Mixed muscle and hepatic derived plasma protein metabolism is differentially regulated in older and younger men following resistance exercise

We sought to determine whether exercise-induced muscle protein turnover alters the subsequent production of hepatically derived acute-phase plasma proteins, and whether age affects how these proteins are regulated. We measured arteriovenous (a-v) balance and the synthesis of mixed muscle protein, albumin (A) and fibrinogen (F) before exercise (REST) and from the beginning of exercise to 10, 60, and 180 min following a single bout of moderate-intensity leg extension exercise (POST-EX) in postabsorptive untrained older (n = 6) and younger (n = 6) men using L-[ring-2H5]phenylalanine (Phe). Subjects performed 6 sets of 8 repetitions of leg extension at 80% of their 1-RM (one-repetition maximum). All data are presented as the difference from REST (Delta from REST at 10, 60, and 180 min POST-EX). Mixed muscle fractional synthesis rate (FSR-M) increased significantly from the beginning of exercise until 10 min POST-EX in the older men (DeltaFSR-M: 0.044%/h), whereas FSR-M in the younger men was not elevated until 180 min POST-EX (DeltaFSR-M: 0.030%/h). FSR-A and FSR-F increased at all POST-EX periods in the older men (DeltaFSR-A = 10 min: 1.90%/day; 60 min: 2.72%/day; 180 min: 2.78%/day; DeltaFSR-F = 10 min: 1.00%/day; 60 min: 3.01%/day; 180 min: 3.73%/day). No change occurred in FSR-A in the younger men, but FSR-F was elevated from the beginning of exercise until 10 and 180 min POST-EX (10 min: 3.07%/day and 180 min: 3.96%/day). Net balance of Phe was positive in the older men in the immediate POST-EX period. Our data indicate that mixed muscle and hepatic derived protein synthesis is differentially regulated in younger and older men in response to a single bout of moderate-intensity leg extension exercise. Moreover, our data suggest that with age may come a greater need to salvage or make available amino acids from exercise-induced muscle protein breakdown to mount an acute-phase response.     

Resistance training alters the response of fed state mixed muscle protein synthesis in young men

Ten healthy young men (21.0 +/- 1.5 yr, 1.79 +/- 0.1 m, 82.7 +/- 14.7 kg, means +/- SD) participated in 8 wk of intense unilateral resistance training (knee extension exercise) such that one leg was trained (T) and the other acted as an untrained (UT) control. After the 8 wk of unilateral training, infusions of L-[ring-d(5)]phenylalanine, L-[ring-(13)C(6)]phenylalanine, and d(3)-alpha-ketoisocaproic acid were used to measure mixed muscle protein synthesis in the T and UT legs by the direct incorporation method [fractional synthetic rate (FSR)]. Protein synthesis was determined at rest as well as 4 h and 28 h after an acute bout of resistance exercise performed at the same intensity relative to the gain in single repetition maximum before and after training. Training increased mean muscle fiber cross-sectional area only in the T leg (type I: 16 +/- 10%; type II: 20 +/- 19%, P < 0.05). Acute resistance exercise increased muscle protein FSR in both legs at 4 h (T: 162 +/- 76%; UT: 108 +/- 62%, P < 0.01 vs. rest) with the increase in the T leg being significantly higher than in the UT leg at this time (P < 0.01). At 28 h postexercise, FSR in the T leg had returned to resting levels; however, the rate of protein synthesis in the UT leg remained elevated above resting (70 +/- 49%, P < 0.01). We conclude that resistance training attenuates the protein synthetic response to acute resistance exercise, despite higher initial increases in FSR, by shortening the duration for which protein synthesis is elevated.     

Dietary protein intake impacts human skeletal muscle protein fractional synthetic rates after endurance exercise

This investigation evaluated the physiological impact of different dietary protein intakes on skeletal muscle protein synthesis postexercise in endurance runners. Five endurance-trained, male runners participated in a randomized, crossover design diet intervention, where they consumed either a low (0.8 g/kg; LP)-, moderate (1.8 g/kg; MP)-, or high (3.6 g/kg; HP)-protein diet for 4 wk. Diets were designed to be eucaloric with carbohydrate, fat, and protein approximating 60, 30, and 10%; 55, 30, and 15%; and 40, 30, and 30% for LP, MP, and HP, respectively. Substrate oxidation was assessed via indirect calorimetry at 3 wk of the dietary interventions. Mixed-muscle protein fractional synthetic rate (FSR) was measured after an endurance run (75 min at 70% V(O2 peak)) using a primed, continuous infusion of [(2)H(5)]phenylalanine. Protein oxidation increased with increasing protein intake, with each trial being significantly different from the other (P < 0.01). FSR after exercise was significantly greater for LP (0.083%/h) and MP (0.078%/h) than for HP (0.052%/h; P < 0.05). There was no difference in FSR between LP and MP. This is the first investigation to establish that habitual dietary protein intake in humans modulates skeletal muscle protein synthesis after an endurance exercise bout. Future studies directed at mechanisms by which level of protein intake influences skeletal muscle turnover are needed.     

Tendon collagen synthesis at rest and after exercise in women.

In general, there is a higher incidence of musculoskeletal injuries during physical activity in women than in men. We hypothesized that in women rates of tendon collagen synthesis would be lower than in men at rest and after exercise, especially in the later luteal phase when estrogen and progesterone concentrations are higher than the early follicular phase. We studied tendon collagen fractional synthesis rate (FSR) in 15 young, healthy female subjects in either the early follicular (n = 8) or the late luteal phase (n = 7) 72 h after an acute bout of one-legged exercise (60 min kicking at 67% workload maximum) (72 h) and compared the results with those previously obtained for men. Samples were taken from the patellar tendon in both the exercised and rested legs to determine collagen FSR by the incorporation of [15N]proline into tendon collagen hydroxyproline. There was no effect of menstrual phase on tendon collagen synthesis either at rest or after exercise. However, there was a significant difference between women and men at rest (women = 0.025 +/- 0.002%/h, men = 0.045 +/- 0.008%/h; P < 0.05) and 72 h after exercise (women = 0.027 +/- 0.005%/h; men = 0.058 +/- 0.008%/h). Furthermore, rest and 72-h tendon collagen synthesis were not different in women, whereas in men tendon collagen synthesis remained significantly elevated 72 h after exercise. It is concluded that both in the resting state and after exercise, tendon collagen FSR is lower in women than in men, which may contribute to a lower rate of tissue repair after exercise.     

Acute response of net muscle protein balance reflects 24-h balance after exercise and amino acid ingestion

The purpose of this study was to determine if the acute anabolic muscle response to resistance exercise and essential amino acids (EAA) reflects the response over 24 h. Seven subjects participated in the following two 24-h studies: 1) resting (REST) and 2) rest plus resistance exercise and consumption of EAA (ES). Net balance (NB) across the leg was determined for four amino acids. [(13)C(6)]phenylalanine was infused to determine mixed muscle fractional synthetic rate (FSR). Twenty-four-hour FSR was significantly greater for ES than for REST (P = 0.003). Exchange of phenylalanine across the leg was -194 +/- 74 (SE) mg for ES and -371 +/- 88 mg for REST (P = 0.07) over 24 h and 229 +/- 42 mg (ES) and 28 +/- 15 mg (REST; P < 0.01) over 3 h corresponding to exercise and EAA consumption for ES. The difference in phenylalanine exchange between REST and ES was not different for measurements over 24 and 3 h. Increases in NB during ES were primarily the result of increases in protein synthesis. Results for other amino acids were similar. The acute anabolic response of muscle to EAA intake and exercise is additive to the response at rest and thus reflects the 24-h response.     

Resistance-training-induced adaptations in skeletal muscle protein turnover in the fed state

Resistance training changes the balance of muscle protein turnover, leading to gains in muscle mass. A longitudinal design was employed to assess the effect that resistance training had on muscle protein turnover in the fed state. A secondary goal was investigation of the potential interactive effects of creatine (Cr) monohydrate supplementation on resistance-training-induced adaptations. Young (N = 19, 23.7 +/- 3.2 year), untrained (UT), healthy male subjects completed an 8-week resistance-training program (6 d/week). Supplementation with Cr had no impact on any of the variables studied; hence, all subsequent data were pooled. In the UT and trained (T) state, subjects performed an acute bout of resistance exercise with a single leg (exercised, EX), while their contralateral leg acted as a nonexercised (NE) control. Following exercise, subjects were fed while receiving a primed constant infusion of [d5]- and [15N]-phenylalanine to determine the fractional synthetic and breakdown rates (FSR and FBR), respectively, of skeletal muscle proteins. Acute exercise increased FSR (UT-NE, 0.065 +/- 0.025 %/h; UT-EX, 0.088 +/- 0.032 %/h; P < 0.01) and FBR (UT-NE, 0.047 +/- 0.023 %/h; UT-EX, 0.058 +/- 0.026 %/h; P < 0.05). Net balance (BAL = FSR - FBR) was positive in both legs (P < 0.05) but was significantly greater (+65%) in the EX versus the NE leg (P < 0.05). Muscle protein FSR and FBR were greater at rest following T (FSR for T-NE vs. UT-NE, +46%, P < 0.01; FBR for T-NE vs. UT-NE, +81%, P < 0.05). Resistance training attenuated the acute exercise-induced rise in FSR (T-NE vs. T-EX, +20%, P = 0.65). The present results demonstrate that resistance training resulted in an elevated resting muscle protein turnover but an attenuation of the acute response of muscle protein turnover to a single bout of resistance exercise.     

Leg glucose and protein metabolism during an acute bout of resistance exercise in humans.

The present study investigated the responses of leg glucose and protein metabolism during an acute bout of resistance exercise. Seven subjects (5 men, 2 women) were studied at rest and during a strenuous lower body resistance exercise regimen consisting of approximately 8 sets of 10 repetitions of leg press at approximately 75% 1 repetition maximum and 8 sets of 8 repetitions of knee extensions at approximately 80% 1 repetition maximum. L-[ring-2H5]phenylalanine was infused throughout the study for measurement of phenylalanine rates of appearance, disappearance, protein synthesis, and protein breakdown across the leg. Femoral arterial and venous blood samples were collected at rest and during exercise for determination of leg blood flow, concentrations of glucose, lactate, alanine, glutamine, glutamate, leucine, and phenylalanine, and phenylalanine enrichments. Muscle biopsies were obtained at rest and immediately after exercise. Leg blood flow was nearly three times (P <0.009) higher and glucose uptake more than five times higher (P=0.009) during exercise than at rest. Leg lactate release was 86 times higher than rest during the exercise bout. Although whole body phenylalanine rate of appearance, an indicator of whole body protein breakdown, was reduced during exercise; leg phenylalanine rate of appearance, rate of disappearance, protein synthesis, and protein breakdown did not change. Arterial and venous alanine concentrations and glutamate uptake were significantly higher during exercise than at rest. We conclude that lower body resistance exercise potently stimulates leg glucose uptake and lactate release. In addition, muscle protein synthesis is not elevated during a bout of resistance exercise.     

Regular Multicomponent Exercise Increases Physical Fitness and Muscle Protein Anabolism in Frail,Obese, Older Adults

Aging is associated with a decline in strength, endurance, balance, and mobility. Obesity worsens the age‐related impairment in physical function and often leads to frailty. The American College of Sports Medicine recommends a multicomponent (strength, endurance, flexibility, and balance) exercise program to maintain physical fitness. However, the effect of such an exercise program on physical fitness in frail, obese older adults is not known. We therefore determined the effect of a 3‐month long multicomponent exercise training program, on endurance (peak aerobic capacity (VO₂ peak)), muscle strength, muscle mass, and the rate of muscle protein synthesis (basal rate and anabolic response to feeding) in nine 65‐ to 80‐year‐old, moderately frail, obese older adults. After 3 months of training, fat mass decreased (P < 0.05) whereas fat‐free mass (FFM), appendicular lean body mass, strength, and VO₂ peak increased (all P < 0.05). Regular strength and endurance exercise increased the mixed muscle protein fractional synthesis rate (FSR) but had no effect on the feeding‐induced increase in muscle protein FSR (～0.02%/h increase from basal values both before and after exercise training; effect of feeding: P = 0.02; effect of training: P = 0.047; no interaction: P = 0.84). We conclude that: (i) a multicomponent exercise training program has beneficial effects on muscle mass and physical function and should therefore be recommended to frail, obese older adults, and (ii) regular multicomponent exercise increases the basal rate of muscle protein synthesis without affecting the magnitude of the muscle protein anabolic response to feeding.     

Age and aerobic exercise training effects on whole body and muscle protein metabolism

Aging in humans is associated with loss of lean body mass, but the causes are incompletely defined. Lean tissue mass and function depend on continuous rebuilding of proteins. We tested the hypotheses that whole body and mixed muscle protein metabolism declines with age in men and women and that aerobic exercise training would partly reverse this decline. Seventy-eight healthy, previously untrained men and women aged 19-87 yr were studied before and after 4 mo of bicycle training (up to 45 min at 80% peak heart rate, 3-4 days/wk) or control (flexibility) activity. At the whole body level, protein breakdown (measured as [13C]leucine and [15N]phenylalanine flux), Leu oxidation, and protein synthesis (nonoxidative Leu disposal) declined with age at a rate of 4-5% per decade (P < 0.001). Fat-free mass was closely correlated with protein turnover and declined 3% per decade (P < 0.001), but even after covariate adjustment for fat-free mass, the decline in protein turnover with age remained significant. There were no differences between men and women after adjustment for fat-free mass. Mixed muscle protein synthesis also declined with age 3.5% per decade (P < 0.05). Exercise training improved aerobic capacity 9% overall (P < 0.01), and mixed muscle protein synthesis increased 22% (P < 0.05), with no effect of age on the training response for either variable. Fat-free mass, whole body protein turnover, and resting metabolic rate were unchanged by training. We conclude that rates of whole body and muscle protein metabolism decline with age in men and women, thus indicating that there is a progressive decline in the body's remodeling processes with aging. This study also demonstrates that aerobic exercise can enhance muscle protein synthesis irrespective of age.     

Oral exposure of pigs to the mycotoxin deoxynivalenol does not modulate the hepatic albumin synthesis during a LPS-induced acute-phase reaction

The sensitivity of pigs to deoxynivalenol (DON) might be influenced by systemic inflammation (SI) which impacts liver. Besides following acute-phase proteins, our aim was to investigate both the hepatic fractional albumin (ALB) synthesis rate (FSR) and the ALB concentration as indicators of ALB metabolism in presence and absence of SI induced by LPS via pre- or post-hepatic venous route. Each infusion group was pre-conditioned either with a control diet (CON, 0.12 mg DON/kg diet) or with a DON-contaminated diet (DON, 4.59 mg DON/kg diet) for 4 wk. A depression of ALB FSR was observed 195 min after LPS challenge, independent of feeding group or LPS application route, which was not paralleled by a down-regulated ALB mRNA expression but by a reduced availability of free cysteine. The drop in ALB FSR only partly explained the plasma ALB concentrations which were more depressed in the DON-pre-exposed groups, suggesting that ALB levels are influenced by further mechanisms. The abundances of haptoglobin, C-reactive protein, serum amyloid A, pig major acute-phase protein, fibrinogen and LPS-binding protein mRNA were up-regulated upon LPS stimulation but not accompanied by increases in the plasma concentrations of these proteins, pointing at an imbalance between synthesis and consumption.     

Impaired substrate oxidation in healthy elderly men after eccentric exercise.

The metabolic response to eccentric exercise in healthy older adults is unknown. Therefore, substrate metabolism was examined in the basal state and after sustained hyperglycemia (180 min, 10 mM) in eight healthy, sedentary older [66 +/- 2 yr; body mass index (BMI) of 25.5 +/- 1.2 kg/m] and nine younger (23 +/- 1 yr; BMI of 23.6 +/- 1.7 kg/m) men, under control conditions and 48 h after eccentric exercise. Indirect calorimetry was performed to evaluate carbohydrate and lipid oxidation (C(ox) and L(ox), respectively). Eccentric exercise caused muscle soreness and increased plasma creatine kinase in both groups of men (P < 0.02). Although a similar level of hyperglycemia was maintained in the two groups, glucose infusion rates were lower (P < 0.001) in the older men. Compared with basal levels, hyperglycemia stimulated an increase in C(ox) and a decrease in L(ox) during the control and exercise trials in the younger group (P < 0.03), but only during the control trial in the older subjects (P < 0.007). C(ox) was unchanged after eccentric exercise in the younger men [4.00 +/- 0.30 vs. 3.54 +/- 0.44 mg x kg fat-free mass (FFM)(-1) x min(-1); exercise vs. control] but was suppressed by 20% in the older group (3.37 +/- 0.37 vs. 4.21 +/- 0.23 mg x kg FFM(-1) x min(-1); P < 0.04). Moreover, L(ox) was reduced by 38% in the younger subjects (0.47 +/- 0.09 vs. 0.76 +/- 0.10 mg x kg FFM(-1) x min(-1); P< 0.03) but was augmented by 89% in the older group (0.68 +/- 0.11 vs. 0.36 +/- 0.08 mg x kg FFM(-1) x min(-1); P < 0.04). In addition, hyperglycemia-stimulated C(ox), L(ox), and respiratory exchange ratio responses to eccentric exercise were related to abdominal adiposity (r = -0.57, P < 0.04, r = 0.68, P < 0.02 and r = -0.60, P < 0.02, respectively). Despite normal glucose tolerance and the absence of obesity per se, older men experience a reduction in carbohydrate oxidation in response to hyperglycemia after eccentric exercise.     

Impact of protein coingestion on muscle protein synthesis during continuous endurance type exercise

This study investigates the impact of protein coingestion with carbohydrate on muscle protein synthesis during endurance type exercise. Twelve healthy male cyclists were studied during 2 h of fasted rest followed by 2 h of continuous cycling at 55% W(max). During exercise, subjects received either 1.0 g·kg(-1)·h(-1) carbohydrate (CHO) or 0.8 g·kg(-1)·h(-1) carbohydrate with 0.2 g·kg(-1)·h(-1) protein hydrolysate (CHO+PRO). Continuous intravenous infusions with l-[ring-(13)C(6)]phenylalanine and l-[ring-(2)H(2)]tyrosine were applied, and blood and muscle biopsies were collected to assess whole body protein turnover and muscle protein synthesis rates at rest and during exercise conditions. Protein coingestion stimulated whole body protein synthesis and oxidation rates during exercise by 22 ± 3 and 70 ± 17%, respectively (P < 0.01). Whole body protein breakdown rates did not differ between experiments. As a consequence, whole body net protein balance was slightly negative in CHO and positive in the CHO+PRO treatment (-4.9 ± 0.3 vs. 8.0 ± 0.3 μmol Phe·kg(-1)·h(-1), respectively, P < 0.01). Mixed muscle protein fractional synthetic rates (FSR) were higher during exercise compared with resting conditions (0.058 ± 0.006 vs. 0.035 ± 0.006%/h in CHO and 0.070 ± 0.011 vs. 0.038 ± 0.005%/h in the CHO+PRO treatment, respectively, P < 0.05). FSR during exercise did not differ between experiments (P = 0.46). We conclude that muscle protein synthesis is stimulated during continuous endurance type exercise activities when carbohydrate with or without protein is ingested. Protein coingestion does not further increase muscle protein synthesis rates during continuous endurance type exercise.     

No effect of menstrual cycle on myofibrillar and connective tissue protein synthesis in contracting skeletal muscle

We tested the hypothesis that acute exercise would stimulate synthesis of myofibrillar protein and intramuscular collagen in women and that the phase of the menstrual cycle at which the exercise took place would influence the extent of the change. Fifteen young, healthy female subjects were studied in the follicular (FP, n=8) or the luteal phase (LP, n=7, n=1 out of phase) 24 h after an acute bout of one-legged exercise (60 min of kicking at 67% W(max)), samples being taken from the vastus lateralis in both the exercised and resting legs. Rates of synthesis of myofibrillar and muscle collagen proteins were measured by incorporation of [(13)C]leucine. Myofibrillar protein synthesis (means+/-SD; rest FP: 0.053+/-0.009%/h, LP: 0.055+/-0.013%/h) was increased at 24-h postexercise (FP: 0.131+/-0.018%/h, P<0.05, LP: 0.134+/-0.018%/h, P< 0.05) with no differences between phases. Similarly, muscle collagen synthesis (rest FP: 0.024+/- 0.017%/h, LP: 0.021+/- 0.006%/h) was elevated at 24-h postexercise (FP: 0.073+/- 0.016%/h, P<0.05, LP: 0.072+/- 0.015%/h, P<0.05), but the responses did not differ between menstrual phases. Therefore, there is no effect of menstrual cycle phase, at rest or in response to an acute bout of exercise, on myofibrillar protein synthesis and muscle collagen synthesis in women.     

Effect of ibuprofen and acetaminophen on postexercise muscle protein synthesis

We examined the effect of two commonly consumed over-the-counter analgesics, ibuprofen and acetaminophen, on muscle protein synthesis and soreness after high-intensity eccentric resistance exercise. Twenty-four males (25 +/- 3 yr, 180 +/- 6 cm, 81 +/- 6 kg, and 17 +/- 8% body fat) were assigned to one of three groups that received either the maximal over-the-counter dose of ibuprofen (IBU; 1,200 mg/day), acetaminophen (ACET; 4,000 mg/day), or a placebo (PLA) after 10-14 sets of 10 eccentric repetitions at 120% of concentric one-repetition maximum with the knee extensors. Postexercise (24 h) skeletal muscle fractional synthesis rate (FSR) was increased 76 +/- 19% (P < 0.05) in PLA (0.058 +/- 0.012%/h) and was unchanged (P > 0.05) in IBU (35 +/- 21%; 0.021 +/- 0.014%/h) and ACET (22 +/- 23%; 0.010 +/- 0.019%/h). Neither drug had any influence on whole body protein breakdown, as measured by rate of phenylalanine appearance, on serum creatine kinase, or on rating of perceived muscle soreness compared with PLA. These results suggest that over-the-counter doses of both ibuprofen and acetaminophen suppress the protein synthesis response in skeletal muscle after eccentric resistance exercise. Thus these two analgesics may work through a common mechanism to influence protein metabolism in skeletal muscle.     

Leucine-enriched essential amino acid and carbohydrate ingestion following resistance exercise enhances mTOR signaling and protein synthesis in human muscle

We recently showed that resistance exercise and ingestion of essential amino acids with carbohydrate (EAA+CHO) can independently stimulate mammalian target of rapamycin (mTOR) signaling and muscle protein synthesis in humans. Providing an EAA+CHO solution postexercise can further increase muscle protein synthesis. Therefore, we hypothesized that enhanced mTOR signaling might be responsible for the greater muscle protein synthesis when leucine-enriched EAA+CHOs are ingested during postexercise recovery. Sixteen male subjects were randomized to one of two groups (control or EAA+CHO). The EAA+CHO group ingested the nutrient solution 1 h after resistance exercise. mTOR signaling was assessed by immunoblotting from repeated muscle biopsy samples. Mixed muscle fractional synthetic rate (FSR) was measured using stable isotope techniques. Muscle protein synthesis and 4E-BP1 phosphorylation during exercise were significantly reduced (P < 0.05). Postexercise FSR was elevated above baseline in both groups at 1 h but was even further elevated in the EAA+CHO group at 2 h postexercise (P < 0.05). Increased FSR was associated with enhanced phosphorylation of mTOR and S6K1 (P < 0.05). Akt phosphorylation was elevated at 1 h and returned to baseline by 2 h in the control group, but it remained elevated in the EAA+CHO group (P < 0.05). 4E-BP1 phosphorylation returned to baseline during recovery in control but became elevated when EAA+CHO was ingested (P < 0.05). eEF2 phosphorylation decreased at 1 and 2 h postexercise to a similar extent in both groups (P < 0.05). Our data suggest that enhanced activation of the mTOR signaling pathway is playing a role in the greater synthesis of muscle proteins when resistance exercise is followed by EAA+CHO ingestion.     

Androgen receptors and testosterone in men--effects of protein ingestion, resistance exercise and fiber type

The purpose of this study was to examine the impact of protein ingestion on circulating testosterone and muscle androgen receptor (AR) as well as on insulin-like growth factor-I (MGF and IGF-IEa) responses to a resistance exercise (RE) bout in (57-72 year) men. Protein (15 g whey) (n=9) or placebo (n=9) was consumed before and after a RE bout (5 sets of 10 repetition maximums), and vastus lateralis muscle biopsies were taken pre, 1 and 48 h post-RE. The protein ingestion blunted the RE-induced increase in serum free and total testosterone while the RE bout significantly increased muscle AR mRNA levels in older men (P<0.05). However, protein ingestion did not significantly affect AR mRNA or protein expression, or MGF and IGF-IEa mRNA expression at 1 and 48 h post-RE. Immunohistochemical staining of muscle cross-sections was done with antibodies specific to AR and MyHC I and II and showed that there seems to be within or near the type-I muscle fibers a greater staining of ARs than within or near the type-II fibres. In conclusion, the protein ingestion hinders RE-induced increase in serum testosterone in older men but may not significantly affect muscle AR, MGF or IGF-IEa gene expression. Furthermore, the present study shows that even older men are able to increase muscle AR mRNA expression in response to a RE bout.     

Enhanced protein breakdown after eccentric exercise in young and older men

The effects of eccentric exercise on whole body protein metabolism were compared in five young untrained [age 24 +/- 1 yr, maximal O2 uptake (VO2max) = 49 +/- 6 ml.kg-1.min-1] and five older untrained men (age 61 +/- 1 yr, VO2max = 34 +/- 2 ml.kg-1.min-1). They performed 45 min of eccentric exercise on a cycle ergometer at a power output equivalent to 80% VO2max (182 +/- 18 W). Beginning 5 days before exercise and continuing for at least 10 days after exercise, they consumed a eucaloric diet providing 1.5 g.kg-1.day-1 of protein. Leucine metabolism in the fed state was measured before, immediately after, and 10 days after exercise, with intravenous L-[1-13C]leucine as a tracer (0.115 mumol.kg-1.min-1). Leucine flux increased 9% immediately after exercise (P less than 0.011) and remained elevated 10 days later, with no effect of age. Leucine oxidation increased 19% immediately after exercise and remained 15% above baseline 10 days after exercise (P less than 0.0001), with no effect of age. In the young men, urinary excretion of 3-methylhistidine per gram of creatinine did not increase until 10 days postexercise (P less than 0.05), but in the older men, it increased 5 days after exercise and remained high through 10 days postexercise (P less than 0.05), averaging 37% higher than in the young men. These data suggest that eccentric exercise produces a similar increase in whole body protein breakdown in older and young men, but myofibrillar proteolysis may contribute more to whole body protein breakdown in the older group.     

Resistance exercise acutely increases MHC and mixed muscle protein synthesis rates in 78-84 and 23-32 yr olds

We determined whether short-term weight-lifting exercise increases the synthesis rate of the major contractile proteins, myosin heavy chain (MHC), actin, and mixed muscle proteins in nonfrail elders and younger women and men. Fractional synthesis rates of mixed, MHC, and actin proteins were determined in seven healthy sedentary 23- to 32-yr-old and seven healthy 78- to 84-yr-old participants in paired studies done before and at the end of a 2-wk weight-lifting program. The in vivo rate of incorporation of 1-[(13)C]leucine into vastus lateralis MHC, actin, and mixed proteins was determined using a 14-h constant intravenous infusion of 1-[(13)C]leucine. Before exercise, the mixed and MHC fractional synthetic rates were lower in the older than in the younger participants (P < or = 0.04). Baseline actin protein synthesis rates were similar in the two groups (P = not significant). Over a 2-wk period, participants completed ten 1- to 1. 5-h weight-lifting exercise sessions: 2-3 sets per day of 9 exercises, 8-12 repetitions per set, at 60-90% of maximum voluntary muscle strength. At the end of exercise, MHC and mixed protein synthetic rates increased in the younger (88 and 121%) and older participants (105 and 182%; P < 0.001 vs. baseline). These findings indicate that MHC and mixed protein synthesis rates are reduced more than actin in advanced age. Similar to that of 23-32 yr olds, the vastus lateralis muscle in 78-84 yr olds retains the capacity to increase MHC and mixed protein synthesis rates in response to short-term resistance exercise.