Underwater exoskeleton reduces oxygen consumption during diving

A research team from Peking University (PU) has developed an exoskeleton for divers that supports fin strokes and simplifies the diving process. Due to the reduced muscle strain, the system is also intended to lower divers' oxygen consumption, thus ensuring longer dive times with the same oxygen volume in the tank.

During diving, the legs, with the body's largest muscle groups, are heavily strained. Consequently, a lot of oxygen is needed. In diving, this comes from oxygen tanks, which last for varying lengths of time depending on factors such as volume, operating pressure, dive depth, diver size, and physical exertion. A diver needs about 20 to 25 liters of oxygen per minute. A 10-liter tank, at an operating pressure of 200 bar and a maximum dive depth of 20 m, would be able to supply oxygen for approximately 40 minutes.

The Chinese researchers intend to extend dive time with the same tank volume, as they write in the study "An Underwater Exoskeleton for Scuba Diving: Reducing Air Consumption and Muscle Activation Through Knee Assistance" (PDF), which was published in IEEE Transactions on Robotics. They are pursuing the approach of reducing the diver's oxygen demand by reducing the activity of the highly oxygen-consuming muscles through an exoskeleton.

Support in specific phases

The exoskeleton developed by the scientists uses two electric motors, housed waterproof on the diver's back. They move pull ropes attached to cuffs on the diver's upper and lower legs, thus supporting fin movements. A hip belt stabilizes the entire system. In total, the underwater exoskeleton weighs 9 kg. Most of the weight rests on the diver's back.

The leg position is determined by Inertial Measurement Units (IMU), so that leg movements are only supported in specific positions and when needed. For example, the motor is engaged via a clutch during the downward fin stroke. During the upward stroke, the motor is disengaged and offers no support, so as not to negatively affect the diver's recovery movement. Previously, the researchers had analyzed the movements of divers and thus identified the optimal support phases.

The scientists tested the exoskeleton with a total of six certified divers in a 50 m long swimming pool at a depth of 2 m. They had to swim a distance of 100 m three times with fin strokes – once with and once without the exoskeleton switched on. With the exoskeleton activated, activity in the quadriceps and calf muscles was reduced by more than 20 percent, and oxygen uptake decreased by 22.7 percent.

The researchers believe that oxygen demand can be further reduced with an improved exoskeleton. They therefore intend to expand their studies. Using computational fluid dynamics, they want to map and investigate the water resistance acting on the diver. Additionally, the exoskeleton is to be tested under real conditions in open water, and lighter materials are to be used for the exoskeleton. Further sensors, in addition to oxygen measurement, are also to determine additional measured values, such as the diver's heart rate.

(olb)