Bed‐rest and exercise remobilization: Concurrent adaptations in muscle glucose and protein metabolism

Abstract Background Bed‐rest (BR) of only a few days duration reduces muscle protein synthesis and induces skeletal muscle atrophy and insulin resistance, but the scale and juxtaposition of these events have not been investigated concurrently in the same individuals. Moreover, the impact of short‐term exercise‐supplemented remobilization (ESR) on muscle volume, protein turnover and leg glucose uptake (LGU) in humans is unknown. Methods Ten healthy males (24 ± 1 years, body mass index 22.7 ± 0.6 kg/m2) underwent 3 days of BR, followed immediately by 3 days of ESR consisting of 5 × 30 maximal voluntary single‐leg isokinetic knee extensions at 90°/s each day. An isoenergetic diet was maintained throughout the study (30% fat, 15% protein and 55% carbohydrate). Resting LGU was calculated from arterialized‐venous versus venous difference across the leg and leg blood flow during the steady‐state of a 3‐h hyperinsulinaemic–euglycaemic clamp (60 mU/m2/min) measured before BR, after BR and after remobilization. Glycogen content was measured in vastus lateralis muscle biopsy samples obtained before and after each clamp. Leg muscle volume (LMV) was measured using magnetic resonance imaging before BR, after BR and after remobilization. Cumulative myofibrillar protein fractional synthetic rate (FSR) and whole‐body muscle protein breakdown (MPB) were measured over the course of BR and remobilization using deuterium oxide and 3‐methylhistidine stable isotope tracers that were administered orally. Results Compared with before BR, there was a 45% decline in insulin‐stimulated LGU (P