Heat production during exercise in pregnancy: discerning the contribution of total body weight.

Studies have reported enhanced thermoregulatory function as pregnancy progresses; however, it is unclear if differences in thermoregulation are attributed to weight gain or other physiological changes. This study aimed to determine if total body weight will influence thermoregulation (heat production (Hprod)), heart rate, and perceptual measurements in response to weight-bearing exercise during early to late pregnancy. A cross-sectional design of healthy pregnant women at different pregnancy time points (early, T1; middle, T2; late, T3) performed a 7-stage weight-bearing incremental exercise protocol. Measurements of Hprod, HR, and RPE were examined. Two experimental groups were studied: (1) weight matched and (2) non-weight matched, in T1, T2, and T3. During exercise, equivalent Hprod at T1 (326 ± 88 kJ), T2 (330 ± 43 kJ), and T3 (352 ± 52 kJ) (p = 0.504); HR (p = 0.830); and RPE (p = 0.195) were observed in the WM group at each time point. In the NWM group, Hprod (from stages 1-6 of the exercise) increased across pregnancy time points, T1 (291 ± 76 kJ) to T2 (347 ± 41 kJ) and T3 (385 ± 47 kJ) (p < 0.001). HR increased from T1 to T3 in the warm-up to stage 6 (p = 0.009). RPE did not change as pregnancy time point progressed (p = 0.309). Total body weight, irrespective of pregnancy time point, modulates Hprod and HR during exercise. Therefore, accounting for total body weight is crucial when comparing thermoregulatory function during exercise across pregnancy.

Heat loss responses at rest and during exercise in pregnancy: A scoping review.

BACKGROUND: The teratogenic risk associated with maternal hyperthermia (i.e., core temperature ≥39.0 °C) has been a crucial motive in understanding thermoregulatory responses in pregnancy. To date, a substantial number of studies have focused on core temperature responses in a wide range of exercise intensities, duration, and ambient temperatures. Fortunately, none have reported core temperatures exceeding 39.0 °C. Nonetheless, there are limited studies that have provided substantial insight into both dry and evaporative heat loss mechanisms involved in facilitating the maintenance of core temperature (≥39.0 °C) during heat stress in pregnant women. The purpose of this scoping review was to summarize the available literature that has assessed heat loss responses in studies of human pregnancy. METHODS: A search strategy was developed combining the terms pregnancy, thermoregulation, and adaptation. A systematic search was performed in the following databases: PubMed, Embase, Scopus, and ProQuest. Studies eligible for inclusion included pregnant women between the ages of 18-40 years old, and at least one measurement of the following: sweating, blood flow, skin temperature, and behavioural responses. Retrieved data were categorized as evaporative (sweating), dry or behavioural heat loss responses and summarized narratively. RESULTS: Thirty-three studies were included in this review (twenty-nine measured physiological responses and four measured behavioural responses). Studies suggest that during exercise, evaporative (sweating) and dry (skin blood flow and temperature) heat loss responses increase from early to late pregnancy in addition to greater cardiac output, blood volume and reduced vascular resistance. Behavioural practices related to heat loss responses are also influenced by cultural/religious expectations, personal preferences and sociodemographics. CONCLUSION: The findings from this review suggest that pregnancy modifies evaporative (sweating), dry and behavioural heat loss. However, future studies have an opportunity to compare heat loss measurements accounting for gestational weight gain and thermal sensation/comfort scale to associate physiological responses with perceptual responses across pregnancy.

Central and peripheral factors in thermal, neuromuscular, and perceptual adaptation of the hand to repeated cold exposures.

We investigated the role of central and peripheral factors in repeated cold exposure of the hand and their effects on temperature response, neuromuscular function, and subjective thermal sensation. Eleven subjects immersed their left hand repeatedly in 8 degrees C cold water for 30 min, 5 d/week, for 2 weeks. Before and following the 2 weeks of exposure, neuromuscular function, blood markers, thermal sensation, and temperature responses of both acclimated (left) and control (right) hands were tested. Minimum index finger temperature pre-acclimation was 10.9 +/- 3.4 degrees C and 10.0 +/- 2.0 degrees C in the left and right hand, respectively, and did not change significantly post-acclimation (left, 12.8 +/- 4.2 degrees C; right, 10.2 +/- 1.1 degrees C). Neuromuscular function was impaired with cooling, but this was significantly different neither between the hands nor over time. Central factors, measured by catecholamines and changes in temperature and cardiovascular response over time, did not change and there were no differences in responses between the exposed and non-exposed hand over time (peripheral adaptation) nor were there any differences in local factors endothelial-1 and nitric oxide. Subjective thermal comfort was improved and the discrepancy that was found between the change in actual and perceived temperature may increase the risk of cold injury in partially acclimatized individuals, owing to an adjustment in behavioural thermoregulation.

Local cold acclimation during exercise and its effect on neuromuscular function of the hand.

Most acclimation research is performed on resting individuals, whereas in real life, cold exposure is often accompanied by physical activity. We examined the effects of 2 weeks of repeated cold exposure of the hand with or without an elevated core temperature from exercise on neuromuscular function of the first dorsal interosseus (FDI) muscle and manual performance of the hand. The experimental group (4 female, 6 male; age, 25.1 +/- 6.9 y) cooled their hands in 8 degrees C water for 30 min daily while cycling (50% of heart rate reserve); the control group (4 female, 4 male; age, 25.1 +/- 5.7 y) remained still. Manual function testing consisted of tactile sensitivity, grip strength, manual dexterity, and evoked twitch force in a custom-made myograph. Thermal sensation, skin temperature of index finger (Tif) and hand (Tfdi), as well as rectal temperature (Tre), were recorded daily. Tre increased significantly during bicycling, by 0.6 +/- 0.2 degrees C. Minimal Tif and Tfdi of the groups combined increased significantly during exposure days from 8.7 +/- 0.7 degrees C and 12.4 +/- 2.8 degrees C to 10.1 +/- 1.3 degrees C and 15.0 +/- 3.0 degrees C, respectively (p=0.04), with no significant difference between groups. Thermal ratings improved significantly on exposure days. Manual function was impaired with cooling, but with no significant difference between groups or across time. Deterioration of twitch characteristics with cooling did not change with repeated cold exposure. Although the increasing core temperature during cold water immersion changed the acute temperature response and thermal ratings, it had no effect on local cold acclimation or manual function.

Effect of cold-induced vasodilatation in the index finger on temperature and contractile characteristics of the first dorsal interosseus muscle during cold-water immersion.

We investigated whether cyclic elevations in index finger temperature (cold-induced vasodilatation, CIVD) during prolonged cold exposure correlated with hand temperature and neuromuscular function. Evoked twitch force of the first dorsal interosseus (FDI) muscle was measured every minute in eight males and four females [age 25.4 (5.7) years, mean (SD)] during cooling of the hand for 30 min in 9 degrees C water, and in thermoneutral 30 degrees C water. During cooling, index finger temperature increased from 9.4 (0.9) degrees C at the nadir to 13.3 (2.4) degrees C (P<0.01) at the apex of the CIVD. However, the minimum skin temperature above the FDI muscle was 14.2 (2.1) degrees C, with no CIVD detected in any of the subjects. Peak twitch force was 2.5 (0.7) N at the nadir of the finger CIVD and 2.0 (0.8) N at the apex (P=0.07), time-to-peak increased from 189 (18) ms to 227 (26) ms (P<0.01), and half relaxation time increased from 135 (14) ms to 183 (32) ms (P<0.01). We conclude that CIVD is a local phenomenon isolated to the fingers, and that it does not have beneficial effects on either temperature or neuromuscular function of the FDI muscle during cold exposure.

Temperature effects on the contractile characteristics and sub-maximal voluntary isometric force production of the first dorsal interosseus muscle.

Cooling of a muscle has a detrimental effect on its force, power and contraction velocity, but may improve force control during precision movements by reducing physiological tremor. We investigated if the contractile characteristics of the first dorsal interosseus muscle (FDI) were linked to voluntary force control in warm and hypothermic conditions. Evoked peak twitch force, force at repetitive stimulation of 10 and 20 Hz, and submaximal force control at 25 and 50% maximal voluntary contraction (MVC) of the FDI were measured with cooled [mean (SD); 17.7 (1.3) degrees C] and warm [27.9 (2.3) degrees C] local skin temperatures in six males and four females. With evoked twitches, the time to peak tension was increased after cooling from 161 (38) ms to 219 (34) ms ( P=0.001) and half-relaxation time increased from 94 (24) ms to 157 (46) ms ( P=0.013). Peak force evoked from the repetitive stimulation contraction (10 Hz) increased significantly after cooling from 13.1 (10.2) N to 19.9 (12.1) N ( P=0.026). The coefficient of variation (CV)-representative of the degree of fusion-for evoked repetitive stimulation force (10 Hz) was significantly higher in the warm [3.6 (2.7)%] versus hypothermic condition [2.2 (3.6)%] ( P<0.05). At 25% and 50% MVC, there were no differences in the CV between warm and hypothermic conditions. FDI contractile characteristics change with local cooling, but have little effect upon voluntary submaximal isometric force control. Results are given as mean (SD).