A Physiotherapist's Perspective — Why Hydration Is a Performance AND Injury Issue

Most conversations about hydration in endurance sport focus on performance — cramping, fading, finishing time. But as a physiotherapist who works with endurance athletes on both performance and injury prevention, I see hydration from a different angle.

Dehydration and sodium depletion don't just slow you down on race day. They change how your body moves and responds to load over time.

What happens to the musculoskeletal system under dehydration

Muscle tissue is roughly 75% water. When dehydration progresses, muscle function degrades in ways that extend beyond cramping. Research shows that dehydrated muscles have reduced strength output, slower reaction times, and impaired coordination. From a movement quality perspective, this matters.

When athletes train in a chronically under-hydrated state — which many do, without realising it — the compensations their bodies make to manage reduced muscle efficiency put additional stress on joints, tendons, and connective tissue. Over time, this contributes to overuse injuries.

Cartilage is also significantly affected by hydration status. Joint cartilage is largely avascular — it relies on fluid exchange through movement for nutrient delivery and waste removal. Poor hydration compromises this process.

The training load connection

One of the things I look at with athletes who are experiencing recurrent soft tissue injuries is their hydration strategy — particularly around hard training blocks. Athletes who are consistently under-fuelled and under-hydrated heading into hard sessions are asking their bodies to perform high-intensity work with impaired tissue integrity.

This doesn't mean every overuse injury is a hydration problem. But it's a variable that's often entirely unexamined when we look at why an athlete keeps breaking down.

Recovery and hydration

The recovery process after hard training is heavily sodium-dependent. Protein synthesis, fluid redistribution into muscle tissue, and the removal of metabolic waste products all involve sodium transport mechanisms.

Athletes who sweat heavily and don't replace sodium adequately often feel more fatigued than expected after hard sessions, and take longer to feel ready to train again. When this pattern shows up across a training block, it's worth investigating whether their sodium losses are being adequately replaced.

The practical takeaway

I'm not suggesting that a sweat test is a replacement for good load management, sleep, or progressive training. It's not. But for athletes who are puzzled by recurring injury patterns, persistent fatigue, or poor recovery, looking at hydration from a precise, data-driven angle is a worthwhile step — and one that's often skipped.