Neuromuscular Function During Therapeutic Knee Exercise Under Water and on Dry Land

Objectives: To compare muscle activity and resistive drag force during knee extension-flexion exercises while barefoot and while wearing a Hydro Boot (increased frontal area) both under water and on dry land.

Design: Participants performed the exercises while seated on an elevator chair under water.

Setting: A hydrotherapy pool.

Participants: Eighteen healthy persons (10 women, 8 men).

Interventions: Not applicable.

Main Outcome Measures: Isokinetic and isometric forces were measured with a dynamometer. The electromyographic activity of the quadriceps (vastus medialis, vastus lateralis) and hamstring muscles (biceps femoris) was recorded. The underwater drag for the range of motion was calculated by using the general fluid equation.

Results: The underwater electromyographic patterns showed an early decrease in the concentric activity of the agonists with coincidental activation of the antagonists. In addition, the electromyographic amplitudes were similar between the 2 underwater conditions, but the Hydro Boot produced a higher level (p < .001) of drag than did the barefoot condition. As expected, in most cases the forces on dry land were higher (p < .001) than underwater drag. In flexion, however, the peak drag with Hydro Boot and isokinetic force did not differ.

Conclusions: Increasing the frontal area of the lower leg with a Hydro Boot significantly increased the level of water resistance, thus, providing flexion forces that approach those measured on dry land. This type of water training offers stimulation to enhance the functional capacity and performance of the neuromuscular system. In addition, hydrodynamic principles and forces that influence the exercising limb must be considered to ensure appropriate progression.