ORIGINAL RESEARCH article
Front. Physiol.
Sec. Striated Muscle Physiology
Impact of passive, diet-based, hydration on muscle morphology: Implications for muscle quantity assessments
Provisionally accepted
- 1Norwegian School of Sport Sciences, Oslo, Norway
- 2Olympiatoppen, Oslo, Norway
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Background: This study investigated the impact of passive changes in hydration level on measurements of lean tissue mass (LTM) and muscle morphology. Methods: Sixteen healthy participants (13 males, 3 females) completed two testing sessions 24 hours apart, including dual-energy X-ray absorptiometry (DXA), 3D ultrasound imaging of the vastus lateralis (VL), and bioelectrical impedance analysis (BIA). Participants fasted for 12 hours before each session. Hydration was manipulated by assigning participants randomly to either a non-hydrated state, abstaining from fluids until testing, or a hydrated state, consuming water equal to 1.5% of body mass two hours prior. Results: Total body water, measured using bioelectrical impedance analysis (BIA), was lower in the non-hydrated condition (48.6 ± 9.7 kg) than in the hydrated condition (49.0 ± 9.8 kg, p = 0.015). In the hydrated condition, total LTM, measured using DXA, was higher for the full body (60.8 ± 11.8 kg vs. 60.0 ± 11.9 kg, p < 0.001) and the trunk (29.2 ± 5.3 kg vs. 28.6 ± 5.4 kg, p < 0.001). Hydration did not significantly affect LTM in the upper (p = 0.251) or lower limbs (p = 0.298), or the thigh (p = 0.051). Volume (p = 0.105) and cross-sectional area (CSA; p = 0.114) of the VL were also unaffected. Conclusion: Small changes in hydration levels induced passively under temperate conditions may not significantly affect measurements of muscle morphology or limb measurements of LTM. However, monitoring changes in muscle quantity with total LTM may be biased by water intake and trunk hydration if these factors are not controlled. Caution is warranted (e.g. standardisation) when using total LTM to monitor changes in muscle quantity.
Keywords: water content, muscle mass, Muscle Volume, Hypertrophy, ultrasound, DXA
Received: 14 Oct 2025; Accepted: 10 Nov 2025.
Copyright: © 2025 Viken, Nettum, Paulsen and Seynnes. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Julian Seiler Viken, julianv@nih.no
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