Nick Pelios
Freediver, Creator
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Nick Pelios
Freediver, Creator
Most freedivers talk about carbon fins as if the magic is in the carbon itself. They focus on the weave, the rails, the footpockets, the hydrodynamics, the angle that creates that clean line from hip to toe. All of that matters, and the industry has built countless hours of research and engineering on those details. Yet the element that quietly dictates how a diver moves through the water, how much energy they spend, how their body responds to depth, and how far they can safely and comfortably go, is stiffness.
It is strange how stiffness often becomes the last thing people think about when buying a new pair of carbon fins. It is even stranger when you consider that stiffness is the single factor most closely connected to your physiology, your diving style, your technique, your training background, and your goals. Stiffness is not a specification. It is an interface between your body and the ocean. It determines whether a blade bends too early or too late, whether you accelerate smoothly after the turn, whether your ankles fatigue, and whether you feel as if the fin is working with you or against you.
A fin does not generate propulsion on its own. It transfers energy from your legs, ankles, hips, and core. The stiffness determines how much resistance the blade offers before it loads and releases. That small detail affects almost everything that follows. A light diver with lower leg mass and a softer kick pattern will overpower a medium blade without gaining extra speed, while a heavier diver may have to work much harder to get any meaningful bend out of a soft blade. These relationships seem obvious when phrased this way, yet divers repeatedly underestimate how personal stiffness selection is. Two divers using identical blades can produce completely different results simply because their bodies behave differently underwater.
Pavel Tomm weighs just under seventy kilos. He stands at one meter seventy eight and describes himself as someone with naturally relaxed ankles. He has spent more than a decade diving with Alchemy fins, beginning with V2HS, migrating to V3, and eventually to V330. His years of experience reveal something important. Your ideal stiffness is not static. It evolves with your diving and with your current life stage. Early in his training he used softer blades because they allowed him to maintain rhythm without generating fatigue. Soft blades matched his technique and weight. They rewarded his more relaxed kick pattern and allowed him to stay fresh after long sessions in the water.
Then his role changed. Instead of training only for depth, he became a safety diver at the world championships in Limassol. Rescue diving is not a discipline where softness helps you. The acceleration you need at twenty or thirty meters when lifting another diver simply demands more authority from the blade. On those days, the soft stiffness that felt perfect for technical training now felt insufficient. He needed a blade that would push water even when loaded heavily. Softness was no longer enough. The medium stiffness, which once felt excessive, became a tool designed for an entirely different purpose.
A year later, while working in Kalamata, the medium blades that were so helpful for safety work suddenly felt too stiff for daily long sessions that involved multiple ascents and descents. The stiffness fatigued his ankles. The power delivery felt abrupt. The rhythm was not as smooth or sustainable as he needed. That is when medium soft became the Goldilocks zone for him. Soft was too gentle. Medium was too demanding. Medium soft combined acceleration with comfort, giving him the sense of connection he needed without taxing him.
There is a lesson here. Stiffness does not exist in a vacuum. It fits into your physiology, your goals, your body weight, your technique patterns, and even your available energy on any given day.
Freediving is full of theory, but stiffness is something that exposes its truths in the water, not on paper. Pavel decided to put his blades to a practical test. He performed identical dives with three stiffness levels of the V330. The dives were chosen carefully. Thirty meter constant weight dives represent the bread and butter of instructional work. Fifty meter dives represent the point where technique and efficiency begin to matter significantly more. Rescue dives from twenty meters simulate high load ascents where a stiff blade reveals both its strengths and its weaknesses.
The thirty meter dives were simple. No freefall was used. He kicked all the way down and almost all the way up. He performed the same dive three times, once with soft, once with medium soft, and once with medium. His dive times were nearly identical at forty seven to forty eight seconds. On paper this suggests stiffness does not matter. But under the surface something different was happening. The number of kicks required changed. Soft blades required forty four kicks. Medium soft required forty. Medium required thirty six. The physics behind it are straightforward. A softer blade loads earlier and cannot transfer as much force. You compensate by increasing the number of kicks. A stiffer blade loads later but transfers power more efficiently. You compensate by increasing your physical effort but decreasing the number of kicks.
This is why technique becomes intertwined with stiffness. With soft blades your kick amplitude must remain small. The moment you try to add power the blade folds under you and stops giving propulsion. You must adjust your mechanics to match softness. With medium soft, you can expand your kick slightly and feel the blade engage more fully. With medium, your technique can be more forceful, but the cost is that your ankles absorb more strain and your legs recruit more muscle fibers, especially during ascent.
The fifty meter dives revealed even more. With soft blades, Pavel’s descent was controlled and relaxed. His ascent from fifty to eight meters required eighty three kicks. His dive time was one minute twenty six seconds. He reported feeling comfortable and fresh afterwards, which shows the value of softness for long training sessions. Yet he noted one limitation. After the turn at depth, when the diver is at maximum negative buoyancy, the soft blade did not give him the immediate acceleration he wanted. There was acceleration, but not the satisfying shift that helps divers establish a strong rhythm early in the ascent.
Switching to medium soft changed everything. His descent remained relaxed, but the ascent required only seventy kicks. Thirteen fewer than soft, and the difference felt even greater to him than the number suggested. The blade engaged earlier. The energy transfer felt cleaner. The acceleration after the turn felt more decisive. His dive time was one second shorter, effectively identical, but his subjective experience changed dramatically. He enjoyed the blade more, and his rhythm felt smoother. This is the effect that well balanced stiffness brings to deeper dives. A blade that cooperates with your natural movement, rather than resisting it or collapsing under it, becomes invisible. The diver stops thinking about the equipment because the equipment is finally fitting the diver.
With medium stiffness, his ascent again required seventy kicks, but something else happened. He felt his ankles working harder. He felt an early sense of wanting the surface to arrive sooner. The power was there, but the cost was higher. That cost may be acceptable to divers with greater muscle mass or a heavier body weight. For Pavel, it introduced fatigue at a point in the dive where relaxation matters most.
This is where a deeper physiological truth emerges. Stiffness does not only influence propulsion. It influences the diver’s mental state. When a blade charges aggressively, it invites a more forceful technique pattern. This naturally increases muscle activation. Increased activation increases carbon dioxide production. Higher carbon dioxide changes the sensory quality of the dive. What feels like physical tiredness can often be the psychological result of elevated effort.
Softness invites relaxation. Medium invites power. Medium soft allows the diver to move between the two states without feeling trapped in either.
In many parts of the world, freediving is presented as a meditative sport built entirely around personal performance. In places like Kalamata, Dahab, and Limassol, freediving is also a workplace. Safety divers must be prepared to act, and stiffness becomes an operational decision.
Pavel tested rescues from twenty meters using the Molchanovs style under arm grab. With soft fins, the beginning of the ascent felt slow. The blade did not give him the immediate lift he wanted. Once buoyancy began to assist, the ascent became easier, but the early meters were inefficient. He needed fifty kicks to reach the surface in twenty four seconds.
With medium soft, the entire experience changed. He felt immediate movement as soon as he engaged the blade. The dive time dropped to twenty two seconds with forty four kicks. The difference seemed small but in rescue diving small differences compound quickly. If the rescue had been deeper, the inefficiencies of a soft blade would have been amplified.
With medium stiffness, the ascent was twenty seconds with forty kicks. It was the fastest of the three and required the fewest kicks. The reason is simple. Medium stiffness resists deformation under heavy load. When carrying another diver, the diver becomes a heavier system, and stiffness begins to work in the rescuer’s favor.
This is why safety divers and spearfishers often gravitate toward stiffer fins. The demands are different. The environment is different. The movements are different. When pushing a large camera housing through a current or towing a diver who has lost consciousness, the blade does not need to be gentle. It needs to be authoritative.
The choice of stiffness is therefore tied not only to body weight and technique, but also to purpose. The same diver may need soft for training, medium soft for recreational depth, and medium for safety work or underwater photography.
By now the patterns are clear. Selecting stiffness is not an abstract technical decision. It is a process of understanding your own body, your own diving, and your own goals. Lighter divers, especially those under seventy five kilos with a relaxed kick and refined technique, often feel naturally aligned with soft or medium soft. The blade bends enough to reward smaller movements and keeps fatigue low during repetitions.
Divers with more muscle mass or more explosive power often find soft too permissive. They load the blade too quickly and lose energy. Medium soft allows the blade to store and release energy in harmony with the diver’s strength. Medium becomes the appropriate choice only when the diver can fully engage the blade without collapsing technique.
Depth adds another dimension. At thirty meters, almost any stiffness can be adapted to. At fifty meters and beyond, the blade begins to reveal its behavior during the turn, the early ascent, and the transition into positive buoyancy. Soft requires patience until buoyancy returns. Medium soft gives acceleration without demanding too much from the legs. Medium gives acceleration instantly but asks the diver to spend more energy to maintain rhythm.
Use case adds yet another dimension. Training sessions that involve repeated descents reward softness because soft stiffness supports endurance and relaxation. Deep diving often rewards medium soft because it offers both comfort and efficiency. Safety diving, spearfishing, and underwater documentation often reward medium because the movements involve higher load phases that require firmness.
Pavel’s story reflects this universal truth. The stiffness that felt perfect during years of training became inadequate during safety work. The stiffness that felt appropriate during rescue work became excessive during long days of deep safety. The stiffness that felt like the sweet spot emerged only after he compared real dives under equal conditions.
This is why stiffness is referred to as a hidden engine. It is the element that makes everything else function smoothly. The right stiffness expands a diver’s usable energy. It protects the ankles. It enhances technique. It creates acceleration at the exact moment it is needed. It transforms the dive from something you must manage into something you simply experience.
Stiffness is not a performance detail. It is a foundation.