How to Build Underwater Power, Your 5th Stroke in Swimming

By SwimSwam Partner Content
January 22nd, 2020

courtesy of, a SwimmersBest brand

Underwater undulations, or the 5th Stroke, is arguably the most important area of growth in the competitive swimming industry for the foreseeable future. From the early advancement made by Jesse Vassallo, David Berkoff, Missy Hyman and coach Bob Gillett, the importance of underwaters continues to expand and grip the industry as the single most technique needed for any swimmer to reach excellence in nearly all race events.

Technique: The first problem is the technique used by most swimmers. Like any other stroke the technique for undulations have a wide range of critical components that must be addressed:

Hyper Streamline: This is perhaps the most obvious thing to fix. If you are not in a tight streamline with your ears slightly below your biceps and our elbows locked straight, you are creating undue frontal resistance. STAY in hyper streamline until you are ready to take your first stroke. Do NOT lift you head to see where the surface is since your head is as large as an 8” red parachutes and can impact your speed just as much as a parachute!

True Bilateral Undulation: A ‘knee kick’ is NOT the same thing as a true bilateral undulation. Most people simply bend their knees back and then kick hard forward. Instead the feet should flow equally across the body’s center line, to the front and the back of the body. For many the most elusive challenge is to get the legs to continue past the center line to the front half of the body. The only effective way to create true bilateral undulation is to lead from the sternum of the chest (i.e chest-led) and ripple that arch through the chest and down to the feet. This is how an eel swims, not how a dolphin swims. Humans move through the water best by creating and propelling off vortices with an eel-like motion through the water.

Easy Speed off Your Vortices: As you quickly draw your chest in and out (leading from your sternum), the void that is left in the wake of the chest draws in water and creates a vortex (i.e a little whirlpool) of water. The first vortex starts on your front and then as you change directions with your chest, a second vortex develops in the small of your back. Each of these vortexes then follow the ripple motion of your body down to your toes. The KEY is that a fast whip action of your feet changing directions will get propulsion as they push against the vortex that is leaving the ends of your toes (hence you need to cross well over your center line to connect with these vortexes). Without the in and out movement of your chest, you do not create bilateral vortexes on both sides of your body. So if you merely kick from your knees, this over-exertion causes a delay in the time it takes for you to change direction with your feet and causes you to miss any vortex propulsion at the end of your kick and simply not create a second vortex on the back of your body. This means you are fighting to build power solely from your own muscles instead of using the vortex ‘easy speed’ that the eel uses to move through the water.

Straight Ankles and Knees on Recovery: The ankles and knees must stay straight as the legs are brought across the centerline, from the front of the body to the back of the body. This requires specialized muscles and should engage the glute muscles first. Early on young swimmers tend to ‘drop’ or bend their ankles as the feet cross from the front to the back of the body and this neglects to catch power off the vortex wave and greatly reduces forward speed.

Knees Should Stay Together: The vortices that are created by the chest must follow the body down to the toes. If the knees come open the vortex is absorbed and may even cause a net loss instead of the ‘easy speed’ you want from the vortex. Once the knees drift apart, on any phase of the undulation, power is lost. Again, this will require good habits and the development of the muscles needed for the additional power.

Tempo: A few studies have suggested that the chest should press 2x per second (a tempo of 0:40 or 0:45 seconds) per FULL bilateral undulation. The Regular Eel-Fin by will build this tempo by moving the weight like a grandfather clock pendulum. As the weight is moved closer to the feet, the shortened pendulum will force the body to undulate at a rate of 2 per second. Tempo Trainers are also helpful in creating this tempo but at first most swimmers will only listen to every other beep and try to undulate at a rate of slightly less than 1 undulation per second. The chest should move up and down 2 full cycles in less than 1 second.

Power: Once you create a good technical undulation and can sustain the proper tempo, the never-ending goal is to maximize the power to both the forward and back directions of each undulation. The goal is to maximize the distance per undulation and, while that starts with proper chest-led technique, it eventually has to advance by gaining power through the entire undulation. So how do we create more and more power with an undulating body movement?

Focus on ‘distance per undulation’. By gradually changing the intensity of your workout and diversifying your equipment, you will constantly improve your distance per undulation. Underwaters require regular focus every day, off every wall. But the undulation movement is a complex combination of muscle power. Therefore, it is important to include regular changes in equipment and training methods in order to build powerful bilateral propulsion.

Build maximum power per undulation. Bilateral undulations require muscle power to both sides of the undulation. This means regular focus on the muscles in the core, recovery muscles (backwards), and propulsive (forward) muscles. This requires constant variations in your training methods and equipment so you can target ALL your undulation muscles and technique simultaneously.

Measure your progress. The longterm goal should be to breakout off every wall with your head surfacing legally just in front of the 15 meter mark and your first stroke reaching across the 15 meter mark. Of course the number of undulations is not the only factor… large knee-driven kicks will not win races so you also need regular measurements of your speed to the 15 meter mark. Targeting 11 undulations to the 15 meter mark with regular improvements to your breakout times is the best longterm plan for your underwater development.

The Process: Now let’s get down to the nitty gritty of daily work you need to be doing with the 5th stroke.

ONE: Fix Your Flaws. Most flaws include not leading with your chest, not finishing past your centerline on the front, kicking too much with your knees, and not undulating fast enough. All of these problems can be resolved by systematic use of the ONE Regular Eel-Fin. This monofin uses a movable weight like the pendulum on a grandfathers clock. This pendulum effect ensures you finish your feet to the front of your centerline. As you move the weight closer to the feet it will then help increase your tempo to have 2 full undulations in 1 second or less.

TWO: Build Overall Power. Power can be improved with regular use of the ONE Pro Eel-Fin monofin. The Pro Eel-Fin requires and builds power to both sides of the undulation. It locks the knees together to help build the proper muscle memory of knees and thighs touching during both directions of the undulation. The Pro Eel-Fin also helps engage the glute muscles to trigger your largest muscle group for maximum power. It does not correct some of the fundamental flaws (like the Regular Eel-Fin can do) but is designed to build power for those swimmers that already have an efficient technique. A tempo trainer (set at 0:45 or 0:50 seconds) can be coupled with your Pro Eel-Fin sessions to ensure you are pressing your chest with each beep and flowing 2 full cycles per second. Don’t confuse the Eel-Fins with normal monofins. Regular monofins are too wide and will force most swimmers to drop their ankles on the recovery phase of their undulation. This will build a muscle memory that will be hard to correct and will slow down the process of building the proper muscle groups. Normal monofins are FUN for the swimmers because they move so much faster through the water. But fun comes at a cost of power, technique and lack of training experience. The Pro Eel-Fin will not provide any significant change in your forward speed, but instead will build muscle power. Once you master and use it regularly, the Pro Eel-fin will give you nearly identical distance per undulation as without the fin. But the Pro Eel-Fin will build the power and body position you need to race fast underwater.

THREE: Build Recovery Power. Recovery power relies on keeping your ankles straight on the recovery of the undulation. To test the type of power needed for a straight knee and straight ankle recovery, lay on the floor and lift both legs without bending your knees or ankles. This requires the glute muscles and will flex those muscle groups throughout the process. These are the muscles that need to be developed more and more every day for your 5th stroke as well as Back, Free, and Fly. The ONE FlexRights are one of the few options available to help engage the glutes and minimize knee bend at the same time. They are flat panels that are strapped to the back sides of your knees to help train your glutes. The FlexRights are an ideal way to train your recovery power for your 5th stroke.

FOUR: Building Overall Intensity. ONESwim has invented a wide range of unique equipment needed to build a well-rounded underwater undulation. Their Ankle Weights can be custom selected from ¼ pound and up to use as much a 1 pound per ankle to provide a great way to power your propulsive muscle groups. The ONE Weight Belts can also be adjusted by ¼ or ½ pound increments to build belts from 1 pound up to 18 pounds. The Weight Belts are ideal to build overall intensity of the undulations. The ONE Power Bags are drag socks that fit on your feet, your calves, arms, and as a drag skirt. The Power Bags on the calves provide a constant frontal drag as well as powering both propulsive and recovery muscle groups. On the feet, the power bags are a serious workout as part of your undulation power development. But when the Power Bags are placed over a pair of fins, they provide the maximum resistance of nearly any product to help you focus on your ‘distance per undulation’. The ONE Power Chute is a parachute you wear on your hips. Unlike any other parachute, this product creates force before you even finish pushing off the wall. This provides immediate focus to your wall power and to each undulation. But the latest addition to the ONE line of power development equipment is their Long Cords. The ONE Long Cords are really a set of 2 half length cords that when clipped together will allow you to race the entire pool underwater or on the surface. Long Cords are ideal to build intensity to the 15 meter mark breakout as the last 5-10 undulations will have increasing amounts of drag which forces you to build intensity into your final breakout

FIVE: Diversify your Vertical Kicking Methods. Just like your underwaters, vertical kicking can be done wrong (i.e just knee kicking or not finishing past your mid-line), particularly if you don’t work to constantly improve your technique and your resistance levels. Just like the 5th stroke, you need to finish your kick past your centerline on the front, keep your knees together, and whip your feet quickly from each terminal side of the undulation. The obvious way to improve your intensity (and thereby ‘find’ better technique), is to put your arms in streamline for 5-15 second while keeping your FACE OUT OF THE WATER. Interval training between your arms across your chest and 5-15 seconds of streamline arms will help train better undulation technique by itself. But over time, you will want to constantly add diversity to your vertical kicking drills to help build the full core and all muscle chains needed for your underwaters. Many of the ONE products discussed for underwater undulation training also pertain to the diversity you need for your vertical kicking sets. Again, the goal remains that you have a host of core and secondary muscle groups that need to be developed on a constant basis. Just doing the same drills and the same methods over and over will engrain bad habits and neglect the muscle groups that need to be improved.

At an Olympic and college level it is easy to see that more and more race time is spent underwater by the top medalist in nearly all events. We already have races that can be over 30% of the distance underwater for long course event but in short course events it can be as much as 60% of the race underwater. The question is, are you putting 30+% of your training time on building fast underwaters? This doesn’t mean just hypoxic training to build lung capacity but truly focusing on the speed and power of distance per undulation? Are your competitors putting in that time? How long can you avoid quality training of your 5th stroke?