Immobilisation induces sizeable and sustained reductions in forearm glucose uptake in just 24 h but does not change lipid uptake in healthy men.

The trajectory and magnitude of metabolic perturbations caused by muscle disuse are unknown yet central to understanding the mechanistic basis of immobilisation-associated metabolic dysregulation. To address this gap, forearm glucose uptake (FGU) was determined in 10 healthy men (age 24.9 ± 0.6 years, weight 71.9 ± 2.6 kg, BMI 22.6 ± 0.6 kg/m2 ) during a 180 min oral glucose challenge before (0) and after 24, 48 and 72 h of arm immobilisation, and before and after 72 h in the contralateral non-immobilised arm (Study A). FGU was decreased from baseline at 24 h (38%, P = 0.04), 48 h (57%, P = 0.01) and 72 h (46%, P = 0.06) of immobilisation, and was also 63% less than the non-immobilised limb at 72 h (P = 0.002). In a second study, FGU and forearm lipid uptake were determined in nine healthy men (age 22.4 ± 1.3 years, weight 71.4 ± 2.8 kg, BMI 22.6 ± 0.8 kg/m2 ) during a 420 min mixed-meal challenge before (0) and after 24 and 48 h of arm immobilisation and before and after 72 h in the contralateral non-immobilised arm (Study B). FGU responses were similar to Study A, and forearm lipid uptake was unchanged from pre-immobilisation in both arms over the study. A sizeable decrement in FGU in response to glucose feeding occurred within 24 h of immobilisation that was sustained and specific to the immobilised limb. Increasing lipid availability had no additional impact on the rate or magnitude of these responses or on lipid uptake. These findings highlight a lack of muscle contraction per se as a fast-acting physiological insult to FGU.