Cardiovascular Adaptations Supporting Human Exercise-Heat Acclimation reviewed the examination of cardiovascular adaptations, as well as changes in total body water and plasma volume, in correspondence to human exercise in hot conditions. According to Periard et al. (2016), cardiovascular adaptations during heat acclimation include decreased heart rate, increased stroke volume, better sustained cardiac output and blood pressure, increased myocardial compliance and efficiency, and increased cardioprotection. Repeated exposure to hot conditions also led to the development of phenotypic and physiological adaptations, including improved performance, increased maximal aerobic capacity, enhanced thermal comfort, plasma volume expansion, better maintenance of fluid balance, enhanced sweating and blood flow responses, lowered exercising metabolic rate, and acquired thermal tolerance through heat shock response (Periard et al., 2016). Consistent heat exposure is necessary to maintain these adaptations or they will gradually disappear. During the acclimation process, body water increased about five to seven percent, which was divided into extracellular and intracellular compartments, and plasma volume typically increased between four and 15 percent, but ranged from three to 27 percent, possibly due to an increase in intravascular protein. Benefits to aerobic performance included decreased oxygen uptake, reduction of blood and muscle lactate accumulation, and increased power output. This required a greater reliance on carbohydrates as a fuel source and intake of sufficient fluids to prevent dehydration. The study also recognizes that these beneficial adaptations depend on exercise intensity, duration of exposure, frequency and the total number of exposures, and environmental conditions such as humidity (Periard et al., 2016).Prolonged Self-Paced Exercise in the Heat — Environmental Factors Affecting Performance reviewed the examination of self-paced performance during cycling and running timed trials in hot conditions. Junge et al. (2016) noted a 15 percent reduction of power output during prolonged cycling trials. Running was affected even at low temperatures, therefore, concluding that heat stress impacted self-paced endurance performance. However, both cycling and running exercises were strongly influenced by other environmental factors. In studies where wind speed, humidity, and radiation were controlled and remained constant, allowing elevated air temperature to be the main variable, the occurrence of limited dry heat loss, restricted limit for heat dissipation, elevated skin temperature, increased need for skin perfusion, and cardiovascular restrain restricted exercise intensity and imposed the body’s ability to maintain heat balance. The study also concluded that human performance depended on, not only environmental factors but on participants’ acclimatization status and exercise mode as well (Junge et al., 2016).The Effects of a Systematic Increase in Relative Humidity on Thermoregulatory and Circulatory Responses during Prolonged Running Exercise in the Heat reviewed the examination of thermoregulatory and circulatory responses and performance during five steady-state runs lasting one hour each in hot conditions at 23, 43, 52, 61, and 71 percent humidities. Following exercise, participants’ core and mean skin temperature, cardiac output, heart rate, and stroke volume were recorded. Muhamed et al. (2016) noted significant bodily changes during 61 and 71 percent humidity environments. While there were no differences in cardiac output and whole body sweat loss, there were significant increases in core and mean body temperature and heart rate and a decline in stroke volume. As relative humidity increased, time to exhaustion reduced but and dry heat loss increased, but thermoregulatory and circulatory stress elevated, ultimately limiting performance capacity. Based on their discoveries, the study concluded that performance progression narrows as humidity increases (Muhamed et al., 2016).