The pool is a perfect place to perform progressive resistance exercise (PRE) or strength training during early rehab.

Why? Because it’s efficient to strength-train in the water. (For some strength-training exercises, click

Unlike land workouts, you can quickly transition from one movement to the next without switching weights or retying a knotted piece of band. Resistance comes from the act of pushing through water, so any resistance disappears as soon as the movement is halted.

Also, strength training in the pool is three-dimensional — you’re able to immediately create resistance along the X, Y or Z axis. Another plus: Most PRE in the pool is concentric, meaning delayed onset muscle soreness is less likely to occur.

It’s possible to perform PRE in water without specialized equipment. In contrast to the land, aquatic resistance does not come from attempts to overcome gravity or some external weight. Rather, in the pool, resistance comes from attempting to move rapidly through a thickened or viscous medium — that is, water.

Imagine moving your arm through a vat of molasses. The substance is sticky and thick, and it impedes your movement. Water performs the same function; it’s just slightly less viscous.

To create more resistance in the pool, you don’t need external equipment to increase your “load.” Instead, you can increase your drag by altering the speed of each movement or by increasing the lever arm of the moving part. In addition, it’s possible to make a simple movement “harder” by increasing the frontal surface area of the moving part or by decreasing how streamlined that body part is in the water.

Of course, there are dozens of types of special equipment that can take a PRE program even further in the pool. A simple pair of aquatic gloves will increase resistance and proprioceptive input.

Looking for an even harder workout? A resistance paddle or a resistance bell will dramatically boost resistance by increasing lever arm and frontal surface area, and by decreasing the streamlining of movement.

Keep in mind that a foam or air-filled flotation bell also will create resistance, but primarily in one direction: down toward the bottom of the pool. Most of the “work” of moving that bell through the water will occur when attempting to submerge it.

There are also dozens of variations of resistance equipment for the trunk and legs, such as fins, boots, shoes, noodles and kickboards.

You don’t need much extra space to perform PRE in your pool. Each participant typically requires a 5-by-5-foot area (minimum) to an 8-by-8-foot area (maximum). This allows each individual to take a lunge to the front, rear, left and right directions while maintaining his/her arms out to the side.

Most patients gravitate toward chest-deep water while performing resistance training in the pool. Thus, vessels with plenty of 3 1/2-foot to 4 1/2-foot depths are excellent for PRE.

Therapists should be careful to avoid the trap of providing all resistance training in a standing position. Sitting, plantar grade (weight-bearing on the arms), on all fours, kneeling, supine and prone also are excellent poses for developing strength training.

Temperature isn’t a limiting factor for most vigorous PRE programs. The more active the movements, the less temperature matters. Certainly, a pool with temperatures ranging from 88 degrees to 93 degrees Fahrenheit is adequate for most PRE.

Cooler pools —even those as cold as 80 degrees — are usable for short periods of training as long as the patient doesn’t have thermoregulatory issues.

There is no single“path” for learning aquatic progressive resistance exercise. Many therapists do find value in becoming certified aquatic fitness instructors. But the critical issue in PRE is simple for therapists to master: Resistance in water is created by drag, not gravity. Therefore, weights, Thera-band and other “gravity-based” methods of resistance training do not have a place in a pool-based PRE program.