title: The effects of progressive dehydration on strength and power: is there a dose response?
abstract: This study examined the effect of exercise- and heat-induced dehydration on strength, jump capacity and neuromuscular function. Twelve recreationally active males completed six resistance exercise bouts (baseline and after each 5 exposure sessions) in an increasing state of hypohydration obtained by repeated heat exposure and exercise sessions (5 periods of 20 min jogging at up to approximately 80% age predicted heart rate maximum at 48.5 +/- 0.48 degrees C, relative humidity 50 +/- 4%). Relative to starting values, body mass decreased 1.0 +/- 0.5, 1.9 +/- 0.7, 2.6 +/- 0.8, 3.3 +/- 0.9 and 3.9 +/- 1.0% after exposure 1, 2, 3, 4 and 5, respectively. However, plasma volume remained constant. No significant differences existed amongst trials in vertical jump height, electromyography data or isokinetic leg extension at a rate of 120 degrees s(-1). Isometric leg extensions were significantly reduced (P < 0.05) after the first (1% body mass loss) and subsequent exposures in comparison to baseline. Isokinetic leg extensions at a rate of 30 degrees s(-1) were significantly reduced after the third (2.6% body mass loss) and subsequent exposures compared with baseline. No dose response was identified in any of the tested variables yet a threshold was observed in isometric and isokinetic strength at 30 degrees s(-1). In conclusion, dehydration caused by jogging in the heat had no effect on vertical jumping or isokinetic leg extensions at a rate of 120 degrees s(-1). Alternatively, exercise-induced dehydration was detrimental to isometric and isokinetic leg extensions at a rate of 30 degrees s(-1), suggesting the force-velocity relationship in hypohydration merits further research.
authors.affiliation: Department of Exercise and Sports Science, Manchester Metropolitan University, Hassall Road, Alsager, ST7 2HL, UK. Lawrence.d.hayes@student.mmu.ac.uk
authors.forename: Lawrence D
authors.initials: LD
authors.lastname: Hayes
authors.forename: Christopher I
authors.initials: CI
authors.lastname: Morse
mesh_terms: D000328:Adult; D001834:Body Water / Q000502:physiology; D003681:Dehydration / Q000503:physiopathology*; D004305:Dose-Response Relationship, Drug; D004576:Electromyography; D005080:Exercise Test; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology; D053580:Muscle Strength / Q000187:drug effects / Q000502:physiology*; D010807:Physical Endurance / Q000187:drug effects / Q000502:physiology; D010953:Plasma Volume / Q000502:physiology; D013546:Sweating / Q000502:physiology; D013997:Time Factors; D014867:Water / Q000494:pharmacology* / Q000502:physiology; D055815:Young Adult
chemical_list: D014867:Water