Dear Coaches,
Here’s what’s coming up today:
Expert Opinion
Sodium Research Findings
1000 mg sodium stick packs are popular right now—but how necessary are they during training in temperate conditions?
A new study led by Wee Lun Foo, first team nutritionist and PhD student at Tottenham Hotspur, challenges the blanket use of sodium supplementation in elite soccer training.
Researchers assessed English Premier League (EPL) players during two separate pre-season training sessions conducted in temperate conditions (19–23°C).
Session 1: 14 players
Session 2: 17 players
Note: Not all players participated in both sessions.
Using sweat testing and predictive modelling, the study estimated players’ sweat rates, sodium losses, and theoretical changes in plasma sodium concentration.
The authors observed:
Session 1: About 29% of players were predicted to have mildly reduced plasma sodium concentration following training.
Session 2: Only 6% of players showed this outcome.
Most of these cases involved players who had engaged in aggressive fluid replacement, consuming 84–100% of their fluid losses while losing less than 0.5% of body mass.
This suggests the mild reduction in plasma sodium was driven by fluid intake volume, not a lack of sodium replacement.
Key takeaways:
The study found large individual differences in sweat rate and sodium losses.
Sodium supplementation was not necessary for most players during training in temperate climates.
Fluid strategies should be based on individual needs and behaviours, not blanket recommendations.
Resource Roundup
News & Resources
Performance Tech
Nix Hydration Biosensor
Sweat rate is highly individual, changes with environment and is notoriously hard to estimate. The Nix Hydration Biosensor aims to solve that.
This single-use patch is about the size of a watch face and weighs just 14 grams.
With a 36-hour lifespan, it adheres to the skin using kinesiology tape.
Real-time notifications guide athletes on when to drink, what to consume, and the precise amounts needed, eliminating uncertainty around hydration timing.
What sets Nix apart is its growing acceptance in elite sport.
UCI approval allows use in competition for 2025, enabling teams to adjust hydration based on real‑time data (source).
EF Pro Cycling reports the system is accurate and easy to use.
Precision Hydration tested the Nix biosensor in cool and hot conditions and found it underestimated both sweat rate (by 0.44 L/h) and sweat sodium concentration (by 212 mg/L) compared to their own measurement methods (source).
Cost starts around $129 for a pod and patches.
