BACKGROUND:The primary protein source of a diet may impact skeletal muscle maintenance with advancing age. The impact of the animal and plant protein contents of a typical protein-containing diet on muscle anabolism in middle-to-older aged adults is unknown. OBJECTIVES:To determine muscle adaptive remodeling response to a 10-d dietary intervention containing divergent protein sources, with and without resistance exercise training (RET) in middle-to-older aged adults. METHODS:In a single-blind randomized controlled trial, 27 50- to 70-y-old participants consumed 1.0 g·kg BM-1·d-1 of protein from an animal-focused whey protein-supplemented diet (AW-D) or plant-focused pea protein-supplemented diet (PP-D). Throughout the 10-d diet intervention, unilateral knee extensor RET was performed every other day. Deuterated water ingestion and skeletal muscle biopsies enabled measurement of daily integrated myofibrillar protein synthesis (iMyoPS) rates in the trained and untrained legs. Changes in metabolic rate, body composition, lipid profiles, renal function, whole-body nitrogen balance (WBNB), strength, and muscle architecture were also determined. RESULTS:Daily iMyoPS rates were significantly greater (P < 0.001) in the trained leg compared with the untrained leg for AW-D (1.44 ± 0.26 vs. 1.29 ± 0.27 %⋅d-1) and PP-D (1.50 ± 0.17 vs. 1.34 ± 0.21 %⋅d-1) with no differences between groups, within leg. Training and diet did not affect intracellular anabolic signaling, muscle architecture, strength, metabolic rate, renal function, or WBNB. Serum non-HDL-cholesterol was significantly (P = 0.014) lower following the intervention for PP-D only (pre: 3.89 ± 0.84; post: 3.37 ± 0.78 mmol⋅L) with no other changes in lipid profiles. CONCLUSIONS:The 10-d provision of 1.0g·kg BM-1·d-1 from predominantly plant-derived or animal-derived protein does not influence daily iMyoPS rates in middle-to-older aged adults and has little impact on metabolic and renal health parameters. RET enhances rates of daily iMyoPS in middle-to-older aged adults consuming a typical protein-containing diet, with no influence of protein source. CLINICAL TRIAL REGISTRY NUMBER:ClinicalTrials.gov NCT05574205 (https://clinicaltrials.gov/study/NCT05574205).

BACKGROUND:Industrial processing and storage of milk products can strongly increase protein glycation level. Previously, we have reported that a high protein glycation level impairs protein digestion, thereby compromising lysine bioavailability. The lower postprandial lysine availability may restrict the anabolic properties of a high glycated protein. OBJECTIVES:The objective of this study was to assess the impact of milk protein glycation on postprandial plasma amino acid availability and subsequent postprandial muscle protein synthesis rates during recovery from a single bout of resistance-type exercise. METHODS:Forty-five recreationally active, healthy young males participated in this double-blinded, randomized parallel study. After performing a single bout of whole-body resistance-type exercise, subjects ingested 20 g milk protein with either a low (4%; LOW-GLYC) or high (47%; HIGH-GLYC) glycation level or a noncaloric placebo (PLA). Continuous intravenous infusion of L-[ring-13C6]-phenylalanine was combined with the collection of blood and muscle tissue samples during a 6-h postprandial period to assess plasma amino acid concentrations and muscle protein synthesis rates. RESULTS:Protein ingestion increased plasma total and essential amino acid concentrations compared with placebo (time × treatment interaction: P < 0.001), with no differences between the low and high glycated milk protein. Plasma lysine availability, assessed over the full 6 h postprandial period, was substantially lower following ingestion of the protein with the high versus low glycation level (-5 ± 7 compared with 10 ± 9 mmol · L-1 · 360 min, respectively, P < 0.001). Postprandial muscle protein synthesis rates did not differ between treatments (0.059 ± 0.016, 0.061 ± 0.012, and 0.061 ± 0.018 % · h-1, in LOW-GLYC, HIGH-GLYC and PLA, respectively, P = 0.939). CONCLUSIONS:Ingestion of protein with a higher glycation level attenuates postprandial plasma lysine availability. Milk protein glycation does not modulate postprandial muscle protein synthesis rates during recovery from resistance exercise in healthy, young males. This trial was registered at the Dutch Trial Register as NL8690; https://onderzoekmetmensen.nl/nl/trial/49398.

Background The polyphenol oleuropein activates mitochondrial calcium import, which increases pyruvate dehydrogenase (PDH) activity. Preclinically, this increase in PDH activity following oleuropein supplementation resulted in improved mitochondrial bioenergetics and fatigue resistance. Objectives This study aimed to examine the effects of acute and chronic oleuropein supplementation on muscle energy metabolism, whole-body substrate metabolism, strength, and fatigue resistance in older males. Methods In a randomized, double-blind, placebo-controlled trial, 40 healthy older males (60 ± 5y) received either placebo (PLA) or 100 mg oleuropein from 250 mg olive leaf extract (OLE) supplementation daily for 36 d. On day 1 and day 36, muscle and blood samples were collected, and indirect calorimetry was performed before and ≤120 min following supplement intake. Leg strength and fatigue were measured before and after 29 d of supplementation. Results were analyzed using analysis of covariance or robust analysis of covariance. Results OLE ingestion on day 1 and day 36 increased plasma oleuropein metabolites (P < 0.001). On day 1, no differences were observed in muscle PDH activity, mitochondrial respiration, or whole-body substrate metabolism 120 min after acute OLE ingestion. Ribonucleic acid sequencing revealed upregulation of oxidative phosphorylation gene pathways (false discovery rate < 0.05), whereas PDH-Serine293-phosphorylation was higher after acute OLE compared with PLA ingestion (P = 0.015). Following chronic supplementation, fractional PDH activity was ∼25% greater in OLE compared with PLA (49 ± 14 compared with 38 ± 10%; P = 0.016) with no differences in absolute PDH activity and PDH-Serine293-phosphorylation between groups. Mitochondrial respiration and protein content, whole-body substrate metabolism, leg strength, and fatigue resistance were not different between OLE and PLA. Plasma low-density lipoprotein cholesterol was lower after chronic OLE compared with PLA (P = 0.043), with no differences in other blood metabolic markers. Conclusions Chronic OLE supplementation resulted in higher skeletal muscle fractional PDH activity in healthy, older males, which may impact resting energy metabolism. Acute or chronic oleuropein supplementation does not modulate skeletal muscle mitochondrial respiration, muscle strength, muscle fatigue, or whole-body substrate metabolism.This trial was registered at clinicaltrials.gov as NCT05217433.

BACKGROUND:Protein ingestion during recovery from exercise can further increase muscle protein synthesis rates. Plant-derived proteins are generally believed to have lesser anabolic properties than animal-derived proteins. To our knowledge, no studies have compared the impact of plant-derived with that of animal-derived protein ingestion on postexercise muscle protein synthesis rates in healthy, young females. OBJECTIVES:This study compared muscle protein synthesis rates following the ingestion of 20 g native canola protein, 20 g whey protein, or a noncaloric placebo during recovery from a single bout of resistance exercise in healthy, young females. METHODS:In this randomly assigned, parallel group, double-blind placebo-controlled design, 36 healthy young (age, 23 ± 4 y; BMI, 22.7 ± 2.2 kg/m2) females performed 8 sets of lower-body resistance exercise at 80% of their predetermined 1-repetition maximum after which they ingested 20 g native canola protein isolate, 20 g whey protein isolate, or a noncaloric placebo. Primed continuous L-[ring-13C6]-phenylalanine infusions were applied with frequent sampling of blood and muscle tissue to assess postprandial plasma amino acid profiles and 5-h postexercise muscle protein synthesis rates. Data are presented as mean ± SD. RESULTS:Plasma essential amino acid concentrations strongly increased following ingestion of both whey and canola protein when compared with the placebo treatment (peak: 2113 ± 354, 1249 ± 173, and 780 ± 60 μmol/L, respectively; P < 0.001) with greater postprandial plasma essential amino acid availability following whey than after canola protein ingestion (incremental AUC, 158 ± 50 and 90 ± 23 mmol/L × 5 h; P < 0.001). No significant differences in postexercise muscle protein synthesis rates were observed following the ingestion of whey protein isolate, canola protein isolate, and placebo (0.071 ± 0.015, 0.069 ± 0.016, and 0.061 ± 0.013%/h, respectively; treatment; P = 0.200). CONCLUSIONS:A single session of resistance exercise strongly increases muscle protein synthesis rates in young females. Ingestion of 20 g whey or native canola protein does not further augment muscle protein synthesis rates during the early stages of postexercise recovery in healthy, young females. This trial was registered at clinicaltrials.gov as NCT05664269.

(195 WORDS)It has been suggested that different nutritional stimuli are required to augment myofibrillar versus muscle connective protein synthesis rates. To study such different aspects of skeletal muscle remodeling, researchers often isolate myofibrillar or connective protein fractions from muscle tissue samples. However, the composition of these muscle protein fractions remains poorly defined. Here, we evaluated the amino acid profiles and protein compositions of the myofibrillar and muscle connective protein fractions within skeletal muscle tissue. The muscle connective protein fraction was shown to contain ∼70% of the total mixed muscle collagen content, with 4.4 ± 0.9% collagen relative to total protein content. This was 3-4 fold greater than the collagen content in mixed muscle tissue (1.2 ± 0.2%; p < 0.05). Myofibrillar proteins, such as actin and myosin, accounted for 39% of the myofibrillar protein fraction and 32% of the muscle connective protein fraction. The muscle connective protein fraction contained a higher proportion (42%) of key scaffolding proteins compared to the myofibrillar protein fraction (11%). In conclusion, the muscle connective protein fraction contains an enriched proportion of collagen among a large proportion of intra- and extracellular scaffolding and cell adhesion proteins, all of which are far less abundant in the myofibrillar protein fraction.

PURPOSE:This study aimed to assess the effect of ingesting a single bolus of hydrolyzed collagen or free amino acids on myofibrillar and muscle connective protein synthesis rates. METHODS:In a randomized, double-blind, parallel design, 45 young male ( n = 21) and female ( n = 24) adults (age, 23 ± 3 yr; BMI, 22.3 ± 2.2 kg·m -2 ) received intravenous infusions with L-[ ring - 13 C 6 ]-phenylalanine. After unilateral resistance exercise, participants ingested either 30 g hydrolyzed collagen (COLL, n = 15), 30 g free amino acids reflecting the collagen amino acid profile (AA, n = 15), or a noncaloric placebo (PLA, n = 15). Blood and muscle tissue samples were collected over 6 h to assess myofibrillar and muscle connective protein synthesis rates and associated signaling responses. RESULTS:Both collagen and free amino acid ingestion substantially increased circulating plasma amino acids concentrations and affected collagen turnover proteins. Collagen and free amino acid ingestion did not significantly increase myofibrillar protein synthesis rates in the rested (0.039 ± 0.011, 0.037 ± 0.010, and 0.036 ± 0.015%·h -1 in PLA, COLL, and AA, respectively) or the exercised (0.049 ± 0.010, 0.048 ± 0.011, and 0.045 ± 0.013%·h -1 ) leg ( P > 0.05). Similarly, both collagen and free amino acid ingestion did not significantly increase muscle connective protein synthesis rates in the rested (0.065 ± 0.014, 0.063 ± 0.017, and 0.061 ± 0.025%·h -1 in PLA, COLL, and AA, respectively) or the exercised (0.098 ± 0.023, 0.092 ± 0.028, and 0.085 ± 0.024%·h -1 ) leg ( P > 0.05). CONCLUSIONS:The ingestion of a single bolus of collagen hydrolysate or free amino acids substantially increases circulating amino acids concentrations, particularly glycine, but does not further increase myofibrillar or muscle connective protein synthesis rates at rest or during recovery from exercise in healthy, recreationally active young men and women.

BACKGROUND:Industrial processing and storage of milk products can strongly increase protein glycation level. Previously, we have reported that ingestion of highly glycated milk protein attenuates the postprandial rise in plasma lysine concentrations compared to the ingestion of an equivalent amount of milk protein with a low glycation level. Whether the attenuated increase in plasma lysine availability is attributed to compromised protein digestion and subsequent lysine absorption remains to be established. OBJECTIVES:The present study combined stable-isotope methodology with the ingestion of specifically produced, intrinsically labeled protein to assess protein digestion and amino acid absorption following ingestion of milk protein with a high versus low glycation level in vivo in humans. METHODS:Fifteen recreationally active, healthy young males participated in this double-blinded, randomized cross-over study. Subjects ingested 40 g intrinsically L-[1-13C]-lysine-labeled milk protein with either a low (3%) or high (50%) glycation level. Continuous intravenous infusion of L-[4,4,5,5-2H4]-lysine was combined with frequent blood sample collection during a 6-h postprandial period to evaluate dietary protein-derived lysine release into the circulation. RESULTS:Postprandial plasma lysine concentrations were lower following the ingestion of milk protein with a high versus low glycation level (time × treatment effect: P = 0.002; ƞ2 = 0.214), resulting in a 23 mmol/L x 360 min (95% confidence interval [CI]: 13, 32) lower incremental area under the curve (0 ± 12 vs 23 ± 11 mmol/L x 360 min, respectively, P < 0.001). The postprandial release of milk protein-derived lysine into the circulation was attenuated following ingestion of the protein with the high versus low glycation level (time × treatment effect: P < 0.001; ƞ2 = 0.640) and was 31% (95% CI: 26, 36) lower over the full 6-h postprandial period (18 ± 4 vs 49 ± 10% of the ingested lysine, respectively, P < 0.001). CONCLUSIONS:A high level of milk protein glycation strongly reduces postprandial plasma lysine availability in vivo in humans. Industrial processing and storage of (milk) protein products can strongly modulate protein bioavailability and, as such, lower the nutritional value of a protein source. This trial was registered at www. CLINICALTRIALS:gov as NCT05479916.

Canola protein is a rapeseed-derived protein that contains all essential amino acids in proportions that meet the WHO amino acid scoring requirements, making it an interesting protein for human food applications. It is currently unknown whether canola protein processing modulates postprandial plasma amino acid bioavailability in vivo in humans. This study compared postprandial plasma amino acid profiles following the ingestion of unprocessed (native) canola, processed canola, and whey protein isolate in healthy, young, females. In a randomized, clinical, cross-over design, 15 healthy young females (25 ± 3 y) participated in four test days on which they consumed 20 g protein as either native canola, enzyme processed or heat processed canola protein, or 20 g whey protein. Blood samples were collected for 5 h following protein ingestion to assess plasma amino acid concentrations. Ingestion of native canola protein resulted in lower increases in plasma total amino acid (TAA) concentrations compared to whey protein (3191 ± 794 vs. 4429 ± 84 µmol∙L− 1, P < 0.001). Canola protein processing resulted in greater peak plasma total amino acids concentrations, reaching statistical significance for enzyme (3599 ± 687 µmol∙L− 1, P = 0.045) but not heat (3565 ± 722 µmol∙L− 1, P = 0.166) treated compared to native canola protein. Plasma total amino acid availability, expressed as incremental area under the curve over a 5 h postprandial period, did not differ between treatments and averaged 163 ± 81, 171 ± 76, 194 ± 82, and 207 ± 85 mmol∙300 min∙L− 1 following ingestion of native, enzyme- and heat processed canola, and whey protein, respectively (P > 0.05). Ingestion of whey protein allows for a more rapid postprandial rise in circulating essential and non-essential amino acids and greater postprandial plasma total amino acid availability when compared to the ingestion of native canola protein. Ingestion of enzyme- or heat processed canola protein accelerates the postprandial rise in circulating amino acids but does not further augment overall plasma amino acid availability throughout a 5 h postprandial period when compared to the ingestion of native canola protein.

Post-exercise carbohydrate intake is required to replenish endogenous glycogen stores. Although adequate carbohydrate consumption has been reported to restore muscle glycogen contents within 24 h of post-exercise recovery, the time required to replenish liver glycogen contents is less evident. Twelve well-trained male cyclists (age: 25 ± 5 years; V̇O2peak: 67 ± 5 ml/min/kg; Wmax: 5.8 ± 0.7 W/kg) participated in this trial. Ultra-high-field (UHF) 13C magnetic resonance spectroscopy (13C MRS) was applied to assess muscle and liver glycogen concentrations before and immediately after glycogen-depleting exercise on two test days. This was followed by 12 h of recovery during which participants remained fasted (CON) or consumed 10 g carbohydrate per kg body mass (BM) in the form of sucrose-containing beverages (1.2 g/kg BM/h over the first 6 h) and carbohydrate-rich meals (CHO). Muscle and liver glycogen concentrations were again assessed at 6 and 12 h into recovery using 13C MRS. Furthermore muscle biopsies were collected to assess muscle glycogen concentrations using biochemical analysis. Exercise significantly reduced muscle (from 159 ± 32 to 56 ± 19 mmol/l; -64%) and liver (from 166 ± 40 to 110 ± 44 mmol/l; -34%) glycogen concentrations (P < 0.05), with no significant differences between test days (P > 0.05). In the absence of carbohydrate intake (CON) muscle and liver glycogen concentrations remained unchanged during recovery. After carbohydrate intake (CHO) muscle glycogen concentrations increased from 56 ± 19 to 88 ± 16 and 110 ± 19 mmol/l (or from 269 ± 90 to 418 ± 78 and 523 ± 92 in mmol/kg dry mass), after 0, 6 and 12 h of recovery, respectively, remaining well below pre-exercise values (i.e. 55% of pre-exercise at 6 h and 69% at 12 h). Liver glycogen concentrations increased from 110 ± 44 to 236 ± 39 and 258 ± 40 mmol/l, after 0, 6 and 12 h of recovery, respectively, exceeding pre-exercise values within 6 h of recovery (i.e. 142% of pre-exercise). A very strong correlation (r = 0.89, P < 0.001), good agreement (ICC: 0.87) and low bias (4.1 ± 23.7 mmol/l) were observed when comparing muscle glycogen concentrations assessed using 13C MRS and biochemical analyses. Sucrose ingestion (1.2 g/kg BM/h) fully restored liver glycogen concentrations well within 6 h of post-exercise recovery. Ingesting large amounts of carbohydrate (10 g/kg BM) did not allow muscle glycogen stores to be replenished within 12 h of post-exercise recovery. KEY POINTS: Carbohydrate ingestion is required to replenish muscle and liver glycogen stores after a strenuous bout of exercise. Carbon-13 magnetic resonance spectroscopy at ultra-high-field (7T) allows non-invasive measurement of both muscle and liver glycogen contents before and after exercise, and at 6 and 12 h of recovery with (CHO) and without (CON) carbohydrate ingestion (10 g per kg body mass). Exercise strongly reduces glycogen contents of both muscle and liver tissue. Without carbohydrate ingestion muscle and liver glycogen levels remain depleted. After ingestion of large amounts of carbohydrate both muscle and liver glycogen contents increase rapidly, with liver glycogen stores being fully repleted within 6 h. Ample carbohydrate ingestion allows rapid replenishment of liver but not muscle glycogen stores within 6 and 12 h of post-exercise recovery.

Background Intermittent fasting (IF) is an effective energy restricted dietary strategy to reduce body and fat mass and improve metabolic health in individuals with either an overweight or obese status. However, dietary energy restriction may impair muscle protein synthesis (MPS) resulting in a concomitant decline in lean body mass. Due to periods of prolonged fasting combined with irregular meal intake, we hypothesised that IF would reduce rates of MPS compared to an energy balanced diet with regular meal patterns. Aims We assessed the impact of a short-term (ten days) alternate day fasting or a continuous energy restricted diet to a control diet on integrated rates of skeletal MPS in middle-aged males with overweight or obesity. Methods Twenty-seven middle-aged males with overweight or obesity (age: 44.6±5.4 y; BMI: 30.3±2.6 kg/m2) consumed a three-day lead-in diet, followed by a ten-day controlled dietary intervention matched for protein intake, as alternate day fasting (ADF: 62.5 energy (En)%, days of 25 En% alternated with days of 100 En% food ingestion), continuous energy restriction (CER: 62.5 En%), or an energy balanced, control diet (CON: 100 En%). Deuterated water (D2O) methodology with saliva, blood, and skeletal muscle sampling were used to assess integrated rates of MPS over the ten-day intervention period. Secondary measures included fasting plasma glucose, insulin, and gastrointestinal hormone concentrations, continuous glucose monitoring, and assessment of body composition. Results There were no differences in daily rates of MPS between groups (ADF: 1.18±0.13, CER: 1.13±0.16, and CON: 1.18±0.18%/day, P>0.05). The reductions in body mass were greater in ADF and CER compared to CON (P<0.001). Lean and fat mass were decreased by a similar magnitude across groups (main time effect, P<0.001; main group effect, P>0.05). Fasting plasma leptin concentrations decreased in ADF and CER (P<0.001), with no differences in fasting plasma glucose or insulin concentrations between groups. Conclusion Short-term alternate day fasting does not lower rates of MPS compared to continuous energy restriction or an energy balanced, control diet with matched protein intake. The prolonged effects of IF and periods of irregular energy and protein intake patterns on muscle mass maintenance remain to be investigated. This trial was registered under Australian New Zealand Clinical Trial Registry (https://www.anzctr.org.au), identifier no. ACTRN12619000757112.

Whey protein ingestion during recovery from exercise increases myofibrillar but not muscle connective protein synthesis rates. It has been speculated that whey protein does not provide sufficient glycine to maximize postexercise muscle connective protein synthesis rates. In the present study, we assessed the impact of coingesting different amounts of collagen with whey protein as a nutritional strategy to increase plasma glycine availability during recovery from exercise. In a randomized, double-blind, crossover design, 14 recreationally active men (age: 26 ± 5 years; body mass index: 23.8 ± 2.1 kg·m−2) ingested in total 30 g protein, provided as whey protein with 0 g (WHEY), 5 g (WC05); 10 g (WC10), and 15 g (WC15) of collagen protein immediately after a single bout of resistance exercise. Blood samples were collected frequently over 6 hr of postexercise recovery to assess postprandial plasma amino acid kinetics and availability. Protein ingestion strongly increased plasma amino acid concentrations (p < .001) with no differences in plasma total amino acid availability between treatments (p > .05). The postprandial rise in plasma leucine and essential amino acid availability was greater in WHEY compared with the WC10 and WC15 treatments (p < .05). Plasma glycine and nonessential amino acid concentrations declined following whey protein ingestion but increased following collagen coingestion (p < .05). Postprandial plasma glycine availability averaged −8.9 ± 5.8, 9.2 ± 3.7, 23.1 ± 6.5, and 39.8 ± 11.0 mmol·360 min/L in WHEY, WC05, WC10, and WC15, respectively (incremental area under curve values, p < .05). Coingestion of a small amount of collagen (5 g) with whey protein (25 g) is sufficient to prevent the decline in plasma glycine availability during recovery from lower body resistance-type exercise in recreationally active men.

Background: Plant-derived proteins are considered to have fewer anabolic properties when compared with animal-derived proteins. The anabolic properties of isolated proteins do not necessarily reflect the anabolic response to the ingestion of whole foods. The presence or absence of the various components that constitute the whole-food matrix can strongly impact protein digestion and amino acid absorption and, as such, modulate postprandial muscle protein synthesis rates. So far, no study has compared the anabolic response following ingestion of an omnivorous compared with a vegan meal. Objectives: This study aimed to compare postprandial muscle protein synthesis rates following ingestion of a whole-food omnivorous meal providing 100 g lean ground beef with an isonitrogenous, isocaloric whole-food vegan meal in healthy, older adults. Methods: In a randomized, counter-balanced, cross-over design, 16 older (65-85 y) adults (8 males, 8 females) underwent 2 test days. On one day, participants consumed a whole-food omnivorous meal containing beef as the primary source of protein (0.45 g protein/kg body mass; MEAT). On the other day, participants consumed an isonitrogenous and isocaloric whole-food vegan meal (PLANT). Primed continuous L-[ring-C-13(6)]-phenylalanine infusions were applied with blood and muscle biopsies being collected frequently for 6 h to assess postprandial plasma amino acid profiles and muscle protein synthesis rates. Data are presented as means +/- standard deviations and were analyzed by 2 way-repeated measures analysis of variance and paired-samples t tests. Results: MEAT increased plasma essential amino acid concentrations more than PLANT over the 6-h postprandial period (incremental area under curve 87 +/- 37 compared with 38 +/- 54 mmol6 h/L, respectively; P-interaction < 0.01). Ingestion of MEAT resulted in similar to 47% higher postprandial muscle protein synthesis rates when compared with the ingestion of PLANT (0.052 +/- 0.023 and 0.035 +/- 0.021 %/h, respectively; paired-samples t test: P = 0.037). Conclusions: Ingestion of a whole-food omnivorous meal containing beef results in greater postprandial muscle protein synthesis rates when compared with the ingestion of an isonitrogenous whole-food vegan meal in healthy, older adults.

We measured the impact of blood flow restriction on muscle protein synthesis rates, muscle mass and strength during 2 weeks of strict bed rest. Twelve healthy, male adults (age: 24 ± 3 years, body mass index: 23.7 ± 3.1 kg/m2) were subjected to 14 days of strict bed rest with unilateral blood flow restriction performed three times daily in three 5 min cycles (200 mmHg). Participants consumed deuterium oxide and we collected blood and saliva samples throughout 2 weeks of bed rest. Before and immediately after bed rest, lean body mass (dual-energy X-ray absorptiometry scan) and thigh muscle volume (magnetic resonance imaging scan) were assessed in both the blood flow restricted (BFR) and control (CON) leg. Muscle biopsies were collected and unilateral muscle strength (one-repetition maximum; 1RM) was assessed for both legs before and after the bed rest period. Bed rest resulted in 1.8 ± 1.0 kg lean body mass loss (P < 0.001). Thigh muscle volume declined from 7.1 ± 1.1 to 6.7 ± 1.0 L in CON and from 7.0 ± 1.1 to 6.7 ± 1.0 L in BFR (P < 0.001), with no differences between treatments (P = 0.497). In addition, 1RM leg extension strength decreased from 60.2 ± 10.6 to 54.8 ± 10.9 kg in CON and from 59.2 ± 12.1 to 52.9 ± 12.0 kg in BFR (P = 0.014), with no differences between treatments (P = 0.594). Muscle protein synthesis rates during bed rest did not differ between the BFR and CON leg (1.11 ± 0.12 vs. 1.08 ± 0.13%/day, respectively; P = 0.302). Two weeks of bed rest substantially reduces skeletal muscle mass and strength. Blood flow restriction during bed rest does not modulate daily muscle protein synthesis rates and does not preserve muscle mass or strength. KEY POINTS: Bed rest, often necessary for recovery from illness or injury, leads to the loss of muscle mass and strength. It has been postulated that blood flow restriction may attenuate the loss of muscle mass and strength during bed rest. We investigated the effect of blood flow restriction on muscle protein synthesis rates, muscle mass and strength during 2 weeks of strict bed rest. Blood flow restriction applied during bed rest does not modulate daily muscle protein synthesis rates and does not preserve muscle mass or strength. Blood flow restriction is not effective in preventing muscle atrophy during a prolonged period of bed rest.

Resistance exercise training is effective to counteract the adverse effects of androgen deprivation therapy (ADT) on body composition, muscle mass and leg strength in prostate cancer patients (PCa). However, it is unknown whether these effects can be autonomously maintained after cessation of the supervised program. Sixty-eight PCa patients on ADT were included. The exercise intervention group (EX, n = 37) performed 20 weeks of supervised resistance exercise training. Thereafter, patients were advised to autonomously continue exercise training. The control group (CON, n = 31) only received usual care. Outcome measures were compared between baseline and after 1 year. Changes during the intervention (baseline vs. 20 weeks) and follow-up period (20 weeks vs. 1 year) were descriptively explored. In EX, 83% reported to have continued exercise training themselves. After 1 year, fat mass gains were attenuated in EX compared to CON (1.2 +/- 2.6 and 2.8 +/- 1.9 kg, respectively; time x treatment effect p = 0.032). The fat percentage increased, and lean mass and quadriceps muscle cross-sectional area decreased over time, with no differences between groups (overall 1.6 +/- 2.1%, -0.7 +/- 2.3 kg and -2.2 +/- 2.9 cm(2), respectively; time effects, all p < 0.05). For muscle strength, an increase of similar to 5% in EX was observed, significantly different from the similar to 10% decrease in CON (p < 0.001). Subsequent analyses showed that the initial exercise training-obtained gains in lean mass, muscle mass and strength in EX compared to CON, declined during the follow-up period. In conclusion, PCa patients on ADT are not capable to autonomously maintain the exercise-obtained gains of a 20-week supervised training program over a subsequent 1-year period.

PURPOSE:Ingestion of whey protein increases myofibrillar but not muscle connective protein synthesis rates. Recently, we defined a whey and collagen protein blend (5:1 ratio) to optimize post-prandial plasma amino acid availability. Here, we assessed the ability of this blend to increase myofibrillar and muscle connective protein synthesis rates at rest and during early recovery from exercise. METHODS:In a randomized, double-blind, parallel design, 28 men (age: 25 ± 5 yr; body mass index: 23.6 ± 2.3 kg·m -2 ) were randomly allocated to ingest either 30 g of protein (25 g whey/5 g collagen; BLEND, n = 14) or a noncaloric placebo (PLA, n = 14) following a single session of unilateral leg resistance-type exercise. Participants received primed continuous l -[ ring - 13 C 6 ]-phenylalanine infusions with blood and muscle biopsy samples collection for 5 h post-prandially to assess myofibrillar and muscle connective protein synthesis rates. RESULTS:Protein ingestion strongly increased plasma amino acid concentrations, including plasma leucine and glycine concentrations ( P < 0.001), with no changes following placebo ingestion ( P > 0.05). Post-prandial myofibrillar and muscle connective protein synthesis rates were higher in the exercised compared with the rested leg ( P < 0.001). In addition, myofibrillar protein synthesis rates were higher in BLEND compared with PLA in both the rested (0.038 ± 0.008 and 0.031 ± 0.006%·h -1 , respectively; P < 0.05) and exercised (0.052 ± 0.011 and 0.039 ± 0.009%·h -1 , respectively; P < 0.01) leg. Muscle connective protein synthesis rates were higher in BLEND compared with PLA in the rested (0.062 ± 0.013 and 0.051 ± 0.010%·h -1 , respectively; P < 0.05), but not the exercised (0.090 ± 0.021 and 0.079 ± 0.016%·h -1 , respectively; P = 0.11) leg. CONCLUSIONS:Ingestion of a whey (25 g) plus collagen (5 g) protein blend increases both myofibrillar and muscle connective protein synthesis rates at rest and further increases myofibrillar but not muscle connective protein synthesis rates during recovery from exercise in recreationally active, young men.

Prolonged passive heat treatment (PHT) has been suggested to trigger skeletal muscle adaptations that may improve muscle maintenance in older individuals. To assess the effects of PHT on skeletal muscle tissue capillarization, perfusion capacity, protein synthesis rates, hypertrophy and leg strength, 14 older adults (9 males, 5 females; 73 ± 6 years) underwent 8 weeks of PHT (infrared sauna: 3× per week, 45 min at ∼60°C). Before and after PHT we collected muscle biopsies to assess skeletal muscle capillarization and fibre cross-sectional area (CSA). Basal and postprandial muscle tissue perfusion kinetics and protein synthesis rates were assessed using contrast-enhanced ultrasound and primed continuous l-[ring-13C6]phenylalanine infusions, respectively. One-repetition maximum (1RM) leg strength and vastus lateralis muscle CSA were assessed. Type I and type II muscle fibre capillarization strongly increased following PHT (capillary-to-fibre perimeter exchange index: +31 ± 18 and +33 ± 30%, respectively; P < 0.001). No changes were observed in basal (0.24 ± 0.27 vs. 0.18 ± 0.11 AU; P = 0.266) or postprandial (0.20 ± 0.12 vs. 0.18 ± 0.14 AU; P = 0.717) microvascular blood flow following PHT. Basal (0.048 ± 0.014 vs. 0.051 ± 0.019%/h; P = 0.630) and postprandial (0.041 ± 0.012 vs. 0.051 ± 0.024%/h; P = 0.199) muscle protein synthesis rates did not change in response to prolonged PHT. Furthermore, no changes in vastus lateralis muscle CSA (15.3 ± 4.6 vs. 15.2 ± 4.6 cm2; P = 0.768) or 1RM leg strength (46 ± 12 vs. 47 ± 12 kg; P = 0.087) were observed over time. In conclusion, prolonged PHT increases muscle tissue capillarization but this does not improve muscle microvascular blood flow or increase muscle protein synthesis rates in healthy, older adults. Prolonged PHT does not induce skeletal muscle hypertrophy or increase leg strength in healthy, older adults. KEY POINTS: Repeated exposure to heat has been suggested to trigger skeletal muscle adaptive responses. We investigated the effect of 8 weeks of whole-body passive heat treatment (PHT; infrared sauna: 3× per week for 45 min at ∼60°C) on skeletal muscle tissue capillarization, perfusion capacity, basal, and postprandial muscle protein synthesis rates, muscle (fibre) hypertrophy, and leg strength in healthy, older adults. Prolonged PHT increases muscle tissue capillarization, but this does not improve muscle microvascular blood flow or increase muscle protein synthesis rates. Despite increases in muscle tissue capillarization, prolonged PHT does not suffice to induce skeletal muscle hypertrophy or increase leg strength in healthy, older adults.