Participants will be randomized into two groups - one group receives protein-enriched, milk-based supplements and the other group receives iso-energetic placebo products. Both groups participate in the same standardized resistance training program, and will be blinded to the supplement content. One training session consists of three exercises of the lower extremities (3 sets of 10 repetitions, pursuing an intensity of 8-12 repetition maximum (RM)). While admitted, supervised resistance training is offered daily. After discharge, the participants are encouraged to perform the same program as self-training four times per week.To ensure progression (or regression if necessary) the participants receive follow-up home visits by a physiotherapist, and thus after discharge the participants are closely monitored. All participants, irrespective of allocation, will get a daily vitamin D supplement.