The appropriate intensity of exercise needed to reduce the risk of hypoglycemia (≤3.9 mmol/L) in persons with type 1 diabetes (T1D) is not known. Ten participants with T1D performed four exercise sessions on a treadmill lasting 45 minutes: a control condition at 45-55% of heart rate reserve and three high intensity sessions at 70, 80, and 90% of heart rate reserve. A blinded continuous glucose monitor was used to measure time spent ≤3.9 mmol/L and glucose variability in the 12 hours following exercise. There were no significant changes in the percentage of time spent ≤3.9 mmol/L (p=0.58) and glucose variability as measured by mean absolute glucose change (p=0.53) and continuous overall net glycemic action (CONGA1: p=0.95; CONGA2: p=0.90; CONGA4: p=0.72) between the sessions. High intensity exercise at 70, 80, and 90% of HRR does not significantly reduce the amount of time spent ≤3.9 mmol/L or glucose variability compared to the 45-55% session alone. / October 2015

The hyperbolic power-duration relationship for high-intensity exercise is defined by two parameters: an asymptote (critical power; CP) reflecting the highest sustainable rate of oxidative metabolism, and a curvature constant (W'), which indicates a fixed amount of work that can be completed above CP (W>CP). According to the CP model of bioenergetics, constant work rate exercise above CP depletes the capacity-limited W' with fatigue occurring when W' is completely expended. The complete depletion of W' has been reported to occur when VO2max is attained and a critical degree of muscle metabolic perturbation (decline of finite anaerobic substrates and accumulation of fatigue-related metabolites) is reached. However, while the CP model is effective at predicting metabolic perturbation and the tolerable duration of severe-intensity constant work rate (CWR) exercise, it is unclear if metabolic perturbation and exercise performance can be explained by the CP model when different methods of work rate imposition are applied. Therefore, the purpose of this thesis was to: 1) investigate the efficacy of the CP concept to predict performance in exercise tests using different work rate forcing functions; and 2) explore whether the physiological bases for W' are consistent across different methods of work rate imposition. In study 1, compared to severe-intensity CWR exercise, the tolerable duration of intermittent severe-intensity exercise with heavy- (S-H) moderate- (S-M) and light-intensity (S-L) ‘recovery’ intervals was increased by 47%, 100% and 219%, respectively. W>CP (W') was significantly greater by 46%, 98%, and 220% for S-H, S-M and S-L, respectively, when compared to S-CWR, and the slopes for the increases in VO2 and iEMG were progressively lowered as the recovery work rate was reduced. In study 2, both the VO2max and W>CP were similar across incremental cycling protocols that imposed a fixed ramp rate and cadence (4.33 ± 0.60 L•min-1; 14.8 ± 9.2 kJ), a fixed ramp rate with cadence self-selected by the subjects (4.31 ± 0.62 L•min-1; 15.0 ± 9.9 kJ) and a step incremental test where subjects were instructed to select power output according to prescribed increments in ratings of perceived exertion (4.36 ± 0.59 L•min-1; 13.0 ± 8.4 kJ). In study 3, the VO2max and W>CP were also not different across a 3 min all-out cycling test (4.10 ± 0.79 L•min-1; 16.5 ± 4.0 kJ), cycling at a constant work rate predicted to lead to exhaustion in 3 min until the limit of tolerance (4.20 ± 0.77 L•min-1; 16.6 ± 7.4 kJ) and a self-paced 3 min work-trial (4.14 ± 0.75 L•min-1; 15.3 ± 5.6 kJ). In study 4, after completing severe-intensity exercise (>CP) to exhaustion, muscle homeostasis ([PCr], pH, [ADP] and [Pi]) returned towards baseline and subjects were able to exercise for at least 10 min at a heavy-intensity work rate (<CP); however, when the work rate was lowered but remained in the severe-intensity domain (>CP), muscle metabolites ([PCr], pH, [ADP] and [Pi]) did not recover and exercise tolerance was severely limited (39 ± 31 s). Finally in study 5, during severe-intensity intermittent knee extension exercise, the tolerable duration of exercise was 304 ± 68 s when 18 s recovery was allowed and was increased by ~69% and ~179% when the intermittent recovery periods were extended to 30 s and 48 s, respectively. The increased exercise tolerance with longer recovery periods occurred in concert with increased W>CP (3.8 ± 1.0 kJ, 5.6 ± 1.8 kJ and 7.9 ± 3.1 kJ for the intermittent protocols with 18, 30 and 48 s of recovery, respectively) and a delayed attainment of critical intramuscular metabolite concentrations ([PCr], pH, [ADP] and [Pi]). Therefore, the results of this thesis demonstrate that fatigue during various high-intensity exercise protocols is influenced by the capacity to complete work above the CP (W') and that W' depletion is linked to the attainment of VO2max and the attainment of critical levels of intramuscular [PCr], pH, [ADP] and [Pi]. These findings suggest that the CP model can be adapted to predict the degree of metabolic perturbation and exercise performance across a range of exercise settings in humans.

Athletes use a wide range of interventions to promote recovery from strenuous exercise, but few data are available regarding the efficacy of such practices. OBJECTIVE: To examine the effectiveness of commonly used interventions [Rest, light exercise (AR), contrast therapy (CT) and cryotherapy (CR)] during recovery between bouts of intense exercise. We tested the hypothesis that hydrotherapy interventions (CT and CR) would induce favorable physiological and/or psychological alterations such that performance would be improved versus AR and Rest. METHODS: In Study I, 12 active men (25-35 yrs; VO2peak = 46±3 ml·kg-1·min-1; mean±SD) performed 5 consecutive days of HI exercise (4-6 bouts x 30 sec 'all out' Wingate Tests, with 4-min recovery, each day). After each training session, subjects either rested for 20 min (CON, n=6) or completed a CT protocol (n=6) that consisted of alternating cold (10°C) and hot (40°C) tubs using a 4x2:3 min ratio. Performance measures [Peak (Wmax) and mean (Wmean) power, VO2peak, and a 250 kJ Time Trial (TT)] were assessed before and after the HIT. In Study II, 9 active men (29±6 yr, VO2peak = 44±8 ml·kg-1·min-1) performed 3 exercise trials separated by 1 wk. Each trial consisted of 3 x 50 KJ time trials(~100-120%VO2peak) with a different 20-min recovery period [CON, AR (cycling@ SOW) or CR (cold tub@ 10°C)] between rides each week. Venous blood samples were obtained after each recovery period, and analyzed for lactate, interleukin-6, neutrophils, and lymphocytes. Questionnaires designed to assess exercise preparedness were also completed daily in both studies. RESULTS: In Study I, Wmax and TT performance improved after 5 d of HI exercise (time effect, P<0.05), but there were no differences between groups (Wmax-CT: Post: 1310±45 vs Pre: 1215±86; CON: Post: 1343±54 vs Pre: 1220±74 W: TT-CT: Post: 15.8±0.6 vs Pre: 16.7±0.7; Rest: Post: 18.1±1.0 vs Pre: 18.8±1.2 min, means±SEM). In Study II, TT performance averaged 118±10 sec for bout 1 and was 8% and 14% slower during bouts 2 (128±11 sec) and 3 (134±11 sec), respectively, with no difference between treatments (Time effect, P≤0.05). Blood lactate was lower after AR compared to CR and Rest, and neutrophils and lymphocytes were higher and lower respectively (P≤0.05), after CR (8.7±1.3 and 1.4±0.2 x 109cells/L) versus AR (7.1±1.0 and 1.6±0.1) and Rest (6.7±0.7 and 1.6±0.1). With respect to the psychological measurements, the CT and CR groups in both studies reported feeling more revitalized after each treatment session and greater preparedness for subsequent exercise (Treatment effect, P≤.05). CONCLUSIONS: Exercise performance during repeated bouts of intense cycling was not influenced by the type of recovery intervention employed, either during a single session or over the course of a 5 d training session. CR caused greater perturbations in blood immune markers and most notably, hydrotherapy interventions created the perception that subjects were better prepared for subsequent exercise. / Thesis / Master of Science (MS)

Adaptation to the shortage of oxygen at altitude (hypoxia) promotes physiological changes which could enhance endurance performance. Consequently, altitude training has become a popular practice among competitive endurance athletes. Since its inception, the live-high train-low paradigm (LHTL) has been widely regarded as the most effective approach to altitude training. Over the past decade, brief intermittent simulation of LHTL via the use of hypoxic inhalers and re-breathing devices has gained increased popularity, but the evidence supporting their use is limited and conflicting. The experimental studies in this thesis investigated the response of sea level exercise performance and related physiological measures following adaptation to the usual and a novel protocol of brief intermittent hypoxia. I intended to perform all experimental studies on flat-water kayakers. Therefore, an initial requirement of this thesis was to establish the smallest worthwhile effect in performance for this sport. The final study utilising a meta-analytic approach was conducted to compare the effectiveness of brief intermittent hypoxia to other natural and simulated protocols, and to investigate the topical issue of what physiological responses mediate performance changes following hypoxic exposure. In Study 1, the typical variation in competitive performance of elite flat-water canoeists was investigated using a repeated-measures analysis of race times. For individual flat-water canoeing events, the smallest worthwhile change in performance time was ~0.5%. In two separate experimental studies, adaptation to 60 min per day of brief intermittent hypoxia consisting of alternating 5 min intervals of hypoxia and normoxia for 3 weeks (5 days per week) using a nitrogen filtration device resulted in clear enhancement of endurance performance (~5%) for kayakers (Study 2) and cyclists (Study 3). Clear enhancements in repeat sprint performance were observed for kayaking only. The physiological mechanisms underlying performance changes were unclear. Modification of the hypoxic and normoxic intervals (Study 3) did not result in any clear alterations in performance or physiological mechanisms. The meta-analysis (Study 4) revealed clear enhancements in endurance power output of 1-3% in sub-elites following adaptation to hypoxia with the natural altitude protocols, and with two of the artificial-altitude protocols (LHTL-long and LHTL-brief-intermittent). In elite athletes the enhancements tended to be smaller and were clear only for the natural protocols. These enhancements could be mediated by VO2max, although other mechanisms may be possible.

The aim of this series of studies was to investigate the effects of oral caffeine ingestion (5 mg . kg-1) on whole-body, short-term, high-intensity exercise (ST; representing an exercise intensity of between 100% -150% V02 max), an area that has received scant attention in the past. It was found that, in common with other 'open-ended' tests, one ST assessment, the maximal accumulated oxygen deficit (MAOD), appeared to lack both validity and reliability. Although traditional reliability markers of MAOD were favourable, the 95% limits of agreement were unacceptably large. In addition, the validity of MAOD was also found to be questionable because a study of elite runners revealed that a large proportion were unable to accomplish a plateau in the V02 -exercise intensity relationship. A follow-up study developed an original bespoke 'preloaded' ST cycling protocol that combined constant-rate exercise with an 'all-out' effort. This protocol appears to have several features that make it a more appropriate assessment to use in ergogenic studies than the MAOD. The work also considered the original, and as yet, undeveloped potential, for the assessment of rating of perceived exertion (RPE) during ST. It was shown for the first time that RPE (Borg scale; 6-20) could be used reliably during constant-rate ST. Three of the ten studies demonstrated that caffeine can be ergogenic during ST, with improvements averaging 11 % (95% GI, 7.4% -14.5%) above placebo treatment. In addition, the caffeine studies contributed to a meta-analysis of the effects of caffeine on test outcome that resulted in an effect size greater than zero, with 95% confidence intervals not crossing zero. The studies have examined potential physiological and metabolic mechanisms of action that may help explain caffeine's impact on ST. These suggest that there is some evidence that caffeine both stimulates anaerobic glycolysis and reduces electrolyte disturbance during ST. Finally this work has demonstrated for the first time that the perceptual response during constant-rate ST, as measured by RPE, is blunted following caffeine ingestion. It is concluded that caffeine is ergogenic during ST, and that while the exact mechanism(s) of action remains unknown, one consistent test outcome is a reduction in RPE during constant-rate ST.

Adaptation to the shortage of oxygen at altitude (hypoxia) promotes physiological changes which could enhance endurance performance. Consequently, altitude training has become a popular practice among competitive endurance athletes. Since its inception, the live-high train-low paradigm (LHTL) has been widely regarded as the most effective approach to altitude training. Over the past decade, brief intermittent simulation of LHTL via the use of hypoxic inhalers and re-breathing devices has gained increased popularity, but the evidence supporting their use is limited and conflicting. The experimental studies in this thesis investigated the response of sea level exercise performance and related physiological measures following adaptation to the usual and a novel protocol of brief intermittent hypoxia. I intended to perform all experimental studies on flat-water kayakers. Therefore, an initial requirement of this thesis was to establish the smallest worthwhile effect in performance for this sport. The final study utilising a meta-analytic approach was conducted to compare the effectiveness of brief intermittent hypoxia to other natural and simulated protocols, and to investigate the topical issue of what physiological responses mediate performance changes following hypoxic exposure. In Study 1, the typical variation in competitive performance of elite flat-water canoeists was investigated using a repeated-measures analysis of race times. For individual flat-water canoeing events, the smallest worthwhile change in performance time was ~0.5%. In two separate experimental studies, adaptation to 60 min per day of brief intermittent hypoxia consisting of alternating 5 min intervals of hypoxia and normoxia for 3 weeks (5 days per week) using a nitrogen filtration device resulted in clear enhancement of endurance performance (~5%) for kayakers (Study 2) and cyclists (Study 3). Clear enhancements in repeat sprint performance were observed for kayaking only. The physiological mechanisms underlying performance changes were unclear. Modification of the hypoxic and normoxic intervals (Study 3) did not result in any clear alterations in performance or physiological mechanisms. The meta-analysis (Study 4) revealed clear enhancements in endurance power output of 1-3% in sub-elites following adaptation to hypoxia with the natural altitude protocols, and with two of the artificial-altitude protocols (LHTL-long and LHTL-brief-intermittent). In elite athletes the enhancements tended to be smaller and were clear only for the natural protocols. These enhancements could be mediated by VO2max, although other mechanisms may be possible.

The aim of this thesis was to develop and validate squash-specific fitness tests to identify physiological determinants of repeat-sprint ability and performance in sub-elite and elite-standard squash players. Study one examined the validity of a squash-specific test of endurance capability and VO[2max]. Trained squash players and runners completed squash-specific and treadmill incremental tests to exhaustion. Squash players achieved greater VO[2max] on the squash-specific than the treadmill test while runners did not differ. Squash players exercised longer than runners on the squash-specific test despite similar VO2max. The squash test discriminated endurance capability between squash and non-squash players of similar fitness and elicited higher VO[2max] in squash players. The results suggest that it is a valid test of aerobic fitness in squash players. Study two assessed the reproducibility of physiological and performance measures from the squash specific test in county-standard players. Test-retest variability was low for all measures (Typical error < 5%) though the magnitude varied depending on the metric used. Studies three and four examined the validity and reproducibility of squash-specific tests of change-of-direction speed and multiple-sprint ability. County-standard squash players and footballers completed squash-specific and equivalent non-specific tests on separate days. Performance time was recorded. Participants repeated the tests seven days later to assess reproducibility. Squash outperformed non-squash players on the squash-specific tests despite similar non-specific capabilities. Squash-specific tests discriminated squash player rank while non-specific tests did not. Test-retest variability was low (Typical Error < 3%) for both tests. Squash-specific tests predicted ability in squash players and discriminated between squash and non-squash players of equal nonspecific fitness. The findings suggest that the squash-specific tests are valid for the assessment of high-intensity exercise capabilities in squash players. Studies five and six explored correlates of multiple-sprint ability and performance in sub-elite and elite squash players. Squash-specific and general tests were performed by regional league players ranging from division three to premier standard and elite players on three tiers of a national performance program. In sub-elites, multiple-sprint ability and endurance capability discriminated performance and multiple-sprint ability was related to change-of-direction-speed, VO[2max] and endurance capability. In world-ranked men and women, the ability to perform and sustain rapid changes of direction correlated with multiple-sprint ability and together with multiple-sprint ability discriminated performance. Aerobic fitness was not related to performance or multiple-sprint ability in elite players. Senior elites performed better than players on the talented athlete scholarship scheme (TASS) on all tests except VO[2max] and counter-movement jump. Drop-jump power and reactive strength discriminated senior and transition level from TASS players and indices from the multiple-sprint test discriminated seniors from transition and TASS players. This thesis has validated squash-specific tests of endurance and high-intensity exercise capabilities. These tests have shown that high-intensity exercise capabilities determine performance in elites while sub-elite performance is determined by multiple-sprint ability and endurance capability. The findings can be used to improve assessment of training effects and to inform the design of effective training methods.

abstract: Physical activity is critical for optimal health and has emerged as a viable option to improve sleep. Moderate- and vigorous-intensity physical activity comparisons to improve sleep in non-exercising adults with sleep problems is limited. The purpose was to determine the effects of moderate- or vigorous-intensity exercise on sleep outcomes and peripheral skin temperature compared to a no-exercise control. The exercise intensity preference also was determined. Eleven women (46.9±7.0 years) not participating in regular exercise and self-reporting insomnia completed a graded maximal exercise test followed by a crossover trial of three randomly assigned conditions separated by a 1-week washout. Participants performed moderate-intensity [MIC, 30 minutes, 65-70% maximum heart rate (HRmax)] or high-intensity (HIT, 20 minutes, 1-minute bouts at 90-95% HRmax alternating with 1-minute active recovery) treadmill walking or a no-exercise control (NEC) on two consecutive weekdays 4-6 hours prior to typical bed time. A dual-function wrist-worn accelerometer/temperature monitor recorded movement and skin temperature from which sleep-onset latency (SOL), sleep maintenance, sleep efficiency, total sleep time (TST), and peripheral skin temperature changes were calculated. Participants self-reported sleep outcomes weekly, enjoyment of exercise the morning after HIT and MIC, and exercise intensity preference upon completing all conditions. Mixed models analysis of variance examined differences between and within conditions controlling for demographic characteristics and habitual physical activity. HIT resulted in up to a 90-minute TST increase on night four (448 minutes, 95% CI 422.4-474.2) compared to nights one-three. MIC nights three (43.5 minutes, 95% CI 30.4-56.6) and four (42.1 minutes 95% CI 29.0-55.2) showed nearly a 30-minute SOL worsening compared to nights one-two. No other actigraphy-measured sleep parameters differenced within or between conditions. Self-reported sleep outcomes, peripheral skin temperature change, and exercise enjoyment between conditions were similar (p>0.05). More participants preferred lower (n=3) to higher (n=1) intensity activities. Early evening high-intensity and moderate-intensity exercise had no effect on sleep outcomes compared to a control in non-exercising adults reporting sleep complaints. Sleep benefits from HIT may require exercise on successive days. Participants indicated partiality for lower intensity exercise. More information on timing and mode of physical activity to improve sleep in this population is warranted. / Dissertation/Thesis / Doctoral Dissertation Physical Activity, Nutrition and Wellness 2016

No description available.

Every runner faces changes in speed and slope while exercising. While running faster or on a steepier surface represent different stimuli, both conditions lead to an increase in metabolic demand and therefore in heart rate (HR). The control of HR is given by both neural and non-neural components and can be accessed analyzing the heart rate variability (HRV). During exercise, HRV is known to be influenced by both sympathetic and parasympathetic branches of the autonomic nervous system, by breathing frequency, cadence, amongst other components. Hence, the present study sought to address how changes in speed and slope during running impact HR and HRV and whether the patterns observed for a restricted population were applicable to a broader group. We collected ECG records from volunteers divided into 2 groups: Experiment 1 (N = 12, with a broader range of ages and fitness level) and Experiment 2 (N = 9, composed of a more homogeneous population). Subjects ran on 9 (Experiment 1) or 16 (Experiment 2) combinations of speed and slope for a few minutes. Our data shows that the relationship between slope (%), relative speed (v) and relative HR is HR = 0.36 + 0.643 * v + 0.033 * s * v . HR behaved as predicted by a general equation of cost of locomotion in mammals and avians when it comes to the proportional impact of speed and slope, but not regarding the magnitude of such responses. This must reflect the loss of linearity between metabolic demand and HR at very high exercise intensities. Changes in HR could explain the behavior of most HRV estimators. However, one estimator (a1ApEn) could better be explained by changes in speed and slope. This indicates that HRV responds primarily to metabolic demand. The same general pattern of response of HRV to the different running conditions was observed in both groups, although, likely due to age-associated changes in cardiac control, how much a given HRV estimators changes differ between groups / Todo corredor se depara com mudanças de velocidade (v) e inclinação (i) durante o exercício. Correr mais rápido ou em uma superfície mais íngreme representam estímulos diferentes, porém ambos levam a um aumento na demanda metabólica e, portanto, na freqüência cardíaca (FC). O controle da FC é dado por componentes neurais e não neurais e pode ser acessado analisando-se a variabilidade da frequência cardíaca (VFC). Durante o exercício a VFC é influenciada pelos ramos simpático e parassimpático, freqüência ventilatória, cadência, dentre outros componentes. Assim, buscamos abordar como mudanças de velocidade e inclinação durante a corrida impactam a FC e a VFC e se os padrões observados para uma população restrita aplicam-se à um grupo mais amplo. Foram coletados registros de ECG de voluntários divididos em 2 grupos: Experimento 1 (N = 12, com faixa etária e nível de condicionamento físico mais amplos) e Experimento 2 (N = 9, composto por uma população mais homogênea). Os voluntários correram em 9 (Experimento 1) ou 16 (Experimento 2) combinações de velocidade e inclinação por alguns minutos. Nossos dados mostram que a relação entre inclinação (%), velocidade relativa (v) e FC relativa é FC = 0.36 + 0.643 * v + 0.033 * s * v . A FC se comportou como previsto por uma equação geral do custo de locomoção em mamíferos e aves quando se trata do impacto proporcional de velocidade e inclinação, mas não em relação à magnitude de tais respostas. Isso deve refletir a perda de linearidade entre a demanda metabólica e a FC em intensidades de exercício muito altas. Mudanças na FC explicam o comportamento da maioria dos estimadores de VFC. No entanto, um estimador (a1ApEn) foi melhor explicado por mudanças de velocidade e inclinação. Isso indica que a VFC responde principalmente à FC. O mesmo padrão de resposta da VFC às diferentes condições de corrida foi observado em ambos os grupos, embora, possivelmente devido à mudanças no controle cardíaco associadas à idade, o quanto um determinado estimadores se altera difere entre os grupos