Regional Variation in the Prevalence of Frailty Among Very Old Adults in Germany: Findings of the Nationwide Study "Old Age in Germany" (D80+).

Resistance training (RT) is a common method of physical activity that is performed across the lifespan to develop and maintain muscle strength. Muscle strength is an important outcome for improvement in quality of life, rehabilitation, functional capacity and physical performance [, ]. To develop muscle strength, the manipulation of training variables, such as (1) exercise selection and order, (2) rest intervals, (3) sets and repetitions, (4) intensity, (5) frequency and (6) duration, is necessary. Three ways in which training variables interact with one another have been proposed []. Resistance training dose (RT volume [sets × repetitions × exercises] × intensity), which considers a single RT session, RT dosing (RT dose × frequency) indicates the RT stimulus over the course of a week and RT dosage (RT dosing × duration of a programme) encompasses all RT sessions performed across a training programme. Other training variables such as the duration of eccentric and concentric phases of muscle contraction, which allows for the calculation of training density ([sets × repetitions × external load] ÷ time) [], or the utilisation of velocity-based training data, could be included in these composite variables (dose, dosing and dosage). For the current intended purpose, including time or velocity would limit the practical application of the dose metric to quantify the total training stimulus and modify exercise programming. This is because of the difficulty in accurately adhering to cadences for each repetition and exercise, device availability and accuracy, cost and the required knowledge of specific velocity profiles to develop specific outcomes such as muscle strength [, ]. At present, exercise prescription guidelines have been established for both apparently healthy adults and older adult populations. For example, the American College of Sports Medicine recommends 3–4 sessions per week, composed of 1–3 sets of 8–12 repetitions at 60–70% 1-repetition maximum (RM) to develop muscle strength in healthy adults [, ]. Although prescription guidelines are valuable, they are broad and lack specificity. For instance, when presented with two examples, (a) a single set of 12 repetitions, across seven exercises, at 60% 1RM (RT dose = 5040 arbitrary units [au]) has a substantially different dose than (b) 3 sets of 8 repetitions, across seven exercises, at 75% 1RM (RT dose = 12,600 au). This difference is amplified further when a range is recommended for the frequency of training sessions. If example (a) was prescribed 3 days of RT, the dosing would increase to 15,120 au, whereas, if example (b) was prescribed 4 days, the dose would be 50,400 au. This difference only increases when considering the duration of a training programme, for instance, over the course of 16 weeks the dosage would increase to (a) 241,920 au and (b) 806,400 au, respectively. Given that the guidelines are broad, and that the RT dose, dosing and dosage can vary greatly, more information is needed to optimise the development of strength across the broad spectrum of guidelines established [, ].