Underwater Swimming: Efficiency, Advantages, and Limitations

Is swimming underwater more efficient?

Generally, no, not for sustained swimming, due to the physiological limitations of breath-holding and increased energy demands. However, for short, powerful bursts like competitive starts and turns, swimming underwater significantly enhances efficiency and speed by minimizing drag and maximizing propulsion.

Understanding Efficiency in Swimming

To assess whether swimming underwater is "more efficient," we must first define efficiency in the context of swimming. Efficiency can be measured by:

• Speed: How quickly a swimmer can cover a given distance.
• Energy Cost: The amount of energy (oxygen consumption, caloric expenditure) required to cover a given distance or maintain a certain speed. A more efficient stroke or technique requires less energy for the same output.
• Propulsion vs. Drag: The balance between the forces propelling the swimmer forward and the resistive forces (drag) slowing them down. Higher efficiency means greater propulsion relative to drag.

The Physics of Underwater Swimming

The primary reason underwater swimming can be faster and, in specific contexts, more efficient, lies in its hydrodynamic advantages:

• Reduced Wave Drag: When swimming on the surface, a significant portion of drag comes from the creation of waves. This "wave drag" increases exponentially with speed. Underwater, swimmers eliminate wave drag almost entirely, encountering only form drag (due to body shape) and skin friction drag (due to water moving over the skin).
• Streamlined Body Position: The most efficient underwater swimming technique, particularly the dolphin kick, emphasizes a highly streamlined, torpedo-like body position. This minimizes the frontal surface area presented to the water, reducing form drag.
• Powerful Propulsion: The dolphin kick, executed with a strong undulatory motion from the core through the legs, is one of the most powerful propulsive movements in swimming. When performed underwater, this power can be fully leveraged without the energy dissipation associated with breaking the surface or needing to maintain buoyancy with arm strokes.

Advantages of Underwater Swimming (Context-Specific)

While not universally more efficient, underwater swimming offers distinct advantages in specific scenarios:

• Competitive Starts: The initial dive and subsequent underwater dolphin kicks are crucial for a fast start. Swimmers can achieve significantly higher speeds underwater immediately after a dive than they can on the surface, due to the elimination of wave drag and the powerful propulsion of the kick.
• Turns: Similar to starts, underwater turns allow swimmers to maintain momentum and accelerate off the wall with a powerful push and dolphin kick, again leveraging reduced drag and powerful propulsion.
• Short Sprints (e.g., 50m Freestyle): In events where anaerobic capacity and maximal speed are paramount, elite swimmers utilize extensive underwater sections (up to 15 meters from the start and turns, as per FINA rules) to gain a competitive edge. The speed gained underwater often outweighs the temporary physiological cost.
• Breath-Holding Training: While not directly about efficiency, practicing underwater swimming can improve a swimmer's breath-holding capacity and comfort in hypoxic states, which can indirectly benefit surface swimming by allowing for longer stroke cycles between breaths.

Limitations and Disadvantages

Despite its hydrodynamic advantages, sustained underwater swimming is generally less efficient due to physiological and practical constraints:

• Oxygen Deprivation (Hypoxia): Humans are not aquatic mammals. We require continuous oxygen supply for aerobic metabolism. Holding one's breath severely limits oxygen intake, forcing the body into anaerobic metabolism much more quickly. Anaerobic processes are less efficient for sustained energy production and lead to faster fatigue and accumulation of lactic acid.
• Increased Energy Cost per Unit Time: While hydrodynamically efficient, the effort required to maintain high speed underwater with a powerful dolphin kick is very high. The energy expenditure per second can be greater than surface swimming, making it unsustainable for longer distances.
• Skill and Strength Requirements: Effective underwater swimming, particularly the dolphin kick, demands significant core strength, ankle flexibility, and highly refined technique. Without these, the "efficiency" gains are lost, and the movement becomes cumbersome and tiring.
• Competitive Rules: FINA (Fédération Internationale de Natation) rules limit the distance a swimmer can travel underwater after a start or turn to 15 meters. This acknowledges the speed advantage and prevents races from becoming underwater breath-holding contests.

When Is Underwater Swimming "More Efficient"?

The answer to the core question is highly contextual:

• For maximum speed over short distances (starts, turns, short sprints): Yes, underwater swimming is demonstrably more efficient and faster due to reduced drag and powerful propulsion. The physiological cost is acceptable for these brief, maximal efforts.
• For sustained swimming over longer distances: No, it is significantly less efficient. The inability to breathe continuously and the high energy expenditure of powerful underwater propulsion make it unsustainable and less economical than rhythmic surface swimming, which allows for continuous oxygen intake and a more balanced use of aerobic metabolism.

Surface Swimming: A Baseline for Comparison

Surface swimming, while incurring wave drag, allows for continuous respiration, making it the only viable method for sustained swimming and endurance events. Efficiency in surface swimming focuses on:

• Minimizing Form Drag: Achieving a long, streamlined body position.
• Optimizing Propulsion: Effective catch and pull phases with the arms, and a consistent, propulsive kick (flutter kick or breaststroke kick).
• Rhythmic Breathing: Integrating breathing into the stroke cycle to ensure adequate oxygen supply and CO2 removal, maintaining aerobic efficiency.

Training Considerations

For swimmers looking to leverage underwater efficiency in competitive contexts:

• Dolphin Kick Development: Focus on core strength, hip mobility, and ankle flexibility. Practice the kick with a snorkel and fins to refine technique without breath-holding limitations.
• Hypoxic Training: Gradually increase breath-holding capacity through controlled drills, but always under supervision and with caution, as excessive breath-holding can be dangerous.
• Underwater Pushing and Gliding: Practice powerful pushoffs from the wall, maintaining a tight streamline for maximum glide distance before initiating the dolphin kick.
• Consistency: Integrate underwater work into every start and turn during training to build muscle memory and efficiency.

Conclusion

Underwater swimming is a powerful tool in a swimmer's arsenal, offering significant speed and hydrodynamic advantages for short, explosive efforts like starts and turns. In these specific scenarios, it is indeed "more efficient" in terms of covering distance quickly with minimal drag. However, for continuous, sustained swimming, the physiological necessity of breathing renders surface swimming overwhelmingly more efficient. Elite swimmers strategically combine the speed of underwater bursts with the aerobic sustainability of surface swimming to achieve optimal performance.