1. Introduction
±, RET, muscle contraction
CONTRACTION
Choline plays many important roles, including the synthesis of acetylcholine, and may affect muscle responses to exercise. We previously observed correlations between low choline intake and reduced gains in strength and lean mass following a 12-week resistance exercise training (RET) program for older adults. To further explore these findings, we conducted a randomized controlled trial. Three groups of 50-to-69-year-old healthy adults underwent a 12-week RET program (3x/week, 3 sets, 8–12 reps, 70% of maximum strength (1RM)) and submitted >48 diet logs (>4x/week for 12 weeks). Participants’ diets were supplemented with 0.7 mg/kg lean/d (low, n = 13), 2.8 mg/kg lean/d (med, n = 11), or 7.5 mg/kg lean/d (high, n = 13) of choline from egg yolk and protein powder. The ANCOVA tests showed that low choline intake, compared with med or high choline intakes, resulted in significantly diminished gains in composite strength (leg press + chest press 1RM; low, 19.4 ± 8.2%; med, 46.8 ± 8.9%; high, 47.4 ± 8.1%; Choline plays crucial roles in several physiological processes, such as neurotransmission and muscle contraction via synthesis of the chemical messenger acetylcholine (ACh), lipid transport via lipoprotein synthesis, and methyl-group metabolism as a precursor to betaine [Insufficient choline intake can negatively affect exercises because choline is a precursor to ACh, which mediates muscle contraction and force generation [Previously, we have observed that a lower intake of choline was associated with reduced strength and lean mass gains following 12 weeks of resistance exercise training (RET) in 60-to-69-year-old individuals [Previous studies regarding choline supplementation and exercise generally reported that choline intake exceeding AI, sufficient to increase blood concentrations of choline, does not positively affect exercise performance [The purpose of the present study was to determine the effects of different amounts of choline intakes (approximately 50%, 70%, and 120% of AI) on muscle responses to RET. To maintain consistency with our previous study, we used similar exercise and nutrition control protocols [