E-Thesis 206 views
A Preliminary Analysis of The Additive Effect of Ischemic Preconditioning on the Physiological Adaptations to Short, Medium and Long-Term Heat Acclimation / JAMES AGGETT
Swansea University Author: JAMES AGGETT
Abstract
Introduction: Exposure to hot environments, in combination with exercise, exacerbates thermal strain, which can result in a loss of performance or adverse health outcomes (Galloway & Maughan, 1997). Heat acclimation (HA), achieved through repeated heat exposure, enhances the body’s ability to di...
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Swansea University, Wales, UK
2025
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| Institution: | Swansea University |
| Degree level: | Master of Research |
| Degree name: | MRes |
| Supervisor: | Waldron, M., and Heffernan, S. |
| URI: | https://cronfa.swan.ac.uk/Record/cronfa69768 |
| Abstract: |
Introduction: Exposure to hot environments, in combination with exercise, exacerbates thermal strain, which can result in a loss of performance or adverse health outcomes (Galloway & Maughan, 1997). Heat acclimation (HA), achieved through repeated heat exposure, enhances the body’s ability to dissipate heat through mechanisms such as increased sweat rate, expanded plasma volume, and lower core temperature thresholds for heat-dissipating responses. These adaptations reduce thermal strain, delay fatigue, and mitigate the risk of heat-related illnesses, making HA crucial for military personnel who endure prolonged physical activity in hot environments (Périard et al., 2015; Sawka et al., 2011). In addition to HA, ischemic preconditioning (IPC), involving repeated short bouts of restricted blood flow, has emerged as a potential additive strategy providing short- and long-term protection to tissues from myocardial and vascular damage caused by ischemia, through acute and systemic vascular adaptations. Collective adaptations from IPC could possibly be advantageous in thermal conditions, aiding convective and evaporative heat loss (Waldron et al., 2020). The aim was to evaluate preliminary data on the time-course of thermo-physiological adaptations between three independent intervention groups: heat acclimation (HA),ischemic-preconditioning combined with heat acclimation (HA+IPC) and a control group (CON). It was hypothesised that both experimental groups (HA and IPC + HA) would improve physiological responses to the heat compared to CON; however, it was considered that the combination of IPC + HA would elicit the greatest physiological adaptations.Methods: Participants (n = 13; M = 9, F = 4) were randomly allocated to a CON group (n = 4; mean ± SD, age 25 ± 5; stature 177.7 ± 3.2 cm; body mass 76.9 ± 8.8 kg), HA group (n = 4; mean ± SD age 22 ± 1 years; stature 179.1 ± 5.0 cm; body mass 76.8 ± 7.1 kg) and IPC + HA group (n = 5; mean ± SD age 26 ± 6 years; stature 175.1 ± 10.4 cm; body mass 73.0 ± 11.6 kg). They completed 17 visits, involving a graded exercise test, 8 heat acclimation sessions, 4 heat stress tests at baseline, day 7, day 13 and day 17 of the protocol.During the intervention visit, IPC + HA group had limbs occluded to individual limb occlusive pressures. The protocol involved 5 min occlusions, followed by 5 min reperfusion, repeated 4 times. The CON and HA groups used the same automatic cuffs but at a lower pressure (20 mmHg). The CON group performed theircycling exercise in controlled conditions (20C, 30-40% relative humidity (RH)). The HA and IPC + HA groups performed cycling exercise in a thermal environment (38C, 40% RH). This study followed a randomised control trial design, comprising three arms (CON, HA, HA + IPC).Results: During the heat stress tests, there were no changes in peak power output, maximal oxygen consumption, mean or peak exercising core (Tcore) and skin temperature (Tskin), whole-body sweat loss (WBSL) and heart rate (HR), WBSL, mean HR and delta Tcore, Tskin, WBSL and HR between IPC + HA, HA and CON groups (p > 0.05). Also, there were no interaction effects for mean exercising, resting, and final Tcore during the heat acclimation sessions (p > 0.05). However, there were group x visit interactions at the back site for sweating entropy (SweatEn) during the fixed-Hprod stage of the heat stress tests (p < 0.05), with both the IPC + HA and HA groups demonstrating lower sweating entropy compared to the CON group.Conclusion: There were no significant changes in key performance and physiological markers, including end-exercise power output, whole-body sweat rate, cardiovascular parameters, core and skin temperature, skin blood perfusion and local sweat rate across groups. However, both IPC + HA and HA significantly lowered SweatEn at the at the back site compared to CON during the final HST, demonstrating improved thermoregulatory stability. |
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| Keywords: |
Thermoregulation, Military, IPC, Exercise, Physiology |
| College: |
Faculty of Science and Engineering |