title: Hypohydration adversely affects lactate threshold in endurance athletes.
abstract: The purpose of this investigation was to observe the effect of hypohydration (-4% body mass) on lactate threshold (LAT) in 14 collegiate athletes (8 men and 6 women; age, 20.9 +/- 0.5 years; height, 171.1 +/- 2.4 cm; weight, 64.8 +/- 2.3 kg; V(O)2 max, 62.8 +/- 1.9 ml x kg(-1) x min(-1); percentage of fat, 11.4 +/- 1.5%). Subjects performed 2 randomized, discontinuous treadmill bouts at a dry bulb temperature (T(db)) of 22 degrees C to volitional exhaustion in 2 states of hydration, euhydrated and hypohydrated. The hypohydrated condition was achieved in a thermally neutral environment (T(db), 22 degrees C; humidity, 45%), with exercise conducted at a moderate intensity as defined by rating of perceived exertion (RPE, approximately 12) 12-16 hours before testing. On average, subjects decreased 3.9% of their body mass before the hypohydration test. Blood lactate, hematocrit, V(O)2, minute ventilation (VE), R value, heart rate (HR), and RPE were measured during each 4-minute stage of testing. In the hypohydrated condition, LAT occurred significantly earlier during exercise and at a lower absolute V(O)2, VE, respiratory exchange ratio, RPE, and blood lactate concentration. Also, the blood lactate concentration was significantly lower in the hypohydrated condition (6.7 +/- 0.8 mmol) compared with the euhydrated condition (10.2 +/- 0.9 mmol) at peak exercise. There were no differences in HR or percentage of maximum HR at LAT nor did plots of V(CO2):V(O)2 reveal differences in bicarbonate buffering during exercise between the 2 conditions. From these results, we speculate that hypohydration did not significantly alter cardiovascular function or buffering capacity but did cause LAT to occur at a lower absolute exercise intensity.
authors.affiliation: Department of Kinesiology, University of New Hampshire, New Hampshire Hall, Durham, New Hampshire 03824, USA. rwk@hopper.unh.edu.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Kenefick
authors.forename: Nicholas V
authors.initials: NV
authors.lastname: Mahood
authors.forename: Craig O
authors.initials: CO
authors.lastname: Mattern
authors.forename: Robert
authors.initials: R
authors.lastname: Kertzer
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Quinn
mesh_terms: D000328:Adult; D001835:Body Weight; D003681:Dehydration / Q000097:blood*; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D013177:Sports / Q000502:physiology*
chemical_list: D019344:Lactic Acid