OPAC-ALL: Online Physical Activity and Health Counseling for Survivors of Childhood Acute Lymphoblastic Leukemia

Physical activity and sedentary time are assessed by accelerometers worn for 7 days. The accelerometers (ActiGraph™ model GT3X+, ActiGraph LLC, Pensacola FL, USA) measures accelerations of ±6 G. The sample rate will be set to measure raw signals at 100 Hz, translated into metabolic energy equivalents of light, moderate and vigorous physical activity, and sedentary time. The validity of the Actigraph accelerometer is good, with correlations of 0.65 between accelerometer assessed metabolic energy equivalents and indirect calorimetry Further, we will investigate whether international guidelines for physical activity are met according to established cut-off levels.

The primary outcome is the difference in cardiorespiratory fitness (VO2peak (ml/min/kg)) between the intervention group and the waiting list control group after 26- weeks. VO2peak is defined as the highest mean over 30 s and expressed in mL/kg/min Furthermore, two objective criteria need to be fulfilled before the test is valid. The criteria are heart rate >85% of estimated maximal heart rate and a respiratory exchange ratio (RER)>1.1.

Isometric leg extension is tested using a special-build strength ergometer (Gym 2000®) with a dynamometer (US2A100 kg, Holtinger, Germany) and amplifier. Data is collected through an AD-card (100 HZ) with customized software (LabVIEW ®, National Instruments, Texas, USA). Each participant receives detailed instructions on how to perform each test and is given time to familiarize with each test to secure valid measures. The participant is instructed to kick (forward) with maximal force and is obligated to keep maximal intensity for at least five seconds. Three attempts with a two-minute break is carried out, however the participant can try as many attempts as possible if the participant keeps showing improvements. The highest score is noted.

Handgrip strength is measured using a hand-held dynamometer. Participants are placed in a seated position with the elbow flexed at 90°, with three attempts performed for each hand. During testing, the participant will be encouraged to exhibit the best possible force, and the best measure in the strongest hand will be used as test score.

Maximal voluntary muscle force will be measured from both legs following a fixed protocol. Leg extensor power will be measured using an extension Power Rig (Nottingham Power Rig, Queen's Medical Centre Nottingham, NG7 2UH, United Kingdom), with subjects positioned with joint angles as if the participant was rising from a chair. Participants are carefully instructed to keep their hands across the chest and to not move the upper body while pushing. Verbal encouragement will be given to ensure maximal performance. The participants extend one leg as forcefully as possible, and the velocity of the flywheel is measured by an opto-switch and used to calculate average leg extensor power in the push. Dominant leg will be tested, a minimum of 5 attempts is carried out for each leg, however the participant continues until two attempts are lower than the maximum (50). The result is expressed in watt (W).

Height (m) will be assessed without shoes to the nearest 0.1 cm. Weight (kg) will be measured (no shoes, with underwear or light clothing) to the nearest 0.1 kg and subsequently body mass index (BMI) will be calculated (kg/m2).

Waist circumference will be measured around the abdomen at the level of the umbilicus (cm)

The Pediatric Quality of Life Inventory (PedsQL Core) [44] measures the quality of life in children using 23 items on a five-point response scale from never to almost always. The answers are divided into four domains: health and physical activity, emotions, dealing with others, and school activity.

Composed of 18 items, the PedsQL Multidimensional Fatigue Scale [44] possesses three subscales: general fatigue, sleep and rest fatigue, and cognitive fatigue.

Metabolic syndrome is based on waist and hip circumference, BMI, triglycerides, total cholesterol, high-density lipoprotein (HDL) cholesterol and low-density lipoprotein (LDL) cholesterol, blood pressure, fasting blood sugar and insulin; Within these parameters the International Diabetes Foundation (IDF) Blood samples will be obtained following an overnight fast, measuring serum insulin, glucose, total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, total cholesterol, and triglyceride levels. We will collect 15-20 ml per blood sample, (maximum of 2 ml/kg/day including the volume taken for routine clinical analysis). Blood samples will be drawn from an antecubital vein. In accordance with the WHO recommendations, no more than 2 ml/kg/day will be drawn and a maximum of 20mL (5). Local anesthetics cream will be used to minimize pain. in mmol/L

Hip circumference (in CM) at a level parallel to the floor, at the largest circumference of the buttocks following standards described by the World Health Organization. Metabolic syn-drome is based on age-based criterias defined by the International Diabetes Foundation

Weight and Height is combined to report BMI in kg/m^2

Fat-Free Mass (kg and %) will be analyzed by whole-body DXA scan (DPX-IQ) (Lunar, Lunar Corporation Madison, WI, USA). Transverse scans at 1 cm intervals are made from head to toe measuring the absorption of x-ray beams at two different energy levels as these are sent through the body

Bone Mineral Density (g/cm2) will be analyzed by whole-body DXA scan (DPX-IQ) (Lunar, Lunar Corporation Madison, WI, USA). Transverse scans at 1 cm intervals are made from head to toe measuring the absorption of x-ray beams at two different energy levels as these are sent through the body

Bone Mineral Content (kg) will be analyzed by whole-body DXA scan (DPX-IQ) (Lunar, Lunar Corporation Madison, WI, USA). Transverse scans at 1 cm intervals are made from head to toe measuring the absorption of x-ray beams at two different energy levels as these are sent through the body.

Body Fat (kg and %) will be analyzed by whole-body DXA scan (DPX-IQ) (Lunar, Lunar Cor-poration Madison, WI, USA). Transverse scans at 1 cm intervals are made from head to toe measuring the absorption of x-ray beams at two different energy levels as these are sent through the body

Experienced project members will conduct semi-structured, in-depth interviews of children and parents (interviewed separately) to understand factors that can influence an individual's likelihood of engaging in physical activity and their perceived experience with participating in the project. Moreover, the feasibility of the intervention components (i.e., online physical activity program, health counseling, lifestyle physical activity website, and education of local trainers) will be explored qualitatively. Furthermore, the health counseling sessions will be recorded. Analysis: All data will be transcribed and analyzed according to principles of pragmatic thematic analysis (semi-structured in-depth interviews) or content analysis (recording of health counseling sessions).

An validated questionnaire used in the UNGkan and HEIA project will be used to assess self-reported physical activity, physical function, sedentary time, screen time, diet habits, active transportation behavior, physical education participation, perceived barriers/facilitators to physical activity, health-related behaviors. The questionnaire contains 35 items