Background Protein intake is important for skeletal muscle mass maintenance with aging and the ingestion of specifically-timed protein supplements could increase overall protein intake and thereby contribute to skeletal muscle mass maintenance. Recently, more attention has been given to the ingestion of plant-based protein blends as a more sustainable high-quality alternative to milk protein, as a means to increase muscle protein build-up and, as such, support muscle maintenance, especially when consuming suboptimal amounts of protein in the regular diet. Objective To assess the benefit of daily protein supplementation with either a plant-based protein blend or a milk protein on top of a standard diet to stimulate integrated muscle protein synthesis rates in healthy older individuals with and without exercise. Hypotheses It is hypothesized that both the plant protein blend and the milk protein supplement will result in greater muscle protein build-up when compared with a standard diet control condition. It is also hypothesized that exercise will result in greater muscle protein build-up when compared to the resting leg in all conditions, with similar effects of the protein supplements vs the control diet as in the non-exercised leg. This study will show the potential benefit of protein supplementation with alternative protein sources to support skeletal muscle maintenance in older individuals.