IGF1R and sarcopenia: Five genetically predicted factors of the IGF family (IGF-1, IGF-1R, IGF-2R, IGFBP-3, IGFBP-7) as one sample, while four relevant features of sarcopenia (low hand grip strength, appendicular lean mass, whole body fat-free mass, and walking pace) as another sample, in conducting a two-sample MR analysis.