Blood flow and muscle bio-energetics by31P-nuclear magnetic resonance after local cold acclimation

To clarify the origin of local cold adaptation and to define precisely its influence on muscle bio-energetics during local exercise, five subjects were subjected to repeated 5°C cold water immersion of the right hand and forearm. The first aim of our investigation was therefore carried out by measuring local skin temperatures and peripheral blood flow during a cold hand test (5°C, 5 min) followed by a 10-min recovery period. The31P by nuclear magnetic resonance (31PNMR) muscle bio-energetic changes, indicating possible heat production changes, were measured during the recovery period. The second aim of our investigation was carried out by measuring31PNMR muscle bioenergetics during handgrip exercise (10% of the maximal voluntary contraction for 5 min followed by a 10-min recovery period) performed both at a comfortable ambient temperature (22°C; E) and after a cold hand test (EC), before and after local cold adaptation. Local cold adaptation, confirmed by warmer skin temperatures of the extremities (+30%,P<0.05), was related more to an increased peripheral blood flow, as shown by the smaller decrease in systolic peak [−245 (SEM 30) Hz vs −382 (SEM 95) Hz,P<0.05] than to a change in local heat production, because muscle bioenergetics did not vary. Acute local cold immersion decreased the inorganic phosphate: phosphocreatine (PC) ratio during EC compared to E [+0.006 (SEM 0.010) vs +0.078 (SEM 0.002) before acclimation and +0.029 (SEM 0.002) vs +0.090 (SEM 0.002) after acclimation respectively, P<0.05] without significant change in the PC:β-adenosine triphosphate ratio and pH. Local adaptation did not modify these results statistically. The recovery of PC during E increased after acclimation [9.0 (SEM 0.2) min vs 3.0 (SEM 0.4) min,P<0.05]. These results suggested that local cold adaptation is related more to peripheral blood flow changes than to increased metabolic heat production in the muscle.