Controlled Evaluation of an Exercise Program for Overweight Adolescents

Cardiopulmonary exercise testing (CPET) will be performed on a mechanically braked bicycle ergometer (Ergoselect 200, Ergoline GmbH, Germany). Ventilation and gas exchange will be measured breath-by-breath using a face mask connected to a Cortex Metalyzer 3B (Cortex Biophysik GmbH, Germany). Basic spirometry is conducted before testing. A 12-lead ECG (Customed GmbH, Germany) is used at rest and during exercise to monitor heart rate and detect abnormalities. CPET begins with a 3-minute resting phase and continues using one of five established protocols (Wagner et al., 2019). Participants are verbally encouraged throughout. Gas exchange values are averaged every 30 seconds. VO₂max and RERmax are recorded as peak values at or before exhaustion. Subjective exertion is assessed every 2 minutes and post-exercise using the Borg scale (Borg, 1998).

The measurement of isometric maximal voluntary contraction of lower extremity muscles will be performed in a seated position in a dynamometer (Isomed 2000, D. & R. Ferstl GmbH, Hemau, Germany). This test is similar to a typical leg press commonly found in gyms. According to Maffiuletti et al. (2016) the subjects are instructed to extend their legs as fast and forceful as possible and hold the contraction for 3-5s. After a familiarization attempt, the measurement is performed three times with a rest of 45 s in between. Peak torque will be used as primary outcome.

Static retinal vessel diameters will be analysed using a Static Retinal Vessel Analyzer (SVA-T, IMEDOS Health GmbH, Jena, Germany). The system consists of a fundus camera (Topcon TRC NW8) and analysing software (Visualis, IMEDOS Health GmbH), allowing non-invasive and non-mydriatic assessment of retinal vessel diameters. Two valid images from the retina of the left and right eye with an angle of 45° and with the optic disc in the centre will be taken. Reti-nal arterioles and venules, coursing through an area of 0.5-1 disc diameter (d) from the optic disc margin, will be identified semi-automatically at higher magnification using special analysing software (Vesselmap 2, Visualis IMEDOS Health GmbH). Diameters will be averaged to central retinal arteriolar (CRAE) and venular (CRVE) diameters, using the Parr-Hubbard formula de-scribed elsewhere (Ikram et al., 2006) and the AVR will be calculated from the CRAE and CRVE. Retinal vessel diameters are generally presented in measuring units (

Blood pressure will be assessed in a supine position after a rest period of five minutes by use of a validated automated oscillograph (Mindray VS-900, Mindray, Darmstadt, Germany) for use in children and adolescents (Wong et al., 2006) Cuff size will be selected based on the individual circumference of the upper right arm according to the guidelines (Flynn et al., 2017; NHBPE Program, 2004). Blood pressure is measured 3 times with 2 min apart, whereby the last two are averaged and the first is discarded.

To measure psychological acceptance, participants are asked to complete the Acceptance and Fusion Questionnaire for Youth (AFQ-Y). This instrument assesses the willingness to experience private events, values-oriented action, experiential avoidance, and cognitive and emotional fu-sion. The Difficulties in Emotion Regulation Scale (DERS-36) is used to measure difficulties in emotion regulation. Additional information on sleep behavior, perceived stress, and well-being is gathered using the Insomnia Severity Index (ISI), the Perceived Stress Scale-Youth (PSS-Y), and the WHO-5 Well-Being Index.

Body weight and composition in light clothing will be conducted using the gold-standard method, dual-energy x-ray absorptiometry (DEXA), utilizing a GE Lunar iDXA® device (GE Lunar Inc., Madison, WI; software version 13.10). Participants in the study are required to fast for 6 hours prior to the assessment. The analysis will yield both absolute and relative metrics for total body fat mass and fat-free mass. Throughout the assessment, subjects will lie in a supine position (Marra et al., 2019). The effective radiation dose from a single whole-body DEXA (<10 μSv) is similar to the normal background radiation received over one day at sea level.(Shepherd et al., 2017)

Power per body mass, determined from a vertical countermovement jump (CMJ), has been shown to be correlated to leg extension strength in children while representing a more natural movement. The CMJ will be performed on a force plate (Leonardo Mechanograph®, Novo-tec medical, Pforzheim, Germany) with arms akimbo. The instruction will be to jump as high as possible. After familiarization, each participant performs 5 trials, with the best of the two trials with <5% difference being used for the analysis. The most important outcome parameter of this test is the maximum power output (peak power) normalized to body weight. The CMJ had a high intra-trial reproducibility (ICC>0.95) in children, whereas inter-session variation has been re-ported to be high in prebubertal and early pubertal children as well (ICC=0.95, SEE=1.92 stand-ard error of estimate).

The handgrip strength is measured with an adjustable application to accommodate the span of each hand size (Leonardo Mechanograph®, Novotec medical, Pforzheim, Germany). The measurement is performed with the arm held vertically straight, providing a safe and reliable measurement for children (Gąsior et al., 2020). The subjects are instructed to compress the ad-justable application as forceful as possible and hold the contraction for 5s. After a familiarization attempt, the measurement is performed three times with a rest of 1 min in between.

This self-report questionnaire assesses psychological acceptance in children and adolescents. It measures key components such as willingness to experience uncomfortable thoughts and emotions (acceptance), values-based actions, experiential avoidance, and cognitive/emotional fusion.

Scoring: The AFQ-Y consists of 17 items. Scale range: Responses are rated on a Likert scale from 0 ("Not at all true") to 4 ("Very true").

Interpretation: Higher scores indicate greater psychological inflexibility, which is considered a worse outcome.

This 36-item questionnaire measures various aspects of emotion regulation difficulties, including emotional awareness, clarity, acceptance, impulse control, goal-directed behavior, and access to regulation strategies.

Scoring: Each item is rated from 1 ("Almost never") to 5 ("Almost always"). Scale range: Total scores range from 36 to 180. Interpretation: Higher scores indicate more severe difficulties in emotion regulation, reflecting a worse outcome.

The ISI assesses the nature, severity, and impact of insomnia. It includes questions on sleep onset, sleep maintenance, early morning waking, satisfaction with sleep, and impact on daily functioning.

Scoring: 7 items, each rated from 0 ("No problem") to 4 ("Very severe problem").

Scale range: Total scores range from 0 to 28. Interpretation: Higher scores indicate more severe insomnia symptoms, a worse outcome.

This scale measures the degree to which situations in one's life are appraised as stressful, specifically for children and adolescents.

Scoring: Items are typically rated on a 5-point Likert scale. Scale range: Depending on version, generally 0 to 40. Interpretation: Higher scores reflect greater perceived stress, a worse outcome.

This short questionnaire assesses subjective psychological well-being over the past two weeks. It focuses on positive mood, vitality, and general interest.

Scoring: 5 items, each scored from 0 ("At no time") to 5 ("All of the time"). Scale range: Raw scores range from 0 to 25, which are then multiplied by 4 to give a final score from 0 to 100.

Interpretation: Higher scores indicate better well-being, a better outcome. Scores below 50 may indicate reduced well-being or risk of depression.

Physical activity is objectively measured over a 7-day period using a wrist-worn accelerometer. This device collects data on:

Duration, frequency, and intensity of movement Data source: Integrated gyroscope and accelerometer sensors Interpretation: Data is analyzed in line with age-appropriate activity thresholds (e.g., moderate-to-vigorous physical activity levels)

Participants provide a structured recall of the types of physical activities they engaged in during different parts of the day over the same 7-day period. This qualitative input complements the accelerometer data and offers context about activity types and preferences.

This questionnaire assesses physical activity levels over the past 7 days, including walking, moderate activity, vigorous activity, and sitting time.

Scoring: Time spent in each activity type is used to estimate energy expenditure in MET-minutes per week.

Interpretation: Higher MET-minutes indicate higher physical activity, a better outcome.

To assess pubertal development, participants self-rate physical characteristics based on standardized illustrations and descriptions of secondary sexual characteristics (e.g., pubic hair, breast/genital development).

Interpretation: Tanner stages range from Stage 1 (pre-pubertal) to Stage 5 (fully mature), allowing categorization into early, mid, or late pubertal status.