The goal of this prospective, cross-sectional study is to develop updated reference values for the Muscle Power Sprint Test (MPST) in children aged 5-12 years.

The main question it aims to answer is:

• What are reference ('normal') values for the MPST in children aged 5-12 years?

Participants will be asked to perform six short sprints of fifteen meters each, with a ten-second rest between each effort.

SUMMARY Rationale: Children with congenital abnormalities face risks of below-average lung function and exercise tolerance (1-3). As the standard of care, our tertiary hospital enrolls these children in a prospective, longitudinal follow-up program from birth (4). This program involves regular assessments of overall health and development, including spirometry and exercise tolerance tests conducted by pediatric physiotherapists. Historically, the Bruce treadmill protocol was employed for testing maximal exercise tolerance in children aged 4 and above, but it presented limitations such as high muscular demands of the steep inclines and large workload increments, impacting reliability and potentially causing premature discontinuation (5).

In response, the Bruce protocol was replaced in newer follow-up program versions by the Muscle Power Sprint Test (MPST). Unlike the Bruce protocol, which assesses aerobic capacity, the MPST focuses on anaerobic exercise capacity, which is crucial for children's daily activities like playing with peers (6). Performing the MPST involves six short runs of 15 meters, from which the calculated 'mean power' serves as the primary outcome. The distance covered during these runs corresponds well to the distances children cover during daily play activities.

While Dutch norm values for children aged 6-18 exist, gathered mainly in rural areas between 2012 and 2016, the study highlights the need for updated reference values. Lifestyle changes, exacerbated by the Covid-19 pandemic, underscore the urgency of updating exercise tolerance reference values (7). Notably, there is a current lack of established reference values for 5-year-olds undergoing MPST testing in our longitudinal follow-up program, emphasizing the need for comparative data in this age group.

Objective: Our primary goal is to establish reference values for the MPST for primary school children aged 5-12 belonging to a diverse population living in the Netherlands.

Study design: The study adopts a prospective cross-sectional design.

Study population: Primary school or after-school childcare children aged 5-12 years.

Intervention (if applicable): The MPST, which involves six 15-meter sprints at maximum pace between the two cones/lines, with a 10-second rest in between each effort.

Main study parameters/endpoints: The primary outcome is generating reference values for the MPST for typical children aged 5-12.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: We believe the risks of experiencing drawbacks from study participation are minimal. The Muscle Power Sprint Test (MPST) is non-invasive, involving six short, consecutive 15-meter sprints - similar to activities children commonly engage in, such as games like tag or hide-and-seek - with a 10-second rest after every run. Individual testing and warm-up rounds further mitigate potential risks, and we estimate the likelihood of injuries or adverse effects to be lower than those encountered in a standard physical education class.

Inclusion Criteria:

• Age 5-12 years
• Attending primary education at one of the participating schools or attending participating after-school childcare centers.

Exclusion Criteria:

• Contra-indication for maximal exercise due to cardiac or respiratory morbidities
• Injuries limiting maximal exercise capacity
• Known with motor function impairment which may hamper maximal exercise (e.g. neurologic comorbidities)

We can share the raw MPST data when requested by other researchers.