Acute effects of a dopamine/norepinephrine reuptake inhibitor on neuromuscular performance following self-paced exercise in cool and hot environments

Dopamine/norepinephrine (DA/NE) reuptake inhibitors have been used to manipulate the central mechanisms affecting arousal and motivation during exercise. Eight healthy, physically active males performed 30 min fixed-intensity cycling at 50% W_max followed by 30 min of self paced time trial (TT) with each section interspersed with a 30 s maximal sprint at 9, 19 and 29 min. The DA/NE re-uptake inhibitor administered was bupropion (BUP) versus a placebo (PLA) in either warm (32 °C, BUP32 or PLA32) or moderate (20 °C; BUP20, PLA20) ambient conditions. Core and skin temperature, heart rate and perceptual responses, neuromuscular and hormonal measures were assessed at multiple times throughout the trials and post exercise. Time trial performance remained unchanged across conditions (12.7–13.1 km) although core temperature was elevated in the fixed intensity section of the trials for BUP32 and BUP20 but continued to rise only in BUP32 during the time trial reaching 38.6 °C (P<0.05). NE increased in all conditions from pre-exercise with BUP32 values peaking at the end of TT to 1245.3±203.1 pg/mL (P<0.05) compared to the other conditions. Neuromuscular responses were similar among conditions although peak force was significantly reduced from pre (262±31 N) to post (202±31 N, P<0.05) exercise along with contraction duration (22%, P<0.05) in BUP20. We conclude that DA/NE re-uptake inhibitors influenced thermoregulation in the heat but not exercise performance. DA/NE re-uptake inhibitors are likely to act centrally to override the inhibitory signals for the cessation of exercise with these drugs acting peripherally to reduce the twitch characteristics of skeletal muscle in cooler conditions.     

Effect of the timing of ice slurry ingestion for precooling on endurance exercise capacity in a warm environment

It has been demonstrated that precooling with ice slurry ingestion enhances endurance exercise capacity in the heat. However, no studies have yet evaluated the optimal timing of ice slurry ingestion for precooling. This study aimed to investigate the effects of varying the timing of ice slurry ingestion for precooling on endurance exercise capacity in a warm environment. Ten active male participants completed 3 experimental cycling trials to exhaustion at 55% peak power output (PPO) after 15 min of warm-up at 30% PPO at 30 °C and 80% relative humidity. Three experimental conditions were set: no ice slurry ingestion (CON), pre-warm-up ice slurry ingestion (−1 °C; 7.5 g kg⁻¹) (PRE), and post-warm-up ice slurry ingestion (POST). Rectal and mean skin temperatures at the beginning of exercise in the POST condition (37.1±0.2 °C, 33.8±0.9 °C, respectively) were lower than those in the CON (37.5±0.3 °C; P<0.001, 34.8±0.8 °C; P<0.01, respectively) and PRE (37.4±0.2 °C; P<0.01, 34.6±0.7 °C; P<0.01, respectively) conditions. These reductions increased heat storage capacity and resulted in improved exercise capacity in the POST condition (60.2±8.7 min) compared to that in the CON (52.0±11.9 min; effect size [ES]=0.78) and PRE (56.9±10.4 min; ES=0.34) conditions. Ice slurry ingestion after warm-up effectively reduced both rectal and skin temperatures and increased cycling time to exhaustion in a warm environment. Timing ice slurry ingestion to occur after warm-up may be effective for precooling in a warm environment.     

Individualising the exposure of −110 °C whole body cryotherapy: The effects of sex and body composition

The purpose of this study was to investigate the effects of whole body cryotherapy (WBC) on a range of thermoregulatory measures. We also sought to examine the influence of sex and body composition. A convenience sample of 18 healthy participants (10 males and 8 females) (27±6 yr) volunteered for this study. Temperature (core, tympanic, skin and mean body), heart rate, blood pressure, and thermal comfort and sensation were recorded pre- and post- (immediately and every 5 min until 35 min post) exposure to a single bout of WBC (30 s at −60 °C, 150 s at 110 °C). Anthropometric data (height, weight, body surface area, body mass index, fat mass and fat free mass) were also recorded. No significant differences in temperature (core, tympanic, skin and mean body), heart rate, blood pressure, or thermal comfort / sensation were observed between male and females at baseline. Immediately post WBC mean body (male:31.9±0.8 °C; female:31.0±0.9 °C; ∆ mean body temperature:0.9±0.1 °C; P≤0.05, d=0.64) and mean skin (male:22.1±2.2 °C; female:19.6±2.8 °C; ∆ mean skin temperature:−2.5±0.6 °C; d=0.99, P≤0.05) temperature was significantly different between sexes. Sex differences were also observed in regional skin temperature (male thigh, 20.8±1.1 °C; female thigh, 16.7±1.1 °C, ∆ mean thigh skin temperature:−4.1 °C; d=3.72; male calf, 20.5±1.1 °C; female calf, 18.2±1 °C, ∆ mean calf skin temperature:−2.3±0.1 °C; d=3.61; male arm, 21.7±1 °C; female arm, 19±0.4 °C, ∆ mean arm skin temperature: −2.7±0.3 °C; d=3.54; P≤0.05). Mean arterial pressure was significantly different over time (P≤0.001) and between sexes (male 0 mins:94±10 mmHg; female 0 mins:85±7 mmHg; male 35 mins:88±7 mmHg; female 35 mins:80±6 mmHg; P≤0.05). Combined data set indicated a strong negative relationship between skin temperature and body fat percentage 35 min’ post WBC (r=−0.749, P≤0.001) and for core temperature and body mass index in males only (r=0.726, P≤0.05) immediately after WBC. There were no significant differences between sexes in any other variables (heart rate, tympanic and perceptual variables). We observed sex differences in mean skin and mean body temperature following exposure to whole body cryotherapy. In an attempt to optimise treatment, these differences should be taken into account if whole body cryotherapy is prescribed.     

Influence of temperature and exercise on growth performance,muscle, and adipose tissue in pacus (Piaractus mesopotamicus)

The aim of this study was to evaluate the effects of temperature and swimming exercise on fish growth in pacus (Piaractus mesopotamicus). Pacus weighing 0.9 – 1.9 g and 2.7 – 4.2 cm in standard length were cultivated at an initial density of 120 fish m⁻³ in 3 recirculation systems containing 6 water tanks at a volume of 0.5 m³ each at temperatures of 24, 28 and 32 °C. At each temperature, three tanks were modified to generate exercise activity in the specimens and force the fish to swim under a current speed of 27.5 cm s⁻¹. At the end of the experiment, the following metrics were evaluated: fish performance, morphometry (length, width, height and perimeter in different body positions), and the diameter and density of muscle and subcutaneous ventral adipose tissues. At 28 °C, pacus were both heavier and had greater weight gain after 240 days of cultivation. Additionally, exercise improved the feed conversion. An increase of 4 °C (30 °C) did not provide any improvement in the performance of the fish. However, swimming exercise improved the performance of pacus, providing increases of 38% and a 15% improvement in feed conversion. Both temperature and exercise influenced the body morphology (especially in the caudal region) and the cellularity of white and red muscle fibers and adipocytes.     

A reduced core to skin temperature gradient,not a critical core temperature,affects aerobic capacity in the heat

The purpose of this study was to determine the impact of the core to skin temperature gradient during incremental running to volitional fatigue across varying environmental conditions. A secondary aim was to determine if a “critical” core temperature would dictate volitional fatigue during running in the heat. 60 participants (n=49 male, n=11 female; 24±5 yrs, 177±11 cm, 75±13 kg) completed the study. Participants were uniformly stratified into a specific exercise temperature group (18 °C, 26 °C, 34 °C, or 42 °C) based on a 3-mile run performance. Participants were equipped with core and chest skin temperature sensors and a heart rate monitor, entered an environmental chamber (18 °C, 26 °C, 34 °C, or 42 °C), and rested in the seated position for 10 min before performing a walk/run to volitional exhaustion. Initial treadmill speed was 3.2 km h⁻¹ with a 0% grade. Every 3 min, starting with speed, speed and grade increased in an alternating pattern (speed increased by 0.805 km h⁻¹, grade increased by 0.5%). Time to volitional fatigue was longer for the 18 °C and 26 °C group compared to the 42 °C group, (58.1±9.3 and 62.6±6.5 min vs. 51.3±8.3 min, respectively, p<0.05). At the half-way point and finish, the core to skin gradient for the 18 °C and 26 °C groups was larger compared to 42 °C group (halfway: 2.6±0.7 and 2.0±0.6 vs. 1.3±0.5 for the 18 °C, 26 °C and 42 °C groups, respectively; finish: 3.3±0.7 and 3.5±1.1 vs. 2.1±0.9 for the 26 °C, 34 °C, and 42 °C groups, respectively, p<0.05). Sweat rate was lower in the 18 °C group compared to the 26 °C, 34 °C, and 42 °C groups, 3.6±1.3 vs. 7.2±3.0, 7.1±2.0, and 7.6±1.7 g m⁻² min⁻¹, respectively, p<0.05. There were no group differences in core temperature and heart rate response during the exercise trials. The current data demonstrate a 13% and 22% longer run time to exhaustion for the 18 °C and 26 °C group, respectively, compared to the 42 °C group despite no differences in beginning and ending core temperatures or baseline 3-mile run time. This capacity difference appears to result from a magnified core to skin gradient via an environmental temperature advantageous to convective heat loss, and in part from an increased sweat rate.     

Repeatability of a running heat tolerance test

At present there is no standardised heat tolerance test (HTT) procedure adopting a running mode of exercise. Current HTTs may misdiagnose a runner's susceptibility to a hyperthermic state due to differences in exercise intensity. The current study aimed to establish the repeatability of a practical running test to evaluate individual's ability to tolerate exercise heat stress. Sixteen (8M, 8F) participants performed the running HTT (RHTT) (30 min, 9 km h⁻¹, 2% elevation) on two separate occasions in a hot environment (40 °C and 40% relative humidity). There were no differences in peak rectal temperature (RHTT1: 38.82±0.47 °C, RHTT2: 38.86±0.49 °C, Intra-class correlation coefficient (ICC)=0.93, typical error of measure (TEM)=0.13 °C), peak skin temperature (RHTT1: 38.12±0.45, RHTT2: 38.11±0.45 °C, ICC=0.79, TEM=0.30 °C), peak heart rate (RHTT1: 182±15 beats min⁻¹, RHTT2: 183±15 beats min⁻¹, ICC=0.99, TEM=2 beats min⁻¹), nor sweat rate (1721±675 g h⁻¹, 1716±745 g h⁻¹, ICC=0.95, TEM=162 g h⁻¹) between RHTT1 and RHTT2 (p>0.05). Results demonstrate good agreement, strong correlations and small differences between repeated trials, and the TEM values suggest low within-participant variability. The RHTT was effective in differentiating between individuals physiological responses; supporting a heat tolerance continuum. The findings suggest the RHTT is a repeatable measure of physiological strain in the heat and may be used to assess the effectiveness of acute and chronic heat alleviating procedures.     

Conventional and novel body temperature measurement during rest and exercise induced hyperthermia

Despite technological advances in thermal sensory equipment, few core temperature (T_CORE) measurement techniques have met the established validity criteria in exercise science. Additionally, there is debate as to what method serves as the most practically viable, yet upholds the proposed measurement accuracy. This study assessed the accuracy of current and novel T_CORE measurement techniques in comparison to rectal temperature (T_REC) as a reference standard. Fifteen well-trained subjects (11 male, 4 female) completed 60 min of exercise at an intensity equating to the lactate threshold; measured via a discontinuous exercise test. T_REC was significantly elevated from resting values (37.2±0.3 °C) at the end of moderate intensity exercise (39.6±0.04 °C; P=0.001). Intestinal telemetric pill (T_PILL) temperature and temporal artery temperature (T_TEM) did not differ significantly from T_REC at rest or during exercise (P>0.05). However, aural canal temperature (T_AUR) and thermal imaging temperature (T_IMA) were both significantly lower than T_REC (P<0.05). Bland Altman analysis revealed only T_PILL was within acceptable limits of agreement (mean bias; 0.04 °C), while T_TEM, T_AUR and T_IMA demonstrated mean bias values outside of the acceptable range (>0.27 °C). Against T_REC, these results support the use of T_PILL over all other techniques as a valid measure of T_CORE at rest and during exercise induced hyperthermia. Novel findings illustrate that T_IMA (when measured at the inner eye canthus) shows poor agreement to T_REC during rest and exercise, which is similar to other ‘surface’ measures.     

Measuring core body temperature with a non-invasive sensor

In various occupations, workers may be exposed to extreme environmental conditions and physical activities. Under these conditions the ability to follow the workers' body temperature may protect them from overheating that may lead to heat related injuries. The "Dräger" Double Sensor (DS) is a novel device for assessing body-core temperature (T_c). The purpose of this study was to evaluate the accuracy of the DS in measuring T_c under heat stress. Seventeen male participants performed a three stage protocol: 30 min rest in a thermal comfort environment (20–22 °C, 50% relative humidity), followed by an exposure to a hot environment of 40 °C, 40% relative humidity −30 min at rest and 60 min of exercise (walking on a treadmill at 5 km/h and 2% elevation). Simultaneously temperatures measured by the DS (T_DS) and by rectal temperature (T_re) (YSI-401 thermistor) were recorded and then compared. During the three stages of the study the average temperature obtained by the DS was within±0.3 °C of rectal measurement. The correlation between T_DS and T_re was significantly better during the heat exposures phases than during resting under comfort conditions. These preliminary results are promising for potential use of the DS by workers under field conditions and especially under environmental heat stress or when dressed in protective garments. For this goal, further investigations are required to validate the accuracy of the DS under various levels of heat stress, clothing and working levels.     

Thermoregulatory responses of Holstein cows exposed to experimentally induced heat stress

Heat stress (HS) adversely influences productivity and welfare of dairy cattle. We hypothesized that the thermoregulatory mechanisms vary depending on the exposure time to HS, with a cumulative effect on the adaptive responses and thermal strain of the cow. To identify the effect of HS on adaptive thermoregulatory mechanisms and predictors of caloric balance, Holstein cows were housed in climate chambers and randomly distributed into thermoneutral (TN; n=12) or HS (n=12) treatments for 16 days. Vaginal temperature (VT), rectal temperature (Tre), respiratory rate (RR), heart rate (HR), and dry matter intake (DMI) were measured. The temperature and humidity under TN were 25.9±0.2 °C and 73.0±0.8%, respectively, and under HS were 36.3±0.3 °C and 60.9±0.9%, respectively. The RR of the HS cows increased immediately after exposure to heat and was higher (76.02±1.70bpm, p<0.001) than in the TN (39.70±0.71bpm). An increase in Tre (39.87±0.07 °C in the HS vs. 38.56±0.03 °C in the TN, p<0.001) and in VT (39.82±0.10 °C in the HS vs. 38.26±0.03 °C in the TN, p<0.001) followed the increase in RR. A decrease (p<0.05) in HR occurred in the HS (62.13±0.99bpm) compared with the TN (66.23±0.79bpm); however, the magnitude of the differences was not the same over time. The DMI was lower in HS cows from the third day (8.27±0.33 kg d⁻¹ in the HS vs. 14.03±0.29 kg d⁻¹ in the TN, p<0.001), and the reduction of DMI was strongly affected (r=−0.65) by changes in the temperature humidity index. The effect of environmental variables from the previous day on physiological parameters and DMI was more important than the immediate effect, and ambient temperature represented the most determinant factor for heat exchange. The difference in the responses to acute and chronic exposure to HS suggests an adaptive response. Thus, intense thermal stress strongly influence thermoregulatory mechanisms and the acclimation process depend critically on heat exposure time.     

Development response of Spodoptera exigua to eight constant temperatures: Linear and nonlinear modeling

Temperature-dependent development of Spodoptera exigua (Hübner) were evaluated at eight constant temperatures of 12, 15, 20, 25, 30, 33, 34 and 36 °C with a variation of 0.5 °C on sugar beet leaves. No development occurred at 12 °C and 36 °C. Total developmental time varied from 120.50 days at 15 °C to 14.50 days at 33 °C. As temperature increased from 15 °C to 33 °C, developmental rate (1/developmental time) of S. exigua increased but declined at 34 °C. The lower temperature threshold (T_min) was estimated to be 12.98 °C and 12.45 °C, and the thermal constant (K) was 294.99 DD and 311.76 DD, using the traditional and Ikemoto–Takai linear models, respectively. The slopes of the Ikemoto–Takai linear model for different immature stages were different, violating the assumption of rate isomorphy. Data were fitted to three nonlinear models to predict the developmental rate and estimate the critical temperatures. The T_min values estimated by Lactin-2 (12.90 °C) and SSI (13.35 °C) were higher than the value estimated by Briere-2 (8.67 °C). The estimated fastest development temperatures (T_fast) by the Briere-2, Lactin-2 and SSI models for overall immature stages development of S. exigua were 33.4 °C, 33.9 °C and 32.4 °C, respectively. The intrinsic optimum temperature (T_Φ) estimated from the SSI model was 28.5 °C, in which the probability of enzyme being in its native state is maximal. The upper temperature threshold (T_max) values estimated by these three nonlinear models varied from 34.00 °C to 34.69 °C. These findings on thermal requirements can be used to predict the occurrence, number of generations and population dynamics of S. exigua.     

Temperature modulates hepatic carbohydrate metabolic enzyme activity and gene expression in juvenile GIFT tilapia (Oreochromis niloticus) fed a carbohydrate-enriched diet

The effects of rearing temperature on hepatic glucokinase (GK), glucose-6-phosphatase (G6Pase) and Glucose-6-phosphate dehydrogenase (G6PD) activity and gene expression were studied in GIFT (genetically improved farmed tilapia) tilapia fed a high carbohydrate diet containing 28% crude protein, 5% crude lipid and 40% wheat starch. Triplicate groups of fish (11.28 g initial body weight) were fed the diet for 45 days at 22 °C, 28 °C or 34 °C. At the end of the trial, final body weight of juvenile at 28 °C (59.12 g) was higher than that of the fish reared at 22 °C (27.13 g) and 34 °C (43.17 g). Feed intake, feed efficiency and protein efficiency ratio were also better at 28 °C. Liver glycogen levels were higher at 28 °C, while plasma glucose levels were higher in the 22 °C group. Significant (P<0.05) effects of water temperature on enzymes activities and gene expression were observed. Hepatic GK activity and mRNA level were higher at 28 °C than at 34 °C. Higher G6Pase and G6PD activity and gene expression were observed at 22 °C. Overall, the data show that juveniles reared at 28 °C exhibited enhanced liver glycolytic capacity. In contrast, hepatic gluconeogenesis and lipogenesis were increased by low temperature (22 °C).     

Responses in acral and non-acral skin vasomotion and temperature during lowering of ambient temperature

Arteriovenous anastomoses (AVA) in acral skin (palms and soles) have a huge capacity to shunt blood directly from the arteries to the superficial venous plexus of the extremities. We hypothesized that acral skin, which supplies blood to the superficial venous plexus, has a stronger influence on blood flow adjustments during cooling in thermoneutral subjects than does non-acral skin. Thirteen healthy subjects were exposed to stepwise cooling from 32 °C to 25 °C and 17 °C in a climate chamber. Laser Doppler flux and skin temperature were measured simultaneously from the left and right third finger pulp and bilateral upper arm skin. Coherence and correlation analyses were performed of short-term fluctuations at each temperature interval. The flux from finger pulps showed the synchronous spontaneous fluctuations characteristic of skin areas containing AVAs. Fluctuation frequency, amplitude and synchronicity were all higher at 25 °C than at 32 °C and 17 °C (p<0.02). Bilateral flux from the upper arm skin showed an irregular, asynchronous vasomotor pattern with small amplitudes which were independent of ambient temperature. At 32 °C, ipsilateral median flux values from the right arm (95% confidence intervals) were 492 arbitrary units (au) (417, 537) in finger pulp and 43 au (35, 60) in upper arm skin. Flux values gradually decreased in finger pulp to 246 au (109, 363) at 25 °C, before an abrupt fall occurred at a median room temperature of 24 °C, resulting in a flux value of 79 au (31, 116) at 17 °C. In the upper arm skin a gradual fall throughout the cooling period to 21 au (13, 27) at 17 °C was observed. The fact that the response of blood flow to ambient cooling is stronger in acral skin than in non-acral skin suggests that AVAs have a greater capacity to adjust blood flow in thermoneutral zone than arterioles in non-acral skin.     

Body temperature,thermoregulatory behaviour and pelt characteristics of three colour morphs of springbok (Antidorcas marsupialis)

Using intra-abdominal miniature data loggers, we measured core body temperature in female springbok (Antidorcas marsupialis) of three colour morphs (black, normal and white), free-living in the Karoo, South Africa, for one year. During winter, white springbok displayed lower daily minimum body temperatures (37.4 ± 0.5 °C), than both black (38.1 ± 0.3 °C) and normal (38.0 ± 0.6 °C) springbok. During spring, black springbok displayed higher daily maximum body temperatures (40.7 ± 0.1 °C) than both white (40.2 ± 0.2 °C) and normal (40.2 ± 0.2 °C) springbok. These high maximum body temperatures were associated with larger daily amplitudes of nychthemeral rhythm of body temperature (2.0 ± 0.2 °C), than that of white (1.6 ± 0.1 °C) and normal (1.7 ± 0.2 °C) springbok. Biophysical properties of sample springbok pelts were consistent with these patterns, as the black springbok pelt showed lower reflectance in the visible spectral range, and higher heat load from simulated solar radiation, than did the pelts of the other two springbok. Black springbok had lower diurnal activity in winter, consistent with them having to forage less because their metabolic cost of homeothermy was lower, but were disadvantaged in hot periods. White springbok, by contrast, were more protected from solar heat load, but potentially less able to meet the energy cost of homeothermy in winter. Thus energy considerations may underlie the rarity of the springbok colour morphs.     

Hybrid cooling vest for cooling between exercise bouts in the heat: Effects and practical considerations

While continuous cooling strategies may induce some ergonomic problems to occupational workers, cooling between work bouts may be an alternative for cooling them down in hot environments. The purpose of this study was to assess the effects of wearing a newly designed hybrid cooling vest (HCV) between two bouts of exercise. Inside a climatic chamber set at an air temperature of 37 °C and a relative humidity of 60%, twelve male participants underwent two bouts of intermittent exercise interspersed with a 30 min between-bout recovery session, during which HCV or a passive rest without any cooling (PAS) was administered. The results indicated that thermoregulatory, physiological, and perceptual strains were significantly lower in HCV than those in PAS during the recovery session (p≤0.022), which were accompanied with a large effect of cooling (Cohen's d=0.84–2.11). For the second exercise bout, the exercise time following HCV (22.13±12.27 min) was significantly longer than that following PAS (11.04±3.40 min, p=0.005, d=1.23) During this period, core temperature T_c was significantly lower by 0.14±0.0.15 °C in HCV than that in PAS. The heart rate drift over time was declined by 2±2 bpm min⁻¹ (p=0.001, d=1.00) and the rise in physiological strain index was reduced by 0.11±0.12 unit min⁻¹ (p=0.010, d=0.96) following the use of HCV. These findings suggested that using HCV could accelerate between-bout recovery and improve subsequent exercise performance by the enlarged body core temperature margin and blunted cardiovascular drift.     

Passive heat loading links lipolysis and regulation of fibroblast growth factor-21 in humans

There is relativley little information on the serum biomarkers of heat stress. Therefore, the goal of this study was to verify the effect of passive heat loading (PHL) on the expression of fibroblast growth factor-21 (FGF21) and free fatty acids (FFAs). Four PHL protocols based on intensity (39 °C vs. 43 °C, leg immersion, 30 min) and type (leg vs. half immersion, 42 °C, 30 min) were used. Each protocol was applied on a 2 day cycle to 12 healthy adult males (age, 22.4±2.9 years; height, 174.1±4.6 cm; weight, 71.3±5.6 kg; body mass index, 23.1±3.0). The subjects were categorized into two groups according to the study design (randomized, with a parallel trial). Body temperature, FGF21 and FFAs were determined prior to PHL, immediately and 60 min after PHL. Body temperature was significant higher (43 °C) than the 39 °C measured under identical PHL type (leg immersion). PHL was effective for the expression of FGF21 and for lipolysis. The quantitative levels of FGF21 and FFA increased with increasing temperature (39 °C<42 °C<43 °C). A significant difference in the quantitative levels of FGF21 and FFAs was also evident based on the type of PHL (leg<half immersion) even when PHL was applied at the same temperature (42 °C). In conclusion, PHL was effective for expressing FGF21 and for lipolysis. Therefore, PHL may be expected to help in the reduction of body fat. Additionally, when the identical type (leg immersion) of PHL is applied, a loading temperature of 43 °C is more effective for expressing FGF21 and for lipolysis than temperatures of 39 °C and 42 °C, and half immersion is more effective than leg immersion at 42 °C.     

Supplemental intermittent-day heat training and the lactate threshold

Heat acclimation over consecutive days has been shown to improve aerobic-based performance. Recently, it has been suggested that heat training can improve performance in a temperate environment. However, due to the multifactorial training demands of athletes, consecutive-day heat training may not be suitable. The current study aimed to investigate the effect of brief (8×30 min) intermittent (every 3–4 days) supplemental heat training on the second lactate threshold point (LT₂) in temperate and hot conditions. 21 participants undertook eight intermittent-day mixed-intensity treadmill exercise training sessions in hot (30 °C; 50% relative humidity [RH]) or temperate (18 °C; 30% RH) conditions. A pre- and post-incremental exercise test occurred in temperate (18 °C; 30% RH) and hot conditions (30 °C; 50% RH) to determine the change in LT₂. The heat training protocol did not improve LT₂ in temperate (Effect Size [ES]±90 confidence interval=0.10±0.16) or hot (ES=0.26±0.26) conditions. The primary finding was that although the intervention group had a change greater than the SWC, no statistically significant improvements were observed following an intermittent eight day supplemental heat training protocol comparable to a control group training only in temperate conditions. This is likely due to the brief length of each heat training session and/or the long duration between each heat exposure.     

Mathematical modeling of Microcystis aeruginosa growth and [D-Leu1] microcystin-LR production in culture media at different temperatures

The effect of temperature (26 °C, 28 °C, 30 °C and 35 °C) on the growth of native CAAT-3-2005 Microcystis aeruginosa and the production of Chlorophyll-a (Chl-a) and Microcystin-LR (MC-LR) were examined through laboratory studies. Kinetic parameters such as specific growth rate (μ), lag phase duration (LPD) and maximum population density (MPD) were determined by fitting the modified Gompertz equation to the M. aeruginosa strain cell count (cells mL⁻¹). A 4.8-fold increase in μ values and a 10.8-fold decrease in the LPD values were found for M. aeruginosa growth when the temperature changed from 15 °C to 35 °C. The activation energy of the specific growth rate (Eμ) and of the adaptation rate (E₁/LPD) were significantly correlated (R² = 0.86). The cardinal temperatures estimated by the modified Ratkowsky model were minimum temperature = 8.58 ± 2.34 °C, maximum temperature = 45.04 ± 1.35 °C and optimum temperature = 33.39 ± 0.55 °C.Maximum MC-LR production decreased 9.5-fold when the temperature was increased from 26 °C to 35 °C. The maximum production values were obtained at 26° C and the maximum depletion rate of intracellular MC-LR was observed at 30–35 °C. The MC-LR cell quota was higher at 26 and 28 °C (83 and 80 fg cell⁻¹, respectively) and the MC-LR Chl-a quota was similar at all the different temperatures (0.5–1.5 fg ng⁻¹).The Gompertz equation and dynamic model were found to be the most appropriate approaches to calculate M. aeruginosa growth and production of MC-LR, respectively. Given that toxin production decreased with increasing temperatures but growth increased, this study demonstrates that growth and toxin production processes are uncoupled in M. aeruginosa. These data and models may be useful to predict M. aeruginosa bloom formation in the environment.     

Impact of fluctuating temperatures on development of the koinobiont endoparasitoid Venturia canescens

The effect of temperature on the biology of Venturia canescens (Gravenhorst) (Hymenoptera: Ichneumonidae) is well understood under constant temperature conditions, but less so under more natural, fluctuating conditions. Herein we studied the influence of fluctuating temperatures on biological parameters of V. canescens. Parasitized fifth-instar larvae of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) were reared individually in incubators at six fluctuating temperature regimes (15–19.5 °C with a mean of 17.6 °C, 17.5–22.5 °C with a mean of 19.8 °C, 20–30 °C with a mean of 22.7 °C, 22.5–27.5 °C with a mean of 25 °C, 25.5-32.5 °C with a mean of 28.3 °C and 28.5–33 °C with a mean of 30 °C) until emergence and death of V. canescens adults. Developmental time from parasitism to adult eclosion, adult longevity and survival were recorded at each fluctuating temperature regime. In principle, developmental time decreased with an increase of the mean temperature of the fluctuating temperature regime. Upper and lower threshold temperatures for total development were estimated at 34.9 and 6.7 °C, respectively. Optimum temperature for development and thermal constant were 28.6 °C and 526.3 degree days, respectively. Adult longevity was also affected by fluctuating temperature, as it was significantly reduced at the highest mean temperature (7.0 days at 30 °C) compared to the lowest one (29.4 days at 17.6 °C). Survival was low at all tested fluctuating temperatures, apart from mean fluctuating temperature of 25 °C (37%). Understanding the thermal biology of V. canescens under more natural conditions is of critical importance in applied contexts. Thus, predictions of biological responses to fluctuating temperatures may be used in population forecasting models which potentially influence decision-making in IPM programs.     

An analysis of the factors that affect the dissociation of inclusion bodies and the refolding of endostatin under high pressure

An optimization of the refolding of endostatin (ES), by a study of the conditions that can affect (i) dissociation of inclusion bodies (IBs) and (ii) renaturation under high hydrostatic pressure (HHP), is described. IBs produced by bacteria cultivated at 25 °C were shown to be more soluble than those produced at 37 °C and their dissociation by application of 2.4 kbar at 20 °C was shown to be further enhanced at ?9 °C. A red shift in intrinsic fluorescence spectra and an increase in binding of the hydrophobic fluorescent probe bis-ANS show subtle changes in conformation of ES in the presence of 1.5 M GdnHCl at 2.4 kbar, while at 0.4 kbar the native conformational state is favored. The 25% refolding yield obtained via compression of IBs produced at 37 °C by application of 2.4 kbar, was increased to 78% when conditions based on the insights acquired were utilized: dissociation at 2.4 kbar and ?9 °C of the IBs produced at 25 °C, followed by refolding at 0.4 kbar and 20 °C. Besides providing insights into the conformational transitions of ES structure under HHP, this work proposes innovative conditions that are likely to have wide applicability to the HHP-induced refolding of proteins in general.     

Temperature-dependent development models of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) Q biotype on three host plants

Temperature-dependent development of the sweet potato whitefly, Bemisia tabaci (Gennadius), Q biotype was examined on three host plants (bell pepper, oriental melon, and eggplant) at nine temperatures (15, 17.5, 20, 22.5, 25, 27.5, 30, 32.5, and 35 °C). Egg development time (least squares [LS]-mean ± LS-standard error [SE]) varied from 31.78 ± 0.29 days at 15 °C to 4.93 ± 0.25 days at 32.5 °C on bell pepper, from 21.27 ± 0.20 days at 17.5 °C to 4.02 ± 0.23 days at 32.5 °C on oriental melon, and from 26.92 ± 0.19 days at 15 °C to 5.14 ± 0.18 days at 30 °C on eggplant. Nymph development time (LS-mean ± LS-SE) varied from 76.54 ± 0.96 days at 15 °C to 12.96 ± 0.68 days at 27.5 °C on bell pepper, from 48.78 ± 0.38 days at 17.5 °C to 11.32 ± 0.38 days at 32.5 °C on oriental melon, and from 73.08 ± 1.23 days at 15 °C to 11.89 ± 0.70 days at 27.5 °C on eggplant. A non-linear relationship between developmental rate and temperature was described by the Taylor model, and developmental variation was described by the two-parameter Weibull function.