Advanced Aquatic Resistance Training: How The GMX7 X1-PRO Works


How the GMX7 X1-PRO Works on a Biological Level

The goal of all training is to improve our Swimming Machine biology. We want to send the signals to our muscles, blood vessels, heart and nerves that promote improvement which results in faster swimming. The better the training, the better the signal, the better the improvement. The X1-PRO is that better training!

For Sprinters

Sprint training mainly works to improve the nerves and buffering capacity of the swimmer. By forcing the swimmer to apply all their energy for a short period of time, all available muscles fibers need to be fired and coordinated in a controlled manner. Motor units (bunches of muscle cells controlled by the same nerve) don’t usually fire all together, but are recruited one on top of the other to produce more and more power. First, the slow twitch units are recruited, then the fast ones.

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Figure 1: A graph of how many motor units are being activated at certain power levels. The more power you need (the more you pull) the more motor units kick in to help out.

You may think regular all-out swimming will accomplish this, but the water itself does not provide enough resistance for us to maximize that recruitment, that is why we need resistance equipment like the X1-PRO to help. What sets X1-PRO apart from other resistance tools is the ability to accurately control and quickly vary the resistance.

Over time, the nerves “desensitize” and allow more motor units to activate sooner and longer. It’s like taking the safety’s off your nerves. As your body is able to safely handle the power, it allows more of your potential to be unlocked.

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Figure 2: After training with the X1-PRO, more motor units kick in sooner and harder to let you produce more power with the same muscle mass. That results in increased top speed!

Since regular sprint swimming doesn’t usually activate all available muscles fibers, those fibers that are left out don’t get signaled to improve and you aren’t maximizing your training. The X1-PRO helps us use and train all our muscle fibers with every sprint.

As a training session continues, more and more muscle fibers start to break and fail (which causes soreness). Having the ability to accurately control and vary the resistance from zero to immovable allows swimmers to maintain their performance throughout a set. The smooth consistent resistance also helps to mitigate injuries since there are no sudden jolts and stops that create tendinitis and ligament disruption.


Ryan Lochte using the X1-PRO; Photo Courtesy: GMX7 Training

Endurance Training

Swimming is mainly an endurance sport, but it is unique among them. Unlike other endurance sports like running and cycling, water is tough to move through and good swimming endurance requires most of our muscles to be activated at the same time continuously.

Few, if any resistance devices in the past have allowed bi-directional resisted swimming. Since the X1-PRO does, it unlocks a whole new area of training for the miler!

There are many biological parts that improve with endurance training:

  1. Mitochondria grow in size and number helping us extract more oxygen and produce more energy while helping use reduce muscle acid.
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Figure 3: As blood comes in, some oxygen, but not all is extracted by the mitochondria. With endurance training, more and more oxygen is extracting, signaling improved mitochondrial power.


  1. Capillary beds grow between the muscle fibers, allowing increased supply of oxygen and increased clearance of carbon dioxide and acid.
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Figure 4: VEGF (vascular endothelial growth factor) is a local hormone released during low oxygen states like exercise that signals capillary growth.


  1. Heart size grows to allow more blood to be pumped around the body, improving supply and clearance.
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Figure 5: A simplified heart increases the number of sarcomeres in its cardiac muscle fibers, increasing the size of the “balloon” pump, improving cardiac output and VO2.


  1. Acid shuttling increases so that any power coming from the anaerobic system (Glycolysis) can be cleared, allowing more energy to come from that muscle’s engine, increasing our speed.
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Figure 6: Acid and lactate are produced at the same time during exercise. The muscle’s ability to shuttle them to the blood and mitochondria is one of the biggest factors affecting endurance ability. More shuttles, better endurance.


By giving the swimmer the ability to continuously activate their muscles at a higher than normal resistance, the X1-PRO intensifies endurance training and can increase the rate of developing these improvements.



About the size of a cell phone, the X1-PRO attaches to any lane line in any pool. (Olympian Ryan Lochte with the X1-PRO) Photo Courtesy:

As a Coach

I love resisted swimming for my athletes. It teaches them to utilize every stroke efficiently and gives swimmers a great feel for the water. In the past, every resistance tool was tedious to set up or change the resistance. All we could do was set it and hope for the best.

The X1-PRO is so easy to change your resistance, you can literally adjust it every 25, unlocking a whole new avenue of training. Imagine doing 4x25s sprint with slightly more resistance with each 25 to teach sprinters how to build their 100?

And the bi-directional ability is truly unique. I can do the same with my endurance crew. Start at a high resistance and gradually come down over 1000 yards or so, keeping them mentally engaged and trying to get their tempos up as they progress through a simulated race.

Another great use of the X1-PRO is to take advantage of an up-and-coming training method called post-activation potentiation (PAP). By swimming with resistance and then without it, the nerves are unlocked and more muscle recruitment can be obtained. This has been a staple in land sports, but difficult to accomplish in swimming, until now.

And with the ease of transport and set-up taking less than three minutes, the X1-PRO can be set up in warmup pools right at a swim meet to let swimmers take advantage of PAP swimming!

As a Swimmer

In my youth, I was a record holding powerlifter, and a staple question all weightlifters know is “How much you bench, brah?” Why don’t we ever ask each other “How much you pull, brah?” Before the X1-PRO, there was no good way to accurately compare how much a sprinter could pull.

But, with a single twist of the dial, I can easily change my resistance and challenge myself to pull more weight. And the notches on the side let me keep accurate track of my ability and compare to other swimmers around the world.

Finally, I can ask someone “How much you pull… brah!?”


Karl Hamouche, M.D is the founder of Swim Smart and the author of The Biology of Swimming. He uses his experience as a coach, swimmer and medical training to bring simplified insights into how the Swimming Machine works. By helping coaches and swimmers understand the “why” behind the “what,” we can improve our trust in our training and enjoy it even more!


The above press release was posted by Swimming World in conjunction with GMX7 Training.  For press releases and advertising inquiries please contact

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