written by Olivia Crozier
Speed skating is one of the most physiologically demanding sports in the world. Races are decided by fractions of a second, yet peak performance is built over years of training.
Athletes from the U.S. Speedskating team incorporated the Nix Hydration Biosensor into their training and conditioning programs to better understand a variable that is consistently underestimated in cooler conditions and cold weather sports: hydration.
Speed skating is a sport built on power, precision, and physiological stress. Athletes must generate extremely high force through the lower body while maintaining deep hip flexion and static isometric positions for extended periods of time.
Speed skaters are not endurance athletes in the traditional sense, nor are they purely power athletes. The sport demands a unique combination of both.
Training sessions often include:
From a thermoregulatory perspective, this creates a perfect storm. Athletes generate high internal heat while training in cool, mild, or climate-controlled environments that suppress thirst cues and reduce perceived sweat loss.
While these conditions are often assumed to be “low risk” compared to hot or humid environments, they can still drive substantial sweat and electrolyte losses, particularly at the elite level.
Across training sessions captured in the dataset, athletes consistently demonstrated meaningful fluid and electrolyte losses, even when cooler environmental conditions would not intuitively signal dehydration risk.
In many sessions, we saw a Nix Index value of a moderate 59, representing cooler, milder environments commonly seen in indoor rinks or controlled facilities, conditions typical of U.S. Speedskating training.
While athletes are often quick to defer to environmental heat as the primary driver of sweat loss, the dataset shows that moderate or cool environments can produce sweat losses comparable to those seen in hotter conditions, especially when training intensity is high.
The data shows a wide spread of loss rates, with sweat rates in many sessions exceeding 20 oz/hr and some approaching or surpassing 40 oz/hr. These high sweat rates occurred despite the absence of hot or extreme environmental stress, highlighting how environment alone does not dictate sweat response.
One of the most interesting discoveries from the dataset was that average loss rates did not always increase as the Nix Index (environmental conditions) increased. This is a powerful example showcasing that while training environment certainly plays a role, many other factors influence day-to-day sweat responses, including fueling strategies, sleep quality, clothing, perceived exertion, and training modality. When an athlete is training in a colder environment than the previous day, it doesn't necessarily mean that their sweat losses will be more mild.
It’s easy to assume that losses automatically rise only as environmental heat stress increases, but the data shows that this isn’t always the case when other variables are at play. This reinforces the importance of hydration monitoring even in cool or mild training conditions that do not “feel” demanding from a thermal perspective.
Perhaps the most striking insight from the data was not the magnitude of sweat loss, but the variability between athletes, even when training under similar conditions.
We use the Nix Index value to quantify the intensity of the training environment within the Nix Solo app. The Nix Index accounts for temperature, humidity, dew point, solar load, wind speed, and altitude, producing a score from 0 - 100 along with a Low, Moderate, High, or Extreme classification.
Despite training within cool-to-moderate environments according to the Nix Index, sweat profiles among U.S. Speedskating athletes varied dramatically.
Sweat Rate: Some athletes lost more than twice as much fluid per hour as others during similar training sessions. Overall sweat rates ranged from as low as 7 oz/hr to as high as 45 oz/hr.
Electrolyte Loss Rate: Electrolyte loss rates varied by thousands of milligrams per hour, ranging from 212 mg/hr to 3,078 mg/hr. Two skaters training under nearly identical conditions, and even losing similar amounts of fluid, often required completely different electrolyte strategies to maintain balance.
Sodium Loss Rate: Sodium losses differed just as dramatically. Some athletes lost more than ten times as much sodium per hour as others, with rates ranging from 100 mg/hr to 1,459 mg/hr. This variability persisted across similar workout types and environmental conditions.
Sweat Composition: Sweat composition varied widely between individuals as well, ranging from 21 mg/oz to 76 mg/oz. For some athletes, replacing fluid alone would be moderately insufficient; for others, over-consuming electrolytes could be unnecessary or counterproductive.
Two people completing the same workout may require completely different hydration strategies as shown in the comparison of two U.S. Speedskating athletes below. A generic hydration plan could leave one athlete under-fueled and progressively dehydrated and another athlete over-consuming electrolytes they do not need.
This level of variability is what lead U.S. Speedskating’s performance staff to turn to personalized sweat monitoring with Nix during training.
“We did an initial pilot during which Nix’s technology helped us completely overhaul the hydration strategy for one particular athlete who was struggling with their hydration,” said Dr. Jen Day, Sports Dietitian for U.S. Speedskating. “It resulted not only in more powerful performance on the ice, but also faster recovery, and even improved sleep. It was a really dramatic change. After that, we didn’t hesitate to roll it out to the entire team.”
The dataset also highlights that how athletes train matters, but not always in obvious ways.
Perhaps most importantly, high sweat and electrolyte losses were observed even when ambient temperatures were cool and humidity was low, conditions that commonly mask dehydration risk and blunt thirst cues.
Cold environments reduce the sensation of sweating and thirst, but they do not reduce metabolic heat production. Speed skaters still rely heavily on sweating to regulate they core body temperature, particularly during repeated high-intensity efforts.
When hydration deficits go unnoticed, athletes often experience reduced power output, slower recovery, increased perceived exertion, disrupted sleep and other harmful side effects of dehydration.
At the elite level, these effects directly impact training quality, overall performance, and end results when it matters most.
The takeaway from this dataset is not simply confirmation that speed skaters sweat in cool, moderate environments, but that they sweat in drastically different ways from one another.
For U.S. Speedskating, access to individual sweat data during training enabled more precise hydration strategies. These new strategies help to support performance, recovery, and overall athlete health as they compete at the highest level.