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Trial registered on ANZCTR

Registration number

ACTRN12622000732785

Ethics application status

Approved

Date submitted

10/05/2022

Date registered

23/05/2022

Date last updated

23/05/2022

Date data sharing statement initially provided

23/05/2022

Date results provided

23/05/2022

Type of registration

Retrospectively registered

Titles & IDs

Public title

Practical application of a mixed active and passive heat acclimation protocol in elite male Olympic team sport athletes

Scientific title

Practical application of a mixed active and passive heat acclimation protocol in elite male Olympic team sport athletes

Secondary ID [1]

None

Universal Trial Number (UTN)

Trial acronym

Linked study record

Health condition

Health condition(s) or problem(s) studied:

Heat acclimation

Athletic Performance

Condition category

Condition code

Physical Medicine / Rehabilitation

Other physical medicine / rehabilitation

Intervention/exposure

Study type

Interventional

Description of intervention(s) / exposure

Brief Name
The intervention examined the physiological, perceptual, and performance effects of 10-days of mixed active and passive heat acclimation incorporated into two weeks of normal rugby sevens training.

Why
Rugby sevens is often played in hot environmental conditions, and recent research has demonstrated the regular occurrence of high Tc (>39 °C) during international rugby sevens in hot/humid conditions; thus, the inclusion of heat acclimation (HA) when preparing for international rugby sevens tournaments in hot conditions is well-indicated. Consideration of the multiple factors influencing (HA) induction and retention, along with practical considerations for integration within an elite training schedule, creates complex questions regarding the optimal design of heat acclimation protocols.

What
Thermoregulatory, cardiovascular, and perceptual responses to heat stress were assessed using a specifically designed heat response test (HRT), intended to replicate the fixed and maximal intensity demands of a rugby sevens warm up and game. In total, four HRT were performed: Pre-HA (before the commencement of HA); Mid-HA (after five days of HA); Post-HA (after 10 days of HA); Decay (16 days after the end of HA). All HRTs and active HA sessions were performed in an environmental chamber maintained at 35 °C, 80% relative humidity (RH), replicating a possible scenario at the Tokyo 2020 Olympic Games. Participants refrained from strenuous exercise in the 24-hr before each HRT, and were instructed to arrive to the HRT in a euhydrated state (not thirsty). All HRT’s were performed at the same time of day (mornings) to account for circadian rhythms. During the HA protocol, all participants undertook a mixture of active (exercise) and passive (hot water immersion; HWI) heat exposures (see below for details). Participants were asked to undertake permissive dehydration (i.e. refrain from drinking if possible) during the HA sessions, as this has previously been shown to enhance responses to HA. During the entire 10-day acclimation process, the total heat exposure for each participant was 7 h 45 min.
Physiological and perceptual measures (as described below) were recorded during seated rest, after each warm-up stage, and after every third interval of the intermittent sprint section.
All participants undertook two active HA sessions per week (four active heat sessions in total), with these sessions being performed within 15 minutes of an on-field training session. The first session (HA1) consisted of ten 2-min intervals performed on a cycle ergometer separated by 2-min rest. During each cycling interval, participants were instructed to rapidly elevate and maintain their heart rate to 85% of their measured maximum. Mean 2-min power output was recorded by a researcher. The second session (HA2) consisted of 10-min fixed intensity cycling (5-min at 2.0 W·kg-1; 5-min at 3.0 W·kg-1); six 500 m rowing intervals (Concept 2 Inc., Morrinsville, VT), at a target pace of 1-min 50-s per 500 m, separated by 2-min rest; followed by a 10-min cycling interval where participants were instructed to keep their heart rate at 85% of their measured maximum, with mean power output being recorded.
All participants undertook four passive HWI sessions (two per week). HWI1 was performed without any prior exercise, as this coincided with a scheduled mid-week non-training day, while HWI2 was performed within 15 min of an on-field training session. All HWI were undertaken in an upright tub for 40 min in 40 °C water. Participants were instructed to stand, immersed to the top of the chest (including arms) for the first 25 min of each exposure, after which time they could elevate to the mammillary line, and bring their arms out of the water.
During all HRT’s, Tc was measured using a rectal thermistor (U thermistor, Grant Instruments Ltd., Cambridge, United Kingdom), self-inserted to a depth of 10 cm beyond the anal sphincter. Tc was recorded at 1-min intervals on a portable data logger (2020 series data logger, Grant Instruments Ltd., Cambridge, United Kingdom) and averaged over each measurement period. Heart rate (HR; Polar H10, Polar Electro Oy, Kempele, Finland) was monitored throughout each HRT as well as during the active HA sessions to prescribe exercise intensity. To estimate sweat loss, towel-dried, nude body mass (NBM) was recorded to 0.1 kg using digital scales (Tanita HD-351, Tanita Health Equipment H.K. Limited) before and immediately after each HRT and each HA session, this value was adjusted for a standardised amount of ingested liquid during the HRT (640 mL).
Rating of perceived exertion (RPE: 6-20 scale), thermal sensation (1-13 point scale), thermal comfort (1-10-point scale), and thirst sensation (Thirst: 1-9 point scale) were collected at the same time points described above. Additionally, RPE, thermal sensation and thermal comfort were collected at the end of each HA session (RPE during active sessions only).

Who Provided
All HRT and HA sessions were undertaken by trained physiologists and strength and conditioning practitioners

How
The intervention was face-to-face, and provided in groups

Where
The intervention was undertaken at the University of Waikato Adams Centre for High Performance, Mount Maunganui, New Zealand. The intervention utilized the environmental chamber and hot water immersion facilities at the centre.

When and How Much
In total, four HRT were performed: Pre-HA (before the commencement of HA); Mid-HA (after five days of HA); Post-HA (after 10 days of HA); Decay (16 days after the end of HA).
All participants undertook two active HA sessions per week and four passive HWI sessions (two per week). During the entire 10-day acclimation process, the total heat exposure for each participant was 7 h 45 min.

Tailoring
The intervention was not planned to be personalised or adapted.

Modifications
The intervention was not modified or adapted.

How Well
The intervention was 100% adhered to and delivered as planned. Attendance records
were used to monitor adherence to the intervention.

Intervention code [1]

Treatment: Other

Comparator / control treatment

No control group

Control group

Uncontrolled

Outcomes

Primary outcome [1]

Core temperature; measured using a rectal thermistor (U thermistor, Grant Instruments Ltd., Cambridge, United Kingdom), self-inserted to a depth of 10 cm beyond the anal sphincter. Tc was recorded at 1-min intervals on a portable data logger (2020 series data logger, Grant Instruments Ltd., Cambridge, United Kingdom) and averaged over each measurement period.

Timepoint [1]