This study investigates whether taking daily collagen peptides, combined with long-term endurance or concurrent training can enhance running economy through muscle and/or tendon adaptations.

An adequate and high-quality intake of proteins and amino acids is crucial for synthesizing the body's own connective tissue-like structures, such as muscles, tendons, ligaments, and bones. Various metabolic and hormonal processes are regulated or influenced by proteins. It is undisputed that measurable improvements are only possible through the combination of training and protein intake. Simply increasing protein intake without physical activity cannot be expected to result in structural or metabolic adaptations.

In recent years, interest in regular collagen intake in sports nutrition, particularly in connection with moderate to intense physical activity, has increased. Since collagen and its peptides are primarily found in force-transmitting structures such as tendons, studies have been conducted to examine how tendons adapt to collagen peptide supplementation. Studies by Jerger et al. (2022 & 2023) have shown that both the patellar and Achilles tendons adapt to collagen supplementation, as evidenced by an increased cross-sectional area compared to a non-caloric placebo. This increase allows tendons to withstand greater forces, making them more resilient and thus playing an important role in injury prevention. These results were achieved with a dose of 5g of collagen combined with three months of strength training.

Additionally, multi-month collagen peptide supplementation combined with concurrent training (strength and endurance training in one session) led to improved endurance performance. Both running distance and speed at the aerobic and anaerobic thresholds significantly increased compared to a placebo group with a daily intake of 15g of collagen over three months (Jerger et al. 2023, Jendricke et al. 2020).

Based on these results, the question arises as to whether regularly supplemented collagen peptides, combined with pure endurance training, lead to similar metabolic and/or tendon-specific adaptations. Therefore, the aim of this proposed study is to investigate both metabolic and specific (morphological, mechanical, and material) properties of the Achilles and patellar tendons to determine the mechanism through which the so-called "running economy" develops in connection with collagen peptides. The results will be compared to those of concurrent training, which has already shown metabolic adaptations as described above.

Inclusion Criteria:

Male gender Age 18-40 years No subjective symptoms during physical exertion BMI of 18.5 to 26 Stable weight and dietary habits No extensive strength/endurance training (less than 3 hours per week) No contraindications to physical exertion according to ACSM guidelines No contraindications to supplemental nutrition or ergogenic supplements

Exclusion Criteria:

Contraindications to physical activity (e.g., chronic heart disease, arrhythmia, heart valve disease, arthritis, etc.; general exclusion criteria according to ACSM 2009; intolerance/aversion to animal protein) Arterial hypertension (systolic BP > 200 mmHg and/or diastolic BP > 105 mmHg) at rest Insulin-dependent diabetes mellitus (IDDM) Liver and/or kidney disease that excludes a high protein load

men