Hydration is frequently discussed in athletic contexts, but its specific importance for physical therapy outcomes is less appreciated. Dehydration affects muscle function, connective tissue mechanical properties, pain sensitivity, and cognitive engagement during rehabilitation sessions — all of which directly influence the quality and safety of physical therapy work.
Connective tissue hydration
Tendons, cartilage, and intervertebral discs are largely water. Cartilage is approximately 70–80% water — this water content is what gives it compressive resistance and shock-absorbing capacity. Chronic dehydration reduces cartilage water content, increasing its rigidity, reducing its ability to distribute load evenly, and increasing the compressive force transmitted to subchondral bone. For patients with cartilage-related conditions, consistent hydration is directly relevant to joint mechanics.
Muscle function and strength testing
A dehydration level of as little as 2% of body weight produces measurable reductions in muscle strength (3–8%), endurance, and power output. For physical therapy sessions where strength assessment and progressive loading are central tools, attending sessions dehydrated produces unreliable baseline measurements and reduced ability to meet therapeutic loading targets. Patients should consume 400–600ml of water in the 2 hours before a session.
Pain perception and dehydration
Dehydration increases pain sensitivity through multiple mechanisms, including reduced circulation to pain-sensitive structures and increased levels of substance P (a pain-signaling neuropeptide). This means dehydrated patients during PT sessions may experience pain at lower thresholds, potentially limiting therapeutic range of motion and loading, and confounding pain-based assessment. Simply being adequately hydrated can meaningfully improve functional participation in rehabilitation exercises.
Practical hydration guidance for rehab patients
Aim for pale yellow urine as a practical hydration indicator throughout the day. Consume 400–600ml of water before sessions. Continue drinking during and after sessions proportional to exertion and sweat loss. Electrolyte replacement is only necessary for sessions exceeding 60–90 minutes of significant exertion or sessions in hot environments. High-water foods — soups, fruits, and vegetables — contribute meaningfully to hydration status alongside beverages.