The Effect of Progressive Dehydration on Strength and Power: Is There a Dose Response?

1. Lawrence Hayes1,2 and Dr Chris Morse1 • Department of Exercise & Sport Science, Manchester Metropolitan University, Alsager, ST7 2HL. • Department of Exercise & Sports Science. University of the West of Scotland, Hamilton, ML3 0JB. • Lawrence.Hayes@uws.ac.uk • Dehydration was obtained by repeated heat exposure and exercise sessions (five periods of 20 min jogging at up to ~80% age predicted heart rate maximum at 48.5°C ± 0.48°C, relative humidity 50% ± 4% in an environmental chamber) • Before the initial exposure and after subsequent exposure sessions, the following measurements will be taken (in the same order to maintain reliability) in a thermoneutral environment (~20°C): • Three countermovement SVJs with 1 min rest intervals between bouts (as used by Gutierrez, Mesa, Ruiz, Chirosa, and Castillo (2003)). Centre of mass displacement (disCoM) will be measured • Unilateral (right) knee extension maximum voluntary contraction (MVC) tests in both isometric and isokinetic concentric conditions on an isokinetic dynamometer (Cybex NORM; N.Y., USA). Trials were separated by a recovery period of 2 min and the best result were taken. • 3. EMG activity was recorded in the distal end of the vastuslateralis during isometric MVC (Guidelines from Reeves, Narici and Maganaris (2004)). • 4. Nude Mb was determined to the nearest 0.05 kg using Seca 835 portable digital scales (Vogel & Halke, Hamburg, Germany). • Once 5% Mb loss was achieved or five exposures had been completed, testing was terminated. Participants were rehydrated with hypotonic solution to within 2% resting Mb. • RESULTS • Table 1:Mean ± SD (n = 12) body mass, maximal isometric and isokinetic strength, jump height, and EMG data for each stage of the investigation. • Denotes significant difference from baseline * = P < 0.05; ** = P < 0.01; † = P < 0.001 • DISCUSSION • In conclusion, dehydration caused by jogging in the heat had no effect on vertical jumping or isokinetic leg extensions at a rate of 120°•s-1. Alternatively, exercise induced dehydration was detrimental to isometric and isokinetic leg extensions at a rate of 30°•s-1. Although no dose response existed in the present investigation, thresholds were identified for velocity-specific contractions and may suggest a lower threshold for slower contractions. This suggests that the force–velocity relationship merits further research in hypohydration. • INTRODUCTION • It has previously been reported that hypohydration inconsistently affects muscular force due to confounding variables (e.g. caloric restriction, training status, accumulation of catabolites and heat stress as reviewed by Judelson et al. 2007a). It is currently unclear whether and by which mechanism hypohydration affects strength and power. • One characteristic of hypohydration is decreased body mass (Mb) and several studies examining power employed measurements in which only the subject’s Mb resisted the testing movement (e.g. standing vertical jump (SVJ) or short sprint) (Viitasalo, Kyrolainen, Bosco, and Alen, 1987). With a number of authors reporting no significant change in muscle function during hypohydration, performance in Mb based tests may actually improve. • PURPOSE • The purpose of the present investigation was to examine the effect of hydration state on maximal strength, jump performance and activation capacity. In particular, the investigation aimed to determine if a dose response existed. • PARTICIPANTS • Twelve male university students with a mean ± SD age, stature, body mass and BMI of 21.2 ± 1.0 years, 180.0 ± 5.0 cm 78.0 ± 9.5 kg and, 24.1 ± 1.9 respectively, volunteered to participate in the study. • Inclusion criteria: • All participants are healthy and able to exercise without adverse effects. • All participants are 18-30 year old males. • To ensure euhydration, urine osmolality was tested using a digital hand-held urine osmolality refractometer (Advanced Instruments Inc, MA, USA) with a value below 600mmol·kgˉ¹ required as inclusion criteria (Nagashima et al. 2001). • Exclusion Criteria: • Core temperature was monitored throughout via the tympanic membrane. If temperature exceeded 39.5ºC, testing was terminated. • Jogging in the heat may be mildly uncomfortable. If this stress became too painful for the participant, intensity was decreased or testing terminated. • If 80% age predicted max HR (HRmax) was exceeded, treadmill velocity was reduced or testing terminated. • EXPERIMENTAL PROCEDURES • Figure 1:Schematic representation of experimental methodology. The Effect of Progressive Dehydration on Strength and Power: Is There a Dose Response? REFERENCES Adam GE, Carter Iii R, Cheuvront SN, Merullo DJ, Castellani JW, Lieberman HR, Sawka MN (2008) Hydration effects on cognitive performance during military tasks in temperate and cold environments.Physiol Behav 93:748–756. Gutierrez A, Mesa JLM, Ruiz JR, Chirosa LJ, Castillo MJ (2003) Sauna-induced rapid weight loss decreases explosive power in women but not in men. Int J Sports Med 24:518–522. Jones LC, Cleary MA, Lopez RM, Zuri RE, Lopez R (2008) Active dehydration impairs upper and lower body anaerobic muscular power. J Strength Cond Res 22:455–463. Judelson DA, Maresh CM, Anderson JM, Armstrong LE, Casa DJ, Kraemer WJ, Volek JS (2007a) Hydration and muscular performance: does fluid balance affect strength, power and high-intensity endurance? Sports Med 37:907–921. Nagashima K, Wu J, Kavouras SA, Mack GW (2001) Increased renal tubular sodium reabsorption during exercise-induced hypervolemia in humans. J Appl Physiol 91:1229–1236. Reeves ND, Narici MV, Maganaris CN (2004) Effect of resistance training on skeletal muscle-specific force in elderly humans. J Appl Physiol 96:885–892. Viitasalo JT, Kyrolainen H, Bosco C, Alen M (1987) Effects of rapid weight reduction on force production and vertical jumping height. Int J Sports Med 8:281–285.