Development of Muscle Function in Prepubertal Children As a Response to Growth and Resistance Training

N/AEnrolling By InvitationNCT06594900

Ralf Roth52 enrolled

Overview

Healthy skeletal muscle development is crucial for a life-long quality of life. Childhood and puberty may be key periods for developing muscle growth and neuromuscular capacities, which are essential for bone-muscle interaction, metabolism, and participation in various sports. Even though the central role of physical activity in healthy physical development is well recognized, the decline in muscular fitness in today's children is alarming. This can lead to lasting deficits in muscle development and have a negative impact on overall health. Well-designed resistance training (RT) could address this problem, since it has an effective positive impact on muscular strength, bone density, metabolism, and spontaneous physical activity especially in childhood. In general, muscles adapt according to physical activity stimuli. However, children show different responses to exercise and training. The physiologic differences, which are reflected in lower neuromuscular capacities and hormonal responses, but also in a better resistance to fatigue than in adults, are not yet fully understood. It is well established, that RT in children is safe, effective and has multiple benefits for health. However, the underlying mechanisms that lead to increased muscle strength are unclear and it is unknown how sustainable these are. Today's common conception is that increased muscular strength is predominantly caused by neural adaptations and changes in muscle morphology due to lower androgenic responses are negligible. Although higher neuromuscular adaptation potential is evident, it is still not sufficient to explain all strength increases, suggesting that additional mechanisms are involved in the process. Most studies are outdated, had methodological and statistical limitations, and many state-of-the-art methods have not yet been applied to children, hence, there is a need for a comprehensive, in-depth investigation to understand muscle adaptations to training and growth in children. With this better understanding of the impact and adaption to RT stimuli on neuromuscular and structural development the proposed project can serve as a foundation for more targeted prevention strategies. The aim of this study is to investigate neuromuscular, hormonal, and morphological adaptations following 4 and 20 weeks of RT, while also examining their longitudinal retention through two consecutive follow-ups over 1.5 years. In this randomized controlled trial, state-of-the-art measurement methods are employed to accurately delve into mechanisms of adaptation, some of which have not yet used in children before due to limited time or infrastructure resources. The neuromuscular assessments include maximal and explosive strength of leg extensors, voluntary activation, motor unit decomposition, as well as central and peripheral neuromuscular fatigability. The hormonal changes are measured acutely (testosterone, cortisol, IGF-1 and growth hormone) and chronically (testosterone, progesterone and IGF-1) in response to one or several training sessions. Static and dynamic ultrasound imagining is used to quantify muscle size, fascicle shortening velocity and muscle architecture. This design allows in-depth insights into short- and long-term adaptations on several physiological levels to provide a novel mechanistic understanding of muscle growth and function in children. The major innovation of this research is the integration of diverse scientific perspectives, combining insights from neuromuscular physiology, endocrinology, and muscle morphology to provide a holistic understanding of RT adaptations and development in children of both sexes. This comprehensive approach can form the basis for future training programs, enabling next generations to better understand the potential impact of musculature on health.

Interventions

resistance training interventionBEHAVIORAL

The RT intervention focuses on knee extensor muscles, following current guidelines. Children will attend two supervised 1-hour sessions per week, proven sufficient for adaptations. Trained coaches and a scientific assistant, supported by master students, will document the sessions. Sessions are spaced 48 hours apart, totaling 40 over 20 weeks, with eight sessions between PRE and MID. Each session has three phases: warm-up, strength, and coordination. Warm-up involves whole-body games to increase heart rate and prepare for strength training. The strength phase, documented for effort and adjustments, includes squats, lunges, and step-ups, with intensity changes over time. Four sets of 8-12 repetitions per exercise are performed, aiming for strength increase and hypertrophy. Movements are done with great effort but not until voluntary failure. The coordination phase focuses on age-appropriate strength and motor skills through a circuit of challenges.

Outcomes

Primary Outcomes

maximal isometric voluntary contraction of knee extensor muscles

Maximal isometric voluntary contraction (MVC) of knee extensor muscles refers to the level of maximal force, which can be transferred to a resisted dynamometer. It is highly adaptive from stimuli like training through mainly two pathway: by neuromuscular adaptation or muscle hypertrophy. Therefore, this is a sensitive measure during growth and resistance training intervention. The measurement of isometric MVC of knee extensor muscles will be performed in a seated position in a dynamometer (Isomed 2000, D. \& R. Ferstl GmbH, Germany). The test subjects are fixed at a hip and knee angle of 120° and 60° respectively. 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 against lever arm of the dynamometer. After a familiarization attempt, the measurement is performed 2-5 times (until \<5% difference between two trials) with a rest of 1 min in between. Peak torque will be used as outcome.