title: Hypovolemic intolerance to lower body negative pressure in female runners.
abstract: OBJECTIVE
  An attenuated baroreflex response and orthostatic intolerance have been reported in endurance-trained male athletes; however, it is still unknown whether this occurs also in females. The purpose of the present study was to examine whether endurance exercise-trained women had a predisposition to orthostatic compromise, and if so, what causative factor(s) may induce orthostatic intolerance.
  
  
  METHODS
  We studied cardiovascular and hormonal responses to graded lower body negative pressure (LBNP) (0 to -60 mm Hg) in 26 middle-distance female runners (18.6 +/- 0.1 yr) as the exercise-trained (ET) subjects and 23 age-matched untrained (UT) control subjects. On the basis of the occurrence of syncope episodes during LBNP, ET and UT subjects were further allocated to two groups; ET with presyncope (ET+syncope) and without presyncope (ET-syncope) and UT with presyncope (UT+syncope) and without presyncope (UT-syncope).
  
  
  RESULTS
  Occurrence of presyncope episodes during LBNP was higher in ET (65.4%, P < 0.05) than that for UT (34.8%). Leg compliance was higher (P < 0.05) in ET than in UT. LBNP reduced stroke volume (SV) more (P < 0.05), increased heart rate (HR) higher (P < 0.05), and increased forearm vascular resistance (FVR) more in ET+syncope as compared with the other groups. Response of vasoactive hormones to LBNP was higher in ET+syncope (P < 0.05) than that of the other groups except for norepinephrine (NE); high in both ET+syncope and UT+syncope. The relationship between SV and NE, an index of sympathetic neuronal response, had no training-related changes during LBNP.
  
  
  CONCLUSIONS
  We conclude that exercise-trained females have a high incidence of orthostatic intolerance during LBNP, with a greater reduction of SV independent of changes in baroreflex and neurohumoral function. A lower incidence of LBNP intolerance in UT may be accounted for by a lower reduction of SV during LBNP. An increase in leg compliance in the exercise-trained females may play an important role in inducing pronounced reduction of SV and hence the intolerance to LBNP.
authors.affiliation: Department of Physiology, School of Medicine, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, 807-8555 Kitakyushu, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Morikawa
authors.forename: S
authors.initials: S
authors.lastname: Sagawa
authors.forename: R
authors.initials: R
authors.lastname: Torii
authors.forename: Y
authors.initials: Y
authors.lastname: Endo
authors.forename: F
authors.initials: F
authors.lastname: Yamazaki
authors.forename: K
authors.initials: K
authors.lastname: Shiraki
mesh_terms: D000293:Adolescent; D000328:Adult; D017704:Baroreflex / Q000502:physiology; D005260:Female; D006801:Humans; D007024:Hypotension, Orthostatic / Q000097:blood / Q000503:physiopathology*; D020896:Hypovolemia / Q000097:blood / Q000503:physiopathology*; D008150:Lower Body Negative Pressure; D009638:Norepinephrine / Q000097:blood; D010807:Physical Endurance / Q000502:physiology; D012083:Renin / Q000097:blood; D012420:Running / Q000502:physiology*; D012737:Sex Factors; D013318:Stroke Volume / Q000502:physiology; D013575:Syncope / Q000097:blood / Q000503:physiopathology*; D014667:Vasopressins / Q000097:blood
chemical_list: D014667:Vasopressins; D012083:Renin; D009638:Norepinephrine