title: Predicting responses to a heat acclimation protocol in trained triathletes

authors: Miller, Liam

abstract: Chapter One reviews the differences between performing in temperate and hot and humid environments. When compared to performance in temperate environments, heat-stressful environments acutely alter physiology heart rate, sweat rate, both core and skin temperature, plasma volume and local blood flow. Heat acclimation (HA) protocol introduced prior to competition in varying ways specific to the competition type has been shown to have large impacts on eventual performance, often summarised through heat response tests (HRT) or adaptations of thermoregulatory physiology. Individual responses to HA have been proven to vary between individuals with little evidence presented to explain why such variation occurs. In Chapter Two, 10 endurance-trained competitive triathletes (aged 33.6 ± 10.6 years, 8 males and 2 females; VO2 max 56.9 ± 11.1) completed a 14-day, cycling-based HA protocol (36 °C, 65% relative humidity). Participants completed two HRTs (Day 1 & Day 13), composed of 20 minutes at a steady state intensity immediately followed by a 30-kilometer time trial. Between these HRTs were seven HA sessions. Performance in the 30-kilometer time trial significantly increased as a result of the HA protocol (p = 0.037). Two regression models for predicting performance outcomes were generated using stepwise regression analysis. A ‘best overall fit’ model using baseline VO2, sweat loss, and sweat sodium composition explains 53% of the variability of performance improvement (R2 = 0.53), and a ‘best practical fit’ model using baseline VO2 and sweat loss explains 49% of the variability of performance improvement (R2 = 0.49). Both models are statistically significant (p = 0.017; p = 0.023). The ‘best practical fit’ model interprets that those with low baseline VO2 but greater sweat loss in the first HRT demonstrated the best performance improvement, whereas those with high baseline VO2 and low sweat loss do not see much performance improvement. Chapter Three investigates the validity of the Kenzen™ wearable core temperature sensor. Ten participants engaged in two HRTs each (20 minutes at a steady state intensity immediately followed by a 30-kilometer time trial) whilst wearing a Kenzen™ device and a rectally inserted thermometer. Bland-Altman plots were used in conjunction with a direct comparison of the differences of the measures to determine validity. The Kenzen™ device is accurate between the range of 37-38 °C, but once core temperature measured rectally reaches 38.5 °C, the validity of the Kenzen™ device comes into question (when rectal temperature ≥ 39 °C, mean difference = 0.79 °C). The difference in measurements suggests that the Kenzen™ is not valid once moderate hyperthermia is reached (38.5 °C). Chapter Four presents a summary of the previous chapters. There is evidence to suggest that predicting variation in HA success is possible, potentially even more so with some refinement of the model through additional thermoregulatory measurement or protocol modification. The validity of wearable core temperature technology does not currently appear suitable in high-performance athletic environments where athletes are expected to reach core temperatures defined as hyperthermic, as most wearable sensors do not seem valid compared to gold standard measures. It is likely that the technology will advance as the popularity of such wearables increases.

text: Predicting responses to a heat acclimation protocol in trained triathletes Chapter One reviews the differences between performing in temperate and hot and humid environments. When compared to performance in temperate environments, heat-stressful environments acutely alter physiology heart rate, sweat rate, both core and skin temperature, plasma volume and local blood flow. Heat acclimation (HA) protocol introduced prior to competition in varying ways specific to the competition type has been shown to have large impacts on eventual performance, often summarised through heat response tests (HRT) or adaptations of thermoregulatory physiology. Individual responses to HA have been proven to vary between individuals with little evidence presented to explain why such variation occurs. In Chapter Two, 10 endurance-trained competitive triathletes (aged 33.6 ± 10.6 years, 8 males and 2 females; VO2 max 56.9 ± 11.1) completed a 14-day, cycling-based HA protocol (36 °C, 65% relative humidity). Participants completed two HRTs (Day 1 & Day 13), composed of 20 minutes at a steady state intensity immediately followed by a 30-kilometer time trial. Between these HRTs were seven HA sessions. Performance in the 30-kilometer time trial significantly increased as a result of the HA protocol (p = 0.037). Two regression models for predicting performance outcomes were generated using stepwise regression analysis. A ‘best overall fit’ model using baseline VO2, sweat loss, and sweat sodium composition explains 53% of the variability of performance improvement (R2 = 0.53), and a ‘best practical fit’ model using baseline VO2 and sweat loss explains 49% of the variability of performance improvement (R2 = 0.49). Both models are statistically significant (p = 0.017; p = 0.023). The ‘best practical fit’ model interprets that those with low baseline VO2 but greater sweat loss in the first HRT demonstrated the best performance improvement, whereas those with high baseline VO2 and low sweat loss do not see much performance improvement. Chapter Three investigates the validity of the Kenzen™ wearable core temperature sensor. Ten participants engaged in two HRTs each (20 minutes at a steady state intensity immediately followed by a 30-kilometer time trial) whilst wearing a Kenzen™ device and a rectally inserted thermometer. Bland-Altman plots were used in conjunction with a direct comparison of the differences of the measures to determine validity. The Kenzen™ device is accurate between the range of 37-38 °C, but once core temperature measured rectally reaches 38.5 °C, the validity of the Kenzen™ device comes into question (when rectal temperature ≥ 39 °C, mean difference = 0.79 °C). The difference in measurements suggests that the Kenzen™ is not valid once moderate hyperthermia is reached (38.5 °C). Chapter Four presents a summary of the previous chapters. There is evidence to suggest that predicting variation in HA success is possible, potentially even more so with some refinement of the model through additional thermoregulatory measurement or protocol modification. The validity of wearable core temperature technology does not currently appear suitable in high-performance athletic environments where athletes are expected to reach core temperatures defined as hyperthermic, as most wearable sensors do not seem valid compared to gold standard measures. It is likely that the technology will advance as the popularity of such wearables increases.

year: 2023

title: Late Holocene cool climate episodes, recorded on Lake Bonney, an Antarctic amplifier lake

authors: Croall, Jacob Grant

abstract: Chemical, stable isotope and natural abundance radionuclide analysis of cores taken through sediments below Lake Bonney, Taylor Valley, Antarctica, show evidence of multiple episodes of flooding by meltwaters from Taylor Glacier and desiccation to brines sufficiently concentrated to produce ice free conditions. The last three identified desiccation events date 1550 ± 40, 800 ± 100 and 450 ± 160 yr B.P. and match the last three periods of sustained cooling identified by isotope changes in the Taylor Dome ice core. Similar cooling events have been identified by other authors elsewhere in Antarctica.

The desiccation events have produced dramatic changes in the sediment character of Lake Bonney East Lobe, but show little impact in the West Lobe. In East Lobe halite, hydrohalite, gypsum, and aragonite are precipitated and extreme isotopic enrichment of carbon (up to 813C of +12.0%0) occurred as aragonite was forced from solution by rapid freezing of the brine over winter. Reflooding events were often associated with algal blooms and resulted in radical changes in the 180/1 60 ratio in the water column.

It is speculated that Taylor Glacier retreated to expose a 250 m deep subglacial depression during the last glacial maximum allowing Glacial Lake Washburn to extend westwards to perhaps Cavendish Rocks. The reduced Taylor Glacier enabled Taylor Dome to lower causing deposition of more 180 enriched ice than would otherwise have been expected. Taylor Glacier and Taylor Dome have continued to advance throughout the Holocene.

text: Late Holocene cool climate episodes, recorded on Lake Bonney, an Antarctic amplifier lake Chemical, stable isotope and natural abundance radionuclide analysis of cores taken through sediments below Lake Bonney, Taylor Valley, Antarctica, show evidence of multiple episodes of flooding by meltwaters from Taylor Glacier and desiccation to brines sufficiently concentrated to produce ice free conditions. The last three identified desiccation events date 1550 ± 40, 800 ± 100 and 450 ± 160 yr B.P. and match the last three periods of sustained cooling identified by isotope changes in the Taylor Dome ice core. Similar cooling events have been identified by other authors elsewhere in Antarctica.

The desiccation events have produced dramatic changes in the sediment character of Lake Bonney East Lobe, but show little impact in the West Lobe. In East Lobe halite, hydrohalite, gypsum, and aragonite are precipitated and extreme isotopic enrichment of carbon (up to 813C of +12.0%0) occurred as aragonite was forced from solution by rapid freezing of the brine over winter. Reflooding events were often associated with algal blooms and resulted in radical changes in the 180/1 60 ratio in the water column.

It is speculated that Taylor Glacier retreated to expose a 250 m deep subglacial depression during the last glacial maximum allowing Glacial Lake Washburn to extend westwards to perhaps Cavendish Rocks. The reduced Taylor Glacier enabled Taylor Dome to lower causing deposition of more 180 enriched ice than would otherwise have been expected. Taylor Glacier and Taylor Dome have continued to advance throughout the Holocene.

year: 2005

title: Evaluating the effects of invasive brown bullhead catfish (Ameiurus nebulosus) on kōura (freshwater crayfish, Paranephrops planifrons) in Lake Rotoiti

authors: Francis, Laura Beverley

subjects: catfish

abstract: Brown bullhead catfish (Ameiurus nebulosus) are opportunistic carnivores native to North America and were first detected in Te Weta Bay, Lake Rotoiti, in March 2016. A cordon was placed across the bay to try and contain catfish, but they had already established populations elsewhere. Spread of catfish in the lake raised concern for resident populations of freshwater crayfish or kōura (Paranephrops planifrons), which are of ecological and cultural significance to Māori. Given the limited knowledge of the potential impacts of catfish on native biota, this thesis aims to evaluate the effects of catfish on kōura in Lake Rotoiti. To do this, Bay of Plenty Regional Council (BOPRC) routine fyke netting data was used to explore species trends and relationships. A habitat survey was also conducted using whakaweku (bracken fern bundles) and fyke nets, to generate data on species’ habitat preferences and kōura metrics (e.g., sizes and sex ratios). In addition to fishing, kōura and catfish stomachs were dissected to determine diet. Potential food items of catfish were also collected for stable isotope analysis to estimate dietary overlap between catfish and kōura, and long-term resource acquisition. 

Routine BOPRC fyke netting results indicated that kōura catch per unit effort (CPUE) has declined in Lake Rotoiti, with mean catch rates dropping from 10.6 kōura net-1 night-1 in 2016 to 4.2 kōura net-1 night-1 in 2018. Over the same period, catfish CPUE has increased in the lake, with the highest catch rates in Te Weta Bay, where mean catch rates have increased from 1.1 catfish net-1 night-1 in 2016 to 63.7 catfish net-1 night-1 in 2018. Catfish catch rates were negatively associated with catch rates of kōura (r = −0.180). Mean catfish density also had a significant effect on kōura catch rates, with significantly more kōura being caught at sites without catfish. The negative association between catfish and kōura could be due to catfish eating or competing with kōura, or their differing habitat preferences. Catfish were positively associated with sites that are weedy or muddy and kōura were negatively associated with muddy habitats and were positively associated with rocky habitats. Whakaweku set at shallow depths <1 m in the lake littoral zone were ineffective at catching kōura during the habitat survey. 

Catfish diet consisted largely of chironomid larvae (Chironomidae), detritus, common bullies (Gobiomorphus cotidianus), and to a lesser extent kōura. Kōura were found in 12% of large catfish (>200 mm fork length; FL) stomachs analysed and contributed 5% volumetrically to large catfish diet. Unfortunately, the contribution of kōura to catfish diet could not be established using stable isotopes because isotopic signatures of kōura and bullies were too close to differentiate. Kōura diet consisted primarily of animal remains (common bullies and invertebrates) and detritus. Stable isotopes of carbon and nitrogen revealed that diets of kōura and catfish overlapped, with kōura sharing more of their diet with catfish than vice versa, likely reflecting catfish’s broad diet. This study suggests that catfish are responsible for the recent decline in kōura CPUE in Lake Rotoiti and that catfish are directly and indirectly affecting kōura through predation and competition for shared food resources.

text: Evaluating the effects of invasive brown bullhead catfish (Ameiurus nebulosus) on kōura (freshwater crayfish, Paranephrops planifrons) in Lake Rotoiti Brown bullhead catfish (Ameiurus nebulosus) are opportunistic carnivores native to North America and were first detected in Te Weta Bay, Lake Rotoiti, in March 2016. A cordon was placed across the bay to try and contain catfish, but they had already established populations elsewhere. Spread of catfish in the lake raised concern for resident populations of freshwater crayfish or kōura (Paranephrops planifrons), which are of ecological and cultural significance to Māori. Given the limited knowledge of the potential impacts of catfish on native biota, this thesis aims to evaluate the effects of catfish on kōura in Lake Rotoiti. To do this, Bay of Plenty Regional Council (BOPRC) routine fyke netting data was used to explore species trends and relationships. A habitat survey was also conducted using whakaweku (bracken fern bundles) and fyke nets, to generate data on species’ habitat preferences and kōura metrics (e.g., sizes and sex ratios). In addition to fishing, kōura and catfish stomachs were dissected to determine diet. Potential food items of catfish were also collected for stable isotope analysis to estimate dietary overlap between catfish and kōura, and long-term resource acquisition. 

Routine BOPRC fyke netting results indicated that kōura catch per unit effort (CPUE) has declined in Lake Rotoiti, with mean catch rates dropping from 10.6 kōura net-1 night-1 in 2016 to 4.2 kōura net-1 night-1 in 2018. Over the same period, catfish CPUE has increased in the lake, with the highest catch rates in Te Weta Bay, where mean catch rates have increased from 1.1 catfish net-1 night-1 in 2016 to 63.7 catfish net-1 night-1 in 2018. Catfish catch rates were negatively associated with catch rates of kōura (r = −0.180). Mean catfish density also had a significant effect on kōura catch rates, with significantly more kōura being caught at sites without catfish. The negative association between catfish and kōura could be due to catfish eating or competing with kōura, or their differing habitat preferences. Catfish were positively associated with sites that are weedy or muddy and kōura were negatively associated with muddy habitats and were positively associated with rocky habitats. Whakaweku set at shallow depths <1 m in the lake littoral zone were ineffective at catching kōura during the habitat survey. 

Catfish diet consisted largely of chironomid larvae (Chironomidae), detritus, common bullies (Gobiomorphus cotidianus), and to a lesser extent kōura. Kōura were found in 12% of large catfish (>200 mm fork length; FL) stomachs analysed and contributed 5% volumetrically to large catfish diet. Unfortunately, the contribution of kōura to catfish diet could not be established using stable isotopes because isotopic signatures of kōura and bullies were too close to differentiate. Kōura diet consisted primarily of animal remains (common bullies and invertebrates) and detritus. Stable isotopes of carbon and nitrogen revealed that diets of kōura and catfish overlapped, with kōura sharing more of their diet with catfish than vice versa, likely reflecting catfish’s broad diet. This study suggests that catfish are responsible for the recent decline in kōura CPUE in Lake Rotoiti and that catfish are directly and indirectly affecting kōura through predation and competition for shared food resources.

year: 2019