Metformin inhibits mitochondrial adaptations to aerobic exercise training in older adults

Metformin and exercise independently improve insulin sensitivity and decrease the risk of diabetes. Metformin was also recently proposed as a potential therapy to slow aging. However, recent evidence indicates that adding metformin to exercise antagonizes the exercise‐induced improvement in insulin sensitivity and cardiorespiratory fitness. The purpose of this study was to test the hypothesis that metformin diminishes the improvement in insulin sensitivity and cardiorespiratory fitness after aerobic exercise training (AET) by inhibiting skeletal muscle mitochondrial respiration and protein synthesis in older adults (62 ± 1 years). In a double‐blinded fashion, participants were randomized to placebo (n = 26) or metformin (n = 27) treatment during 12 weeks of AET. Independent of treatment, AET decreased fat mass, HbA1c, fasting plasma insulin, 24‐hr ambulant mean glucose, and glycemic variability. However, metformin attenuated the increase in whole‐body insulin sensitivity and VO₂max after AET. In the metformin group, there was no overall change in whole‐body insulin sensitivity after AET due to positive and negative responders. Metformin also abrogated the exercise‐mediated increase in skeletal muscle mitochondrial respiration. The change in whole‐body insulin sensitivity was correlated to the change in mitochondrial respiration. Mitochondrial protein synthesis rates assessed during AET were not different between treatments. The influence of metformin on AET‐induced improvements in physiological function was highly variable and associated with the effect of metformin on the mitochondria. These data suggest that prior to prescribing metformin to slow aging, additional studies are needed to understand the mechanisms that elicit positive and negative responses to metformin with and without exercise.     

Adaptations in muscular activation of the knee extensor muscles with strength training in young and older adults

The purpose of this study was to compare the extent of muscular activation during maximal voluntary knee extension contractions in old and young individuals and to examine the effects of resistance training on muscular activation in each group. The interpolated twitch technique was used to estimate muscular activation during two pre-training baseline tests, and after two and six weeks of resistance training. Throughout the study, the older group was 30% less strong than the young group (p=0.02). The training protocol was effective in both groups with overall isometric strength gains of 30 and 36% in the older (p=0.01) and young (p<0.01) groups, respectively. 10-RM training loads increased by 66% in the old group (p<0.01) and by 77% in the young group (p<0.01) throughout training. At the first baseline test, a 2% difference in muscular activation between groups (p=0.3) did not explain the large disparity in strength. Muscular activation increased by 2% in both groups throughout training (p<0.01). Despite considerably less muscular strength in the older group, muscular activation was greater than 95% of maximum and appears to be equal in both young and older individuals. Both groups demonstrated similar but small increases in muscular activation throughout training.     

Metabolic adaptations to training precede changes in muscle mitochondrial capacity.

To determine whether increases in muscle mitochondrial capacity are necessary for the characteristic lower exercise glycogen loss and lactate concentration observed during exercise in the trained state, we have employed a short-term training model involving 2 h of cycling per day at 67% maximal O2 uptake (VO2max) for 5-7 consecutive days. Before and after training, biopsies were extracted from the vastus lateralis of nine male subjects during a continuous exercise challenge consisting of 30 min of work at 67% VO2max followed by 30 min at 76% VO2max. Analysis of samples at 0, 15, 20, and 60 min indicated a pronounced reduction (P less than 0.05) in glycogen utilization after training. Reductions in glycogen utilization were accompanied by reductions (P less than 0.05) in muscle lactate concentration (mmol/kg dry wt) at 15 min [37.4 +/- 9.3 (SE) vs. 20.2 +/- 5.3], 30 min (30.5 +/- 6.9 vs. 17.6 +/- 3.8), and 60 min (26.5 +/- 5.8 vs. 17.8 +/- 3.5) of exercise. Maximal aerobic power, VO2max (l/min) was unaffected by the training (3.99 +/- 0.21 vs. 4.05 +/- 0.26). Measurements of maximal activities of enzymes representative of the citric acid cycle (succinic dehydrogenase and citrate synthase) were similar before and after the training. It is concluded that, in the voluntary exercising human, altered metabolic events are an early adaptive response to training and need not be accompanied by changes in muscle mitochondrial capacity.     

Muscle morphological and strength adaptations to endurance vs. resistance training

Fascicle angle (FA) is suggested to increase as a result of fiber hypertrophy and furthermore to serve as the explanatory link in the discrepancy in the relative adaptations in the anatomical cross-sectional area (CSA) and fiber CSA after resistance training (RT). In contrast to RT, the effects of endurance training on FA are unclear. The purpose of this study was therefore to investigate and compare the longitudinal effects of either progressive endurance training (END, n = 7) or RT (n = 7) in young untrained men on FA, anatomical CSA, and fiber CSA. Muscle morphological measures included the assessment of vastus lateralis FA obtained by ultrasonography and anatomical CSA by magnetic resonance imaging of the thigh and fiber CSA deduced from histochemical analyses of biopsy samples from m. vastus lateralis. Functional performance measures included VO2max and maximal voluntary contraction (MVC). The RT produced increases in FA by 23 ± 8% (p < 0.01), anatomical CSA of the knee extensor muscles by 9 ± 3% (p = 0.001), and fiber CSA by 19 ± 7% (p < 0.05). RT increased knee extensor MVC by 20 ± 5% (p < 0.001). END increased VO2max by 10 ± 2% but did not evoke changes in FA, anatomical CSA, or in fiber CSA. In conclusion, the morphological changes induced by 10 weeks of RT support that FA does indeed serve as the explanatory link in the observed discrepancy between the changes in anatomical and fiber CSA. Contrarily, 10 weeks of endurance training did not induce changes in FA, but the lack of morphological changes from END indirectly support the fact that fiber hypertrophy and FA are interrelated.     

Muscle strength response to strength training is influenced by insulin-like growth factor 1 genotype in older adults.

Strength training (ST) is considered an intervention of choice for the prevention and treatment of sarcopenia. Reports in the literature have suggested that the insulin-like growth factor I protein (IGF-I) plays a major role in ST-induced skeletal muscle hypertrophy and strength improvements. A microsatellite repeat in the promoter region of the IGF1 gene has been associated with IGF-I blood levels and phenotypes related to IGF-I in adult men and women. To examine the influence of this polymorphism on muscle hypertrophic and strength responses to ST, we studied 67 Caucasian men and women before and after a 10-wk single-leg knee-extension ST program. One repetition maximum strength, muscle volume via computed tomography, and muscle quality were assessed at baseline and after 10 wk of training. The IGF1 repeat promoter polymorphism and three single-nucleotide polymorphisms were genotyped. For the promoter polymorphism, subjects were grouped as homozygous for the 192 allele, heterozygous, or noncarriers of the 192 allele. After 10 wk of training, 1-repetition maximum, muscle volume, and muscle quality increased significantly for all groups combined (P < 0.001). However, carriers of the 192 allele gained significantly more strength with ST than noncarriers of the 192 allele (P = 0.02). There was also a nonsignificant trend for a greater increase in muscle volume in 192 carriers than noncarriers (P = 0.08). No significant associations were observed for the other polymorphisms studied. Thus these data suggest that the IGF1 promoter polymorphism may influence the strength response to ST. Larger sample sizes should be used in future studies to verify these results.     

Exercise training increases intramyocellular lipid and oxidative capacity in older adults

Intramyocellular lipid (IMCL) has been associated with insulin resistance. However, an association between IMCL and insulin resistance might be modulated by oxidative capacity in skeletal muscle. We examined the hypothesis that 12 wk of exercise training would increase both IMCL and the oxidative capacity of skeletal muscle in older (67.3 +/- 0.7 yr), previously sedentary subjects (n = 13; 5 men and 8 women). Maximal aerobic capacity (Vo(2 max)) increased from 1.65 +/- 0.20 to 1.85 +/- 0.14 l/min (P < 0.05), and systemic fat oxidation induced by 1 h of cycle exercise at 45% of Vo(2 max) increased (P < 0.05) from 15.03 +/- 40 to 19.29 +/- 0.80 (micromol.min(-1).kg fat-free mass(-1)). IMCL, determined by quantitative histological staining in vastus lateralis biopsies, increased (P < 0.05) from 22.9 +/- 1.9 to 25.9 +/- 2.6 arbitrary units (AU). The oxidative capacity of muscle, determined by succinate dehydrogenase staining intensity, significantly increased (P < 0.05) from 75.2 +/- 5.2 to 83.9 +/- 3.6 AU. The percentage of type I fibers significantly increased (P < 0.05) from 35.4 +/- 2.1 to 40.1 +/- 2.3%. In conclusion, exercise training increases IMCL in older persons in parallel with an enhanced capacity for fat oxidation.     

Healthy older adults have insufficient hip range of motion and plantar flexor strength to walk like healthy young adults

Limited plantar flexor strength and hip extension range of motion (ROM) in older adults are believed to underlie common age-related differences in gait. However, no studies of age-related differences in gait have quantified the percentage of strength and ROM used during gait. We examined peak hip angles, hip torques and plantar flexor torques, and corresponding estimates of functional capacity utilized (FCU), which we define as the percentage of available strength or joint ROM used, in 10 young and 10 older healthy adults walking under self-selected and controlled (slow and fast) conditions. Older adults walked with about 30% smaller hip extension angle, 28% larger hip flexion angle, 34% more hip extensor torque in the slow condition, and 12% less plantar flexor torque in the fast condition than young adults. Older adults had higher FCU than young adults for hip flexion angle (47% vs. 34%) and hip extensor torque (48% vs. 27%). FCUs for plantar flexor torque (both age groups) and hip extension angle (older adults in all conditions; young adults in self-selected gait) were not significantly <100%, and were higher than for other measures examined. Older adults lacked sufficient hip extension ROM to walk with a hip extension angle as large as that of young adults. Similarly, in the fast gait condition older adults lacked the strength to match the plantar flexor torque produced by young adults. This supports the hypothesis that hip extension ROM and plantar flexor strength are limiting factors in gait and contribute to age-related differences in gait.     

Changes in H reflex and V wave following short-term endurance and strength training

This study examined the effects of 3 wk of either endurance or strength training on plasticity of the neural mechanisms involved in the soleus H reflex and V wave. Twenty-five sedentary healthy subjects were randomized into an endurance group (n = 13) or strength group (n = 12). Evoked V-wave, H-reflex, and M-wave recruitment curves, maximal voluntary contraction (MVC), and time-to-task-failure (isometric contraction at 40% MVC) of the plantar flexors were recorded before and after training. Following strength training, MVC of the plantar flexors increased by 14.4 ± 5.2% in the strength group (P < 0.001), whereas time-to-task-failure was prolonged in the endurance group (22.7 ± 17.1%; P < 0.05). The V wave-to-maximal M wave (V/M(max)) ratio increased significantly (55.1 ± 28.3%; P < 0.001) following strength training, but the maximal H wave-to-maximal M wave (H(max)/M(max)) ratio remained unchanged. Conversely, in the endurance group the V/M(max) ratio was not altered, whereas the H(max)/M(max) ratio increased by 30.8 ± 21.7% (P < 0.05). The endurance training group also displayed a reduction in the H-reflex excitability threshold while the H-reflex amplitude on the ascending limb of the recruitment curve increased. Strength training only elicited a significant decrease in H-reflex excitability threshold, while H-reflex amplitudes over the ascending limb remained unchanged. These observations indicate that the H-reflex pathway is strongly involved in the enhanced endurance resistance that occurs following endurance training. On the contrary, the improvements in MVC following strength training are likely attributed to increased descending drive and/or modulation in afferents other than Ia afferents.     

Neuromuscular and hormonal adaptations in athletes to strength training in two years

Neuromuscular and hormonal adaptations to prolonged strength training were investigated in nine elite weight lifters. The average increases occurred over the 2-yr follow-up period in the maximal neural activation (integrated electromyogram, IEMG; 4.2%, P = NS), maximal isometric leg-extension force (4.9%, P = NS), averaged concentric power index (4.1%, P = NS), total weight-lifting result (2.8%, P less than 0.05), and total mean fiber area (5.9%, P = NS) of the vastus lateralis muscle, respectively. The training period resulted in increases in the concentrations of serum testosterone from 19.8 +/- 5.3 to 25.1 +/- 5.2 nmol/l (P less than 0.05), luteinizing hormone (LH) from 8.6 +/- 0.8 to 9.1 +/- 0.8 U/l (P less than 0.05), follicle-stimulating hormone (FSH) from 4.2 +/- 2.0 to 5.3 +/- 2.3 U/l (P less than 0.01), and testosterone-to-serum sex hormone-binding globulin (SHBG) ratio (P less than 0.05). The annual mean value of the second follow-up year for the serum testosterone-to-SHBG ratio correlated significantly (r = 0.84, P less than 0.01) with the individual changes during the 2nd yr in the averaged concentric power. The present results suggest that prolonged intensive strength training in elite athletes may influence the pituitary and possibly hypothalamic levels, leading to increased serum levels of testosterone. This may create more optimal conditions to utilize more intensive training leading to increased strength development.     

Similarity in adaptations to high-resistance circuit vs. traditional strength training in resistance-trained men

To compare the effects of 8 weeks of high-resistance circuit (HRC) training (3-6 sets of 6 exercises, 6 repetition maximum [RM], ～35-second interset recovery) and traditional strength (TS) training (3-6 sets of 6 exercises, 6RM, 3-minute interset recovery) on physical performance parameters and body composition, 33 healthy men were randomly assigned to HRC, TS, or a control group. Training consisted of weight lifting 3 times a week for 8 weeks. Before and after the training, 1RM strength on bench press and half squat exercises, bench press peak power output, and body composition (dual x-ray absorptiometry ) were determined. Shuttle run and 30-second Wingate tests were also completed. Upper limb (UL) and lower limb 1RM increased equally after both TS and HRC training. The UL peak power at various loads was significantly higher at posttraining for both groups (p ≤ 0.01). Shuttle-run performance was significantly better after both HRC and TS training, however peak cycling power increased only in TS training (p ≤ 0.05). Significant decreases were found in % body fat in the HRC group only; HRC and TS training both resulted in an increased lean but not bone mass. The HRC training was as effective as TS for improving weight lifting 1RM and peak power, shuttle-run performance and lean mass. Thus, HRC training promoted a similar strength-mass adaptation as traditional training while using a shorter training session duration.     

Effects of 4 weeks of traditional resistance training vs. superslow strength training on early phase adaptations in strength, flexibility, and aerobic capacity in college-aged women

This study compared SuperSlow resistance training (SRT) to traditional resistance training (TRT) during early phase adaptations in strength, aerobic capacity, and flexibility in college-aged women. Subjects were randomly assigned to SRT (n = 14); TRT (n = 13); or control (CON; n = 8) groups. To equalize training times, TRT trained 3 times per week for 25 minutes each session, whereas SRT trained twice a week for 35 minutes each session. Both groups trained for 4 weeks, whereas the CON group maintained normal daily activities. Workouts consisted of 5 exercises: shoulder press, chest press, leg press, low row, and lat pull down. The SRT group completed 1 set of each exercise at 50% 1RM until momentary failure with a 10-second concentric and a 10-second eccentric phase. The TRT group completed 3 sets of 8 repetitions at 80% 1RM for each exercise, with 4 seconds of contraction time for each repetition. Groups were statistically similar at baseline. There was a significant (p ≤ 0.01) time main effect for flexibility with the greatest improvements occurring for the training groups (SRT 14.7% and TRT 11%). All strength tests had significant (p ≤ 0.01) time main effects but no group or group by time interactions. Both training groups had large percent improvements in strength compared to CON, but the large variability associated with the SRT group resulted in only the TRT group being significantly different from the CON group. In conclusion, percent improvements were similar for the TRT and SRT groups, but only the TRT group reached statistical significance for the strength improvements, and both groups were equally effective for improving flexibility.     

Sympathetic adaptations to one-legged training.

The purpose of the present study was to determine the effect of leg exercise training on sympathetic nerve responses at rest and during dynamic exercise. Six men were trained by using high-intensity interval and prolonged continuous one-legged cycling 4 day/wk, 40 min/day, for 6 wk. Heart rate, mean arterial pressure (MAP), and muscle sympathetic nerve activity (MSNA; peroneal nerve) were measured during 3 min of upright dynamic one-legged knee extensions at 40 W before and after training. After training, peak oxygen uptake in the trained leg increased 19 +/- 2% (P < 0.01). At rest, heart rate decreased from 77 +/- 3 to 71 +/- 6 beats/min (P < 0.01) with no significant changes in MAP (91 +/- 7 to 91 +/- 11 mmHg) and MSNA (29 +/- 3 to 28 +/- 1 bursts/min). During exercise, both heart rate and MAP were lower after training (108 +/- 5 to 96 +/- 5 beats/min and 132 +/- 8 to 119 +/- 4 mmHg, respectively, during the third minute of exercise; P < 0.01). MSNA decreased similarly from rest during the first 2 min of exercise both before and after training. However, MSNA was significantly less during the third minute of exercise after training (32 +/- 2 to 22 +/- 3 bursts/min; P < 0.01). This training effect on MSNA remained when MSNA was expressed as bursts per 100 heartbeats. Responses to exercise in five untrained control subjects were not different at 0 and 6 wk. These results demonstrate that exercise training prolongs the decrease in MSNA during upright leg exercise and indicates that attenuation of MSNA to exercise reported with forearm training also occurs with leg training.     

Physiological adaptations to strength and circuit training in postmenopausal women with bone loss

Strength training (ST; high intensity/low volume/long rest) has been used in several populations, including children, young adults, and older adults. However, there is no information about circuit weight training (CWT; low intensity/high volume/short rest) in apparently healthy postmenopausal women. The purpose of the present study was to analyze the effects of high-intensity ST and circuit training on isometric strength (IS), upper limb dynamic strength (ULS) and lower limb dynamic strength (LLS), muscle activation of quadriceps (EMG quad), maximal oxygen uptake (VO2 max), time to exhaustion (TE), and bone mineral density (BMD). Twenty-eight postmenopausal women were divided into 3 groups: 1) ST group (STG, n = 9, 45-80% 1 repetition maximum (1RM), 2-4 sets, 20-6 reps), 2) circuit training group (CTG, n = 10, 45-60% 1RM, 2-3 sets, 20-10 reps), and 3) a control group (CON, n = 9, no exercise). Significance level was defined as p 相似文献   

Effects of strength training on submaximal and maximal endurance performance capacity in middle-aged and older men

Effects of a 16-week progressive strength-training program on blood lactate accumulation (LA), maximal workload (W(max)) attained during progressive cycling exercise, maximum half-squat (1RM(HS)), muscle cross-sectional area of the quadriceps femoris muscle group (CSA(QF)), and serum hormone concentrations were examined in 11 middle-aged (46 year old [M46]) and 11 older (64 year old [M64]) men. During the 16 weeks of training, significant increases were observed in 1RM(HS) in M46 and M64 (41-45%; p < 0.001). The muscle CSA(QF) increased (13-11%; p > 0.01) for both groups. The first 8 weeks of training led to significant increases in W(max) (6-11%; p < 0.001) and decreases in submaximal (LA) in both groups, but no further training-induced changes were observed during the subsequent 8 weeks of training. Statistically significant relationships were observed in M64 and in the combined group M46 + M64 between the training-induced changes observed in W(max) and serum testosterone-cortisol and free-testosterone-cortisol ratios, whereas in M46 the respective correlations values did not reach statistically significant levels. These data indicate that strength training results in a significant improvement in maximal and submaximal endurance during the first 8 weeks of strength training in both age groups, related in part to the intensity and the volume of resistance training used and to the training status of the subjects. The relationships found in this study between various indices of cycling testing and serum hormone concentrations after strength training suggest that maximal incremental cycling might be used as an additional test to detect anabolic-catabolic responses to prolonged strength training in middle-aged and older men.     

Early-phase adaptations to intrahospital training in strength and functional mobility of children with leukemia

Improvements in chemotherapy and radiotherapy have contributed to the high survival rate (approximately 70%) of childhood acute lymphoblastic leukemia (ALL). However, during treatment, lack of physical activity and treatment cause various short- to long-term side effects, such as muscle atrophy and physical deconditioning. The purpose of this study was to determine the effects of an intrahospital, short-duration (8 weeks) exercise training program on muscle strength and endurance and functional mobility of children with ALL. Seven children (4 boys and 3 girls; 4-7 years of age) who were in the maintenance phase of treatment for ALL were selected as subjects. Three training sessions of 90- to 120-minute duration were performed each week. Each session included 11 different strength exercises engaging the major muscle groups and aerobic training. Gains in strength and endurance were assessed with a 6 repetition maximum test for upper (seated bench press and seated lateral row) and lower extremities (leg press). Gains in functional mobility were assessed with the time up and go test (TUG) and the timed up and down stairs test (TUDS). Performance was significantly improved after the training program in all strength tests (p < 0.01 for seated bench press and p < 0.05 for both seated lateral row and seated leg press) and in the TUG test (p < 0.05). In summary, a period of time as short as 8 weeks is enough to produce clinically relevant early-phase adaptations in children receiving treatment against ALL (i.e., improved functional mobility and muscle strength). Although more research is needed in the area of exercise training and pediatric cancer, exercise sciences can play a beneficial role in assisting both oncologists in treating cancer and improving children's quality of life during and after treatment.     

Early-phase neuroendocrine responses and strength adaptations following eccentric-enhanced resistance training

The purpose of this study was to evaluate the early-phase muscular performance adaptations to 5 weeks of traditional (TRAD) and eccentric-enhanced (ECC+) progressive resistance training and to compare the acute postexercise total testosterone (TT), bioavailable testosterone (BT), growth hormone (GH), and lactate responses in TRAD- and ECC+-trained individuals. Twenty-two previously untrained men (22.1 +/- 0.8 years) completed 1 familiarization and 2 baseline bouts, 15 exercise bouts (i.e., 3 times per week for 5 weeks), and 2 postintervention testing bouts. Anthropometric and 1 repetition maximum (1RM) measurements (i.e., bench press and squat) were assessed during both baseline and postintervention testing. Following baseline testing, participants were randomized into TRAD (4 sets of 6 repetitions at 52.5% 1RM) or ECC+ (3 sets of 6 repetitions at 40% 1RM concentric and 100% 1RM eccentric) groups and completed the 5-week progressive resistance training protocols. During the final exercise bout, blood samples acquired at rest and following exercise were assessed for serum TT, BT, GH, and blood lactate. Both groups experienced similar increases in bench press (approximately 10%) and squat (approximately 22%) strength during the exercise intervention. At the conclusion of training, postexercise TT and BT concentrations increased (approximately 13% and 21%, respectively, p < 0.05) and GH concentrations increased (approximately 750-1200%, p < 0.05) acutely following exercise in both protocols. Postexercise lactate accumulation was similar between the TRAD (5.4 +/- 0.4) and ECC+ (5.6 +/- 0.4) groups; however, the ECC+ group's lactate concentrations were significantly lower than those of the TRAD group 30 to 60 minutes into recovery. In conclusion, TRAD training and ECC+ training appear to result in similar muscular strength adaptations and neuroendocrine responses, while postexercise lactate clearance is enhanced following ECC+ training.     

The influence of volume of exercise on early adaptations to strength training

The purpose of this investigation was to compare the effects of single-set strength training and 3-set strength training during the early phase of adaptation in 18 untrained male subjects (age, 20-30 years). After initial testing, subjects were randomly assigned to either the 3L-1U group (n = 8), which trained 3 sets in leg exercises and 1 set in upper-body exercises, or the 1L-3U group (n = 10), which trained 1 set in leg exercises and 3 sets in upper-body exercises. Testing was conducted at the beginning and at the end of the study and consisted of 2 maximal isometric tests (knee extension and bench press) and 6 maximal dynamic tests (1 repetition maximum [1RM] tests). Subjects trained 3 days per week for 6 weeks. After warm-up, subjects performed 3 leg exercises and 4 upper-body exercises. In both groups, each set consisted of 7 repetitions (reps) with the load supposed to induce muscular failure after the seventh rep (7RM load). After 6 weeks of training, 1RM performance in all training exercises was significantly increased (10-26%, p < 0.01) in both groups. The relative increase in 1RM load in the 3 leg exercises was significantly greater in the 3L-1U group than in the 1L-3U group (21% vs. 14%, p = 0.01). However, the relative increase in 1RM load in the 3 upper-body exercises was similar in the 3L-1U group (16%) and the 1L-3U group (14%). These results show a superior adaptation to 3-set strength training, compared with 1-set strength training, in leg exercises but not in upper-body exercises during the early phase of adaptation.     

Influence of acetaminophen and ibuprofen on skeletal muscle adaptations to resistance exercise in older adults

Evidence suggests that consumption of over-the-counter cyclooxygenase (COX) inhibitors may interfere with the positive effects that resistance exercise training has on reversing sarcopenia in older adults. This study examined the influence of acetaminophen or ibuprofen consumption on muscle mass and strength during 12 wk of knee extensor progressive resistance exercise training in older adults. Thirty-six individuals were randomly assigned to one of three groups and consumed the COX-inhibiting drugs in double-blind placebo-controlled fashion: placebo (67 ± 2 yr; n = 12), acetaminophen (64 ± 1 yr; n = 11; 4 g/day), and ibuprofen (64 ± 1 yr; n = 13; 1.2 g/day). Compliance with the resistance training program (100%) and drug consumption (via digital video observation, 94%), and resistance training intensity were similar (P > 0.05) for all three groups. Drug consumption unexpectedly increased muscle volume (acetaminophen: 109 ± 14 cm(3), 12.5%; ibuprofen: 84 ± 10 cm(3), 10.9%) and muscle strength (acetaminophen: 19 ± 2 kg; ibuprofen: 19 ± 2 kg) to a greater extent (P < 0.05) than placebo (muscle volume: 69 ± 12 cm(3), 8.6%; muscle strength: 15 ± 2 kg), when controlling for initial muscle size and strength. Follow-up analysis of muscle biopsies taken from the vastus lateralis before and after training showed muscle protein content, muscle water content, and myosin heavy chain distribution were not influenced (P > 0.05) by drug consumption. Similarly, muscle content of the two known enzymes potentially targeted by the drugs, COX-1 and -2, was not influenced (P > 0.05) by drug consumption, although resistance training did result in a drug-independent increase in COX-1 (32 ± 8%; P < 0.05). Drug consumption did not influence the size of the nonresistance-trained hamstring muscles (P > 0.05). Over-the-counter doses of acetaminophen or ibuprofen, when consumed in combination with resistance training, do not inhibit and appear to enhance muscle hypertrophy and strength gains in older adults. The present findings coupled with previous short-term exercise studies provide convincing evidence that the COX pathway(s) are involved in the regulation of muscle protein turnover and muscle mass in humans.     

Hepatic adaptations to iron deficiency and exercise training.

Brooks et al. [Am. J. Physiol. 253 (Endocrinol. Metab. 16): E461-E466, 1987] demonstrated an elevated gluconeogenic rate in resting iron-deficient rats. Because physical exercise also imposes demand on this hepatic function, we hypothesized that exercise training superimposed on iron deficiency would augment the hepatic capacity for amino acid transamination/deamination and pyruvate carboxylation. Sprague-Dawley rats (n = 32) were obtained at weaning (21 days of age) and randomly assigned to iron-sufficient (dietary iron = 60 mg iron/kg diet) or iron-deficient (3 mg iron/kg) dietary groups. Dietary groups were subdivided into sedentary and trained subgroups. Treadmill training was 4 wk in duration, 6 days/wk, 1 h/day, 0% grade. Treadmill speed was initially 26.8 m/min and was decreased to 14.3 m/min over the 4-wk training period. The mild exercise-training regimen did not affect any measured variable in iron-sufficient rats. In contrast, in iron-deficient animals, training increased endurance capacity threefold and reduced blood lactate and the lactate-to-alanine ratio during submaximal exercise by 34 and 27%, respectively. The mitochondrial oxidative capacity of gastrocnemius muscle was increased 46% by training. However, the oxidative capacity of liver was not affected by either iron deficiency or training. Maximal rates of pyruvate carboxylation and glutamine metabolism by isolated liver mitochondria were also evaluated. Iron deficiency and training interacted to increase pyruvate carboxylation by intact mitochondria. Glutamine metabolism was increased roughly threefold by iron deficiency alone, and training amplified this effect to a ninefold increase over iron-sufficient animals.(ABSTRACT TRUNCATED AT 250 WORDS)