4.1.2. Mastering Anabolic Resistance

At old age, the stimulating effects of exercise on MPS become blunted, which is referred to as anabolic resistance [206]. It was also recently demonstrated that masters triathletes aged >50 years display lower MPS rates following a bout of downhill running than younger triathletes, suggesting slower acute recovery with aging [207]. However, the latter study was not designed to address the impact of chronic exercise training on muscle anabolism with aging. The only study to date to investigate MPS in masters athletes compared to untrained older individuals reported that endurance-trained masters athletes, with an average of ~50 years of continuous training, do not display an elevated capacity to upregulate intramuscular signalling and integrated myofibrillar protein synthesis in response to unaccustomed resistance exercise training [208]. This is somewhat surprising, since masters athletes typically display superior physiological function and indices of muscle morphology compared with healthy untrained older individuals (see above, [209]). Obviously, lifelong exercise is the best approach to achieve whole-body health, but even starting later on in life will help delay age-related muscle weakness and physical disability.

There is a grea<sup>t</sup> interest how modifiable factors, such as diet and PA, can modulate the rate of age-related muscle loss. Stable isotope approaches revealed that the older muscle displays a reduced responsiveness to anabolic properties of amino acid feeding [210,211]. Older women in particular exhibit a blunted MPS response to feeding [206]. This anabolic resistance is now widely believed to be a key factor responsible for age-related muscle loss [212]. However, performing exercise in close temporal proximity to protein ingestion, and increasing the amount of protein ingested per meal (see above) can—at least to some extent—overcome anabolic resistance [213,214]. In support of this, cross sectional data show that senior athletes who consume protein modestly above the RDA experience higher muscle strength and quality than those consuming the RDA [215]. Moreover, supplementing with a daily dose of ∼3.5 g omega-3 fatty acids has been shown to stimulate MPS and may improve muscle mass and function in healthy older adults [216,217].

#### *4.2. Bone Health and Injury Recovery*

In addition to its mechanical susceptibility, bone is also a nutritionally modulated tissue and nutritional inadequacies are a risk factor for low bone mass in athletic individuals [218]. What is less clear is the influence of feeding practices on the bone response to intense exercise and training, and the current knowledge is well covered in the recent review by Sale et al. [219]. Evidence suggests that an energy availability >30 kcal/kg of lean body mass/day minimize negative effects on the bone and an energy availability of 45 kcal/kg of lean body mass/day is optimal to support bone health in the athlete [220]. This requirement is particular important to prevent the female athlete triad and to thereby prevent fatigue fractures [107]. Apart from energy availability, low carbohydrate availability negatively affects the bone, while consuming carbohydrate before, during or after exercise attenuates bone resorption to intense exercise and training in the athlete [221]. Masters athletes require protein intakes higher than the RDA (between 1.2 and 1.6 up to 2.2 g/kg body mass/day) through its support for muscle mass and function [201], but also via the increase in circulating hormones and growth factors, such as IGF-1, which have an anabolic effect on bone [222]. Nevertheless, it seems unlikely that a diet high in animal protein ( ∼2 g/kg) is harmful for bone health, provided that dietary calcium intake is adequate [223]. Findings even indicate beneficial effects of animal protein sources on bone strength in older adults with exercise training [224]. In addition, diets high in animal protein appear to protect against bone loss during periods of weight loss [225]. Fermented dairy products, in particular, exert beneficial effects on bone growth and mineralization, attenuation of bone loss, and reduce fracture risk [226]. Perhaps more attention should be paid to increasing fruit and vegetable intake in older athletes, because of their potassium alkali salts that the body metabolizes to bicarbonate [227,228], rather than reducing animal protein sources. An important direct or indirect mediator of bone and skeletal health is vitamin D. Vitamin D is mainly obtained through sunlight ultraviolet-B exposure (UVB) of the skin, with a small amount typically coming from the diet. It is now clear that vitamin D has important roles beyond its well-known effects on calcium and bone homeostasis. Vitamin D deficiency and insufficiency are common in athletes [229] and associated with a greater risk of low bone mass and bone injuries, such as fatigue fractures [230], which appeared to be protected by calcium (2000 mg/day) and vitamin D (800 IU/day) supplementation [231]. Higher doses with at least 1500–2000 IU/day vitamin D are required in athletes with insufficient status (circulating 25(OH)D < 40 nmol/L) [232].
