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Thesis Defence

PhD degree for Coen Bongers

CoenB 29 Jun 2018

Coen Bongers successfully defended his thesis entitled "Thermoregulatory Responses and Fluid Balance Control During Exercise". 

Outline of thesis 

It is well known that exercise leads to an increase in Tc and to disturbances in fluid balance, which can even result in heat-related illnesses and/or severe dehydration. However, the thermoregulatory burden during exercise may increase even further with global warming. Nowadays this is particularly relevant for professional athletes, since future major sport events will be more often organized in hot and humid ambient conditions (i.e. Athletic World Championships of Doha 2019, Olympic Games of Tokyo 2020, FIFA World Cup in Qatar 2022). A better understanding of the thermoregulatory and fluid balance responses to exercise is therefore of great importance, as well as a better insight into interventions to counteract the negative consequences of Tc elevations on exercise performance. Therefore, the general aim of this thesis was to evaluate the thermoregulatory and fluid balance responses to exercise in young and elderly individuals, using State-of-the-Art equipment. Second, we aimed to get more insight into cooling strategies to determine the most beneficial cooling strategy to improve exercise performance in the heat.

Chapter 2-4. An accurate measurement of Tc is of great importance to measure thermoregulatory strain at rest and during exercise. Therefore, we described in Chapter 2 the use of an ingestible telemetric temperature capsule to measure the intestinal temperature as a surrogate marker for Tc. In Chapter 3 we assessed the validity and reliability of a new ingestible telemetric temperature capsule system using an ex-vivo water bath, in which the water temperature was increased step wisely from 33°C to 43°C. Subsequently, in Chapter 4 we compared the validity, reliability and inertia characteristics of four different temperature capsule systems, including the new myTemp system, using an ex-vivo water bath.

Chapter 5-6. The negative impact of a high Tc on exercise performance is already described in previous studies. Interventions to attenuate the increase in Tc could therefore be effective in improving exercise performance in the heat. The use of cooling strategies prior to, during or directly after exercise are proven to be suitable to decrease the Tc. In Chapter 5 we performed a meta-analytical review to examine the effects of cooling prior to or during exercise on exercise performance. Furthermore, we determined the most beneficial timing of cooling and cooling strategy. In Chapter 6 the potential mechanisms for the beneficial effects of cooling on exercise performance were described.

Chapter 7.  The use of cooling during exercise may elongate the effectiveness of the intervention to limit the increase in Tc and therefore enhance exercise performance. Furthermore, using a light-weight cooling vest, which covers a large part of the body, is easily applicable during exercise in lab- and field-based settings and may result in a further increase in exercise performance levels. Therefore, we examined in Chapter 7 the effects of wearing a cooling vest during a 5 km running time trial on exercise performance in moderate ambient conditions.

Chapter 8. Individuals with a spinal cord injury are known to have a reduced afferent input to the thermoregulatory center and an impairment of the efferent system leading to an attenuated sweating response and vasomotor control below the level of the lesion. Spinal cord injured individuals are therefore at greater risk to develop heat-related illnesses. Therefore, the aim of Chapter 8 was to examine the effects of wearing a cooling vest during exercise on Tc response of individuals with a thoracic SCI.

Chapter 9. Advanced age is associated with a negative impact on thermoregulatory and fluid balance responses during exercise. Moreover, elderly have a decreased sensitivity of the thermal receptors, a less effective sweat response, a lower total body water and a decreased thirst sensation. However, it is unknown whether thermoregulation and fluid balance control deteriorates further with aging or plateaus at some point. Therefore, in Chapter 9 we assessed the differences in thermoregulatory and fluid balance responses to prolonged walking exercise in 60- versus 80-year-old participants of the Nijmegen Four Days Marches. 

Chapter 10-11. Exercise and exercise-induced dehydration are known to alter kidney function and stimulate the kidneys to reabsorb water. These renal responses to exercise may lead to acute, but transient, kidney injury. Athletes training programs usually consists of exercise bouts on consecutive days. Therefore, it is relevant to know whether renal function might be affected in a cumulative way. For that reason the purpose of Chapter 10  was to examine the effect of a single versus repetitive bout of endurance exercise on markers for kidney injury. Furthermore, previous studies primarily focus on the effects of exercise-induced dehydration on kidney function and kidney injury. However, the acute effects of exercise, with less dehydration but with ischemic kidney stress, are not studied yet. Therefore, in Chapter 11 we distinguish between the effects of acute and prolonged exercise on kidney function and kidney injury.

Chapter 12 provided a general discussion on the main findings of the present thesis. In this chapter we discussed the relationship between thermoregulation, fluid balance and exercise performance, in which we addressed the impact of cooling and aimed to identify the best practice cooling strategy to improve exercise performance. Furthermore, we speculated about the effects of global warming on thermal strain in healthy individuals and individuals with a compromised thermoregulation.

Click here to access Coens' thesis digitally.




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