Individual Variability in the Core Interthreshold Zone as Related to Body Physique, Somatotype, and Physical Constitution

Abstract

For evaluating the effect of body physique, somatotype, and physical constitution on individual variability in the core interthreshold zone (CIZ), data from 22 healthy young Japanese male subjects were examined. The experiment was carried out in a climatic chamber in which air temperature was maintained at 20-24°C. The subjects' body physique and the maximum work load were measured. Somatotype was predicted from the Heath-Carter Somatotype method. In addition, factors reflecting physical constitution, for example, susceptibility to heat and cold, and quality of sleep were obtained by questionnaire. The subjects wore a water-perfused suit which was perfused with water at a temperature of 25°C and at a rate of 600 cc/min, and exercised on an ergometer at 50% of their maximum work rate for 10-15 min until their sweating rate increased. They then remained continuously seated without exercise until shivering increased. Rectal temperature (T re ) and skin temperatures at four sites were monitored by thermistors, and sweating rate was measured at the forehead with a sweat rate monitor. Oxygen uptake was monitored with a gas analyzer. The results showed individual variability in the CIZ. According to the reciprocal crossinhibition (RCI) theory, thermoafferent information from peripheral and core sensors is activated by T re , mean skin temperature (T sk ), and their changes. Since T sk was relatively unchanged, the data were selected to eliminate the influence of the core cooling rate on the sensor-to-effector pathway before RCI, and the relationship between the CIZ and the various factors was then analyzed. The results revealed that susceptibility to heat showed a good correlation with the CIZ, indicating that individual awareness of heat may change the CIZ due to thermoregulatory behavior.

The Physiological Profile of a Multiple Tour de France Winning Cyclist

“…The improved GE and submaximal power outputs in HH conditions appear to support this; however, it should be noted that because both ambient and HH trials were performed on the same day, we were unable to control for circadian rhythm and any associated fluctuations in physiology (41). Despite the higher than anticipated body fat percentage for an elite cyclist, the athlete_s low body mass index (19.4 kgIm j2 ) and ectomorphic somatotype may predispose to maintenance of performance or reduced decrement in performance in the heat (11,18,42). Furthermore, in line with other highly trained athletes, the participant_s sweat rate was relatively high in both ambient and HH conditions, suggesting an efficient thermoregulatory response to exercise (38).…”

Diurnal variation in the core interthreshold zone and its relation to cutaneous sensation threshold zone

“…Kakitsuba et al [4] reported a strong correlation between the CIZ and the temperature difference between T c-init and the core shivering threshold. In other words, the CIZ mainly depends on a decrease in T c from T c-init .…”

“…Because the lighting and season effect to the CIZ was confirmed in the previous study [3], illuminance was carefully controlled to be at 1000 lx, and all experiments were conducted from August to September as described in the experimental protocol of our previous study [4]. …”

“…In one previous study [3], it was found that the CIZ was twofold wider in the summer than in the winter, and also found that the CIZ was a nearly twofold wider range at a luminance of 36 cd/m 2 compared with that observed at 18 cd/m 2 , indicating the possible incorporation of a non-visual pathway into the temperature regulation system. In another previous study [4], it was found that the peripheral interthreshold zone (PIZ) was proportionally correlated with the CIZ. This finding suggested that diurnal variation in the CIZ may be correlated with the cutaneous sensation threshold zone (CSZ), a determinant of the PIZ.…”

Diurnal Variation in the Core Interthreshold Zone in Women and its Sex Difference

“…Since both the T c and mean skin temperature contribute to the control of sweating and shivering, constant is required to be independent of thermal responses due to changes in Although three different experimental methods have been proposed to keep constant 1,2,3 , Kakitsuba et al 4 devised an alternative method using water-perfused suits, following the method proposed by Mekjavic et al 3 , and demonstrated a seasonal change in the CIZ, and light dependence of the CIZ, which indicated the possible incorporation of a non-visual pathway into the human thermoregulation 5 .…”