A boxing-oriented exercise intervention for obese adolescent males: findings from a pilot study.

Author:Shultz, Sarah P.
Position:Case report - Report
 
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Introduction

Within New Zealand, 23% of youth (15-18 y) are considered overweight or obese; Maori (28%) and Pasifika (35%) youth have a much greater risk for obesity than other ethnicities (21%) (University of Otago and Ministry of Health, 2011). The increased prevalence places these cohorts at greater risk for obesity-related cardio-metabolic conditions, which independently and additively increase cardiovascular disease (CVD) risk (Nakagami et al., 2006; Oliver et al., 2010; Reinehr et al., 2006; Winer et al., 2006). There is consensus that a sedentary lifestyle has contributed significantly to the current obesity epidemic (Hill et al., 2003). Unlike dieting, which can lead to loss of fat-free mass, physical activity maximizes weight lost from fat mass and minimises the loss of fatfree mass (Watts et al., 2005). Previous research has not focused on the effects of physical activity interventions on Maori and Pasifika adolescents, and given the high risks of obesity-related cardio-metabolic conditions in this population, the aim of the present study was to test the effectiveness of a non-contact boxing intervention.

There is evidence that shows aerobic and resistance training independently improves abdominal obesity and cardio-metabolic health (Lee et al., 2012), yet a combination of both training modes may demonstrate even greater benefits (de Piano et al., 2012). Exercise intensity also plays an important role. Indeed, high-intensity exercise has been associated with the greatest decreases in obesity, cardio-metabolic conditions, and the progression of CVD (Montero et al., 2012; Murphy et al., 2009; Tjonna et al., 2009). In light of the previous findings, non-contact boxing was identified as appropriate for use in an exercise intervention. Boxing training is characterized by high-intensity, intermittent activities (Arseneau et al., 2011; Bellinger et al., 1997) and, in previously untrained individuals, has been shown to result in favourable changes in cardiovascular fitness (Kravitz et al., 2003) and lipid profiles (Chatterjee et al., 2007). Besides improving physical health, boxing training can also lead to increased self-confidence, self-discipline, and character development (Sokol, 2004); it also seems that Maori and Pasifika prefer sports in which strong bonds can be made with their 'team-mates' and this extends to boxing training, perhaps perceived to be a 'family away from family'. Therefore, the purpose of this pilot study was to identify physiological and psychological benefits of a non-contact boxing-oriented training programme on obese Maori and Pasifika adolescent boys.

Methods

Recruitment

The objective of the pilot study was to recruit twenty obese adolescent males, who would be randomly assigned to a control or intervention group. Recruitment of participants for the pilot intervention included contacting local schools and physicians to help with referrals, and utilising print and television media to promote the study within the local community. One participant was recruited through print media, while two participants were recruited through physician referrals. An additional four males were also approached through physician referral and word of mouth, but did not participate in the exercise intervention because of scheduling conflicts. School referrals proved ineffective.

Participants

Three adolescent males (14.4 [+ or -] 0.2 y) were recruited. Participants were categorized as obese (body mass index [BMI]: 39.3 [+ or -] 4.1 kg x [m.sup.-2]) based on international cut-off points (Cole et al., 2000). Two participants identified with Pacific Island ethnicity, while one participant was identified as Maori. Prior to participating, a health history questionnaire was completed; participants were excluded if there was a recent history (

Intervention

Participants completed one-hour training sessions on three non-consecutive days each week, for a total of 12 weeks. The exercise intervention was divided into thirty minutes of high-intensity aerobic activity (i.e. boxing) and thirty minutes of resistance training, as a mixed modality has shown to be more effective than aerobic exercise alone in obese adolescents (Damaso et al., 2014). The boxing training was sub-divided equally into shadow boxing, bag work, and one-on-one focus-pad work. Intensity was monitored in real time, using heart monitors (Polar [Team.sup.2]; Polar Electro Inc., New York). Maximal heart rate was calculated using age-specific equations (Mahon et al., 2010), and exercise intensity was maintained at 90% of predicted maximal heart rate during the standard boxing training. Although 90% of predicted maximal heart rate may be deemed to be of a strenuous nature for this cohort, the basic upper body movements involved in the boxing elicited sharp elevations in cardiorespiratory responses, despite only a moderate perception of exertion being reported, mostly likely due to the large body mass and poor underlying level of fitness of the adolescents.

The progressive, closed kinetic, resistance training immediately followed the boxing training. Each resistance training session included at least six exercises, with each exercise targeting a specific area of the body: shoulders, arms, back, chest, legs, and abdomen. Initial intensity was maintained at 70% of maximal heart rate and progressed fortnightly in 5% increments, until a maximal exercise intensity of 90% was reached.

Physiological assessments

Health assessments were completed before and after the 3-month intervention. All assessments have been described previously (Stoner et al., 2013b). Briefly, body composition variables included height, weight, abdominal circumference, BMI, and abdominal-to-height ratio. Visceral fat thickness was measured using a B-mode ultrasound device (t3200; Terason, Burlington, MA), defined as the distance between the anterior wall of the aorta and the posterior surface of the rectus abdominis muscle, measured 1-5 cm above the umbilicus at the xiphoumbilical line (Iacobellis, 2005). Central arterial stiffness (augmentation index, AIx) and central blood pressure were assessed using pulse wave analysis (PulseCor R7, Auckland, New Zealand) (Stoner et al., 2013a). Carotid arterial stiffness was estimated using the stiffness index ([beta]), where arterial distension was measured using B-mode ultrasound and central blood pressures were derived from pulse wave analysis.

Psychological assessments

During week 10 of the intervention, all participants and two parents completed semi-structured interviews. The semi-structured interview schedule included open-ended questions to explore perceptions of i) participants' previous experience in playing sport and ii) participants' experiences of the programme, including what they perceived to have been difficult, enjoyable and challenging. An additional area of questioning was asked to the parents only, and explored issues of recruitment. Prior to the interviews, all questions were developed and discussed with a cultural advisor from the Maori community, and deemed culturally appropriate. Consistent with previous qualitative investigations, an inductive-deductive approach to data analysis was used in the current study (Esterberg, 2002) with the three main areas of questioning being used to guide data analysis. Interviews were completed in a private and quiet room by a single researcher and lasted approximately...

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