Research and Development | Case Study: Kansas City Current

written by Meg Garvey, PhD.

Abstract

Soccer players experience an increase in metabolic rate due to the aerobic and intermittent nature of the game. This causes an increase in core body temperature which triggers sweat production, especially in warmer conditions or higher-intensity training competition. High sweat rates with inadequate fluid intake/replenishment can put athletes at risk for dehydration, affecting physical and technical performance.

This study aimed to determine the feasibility of deploying Nix Biosensors as a real-time hydration monitoring tool during practice sessions in-season with professional soccer players. All sensors were applied and retrieved with minimal disruption to their typical training routines. Sweat rate and sweat concentration were measured using Nix Biosensors in female soccer players (N=9, age 26.0 + 2.4 years; six defensive, one forward, one mid-field, and one goalkeeper) participating in practice sessions over three weeks while in-season. The average fluid and electrolyte losses were 20.8 + 10.2 oz and 960.2 + 646.6 mg, respectively, and the average sweat rate was 16.1 + 8.9 oz/hr. The average duration of sensor wear time was 80.1 min + 17.7. It was found that fluid loss, sweat rate, total electrolytes lost, and electrolyte concentration varied among position groups. Although more research is needed, measuring individual sweat rate and concentration with Nix Biosensors can provide valuable information to create individual hydration recommendations.

Introduction

Soccer is a dynamic team sport consisting of activity levels ranging from low-intensity to high-intensity intermittent bursts, leading to elevated metabolic rates and players' body temperatures. This increase in metabolism during training and metabolism causes sweat to be produced and can lead to dehydration, especially during intense training in hot environments. Dehydration is a concern for players as it increases physiological strain and can reduce physical and technical soccer performance (1).

Mitigating the potential adverse effects of dehydration is an essential strategy for players to perform at their best during training and competition. One of the most common and popular strategies is to consume fluids before and during training to combat dehydration. An issue commonly seen amongst players is the prevalence of being dehydrated before even commencing training or competition. Between 54% (2) and 56% (3) of female and male soccer players, respectively, were found to be dehydrated (via urine-specific gravity) before training. It was also found that relying on self-assessment of thirst perception to guide fluid intake was not an appropriate indicator of hydration status. This can be why players fail to commence training in an euhydrated status.

Another challenge soccer players face is that they train and compete in different environmental conditions throughout the year (i.e., heat and humidity), which has been shown to elicit different sweat rates and sweat concentrations (4), making it challenging to come up with proper hydration protocols for them to follow year-round. In addition, soccer players train at different intensities based on the individual team’s periodization and scheme (4). Significantly greater sweat rates and electrolyte losses were observed during high-intensity and game simulation training compared with lower intensity, even with similar environmental conditions (5), highlighting the need to adjust hydration recommendations based on temperatures and training intensity.

Not only do players have different sweat rates and concentrations in different temperatures and training intensities, but it has also been found that sweat rates and body mass changes were higher during competition than during training (6). When matches occur in hot conditions, results show that substantial sweat and electrolyte losses can occur, and fluid replenishment amounts to only ~55% of losses, even when adequate fluids (water and sports drink) are readily available for consumption (7). This has been previously established as voluntary fluid intake varies greatly and is not sufficient to match fluid losses (8)(9). This has also been shown in players training in a cool environment where sweat loss data were similar to those recorded in warm climates, but the volume of fluid ingested in cooler conditions was less (10). Some of these findings can be attributed to the different fluid intakes by position, as it has been found that defensive (DF) players had a greater total fluid intake and lower body mass change % compared to forwards (FW), mid-fielders (MF), and goalkeepers (GK) in both low and moderate risk environments for hyperthermia (11).

It is well established that sweat rate and sweat composition vary extensively between individuals, and quantification of these losses has a role in individualizing a hydration strategy to optimize training and competitive performance. Monitoring hydration status and providing coaching strategies for athletes has greatly improved hydration practices and status and reduced dehydration incidences throughout a national team training camp (12).

Proper hydration strategies are crucial for players but must be consistently modified due to soccer's unique physical and environmental demands. Players' varying needs, hydration habits, and preferences are critical in determining the best plan to keep them adequately hydrated. Individual monitoring to determine fluid and electrolyte requirements and to drive appropriate behavior change should be an essential part of a player’s hydration strategy. To achieve this, individualized sweat testing during training providing real-time feedback to the players and their team is proposed to have the most significant impact towards achieving these goals.

Research Objectives

This study aimed to determine the feasibility of deploying Nix Biosensors as a real-time hydration monitoring tool during training sessions with professional soccer players. The primary objectives for this study were as follows:

What is the feasibility of utilizing Nix Biosensors for sweat testing and hydration monitoring with professional soccer players?
Is the sensor a practical solution to supporting this population’s hydration strategy in the field?
What is/are the appropriate anatomical sensor placement(s) based on this population?
Does the sensor produce usable data for this population?

Study Design & Methods

Based on the study objectives, a simple data collection protocol was derived based on the location and duration of the practice sessions and availability of players in-season over three weeks in August.

Nine players were identified as participants in 4 different position groups (6 DF, 1 MF, 1 FW, and 1 GK). Each player was made aware in advance of voluntary participation in the study, and each provided consent. Before each scheduled practice session, a Nix Biosensor was activated and placed on the left bicep of each player. The time of activation and the time the sensor was applied and taken off was recorded. The duration of sensor wear was extrapolated after the fact using the times recorded. During the final week of data collection, two players wore an additional sensor in a different location (one on the left scapula, one on the left quad). Temperature and humidity were recorded for each practice session, along with the rating of perceived exertion.

Data & Results

Sweat loss, sweat rate, and total electrolytes lost differed among players and between positions.
The mean sweat loss was 20.8 oz (7.4 – 42.8 oz) throughout practice.
The mean electrolyte loss was 960.2 mg (139.7 – 2316.9 mg)
The average duration of sensor wear time was 80.1 min + 17.7 (range 60 – 105 min)
Data were obtained from all nine players over four days
The sensor and patch stayed on for all players except for the GK during one training session.

Table 1: Results For All Players

The average fluid loss per athlete was 34.7 (± 18.2) oz (Figure 1). These players were on the field simultaneously and throughout the training session. Statistically, there is no significant difference between the average sweat loss and the player's field position (p = 0.9) or the individual player (p = 0.21). This analysis bears repeating with more participants to examine the statistical difference in sweat rates between position players, as there are notable variances.

Figure 1: Average Fluid Loss by Athlete

The average sweat rate for each player was 27.7 (± 14.6) oz/hr (Figure 2). These players were on the field simultaneously and throughout the training session. Similar to the average sweat loss per training session, the average sweat rate was not statistically different between field positions (p = 0.9) or the individual player (p = 0.21).

Figure 2: Average Sweat Rate by Athlete

Total electrolyte losses per player averaged 960.2 (± 646.6) mg (Figure 3). While statistically, there was no significant difference between the sweat loss or sweat rate for these players or their field positions; there was a significant difference between field positions for electrolyte loss (p = 0.04) and between individual athletes (p = 0.01). This would indicate that the players must have individual water bottles catering to their electrolyte needs.

Figure 3: Average Electrolyte Loss by Athlete

While there are variances between the athletes, statistically, when it comes to the fluids lost and the rate of that loss, there is no meaningful difference between athletes or positions for this study. The meaningful difference is on the electrolyte side. The mean sweat concentration ranges from 9 mg/oz to 87 mg/oz, with a mean of 40 mg/oz. This would require tailoring fluid replenishment bottles at a minimum by position but most effectively by athlete.

Discussion

Soccer poses unique and different challenges regarding training load, intensities, and environments to players. Sweat rate and concentration show high interindividual variability, even under similar conditions. For this feasibility study, data were collected over nine days with multiple players and positions represented each day. While individual variances were noted regarding sweat losses and rate, no statistically significant differences were found. Statistically significant differences were noted between players and positions concerning electrolyte losses and sweat concentration (p = 0.01 - 0.04).

When comparing variances between players on different days - the day with the highest temperature (40 degrees C) has the least variation in sweat rate (11.6 oz/hr - 17.2 oz/hr); however, the electrolyte loss was more than 3x difference between lowest to highest (139.7 mg - 356.3 mg). On days when more positions were represented in the data sample, the highest variances were noted for sweat rate and electrolyte losses, 7.5 oz/hr - 42.4 oz/hr and 297.7 mg - 1715.4 mg, respectively. These findings warrant more individualized data collection with this team to determine if these differences are rooted in physiological differences between the players or nuances/demands of play on certain positions vs. others. Player hydration habits, beverage preferences, differing workloads, and changes in environmental conditions will affect hydration requirements highlighting the need for consistent and specific hydration monitoring and sweat testing.

When asked about current hydration habits, many players didn’t have specific strategies or plans pre/during/post-practice. At the same time, others choose to hydrate ad libitum or consume limited fluids while training due to fear of over-hydrating and feeling too full of water. Upon observation, the players had plenty of access to water and sports drinks; however, the consumption of electrolyte/carbohydrate beverages appeared limited, with the preference for most players being water. This could indicate the utilization of Nix Biosensors as an educational tool for the players to start to dial in their hydration behaviors to optimize their performance, particularly in varying environmental conditions.

Although the sample size was small, differences in body size, fitness levels, heat acclimatization, training load, pre-practice hydration status, and fluid choice and intake during practice could also explain the players' sweat loss, rate, and concentration variances.

Conclusion

Based on our findings, we can determine that Nix Biosensors is a practical solution for managing the unique hydration needs of professional soccer athletes and can be utilized for sweat testing and hydration monitoring. They could be administered without a considerable disruption of the typical training routine, while gathering actionable data for the team to utilize and build their hydration strategies around individual variances.

As studies within this athlete population are plentiful, hydration relation problems are still seen even within this professional group of athletes. Gaining more insight and knowledge surrounding player habits, as well as hydration beliefs, struggles, and questions, would provide useful information to help tailor individual hydration monitoring and sweat testing protocols and potentially best practices by position. All these initiatives will help solve hydration-related issues within this team and female soccer players overall.

Case Study: Kansas City Current