Effect of Incorporating Lean Beef Into a Protein-rich Diet During Resistance Training on Muscle and Tendon Strength in Older Women

Overview

Loss of muscle mass and strength is a well-established outcome of normal aging. Muscle strength and mobility are also dependent on the quality and strength of connective tissue, which surrounds skeletal muscle. These layers, which are continuous with tendons, allow for the effective transfer of tension from skeletal muscle to bone to enable movement. Importantly, skeletal muscle strength is directly related to connective tissue strength. Greater tendon connective tissue cross-sectional area and stiffness optimize force transfer through tendon to maximize musculoskeletal function. As with skeletal muscle, tendon connective tissue quality declines with age. Previous research indicates that resistance training can improve muscle strength in older adults, but may not counter the effects of aging on tendon. The specific problem is that no approaches are available that benefit both skeletal muscle and tendon health to minimize loss of muscle mass and quality while also improving connective tissue quality and function in older adults. A critical need exists to assess approaches that improve both muscle and connective tissue strength and function. This need is highly relevant for older women, due to their higher risk of sarcopenia than men. Resistance training, especially when combined with higher protein intake, has been consistently shown to improve muscle mass and strength in older adults. Further, emerging research indicates that diets rich in total and indispensable amino acids (as in beef) augment exercise-induced improvements in tendon cross-sectional area in rodents and young humans. However, limited research exists on the impact of beef consumption combined with resistance training on muscle and tendon tissue outcomes, especially in older women. This research study will assess the effects of consuming a healthy, protein-rich diet emphasizing lean beef, compared to a healthy, normal-protein, lower beef diet (control 1), and a healthy protein-rich, lower beef diet emphasizing non-beef/red meat protein (control 2) on resistance training-induced changes in muscle and tendon tissue size, strength, and quality in older women.

Sarcopenia, i.e., loss of muscle mass and strength, is a well-established consequence of normal aging. Skeletal muscle strength and mobility is also dependent on the composition and mechanical properties of connective tissue, which encase skeletal muscle allowing for effective transfer of tension developed during cross-bridge cycling. Importantly, skeletal muscle strength and function is directly related to connective tissue strength. Specifically, greater tendon connective tissue cross-sectional area (CSA) and stiffness optimize force transfer through tendon to maximize musculoskeletal function, including muscle power output, locomotion economy, and control of balance. As with skeletal muscle, aging leads to the decline of tendon connective tissue quality, including reductions in tendon collagen (the primary structural component of tendon), and a decrease in tendon CSA. Previous research indicates that resistance training (RT) can improve muscle mass and strength in older adults but may not counter the effects of aging on tendon. Specifically, a 12-week RT protocol improved tendon properties in young but not older adults. The specific problem is that no approaches are available that target both skeletal muscle and tendon health to minimize loss of muscle mass and quality while simultaneously improving connective tissue quality and function in older adults. Therefore, a critical need exists to scientifically assess interventions that concomitantly improve muscle and connective tissue strength and function. This need is highly relevant for older women, due to their higher risk of sarcopenia than men. Resistance training, especially when combined with higher protein intake, has been consistently shown to improve muscle mass and strength in older adults. However, limited research exists on the impact of beef consumption combined with RT on sarcopenia-related outcomes, especially in older women. Further, emerging research indicates that diets rich in leucine or glycine (as in beef) augment resistance or aerobic exercise-induced improvements in tendon CSA in rodents and young humans. However, the potential benefit of lean proteins, such as beef, on connective tissue adaptations in older adults requires investigation. This study will assess the effects of consuming a healthy, protein-rich diet emphasizing lean beef on RT-induced changes in skeletal muscle and tendon connective tissue size, strength, and quality in older women. It is hypothesized that consumption of a healthy diet high in protein from predominately lean beef will augment improvements in both skeletal muscle and tendon responses to RT, when compared to consuming a healthy diet with normal or high-protein and less total red meat. The overall healthy diet will be modeled from the U.S. Healthy Eating Pattern and consistent with the 2015-2020 Dietary Guidelines for Americans.