{"publication_id":"b09d87ba-d35f-4c9b-aeba-4d2cca7e8d21","traces":[{"claim_id":"claim_1","claim":"Two receipts describe collagen-related metrics that move in different directions depending on the perturbation. The 1975 rat study reports that aging increases the **insoluble collagen fraction** and decreases the **salt-extractable collagen fraction** in red, white, and cardiac muscle. The 2010 human resistance-exercise study reports that intramuscular **collagen fractional synthesis rate (FSR)** is evenly elevated after both light-load and heavy-load knee-extension exercise and is **not affected by feeding**, while **myofibrillar FSR** responds only to heavy load and is further increased by feeding.","candidate_sources":[{"study":"Collagen in aging muscles.","doi":"10.1007/bf02326782","url":"https://doi.org/10.1007/bf02326782"},{"study":"Contraction intensity and feeding affect collagen and myofibrillar protein synthesis rates differently in human skeletal muscle.","doi":"10.1152/ajpendo.00609.2009","url":"https://doi.org/10.1152/ajpendo.00609.2009"}]},{"claim_id":"claim_2","claim":"These two receipts are **not directly comparable** because they use different metric types (collagen fraction composition vs. collagen FSR), different species (rat vs. human), and different timescales (chronic aging vs. acute post-exercise). Treated as an inference only, they suggest a boundary condition: the **same \"collagen\" label can carry opposite-direction signals** depending on whether the perturbation acts on collagen quality/composition (aging: more crosslinked/insoluble, less soluble) or on collagen turnover (acute exercise: FSR up regardless of load or feed).","candidate_sources":[{"study":"Collagen in aging muscles.","doi":"10.1007/bf02326782","url":"https://doi.org/10.1007/bf02326782"},{"study":"Contraction intensity and feeding affect collagen and myofibrillar protein synthesis rates differently in human skeletal muscle.","doi":"10.1152/ajpendo.00609.2009","url":"https://doi.org/10.1152/ajpendo.00609.2009"}]},{"claim_id":"claim_3","claim":"Evidence that light-load and heavy-load resistance exercise differentially alter collagen FSR.","candidate_sources":[{"study":"Collagen in aging muscles.","doi":"10.1007/bf02326782","url":"https://doi.org/10.1007/bf02326782"},{"study":"Contraction intensity and feeding affect collagen and myofibrillar protein synthesis rates differently in human skeletal muscle.","doi":"10.1152/ajpendo.00609.2009","url":"https://doi.org/10.1152/ajpendo.00609.2009"}]}]}