 

The workout and equipment presented below easily allows the simultaneous use of both proactive and reactive balance training. 

Movement-based Reactivity Training

Movement-based training provides a framework for ensuring the exercise programs you design translate to real-world movements. In life, we often slip on a wet floor, stumble or bump into a doorway—all of which require reactivity to maintain equilibrium and balance. Incorporating reactivity into your clients’ training programs may help them react better and faster to life’s stumbles and reduce the likelihood of a fall. In fact, a recent study showed that reactive balance training reduced by a frequency of 60% perturbation-induced falls (meaning, the study design called for the use of induced bumps, trips and slips in a controlled setting), indicating improved balance recovery from trips and slips.

Successful Failure

Your reactivity gets better when you lose equilibrium and then instantly regain it. The following workout challenges reactivity during movement-based resistance training using Aktiv Solutions’ Aqua Bag. It is a water-filled, inflatable tube with handles that works well in a variety of settings and training-session formats (e.g., one-on-one and boot camp−style workouts). After adding a desired amount of water (it holds up to 5.2 gallons), the rest of the bag is filled with air to create firmness. Completely filling the Aqua Bag provides 41.6 pounds of resistance but leaves the water little room to move. Thus, using maximum load decreases the reactivity. For the purposes of this workout, it is best to leave at least a little space for air in the tube and avoid filling it completely with water. Larger versions of the Aqua Bag, which are intended for use with two or more people, also are available. 

ACE IFT Model: Functional Movement and Resistance Training Overview

The following Aqua Bag workout was created using the ACE Integrated Fitness Training ® (ACE IFT®) Model as a guide. The ACE IFT Model provides a framework for movement-based training where we develop stability and mobility as appropriate in a specific area of the body, integrate it into a full-body movement , add external load, creating a stimulus for strength gains, and increasing movement speed to develop bodily control (final phase). Typically, reactivity training is discussed in the final phase of the ACE IFT model.

In this sample workout, the five foundational movements featured in the ACE IFT Model (listed below) are progressed by incorporating reactivity:

  1. Bend and lift: A bilateral hip or glute-dominant movement (e.g., squat and deadlift)
  2. Lunge: A unilateral or asymmetrical lower-body movement (e.g., single-leg squat, lunge)
  3. Push: A vertical or horizontal pushing movement, either bilateral or unilateral
  4. Pull: A vertical or horizontal pulling movement, either bilateral or unilateral
  5. Rotation: A limb, torso or whole-body axial rotation


Manipulating the water inside the Aqua Bag can be done in one of three ways: 

Calm = maintain stability by constantly adjusting the movement to maintain equilibrium as the water continuously shifts gently around inside the Aqua Bag

Churn = intentionally disrupt and move the water inside the using a slower, more controlled motion

Crash/Swirl/Slosh = intentionally disrupt and move the water using a faster, more rapid and violent motion

Each method is executed with circuits. The “Calm” circuit follows repetitions with no rest, while the other two use time-based sets for work:rest in seconds.

Workout Notes

  • Both the “Churn” and “Crash/Swirl/Slosh” circuit exercises employ the use of an initial proactive balance challenge followed by a reactive balance challenge. After completing the proactive motion, the water inside the bag continues to move around, thus creating the reactive challenge. 
  • The nearly continuous increased activation of the smaller muscle actions to maintain stability (in addition to the prime movers) generates a steadily accumulating and surprisingly high amount of internal heat in the body when performing this workout. 
  • In the accompanying videos, the bag is filled with two gallons (7.6 liters) of water weighing approximately 16 pounds (7.3 kg). This load was chosen to allow a lot of space for the water to move around, which emphasizes the reactivity of dealing with the water rather than on the absolute load.

The table below groups each circuit in a vertical column Perform each circuit as instructed before moving on to the next one. The correct handle to grip is given in parentheses after each exercise.  

ACE IFT Model Movement

“Calm” the Water
3x circuit following reps for each move

“Churn” the Water
2x circuit using 30:15 work:rest timing

“Crash/Swirl/Slosh” the Water
2x circuit using 30:15 work:rest timing

Bend and Lift


Squat (outside) 

– 12 reps

Waterfall Squat (outside)

Alternate sides 

Shuffle Squat (inside)

Alternate sides



Shoulder Press (inside)

 – 10 reps

Chest Press on Stability Ball (inside/outside)

Pendulum Lift (outside)

Alternate sides



Bent-over Row (inside, underhand) – 10 reps

Single-arm Row

Alternate arms each round

Pendulum Row (outside)

Alternate sides



Step-back Lunge (inside) 

– 6 reps each side, alternating

Coiling Lunge (inside) Alternate sides

Halo Side Lunge (outside)

Alternate sides



Supine Shift on Stability Ball (outside)

 – 6 reps each side, alternating

Supine Rotation (outside)

Battering Ram (outside)

Alternate sides

Specific Movement Notes

Step-back Lunge – Keep the wrists neutral and the forearms parallel to the floor and the Aqua Bag positioned so that it is not touching the torso.

Supine Shift – The objective is to keep the bag nearly horizontal to minimize the movement of the water inside. 

Chest Press – Keep the wrists neutral as you rotate the bag in the transverse plane while performing the motion.

Coiling Lunge – Intentionally laterally flex the spine toward the lead leg as you perform the lunge.

Supine Rotation – The range of motion for this exercise will be significantly affected by the amount of water in the bag; small increases in water quantity significantly increase the challenge.

Pendulum Row – The target for the inside hand is the center of the chest.


This workout features equipment that keeps the mind constantly engaged and focused while the body receives a unique muscular training challenge by requiring dynamic stability throughout each movement. Additionally, the use of proactive balance training and reactive balance training in sequence has the potential to further heighten focus and elevate the benefits of the workout.