High-intensity interval training (HIIT) consists of short intervals of exercise at high intensity intermitted by intervals of lower intensity and is associated with improvement of body composition and metabolic health in adults. Studies in overweight adolescents are scarce. We conducted a randomized controlled trial in overweight adolescents to compare acceptance and attendance of HIIT with or without weekly motivational encouragement through text messages and access to a study website. HIIT was offered for six months (including summer vacation) twice a week (60 min/session). Participation rates were continuously assessed and acceptance was measured. Clinical parameters were assessed at baseline and after six months. Twenty-eight adolescents participated in this study (age 15.5 +/- 1.4; 54% female). The standard deviation score for body mass index over all participants was 2.33 at baseline and decreased by 0.026 (95% CI - 0.048 to 0.10) units, p = 0.49. Waist to height ratio was 0.596 at baseline and decreased by 0.013 (95% CI 0.0025 to 0.024), p = 0.023. Participation within the first two months ranged from 65% to 75%, but fell to 15% within the last three months. Attendance in the intervention group was 14% (95% CI - 8 to 37), p = 0.18, higher than the control group. Overall program content was rated as \"good\" by participants, although high drop-out rates were observed. Summer months constitute a serious problem regarding attendance. The use of media support has to be assessed further in appropriately powered trials.

The aim of this master thesis is to evaluate the influence of a six-week HIIT (High intensity interval training) on body composition and both aerobic and anaerobic performance. A group of 9 men aged 28-51 years was gathered and who followed an exact six-week training programme according to the chosen hypothesis. The results of our study show that the chosen six-week programme led to statistically significant (p < 0,05) changes in body weight (kg), BMI (kg/m2 ), in FEV (l), and ANC/kg (J/kg). Changes in the other parameters were statistically not significant. Taking into account the size of group (n=9) we conclude that mainly effects on the individual level were attained.

Thesis (MScSportSc)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: There is a growing concern in South Africa and worldwide about the global epidemic of obesity and overweightness among the general population. Obesity mediates the pathogenesis of pathological conditions and is associated with a poor quality of life, high morbidity and mortality rates and a huge burden on an individual’s and the health system’s infrastructure and finances. The answer to this rising epidemic is weight loss. Endurance training has been shown to induce weight loss however, people usually cite lack of time as a barrier to meaningful participation in exercise programmes. High intensity interval training (HIIT) therefore emerges as a potential solution to these barriers as it takes a relatively short period of time compared to endurance training. Despite the differences in exercise durations the most cogent advantage is that HIIT elicits not just similar, but even superior central and peripheral adaptations. The central and peripheral adaptations have been shown to enhance weight loss, improve blood lipids and glucose levels, as well as decreasing blood pressure. The challenge facing exercise physiologists is to find the optimal exercise intensity and duration of HIIT bouts which would be time efficient, safe and well tolerated by overweight and obese people. The shortcomings of literature are that most HIIT studies have focused on healthy, overweight and obese men and these studies cannot be extrapolated to women who have been shown to respond differently to training. Moreover, other interventions investigating the effects of HIIT in women and men have been longer term rather than short term interventions. In order to fill the gaps in the literature, the main aim of this study was to investigate the training and detraining effects of a short-term HIIT programme on selected health-related measures in young overweight and obese women. To this end, a non-random sample of 20 overweight and obese women (aged 18-25) volunteered to participate in this study. Selected health-related outcomes were measured prior to training. The pre-training testing was followed by the HIIT intervention which was two weeks and consisted of six sessions using the 10 – 15x1 minute running at 90% HRmax which was separated by one minute active recovery periods at 50-60% of HRmax. The HIIT intervention was followed by a post test in which baseline measurements were repeated. This was then followed by a two week detraining period and follow up testing. The main finding of this study was that a period of two weeks of HIIT can elicit adaptations that can lower the risk profiles of young overweight and obese women. The results showed a statistically significant decrease in body mass (1.6%, p = 0.001), fat mass (3.7%, p = 0.001) and waist circumference (4.8%, p = 0.001), and an increase in lean mass of 1.9% (p = 0.001). There was also a decrease in blood glucose (11%, p = 0.001), total cholesterol (10.4 %, p = 0.01), systolic (3.4%, p = 0.001) and diastolic blood pressure (5.8%, p = 0.001) levels. Finally there was a statistically significant increase in relative VO2max and exercise capacity after the HIIT The follow-up testing after two weeks of detraining shows that the metabolic adaptations that were achieved by the HIIT protocol are relatively lasting or are at least not completely reversed. The weight loss induced by HIIT is important in that it is the major target in lowering the prevalence of overweightness and obesity. The HIIT protocol in this study emerges as a time efficient strategy in eliciting positive adaptations in clinical populations and healthy people. Moreover these findings suggest that 10 minute and 15 minute HIIT work bouts at near-maximal intensities are possibly the minimum amount of training that is needed to induce significant weight loss and other positive health-related outcomes. / AFRIKAANSE OPSOMMING: Daar bestaan ʼn toenemende besorgdheid in Suid-Afrika en wêreldwyd oor die globale epidemie van obesiteit en oorgewig onder die algemene bevolking. Obesiteit fasiliteer die patogenese van verskeie siektetoestande en word met ʼn swak kwaliteit lewe, hoë morbiditeit en mortaliteit en ʼn geweldige las op ʼn individu en die gesondheidsowerhede se infrastruktuur en finansies geassosieer. Een van die antwoorde op hierdie stygende epidemie is gewigsverlies. Dit is reeds gewys dat uithouvermoë oefening saam met ʼn kalorie beperkende dieet gewigsverlies in die hand werk. Mense dui egter ʼn tekort aan tyd as ʼn hindernis tot betekenisvolle deelname aan ʼn oefenprogram aan. Hoë intensiteit interval inoefening (HIIO) is dus ʼn potensiële oplossing tot hierdie hindernis aangesien dit in vergelyking met uithouvermoë inoefening in ʼn relatiewe korter periode van tyd uitgevoer kan word. Afgesien van die verskille in inoefenperiodes is die mees logiese voordeel dat die HIIO nie net soortgelyke nie, maar self beter sentrale en periferale fisiologiese aanpassing voortbring. Die sentrale en periferale aanpassing verhoog gewigsverlies, verbeter bloedlipiedes en glukose vlakke, en veroorsaak ʼn afname in bloeddruk. Alhoewel ʼn aantal studies die voordele van HIIO by jonger en ouer populasies aandui, is baie min studies op vrouens uitgevoer. Bevindinge kan nie noodwendig na vrouens ekstrapoleer word nie omdat hulle dikwels verskillend op inoefening as mans reageer. Dit is ook nie bekend of ʼn kort HIIO intervensie ʼn betekenisvolle impak op oorgewig en vetsugtige vrouens sou hê nie, asook hoe blywend enige veranderinge sou wees nie. Die hoofdoel van hierdie studie was dus om die inoefening- en die geen-inoefening effekte van ʼn korttermyn HIIO program op geselekteerde gesondheidskenmerke in jong oorgewig en vetsugtige dames te bepaal. ʼn Nie-ewekansige steekproef van 20 oorgewig en vetsugtige vrouens (18-25 jaar) het vrywillig ingestem om aan hierdie studie deel te neem. Geselekteerde gesondheidskenmerke is voor die aanvang van die inoefening gemeet. Die HIIO intervensie het twee weke geduur en het uit ses sessies bestaan (10 – 15x1 minuut draf by 90% HSmaks en een minuut aktiewe herstel by 50-60% HSmaks). Die HIIO intervensie is deur ʼn na-toets gevolg waarin basislyn metings herhaal is. Dit is deur ʼn twee weke geen-inoefening periode en opvolgtoetse opgevolg. Die hoofbevinding van hierdie studie was dat ses sessies van HIIO fisiologiese aanpassings na vore gebring het wat die risiko profiele van jong oorgewig en vetsugtige vrouens verlaag het. Daar was statisties betekenisvolle afnames in liggaamsmassa (1.6%, p < 0.001), vetmassa (3.7%, p < 0.001) en heupomtrek (4.8%, p < 0.001) en ʼn toename in vetvrye liggaamsmassa van 1.9% (p < 0.001). Daar was ook ʼn afname in bloedglukose (11%, p < 0.001), totale cholesterol (10.4 %, p = 0.01), sistoliese (3.4%, p < 0.001) en diastoliese bloeddruk (5.8%, p < 0.001). Daar was ook statisties betekenisvolle verbeteringe in relatiewe VO2maks en oefeningtoleransie na inoefening. Die opvolgtoetse na twee weke van geen-inoefening het getoon dat metaboliese aanpassings wat deur die HIIO bereik is, relatief blywend van aard was of ten minste nie totaal omgekeerd was nie. Die gewigsverlies wat deur die HIIO veroorsaak was is belangrik in die sin dat dit die hoofdoelwit aanspreek om die voorkoms van oorgewig en vetsugtigheid te verminder. Die studie suggereer verder dat 10 – 15 minute HIIO werksessies, by naby maksimale intensiteite, moontlik die minimum hoeveelheid inoefening is wat benodig word om betekenisvolle gewigsverlies en ander positiewe gesondheidskenmerke te bereik.

High-intensity interval training (HIIT) consists of short intervals of exercise at high intensity intermitted by intervals of lower intensity and is associated with improvement of body composition and metabolic health in adults. Studies in overweight adolescents are scarce. We conducted a randomized controlled trial in overweight adolescents to compare acceptance and attendance of HIIT with or without weekly motivational encouragement through text messages and access to a study website. HIIT was offered for six months (including summer vacation) twice a week (60 min/session). Participation rates were continuously assessed and acceptance was measured. Clinical parameters were assessed at baseline and after six months. Twenty-eight adolescents participated in this study (age 15.5 +/- 1.4; 54% female). The standard deviation score for body mass index over all participants was 2.33 at baseline and decreased by 0.026 (95% CI - 0.048 to 0.10) units, p = 0.49. Waist to height ratio was 0.596 at baseline and decreased by 0.013 (95% CI 0.0025 to 0.024), p = 0.023. Participation within the first two months ranged from 65% to 75%, but fell to 15% within the last three months. Attendance in the intervention group was 14% (95% CI - 8 to 37), p = 0.18, higher than the control group. Overall program content was rated as \"good\" by participants, although high drop-out rates were observed. Summer months constitute a serious problem regarding attendance. The use of media support has to be assessed further in appropriately powered trials.