Page 112 - 《运动与健康科学》(英文)2024年第2期

TaggedAPTARAEnd234 X.R. Tan et al.
evidence implicating the role of the central nervous system in an and (d) control (Fig. 1A). These randomized controlled
earlier onset of fatigue during hyperthermia. For instance, force trials were conducted in a crossover manner, with partici-
production during sustained maximal voluntary contractions and pants serving as their own controls. Each trial was spaced
central motor drive were reduced by exertional hyperthermia. 12 at least 7 days apart for recovery. A preliminary session
Moreover, a study showed that male cyclists exercising in the for anthropometric measurements and VO 2peak assessment
heat exhibited elevated a/b index as assessed by electroencepha- preceded the trials.TaggedAPTARAEnd
logram, indicating suppressed arousal. 13 Brain electrical activity TaggedAPTARAPVO 2peak was measured using an incremental exercise
is shown to be altered by hyperthermia but not dehydration. 14 protocol. Each participant ran at 4 different speeds on a tread-
Our previous work demonstrated that exertional hypohydration mill (Mercury; h/p/cosmos, Bayern, Germany), starting at a
did not influence motor cortical activity, suggesting heat may speed 1 km/h slower than his expected pace for a 10 km race,
play a greater role in central fatigue. 15 Thus, we propose that with increments of 1 km/h every 3 min, for a total of 12 min.
brain functional activity is impaired by hyperthermia, Heart rate (HR) and ratings of perceived exertion (Borg
17
scale ) were recorded during the last 10 s of each 3-min
compromising both motor and cognitive functions.TaggedAPTARAEnd
TaggedAPTARAPTo date, evidence on central fatigue during hyperthermia stage. Oxygen uptake (VO 2 ) was assessed over the final
has been indirect, and the underlying central alterations that minute of each stage with a metabolic cart (Parvomedics, Salt
hinder optimal neural function in the heat remain unclear. Lake City, UT, USA). After 510 min rest, the participant ran
Efforts at assessing brain temperature and function have been at a fixed speed of moderate intensity (determined based on
challenging due to the relatively inaccessible nature of human the preceding run) with an initial gradient of 1%, which
brain tissue. With excellent spatial resolution and versatility, increased by 1% every min until volitional exhaustion.
magnetic resonance imaging (MRI) presents a useful non-in- VO 2peak was recorded as the mean VO 2 over the last min
vasive tool to examine the human brain. While MRI has been before termination, and the data was used to determine running
employed to investigate the brain functional connectivity in intensity in subsequent trials.TaggedAPTARAEnd
humans exposed to passive hyperthermia, 16 no studies have TaggedAPTARAPPrior to each experimental trial, participants’ baseline body
examined real-time brain activity changes during hyperthermia mass was measured, and pre-trial blood sample (10 mL) was
taken by a phlebotomy-trained nurse. Each trial consisted of 2
in relation to a physical or cognitive task.TaggedAPTARAEnd
TaggedAPTARAPThe purpose of the present study was to investigate altera- MRI scans: a first scan (baseline; S1) before each trial, and a
tions in brain properties and functional activity in healthy second scan after the completion of intervention (post; S2).
volunteers exposed to exertional or passive hyperthermia. After the post scan, the body mass was recorded, and a post-
Using MRI-based evaluation of brain temperature, resting trial blood sample (10 mL) was taken.TaggedAPTARAEnd
cerebral perfusion, and task-based brain activity, we identified
the implicated brain regions and neural changes in hyper-
TaggedAPTARAP2.2.1. Familiarization/Exertional hyperthermia trial (EX)TaggedAPTARAEnd
thermic humans. We further explored ice ingestion as a poten-
TaggedAPTARAPAfter the baseline scan, participants were given 6 aliquots
tial heat mitigation strategy.TaggedAPTARAEnd
of ambient temperature water (25˚C; portioned from a volume
equivalent to 8 g/kg body mass), with each aliquot given at
TaggedAPTARAH12. MethodsTaggedAPTARAEnd
5-min intervals over 30 min. After the drinking phase, the
participants ran at 70% VO 2peak on a treadmill for up to
TaggedAPTARAH22.1. ParticipantsTaggedAPTARAEnd
60 min, while wearing a disposable raincoat to retain body
TaggedAPTARAPEleven healthy males between 21 and 35 years of age were
heat, until the rectal temperature (T re ) reached 39.5˚C. HR
recruited. Participant characteristics were as follows: age = 23
(A300 heart rate monitor; Polar Electro, Kempele, Finland)
§ 2 years; body mass = 64.0 § 6.4 kg; height = 1.70 § 0.04 m;
and T re (fiber optic sensor; Opsens, Quebec City, Canada)
body fat percentage = 10% § 2%; peak oxygen consumption
were monitored and recorded at 5-min intervals. VO 2 , ratings
(VO 2peak )=59 § 5 mL/kg/min (mean § SD). All participants
of perceived exertion, and ratings of thermal sensation (Young
self-reported to be right handed. Individuals with medical 18
et al. ) were recorded at 15-min intervals. Ambient water
implants, non-MRI-compatible dentures, and claustrophobia
(1.5 g/kg body mass) was given every 15 min. After post-run
were excluded. All protocols were approved by the institu-
body mass measurement, they proceeded with the second
tional review board of the National University of Singapore
scan. Prior to this, the participant donned thermal insulative
(B-15-123; NUS 2700). Details of trial procedures, risks
clothing (Heat-tech; Uniqlo Co. Ltd., Tokyo, Japan) and
involved, precautions taken, and special instructions or risks
woolen socks in addition to a water-perfused thermosuit (Med-
pertaining to MRI were made clear to participants before
Eng, Ottawa, Canada) with circulating water maintained at 41˚C
written informed consent. All participants completed a health
by an external heater (GR08-1-A; uCoolz, Singapore) to mini-
declaration form and were certified fit for trials by a physician
mize heat loss (Fig. 1B1D).TaggedAPTARAEnd
prior to enrollment.TaggedAPTARAEnd
TaggedAPTARAH22.2. Experimental trialsTaggedAPTARAEnd
TaggedAPTARAP2.2.2. Passive hyperthermia trial (PA)TaggedAPTARAEnd
TaggedAPTARAPThe study comprised 1 familiarization trial and 4 experi- TaggedAPTARAPThe protocol was similar to EX trial except that partici-
mental trials: (a) exertional hyperthermia, (b) passive pants were passively heated by immersing (up to shoulder
hyperthermia, (c) exertional hyperthermia with cooling, level in a seated position) in a water tub maintained at