written by Meridith Cass and Olivia Crozier
Football players are exposed to a variety of environmental challenges which puts them at risk for dehydration. As a fall sport, preseason and the early parts of the season fall in the hottest and most humid months of the year, particularly when athletes may not be well acclimatized to intense exertion in the heat. Particularly for teams in the southern United States, this can lead to an increased risk of heat illness.
The purpose of this study was to determine the feasibility of deploying Nix Biosensors’ as a non-invasive hydration monitoring tool during training sessions for a high school football team in southern Georgia. Sweat rate and electrolyte concentration were measured using Nix Biosensors on football players at Tiftarea Academy (n=15, 100% male) training over 3 days of varying workout intensities with weather conditions.
The average fluid and electrolyte losses over the course of the full practice were 36.4 (±11.7) oz and 1,793 (±909) mg respectively. The average sweat composition was 46 (±13) mg/oz. It was found that total fluid loss, total electrolytes loss, and sweat composition varied significantly among football players with the minimum and maximum total fluid loss and total electrolyte loss spanning a 2.6x range, and 4.6x range, respectively. Although more research is needed, measuring individual sweat rate and concentration with Nix Biosensors can provide valuable information to create individual hydration recommendations.
The primary objectives for this study were as follows:
- How much variation exists between subjects within this population?
- How much variation exists in different environmental conditions?
- How often is this population experiencing dehydration?
- What are the optimal personal hydration strategies for each of the study participants within the student-athlete population?
Study Design & Methods
Two representatives from Nix were on site to administer the study. Sensors were activated and applied by the Nix team during pre-practice lifting sessions between 2:45-3:00pm each day prior to the start of practice promptly at 3:20pm. Sensors were deactivated and collected at 5:45pm at the conclusion of practice. As a feasibility study, ground truth data (i.e., weigh-ins) was not obtained and subjects drank fluids ad libitum.
Data & Results
- Workout: Practice consisted of lighter intensity play walk-throughs
- Equipment: Light equipment of just shoulder pads and lightweight pinny jerseys
- Environment: Nix Index was High at 87
- Thunder and lightning midway through practice drenched the subjects and forced practice indoors to a gymnasium with a Moderate Nix Index of 59.
- Adhesive: Sensors were applied directly to the bicep without additional taping or securing. Due to the extreme heat and humidity (see Nix Index data below) as well as torrential rain, 5 of the 15 subjects experienced adhesive failures.
- Workout: Practice was higher intensity with full contact
- Equipment: Full pads and uniforms
- Environment: Nix Index was Extreme at 97
- Adhesive: Sensors were secured to the bicep with self-adhesive tape wrapped around the bicep, and 2 of 15 subjects experienced adhesive failures.
- Workout: Practice consisted of higher intensity, followed by a short game for the B team
- Equipment: Full pads and uniforms
- Environment: Nix Index was Extreme at 90
- Adhesive: Sensors were secured with pre-wrap and traditional athletic tape, and no adhesive failures were observed
Nix Hydration Assessment
From this data, Tiftarea Football can start to get a sense of the magnitude of fluid and electrolyte losses, and the massive inter-individual variation within the team during the same conditions. This massive variability articulates the need for individual rehydration strategies. For a full report of individual athlete data, please see the Appendix below.
When comparing athletes’ total fluid losses, the range across all subjects was measured to be 21.0 to 55.4 oz, which represents a 2.6x range. The average fluid loss was 36.4 oz (Figure 2). While the fluid consumption was not measured for this specific study, this level of fluid loss could represent a range of dehydration of 0.8 to 1.9%. It should be noted that significant performance impairment is typically onset at 2.0% dehydration (Figure 3).
The range of total fluid loss was 21.0 to 55.4 oz with an average of 36.4 oz. demonstrating a clear need for individual hydration strategies.
This study was not designed to capture fluid consumption, however total fluid losses comprised 0.8% to 1.9% of individual subjects’ body mass, demonstrating a risk of dehydration that borders on performance impairment.
When comparing athletes’ total electrolyte losses, the range across all subjects was measured to be 703 to 3,229 mg, which represents a 4.6x range. The average electrolyte loss was 1,793 mg (Figure 4). Sweat composition ranged from 32 to 75 mg/oz with an average of 46 (Figure 5). This represents a 2.4x range, further emphasizing the need for custom hydration strategies for each athlete. Sweat Composition is a measure of the relative concentration of electrolytes in a subject’s sweat on a per oz basis and is reported in units of mg/oz. This metric allows direct comparison of sweat composition to the electrolyte content in various popular hydration formulas. (Figure 6). The team is currently providing water during practice – which does not contain electrolytes – and should consider providing an electrolyte formula for its athletes – particularly the heaviest sweaters, who also lose the highest quantity of electrolytes.
The range of total fluid loss was 703 to 3,229 mg with an average of 1,793 mg, demonstrating a clear need for individual hydration strategies.
Sweat composition ranged from 32 to 75 mg/oz which is a 2.2x range.
The range of sweat composition observed was 32 to 75 mg/oz, with an average of 46 mg/oz. This is in contrast to water, which is currently the hydration option available during practice, which contains no electrolytes.
Summary & Next Steps
Total fluid and electrolyte losses exhibit significant inter-individual variability (one individual to the next), but also intra-individual variability (for one athlete, one day to the next). Due to this massive variability, it is important to have ample data to understand an athlete’s individual needs and the best strategy to replenish both fluids and electrolytes to ensure safety and optimize performance. During this initial data collection, Tiftarea Football players exhibited a 2.6x range for fluid losses, 4.6x range for electrolyte losses, and 2.4x range for sweat composition over the course of practice. This data illustrates the value for individualized sweat analysis and hydration strategy.
The Nix Physiology Team recommends continued sweat testing with their athletes in a variety of workout types (i.e., gym vs on-field), workout intensities (walk-through vs full contact) , and environmental conditions (i.e., throughout the fall football season and even spring football) to fully understand athletes’ needs throughout the season.
In order to reduce the frequency of adhesive failures, it is recommended that pre-wrap and athletic tape, or compression sleeves, be worn over the sensors when placed on the bicep. Further study is warranted to explore sensor placement on other sites of the body, such as chest, scapula, or flank.