Background: Marathon running involves running long distances and is associated with a high prevalence of running-related injuries. The calf has been identified as one of the most commonly injured structures during running. Running training causes an overload on muscle and stimulates a physiological adaptation to create a training response. Specific adaptations in metabolic and physiological function of a muscle may be further achieved through specificity of exercise training. Resistance training programmes are commonly implemented to enhance specific muscle strength and endurance; and are effective methods of performance and injury prevention. While evidence-based guidelines for resistance training exist, it is unclear whether runners are routinely incorporating evidence-based resistance training into marathon training programmes. If runners are performing habitual resistance training, it is also unknown if the resistance training is of sufficient magnitude or intensity to induce dose-related responses in calf muscle structure or function. Aim: The aim of this study was to evaluate gastrocnemius muscle structure and function in marathon runners who performed habitual resistance training in addition to regular endurance training, compared to marathon runners who performed traditional endurance running training only. Specific Objectives: • To describe the demographic and training characteristics of habitually resistance-trained marathon runners and traditionally running-trained marathon runners. • To determine if there were differences in gastrocnemius endurance, power and flexibility between habitually resistance-trained marathon runners and traditionally running-trained marathon runners. • To evaluate if there were differences in the gastrocnemius muscle structure and architecture in habitually resistance-trained marathon runners compared to traditionally running-trained marathon runners. • To establish if there were any differences in the number of calf injuries sustained in habitually resistance-trained marathon runners and traditionally running-trained marathon runners. Methods: Healthy male runners between 20 and 50 years were included in the study. Participants were required to have completed at least one marathon in the 12-month period prior to the study. Runners forming the "traditionally running-trained" group were required to be participating in regular endurance running training only. Runners in the "habitually resistance-trained group" were required to be performing resistance training in addition to regular endurance running training. Runners with any injury at the time of recruitment or runners who reported a calf injury within the six-month period prior to the study were excluded. Participants with any medical abnormalities detected during screening were also excluded from the study. Eight marathon runners participating in habitual resistance training plus standard running training and eleven marathon runners participating in traditional running training only were recruited for this study. Runners who met the criteria attended two testing sessions at least three days apart. During the first session, informed consent was obtained and the Physical Activity Readiness Questionnaire (PAR-Q) was completed to ensure participants could safely complete physical testing. A questionnaire was completed to determine relevant training and injury history. Body mass, height and the sum of seven skinfolds were recorded. Muscle architecture measurements, including fascicle length, pennation angle, thickness and volume, were performed via imaging ultrasound. Participants were then familiarised with the physical testing procedures. In the second testing session, calf muscle flexibility and endurance were assessed; and isokinetic testing was performed for the left and right triceps surae. Results: There were no significant differences in descriptive characteristics between groups. Participants in the habitually resistance-trained group performed in an average of two hours (range 0.5-2.5 hours) of resistance training of between one to four sessions per week. Participants combined upper and lower body training in the form of circuit training, body weight training, core and proprioceptive training. Resistance training sessions were performed at a varied intensity for load (light to high) according to an estimated 1RM. Participants in the habitually resistancetrained group had completed a significantly greater number of 21.1 km races compared to the traditionally running-trained group (p < 0.05); but there were no other differences in running training or competition history between groups. There were also no significant differences in the number of reported injuries between groups. Average pennation angle was significantly increased in the habitually resistance-trained group compared to the traditional running-trained group (p < 0.05). No other significant differences in architectural measurements were identified. There were no significant differences in calf muscle flexibility, strength, power or endurance between the two groups. However, the small sample size limits the interpretation of the study findings. Conclusion: Wide variability in habitual resistance training patterns were identified. While pennation angle was significantly greater in the habitually resistance-trained group; no differences in all other architectural measurements; or calf muscle strength, power, endurance or flexibility between groups were identified. However, one of the key findings emerging from this study is the variable resistance training practices in endurance runners; and that resistance training practices were not aligned to current evidence-based guidelines for resistance training. Resistance training has a critical role in enhancing endurance running performance, injury prevention and rehabilitation. Future research should investigate the knowledge, attitudes and practices of endurance runners regarding resistance training; to facilitate the development of appropriate education interventions, and to effectively disseminate evidence-based training guidelines to lay communities.

Epidemiological data is important to better understand injury and illness patterns in para athletes. Medical teams used a web-based injury and illness surveillance system (WEB-IISS system) to all the para-athlete injuries and illnesses during the 2012 London Paralympic games. All team physicians could access the system at any time to log data, providing a vast database for potential research. The relative ease of data collection permits large amounts of data to be analysed, providing important surveillance data on injury and illness. Data on the South African para-athletes, provided by the team's Chief Medical Officer, were assessed and compared to all countries. This study aimed to describe the illness and injury profiles in South African elite paraathletes who participated in the 2012 Summer Paralympic Games; and compare these profiles to data from the other countries that participated. A retrospective sub-analysis of the data-set collected from a large prospective study of injury and illness at the London Summer Paralympic Games in 2012 was compared to data collected on all para-athletes from input by team physicians into the WEB-ISS system. In total, 62 South African para-athletes presented with 19 injuries, with an injury rate of 21.9 per 1000 athlete days. Twenty-five para-athletes presented illness, with an illness rate of 28.8 per 1000 athlete days. The overall injury and illness rate in the South African para-athletes was higher than the injury and illness rate in all para-athlete participants at the London Paralympic Games. The anatomical distribution of injuries (lower limbs, axial and upper limbs) and the nature of illness (respiratory, skin & subcutaneous and digestive systems) were however similar. Causative factors are not evident and need to be further studied. Increased efforts in injury and illness surveillance and preventative programmes should be employed to reduce the incidence of injury and illness, and their severity . Such efforts in para-athlete care should be ongoing with surveillance to monitor and manage trends to ensure the culmination of Paralympic competition does not result in high rates of injury and illness. Education of healthcare providers, para-athletes, coaches and others in the management of para-athletes, is key.

This thesis comprises a series of independent investigations examining rugby injuries occurring to players from under 14 to senior provincial level in the Cape Province (now the Western Cape). The first two studies report data aimed at gaining a more detailed understanding of rugby injuries in specific populations or under specific conditions, whilst the remainder of the thesis reports injury data from both a retrospective and a prospective epidemiological survey involving the same 3990 boys from 25 high schools. Following publication of data showing a progressive rise in the number of spinal cord injuries in the Western Cape, coupled with a sustained media attack on the attitudes of the (then) South African Rugby Board, certain experimental law changes were introduced to South African schoolboy rugby in 1990 and 1991. The purpose of the law changes was either to make the game safer or to make it more open and flowing, or both. Accordingly, the studies described in chapters 4 -8 set out to analyse the effects of these law changes on the incidence and nature of rugby injuries. This was accomplished by comparing data with a similar study conducted in 1983 and 1984 in the same 25 schools (Roux, 1992). The study reported in chapter 2 determined whether the use of neoprene (thermal) pants might reduce the risk of hamstring injury amongst 60 senior club rugby players, all of whom had previously sustained a hamstring muscle tear. The rationale was that the few seasons prior to this 1992 study had been characterised by an increasing use by rugby players of thermal or neoprene pants; a practice which seemed to have evolved spontaneously and without any scientific assessment of its value. We concluded that the wearing of thermal pants can reduce the risk of hamstring injury during rugby. However, other risk factors for injury are probably more important. These include levels of preseason physical fitness, correct warm up and stretching procedures before activity and adequate rehabilitation before returning to activity following injury. The objective of the study reported in chapter 3 was to determine the influence of preseason strength and endurance training on risk of injury in rugby players from two South African provincial teams during the 1992 rugby season. Players from one province followed a supervised scientifically-designed physical training programme, while those from the other did not follow a structured programme. The findings of the study, the first study to prove the relationship between pre-season preparation and early season injury, showed that inadequate pre-season endurance training is a major contributor to the high injury rate at the beginning of the season amongst provincial rugby players. Further, strength and endurance training are interrelated as risk factors. Thus, compared to players with adequate strength and endurance training, those with adequate strength training and insufficient endurance training are at greatest risk of injury, followed by players with insufficient strength and endurance training. It was also shown that contact practices 2 days after inter-provincial match contributed more to an increased number of injuries than to success; that "niggling" injuries may develop into more serious injury if players attempt to "play through" them; and that the lack of structured treatment and rehabilitation of an injury places players at risk of being re-injured.

The main objectives of this dissertation was: 1) to review the available evidence with respect to the period prevalence of pre-race upper respiratory tract infections (the week before a distance running event) in distance runners, the relationship between exercise and infections, and the possible health consequences of participating in sport whilst suffering from an acute infective illness; 2) to document the period prevalence of runners with an acute illness in the 7-day period prior to an endurance race; 3) to determine the period prevalence of runners who "fail" the "neck check", and would be advised not to participate in the race, 4) to determine the incidence of runners with an acute illness, and who received educational information and guidelines, and who then not start the race, 5) to determine the incidence of runners with an acute illness who chose to start the race, but do not finish the race, and 6) to determine the incidence of runners with an acute illness who chose to start the race, but develop medical complications during the race.

Background: Chronic diseases of lifestyle (CDL) are associated with high rates of morbidity and mortality in South Africa. Although prevalence of CDL has been established in the general population, there is limited research regarding the prevalence and risk factors for CDL in individuals taking part in regular physical activity. Endurance running is a popular sport, with growing levels of participation. Anecdotally, many individuals who participate in endurance running do not undergo formal pre-participation cardiovascular screening. It is also unclear if endurance runners are meeting the World Health Organisation’s recommended weekly moderate to vigorous intensity physical activity hours, or if they have other risk factors for CDL. It is therefore important to establish the prevalence and risk factors of CDL in this active population. Aim and Objectives: The aim of this study was to determine the prevalence of CDL and the associated risk factors in endurance runners in South Africa. The specific objectives of the study were: (a) to determine the presence of risk factors for the development of chronic diseases of lifestyle, including body mass index (BMI), waist circumference, body fat percentage, blood pressure, blood glucose, blood cholesterol, smoking history, dietary intake and weekly physical activity time in South African endurance runners; (b) to determine the presence of non-modifiable risk factors to the development of CDL, namely age and income, in South African endurance runners; (c) to determine whether South African endurance runners are fulfilling the World Health Organization’s recommended weekly moderate to vigorous intensity physical activity hours; and (d) to assess whether there are any relationships between the running characteristics, namely weekly training hours, running speed and level of competition; and the risk factors for chronic diseases of lifestyle. Methods: This study had an analytical, cross-sectional design. Two hundred participants between the ages of 18 to 69 years old, who reported endurance running as their main sport, and ran at least three kilometres twice a week for the past year were included in the study. Participants were excluded if they were pregnant or within six months post-partum, had an injury that required a minimum of two weeks rest or did not complete the questionnaire or physical testing component of the testing process. Participants were recruited through local running clubs and running races in the areas of Nelspruit, Mpumalanga and Cape Town, Western Cape. All participants gave written informed consent, and completed a questionnaire including socio-demographic characteristics, running training characteristics, the International Physical Activity Questionnaire short questionnaire, the modified Borg scale of perceived exertion, and the five-a-day community evaluation tool. Body mass, stature, skin folds and waist circumference were assessed. Blood pressure was measured using an automatic blood pressure monitor. A finger prick test was used to determine random blood glucose and cholesterol concentrations. Participants were requested to fast for three hours prior to testing to standardise the test in a non-fasted state (20). Results: One hundred and twenty four (62%) participants were found to have at least one risk factor for CDL. A high BMI was the most common risk factor for CDL (n=90; 45%). Nineteen participants (9.5%) did not meet the recommended duration of 150 minutes of physical activity per week. Seven percent of female participants (n=7) smoked, which is equivalent to the female population average of South Africa. Multiple risk factors were identified in fifty seven (28.5%) participants, ranging from two risk factors (n=37; 18.5%) to six risk factors (n=1; 0.5%). The majority of participants had no prior medical diagnosis of CDL or risk factors for CDL. The overall self-reported prevalence of a medically diagnosed CDL was 5.5% (n=11). Type 2 diabetes was the most commonly diagnosed CDL (n=6; 3%). Waist circumference, systolic blood pressure and cholesterol were significantly elevated in the older age group. There were no significant differences in risk factors for CDL according to income status. Female runners had significantly higher average sitting times compared to male runners. In addition, participants with a BMI ≥ 25 kg.m-2 had significantly slower 10 km running speeds and lower average weekly training distance, compared to participants with BMI within normal ranges. Conclusion: A high prevalence of risk factors for CDL was identified in South African endurance runners. The majority of endurance runners included in this sample are fulfilling the World Health Organisation’s recommended weekly moderate to vigorous intensity hours. However, the endurance runners in this study remain at risk for developing a CDL due to the presence of other risk factors for CDL. The knowledge and awareness of risk factors for CDL among South African endurance runners needs to be further investigated. Health care professionals are required to improve the prevention and management of risk factors of CDL through education and promotion of healthy lifestyles. A stronger emphasis on the prevention of risk factors for CDL in South African endurance runners is needed.

Background: Beach volleyball (BVB) is rapidly developing into a popular activity both for recreational and competitive athletes. The majority of injuries sustained playing volleyball (beach and indoor) are considered non-contact. While commonly injured areas (ankle, knee, lower back and shoulder) are similar in beach volleyball (BVB) and indoor volleyball (IVB), injury incidence in BVB players is reported as 3.9-4.9 per 1000 hours, which is significantly lower than in IVB (1.7-10.7 per 1000 hours). Several factors contribute to the level of performance as well as to injury risk in volleyball players: body composition, changes in training load, previous injury, balance, proprioception, joint kinematics and muscle strength. There has been recent growth in the literature investigating the role of proprioception in the assessment, management and prevention of musculoskeletal injuries. Proprioceptive retraining strategies are diverse and yet no conclusive evidence demonstrating the superiority of one exercise over another is available. However, consensus exists that proprioceptive training requires movement on an unstable or uneven surface. Although proprioceptive exercises are commonly integrated into sports rehabilitation, there is a lack of high-quality evidence proving that proprioception can be trained. Maximal vertical jumping, lateral cutting sprints and diving to play the ball are repetitively demanded of volleyball players. BVB players complete these actions on sand (an uneven and unstable surface), making this sport, by definition, a continuous proprioceptive training exercise. By comparing two groups (IVB and BVB players) who perform a very similar sport on different surfaces (indoor and sand), we wish to investigate whether this may have led to differences in proprioception. Furthermore, we would like to measure the possible influence of this training aspect on functional capacity (lower limb range and strength, agility and vertical jump height). Aim: To compare proprioception, functional lower limb capacity, agility and jumping capacity on two different surfaces, between non-professional BVB and IVB players. Methods: A descriptive, cross-sectional, analytical study was conducted. The study adhered to the research ethics guidelines of the Declaration of Helsinki. The study protocol was submitted and approved by the Faculty of Health Sciences Human Research Ethics Committee, University of Cape Town. Convenience sampling was used to recruit 30 non-professional volleyball players (15 BVB and 15 IVB players) in the Western Cape, who met the inclusion criteria. Each player attended a testing session where they were given an informed consent sheet. If they decided to consent to participate and sign the form, a screening questionnaire was administered to determine eligibility to participate. Due to the COVID pandemic, participants also completed a COVID-19 screening tool. If eligible to continue to take part in the study, participants completed two questionnaires (Training and Injury History questionnaire and OSTRC (Oslo Sports Trauma Research Centre) questionnaire), after which they completed seven physical tests (the wedge test, two-point discrimination test, modified balance error scoring system (mBESS) test, modified star excursion balance test (mSEBT), knee-to-wall test, single leg hamstring bridge test (SLHBT) and eccentric-concentric calf raise test). They then proceeded to perform two jumping tests (countermovement jump with arm swing (CMJA) test and single leg triple hop for distance (SLTHD) test) and an agility test agility (modified agility T-test (MAT)) both on sand and hard surfaces. Descriptive statistics were used to present the demographical data, training and injury history. A t-test was used to determine whether the two groups were comparable on anthropometric data. Differences between the two groups (BVB and IVB players) in proprioception, agility and jumping capacity were analysed using Mann-Whitney U and unpaired t-tests. Repeated measures ANOVA were used to determine any differences in agility, jumping height or hopping distance between IVB and BVB players when tested on different surface conditions (the surface being the within-group factor and player type being the between-group factor). Effect size analysis was also reported for the physical outcome measures data, to determine the strength of any trends in differences existing between the two player groups Results: IVB and BVB groups were similar regarding demographics, training history and injury prevalence. Age was the only variable found to be significantly higher in BVB players than IVB players (p = <.001). There were no significant differences in most measures of balance, strength, agility or jumping capacity between the groups. While the results of the proprioception measure (wedge test) were also not significant (p= 0.08), a medium effect size (Cohen's d = 0.66) was found, with the BVB group identifying more differences in wedge heights correctly. There was a significant difference in the anterior reach of the Y-balance test (right and left legs) between the groups (p < 0.05), with the BVB group out-performing the IVB group. The study showed no significant correlations between proprioceptive measures and functional outcomes. A repeated-measures ANOVA determined that there was a significant main effect of surface type on mean CMJA heights (Wilks' Lambda = 0.799, F (1,28) = 7.040, p = .013), mean left leg SLTHD distances (Wilks' Lambda = 0.522, F (1,28) = 25.654, p = < .001) and mean right leg SLTHD distances (Wilks' Lambda = 0.473, F (1,28) = 31.169, p = < .001). However, no surface by player group interactions emerged, indicating that the impact of the surface was not different between groups of players: All volleyball players ran faster, jumped higher and hopped further on the indoor floor than on the sand. Discussion and conclusion: The findings of this study suggest that there are no consistent differences in functional capacity between IVB and BVB players. Despite limited findings, the current study contributes to the literature, as it is one of a few studies to assess the effect of habitual sand training on functional performance measures between IVB and BVB players. It is hoped that this study could provide a basis for further investigation into training on different surfaces to improve functional outcome measures, for overall performance improvement.

No description available.

No description available.

Background: Rugby is a popular international sport for male and female youth and adult players (6). Injury incidence including sport-related concussion (SRC) is high in youth rugby (7, 8) . This is concerning as youth are more vulnerable to SRC and take longer to recover from SRC than adults (9, 10). Females are also more susceptible to sustaining a SRC, take longer to recover from SRC and have a higher incidence of SRC complications than men (11-15). Most research has focused on SRC in adult male players. There are fewer studies on youth, in particular female youth. Further research into SRC in youth male and female players is thus required. Aim: The aim of this study was to determine the incidence and mechanism of SRC among youth male and female rugby players at the 2011 to 2018 and 2015 to 2018 South African Rugby Union Youth Week Tournaments respectively. Specific objectives: a) To determine the incidence of SRC among boys U13-U18 and girls U16-U18 players; b) To describe SRC mechanism of injury in boys U13-U18 and girls U16-U18 players; c) To determine if a difference in SRC incidence exists between boys U13-U18 and girls U16-U18 players, and also, between age groups; d) To determine if a difference in mechanism of SRC exists between boys U13-U18 and girls U16-U18 players, and also, whether the difference exists between age groups; and e) To describe l factors associated with SRC in boys U13-U18 and girls U16-U18 players. Methods: The study had a retrospective, epidemiological design. The study reviewed SRC injury data collected at the 2011-2018 South African Rugby Union Youth Week Rugby Tournaments. SRC injury data for boys was collected at the 2011-2018 South African Rugby Union Youth Week Rugby Tournaments. SRC injury data for girls was collected only at the 2015-2018 South African Rugby Union Youth Week Rugby Tournaments, as the girl's tournaments were only introduced in 2015. Results: Data from 266 SRC events were analysed in the study. Overall SRC incidence was 7.0 SRC per 1000 match playing hours (95% CI, 6.2.-7.8). Overall SRC incidence for boys was 6.9 SRC per 1000 match playing hours (95% CI, 6.0-7.8). Overall SRC incidence for girls was 7.9 SRC per 1000 match playing hours (95% CI, 5.3-9.9). There was no significant difference in SRC incidence between boys and girls. SRC incidence from 2011-2018 was 10.7 (95% CI, 8.2-13.1), 7.5 (95% CI, 5.5-9.6) and 5.3 (95% CI, 3.4-6.5) SRC per 1000 match playing hours for boys U13, U16 and U18 age groups respectively. SRC incidence from 2015- 2018 was 7.2 (95% CI, 3.7-10.2) and 7.9 (95% CI, 4.7-10.9) SRC per 1000 match playing hours for girls U16 and U18 age groups respectively. There was a significantly higher incidence of SRC in the boys U13 age group when comparing boys U13 and U18 age groups (IRR 2.0; 95% CI, 1.5-2.7; p=0.00014). Boys U13 players were twice as likely to sustain a SRC than their U18 counterparts. The tackle (65%) and ruck (20%) were responsible for the majority of SRC. Boys U13 players were significantly more likely to sustain a SRC from a tackle than boys U18 players (p= 0.01). Boys U16 players had a significantly greater incidence of SRC resulting from the ruck than boys U18 players (p=0.02). Overall the most common primary mechanisms of SRC were front-on tackles (27%) and collisions (18%). Boys U16 players had a significantly higher rate of SRCs due to front-on tackles than boys U18 players (p=0.00007). U16 boy players also had a significantly higher rate of SRCs caused by collisions than U18 boy players (p=0.00007). Similarly, boys U13 players had significantly higher incidences of SRCs due to collision than boys U18 players (p=0.003). Factors that were associated with SRC incidence were tournament day and the use of headgear. SRC was more likely to occur on day two than day four (p=0.0008), day five (p=0.0002) and day six (p<0.001). Players who did not wear headgear were more likely to sustain a concussion than those who did (p<0.001). Conclusion: Overall SRC incidence at the 2011 to 2018 South African Youth Week Rugby Tournaments was 7.0 SRC per 1000 match playing hours. This study is unique as it reports SRC incidence for youth female players. The overall SRC incidence for girls U16 and U18 groups was 7.7 SRC per 1000 match playing hours. As no significant difference was found for the incidence, injury event and mechanism of SRC between male and female players, similar injury prevention strategies can be implemented with these groups. Injury prevention strategies should focus on teaching safe contact technique in the tackle and ruck. Particular attention should be focused on teaching safe contact technique in U13 boys as the SRC incidence was highest in this group. Injury prevention strategies should also focus on teaching U13 and U16 boy players how to avoid collisions; and teaching U16 boy players how to execute safe front-on tackles and rucks. Further research should focus on identifying what aspects of the tackle and ruck result in SRC so more tailored and specific injury prevention strategies can be implemented.

Natural killer (NK) cells are a type of lymphocyte involved in innate and adaptive immunity. In adults, exercise can increase NK cell cytotoxicity both as a total percent of target cell lysis and an increase in the function of each NK cell. Much less is known about this response in children. Thus, the objectives of this study were to examine: 1) the effects of exercise intensity and structure on NK specific lysis and NKCA per cell in youth, and 2) differences in baseline and post-exercise specific lysis and NKCA per cell by pubertal status and sex. We also examined the NK cell and NK subset response to these exercise protocols by pubertal status and sex to help contextualize the NK functional response. We recruited healthy, recreationally active pre-pubertal (8-11 years, N=5) and late/post-pubertal (15-18 years, N=6) children from the Hamilton community. Participants completed 4 experimental cycling sessions in a randomized order including: high intensity intermittent (HI-INT) or continuous (HI-CONT), and moderate intensity intermittent (MOD-INT) or continuous (MOD-CONT) cycling. Blood was collected at baseline (PRE), immediately post-exercise (POST), and at 30- and 60-minutes recovery (REC1 and REC2, respectively). Peripheral Blood Mononuclear Cells (PBMC) were isolated from each timepoint and used in a cytotoxic assay with K562 targets. Flow cytometry was used to quantify target cell death (reported as specific lysis and NKCA per cell), and to determine NK cells and subsets as a proportion of lymphocytes. Exercise significantly increased specific lysis from PRE (25.1± 6.7%) to POST (30.6±11.0%), while NKCA per cell increased from PRE (0.69±0.76) to REC2 (1.3±1.3); p<0.05 for both. These responses were seen irrespective of exercise intensity and structure, pubertal status, and sex. The % total NK cells increased from PRE to POST (6.8±2.8% vs. 13.6±7.2%), and was greater in post-pubertal children vs. pre-pubertal children (20.9±6.2% vs. 9.1±4.3%), and after HI-INT (15.5±8.1%) and MOD-INT (16.2±9.5%) vs. HI-CONT (12.0 ± 5.0%) and MOD-CONT exercises (10.6 ± 4.5%; p<0.05 for all). Acute exercise can enhance NK cell cytotoxicity in youth regardless of exercise intensity, structure, pubertal status, or sex. NK function and mobilization responses to exercise did not always align, which suggests that unique post-exercise processes contribute to changes in NK cell proportions, specific lysis, and NKCA per cell. Our study has enhanced the understanding of exercise-induced changes NK cell cytotoxicity in the growing years. Future research will focus on explaining these effects, and exploring the clinical application of exercise programs in youth. / Thesis / Master of Science (MSc) / The purpose of this study was to determine if exercise can increase the function of Natural Killer cells (NK cells) in children. These cells are a very important part of our immune system that work to protect us from harmful infections and cancers. We also wanted to see if puberty or sex influence how NK cells respond to exercise. We asked boys and girls who were 8-11 years old or 15-18 years old to visit our lab 5 times. During their first visit, we measured their fitness level. In the next 4 visits, they completed one of four different types of exercise including: 1) 30 minutes of hard cycling, 2) 5 minutes of stop-and-start hard cycling, 3) 30 minutes of less hard cycling, and 4) 5 minutes of stop-and-start less hard cycling. We collected blood at four times during each session, including: 1) before the exercise, 2) immediately after the exercise, 3) 30-minutes after exercise, and 4) 60-minutes after exercise. We took NK cells from this blood and added them to cancer cells. We measured how many cancer cells were killed by the NK cells. We were interested in learning if exercise changed the percent of cancer cells killed by NK cells. We also wanted to know if exercise helped make each NK cell a better killer. We found that immediately after exercise, NK cells were able to kill a greater percent of cancer cells than they could before exercise. We also found that at 60-minutes after exercise, each NK cell killed a greater number of cancer cells than they were able to before exercise. There were no differences in NK cell cancer killing capacity between boys and girls, or between pre-pubertal or post-pubertal children. Our study helps us understand how we can increase important immune functions with exercise in children.