Recent studies have shown that vitamin-D intake can improve skeletal muscle function and strength in frail vitamin-D insufficient individuals. We investigated whether vitamin-D intake can improve the muscular response to resistance training in healthy young and elderly individuals, respectively. Healthy untrained young (n = 20, age 20–30) and elderly (n = 20, age 60–75) men were randomized to 16 weeks of daily supplementary intake of either 48 μg of vitamin-D + 800 mg calcium (Vitamin-D-group) or 800 mg calcium (Placebo-group) during a period and at a latitude of low sunlight (December-April, 56°N). During the last 12 weeks of the supplementation the subjects underwent progressive resistance training of the quadriceps muscle. Muscle hypertrophy, measured as changes in cross sectional area (CSA), and isometric strength of the quadriceps were determined. Muscle biopsies were analyzed for fiber type morphology changes and mRNA expression of vitamin-D receptor (VDR), cytochrome p450 27B1 (CYP27B1) and Myostatin. In the vitamin-D groups, serum 25(OH)D concentration increased significantly and at week 12 was significantly different from placebo in both young men (71.6 vs. 50.4 nmol/L, respectively) and elderly men (111.2 vs. 66.7 nmol/L, respectively). After 12 weeks of resistance training, quadriceps CSA and isometric strength increased compared to baseline in young (CSA p < 0.0001, strength p = 0.005) and elderly (CSA p = 0.001, strength p < 0.0001) with no difference between vitamin-D and placebo groups. Vitamin-D intake and resistance training increased strength/CSA in elderly compared to young (p = 0.008). In the young vitamin-D group, the change in fiber type IIa percentage was greater after 12 weeks training (p = 0.030) and Myostatin mRNA expression lower compared to the placebo group (p = 0.006). Neither resistance training nor vitamin-D intake changed VDR mRNA expression. No additive effect of vitamin-D intake during 12 weeks of resistance training could be detected on either whole muscle hypertrophy or muscle strength, but improved muscle quality in elderly and fiber type morphology in young were observed, indicating an effect of vitamin-D on skeletal muscle remodeling. ClinicalTrials with nr. NCT01252381

The present study investigated whether well-tolerated light-load resistance exercise (LL-RE) affects skeletal muscle fractional synthetic rate (FSR) and anabolic intracellular signaling as a way to counteract age-related loss of muscle mass. Untrained healthy elderly (>65-yr-old) men were subjected to 13 h of supine rest. After 2.5 h of rest, unilateral LL-RE, consisting of leg extensions (10 sets, 36 repetitions) at 16% of 1 repetition maximum (RM), was conducted. Subsequently, the subjects were randomized to oral intake of 4 g of whey protein per hour (PULSE, n = 10), 28 g of whey protein at 0 h and 12 g of whey protein at 7 h postexercise (BOLUS, n = 10), or 4 g of maltodextrin per hour (placebo, n = 10). Quadriceps muscle biopsies were taken at 0, 3, 7, and 10 h postexercise from the resting and the exercised leg of each subject. Myofibrillar FSR and activity of select targets from the mechanistic target of rapamycin complex 1-signaling cascade were analyzed from the biopsies. LL-RE increased myofibrillar FSR compared with the resting leg throughout the 10-h postexercise period. Phosphorylated (T308) AKT expression increased in the exercised leg immediately after exercise. This increase persisted in the placebo group only. Levels of phosphorylated (T37/46) eukaryotic translation initiation factor 4E-binding protein 1 increased throughout the postexercise period in the exercised leg in the placebo and BOLUS groups and peaked at 7 h. In all three groups, phosphorylated (T56) eukaryotic elongation factor 2 decreased in response to LL-RE. We conclude that resistance exercise at only 16% of 1 RM increased myofibrillar FSR, irrespective of nutrient type and feeding pattern, which indicates an anabolic effect of LL-RE in elderly individuals. This finding was supported by increased signaling for translation initiation and translation elongation in response to LL-RE.

We provide novel insight, that as little as 6 wk of low-load blood flow-restricted resistance exercise (BFRRE) produces pronounced fiber type-independent hypertrophy, alongside improvements across a broad range of muscle functional capacity in older individuals. Notably, since these results were obtained with a modest exercise volume and in a very time-efficient manner, BFRRE may represent a potent exercise strategy to counteract age-related muscle decay.

For older adults, the dietary protein intake has shown to be skewed towards the evening meal. Resultingly, the vital source of essential amino acids could be insufficient after some meals, while after the evening meal the dietary protein could be suboptimally utilized for protein synthesis. The present study explored if an even distribution of the protein intake could improve the dietary amino acid absorption and whole-body protein net-balance. Twenty-four healthy elderly males and females were included in a randomized controlled trial. Ten days of habituation to either an EVEN (n = 12) or SKEWED (n = 12) protein intake, was followed by a trial day. The total protein intake was controlled at 1.5 g/kg LBM, divided into 30% at each main meal in EVEN, and into 15% at breakfast and lunch and 60% at dinner in SKEWED. Snacks with 5% of the protein intake were served between meals. Energy intake in the meals and snacks were equal in both groups. Intrinsically labelled ²H₅-phenylalanine minced meat was served as the dietary protein to assess the amino acid absorption. On the trial day, infusion of ²H₈-phenylalanine and ²H₂-tyrosine, and blood samples taken over 11 h were used to measure whole-body protein turnover. Vastus lateralis muscle biopsies were taken to measure 9 h muscle protein FSR. Amino acid absorption rates and concentrations were greater in EVEN compared to SKEWED protein intake. Whole-body protein breakdown rates were lower with similar protein synthesis rates, and consequently the net-balance was greater in EVEN after breakfast and lunch compared to SKEWED and were the same in both groups after dinner. Muscle protein FSR were not different between EVEN and SKEWED. The whole-body protein net-balance was more positive in EVEN compared to SKEWED for an extended time of the measured period, driven by a lower whole-body protein breakdown in EVEN. NCT03870425, https://clinicaltrials.gov/ct2/show/NCT03870425.

The consequences of short‐term disuse are well known, but effective countermeasures remain elusive. This study investigated the effects of neuromuscular electrical stimulation (NMES) during 5 days of bed rest on retaining lower limb muscle mass and muscle function in healthy young and old participants. One leg received NMES of the quadriceps muscle (3 × 30min/day) (NMES), and the other served as a control (CON). Isometric quadriceps strength (MVC), rate of force development (RFD), lower limb lean mass, and muscle thickness were assessed pre‐and post‐intervention. Muscle thickness remained unaltered with NMES in young and increased in old following bed rest, while it decreased in CON legs. In old participants, mid‐thigh lean mass (MTLM) was preserved with NMES while decreased in CON legs. In the young, only a tendency to change with bed rest was detected for MTLM. MVC and early‐phase RFD decreased in young and old, irrespective of NMES. In contrast, late‐phase RFD was retained in young participants with NMES, while it decreased in young CON legs, and in the old, irrespective of NMES. NMES during short‐term bed rest preserved muscle thickness but not maximal muscle strength. While young and old adults demonstrated similar adaptive responses in preventing the loss of skeletal muscle thickness, RFD was retained in the young only.