Risk of Heat Stress Clinical Trial
Official title:
Impact of Pre-cooling in Adolescent Athletes While Playing Tennis in Hot Conditions
Many tennis tournaments are played outdoors in hot and humid conditions, which poses a significant challenge particularly for children athletes. The purpose of this investigation is to examine if a precooling method can reduce thermal strain and consequently improve the performance of adolescent tennis athletes while exercising in hot conditions.
Matches were conducted on hard-court surfaces separated by 24h (n=4 pairs) or 144h (n=1pair)
between 9am and 6pm and were played in winning two sets. Participants were paired according
to their level of play and competed against the same component at the same time of the day in
both matches.
Three hours before the start of their scheduled match, each player ingested a telemetric pill
in order to estimate the visceral temperature. Upon arrival, all participants provided a
urine sample for assessment of urine specific gravity as an indicator of their hydration
status and they emptied their bladders before were weighed. They were weighed twice, at
baseline and at the end of the match with a precision weight scale (Kern DE 150K2D, KERN &
SOHN GmbH, Balingen, Germany). During the match the participants consumed water and any other
sport drink and food ad libitum. The total weight of the players' food and fluids that was
consumed was measured using a precision weight scale. If participants wished to urinate
during the match, they were asked to use a urine cup and their urine was weighed.
One hour before the match, the precooling group was wearing a Cooling Cap (WElkins Sideline
Cooling System, SCS) for 45 minutes. On removal from a -20oC freezer, the cap surface was
10.7±2.5oC. After 45 minutes, participants removed the cap and they performed a 5 minutes
standardized warm-up (running around the court and running exercises from baseline to net and
back to baseline) and 10 min tennis specific warm up (rallies and serves) on court. Each
participant, before the warm-up, was outfitted with a heart rate chest strap and iBUTTON
sensors at four sites of the body (chest, upper arm, thigh and calf).
The scoring and timing characteristics of the matches complied with 2016 ITF rules. Three new
balls were used for each match with the players retrieving balls between points. Matches were
filmed from one end of the court, using a digital video camera (Sony DCR-VX2000E PAL, Japan).
Participants were performed on perceptual measurements at baseline, after each set, and at
the end of the match.
Thermoregulatory, cardiovascular and perceptual responses were recorded with standardized
techniques: 1) visceral temperature using telemetric pill (BodyCap, Caen, France) was
continuously recorded throughout the match; 2) skin temperature using iBUTTON sensors (type
DS1921 H, Maxim/Dallas Semiconductor Corp., USA) on chest, upper arm, thigh and calf was
recorded continuously; 3) heart rate (HR) variability data were sampled through short-range
telemetry at 1,000 Hz with a Polar RS800CX (Polar Electro , Kempele, Finland). The heart rate
monitor signal will be transferred to the Polar Precision Performance Software (release 3.00;
Polar Electro Oy); 4) thermal comfort (scale 1-5), thermal sensation (scale 1-10) and rating
of perceived exertion using standardized questionnaires were recorded at baseline, after each
set, and at the end of the match.
Hydration status was recorded with urine specific gravity. All the collected urine samples
will be analyzed using a refractrometer (Atago, Tokyo, Japan) for the determination of urine
specific gravity. Euhydration will be defined as urine specific gravity <1.02 according to
internationally accepted standards.
A digital video camera (Sony DCR-VX2000E PAL, Japan) was used to record the match - play
characteristics. The footage was used to conduct the retrospective notational analysis. The
quantitative performance indices that assessed had been: games and points won in each set and
normalized to the number of games and points that record in each set respectively. Also
unforced errors, first and second serve accuracy, aces, shots per rally and direction changes
in each point calculated. Point's duration, between point-duration as well the effective
point time calculated. The effective point time starting with the ball toss of the serve and
ending when the ball passed the player or bounced twice on court. In case of double fault,
starting time recorded from the beginning of the second serve.
Environmental data including air temperature, relative humidity, and wind speed were measured
continuously using a portable weather station (Kestrel 5500FW Fire Weather Meter Pro, USA).
The weather station was placed 1 meter above the ground according to the manufacturer's
guidelines.
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