Skeletal muscle is critically important, but is often overlooked, not getting the respect or attention the tissue demands. Muscle is responsible for locomotion and physical performance, uses large amount of energy preventing gains in fat mass, and acts as an amino acid reservoir during trauma. Nonetheless, as individuals age, they lose muscle and to a greater extent strength. Maintaining muscle mass and strength is paramount for preventing disability and mortality. There are many aspects of diet that affect muscle tissue, but dietary protein directly activates muscle protein synthesis, so is important to consider as part of a balanced diet. Research regarding dietary protein intake has focused on the amount of protein consumed, but the quality and distribution of dietary protein also determines the body?s anabolic response. Two different cross-sectional studies were completed to determine the associations between dietary protein intake and muscular performance. Dietary intake was measured using three-day food diaries. Isokinetic dynamometry determined lower-body strength and endurance. Handgrip strength measured upper-body strength. Dual x-ray absorptiometry evaluated lean body mass. Thirty-second chair stand and six-meter gait speed tests determined functional ability. Self-reported age and moderate-to-vigorous physical activty, assessed via accelerometry, were included in all models as covariates. Increased intake of higher quality proteins from animal sources was positively associated with lower-body strength (? ? S.E.; 65.874?19.855, p =0.001), lower-body endurance (549.944?232.478, p =0.020), and handgrip strength (0.349?0.171, p = 0.045) in the cross-sectional sample of 91 middle-aged men (n=41) and women (n=50) when controlling for relative energy intake and percent energy from the macronutrients. Using another sample of 192 women 18 to 79 years, achieving intakes of at 25 grams per meal was positively associated with lean mass (1.067?0.273 kg, p<0.001) and upper-body (3.274?0.737 kg, p<0.001) and lower-body strength (22.858?7.918 Nm, p=0.004) controlling for relative energy intake and percent of energy from protein. In a subgroup of this sample aged 61-79, animal-based protein intake was related to increased lower-body strength (14.834?7.287 Nm, p=0.049) and faster gait speed (-0.177?0.087 s, p=0.049). To benefit muscle and performance, people should strive to consume enough high-quality protein at each meal
