Author(s): MACGREGOR, L., BUDDE, A., RODRIGUEZ-SANCHEZ, N., Institution: UNIVERSITY OF STIRLING, Country: UNITED KINGDOM, Abstract-ID: 407

INTRODUCTION:
Many athletes, such as those involved in weight category sports, opt to reduce their body mass temporarily by limiting fluid intake before competing with the goal of improving their performance. However, the negative consequences of decreased hydration levels on endurance performance have been widely acknowledged. Still, there is limited understanding regarding the impact of sub-optimal hydration on strength- and power-related function. In particular, it is unclear whether acute hypohydration - in the absence of fatigue and/ or hyperthermia - influences muscle mechanical properties and neuromuscular control – therefore, performance benefits may be achievable in strength- and/ or power- based activities, without the concomitant decrements commonly observed in endurance events. We aimed to investigate the impact of passively-induced hypohydration, via fluid restriction, on muscle stiffness and contraction speed, and on strength and power performance.
METHODS:
Twenty healthy active participants (12 male, 8 female) were assessed in a randomized cross-over design (EUH = euhydrated and HYPO = hypohydrated conditions). Participants underwent fluid restriction (0 L consumed) during the 14-hour period prior to HYPO testing; 500 mL of water was consumed the night before and on the morning of EUH testing. Hydration status was determined by urine osmolality. Unilateral knee extensor maximal voluntary isometric contraction (MVC) and bilateral countermovement jump (CMJ) were completed to determine lower-limb strength and power, respectively. Vastus lateralis and rectus femoris contractile mechanics were assessed using tensiomyography. Neural activation was estimated from electromyogram amplitude during submaximal isometric knee extension contraction to failure. Between condition differences were explored using paired sample Student’s t-test and effect sizes were described using Cohen’s d.
RESULTS:
Urine osmolality was analysed to verify hydration status (HYPO = 808.5 ± 84.9 mOsm/kg vs. EUH = 251.5 ± 137.5 mOsm/kg, p < 0.001, d = 3.47), participants’ body mass decreased by 1.3 ± 0.1% in HYPO vs. EUH. Hypohydration was associated with a 4.3% reduction in strength (MVC) (p = 0.045, d = 0.51) and a 1.5% reduction in peak power (CMJ) (p < 0.001, d = 1.08). Time to submaximal contraction failure was unaffected by hydration status (p = 0.163). Neural activation was not different between conditions (p = 0.408). Knee extensor muscle contractile mechanics were unaltered between conditions (p = 0.053-0.480).
CONCLUSION:
Strength and power were reduced by fluid restriction-induced hypohydration, but this reduction in function was not associated with impaired muscle contractile mechanics or neural activation, nor was time to contraction failure impacted. Our findings can be used to inform athletes and practitioners regarding the negative impact of hypohydration on performance in strength- and power- related activities, this may be particularly important for competitors in weight category sports.