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Biomedical subjects

J D MacDougall

Publications and source records attributed to J D MacDougall.

At least 37 records · Page 2Linked to original sources
PubMed1997

Plasma concentrations of beta-endorphin in trained eumenorrheic and amenorrheic women.

OBJECTIVE: To characterize the pattern of plasma beta-endorphin throughout the normal menstrual cycle and test the hypothesis that beta-endorphin concentrations are elevated in trained women with amenorrhea compared with trained and sedentary eumenorrheic women. DESIGN: Cohort analytic study. SETTING: Academic research environment. PARTICIPANTS: Healthy female volunteers: 10 eumenorrheic sedentary, 11 eumenorrheic trained, and 11 amenorrheic trained women. INTERVENTIONS: Blood samples were collected three times per week for either one complete menstrual cycle (eumenorrheic sedentary and trained subjects) or for a 4-week period (amenorrheic trained subjects). MAIN OUTCOME MEASURE: Plasma beta-endorphin concentrations. RESULTS: beta-Endorphin levels varied considerably across the sampling period and were not associated with menstrual status, gonadotropin, or gonadal steroid concentrations. Average beta-endorphin levels were not different between the follicular and luteal phases for menstruating subjects, but were greater in the eumenorrheic athletes. Compared with eumenorrheic sedentary subjects, plasma beta-endorphin levels were higher in the athletic groups, regardless of menstrual status. CONCLUSION: There were no cycle-related beta-endorphin changes. Eumenorrheic and amenorrheic athletes have higher beta-endorphin concentrations that may reflect adaptations to intense training and not exercise-associated amenorrhea.

Adult↗
PubMed1997

Effect of oral creatine supplementation on muscle [PCr] and short-term maximum power output.

Our purpose was to determine the effect of creatine supplementation on power output during a 30-s maximal cycling (Wingate) test. Nine males underwent 3 randomly ordered tests following ingestion of a creatine supplementation (CRE), placebo (PLA), and control (CON) CRE was ingested as creatine monohydrate (CrH2O) dissolved in a flavored drink (20g.d-1 for 3 d), while PLA consisted of the drink only. Tests were performed 14 d apart on a Monarch ergometer modified for immediate resistance loading. Needle biopsies were taken from the vastus lateralis at the end of each treatment period and before the exercise test. No difference was found between conditions for peak, mean 10-s, and mean 30-s power output, percent fatigue, or post-exercise blood lactate concentration. Similarly, no difference between conditions was observed for ATP, phosphocreatine (PCr), or total creatine (TCr); however, the TCr/ATP was higher in the CRE condition (P < 0.05) than in the CON and PLA conditions. Findings suggest that 3 d of oral Cr supplementation does not increase resting muscle PCr concentration and has no effect on performance during a single short-term maximal cycling task.

Adenosine Triphosphate↗
PubMed1997

Skeletal muscle adaptations to training under normobaric hypoxic versus normoxic conditions.

This study examined whether training under normobaric hypoxic conditions (simulating medium level altitude) would enhance physical performance and selected muscle adaptations over and above that which occurs with normoxic training. Ten healthy males (19-25 yr) underwent 8 wk of unilateral cycle ergometry training so that one leg was trained while breathing an inspirate of 13.5% O2 and the other while breathing normal ambient air. Pre- and post-training measurements included single leg VO2max and time to fatigue at 95% VO2max. Needle biopsies from quadriceps were assayed for oxidative and glycolytic enzyme activity and analyzed for capillary density, fiber area, % fiber type, and mitochondrial and lipid volume density. VO2max, time to fatigue, citrate synthase (CS), succinate dehydrogenase, and phosphofructokinase activity increased significantly (P > 0.05) in both legs following training. The increase in CS activity in the hypoxically trained leg was also significantly greater than that in the normoxically trained leg. It thus appears that training under moderate normobaric hypoxic conditions enhances muscle citrate synthase activity to a greater extent than training under normoxic conditions.

Adaptation, Physiological↗
PubMed1997

Effect of glucose supplement timing on protein metabolism after resistance training.

We determined the effect of the timing of glucose supplementation on fractional muscle protein synthetic rate (FSR), urinary urea excretion, and whole body and myofibrillar protein degradation after resistance exercise. Eight healthy men performed unilateral knee extensor exercise (8 sets/approximately 10 repetitions/approximately 85% of 1 single maximal repetition). They received a carbohydrate (CHO) supplement (1 g/kg) or placebo (Pl) immediately (t = 0 h) and 1 h (t = +1 h) postexercise. FSR was determined for exercised (Ex) and control (Con) limbs by incremental L-[1-13C]leucine enrichment into the vastus lateralis over approximately 10 h postexercise. Insulin was greater (P < 0.01) at 0.5, 0.75, 1.25, 1.5, 1.75, and 2 h, and glucose was greater (P < 0.05) at 0.5 and 0.75 h for CHO compared with Pl condition. FSR was 36.1% greater in the CHO/Ex leg than in the CHO/Con leg (P = not significant) and 6.3% greater in the Pl/Ex leg than in the Pl/Con leg (P = not significant). 3-Methylhistidine excretion was lower in the CHO (110.43 +/- 3.62 mumol/g creatinine) than P1 condition (120.14 +/- 5.82, P < 0.05) as was urinary urea nitrogen (8.60 +/- 0.66 vs. 12.28 +/- 1.84 g/g creatinine, P < 0.05). This suggests that CHO supplementation (1 g/kg) immediately and 1 h after resistance exercise can decrease myofibrillar protein breakdown and urinary urea excretion, resulting in a more positive body protein balance.

Adult↗
PubMed1996

Effects of rapid weight loss and wrestling on muscle glycogen concentration.

OBJECTIVE: To examine the effect of energy restriction and wrestling on muscle glycogen content in highly-trained male wrestlers. DESIGN: Randomized, unblinded intervention trial. SETTING: McMaster University Nutrition and Metabolism Research Laboratory. PARTICIPANTS: Twelve highly trained male wrestlers volunteered as subjects and were randomly assigned to one of two groups (Group A, n = 6; Group B, n = 6) as defined below. ASSESSMENT OF RISK FACTORS: All subjects were free of medical conditions that would preclude participation in the study and all had performed rapid weight loss at least three times/year with no medical complications. INTERVENTIONS: Group A: simulated wrestling tournament, four 5-min wrestling bouts ( > 7 h) following a 5% body weight loss and 17 h repletion period; Group B: 5% weight loss through energy restriction (1,141 kcal/day), exercise, fluid restriction, and dehydration methods (sauna) > 72 h. MAIN OUTCOME MEASURES: Group A: muscle glycogen content before and after wrestling tournament and plasma lactate after each bout; Group B: muscle glycogen before and after weight loss. RESULTS: Group A: no significant effect on muscle glycogen concentration, yet large increases were observed in blood lactate concentrations (up to 14.7 mmol/L); Group B: weight loss resulted in a 54% (p < 0.018) reduction in muscle glycogen concentration. CONCLUSIONS: The weight loss methods commonly performed by wrestlers resulted in large decreases in muscle glycogen concentration that were largely reversed during the 17-h repletion period between weigh-in and the start of the competition; participation in a wrestling tournament did not have a significant impact upon biceps brachii glycogen concentration when ad libitum feeding is allowed between matches.

Adult↗
PubMed1995

Response to resistance training in young women and men.

Six women and 6 men trained the elbow flexors 3 days per week for 20 wks, one arm performing in each session 3-5 sets of 10 maximal concentric actions on an accommodating resistance device, the other arm 3-5 sets of 8-12 coupled eccentric/concentric actions on a weight training device. With results collapsed across the two training modes, the women made significantly (p < 0.05) greater relative increases than men in strength measured on the weight (116 vs. 46%) and accommodating (99 vs. 46%) resistance devices, and greater absolute (3.5 vs. -1.3 N.m) and relative (13.7 vs. -3.2%) increases in strength measured on an isokinetic dynamometer. Absolute (cm2) and relative (%) biceps, brachialis, and total elbow flexor cross-sectional area (from CT scans) increased significantly; however, the women's vs. men's respective relative and absolute increases did not differ significantly: biceps (13 vs. 7%, 0.9 vs. 1.0 cm2), brachialis (53 vs. 31%, 2.1 vs. 2.3 cm2), and total (26 vs. 15%, 3.1 vs. 3.3 cm2) flexor area. Biceps type I and II fiber area, and the II/I area ratio did not increase significantly. The data indicate that in response to the same short-term training program, muscle size increases similarly in women and men but women make greater relative increases in strength.

Adult↗
PubMed1995

The time course for elevated muscle protein synthesis following heavy resistance exercise.

It has been shown that muscle protein synthetic rate (MPS) is elevated in humans by 50% at 4 hrs following a bout of heavy resistance training, and by 109% at 24 hrs following training. This study further examined the time course for elevated muscle protein synthesis by examining its rate at 36 hrs following a training session. Six healthy young men performed 12 sets of 6- to 12-RM elbow flexion exercises with one arm while the opposite arm served as a control. MPS was calculated from the in vivo rate of incorporation of L-[1,2-13C2] leucine into biceps brachii of both arms using the primed constant infusion technique over 11 hrs. At an average time of 36 hrs postexercise, MPS in the exercised arm had returned to within 14% of the control arm value, the difference being nonsignificant. It is concluded that following a bout of heavy resistance training, MPS increases rapidly, is more than double at 24 hrs, and thereafter declines rapidly so that at 36 hrs it has almost returned to baseline.

Adult↗
PubMed1995

Changes in human skeletal muscle ultrastructure and force production after acute resistance exercise.

Muscle ultrastructure and contractile properties were examined before and after a single bout of resistance exercise (8 sets of 8 repetitions at 80% of 1 repetition maximum). Eight untrained males performed the concentric (Con) phase of arm-curl exercise with one arm and the eccentric (Ecc) phase with the other arm. Needle biopsies were obtained from biceps brachii before exercise (Base), immediately postexercise from each arm (post-Con and post-Ecc), and 48 h postexercise from each arm (48 h-Con and 48 h-Ecc). Electron microscopy was used to quantify the presence of disrupted fibers in each sample. Analysis of variance revealed a greater (P < or = 0.05) proportion of disrupted fibers in post-Con, post-Ecc, 48 h-Con, and 48 h-Ecc samples compared with Base. Significantly more fibers were disrupted in post-Ecc (82%) and 48 h-Ecc (80%) samples compared with post-Con (33%) and 48 h-Con (37%), respectively. Voluntary and evoked strength measurements recovered to Base values within 24 h in the Con arm but remained depressed (P < or = 0.05) for 72-96 h in the Ecc arm. These data indicate that both the raising and lowering phases of weightlifting produced myofibrillar disruption, with the greatest disruption occurring during the lowering phase.

Adult↗
PubMed1995

Carbohydrate loading and metabolism during exercise in men and women.

During endurance exercise at approximately 65% maximal O2 consumption, women oxidize more lipids, and therefore decrease carbohydrate and protein oxidation, compared with men (L.J. Tarnopolsky, M.A. Tarnopolsky, S.A. Atkinson, and J.D. MacDougall. J. Appl. Physiol. 68: 302-308, 1990; S.M. Phillips, S.A. Atkinson, M.A. Tarnopolsky, and J.D. MacDougall. J. Appl. Physiol. 75: 2134-2141, 1993). The main purpose of this study was to examine the ability of similarly trained male (n = 7) and female (n = 8) endurance athletes to increase muscle glycogen concentrations in response to an increase in dietary carbohydrate from 55-60 to 75% of energy intake for a period of 4 days (carbohydrate loading). In addition, we sought to examine whether gender differences existed in metabolism during submaximal endurance cycling at 75% peak O2 consumption (VO2 peak) for 60 min. The men increased muscle glycogen concentration by 41% in response to the dietary manipulation and had a corresponding increase in performance time during an 85% VO2 peak trial (45%), whereas the women did not increase glycogen concentration (0%) or performance time (5%). The women oxidized significantly more lipid and less carbohydrate and protein compared with the men during exercise at 75% VO2-peak. We conclude that women did not increase muscle glycogen in response to the 4-day regimen of carbohydrate loading described. In addition, these data support previous observations of greater lipid and lower carbohydrate and protein oxidation by women vs. men during submaximal endurance exercise.

Adult↗
PubMed1995

Use of double labeling and photo CD for morphometric analysis of injured skeletal muscle.

We used computer-assisted analysis of myofiber cross-sectional areas to measure skeletal muscle responses to injury and disease. We developed a simple, inexpensive method for measuring myofiber size in human muscle samples using Kodak photo compact discs (CDs) as the image source. The photo CD serves as a permanent image storage medium and provides a high-resolution image that can be used to detect small myofibers. The use of double labeling for dystrophin and desmin allowed positive identification of both degenerating and regenerating fibers in a single biopsy specimen.

Antibodies, Monoclonal↗
PubMed1995

Immune response to changes in training intensity and volume in runners.

We examined the acute and chronic effects of changes in training volume and intensity on the blood lymphocyte percentages and immunoglobulin levels in runners. Twelve runners participated in four 10-d phases of low volume/low intensity (LV/LI), high volume/low intensity (HV/LI), or high volume/high intensity (HV/HI) running. Subjects were assigned to one of two different training group orders: 1) LV/LI, HV/LI, LV/LI, HV/HI; or 2) LV/LI, HV/HI, LV/LI, HV/LI. Venous blood was drawn at rest on days 1, 4, and 7; and 5 min post-exercise on days 1 and 7 of each 10-d phase. Lymphocyte subsets were determined by flow cytometry for CD3+, CD4+, CD8+, and HLA-DR+. IgG, and IgM levels were obtained by ELISA analysis. Immunoglobulin, CD8+ and HLA-DR+ levels, and pre-exercise plasma cortisol concentrations were not significantly affected by alterations in volume or intensity. A transient decrease (P < 0.05) was observed in CD4+ and the CD4/CD8 ratio 5 min post-exercise during the HV/LI and HV/HI phases. Results indicate that the exercise-induced lymphocyte subset reduction is transient and suggest that it is more dependent upon training intensity than volume, and the training order of exposure to the high-intensity stimulus may determine the magnitude of subsequent responses.

Adolescent↗
PubMed1995

Comparative effectiveness of accommodating and weight resistance training modes.

Six men and six women trained the elbow flexors of both arms 3 d.wk-1 for 20 wk. In each training session, one arm did 3-5 sets of 10 maximal concentric actions on an accommodating resistance device (ARD), the other arm 3-5 sets of 8-12 coupled eccentric/concentric actions (repetitions) to volitional failure (8-12 RM) on a weight resistance device (WRD). The average "intensity" (force of concentric actions) was approximately 1.25 times greater in ARD training, the average "volume" (number of actions x force of actions) 1.6 times greater in WRD training, and the time required to complete a training session the same for each. Both types of training produced significant increases in a single maximum weight lift (1 RM on the WRD), in the peak force of a single maximal concentric action measured on the ARD and an isovelocity dynamometer, and in biceps, brachialis, and total elbow flexor cross-sectional area (CSA). Biceps Type I and II fiber area did not change significantly. WRD training produced greater increases than ARD training in the 1 RM test on the WRD and in brachialis CSA. The data indicate that both of these common training regimens effectively increase strength and muscle mass, but the weight training regimen may be more effective for increasing muscle mass.

Adult↗
PubMed1994

The effects of tapering on strength performance in trained athletes.

The optimum pre-competition taper procedure for "strength athletes" is not known. We examined voluntary strength and evoked contractile properties of the elbow flexors over a 10 day rest only (ROT) and a 10 day reduced volume taper (RVT) in 8 resistance trained males (23 +/- 2.1 years). Following 3 wks of standardized training of the elbow flexors, subjects were randomly assigned to one of the tapers. Upon completion, they resumed training for 3 wks and completed the other taper. No arm training was performed during the ROT, while high intensity, low volume training was done every second day during the RVT. Maximum isometric (MVC), low (0.52 rad.s-1; LV) and high velocity (3.14 rad.s-1; HV) concentric peak torque, and evoked isometric twitch contractile properties were measured before and after each training phase and every 48 h during each taper. ANOVA comparison of the tapers revealed that MVC increased (p < or = 0.05) over pre-taper values throughout the RVT (measurement days 2, 4, 6, 8 and 10), as did LV at 2, 4, 6, and 8 d. MVC did not change over the ROT but LV was significantly higher on day 2 and lower on days 8 and 10. LV was also greater on days 4, 6, 8 and 10 during the RVT compared to the ROT. The evoked contractile properties remained largely unchanged. The data indicate that resistance-trained athletes can improve low velocity concentric strength for at least 8 days by greatly reducing training volume, but maintaining training intensity.

Adult↗
PubMed1994

Effect of training on the blood pressure response to weight lifting.

Six young men weight trained 3 days.week-1 for 19 weeks, on each day doing 3 warm-up sets of 20 repetitions followed by 1 set each at 15-20, 10-15, and 7-10 RM (Day 1), 3 sets at 15-20 RM (Day 2), and 1 set at 15-20 and 2 sets at 10-15 RM (Day 3) of a seated bilateral leg press exercise. Training increased (P < 0.05) the maximal single leg press lift (1-RM, 26%) and knee extensor cross-sectional area (12%). Arterial (brachial artery catheter) and esophageal (probe) pressure responses were measured before and after training as subjects did sets of as many repetitions as possible up to 20 reps with 50, 70, 80, 85 and 87.5% 1-RM. After training, peak values of systolic pressure attained during a set (M pre/post, mm Hg) were significantly (P < 0.05) increased at 85% (325/360, 10.8%) 1-RM. Peak diastolic pressure increased significantly at 50 (136/151, 11.0%), 70 (185/200, 8.1%), and 80% (215/234, 8.8%). Peak esophageal pressure increased significantly at 80% (71/91, 28.2%) 1-RM. For a given absolute weight lifted, all responses were markedly reduced after training. It is concluded that weight training can (a) increase the peak arterial and esophageal pressure responses attained during maximal weight lifting exercise, and (b) reduce the arterial and esophageal pressure responses to lifting the same absolute weight.

Adaptation, Physiological↗
PubMed1993

Elbow flexion strength curves in untrained men and women and male bodybuilders.

The influence of elbow joint angle on voluntary isometric elbow flexion strength was assessed in 15 young women (F), 18 young men (M) and 11 male bodybuilders (BB). Measurements were made at elbow joint angles of 1.31, 1.57, 1.83, 2.09, 2.36, 2.62 and 2.88 rad (3.14 rad = 180 degrees = full extension). The peak voluntary strength [mean (SE), N.m] in M [69.5 (4.3)] and BB [93.3 (4.8)] occurred at 2.09 rad (120 degrees), but occurred at 1.57 rad (90 degrees) in F [35.4 (2.4)]. Peak torque at 1.31 rad was 20% and 25% lower than at 2.09 rad in M and BB, respectively, but did not differ between these two angles in F. The larger elbow flexor muscle and fibre size in M and BB may have been responsible for their impaired torque production at joint angles corresponding to the shortest muscle lengths.

Adult↗
PubMed1993

Elbow flexor evoked twitch contractile properties in untrained men and women and male bodybuilders.

The influence of elbow joint angle on elbow flexor isometric evoked twitch contractile properties was assessed in 15 young women (F), 18 young men (M) and 11 male bodybuilders (BB). Measurements were made at elbow joint angles of 1.31, 1.57, 1.83, 2.09, 2.36, 2.62 and 2.88 rad (3.14 rad = 180 degrees = full extension). The largest peak twitch torque values [mean (SE) N.m] in F [3.77 (0.20)], M [10.38 (0.68)] and BB [11.38 (1.05)] occurred at 2.88 rad. Peak torque was progressively smaller at smaller joint angles, but the decline from 2.88 to 1.31 rad was greater in M (68%) and BB (76%) than F (59%). Thus, the magnitude of intergroup differences in peak twitch torque (PT) was joint angle dependent. Twitch time to peak torque (TPT) was influenced in a complex way by joint angle in the three groups; BB had the lowest values at small joint angles but the highest values at the largest angles. Half-relaxation time (HRT) generally increased from the smallest to largest joint angles in a pattern that did not differ significantly among the three groups. Maximum rates of twitch torque development and relaxation showed the same pattern of results as PT, indicating that these time-related measures were more sensitive to joint angle effects on PT than on TPT or HRT. The results of this study indicate that careful consideration should be given to the selection of joint angles in the measurement of evoked twitch contractile properties for the purpose of making group comparisons or investigating the effects of interventions such as training.

Adult↗
PubMed1993

Gender differences in strength and muscle fiber characteristics.

Strength and muscle characteristics were examined in biceps brachii and vastus lateralis of eight men and eight women. Measurements included motor unit number, size and activation and voluntary strength of the elbow flexors and knee extensors. Fiber areas and type were determined from needle biopsies and muscle areas by computerized tomographical scanning. The women were approximately 52% and 66% as strong as the men in the upper and lower body respectively. The men were also stronger relative to lean body mass. A significant correlation was found between strength and muscle cross-sectional area (CSA; P < or = 0.05). The women had 45, 41, 30 and 25% smaller muscle CSAs for the biceps brachii, total elbow flexors, vastus lateralis and total knee extensors respectively. The men had significantly larger type I fiber areas (4597 vs 3483 microns2) and mean fiber areas (6632 vs 3963 microns2) than the women in biceps brachii and significantly larger type II fiber areas (7700 vs 4040 microns2) and mean fiber areas (7070 vs 4290 microns2) in vastus lateralis. No significant gender difference was found in the strength to CSA ratio for elbow flexion or knee extension, in biceps fiber number (180,620 in men vs 156,872 in women), muscle area to fiber area ratio in the vastus lateralis 451,468 vs 465,007) or any motor unit characteristics. Data suggest that the greater strength of the men was due primarily to larger fibers. The greater gender difference in upper body strength can probably be attributed to the fact that women tend to have a lower proportion of their lean tissue distributed in the upper body.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗