title: Whole body hyperthermia, but not skin hyperthermia, accelerates brain and locomotor limb circulatory strain and impairs exercise capacity in humans.
abstract: Cardiovascular strain and hyperthermia are thought to be important factors limiting exercise capacity in heat-stressed humans, however, the contribution of elevations in skin (Tsk) versus whole body temperatures on exercise capacity has not been characterized. To ascertain their relationships with exercise capacity, blood temperature (TB), oxygen uptake (V̇O2), brain perfusion (MCA Vmean), locomotor limb hemodynamics, and hematological parameters were assessed during incremental cycling exercise with elevated skin (mild hyperthermia; HYPmild), combined core and skin temperatures (moderate hyperthermia; HYPmod), and under control conditions. Both hyperthermic conditions increased Tskversus control (6.2 ± 0.2°C; P < 0.001), however, only HYPmodincreased resting TB, leg blood flow and cardiac output (Q̇), but not MCA VmeanThroughout exercise, Tskremained elevated in both hyperthermic conditions, whereas only TBwas greater in HYPmodAt exhaustion, oxygen uptake and exercise capacity were reduced in HYPmodin association with lower leg blood flow, MCA Vmeanand mean arterial pressure (MAP), but similar maximal heart rate and TBThe attenuated brain and leg perfusion with hyperthermia was associated with a plateau in MCA and two-legged vascular conductance (VC). Mechanistically, the falling MCA VC was coupled to reductions in PaCO2, whereas the plateau in leg vascular conductance was related to markedly elevated plasma [NA] and a plateau in plasma ATP These findings reveal that whole-body hyperthermia, but not skin hyperthermia, compromises exercise capacity in heat-stressed humans through the early attenuation of brain and active muscle blood flow.
authors.affiliation: Centre for Human Performance, Exercise and Rehabilitation, Brunel University London, Uxbridge, United Kingdom.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Trangmar
authors.affiliation: Centre for Human Performance, Exercise and Rehabilitation, Brunel University London, Uxbridge, United Kingdom.
authors.forename: Scott T
authors.initials: ST
authors.lastname: Chiesa
authors.affiliation: Centre for Human Performance, Exercise and Rehabilitation, Brunel University London, Uxbridge, United Kingdom.
authors.forename: Kameljit K
authors.initials: KK
authors.lastname: Kalsi
authors.affiliation: Centre for Human Performance, Exercise and Rehabilitation, Brunel University London, Uxbridge, United Kingdom.|The Copenhagen Muscle Research Centre, Department of Anaesthesia, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Niels H
authors.initials: NH
authors.lastname: Secher
authors.affiliation: Centre for Human Performance, Exercise and Rehabilitation, Brunel University London, Uxbridge, United Kingdom j.gonzalez-alonso@brunel.ac.uk.
authors.forename: José
authors.initials: J
authors.lastname: González-Alonso
mesh_terms: D000255:Adenosine Triphosphate / Q000097:blood; D000328:Adult; D001784:Blood Gas Analysis; D001794:Blood Pressure; D001831:Body Temperature; D001921:Brain / Q000098:blood supply* / Q000378:metabolism; D002395:Catecholamines / Q000097:blood; D015444:Exercise; D005334:Fever / Q000378:metabolism / Q000503:physiopathology*; D006339:Heart Rate; D018869:Heat-Shock Response; D006439:Hemodynamics; D006801:Humans; D007866:Leg / Q000098:blood supply*; D008297:Male; D020768:Middle Cerebral Artery / Q000503:physiopathology; D010101:Oxygen Consumption; D012879:Skin Physiological Phenomena; D055815:Young Adult
chemical_list: D002395:Catecholamines; D000255:Adenosine Triphosphate
keywords: Hyperthermia; maximal exercise; regional blood flow and metabolism