Post-Exercise Cooling Lowers Skeletal Muscle Microvascular Perfusion and Blunts Amino Acid Incorporation into Muscle Tissue in Active Young Adults

Purpose Cold-water immersion lowers muscle protein synthesis rates during postexercise recovery. Whether this effect can be explained by lower muscle microvascular perfusion and a subsequent decline in postprandial amino acid incorporation into muscle tissue after cooling is currently unknown. Methods Twelve young males (24 ± 4 yr) performed a single resistance exercise session followed by water immersion for 20 min with one leg immersed in cold water (8°C: COLD) and the contralateral leg in thermoneutral water (30°C: CON). After immersion, a beverage was ingested containing 20 g free amino acids, 0.25 g L-[ring-13C6]-phenylalanine, and 45 g carbohydrates. Microvascular perfusion of the vastus lateralis muscle was assessed for both legs using contrast-enhanced ultrasound at rest, immediately after exercise and water immersion, and at t = 60 and t = 180 min after beverage ingestion. A muscle biopsy sample (vastus lateralis) was collected from both legs (t = 240 min) to determine amino acid tracer incorporation. Results Microvascular blood volume was significantly lower in the COLD versus CON leg immediately after water immersion (1.24 ± 0.82 vs 3.13 ± 1.64 video intensity, respectively, P < 0.001) and remained lower at t = 60 and t = 180 min after beverage ingestion (0.90 ± 0.84 vs 1.53 ± 0.98, and 2.10 ± 2.53 vs 2.77 ± 2.81 video intensity, respectively, both P < 0.05). Exogenous amino acid incorporation into muscle protein was lower in the COLD versus CON leg (0.011 ± 0.004 vs 0.016 ± 0.005 mole percent excess, respectively, P < 0.001). The difference in postprandial amino acid incorporation into muscle protein between the COLD and the CON legs was strongly associated with the difference in microvascular blood volume between the two legs during recovery (r = 0.65, P < 0.05). Conclusions Cold-water immersion during postexercise recovery greatly reduces muscle microvascular perfusion and blunts postprandial amino acid incorporation in muscle.