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Biomedical subjects

J D MacDougall

Publications and source records attributed to J D MacDougall.

At least 55 records · Page 3Linked to original sources
PubMed1993

Comparison of blood pressure response to isokinetic and weight-lifting exercise.

Brachial arterial pressure, oesophageal pressure, and knee joint angle were monitored in eight untrained young men as they performed bilateral leg-press actions (simultaneous hip and knee extension and ankle plantarflexion) against resistance. Single maximal leg-press actions on an isokinetic device evoked mean peak arterial (systolic/diastolic) pressures of 35.4/26.2 and 34.0/23.4 kPa at lever arm velocities of 0.262 and 1.31 rad.s-1, respectively. The corresponding oesophageal pressures were 13.2 and 10.4 kPa, respectively. Although the peak force was 30% greater, and duration of the action 3-4 times longer at 0.262 than 1.31 rad.s-1, the arterial and oesophageal pressure responses did not differ. On a weight-lifting machine, a set of repetitions [mean (SEM): 11 (3)] to failure at 80-90% one repetition maximum evoked peak arterial pressures of 45.5/32.8 kPa; the corresponding oesophageal pressure was 15.7 kPa. The peak systolic and diastolic pressures observed during weight-lifting were significantly (P < 0.05) higher than during isokinetic actions at both velocities, whereas oesophageal pressure was more elevated only in relation to isokinetic actions at the higher velocity. These data indicate that resisted leg-press actions cause extreme elevations in arterial blood pressure. The degree of voluntary effort is the major determinant of the blood pressure response, rather than the resistance mode or the type (concentric, eccentric, isometric) of muscle action. Repetitive resistance exercise (e.g. a set of repetitions to failure in weight-lifting) tends to produce greater pressure elevations than isolated, single maximal effort actions.

Adult↗
PubMed1993

Weight-training-induced attenuation of the circulatory response of older males to weight lifting.

We examined the effects of 12 wk of dynamic strength training on the heart rate (HR) and blood pressure of older male subjects during 10 repetitions of single-arm curl and single- and double-leg press at 60 and 80% of both the pre- and posttraining maximum capacities and during single maximum lifts (1 RM). The circulatory responses were greater at 80% of 1 RM than at 60% and increased with active muscle mass. After training, the 1 RMs increased by 24 (legs) to 54% (arms) and there was a marked attenuation of HR and arterial pressure during exercise when subjects lifted the same absolute load. Greatest reductions in HR (108 +/- 4 to 94 +/- 2 beats/min), systolic blood pressure (BPs, 247 +/- 14 to 206 +/- 9 Torr), diastolic pressure (156 +/- 9 to 116 +/- 5 Torr), mean arterial pressure (143 +/- 6 to 131 +/- 5 Torr), and rate-pressure product (268 +/- 22 to 196 +/- 12 HR.BPs/100) occurred during double-leg press at 80% of the pretraining 1 RM. After training, during lifting at 60, 80, and 100% of the posttraining 1 RMs, the HRs and arterial pressures were the same as those during pretraining testing when the same relative, but lighter, absolute loads were used. These observations are consistent with a significant part of the circulatory response to weight lifting being mediated by a feedforward "central command" mechanism coupled to the relative intensity rather than to the absolute level of force.

Aged↗
PubMed1993

Gender differences in leucine kinetics and nitrogen balance in endurance athletes.

The current Canadian Recommended Nutrient Intake (RNI) for protein (0.86 g.kg-1.day-1) makes no allowance for an effect of habitual physical activity. In addition, Tarnopolsky et al. (J. Appl. Physiol. 68: 302-308, 1990) showed that males may catabolize more protein than females consequent to endurance exercise. We examined nitrogen (N) balance and leucine kinetics during submaximal endurance exercise to determine the adequacy of the current Canadian RNI for protein for male and female endurance athletes. Athletes were matched for equal training volume, competitive status, and conditioning and were fed diets isoenergetic with their habitual intake, containing protein at the Canadian RNI. Subjects were adapted to the diet for 10 days before completing a 3-day measurement of N balance. N balance showed that the RNI was inadequate for females (-15.9 +/- 6.0 mg.kg-1.day-1) and males (-26.3 +/- 11.0 mg.kg-1.day-1). Leucine kinetics during exercise were determined for each subject on day 3 of the N balance experiment by use of a primed continuous infusion of L-[1-13C]leucine and the reciprocal pool model. Exercise resulted in a significant (P < 0.01) increase in leucine oxidation for both groups. Males oxidized a greater amount of leucine during the infusion than females (P < 0.01). Leucine flux also increased significantly (P < 0.01) during exercise in both groups. We conclude that the current Canadian RNI for protein is inadequate for those who chronically engage in endurance exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Left ventricular response in healthy young men during heavy-intensity weight-lifting exercise.

We examined cardiac volumes (using echocardiography), intra-arterial blood pressure (BP), and intrathoracic pressure (ITP) in healthy males performing leg press exercise to failure at 95% of their maximum dynamic strength. Compared with preexercise, during the lifting phase of exercise, end-diastolic volume (EDV; 147 +/- 8 to 103 +/- 7 ml) and end-systolic volume (ESV; 54 +/- 5 to 27 +/- 4 ml) decreased (P < 0.05); heart rate (82 +/- 6 to 143 +/- 5 beats/min), systolic BP (160 +/- 6 to 270 +/- 21 Torr), diastolic BP (91 +/- 2 to 183 +/- 18 Torr), ITP (0.8 +/- 0.8 to 57.8 +/- 24 Torr), and peak systolic BP/ESV (SBP/ESV; 3.0 +/- 0.3 to 11.0 +/- 1.5 Torr/ml) increased (P < 0.05); and stroke volume decreased (94 +/- 3 to 77 +/- 4 ml; P > 0.05). Full knee extension was associated with most values returning to preexercise levels except for ESV (38 +/- 7 ml), heart rate (130 +/- 9 beats/min), and ITP (-12.5 +/- 2.1 Torr). During the lowering phase, significant decreases in EDV to 105 +/- 14 ml and ESV to 27 +/- 7 ml were observed with increases in systolic BP to 207 +/- 23 Torr, diastolic BP to 116 +/- 8 Torr, and SBP/ESV to 10.0 +/- 2.5 Torr/ml. Stroke volume decreased to 78 +/- 9 ml (P > 0.05). Thus rapid changes in cardiac volumes, contractility, and pressure occur during weight lifting that are related to different phases of the lift.

Adult↗
PubMed1993

The effects of variations in the anti-G straining maneuver on blood pressure at +Gz acceleration.

The increase in blood pressure provided by the standard AGSM is caused by both the contraction of the muscles of the lower body and by an increased intrathoracic pressure due to a respiratory straining (Valsalva) maneuver. This study examined the relative effectiveness and fatigability of the two components at +1 Gz and during +Gz acceleration in a human centrifuge. Brachial arterial pressure was recorded from a pressure-tip transducer in six subjects performing isometric leg presses only and on a separate occasion while performing respiratory straining only. Measurements were made over a range of intensities for the leg press contractions and Valsalva maneuvers and were conducted at +1 Gz and during slow and rapid onset runs up to +5 Gz in a human centrifuge. Blood pressure was also recorded during pulsing or intermittent contractions of the legs. We found it difficult to completely separate the blood pressure response to the leg press component from that of the respiratory straining alone component, since a moderate respiratory straining maneuver usually accompanied forceful contractions of the legs. We conclude, however, that a major portion of the elevation in blood pressure caused by the AGSM can be attributed to contraction of the muscles of the lower body and that this component is less fatiguing than the respiratory straining component. At +1 Gz a pulsing isometric contraction of the legs was no more effective in elevating blood pressure than a constant isometric contraction over the same duration.

Acceleration↗
PubMed1992

Voluntary dehydration and heat intolerance in cystic fibrosis.

Although exercise may be beneficial in cystic fibrosis (CF), patients' low tolerance to climatic heat stress means that physical exertion can increase morbidity and mortality. We postulated that the high salt content of CF patients' sweat and the consequent absence of body-fluid hyperosmolality during a long episode of sweating might deprive such patients of a thirst stimulus. Eight children with CF (four boys, four girls; aged 9.5-14.1 years) and eight controls, matched for age and sex, attended two randomly ordered sessions of exercise (cycling) in a chamber at 31-33 degrees C, relative humidity 43-47%. 20 min bouts of exercise (at 45% of predetermined maximum oxygen uptake) were interspersed with 25 min rest periods. At one session, chilled water was given every 15-20 min to replace fluid lost; at the other, drinking was guided by the child's thirst. At the thirst-guided session, CF patients drank much less than the controls did (0.80% vs 1.73% initial body weight) and lost twice as much fluid (1.57% vs 0.78% initial body weight). The recovery of heart rate after exercise was slower in CF patients, but there were no other signs of heat strain. The groups did not differ in any variable during the forced drinking session. We conclude that children with CF underestimate their fluid needs and undergo excessive dehydration during extended exposure to hot conditions.

Adolescent↗
PubMed1992

Physiological effects of tapering in highly trained athletes.

This study examined some of the physiological and performance effects of three different tapers in highly trained athletes. After 8 wk of training, nine male middle-distance runners were randomly assigned to one of three different 7-day tapers: a high-intensity low-volume taper (HIT), a low-intensity moderate-volume taper (LIT), or a rest-only taper (ROT). After the first taper, subjects resumed training for 4 wk and performed a second taper and then resumed training for 4 wk and completed the remaining taper, so that each subject underwent all three tapers. Performance was measured before and after each taper by a treadmill run to fatigue at a velocity equivalent each subject's best 1,500-m time. Voluntary isometric strength and evoked contractile properties of the quadriceps were measured before and after each taper, as were muscle glycogen concentration and citrate synthase activity (from needle biopsies) and total blood and red cell volume by 125I and 51Cr tagging. Maximal O2 consumption was unaffected by all three tapers, but running time to fatigue increased significantly after HIT (+22%). It was unaffected by LIT (+6%) and ROT (-3%) procedure. Citrate synthase activity increased significantly with HIT and decreased significantly with ROT. Muscle glycogen concentration increased significantly after ROT and HIT, and strength increased after all three tapers. Total blood volume increased significantly after HIT and decreased after ROT.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Protein requirements and muscle mass/strength changes during intensive training in novice bodybuilders.

This randomized double-blind cross-over study assessed protein (PRO) requirements during the early stages of intensive bodybuilding training and determined whether supplemental PRO intake (PROIN) enhanced muscle mass/strength gains. Twelve men [22.4 +/- 2.4 (SD) yr] received an isoenergetic PRO (total PROIN 2.62 g.kg-1.day-1) or carbohydrate (CHO; total PROIN 1.35 g.kg-1.day-1) supplement for 1 mo each during intensive (1.5 h/day, 6 days/wk) weight training. On the basis of 3-day nitrogen balance (NBAL) measurements after 3.5 wk on each treatment (8.9 +/- 4.2 and -3.4 +/- 1.9 g N/day, respectively), the PROIN necessary for zero NBAL (requirement) was 1.4-1.5 g.kg-1.day-1. The recommended intake (requirement + 2 SD) was 1.6-1.7 g.kg-1.day-1. However, strength (voluntary and electrically evoked) and muscle mass [density, creatinine excretion, muscle area (computer axial tomography scan), and biceps N content] gains were not different between diet treatments. These data indicate that, during the early stages of intensive bodybuilding training, PRO needs are approximately 100% greater than current recommendations but that PROIN increases from 1.35 to 2.62 g.kg-1.day-1 do not enhance muscle mass/strength gains, at least during the 1st mo of training. Whether differential gains would occur with longer training remains to be determined.

Adult↗
PubMed1992

Relationship among running mileage, bone density, and serum testosterone in male runners.

Our purpose was to investigate the relationship between running volume and bone mineral mass in adult male runners. Whole body and regional bone mineral density were determined by dual-photon absorptiometry in 22 sedentary controls and 53 runners who were selected according to their running mileage to fall into a 5- to 10-, 15- to 20-, 25- to 30-, 40- to 55-, or 60- to 75-mile/wk group. All groups were of similar age (20-45 yr) and nutritional status, as determined by 7-day food records. Regional sites for bone density measurements included the trunk, spine, pelvis, thighs, and lower legs. In addition, serum total testosterone was determined in each subject and computed tomography scans were made of the lower legs in 34 subjects to assess bone cross-sectional area. No significant differences were detected for bone density measurements with the exception of the lower legs where it was significantly (P less than 0.05) greater for the 15- to 20-mile/wk group than for the control and 5- to 10-mile/wk groups. With mileage greater than 20 miles/wk, bone density of the lower legs showed no further increase and, in fact, tended to decrease, so that for the 60- to 75-mile/wk group it was similar to that of the controls. Cross-sectional area of the tibia and fibula when normalized to body weight tended to be greater as weekly mileage increased and was significantly greater in the 40- to 55-mile/wk runners than in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Changes in human muscle protein synthesis after resistance exercise.

The purpose of this study was to investigate the magnitude and time course for changes in muscle protein synthesis (MPS) after a single bout of resistance exercise. Two groups of six male subjects performed heavy resistance exercise with the elbow flexors of one arm while the opposite arm served as a control. MPS from exercised (ex) and control (con) biceps brachii was assessed 4 (group A) and 24 h (group B) postexercise by the increment in L-[1-13C]leucine incorporation into muscle biopsy samples. In addition, RNA capacity and RNA activity were determined to assess whether transcriptional and/or translational processes affected MPS. MPS was significantly elevated in biceps of the ex compared with the con arms of both groups (group A, ex 0.1007 +/- 0.0330 vs. con 0.067 +/- 0.0204%/h; group B ex 0.0944 +/- 0.0363 vs. con 0.0452 +/- 0.0126%/h). RNA capacity was unchanged in the ex biceps of both groups relative to the con biceps, whereas RNA activity was significantly elevated in the ex biceps of both groups (group A, ex 0.19 +/- 0.10 vs. con 0.12 +/- 0.05 micrograms protein.h-1.microgram-1 total RNA; group B, ex 0.18 +/- 0.06 vs. con 0.08 +/- 0.02 micrograms protein.h-1.microgram-1 total RNA). The results indicate that a single bout of heavy resistance exercise can increase biceps MPS for up to 24 h postexercise. In addition, these increases appear to be due to changes in posttranscriptional events.

Adult↗
PubMed1992

Factors affecting blood pressure during heavy weight lifting and static contractions.

Brachial arterial pressure was directly recorded in 31 healthy male volunteers through protocols examining the effects of the Valsalva maneuver, muscle size and strength, contraction force, contraction type (concentric, isometric, eccentric), changes in joint angle, and muscle fatigue on the blood pressure response to resistance exercise. Weight lifting at the same relative intensity produced similar increases in blood pressure, regardless of individual differences in muscle size or strength. Concentric, isometric, or eccentric exercise at the same relative intensity caused similar increases despite differences in force production. In weight lifting, the greatest increase in blood pressure occurred at the joint angle corresponding to the weakest point in the strength curve and the least at the angle corresponding to the strongest point. Isometric contractions of the same relative intensity at different joint angles produced identical blood pressures despite differences in absolute force production. When subjects attempted to maintain a maximum isometric contraction for 45 s, the blood pressure increase remained the same despite a marked diminution in force. Thus the magnitude of the blood pressure response depends on the degree of effort or central command and not actual force production. A brief Valsalva maneuver, which exaggerates the increase in blood pressure, is unavoidable when desired force production exceeds approximately 80% maximum voluntary contraction.

Adult↗
PubMed1992

Evaluation of protein requirements for trained strength athletes.

Leucine kinetic and nitrogen balance (NBAL) methods were used to determine the dietary protein requirements of strength athletes (SA) compared with sedentary subjects (S). Individual subjects were randomly assigned to one of three protein intakes: low protein (LP) = 0.86 g protein.kg-1.day-1, moderate protein (MP) = 1.40 g protein.kg-1.day-1, or high protein (HP) = 2.40 g protein.kg-1.day-1 for 13 days for each dietary treatment. NBAL was measured and whole body protein synthesis (WBPS) and leucine oxidation were determined from L-[1-13C]leucine turnover. NBAL data were used to determine that the protein intake for zero NBAL for S was 0.69 g.kg-1.day-1 and for SA was 1.41 g.kg-1.day-1. A suggested recommended intake for S was 0.89 g.kg-1.day-1 and for SA was 1.76 g.kg-1.day-1. For SA, the LP diet did not provide adequate protein and resulted in an accommodated state (decreased WBPS vs. MP and HP), and the MP diet resulted in a state of adaptation [increase in WBPS (vs. LP) and no change in leucine oxidation (vs. LP)]. The HP diet did not result in increased WBPS compared with the MP diet, but leucine oxidation did increase significantly, indicating a nutrient overload. For S the LP diet provided adequate protein, and increasing protein intake did not increase WBPS. On the HP diet leucine oxidation increased for S. These results indicated that the MP and HP diets were nutrient overloads for S. There were no effects of varying protein intake on indexes of lean body mass (creatinine excretion, body density) for either group. In summary, protein requirements for athletes performing strength training are greater than for sedentary individuals and are above current Canadian and US recommended daily protein intake requirements for young healthy males.

Adult↗
PubMed1992

Sweat gland response to exercise in the heat among pre-, mid-, and late-pubertal boys.

Sweating rate (SR) of boys is lower than that of men. To assess the association between the response of individual sweat glands and physical growth and maturation, three groups of circumpubertal boys cycled at 50% VO2max in a climatic chamber (42 degrees C, 20% relative humidity). Based on Tanner staging (pubic hair), 16 were classified as prepubertal (PP, Tanner 1), 15 as midpubertal (MP, Tanner 2-4), and five as late-pubertal (LP, Tanner 5). Population density (PD) of the heat-activated sweat glands, the mean area of sweat drops (DA), and the proportion of skin covered by sweat (%A) were measured by skin photography and computer-assisted imaging analysis. Other measurements included rectal and skin temperatures (Tre, Tsk, respectively), heart rate (HR), and total body SR. The rise in HR, Tre and Tsk did not differ among groups. Whole body SR was significantly higher in the LP group compared with PP (PP = 4.95 +/- 0.23, MP = 5.79 +/- 0.20, LP = 6.70 +/- 0.42 ml.min-1.m-2) (mean +/- SEM). PD was significantly higher in the PP group (PP = 128 +/- 8, MP = 97 +/- 9, LP = 74 +/- 9 glands.cm-2), while DA was higher in the LP group (PP = 5.47 +/- 0.59, MP = 6.92 +/- 0.47, LP = 12.83 +/- 1.41 microns2.10(4)). %A did not differ among groups. The calculated SR per gland was higher among the LP groups compared with the less mature ones (PP = 4.6 +/- 0.3, MP = 7.2 +/- 0.8, LP = 9.6 +/- 1.0 nl.min-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Thermoregulatory responses of pre-, mid-, and late-pubertal boys to exercise in dry heat.

During exercise in a hot climate, children have been reported to have a less effective temperature regulation capability, compared with adults. It is likely that the transition from a child-like to an adult-like response occurs during puberty. To assess the association between the thermoregulatory response and physical maturation, three groups of circum-pubertal boys cycled at 50% VO2max (three 20-min bouts with 10-min rests), in a climatic chamber (42 degrees C, 20% relative humidity). Based on Tanner staging (pubic hair), 10 were classified as prepubertal (PP), 13 as midpubertal (MP), and eight as late pubertal (LP). Measurements included rectal and skin temperatures (Tre, Tsk), heart rate (HR), sweating rate (SR), oxygen consumption (VO2), and forearm blood flow (FBF). Tre, Tsk, and HR increased with time, with no significant difference among groups. Relative VO2 (ml O2.kg-1) was similar among groups. FBF was consistently higher in PP compared with LP. In spite of the higher SR (PP = 4.9 +/- 0.2, MP = 5.7 +/- 0.3, LP = 6.6 +/- 0.4 ml.min-1.m-2) (mean +/- SEM) among LP compared with PP, the rate of heat storage (PP = 5.5 +/- 0.4, MP = 5.3 +/- 0.4, LP = 6.8 +/- 0.3, kJ.h-1.kg-1) was also significantly higher among those in the LP group. Three of eight LP did not complete the session due to high Tre, while two of the 10 PP were unable to complete the session even though the physiologic heat strain was not high. The results suggest that the transition from a child-like to an adult-like thermoregulatory effectiveness in a hot, dry climate may occur at a somewhat later stage, but not during puberty.

Adolescent↗
PubMed1991

The effect of amenorrhea on calcaneal bone density and total bone turnover in runners.

To examine in athletes the effect of long-term amenorrhea on the skeleton, measurements of calcaneal density and whole body retention of 99mTc-imidodiphosphate were made in 42 women who could be allocated to one of 3 groups defined by their level of physical activity and by menstrual status. There was no difference in bone density between eumenorrheic normoactive females and either eumenorrheic or amenorrheic athletes. However, calcaneal density was significantly greater for each group than for previously measured sedentary controls. Total body bone turnover was greater in both eumenorrheic and amenorrheic athletes than in eumenorrheic normoactive women. Sustained, intense physical activity does not significantly increase calcaneal bone density over and above the increase associated with normal levels of activity. This is despite a significant increase in the rate of total body bone mineral turnover.

Adult↗
PubMed1991

Operation Everest II: structural adaptations in skeletal muscle in response to extreme simulated altitude.

Alterations in skeletal muscle structure were investigated in 6 male subjects who underwent 40 days of progressive decompression in a hypobaric chamber simulating an ascent to the summit of Mount Everest. Needle biopsies were obtained from vastus lateralis of 5 subjects before and immediately after confinement in the chamber, and were examined for various structural and ultrastructural parameters. In addition, total muscle area was calculated in 6 subjects from CT scans of the thighs and upper arms. Muscle area at these sites was found to decrease significantly (by 13 and 15%) as a result of the hypobaric confinement. This was substantiated by significant (25%) decreases in cross sectional fibre areas of the Type I fibres and 26% decreases (non significant) in Type II fibre area. Capillary to fibre ratios remained unchanged following hypoxia as did capillary density although there was a trend (non significant) towards an increase in capillary density. There were no significant increases in mitochondrial volume density or other morphometric parameters. These data indicate that chronic, severe hypoxia on its own does not result in an increase in absolute muscle capillary number or a de novo synthesis of mitochondria. The trends toward an increase in capillary density and mitochondrial volume density were interpreted as being secondary occurrences in response to the pronounced muscle atrophy which occurred.

Acclimatization↗
PubMed1991

Sweat lactate in exercising children and adolescents of varying physical maturity.

This study attempts to explain some of the individual variability in sweating pattern by comparing prepubescents and pubescents. Sweating rate and muscular anaerobic capacity are higher in adults than in children; thus we hypothesized that sweat gland anaerobic metabolism, as reflected by lactate excretion, might be higher with advanced physical maturity (PM). Lactate concentration in sweat ([LAC]sw) was measured at various stages of PM in boys who exercised in the heat. The subjects were divided into three groups on the basis of Tanner staging: prepubertal (PP, n = 16), midpubertal (MP, n = 15), and late pubertal (LP, n = 5). Subjects cycled at 50% of maximal O2 uptake for three 20-min bouts, with 10-min rest periods, in 42 degrees C and 18% relative humidity. Sweat samples were harvested, and population density of activated sweat glands was determined after each exercise bout. [LAC]sw during bout 1 was higher in PP than in LP [PP = 22.2 +/- 2.2, MP = 19.5 +/- 1.4, LP = 14.3 +/- 1.3 (SE) mmol/l]. In all groups, [LAC]sw decreased during subsequent bouts, and there were no intergroup differences in [LAC]sw during bout 3 (PP = 11.2 +/- 0.4, MP = 10.6 +/- 0.5, LP = 9.7 +/- 0.2 mmol/l). [LAC]sw was inversely related to sweating rate. Lactate excretion rate per gland was greater with the increase in PM (PP = 61.0 +/- 8.2, MP = 79.1 +/- 11.3, LP = 99.9 +/- 11.0 pmol/min; P = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗