Darren Warburton

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Mar 2019)
Innovations in athlete monitoring and interventions with applications in non-functional overreaching (2017)

Background: The monitoring of an athlete’s training load and cardiac function have demonstrated to be valuable assessment tools in individual sporting events. Additionally, short-term heat acclimation has shown to be effective for stimulating hypervolemia and augmenting cardiovascular performance. A gap in the literature exists indicating further research is required into both heat acclimation protocols and the monitoring of on-field training load and its cause and effect relationship with heart rate variability in team sport. Purpose: The purpose of this investigation was twofold; 1) identify a novel form of heat acclimation using hot yoga for augmenting cardiovascular and aerobic performance, and 2) identify an effective monitoring protocol suitable for team sport using internal training load and heart rate variability.Methods: The Canadian Women’s National Field Hockey team were participants for examining heat acclimation and the relationship between training load and autonomic modulation during the 2016 Olympic cycle. A maximal graded exercise test was completed prior to and following six hot yoga sessions to examine cardiovascular and aerobic performance measures.Results: In Chapter 4, six days of hot yoga developed hypovolemia that lead to trivial improvements in aerobic power, run time to exhaustion, and a small increase in running speed at each ventilatory threshold. A non-existent relationship between markers of exercise stress and alterations in plasma volume during and post hot yoga were observed. Chapter 5 identified a large relationship between the planned and achieved on field training load over a complete mesocycle. Additionally, a moderate relationship was observed between both time spent above anaerobic threshold, training load and alterations in the Ln rMSSD:R-R ratio. Chapter 6 demonstrated how alterations in the Ln rMSSD outside of the coefficient of variation may identify the development of non-functional overreaching, while an unclear relationship was observed between weekly training load and alterations in Ln rMSSDCV.Conclusion: Hot yoga may elicit a delayed hypervolemic response when recommencing exercise. In addition, individually tailored mesocycles may prevent the development of non-functional overreaching when examined using heart rate variability while further research is required to confirm the Ln rMSSDCV relationship to accumulate weekly on-field training load in team sport.

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Cardiac and vascular dynamics in persons of Aboriginal descent (2014)

Introduction: Aboriginal populations currently experience greater rates of cardiovascular disease, than non-Aboriginals. Limited information regarding vascular and cardiac structure and function among this population are known, despite the close relationships of cardiac and vascular physiology to cardiovascular disease.Purposes: Theses investigations evaluate cardiac and vascular dynamics of Aboriginal Canadians, directly compare vascular measures between Aboriginal and European adults and evaluate the cardiac and vascular responses to exercise among Aboriginal and European adults.Methods: In the first investigation, 55 Aboriginal adults underwent a comprehensive vascular assessment. In Study 2, 10 Aboriginal adults underwent a resting echocardiographic evaluation. Study 3 compared the vascular status of 58 Aboriginal and 58 age- and sex-matched European adults. Vascular measures were assessed pre and post-exercise among 12 Aboriginal adults and 12 age- and sex matched European adults in Study 4. Pre and post-exercise cardiac assessments were performed on 12 Aboriginal and 12 age- and sex-matched European adults in Study 5. Results: In study 1, Aboriginal male and female adults (19-91 years) were found to have similar pulse wave velocity and intima-media thickness, with males having greater systolic blood pressure and small arterial compliance, and females having greater baroreceptor sensitivity. Study 2 identified Aboriginal males having larger left ventricular mass, dimensions, and volumes, while females had greater vascular resistance. In study 3, Aboriginal adults arterial compliance and baroreceptor sensitivity was identified as being more strongly associated with blood pressure compared to Europeans. Additionally, only European hypertension (blood pressure ≥140 mmHg systolic or ≥90 mmHg diastolic) rates were found to be associated with obesity (body mass index ≥30.0 kg•m-²). Study 4 identified European adults as having greater reductions in blood pressure following exercise, with a lack of change among Aboriginal adults. In study 5, Aboriginal and European adults were found to have similar cardiac functional responses to maximal aerobic exercise, including decreases in volumes and increases in arterial-ventricular coupling; however, only Aboriginal adults demonstrated decreases in volumes and compliance, and increases in elastance and stiffness following submaximal exercise. Conclusion: Differences in factors affecting blood pressure and blood pressure responses toexercise were identified between Aboriginal and European adults.

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Integrity of spinal autonomic pathways in sub-acute and chronic spinal cord injuries (2013)

The outcome of spinal cord injury (SCI) is still commonly described in terms of motor andsensory function, despite increasing awareness that there is also damage to the autonomicnervous system (ANS). The purpose of this thesis was to examine the integrity of spinalautonomic pathways among individuals with sub-acute and chronic SCI. The selection ofappropriate tests to assess autonomic function is challenging since the ANS is complex.Examining reliability and comparability among measures provides a comprehensiveunderstanding of the validity of specific tools. This doctoral thesis is comprised of three separateinvestigations that focus on determining the integrity of spinal autonomic pathways followingSCI. In the first study (Chapter 2), the focus was on the reliability of heart rate variability (HRV),sympathetic skin responses (SSRs) and an orthostatic challenge (sit-up test). Measures of HRV,SSRs and blood pressure changes during the sit-up test were found to be reliable. Additionally,the sit-up test was compared with the gold standard orthostatic challenge (tilt-table test), whichrevealed that the sit-up test provokes an orthostatic response comparable to the tilt-table test. Inthe last two studies (Chapters 3 and 4) HRV and changes in blood pressure (BP) during anorthostatic challenge, SSRs and the Valsalva manoeuvre (VM) were used to examine spinalautonomic integrity. The novel focus on integrity of spinal autonomic pathways revealed that itis affected by lesion level, neurologic severity of injury, and time post-injury. As expected basedon extensive existing research on cardiovascular autonomic function following SCI, higherlesion levels produced greater cardiovascular impairments. That is, there is greater compromiseto spinal autonomic integrity in high-level compared to low-level SCI. However, the associationbetween neurologic and autonomic “completeness” of injury is unclear. Our findings suggest thattime post-injury may affect the latter. During the sub-acute stage, autonomic tests revealedcardiovascular changes in patients in a one-month follow-up after admission to a rehabilitationhospital. The exact time course of alterations to integrity is unknown. Not acknowledging changeto spinal autonomic integrity is inherently problematic since it is unclear what neurologicseverity of injury infers about autonomic dysfunction.

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Regulation of cerebral and systemic blood flow in humans with high level spinal cord injury: the infleunce of alpha1-agonist midodrine hydrochloride (2013)

RATIONALE: Spinal cord injury (SCI) is a devastating condition, often resulting in severe autonomic dysfunction. Secondary to autonomic dysfunction, many individuals with SCI have low blood pressure, which likely challenges the brain’s capacity to maintain suitable perfusion. Individuals with SCI suffer from a myriad of conditions that may be associated with dysfunctional regulation of cerebral blood flow (CBF), including cognitive dysfunction, orthostatic intolerance and stroke risk. Current knowledge regarding CBF regulation in SCI is limited.AIMS: To comprehensively examine cerebrovascular control in those with SCI, including: 1) the CBF response to cognition, 2) the acute CBF response to tilt, 3) the relationship between baroreflex sensitivity and CBF regulation, 4) the role arterial stiffening plays in baroreflex sensitivity, and 5) to examine the influence of increasing blood pressure through oral administration of 10 mg midodrine (alpha1-agonist). The first investigation found that the CBF response to cognition is absent in those with SCI when compared with able-bodied individuals. When restoring blood pressure to normal levels with midodrine, the CBF response to cognition was improved by 70% which was reflected in a 13% improvement in cognitive function. The second investigation showed that midodrine improved orthostatic tolerance 59% in SCI, and mitigated the reduction of CBF during tilt. The CBF response to tilt was well-maintained in SCI. The third investigation assessed the relationship between common carotid artery stiffness and baroreflex sensitivity in those with SCI. Elevated arterial stiffness (+12%) in those with SCIwere negatively related to reduced in baroreflex sensitivity (R2=0.45; p
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The effects of strenuous exercise on cardiovascular function in healthy men and women (2013)

No abstract available.

Patterns of physical activity and sedentary behaviour and cardiovascular health in children (2011)

Introduction: Physical activity (PA) and sedentary behaviours are important modifiable risk factorsfor cardiovascular disease in adults; however, we know much less about their role for enhancing andsustaining children’s cardiovascular health. The aim of this thesis is to evaluate the relation between PA, sedentary time, and cardiovascular health in children. Methods: Participants were volunteers in a two-year randomized controlled dissemination trial of a whole school PA model (30 schools; 1,529 children). Activity intensity was measured via accelerometry (n=629), arterial compliance by applanation tonometry (n=250), and cardiovascular fitness (CVF) using a 20-meter shuttle run test (n=1,319). Results: In study 1, epoch length influenced the volume of activity recorded; however, the direction and magnitude of the bias depended on activity intensity and volume. In study 2, girls accumulated less moderate-to-vigorous PA (MVPA) and more sedentary time compared with boys, except during physical education. Fewer girls than boys met PA guidelines during school, recess, and lunch. Similarly few boys and girls (
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The Effects of Endurance Training and Age on Left Ventricular Rotation (2009)

No abstract available.

Master's Student Supervision (2010-2017)
An economic evaluation of a twelve week workplace primary prevention program (2016)

With the majority of Canadians waking hours spent at the workplace place, the financial effects of absenteeism and presenteeism due to chronic disease is increasing. Healthy lifestyle behaviours (such as physical activity, proper nutrition, smoking and alcohol reduction, and mental health management) play in reducing absenteeism and presenteeim rates is crucial. A comprehensive multi-faceted 12 week wellness program (i.e., ACCELERATION) was implemented within a workplace setting to determine its effects on absenteeism and presenteeism. One hour education sessions covered a range of topics from physical activity, proper nutrition, smoking and alcohol cessation to mental health management and stress coping. Weekly one hr exercise sessions conducted with exercise logs to monitor activity/exercise levels at home. The specialized workplace wellness program was designed to examine changes healthy lifestyle behaviours in relation to employee health status, as well as absenteeism and presenteeism costs. An economic evaluation of the ACCELERATION program was created via the distribution of online questionnaires at both baseline and a 3 month follow up. A total of 50 participants, 35 females (43.4 ± 11.5 yr) and 15 males (44.9 ± 10.5 yr) completed the 12 week program. The monetary results from the evaluation reported a reduction in absence days by 54.0% from 1.40 to 0.64 per employee and a cost savings average of $155.79 per employee. Presenteeism was reduced by 17.0% from 29.0% to 12.0% equating to an average cost savings of $420.12 per employee. These results indicate that the ACCELERATION program had a positive effect on employee health costs and is a beneficial health program for the workplace.

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Effects of antipsychotic medication on cardiovascular function and fitness in individuals with schizophrenia (2016)

Background: Individuals living with schizophrenia have consistently demonstrated impaired cardiovascular fitness. It is of particular interest whether antipsychotic medications significantly contribute to the reduced cardiovascular fitness in these individuals. A comprehensive review of the literature and meta-analysis was performed to examine the overall dose-dependent effect of antipsychotics on cardiovascular fitness. Also, it was tested in our participants with schizophrenia whether this dose-dependent effect might be independent of body mass index (BMI) and whether cardiovascular fitness might be further reduced in those exposed primarily to clozapine versus other antipsychotics. Methods: For our comprehensive review and meta-analysis, an electronic search of the literature was performed to identify studies that examined the effects of antipsychotics on cardiovascular fitness. For our original research investigation, 30 participants with schizophrenia or schizoaffective disorder stabilized on antipsychotics were recruited. The patients were divided into the clozapine (n = 15) and non-clozapine (n = 15) groups, and a group of healthy age- and sex-matched controls (n = 15) was included. All current antipsychotic doses were converted to chlorpromazine equivalents (CPZE). Each participant completed maximal symptom-limited exercise testing on a cycle ergometer for the assessment of peak aerobic power (VO₂peak). Results: The meta-analysis revealed an overall significant dose-dependent effect of antipsychotics on cardiovascular fitness in a total of 294 participants (correlation coefficient: -0.29, 95% CI: -0.43 to -0.14, p
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Novel recovery strategies for elite athletic performance (2015)

Background: Recovery strategies aim to reduce the inflammatory response that occurs following exercise induced muscle damage (EIMD) via increased venous return. Available research is contradictory regarding whether recovery strategies are effective in reducing recovery time and improving subsequent athletic performance. As a result, further research is warranted.Purpose: To determine which application is effective in accelerating recovery for athletes following eccentric exercise, and maintaining performance.Hypothesis: We hypothesized that the VIP and CWT will be more effective compared to placebo and NormaTec conditions in facilitating recovery.Methods: 24 highly trained participants were tested over five test sessions. Participants underwent measures of VJ, 10m/30m sprints, HRV, VAS and Leg Girth. Participants underwent 100 repetitions of a plyometric drop jump and were then randomly assigned into four conditions: 1) Contrast water therapy (CWT, n=6), 2) Variable intermittent pressure (VIP, n=6), 3) NormaTec IPC (NormaTec, n= 6), 4) Passive Recovery/ Placebo (Placebo, n=6). Perception of recovery was analyzed using a Likert recovery questionnaire. Follow-up measures of outcome variables occurred at 24, 48 and 72 hr.Statistics: Two-way mixed model ANOVA was used to assess between groups and repeated measures. Tukey’s HSD was used when necessary.Results: CWT demonstrated 4.4% increase in mean VJ @ 72 hr (p > 0.05). VIP demonstrated performance maintenance for VJ and sprint measures (p > 0.05). VIP demonstrated significantly (p 0.05) occurred between groups at any time point for any other outcome measures. Conclusion: CWT and VIP appear to be beneficial in facilitating recovery and the maintenance of performance following strenuous exercise compared to placebo and NormaTec conditions. There appear to be differences in subjective perceptions of muscle soreness reflecting the differences in recovery strategy methodologies. Further research is warranted to determine the underlying mechanisms responsible for facilitating recovery and maintaining physical performance.

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Cardiovascular function in HER2-postivie breast cancer survivors (2014)

Background: Trastuzumab, a HER2 antagonist, has been shown to improve rates of overall survival in patients with HER2-positive breast cancer. However, cardiotoxic effects associated with treatment limits these benefits. Due to an increase in survival years, women with a history of HER2-positive breast cancer might be at increased risk of developing cardiotoxicity (i.e., LVEF
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Left ventricular twisting mechanics during incremental exercise : the influence of aerobic fitness and venous return (2012)

The role left ventricular (LV) twisting mechanics play in the stroke volume response to incremental exercise is unknown. Furthermore, the influences of aerobic fitness and venous return on LV twisting mechanics during vigorous exercise have not been investigated previously. To examine this issue, LV twisting mechanics and haemodynamics were assessed in eight endurance-trained (VO₂ max = 68.1 ± 5.6 mL∙kg⁻¹∙min⁻¹) and eight normally active (VO₂ max = 50.1 ± 5 mL∙kg⁻¹∙min⁻¹) males during incremental upright and supine exercise at rest and during heart rates of 110, 130, 150, and 170 bpm. LV twisting mechanics were measured via echocardiography, while haemodynamic measures were collected using impedance cardiography. During both incremental protocols, cardiac output increased continuously in both groups. Stroke volume (SV) and end-diastolic volume increased to a greater extent in endurance-trained athletes compared to normally active individuals during exercise in both postural positions (e.g., SV at 170 bpm supine: ET, 45%; NA, 30.5%; SV at 170 upright: ET, 44.7%; NA, 33.8%; p
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The relationships between fundamental movement patterns, spike jump technique, and overuse pain in collegiate volleyball players (2012)

Despite an exceptionally high prevalence of overuse injury among elite volleyball players, very little is known about the aetiology of these conditions. Fundamental movement patterns have been found to be predictive of serious acute athletic injury, however the relationship between fundamental movement patterns and overuse injury has yet to be determined. Sport-specific jumping biomechanics have been shown to play an additional role in the development of overuse injuries in sport, and it is likely that combining fundamental and sport-specific movement assessment may possess greater predictive power than either alone. The purpose of this investigation was to evaluate how volleyball-related overuse injuries are related to fundamental movement patterns and volleyball spike jump technique. We hypothesized that volleyball players with a history of overuse injury would exhibit more dysfunctional fundamental and sport-specific movement than players without a history of injury. Fifty-seven male and female collegiate volleyball players took part in Functional Movement Screen testing, and athletes free of lower body pain (n=31) took part in a 2-dimensional kinematic analysis of spike jump technique using Dartfish video analysis software. Volleyball players with a history of overuse low back injury had significantly lower Active Straight Leg Raise scores compared to healthy players (p=0.011). Various aspects of hip mechanics during the spike jump were significantly related to a history of shoulder, low back, and knee pain (p
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Community-based physical activity and the risk for cardiovascular disease in Aboriginal Canadians (2010)

Introduction: Aboriginal individuals continue to experience greater levels of cardiovascular disease (CVD) and diabetes than the Canadian general population, though these diseases were historically rare. Increasing evidence indicates rising sedentary behaviours from the traditional healthy and active lifestyles of this population. Various interventions have been implemented to address the health inequities in Aboriginal peoples with mixed results. Unfortunately, limited research has taken a culturally appropriate community approach to improve the health and well-being of Aboriginal peoples. By implementing a community-based and participatory physical activity (PA) and healthy living program, health and wellness can be improved in a culturally relevant context.Purposes: The primary purpose of this investigation was to examine the health benefits of a community-based PA and healthy living intervention program for Aboriginal Canadians.Methods: Participants were recruited through local Aboriginal offices representing male and female participants of wide ranging ages and CVD risk profiles. Each participant completed identical testing days pre- and post-training including a variety of CVD risk factors and four CVD risk scoring systems. Participants were self-assigned to three different community-based PA interventions including walking, walk/running, or running.Results: Significant improvements in health measures and CVD risk scores were observed for both male and female participants of all age groups. The three PA programs produce similar improvements in health measures and risk scores. Individuals of high, moderate and low CVD risk also experienced similar improvements.Discussion: High program compliance indicated success for improving PA of this population. Improvements among both genders and a variety of age groups support this program as a successful intervention for males and females of all ages. The similar changes in health status with each of the programs suggest that Aboriginal adults successfully self-select an appropriate PA intervention for health benefits. Moreover, the similarity in improvements among participants of a variety of CVD risk classifications indicates this individualized program was appropriate for improving the health status of individuals of a range of CVD risk profiles.Conclusion: The self-selected intensities Hearts inTraining program was successful in improving health status and increasing PA for Aboriginal adults of all ages, genders and risk categories.

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