Time course of glycogen accumulation after eccentric exercise.

This study examined the time course of glycogen accumulation in skeletal muscle depleted by concentric work and subsequently subjected to eccentric exercise. Eight men exercised to exhaustion on a cycle ergometer [70% of maximal O2 consumption (VO2max)] and were placed on a carbohydrate-restricted diet. Approximately 12 h later they exercised one leg to subjective failure by repeated eccentric action of the knee extensors against a resistance equal to 120% of their one-repetition maximum concentric knee extension force (ECC leg). The contralateral leg was not exercised and served as a control (CON leg). During the 72-h recovery period, subjects consumed 7 g carbohydrate.kg body wt-1.day-1. Moderate soreness was experienced in the ECC leg 24-72 h after eccentric exercise. Muscle biopsies from the vastus lateralis of the ECC and CON legs revealed similar glycogen levels immediately after eccentric exercise (40.2 +/- 5.2 and 47.6 +/- 6.4 mmol/kg wet wt, respectively; P greater than 0.05). There was no difference in the glycogen content of ECC and CON legs after 6 h of recovery (77.7 +/- 7.9 and 85.1 +/- 4.9 mmol/kg wet wt, respectively; P greater than 0.05), but 18 h later, the ECC leg contained 15% less glycogen than the CON leg (90.2 +/- 8.2 vs. 105.8 +/- 8.9 mmol/kg wet wt; P less than 0.05). After 72 h of recovery, this difference had increased to 24% (115.8 +/- 8.0 vs. 153.0 +/- 12.2 mmol/kg wet wt; P less than 0.05). These data confirm that glycogen accumulation is impaired in eccentrically exercised muscle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Impaired muscle glycogen resynthesis after eccentric exercise

Eight men performed 10 sets of 10 eccentric contractions of the knee extensor muscles with one leg [eccentrically exercised leg (EL)]. The weight used for this exercise was 120% of the maximal extension strength. After 30 min of rest the subjects performed two-legged cycling [concentrically exercised leg (CL)] at 74% of maximal O2 uptake for 1 h. In the 3 days after this exercise four subjects consumed diets containing 4.25 g CHO/kg body wt, and the remainder were fed 8.5 g CHO/kg. All subjects experienced severe muscle soreness and edema in the quadriceps muscles of the eccentrically exercised leg. Mean (+/- SE) resting serum creatine kinase increased from a preexercise level of 57 +/- 3 to 6,988 +/- 1,913 U/l on the 3rd day of recovery. The glycogen content (mmol/kg dry wt) in the vastus lateralis of CL muscles averaged 90, 395, and 592 mmol/kg dry wt at 0, 24, and 72 h of recovery. The EL muscle, on the other hand, averaged 168, 329, and 435 mmol/kg dry wt at these same intervals. Subjects receiving 8.5 g CHO/kg stored significantly more glycogen than those who were fed 4.3 g CHO/kg. In both groups, however, significantly less glycogen was stored in the EL than in the CL.     

No effect of creatine supplementation on human myofibrillar and sarcoplasmic protein synthesis after resistance exercise

Muscle hypertrophy during resistance training is reportedly increased by creatine supplementation. Having previously failed to find an anabolic effect on muscle protein turnover at rest, either fed or fasted, we have now examined the possibility of a stimulatory effect of creatine in conjunction with acute resistance exercise. Seven healthy men (body mass index, 23 +/- 2 kg/m2, 21 +/- 1 yr, means +/- SE) performed 20 x 10 repetitions of leg extension-flexion at 75% one-repetition maximum in one leg, on two occasions, 4 wk apart, before and after ingesting 21 g/day creatine for 5 days. The subjects ate approximately 21 g maltodextrin + 6 g protein/h for 3 h postexercise. We measured incorporation of [1-13C]leucine into quadriceps muscle proteins in the rested and exercised legs. Leg protein breakdown (as dilution of [2H5]phenylalanine) was also assessed in the exercised and rested leg postexercise. Creatine supplementation increased muscle total creatine by approximately 21% (P < 0.01). Exercise increased the synthetic rates of myofibrillar and sarcoplasmic proteins by two- to threefold (P < 0.05), and leg phenylalanine balance became more positive, but creatine was without any anabolic effect.     

Reversal of muscle fatigue during 16 h of heavy intermittent cycle exercise.

This study examined the effects of extended sessions of heavy intermittent exercise on quadriceps muscle fatigue and weakness. Twelve untrained volunteers (10 men and 2 women), with a peak oxygen consumption of 44.3 +/- 2.3 ml.kg(-1).min(-1), exercised at approximately 91% peak oxygen consumption for 6 min once per hour for 16 h. Muscle isometric properties assessed before and after selected repetitions (R1, R2, R4, R7, R12, and R15) were used to quantitate fatigue (before vs. after repetitions) and weakness (before vs. before repetitions). Muscle fatigue at R1 was indicated by reductions (P < 0.05) in peak twitch force (135 +/- 13 vs. 106 +/- 11 N) and by a reduction (P < 0.05) in the force-frequency response, which ranged between approximately 53% at 10 Hz (113 +/- 12 vs. 52.6 +/- 7.4 N) and approximately 17% at 50 Hz (324 +/- 27 vs. 270 +/- 30 N). No recovery of force, regardless of stimulation frequency, was observed during the 54 min between R1 and R2. At R2 and for all subsequent repetitions, no reduction in force, regardless of stimulation frequency, was generally found after the exercise. The only exception was for R2, where, at 20 Hz, force was reduced (P < 0.05) by 18%. At R15, force before repetitions for high frequencies (i.e., 100 Hz) returned to R1 (333 +/- 29 vs. 324 +/- 27 N), whereas force at low frequency (i.e., 10 Hz) was only partially (P < 0.05) recovered (113 +/- 12 vs. 70 +/- 6.6 N). It is concluded that multiple sessions of heavy exercise can reverse the fatigue noted early and reduce or eliminate weakness depending on the frequency of stimulation.     

The combined acute effects of massage, rest periods, and body part elevation on resistance exercise performance

Although massage administered between workouts has been suggested to improve recovery and subsequent performance, its application between bouts of repetitive supramaximal anaerobic efforts within a given workout has received little attention. The purpose of the study compared different forms of very short rest periods administered between resistance exercise sets of individual workouts on subsequent performance. With a within-subjects design methodology, subjects (n = 30) performed three workouts that were identical in terms of the exercises (45 degrees leg press, prone leg curl, seated shoulder press, standing barbell curl), number of sets, and the resistance employed. For each workout, subjects received one of the following treatments between sets: 1 minute of rest as they stood upright, 30 seconds of rest as they stood upright, or 30 seconds of concurrent massage and body part elevation (MBPE), which entailed petrassage of the exercised limbs in a raised and supported position in an attempt to abate fatigue and enhance recovery from the previous set. Subjects were instructed to perform as many repetitions as possible for each set. For each exercise, two dependent variables were calculated: a total work/elapsed time ratio and the cumulative number of repetitions performed. For each exercise, one-way repeated-measures analysis of variance and Tukey's post hoc test revealed the following total work/elapsed time results: 1 minute rest <30 seconds' rest, 30 seconds' MBPE. For each exercise, cumulative repetition results were as follows: 1 minute rest >30 seconds' rest, 30 seconds' MBPE. Results imply that rest period duration exerts more influence on resistance exercise performance than MBPE. Those who seek improved resistance exercise performance should pay particular attention to rest period durations.     

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.     

Reliability of an exercise protocol designed to evaluate resistance exercise performance

The purpose of the present investigation was to evaluate the reliability a protocol used to assess short-term resistance exercise performance. Six men participated in this investigation after giving their consent. Subjects (N = 6) performed 6 sets of leg extensions at 80% of 10 repetition maximum (RM). Ten repetitions were performed during the first 3 sets; during the last 3 sets subjects exercised to fatigue. Ninety seconds of seated passive recovery separated each set. Subsequently, 2 experimental trials were conducted in which the exercise protocol was identical to the familiarization trial. There was a significant decline in performance from set 4 (13.5 +/- 0.9 reps) to set 5 (11.9 +/- 0.8 reps) and set 4 to set 6 (10.8 +/- 1.0 reps), suggesting that the protocol did induce fatigue. The intraclass correlations were 0.992, 0.992, and 0.993 for the fourth, fifth, and sixth sets, respectively. The average coefficients of variation for the fourth, fifth, and sixth sets were 6.7, 2.7, and 7.1%, respectively. These data suggest that the resistance training protocol used in this investigation is reliable and may be useful in evaluating interventions designed to improve fatigue resistance.     

Myofibrillar and collagen protein synthesis in human skeletal muscle in young men after maximal shortening and lengthening contractions

We aimed to determine whether there were differences in the extent and time course of skeletal muscle myofibrillar protein synthesis (MPS) and muscle collagen protein synthesis (CPS) in human skeletal muscle in an 8.5-h period after bouts of maximal muscle shortening (SC; average peak torque = 225 +/- 7 N.m, means +/- SE) or lengthening contractions (LC; average peak torque = 299 +/- 18 N.m) with equivalent work performed in each mode. Eight healthy young men (21.9 +/- 0.6 yr, body mass index 24.9 +/- 1.3 kg/m2) performed 6 sets of 10 maximal unilateral LC of the knee extensors on an isokinetic dynamometer. With the contralateral leg, they then performed 6 sets of maximal unilateral SC with work matched to the total work performed during LC (10.9 +/- 0.7 vs. 10.9 +/- 0.8 kJ, P = 0.83). After exercise, the participants consumed small intermittent meals to provide 0.1 g.kg(-1).h(-1) of protein and carbohydrate. Prior exercise elevated MPS above rest in both conditions, but there was a more rapid rise after LC (P < 0.01). The increases (P < 0.001) in CPS above rest were identical for both SC and LC and likely represent a remodeling of the myofibrillar basement membrane. Therefore, a more rapid rise in MPS after maximal LC could translate into greater protein accretion and muscle hypertrophy during chronic resistance training utilizing maximal LC.     

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.     

No effects of oral ribose supplementation on repeated maximal exercise and de novo ATP resynthesis.

A double-blind randomized study was performed to evaluate the effect of oral ribose supplementation on repeated maximal exercise and ATP recovery after intermittent maximal muscle contractions. Muscle power output was measured during dynamic knee extensions with the right leg on an isokinetic dynamometer before (pretest) and after (posttest) a 6-day training period in conjunction with ribose (R, 4 doses/day at 4 g/dose, n = 10) or placebo (P, n = 9) intake. The exercise protocol consisted of two bouts (A and B) of maximal contractions, separated by 15 s of rest. Bouts A and B consisted of 15 series of 12 contractions each, separated by a 60-min rest period. During the training period, the subjects performed the same exercise protocol twice per day, with 3-5 h of rest between exercise sessions. Blood samples were collected before and after bouts A and B and 24 h after bout B. Knee-extension power outputs were approximately 10% higher in the posttest than in the pretest but were similar between P and R for all contraction series. The exercise increased blood lactate and plasma ammonia concentrations (P < 0.05), with no significant differences between P and R at any time. After a 6-wk washout period, in a subgroup of subjects (n = 8), needle-biopsy samples were taken from the vastus lateralis before, immediately after, and 24 h after an exercise bout similar to the pretest. ATP and total adenine nucleotide content were decreased by approximately 25 and 20% immediately after and 24 h after exercise in P and R. Oral ribose supplementation with 4-g doses four times a day does not beneficially impact on postexercise muscle ATP recovery and maximal intermittent exercise performance.     

Prior exercise increases basal and insulin-induced p38 mitogen-activated protein kinase phosphorylation in human skeletal muscle.

We have examined the effects of insulin on p38 mitogen-activated protein kinase (MAPK) phosphorylation in human skeletal muscle and the effects of prior exercise hereon. Seven men performed 1-h one-legged knee extensor exercise 3 h before the initiation of a 100-min euglycemic-hyperinsulinemic (600 pmol/l) clamp. Glucose uptake across the legs was measured with the leg balance technique, and muscle biopsies were obtained from the rested and exercised vastus lateralis before and during insulin infusion. Net glucose uptake during the clamp was approximately 50% higher (P < 0.05) in the exercised leg than in the rested leg. Insulin induced a modest sustained 1.2- and 1.3-fold increase (P < 0.05) in p38 MAPK phosphorylation in the rested and exercised legs, respectively. However, p38 phosphorylation was approximately 50% higher (P < 0.05) in the exercised compared with the rested leg before and during insulin infusion. We conclude that a physiological concentration of insulin causes modest but sustained activation of the p38 MAPK pathway in human skeletal muscle. Furthermore, the stimulatory effect of exercise on p38 phosphorylation is persistent for at least 3 h after exercise and remains evident during subsequent insulin stimulation. Because p38 MAPK has been suggested to play a necessary role in activation of GLUT-4 at the cell surface, the present data may suggest a putative role of p38 MAPK in the increased insulin sensitivity of skeletal muscle after exercise.     

Muscle glycogenolysis during differing intensities of weight-resistance exercise

Skeletal muscle glycogen metabolism was investigated in eight male subjects during and after six sets of 70% one repetition maximum (1 RM, I-70) and 35% 1 RM (I-35) intensity weight-resistance leg extension exercise. Total force application to the machine lever arm was determined via a strain gauge and computer interfaced system and was equated between trials. Compared with the I-70 trial, the I-35 trial was characterized by almost double the repetitions (13 +/- 1 vs. 6 +/- 0) and half the peak concentric torque for each repetition (12.4 +/- 0.5 vs. 24.2 +/- 1.0 Nm). After the sixth set, muscle glycogen degradation was similar between I-70 and I-35 trials (47.0 +/- 6.6 and 46.6 +/- 6.0 mmol/kg wet wt, respectively), as was muscle lactate accumulation (13.8 +/- 0.7 and 16.7 +/- 4.2 mmol/kg wet wt, respectively). After 2 h of passive recovery without caloric intake, muscle glycogen increased by 22.2 +/- 6.8 and 14.2 +/- 2.5 mmol/kg wet wt in the I-70 and I-35 trials, respectively. Optical absorbance measurement of periodic acid-Schiff-stained muscle sections after the 2 h of recovery revealed larger absorbance increases in fast-twitch than in slow-twitch fibers (0.119 +/- 0.024 and 0.055 +/- 0.024, P = 0.02). Data indicated that when external work was constant, the absolute amount of muscle glycogenolysis was the same regardless of the intensity of resistance exercise. Nevertheless the rate of glycogenolysis during the I-70 trial was approximately double that of the I-35 trial.     

Influence of exercise order in a resistance-training exercise session

The order of resistance exercises within a training session may have a vital impact on the quality of the constituent exercises performed. However, very few studies have documented the specific influence of exercise order. Therefore, the purpose of this study was to examine the effect of exercise order on back squat performance in the context of a whole-body workout. Nine resistance-trained male subjects (age: 24 +/- 4 years, body mass: 81.5 +/- 15.3 kg, resistance-training experience: 7 +/- 4 years) performed the back squat exercise (4 sets at 85% of 1 repetition maximum) on 2 separate occasions in a balanced, crossover design. During one protocol, the squat exercise was performed first (protocol A); during the other protocol, it was performed after a whole-body resistance-exercise session (protocol B). Number of repetitions, average power, and rating of perceived exertion (RPE) were collected during each set of the squat exercise. All subjects performed significantly (p < 0.01) more repetitions during set 1 when they performed protocol A (8.0 +/- 1.9 repetitions) compared with protocol B (5.4 +/- 2.7 repetitions). The average power for each set was higher during protocol B compared with protocol A. There were no significant differences in RPE values between the 2 protocols. In conclusion, performing the barbell back squat first in an exercise session allowed the completion of more total repetitions. However, this study showed that performing the squat exercise after a whole-body workout session may result in greater power output if the squat is preceded by a power exercise (i.e., hang pull). This phenomenon may have been due to postactivation potentiation.     

The effects of carbohydrate loading on repetitive jump squat power performance

The beneficial role of carbohydrate (CHO) supplementation in endurance exercise is well documented. However, only few data are available on the effects of CHO loading on resistance exercise performance. Because of the repetitive use of high-threshold motor units, it was hypothesized that the power output (power-endurance) of multiple sets of jump squats would be enhanced following a high-CHO (6.5 g CHO kg body mass(-1)) diet compared to a moderate-CHO (4.4 g CHO kg body mass(-1)) diet. Eight healthy men (mean +/- SD: age 26.3 +/- 2.6 years; weight 73.0 +/- 6.3 kg; body fat 13.4 +/- 5.0%; height 178.2 +/- 6.1 cm) participated in 2 randomly assigned counterbalanced supplementation periods of 4 days after having their free-living habitual diet monitored. The resistance exercise test consisted of 4 sets of 12 repetitions of maximal-effort jump squats using a Plyometric Power System unit and a load of 30% of 1 repetition maximum (1RM). A 2-minute rest period was used between sets. Immediately before and after the exercise test, a blood sample was obtained to determine the serum glucose and blood lactate concentrations. No significant difference in power performance existed between the 2 diets. As expected, there was a significant (p 相似文献   

Resistance exercise alters MRF and IGF-I mRNA content in human skeletal muscle.

Increasing evidence suggests that the myogenic regulatory factors (MRFs) and IGF-I have important roles in the hypertrophy response observed after mechanical loading. We, therefore, hypothesized that a bout of heavy-resistance training would affect the MRF and IGF-I mRNA levels in human skeletal muscle. Six male subjects completed four sets of 6-12 repetitions on a leg press and knee extensor machine separated by 3 min. Myogenin, MRF4, MyoD, IGF-IEabc (isoforms a, b, and c) and IGF-IEbc (isoform b and c) mRNA levels were determined in the vastus lateralis muscle by RT-PCR before exercise, immediately after, and 1, 2, 6, 24, and 48 h postexercise. Myogenin, MyoD, and MRF4 mRNA levels were elevated (P < 0.005) by 100-400% 0-24 h postexercise. IGF-IEabc mRNA content decreased (P < 0.005) by approximately 44% after 1 and 6 h of recovery. The IGF-IEbc mRNA level was unaffected. The present study shows that myogenin, MyoD, and MRF4 mRNA levels are transiently elevated in human skeletal muscle after a single bout of heavy-resistance training, supporting the idea that the MRFs may be involved in regulating hypertrophy and/or fiber-type transitions. The results also suggest that IGF-IEa expression may be downregulated at the mRNA level during the initial part of recovery from resistance exercise.     

Hyperthermia and central fatigue during prolonged exercise in humans.

The present study investigated the effects of hyperthermia on the contributions of central and peripheral factors to the development of neuromuscular fatigue. Fourteen men exercised at 60% maximal oxygen consumption on a cycle ergometer in hot (40 degrees C; hyperthermia) and thermoneutral (18 degrees C; control) environments. In hyperthermia, the core temperature increased throughout the exercise period and reached a peak value of 40.0 +/- 0.1 degrees C (mean +/- SE) at exhaustion after 50 +/- 3 min of exercise. In control, core temperature stabilized at approximately 38.0 +/- 0.1 degrees C, and exercise was maintained for 1 h without exhausting the subjects. Immediately after the cycle trials, subjects performed 2 min of sustained maximal voluntary contraction (MVC) either with the exercised legs (knee extension) or with a "nonexercised" muscle group (handgrip). The degree of voluntary activation during sustained maximal knee extensions was assessed by superimposing electrical stimulation (EL) to nervus femoralis. Voluntary knee extensor force was similar during the first 5 s of contraction in hyperthermia and control. Thereafter, force declined in both trials, but the reduction in maximal voluntary force was more pronounced in the hyperthermic trial, and, from 30 to 120 s, the force was significantly lower in hyperthermia compared with control. Calculation of the voluntary activation percentage (MVC/MVC + EL) revealed that the degree of central activation was significantly lower in hyperthermia (54 +/- 7%) compared with control (82 +/- 6%). In contrast, total force of the knee extensors (MVC + force from EL) was not different in the two trials. Force development during handgrip contraction followed the same pattern of response as was observed for the knee extensors. In conclusion, these data demonstrate that the ability to generate force during a prolonged MVC is attenuated with hyperthermia, and the impaired performance is associated with a reduction in the voluntary activation percentage.     

Hypertrophy without increased isometric strength after weight training

Eight men (20-23 years) weight trained 3 days.week-1 for 19 weeks. Training sessions consisted of six sets of a leg press exercise (simultaneous hip and knee extension and ankle plantar flexion) on a weight machine, the last three sets with the heaviest weight that could be used for 7-20 repetitions. In comparison to a control group (n = 6) only the trained group increased (P less than 0.01) weight lifting performance (heaviest weight lifted for one repetition, 29%), and left and right knee extensor cross-sectional area (CAT scanning and computerized planimetry, 11%, P less than 0.05). In contrast, training caused no increase in maximal voluntary isometric knee extension strength, electrically evoked knee extensor peak twitch torque, and knee extensor motor unit activation (interpolated twitch method). These data indicate that a moderate but significant amount of hypertrophy induced by weight training does not necessarily increase performance in an isometric strength task different from the training task but involving the same muscle group. The failure of evoked twitch torque to increase despite hypertrophy may further indicate that moderate hypertrophy in the early stage of strength training may not necessarily cause an increase in intrinsic muscle force generating capacity.     

Serum leptin responses after acute resistance exercise protocols.

This study examined the acute effects of maximum strength (MS), muscular hypertrophy (MH), and strength endurance (SE) resistance exercise protocols on serum leptin. Ten young lean men (age = 23 +/- 4 yr; body weight = 79.6 +/- 5.2 kg; body fat = 10.2 +/- 3.9%) participated in MS [4 sets x 5 repetitions (reps) at 88% of 1 repetition maximum (1 RM) with 3 min of rest between sets], MH (4 sets x 10 reps at 75% of 1 RM with 2 min of rest between sets), SE (4 sets x 15 reps at 60% of 1 RM with 1 min of rest between sets), and control (C) sessions. Blood samples were collected before and immediately after exercise and after 30 min of recovery. Serum leptin at 30 min of recovery exhibited similar reductions from baseline after the MS (-20 +/- 5%), MH (-20 +/- 4%), and SE (-15 +/- 6%) protocols that were comparable to fasting-induced reduction in the C session (-12 +/- 3%) (P < 0.05). Furthermore, no differences were found in serum leptin among the MS, MH, SE, and C sessions immediately after exercise and at 30 min of recovery (P > 0.05). Cortisol was higher (P < 0.05) after the MH and SE protocols than after the MS and C sessions. Glucose and growth hormone were higher (P < 0.05) after exercise in the MS, MH, and SE protocols than after the C session. In conclusion, typical resistance exercise protocols designed for development of MS, MH, and SE did not result in serum leptin changes when sampled immediately or 30 min postexercise.     

Glucose formation in human skeletal muscle. Influence of glycogen content.

Eight men exercised at 66% of their maximal isometric force to fatigue after prior decrease in the glycogen store in one leg (low-glycogen, LG). The exercise was repeated with the contralateral leg (control) at the same relative intensity and for the same duration. Muscle (quadriceps femoris) glycogen content decreased in the LG leg from 199 +/- 17 (mean +/- S.E.M.) to 163 +/- 16 mmol of glucosyl units/kg dry wt. (P less than 0.05), and in the control leg from 311 +/- 23 to 270 +/- 18 mmol/kg (P less than 0.05). The decrease in glycogen corresponded to a similar accumulation of glycolytic intermediates. Muscle glucose increased in the LG leg during the contraction, from 1.8 +/- 0.1 to 4.3 +/- 0.6 mmol/kg dry wt. (P less than 0.01), whereas no significant increase occurred in the control leg (P greater than 0.05). It is concluded that during exercise glucose is formed from glycogen through the debranching enzyme when muscle glycogen is decreased to values below about 200 mmol/kg dry wt.     

The effects of high-dose glutamine ingestion on weightlifting performance

The purpose of this study was to determine if high-dose glutamine ingestion affected weightlifting performance. In a double-blind, placebo-controlled, crossover study, 6 resistance-trained men (mean +/- SE: age, 21.5 +/- 0.3 years; weight, 76.5 +/- 2.8 kg(-1)) performed weightlifting exercises after the ingestion of glutamine or glycine (0.3 g x kg(-1)) mixed with calorie-free fruit juice or placebo (calorie-free fruit juice only). Each subject underwent each of the 3 treatments in a randomized order. One hour after ingestion, subjects performed 4 total sets of exercise to momentary muscular failure (2 sets of leg presses at 200% of body weight, 2 sets of bench presses at 100% of body weight). There were no differences in the average number of maximal repetitions performed in the leg press or bench press exercises among the 3 groups. These data indicate that the short-term ingestion of glutamine does not enhance weightlifting performance in resistance-trained men.