Kettlebell-classroom Training

Study intervention The intervention emphasizes full-body exercises which are performed with the own body weight and kettlebells. On every weekday, the intervention classes will receive 15 min of supervised training over 7 weeks. This results in a total number of training sessions of 35 sessions. The movements and exercises in all phases are based on functional, multi-joint movements. The focus will be on age-appropriate whole-body strength and motor skill development. It will be designed with different, varying exercises, which can be individually tailored and adapted to the children's ability. Tailored to the group, the sessions will also include parts which engage social cooperation and teamwork, so that the children will experience a sense of competence, self-determination and enjoyment of exercise while enhancing motor skills and athletic ability.

• kettlebell-training (Behavioral): 15 min of body weight or kettlebell loaded strength training

Primary outcomes

• Maximal strength [seven week intervention]: The mid-thigh pull is measured on the force plate, as is the hand grip force (Leonardo Mechanograph® Novotec Medical GmbH, Pforzheim, Germany). The mid-thigh pull corresponds to a static deadlift, i.e. pulling up a bar in the centre of the thigh, and thus provides an image of the force transmission of the muscle loops up to the hand force to transfer the force to the measuring device. The test subject has a hip and knee angle of 135-140° and tries to pull as quickly and strongly as possible on the vertically fixed bar in the centre of the thigh. As the test subject is standing on the force plate, the transmitted force is measured precisely. In contrast to the dynamic 1-repetition maximum, this simple test offers a high level of safety as an isometric measurement and, in particular, has a high test-retest reliability. This measurement is therefore not only attractive to perform, but also makes it easy to analyse strength curves and maximum strength.

Secondary outcomes

• Handgrip strength [seven week intervention]: The handgrip force is measured using a size-adjustable application to take into account the span of the respective hand size. The measurement is performed with the arm extended vertically and provides a safe and reliable measurement for children.
• sprint performance [seven week intervention]: 20 m Sprint: Electronic measurement of a timed (seconds) 20 m sprint, starting from a resting position. Start follows after an acoustic signal, with a precision of 1/100 second.
• jump performance [seven week intervention]: Countermovement jump: 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®, Novotec medical, Pforzheim, Germany) with arms akimbo. The instruction will be to jump as high as possible. After familiarization, each participant performs 2-5 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 6-8 year old children, whereas inter-session variation has been reported to be high in children aged 6-12 years as well (ICC=0.95, SEE=1.92 standard error of estimate).
• shuttle-run performance [seven week intervention]: 20 m Shuttle-Run-test: This is a validated test which measures aerobic capacity by running forth and back for 20 m, with an initial running pace of 8.0 km/h and a progressive 0.5 km/every minute raise of the running speed given by a sound. The maximal performance will be reached when the child does not cross the 20 m line at the moment of the beep for two consecutive 20 m distances. Number of "paliers" (1 palier≅1 minute) performed will be counted with a precision of 0.5 paliers.
• balance performance [seven week intervention]: This test of coordination includes balancing backward on 3 m long bars with a width of 3, 4.5, and 6 cm, respectively. The number of steps until the child's foot touches the floor will be counted; 3 trials will be performed for each bar width. The sum of these 9 tests will be used for statistical analysis.
• object control [seven week intervention]: The Eye-Hand-Control test is valid and reliable and determines the level of controlling an object (tennis ball) while conducting repetitive movements (i.e., left-hand throw, right-hand catch, or right-hand throw, and left-hand catch, etc.) as frequently as possible in a time-constrained task of 30 sec. The children are free to use overhand and/or underhand techniques or a combination of both for throwing and catching. Children had to stand 1 m from a wall and throw the tennis ball at eye level on a wall. Participants conducted this test twice, with the number of successful ball catches across both trials resulting in the test score.
• blood pressure, body composition [seven week intervention]: Anthropometry and blood pressure will be analysed on a seperate day, in a separate room parallel to the usual school lessons. 3 students will be evaluated at the same time.
• side hop [seven week intervention]: Jumping sidewards: Measurement for speed and coordination. Jumping with both legs together on alternating sides of a bunton of wood, as many times as possible, within 15 seconds. Two trials will be performed. The number of jumps will be counted. The sum of the number of jumps of the two tests will be used for statistical analysis.

Sex: All, ages: 6 Years to 9 Years, accepts healthy volunteers

Inclusion Criteria:

* all of the selected second-graders who can participate in physical education lessons will be included in the study

Exclusion Criteria:

* Children with a medical certificate, that prohibits physical activity, will be excluded from performance testing and training intervention.

• Results publication: Braun N, Ledergerber R, Lichtenstein E, Nebiker L, Roth R. Classroom-Integrated Kettlebell Training: Effects on Motor Performance, Attention, and Health in Primary School Children. J Sch Health. 2026 Apr;96(4):e70136. doi: 10.1111/josh.70136. PMID 41854388