Differences in the postexercise threshold for cutaneous active vasodilation between men and women

Sex differences in adaptation to intermittent post-exercise sauna bathing in trained middle-distance runners

Background

The purpose of this study was to investigate the effect of sex on the efficacy of intermittent post-exercise sauna bathing to induce heat acclimation and improve markers of temperate exercise performance in trained athletes.

Methods

Twenty-six trained runners (16 female; mean ± SD, age 19 ± 1 years, V̇O_2max F: 52.6 ± 6.9 mL⋅kg⁻¹⋅min⁻¹, M: 64.6 ± 2.4 mL⋅kg⁻¹⋅min⁻¹) performed a running heat tolerance test (30 min, 9 km⋅h⁻¹/2% gradient, 40 °C/40%RH; HTT) and temperate (18 °C) exercise tests (maximal aerobic capacity [V̇O_2max] and lactate profile) pre and post 3 weeks of normal exercise training plus 29 ± 1 min post-exercise sauna bathing (101–108 °C) 3 ± 1 times per week.

Results

Females and males exhibited similar reductions (interactions p > 0.05) in peak rectal temperature (− 0.3 °C; p < 0.001), skin temperature (− 0.9 °C; p < 0.001) and heart rate (− 9 beats·min⁻¹; p = 0.001) during the HTT at post- vs pre-intervention. Only females exhibited an increase in active sweat glands on the forearm (measured via modified iodine technique; F: + 57%, p < 0.001; M: + 1%, p = 0.47). Conversely, only males increased forearm blood flow (measured via venous occlusion plethysmography; F: + 31%, p = 0.61; M: + 123%; p < 0.001). Females and males showed similar (interactions p > 0.05) improvements in V̇O_2max (+ 5%; p = 0.02) and running speed at 4 mmol·L⁻¹ blood lactate concentration (+ 0.4 km·h⁻¹; p = 0.001).

Conclusions

Three weeks of post-exercise sauna bathing effectively induces heat acclimation in females and males, though possibly amid different thermoeffector adaptations. Post-exercise sauna bathing is also an effective ergogenic aid for both sexes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40798-021-00342-6.

Adenosine receptor inhibition attenuates the suppression of postexercise cutaneous blood flow

The time-dependent contributions of active vasodilation (e.g. nitric oxide) and noradrenergic vasoconstriction to the postexercise suppression of cutaneous perfusion despite persistent hyperthermia remain unknown. Moreover, adenosine receptors have been shown to mediate the decrease in cutaneous perfusion following passive heating. We examined the time-dependent modulation of nitric oxide synthase, noradrenergic vasoconstriction and adenosine receptors on postexercise cutaneous perfusion. Eight males performed 15 min of high-intensity (85% VO2 max) cycling followed by 60 min of recovery in temperate ambient conditions (25°C). Four microdialysis probes were inserted into the forearm skin and continuously infused with: (1) lactated Ringer solution (Control); (2) 10 mm N(G)-nitro-l-arginine methyl ester (l-NAME; nitric oxide synthase inhibitor); (3) 10 mm bretylium tosylate (BT; inhibitor of noradrenergic vasoconstriction); or (4) 4 mm theophylline (THEO; adenosine receptor inhibitor). Cutaneous vascular conductance (CVC) was expressed as a percentage of maximum and was calculated as perfusion units (laser Doppler) divided by mean arterial pressure. End-exercise CVC was similar in Control, THEO and BT (P > 0.1), but CVC with l-NAME (39 ± 4%) was lower than Control (59 ± 4%, P < 0.01). At 20 min of recovery, Control CVC (22 ± 3%) returned to baseline levels (19 ± 2%, P = 0.11). Relative to Control, CVC was reduced by l-NAME for the first 10 min of recovery whereas CVC was increased with BT for the first 30 min of recovery (P < 0.03). In contrast, CVC with THEO was elevated throughout the 60 min recovery period (P ≤ 0.01) compared to Control. We show that adenosine receptors appear to have a major role in postexercise cutaneous perfusion whereas nitric oxide synthase and noradrenergic vasoconstriction are involved only earlier during recovery.

Physiological and nutritional aspects of post-exercise recovery: specific recommendations for female athletes

Gender-based differences in the physiological response to exercise have been studied extensively for the last four decades, and yet the study of post-exercise, gender-specific recovery has only been developing in more recent years. This review of the literature aims to present the current state of knowledge in this field, focusing on some of the most pertinent aspects of physiological recovery in female athletes and how metabolic, thermoregulatory, or inflammation and repair processes may differ from those observed in male athletes. Scientific investigations on the effect of gender on substrate utilization during exercise have yielded conflicting results. Factors contributing to the lack of agreement between studies include differences in subject dietary or training status, exercise intensity or duration, as well as the variations in ovarian hormone concentrations between different menstrual cycle phases in female subjects, as all are known to affect substrate metabolism during sub-maximal exercise. If greater fatty acid mobilization occurs in females during prolonged exercise compared with males, the inverse is observed during the recovery phase. This could explain why, despite mobilizing lipids to a greater extent than males during exercise, females lose less fat mass than their male counterparts over the course of a physical training programme. Where nutritional strategies are concerned, no difference appears between males and females in their capacity to replenish glycogen stores; optimal timing for carbohydrate intake does not differ between genders, and athletes must consume carbohydrates as soon as possible after exercise in order to maximize glycogen store repletion. While lipid intake should be limited in the immediate post-exercise period in order to favour carbohydrate and protein intake, in the scope of the athlete's general diet, lipid intake should be maintained at an adequate level (30%). This is particularly important for females specializing in long-duration events. With protein balance, it has been shown that a negative nitrogen balance is more often observed in female athletes than in male athletes. It is therefore especially important to ensure that this remains the case during periods of caloric restriction, especially when working with female athletes showing a tendency to limit their caloric intake on a daily basis. In the post-exercise period, females display lower thermolytic capacities than males. Therefore, the use of cooling recovery methods following exercise, such as cold water immersion or the use of a cooling vest, appear particularly beneficial for female athletes. In addition, a greater decrease in arterial blood pressure is observed after exercise in females than in males. Given that the return to homeostasis after a brief intense exercise appears linked to maintaining good venous return, it is conceivable that female athletes would find a greater advantage to active recovery modes than males. This article reviews some of the major gender differences in the metabolic, inflammatory and thermoregulatory response to exercise and its subsequent recovery. Particular attention is given to the identification of which recovery strategies may be the most pertinent to the design of training programmes for athletic females, in order to optimize the physiological adaptations sought for improving performance and maintaining health.

Calorimetric measurement of postexercise net heat loss and residual body heat storage

PURPOSE

Previous studies have shown a rapid reduction in postexercise local sweating and blood flow despite elevated core temperatures. However, local heat loss responses do not illustrate how much whole-body heat dissipation is reduced, and core temperature measurements do not accurately represent the magnitude of residual body heat storage. Whole-body evaporative (H(E)) and dry (H(D)) heat loss as well as changes in body heat content (DeltaH(b)) were measured using simultaneous direct whole-body and indirect calorimetry.

METHODS

Eight participants cycled for 60 min at an external work rate of 70 W followed by 60 min of recovery in a calorimeter at 30 degrees C and 30% relative humidity. Core temperature was measured in the esophagus (T(es)), rectum (T(re)), and aural canal (T(au)). Regional muscle temperature was measured in the vastus lateralis (T(vl)), triceps brachii (T(tb)), and upper trapezius (T(ut)).

RESULTS

After 60 min of exercise, average DeltaH(b) was +273 +/- 57 kJ, paralleled by increases in T(es), T(re), and T(au) of 0.84 +/- 0.49, 0.67 +/- 0.36, and 0.83 +/- 0.53 degrees C, respectively, and increases in T(vl), T(tb), and T(ut) of 2.43 +/- 0.60, 2.20 +/- 0.64, and 0.80 +/- 0.20 degrees C, respectively. After a 10-min recovery, metabolic heat production returned to pre-exercise levels, and H(E) was only 22.9 +/- 6.9% of the end-exercise value despite elevations in all core temperatures. After a 60-min recovery, DeltaH(b) was +129 +/- 58 kJ paralleled by elevations of T(es) = 0.19 +/- 0.13 degrees C, T(re) = 0.20 +/- 0.03 degrees C, T(au) = 0.18 +/- 0.04 degrees C, Tvl = 1.00 +/- 0.43 degrees C, T(tb) = 0.92 +/- 0.46 degrees C, and T(ut) = 0.31 +/- 0.27 degrees C. Despite this, H(E) returned to preexercise levels. Only minimal changes in H(D) occurred throughout.

CONCLUSION

We confirm a rapid reduction in postexercise whole-body heat dissipation by evaporation despite elevated core temperatures. Consequently, only 53% of the heat stored during 60 min of exercise was dissipated after 60 min of recovery, with the majority of residual heat stored in muscle tissue.

Menstrual cycle and oral contraceptive use do not modify postexercise heat loss responses

It is unknown whether menstrual cycle or oral contraceptive (OC) use influences nonthermal control of postexercise heat loss responses. We evaluated the effect of menstrual cycle and OC use on the activation of heat loss responses during a passive heating protocol performed pre- and postexercise. Women without OC (n = 8) underwent pre- and postexercise passive heating during the early follicular phase (FP) and midluteal phase (LP). Women with OC (n = 8) underwent testing during the active pill consumption (high exogenous hormone phase, HH) and placebo (low exogenous hormone phase, LH) weeks. After a 60-min habituation at 26 degrees C, subjects donned a liquid conditioned suit. Mean skin temperature was clamped at approximately 32.5 degrees C for approximately 15 min and then gradually increased, and the absolute esophageal temperature at which the onset of forearm vasodilation (Th(vd)) and upper back sweating (Th(sw)) were noted. Subjects then cycled for 30 min at 75% Vo(2 peak) followed by a 15-min seated recovery. A second passive heating was then performed to establish postexercise values for Th(vd) and Th(sw). Between 2 and 15 min postexercise, mean arterial pressure (MAP) remained significantly below baseline (P < 0.05) by 10 +/- 1 and 11 +/- 1 mmHg for the FP/LH and LP/HH, respectively. MAP was not different between cycle phases. During LP/HH, Th(vd) was 0.16 +/- 0.24 degrees C greater than FP/LH preexercise (P = 0.020) and 0.15 +/- 0.23 degrees C greater than FP/LH postexercise (P = 0.017). During LP/HH, Th(sw) was 0.17 +/- 0.23 degrees C greater than FP/LH preexercise (P = 0.016) and 0.18 +/- 0.16 degrees C greater than FP/LH postexercise (P = 0.001). Postexercise thresholds were significantly greater (P < or = 0.001) than preexercise during both FP/LH (Th(vd), 0.22 +/- 0.03 degrees C; Th(sw), 0.13 +/- 0.03 degrees C) and LP/HH (Th(vd), 0.21 +/- 0.03 degrees C; Th(sw), 0.14 +/- 0.03 degrees C); however, the effect of exercise was similar between LP/HH and FP/LH. No effect of OC use was observed. We conclude that neither menstrual cycle nor OC use modifies the magnitude of the postexercise elevation in Th(vd) and Th(sw).

Hyperthermia modifies the nonthermal contribution to postexercise heat loss responses

PURPOSE

This study investigated the nonthermoregulatory control of cutaneous vascular conductance (CVC) and sweating during recovery from exercise-induced hyperthermia as well as possible sex-related differences in these responses. Two hypotheses were tested in this study: 1) active and passive recovery would be more effective in attenuating the fall in mean arterial pressure (MAP) than inactive recovery, but CVC and sweat rate responses would be similar between all recovery modes; and 2) the magnitude of the change in postexercise heat loss and hemodynamic responses between recovery modes would be similar between sexes.

METHODS

Nine males and nine females were rendered hyperthermic (esophageal temperature = 39.5 degrees C) by exercise, followed by 60 min of 1) active, 2) inactive, and 3) passive recovery. CVC, sweat rate, and MAP were recorded at baseline, after 2, 5, 12, and 20 min, and at every 10 min until the end of recovery.

RESULTS

MAP was elevated above inactive recovery by 6 +/- 2 and 4 +/- 1 mm Hg for active and passive recovery, respectively (P < 0.001). No differences were observed between modes during the initial 10 min of recovery for CVC and 50 min of recovery for sweat rate. However, relative to inactive recovery CVC and sweat rate were subsequently greater by 16.2 +/- 5.8% of CVCpeak and 0.28 +/- 0.04 mg.min.cm, respectively, during active recovery, and by 11.6 +/- 2.9% of CVCpeak and 0.23 +/- 0.03 mg.min.cm, respectively, during passive recovery.

CONCLUSION

We conclude that in the presence of a greater thermal drive associated with hyperthermia, the influence of nonthermal input on postexercise heat loss responses is still observed. However, thermal control predominates over nonthermal factors in the first 10 min of recovery for CVC and for up to 50 min postexercise for sweating. Sex did not influence the effect of recovery mode on any variable.

Postexercise heat loss and hemodynamic responses during head-down tilt are similar between genders

PURPOSE

We evaluated the hypothesis that during recovery from dynamic exercise in the 15 degrees head-down tilt (HDT) position, the attenuation of the fall in mean arterial pressure (MAP), cutaneous vascular conductance (CVC), and sweat rate, and the augmentation of the rate of esophageal temperature (T(es)) decay relative to the upright seated (URS) posture, would be different between males and females.

METHODS

Fourteen subjects (seven males, seven females) performed two experimental protocols: 1) 15 min of cycle ergometry at 75% VO2peak and then 60 min of recovery in the URS posture; or 2) 15 min of cycle ergometry at 75% VO2peak and then 60 min of recovery in the 15 degrees HDT position. Mean skin temperature, Tes, CVC, sweat rate, cardiac output (CO), stroke volume (SV), heart rate (HR), total peripheral resistance (TPR), and MAP were recorded at baseline; end of exercise; 2 min, 5 min, 8 min, 12 min, 15 min, and 20 min after exercise; and every 5 min until the end of recovery (60 min).

RESULTS

During recovery from exercise, we observed significantly greater values for MAP, CVC, and sweat rate with HDT in comparison with the URS recovery posture (P <or= 0.05). The magnitude of these responses to HDT did not differ between genders, and a significantly lower T(es) was subsequently observed with HDT for the duration of recovery (P <or= 0.05) for both males and females. In the URS posture, females showed a greater decrease of postexercise MAP than did males (P <or= 0.05). At the end of 60 min of recovery, T(es) remained significantly elevated above baseline with the URS recovery posture (P <or= 0.05). With HDT, T(es) returned to baseline after 20 min.

CONCLUSION

HDT attenuates the reductions in MAP, CVC, and sweat rate observed after exercise in a gender-independent manner, and this likely is attributable to a nonthermal baroreceptor influence.

Evidence of a greater onset threshold for sweating in females following intense exercise

We evaluated the hypothesis that females would show a greater postexercise hypotension and concurrently a greater increase in the onset threshold for sweating. Fourteen subjects (7 males and 7 females) of similar age, body composition, and fitness status participated in the study. Esophageal temperature was monitored as an index of core temperature while sweat rate was measured by using a ventilated capsule placed on the upper back. Subjects cycled at either 60% (moderate) or 80% (intense) of peak oxygen consumption (VO2speak) followed by 20-min recovery. Subjects then donned a liquid-conditioned suit used to regulate mean skin temperature. The skin was then heated (approximately 4.3 degrees C.h(-1)) until sweating occurred. Esophageal temperatures were similar to baseline before the start of whole body warming for all conditions. The postexercise threshold values for sweating following moderate and intense exercise were an esophageal temperature increase of 0.10+/-0.02 and 0.22+/-0.04 degrees C, respectively for males, and 0.15+/-0.03 and 0.34+/-0.01 degrees C, respectively for females. All were elevated above baseline resting (P<0.05) and a significant sex-related difference was observed for sweating threshold values following intense exercise (P<0.05). This was paralleled by a greater decrease in mean arterial pressure in females at the end of the 20-min recovery (P<0.05). In conclusion, females demonstrate a greater postexercise onset threshold for sweating, which is paralleled by a greater postexercise hypotensive response following intense exercise.

Disturbance of thermal homeostasis following dynamic exercise

Recovery from dynamic exercise results in significant perturbations of thermoregulatory control. These perturbations evoke a prolonged elevation in core body temperature and a concomitant decrease in sweating, skin blood flow, and skin temperature to pre-exercise baseline values within the early stages of recovery. Cutaneous vasodilation and sweating are critical responses necessary for effective thermoregulation during heat stress in humans. The ability to modulate the rate of heat loss through adjustments in vasomotor and sudomotor activity is a fundamental mechanism of thermoregulatory homeostasis. There is a growing body of evidence in support of a possible relationship between hemodynamic changes postexercise and heat loss responses. Specifically, nonthermoregulatory factors, such as baroreceptors, associated with hemodynamic changes, influence the regulation of core body temperature during exercise recovery. The following review will examine the etiology of the post-exercise disturbance in thermal homeostasis and evaluate possible thermal and nonthermal factors associated with a prolonged hyperthermic state following exercise.

Sex differences in postexercise esophageal and muscle tissue temperature response

Factors associated with blood pressure regulation during recovery from exercise dramatically influence core temperature regulation. However, it is unknown whether sex-related differences in postexercise hemodynamics affect core and muscle temperature response. Sixteen participants (8 males, 8 females) completed an incremental isotonic test on a Kin-Com isokinetic apparatus to determine their activity-specific peak oxygen consumption during bilateral knee extensions (V̇o2sp). On a separate day, participants performed 15 min of isolated bilateral knee extensions at a moderate (60% V̇o2sp) exercise intensity followed by a 90-min recovery. Esophageal temperature (Tes), mean arterial pressure (MAP), muscle temperature at four depths in the active vastus medialis (TVM) and three depths in the inactive triceps brachii (TTB) were measured concurrently with sweat rate and cutaneous vascular conductance (CVC). Relative to the preexercise resting Tes of 36.7°C (SD 0.1), between 10 and 50-min of recovery Tes was 0.19°C (SD 0.02) higher for females than males ( P = 0.037). All measurements of TVM (0.036 > P > 0.014) and TTB (0.048 > P > 0.008) were higher for females during the initial 30 min of recovery by between 0.46°C and 0.64°C for TVM and by between 0.53°C and 0.70°C for TTB. In parallel, females showed a 5 to 7 mmHg greater reduction in MAP during recovery relative to males ( P = 0.002) and a significantly lower CVC ( P = 0.020) and sweat rate ( P = 0.034). Therefore, it is concluded that females demonstrate a greater and more prolonged elevation in postexercise esophageal temperature and active and inactive muscle temperatures, which is paralleled by a greater postexercise hypotensive response.

Thermoregulation: some concepts have changed. Functional architecture of the thermoregulatory system

While summarizing the current understanding of how body temperature (Tb) is regulated, this review discusses the recent progress in the following areas: central and peripheral thermosensitivity and temperature-activated transient receptor potential (TRP) channels; afferent neuronal pathways from peripheral thermosensors; and efferent thermoeffector pathways. It is proposed that activation of temperature-sensitive TRP channels is a mechanism of peripheral thermosensitivity. Special attention is paid to the functional architecture of the thermoregulatory system. The notion that deep Tb is regulated by a unified system with a single controller is rejected. It is proposed that Tb is regulated by independent thermoeffector loops, each having its own afferent and efferent branches. The activity of each thermoeffector is triggered by a unique combination of shell and core Tbs. Temperature-dependent phase transitions in thermosensory neurons cause sequential activation of all neurons of the corresponding thermoeffector loop and eventually a thermoeffector response. No computation of an integrated Tb or its comparison with an obvious or hidden set point of a unified system is necessary. Coordination between thermoeffectors is achieved through their common controlled variable, Tb. The described model incorporates Kobayashi’s views, but Kobayashi’s proposal to eliminate the term sensor is rejected. A case against the term set point is also made. Because this term is historically associated with a unified control system, it is more misleading than informative. The term balance point is proposed to designate the regulated level of Tb and to attract attention to the multiple feedback, feedforward, and open-loop components that contribute to thermal balance.