Daniel J Plews

Auckland University of Technology | AUT · Sports Performance Research Institute New Zealand (SPRINZ)

Purpose: To determine whether i) a plasma acidosis contributes to a reduction of mechanical performance and ii) bicarbonate supplementation blunts plasma acidosis and arterial oxygen desaturation to resist fatigue during the end-spurt of a supramaximal trial in elite sprint and endurance cyclists. Methods: Elite/world-class cyclists (n = 6 sprin...

Purpose To determine the effect of prolonged exercise on moderate-to-heavy intensity transition power output and heart rate. Methods Fourteen endurance-trained cyclists and triathletes took part in the present investigation (13 males, 1 female, V·O2peak 59.9 ± 6.8 mL.kg−1.min⁻¹). Following a characterisation trial, participants undertook a five-st...

Background To minimise the deleterious effects of fatigue and muscle soreness and maintain availability for training and competition, triathletes may implement recovery strategies that act on various physiological, biomechanical, neurological or psychological domains. However, the use of common recovery strategies is yet to be investigated in this...

Background: Multiple factors influence substrate oxidation during exercise including exercise duration and intensity, sex, and dietary intake before and during exercise. However, the relative influence and interaction between these factors is unclear. Objectives: Our aim was to investigate factors influencing the respiratory exchange ratio (RER)...

Background Contemporary sports nutrition guidelines recognize that endurance athletes should periodize their daily carbohydrate (CHO) intake according to the demands of their training and competitive schedule. However, objective assessments of the dietary CHO periodization practices adopted by endurance athletes during prolonged training periods ar...

Background The 5ʹ adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a cellular energy sensor that is activated by increases in the cellular AMP/adenosine diphosphate:adenosine triphosphate (ADP:ATP) ratios and plays a key role in metabolic adaptations to endurance training. The degree of AMPK activation during exercise can be influen...

Purpose This randomized controlled parallel-group study examined the effects of a very low-carbohydrate high-fat (VLCHF) diet and high-intensity interval training (HIIT) program over 12-weeks on cardiometabolic risk factors in individuals with overfat constitution. Methods Ninety-one participants out of 109 completed the study. The participants we...

Purpose Whole-body fat oxidation during exercise can be measured non-invasively during athlete profiling. Gaps in understanding exist in the relationships between fat oxidation during incremental fasted exercise and skeletal muscle parameters, endurance performance, and fat oxidation during prolonged fed-state exercise. Methods Seventeen endurance...

The aim of this study was to investigate the relationship between heart rate and heart rate variability (HRV) with respect to individual characteristics and acute stressors. In particular, the relationship between heart rate, HRV, age, sex, body mass index (BMI), and physical activity level was analyzed cross-sectionally in a large sample of 28,175...

Endurance athletes are frequently exposed to environmental heat stress during training. We investigated whether exposure to 33°C during training would improve endurance performance in temperate conditions and stimulate mitochondrial adaptations. Seventeen endurance-trained males were randomly assigned to perform a 3-week training intervention in 18...

Profiling physiological attributes is an important role for applied exercise physiologists working with endurance athletes. These attributes are typically assessed in well-rested athletes. However, as has been demonstrated in the literature and supported by field data presented here, the attributes measured during routine physiological-profiling as...

Nutritional intake can influence exercise metabolism and performance, but there is a lack of research comparing protein-rich pre-exercise meals with endurance exercise performed both in the fasted state and following a carbohydrate-rich breakfast. The purpose of this study was to determine the effects of three pre-exercise nutrition strategies on m...

Purpose: To present a case report of an elite ultra-endurance cyclist, who was the winner and course record holder of 2 distinct races within a 4-month span: a 24-hour solo cycling race and a 2-man team multiday race (Race Across America). Methods: The athlete's raw data (cycling power, heart rate [HR], speed, and distance) were obtained and ana...

This study aimed to investigate the effect of a 12-week very low-carbohydrate, high-fat (VLCHF) diet and exercise on biomarkers of inflammation in healthy individuals. Since the anti-inflammatory effects of a ketogenic diet have been established, we hypothesized that the VLCHF diet, along with exercise, would have an additional favorable effect on...

The primary variables influencing the adaptive response to a bout of endurance training are exercise duration and exercise intensity. However, altering the availability of nutrients before and during exercise can also impact the training response by modulating the exercise stimulus and/or the physiological and molecular responses to the exercise-in...

This review aimed to synthesize evidence regarding interventions based on heart rate variability (HRV)-guided training for VO2max improvements in endurance athletes and address the issues that impact this performance enhancement. The Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL Complete, the Web of Science Core...

Objective: The purpose of this study was to determine the self-reported beliefs and practices relating to pre-exercise nutrition intake among endurance athletes of varying ages and competitive levels and examine differences based on sex, competitive level, and habitual dietary pattern. Method: An anonymous online survey was circulated internatio...

Athletes may choose to perform exercise in the overnight-fasted state for a variety of reasons related to convenience, gut comfort, or augmenting the training response, but it is unclear how many endurance athletes use this strategy. We investigated the prevalence and determinants of exercise performed in the overnight-fasted state among endurance...

Background Breathing retraining and manual therapy (MT), delivered independently or together, influence autonomic activity, and improve symptoms in patients with chronic conditions. This study evaluated the effects of breathing retraining and osteopathic MT on cardiac autonomic measures and breathing symptoms during spontaneous breathing in healthy...

Background It is commonly assumed that increased dietary fat and/or caloric excess induces chronic inflammatory processes, since the association between obesity and chronic adipose tissue with systemic inflammation has been shown previously. As far as we know, the reported health benefits of a VLCHF or ketogenic diet have not adequately involved an...

Many endurance athletes perform specific blocks of training in hot environments in “heat stress training camps.” It is not known if physiological threshold heart rates measured in temperate conditions are reflective of those under moderate environmental heat stress. A total of 16 endurance-trained cyclists and triathletes performed incremental exer...

Fionn T McSwiney,1,2 Lorna Doyle,3 Daniel J Plews,4 Caryn Zinn4 1School of Health and Human Performance, Dublin City University, Dublin, Ireland; 2Setanta College, Thurlus, Tipperary, Ireland; 3Department of Sport and Exercise Science, Waterford Institute of Technology, Waterford, Ireland; 4Sports Performance Research Institute New Zealand (SPRINZ)...

The aim of this study was to determine the acute metabolic effects of different magnitudes of wearable resistance (WR) attached to the lower leg during submaximal running. Fifteen endurance-trained runners (37.8 ± 6.4 years; 1.77 ± 0.7 m; 72.5 ± 9.8 kg; 58.9 ± 7.4 L/min VO2max; 45.7 ± 5.8 min 10 K run time) completed seven submaximal running trials...

Hyperthermia stimulates endogenous carbohydrate metabolism during exercise; however, it is not known if exercise intensity impacts the metabolic effect of heat stress. In the first study of this two-part investigation, endurance-trained male cyclists performed incremental exercise assessments in 18 and 35°C (60 % rH). The stimulatory effect of heat...

The aim of this study was to determine the acute metabolic effects of different magnitudes of wearable resistance (WR) attached to the thigh during submaximal running. Twenty endurance-trained runners (40.8 ± 8.2 years, 1.77 ± 0.7 m, 75.4 ± 9.2 kg) completed six submaximal eight-minute running trials unloaded and with WRs of 1%, 2%, 3%, 4% and 5% b...

Predefined training programs are common place when prescribing training. Within predefined training, block periodization (BP) has emerged as a popular methodology due to its benefits. Heart rate variability (HRV) has been proposed as an effective tool for prescribing training. The aim of this study is to examine the effect of HRV guided-training ag...

Purpose: The aim of this non-randomized parallel group study was to examine the 12 week effects of a very low-carbohydrate high-fat diet (VLCHF) on maximal cardiorespiratory capacity, high-intensity interval training (HIIT) performance, and cardiac autonomic regulation. Methods: Twenty-four recreationally trained participants allocated to either...

A common practice amongst endurance athletes is to purposefully train in hot environments during a ‘heat stress camp’. However, combined exercise-heat stress poses threats to athlete wellbeing, and therefore heat stress training has the potential to induce maladaptation. This case study describes the monitoring strategies used in a successful three...

Background Advancements in wearable technology have provided practitioners and researchers with the ability to conveniently measure various health and/or fitness indices. Specifically, portable devices have been devised for convenient recordings of heart rate variability (HRV). Yet, their accuracies remain questionable. Objective The aim was to qu...

This study investigated the effect of the racemic β-hydroxybutyrate (βHB) precursor, R,S-1,3-butanediol (BD), on time-trial (TT) performance and tolerability. A repeated-measures, randomized, crossover study was conducted in nine trained male cyclists (age, 26.7 ± 5.2 years; body mass, 69.6 ± 8.4 kg; height, 1.82 ± 0.09 m; body mass index, 21.2 ± 1...

Ironman triathlons are ultra-endurance events of extreme duration. The performance level of those competing varies dramatically, with elite competitors finishing in ~ 8:00:00, and lower performing amateurs finishing in ~ 14-15:00:00. When applying appropriate values for swimming, cycling and running economies to these performance times, it is demon...

Purpose: To determine the effect of different high-intensity interval training (IT) sessions on the post-exercise recovery response and time-course across varying recovery measures. Methods: Thirteen highly-trained rowers (♂= 10, ♀= 3; VO2peak 4.9 ± 0.7 L⋅min-1) completed three IT sessions on the rowing ergometer separated by seven days. Session...

The autonomic nervous system plays a major role in optimising function of the cardiovascular (CV) system, which in turn has important implications for CV health. Heart rate variability (HRV) is a measurable reflection of this balance between sympathetic and parasympathetic tone and has been used as a marker for cardiac status and predicting CV outc...

This investigation assessed performance, physiological and perceptual responses to wearing additional clothing during endurance training for two-weeks in temperate environments, to determine if this approach could be used as a practical, alternative, heat acclimation strategy for athletes. Fifteen trained male triathletes assigned to performance-ma...

The purpose of the study was to examine the effects of altering from habitual mixed Western-based (HD) to a very low-carbohydrate high-fat (VLCHF) diet over a 4-week timecourse on performance and physiological responses during high-intensity interval training (HIIT). Eighteen moderately trained males (age 23.8 ± 2.1 years) consuming their HD (48 ±...

Using a short-duration step protocol and continuous indirect calorimetry, whole-body rates of fat and carbohydrate oxidation can be estimated across a range of exercise workloads, along with the individual maximal rate of fat oxidation (MFO) and the exercise intensity at which MFO occurs (Fatmax). These variables appear to have implications both in...

It has been demonstrated that heart rate variability (HRV) is predictive of all-cause and cardiovascular mortality using clinical ECG recordings. This is true for rest, exercise and ambulatory HRV clinical ECG device recordings in prospective cohorts. Recently, there has been a rapid increase in the use of mobile health technologies (mHealth) and c...

The purpose of this study was to compare the training intensity distribution (TID) of the undefeated world champion male rowing New Zealand (kiwi) pair over a four-year Olympic cycle, across training phases, training years, and between individuals. Training data, including heart rate and boat speed, were recorded in the athletes rowing in the same...

This investigation assessed the acute physiological and perceptual responses to wearing additional clothing during outdoor cycling to determine if this strategy could increase the heat load while training in temperate environments. Seven male cyclists (age: 32 ± 13 y, height: 179 ± 10 cm, body mass: 74 ± 10 kg, body fat percentage: 10.3 ± 1.0%) com...

The purpose of the present study was to examine the effects of an oral β-hydroxybutyrate (BHB) supplement on cycling performance. Using a double-blind, placebo-controlled, crossover design, 12 highly-trained cyclists (mean ± SD: age; 35 ± 8 y, mass; 74.5 ± 7.6 kg, VO2peak; 68.0 ± 6.7 ml.min-1kg-1) were supplemented with two 30 ml servings of an ora...

Purpose: To establish the validity of smartphone photoplethysmography (PPG) and heart rate sensor in the measurement of heart rate variability (HRV). Methods: 29 healthy subjects were measured at rest during 5 min of guided breathing (GB) and normal breathing (NB) using Smartphone PPG, heart rate chest strap and electrocardiography (ECG). The ro...

The purpose of the present study was to evaluate two commercially available power meters: the Cyclus ergometer (CYC) and the Stages power meter (STA) in comparison to a highly-validated power meter (SRM). Ten trained cyclists (mean ± SD; age 24 ± 8 y, body mass 69.7 ± 7.3 kg) performed an incremental exercise test to exhaustion (GXT), 2 x 10 sec sp...

Purpose: Heart rate variability (HRV) is a popular tool for monitoring autonomic nervous system status and training adaptation in athletes. It is believed that increases in HRV indicate effective training adaptation, but these are not always apparent in elite athletes. Methods: Resting HRV was recorded in 4 elite rowers (Rower A, B, C and D) ove...

BACKGROUND: Heart rate variability (HRV) is an objective physiological marker that may be useful for monitoring training status in athletes. However, research aiming to interpret daily HRV changes in female athletes is limited. The objectives of this study were (1) to assess daily HRV (i.e., log-transformed root mean square of successive R-R interv...

The determination of a cyclist’s lactate threshold (LT) has become an important test performed in sports science laboratories around the world. A limitation of such testing is that it is relatively expensive and invasive, requiring multiple blood samples. The purpose of the current study was to evaluate a commercially available, wearable lactate th...

The cardiorespiratory, cardiac autonomic (via heart rate variability (HRV)) and plasma volume responses to varying sequences of high-intensity interval training (HIT) of consistent external work were investigated. Twelve moderately trained males underwent three HIT bouts and one control session. The HIT trials consisted of warm-up, followed by 12 m...

Purpose: To determine whether a facilitated recovery via cold water immersion (CWI) following simulated Rugby Sevens would influence parasympathetic reactivation and repeated sprint (RS) performance across six matches within a two-day tournament. Methods: Ten male team sport athletes completed six Rugby Sevens match simulations over two days wit...

Background: Although carbohydrate is the predominant fuel source supporting high-intensity exercise workloads, the role of fat oxidation, and the degree to which it may be altered by training status, is less certain. Methods: We compared substrate oxidation rates, using indirect calorimetry, during a high-intensity interval training (HIT) session i...

To determine the effect of thermal state and thermal comfort on cycling performance in the heat. Seven well-trained male triathletes completed 3 performance trials, consisting of 60-min cycling at a fixed rating of perceived exertion (RPE; 14) followed immediately by a 20-km time trial in hot (30ºC) and humid (80% relative humidity) conditions. In...

Elite endurance athletes may train in a 'polarised' fashion, such that their training intensity distribution preserves autonomic balance. However, field data supporting this is limited. We examined the relationship between heart rate variability and training intensity distribution in 9 elite rowers during the 26-week build-up to the 2012 Olympic Ga...

The aim of this study was to establish the minimum number of days that HRV (i.e., the natural logarithm of square root of the mean sum of the squared differences between R-R intervals, Ln rMSSD) data should be averaged in order to achieve correspondingly equivalent results as data averaged over a 1-week period. Standardised changes in Ln rMSSD betw...

The measurement of heart rate variability (HRV) is often considered a convenient non-invasive assessment tool for monitoring individual adaptation to training. Decreases and increases in vagal-derived indices of HRV have been suggested to indicate negative and positive adaptations, respectively, to endurance training regimens. However, much of the...

The aim of this study was to compare two different methodological assessments when analysing the relationship between performance and heart rate derived indices (resting heart rate (RHR) and heart rate variability (HRV)) in order to evaluate positive adaptation to training. The relative change in estimated maximum aerobic speed (MAS) and 10-km runn...

Measures of an athlete’s heart rate variability (HRV) have shown potential to be of use in the prescription of training. However, little data exists on elite athletes who are regularly exposed to high training loads. This case study monitored daily HRV in two elite triathletes (one male: 22 year, \( \dot{V}\)O2max 72.5 ml kg min−1; one female: 20 y...