IGF-1 measured in athletes: a narrative review of what the performance evidence supports

Description

Insulin-like growth factor 1 is a hormone the body makes in the liver, in response to growth hormone. It circulates attached to carrier proteins, acts on muscle and bone, and shows up in a blood sample. In childhood it drives growth. In adults it moves with food, sleep, illness, age and exercise, which is why sports science keeps measuring it in athletes. The answers do not agree. Values rise after some training blocks and fall after others; some studies find higher levels in better performers, some find nothing. Part of that is biology, part measurement: laboratories use assays that do not give the same number, blood is drawn at different times of day and at different points in a training cycle, and the carrier proteins change what a total value means. This review reads that literature by what each study was using the measurement for: training load, recovery, or performance itself. It stops at the body's own hormone; hormone given as a drug is a separate question and not part of this work. The first table is a list of assays and sampling times, the dull part everything else rests on.

Student responsibilities

Read up on how IGF-1 is made, measured and reported. Take one use of the measurement, read the studies that report it, build the table that goes with them, and write that section of the review.