PubMed Health⌕ Search

Biomedical subjects

C M Maresh

Publications and source records attributed to C M Maresh.

At least 55 records · Page 3Linked to original sources
PubMed1994

The neuromuscular junction. Muscle fibre type differences, plasticity and adaptability to increased and decreased activity.

The neuromuscular junction (NMJ) of adult mammalian muscle is the site of the transduction of electrical stimuli, generated by the nervous system, to the underlying muscle fibres, resulting in muscle action. It has been demonstrated that, in some ways, the morphology of the NMJ is specific to muscle fibre type. It is also known that while the structure of the NMJ generally remains stable in young, healthy adults, a subtle form of remodelling continuously occurs at this synapse. The morphology and physiology of the NMJ have been shown to adapt to both increased, and decreased use. Indeed, morphological changes of the NMJ are associated with functional alterations in neuromuscular transmission. Increased activity of the myoneural synapse results in adaptations that enhance neuromuscular transmission and, thus, muscle performance. Similarly to increased usage, decreased neuromuscular activity results in structural alterations of the NMJ. However, unlike those responses observed with enhanced activity, decreased recruitment of the myoneural synapse can impair neuromuscular transmission and muscle performance. Thus, the NMJ demonstrates both anatomical and physiological adaptations following substantial changes in its pattern of activity. These NMJ adaptations can affect the functional capacity of skeletal muscle in vivo.

Adaptation, Physiological↗
PubMed1993

The effects of exercise training of different intensities on neuromuscular junction morphology.

Little is known about the effects of exercise training on neuromuscular junction morphology in skeletal muscle. The objectives of this investigation were: 1) to determine if exercise training would elicit changes in neuromuscular junction morphology, 2) to determine if exercise training of different intensities would evoke specific changes in neuromuscular junction morphology, and 3) to determine whether changes in neuromuscular junction structure occur independently of changes in muscle fibre type and size. Twenty-four age and size matched male Sprague-Dawley rats were randomly assigned to three groups: high-intensity trained (HIT), low-intensity trained (LIT), or untrained. Neuromuscular junction morphology of the soleus muscle was determined via immunofluorescent staining. Presynaptic acetylcholine vesicles were visualized with SV-2 antibody in conjunction with fluorescein isothiocyanate labelled secondary secondary antibody. Postsynaptic acetylcholine receptors were identified with rhodamine labelled alpha-bungarotoxin. Laser scanning microscopy was used to produce images of synapses, which were used to quantitate the following: total area of SV-2 and alpha-bungarotoxin staining, density of acetylcholine vesicles and receptors, structural complexity, and synaptic coupling. To visualize nerve terminal branching, a smaller number of neuromuscular junctions were stained with C-2 antibody, which reacts with a neurofilament epitope, in conjunction with fluorescein isothiocyanate labelled secondary antibody. Total length of branching, number of branches, average length of branches, and ratio of secondary to primary branches per neuromuscular junction were determined. Citrate synthase activity, fibre type composition and fibre cross-sectional areas of the soleus muscle were assessed to determine the presence of a training effect in that muscle. Results indicate that training did induce hypertrophy of the neuromuscular junction that was independent of muscle hypertrophy. Although the HIT and LIT groups exhibited similar hypertrophic responses of the neuromuscular junction, the HIT group displayed more dispersed synapses than the LIT group. Neither exercise training program, however, resulted in altered densities of acetylcholine vesicles or receptors, nor did training significantly change synaptic coupling. Nerve terminal branching was also affected by exercise training. Neuromuscular junctions from the HIT group demonstrated a greater total length of branching, average length per branch, and number of finer, or secondary, branches than those of the LIT group.

Acetylcholine↗
PubMed1993

Endocrine and performance responses to high volume training and amino acid supplementation in elite junior weightlifters.

To examine the effects of 1 week of high volume weightlifting and amino acid supplementation, 28 elite junior male weightlifters received either amino acid (protein) or lactose (placebo) capsules using double-blind procedures. Weightlifting test sessions were performed before and after 7 days of high volume training sessions. Serum concentrations of testosterone (Tes), cortisol (Cort), and growth hormone (GH) as well as whole blood lactate (HLa) were determined from blood draws. Lifting performance was not altered for either group after training, although vertical jump performance was not altered for either group after training, although vertical jump performance decreased for both groups. Both tests elicited significantly elevated exercise-induced hormonal and HLa concentrations. Significant decreases in postexercise hormonal and HLa concentrations from Test 1 to Test 2 were observed for both groups. Tes concentrations at 7 a.m. and preexercise decreased for both groups from Test 1 to Test 2, while the placebo group exhibited a decreased 7 a.m. Tes/Cort. These data suggest that amino acid supplementation does not influence resting or exercise-induced hormonal responses to 1 week of high volume weight training, but endocrine responses did suggest an impending over-training syndrome.

Adolescent↗
PubMed1993

Bone mineral density in elite junior Olympic weightlifters.

The purpose of this study was to examine the relationship of bone mineral density (BMD) to muscular strength in highly trained young male athletes in order to gain insights concerning the influence of heavy resistance training on BMD. Twenty-five elite junior weightlifters (age, 17.4 +/- 1.4 yr) and 11 age-matched controls (16.9 +/- 1.1 yr) volunteered for this investigation. Measurements of BMD (g.cm-2) utilizing dual energy x-ray absorptiometry were obtained for the lumbar spine (L2-4) and the proximal femur (neck; trochanter, Ward's triangle). The BMD values for the junior lifters were found to be significantly greater at all sites for the junior weightlifters compared with their age-matched control group. The BMD values of the spine and femoral neck of the junior weightlifters when compared with adult reference data (i.e., 20-39 yr old men) were found to be significantly greater. Both simple and multiple regression analyses demonstrated significant relationships of BMD with strength accounting for 30-65% of the variance. These data suggest that in elite junior weightlifters, muscle strength, highly specific to the sport of weightlifting, has a major influence on BMD due to the influence of the chronic overloads experienced in training.

Absorptiometry, Photon↗
PubMed1993

Perceived exertion during hypobaric hypoxia in low- and moderate-altitude natives.

Ratings of perceived exertion (RPE) were examined in six low- (LAN) and eight moderate- (MAN) altitude natives during exercise at their residence (home) altitude (366 m and 2,200 m, respectively) and 1-4 wk later following 2-d decompression to 4,270 m (447 mm Hg). Cardiorespiratory, plasma lactate, and differentiated RPE measures were obtained at exercise intensities representing 35, 55, 75, 85, and 100% VO2peak. In general, cardiorespiratory and plasma lactate values were similar in LAN and MAN at their residence altitudes and during hypobaric hypoxia. However, the decrease in VCO2 was greater (P < 0.05) in LAN than MAN. At their residence altitudes, both LAN and MAN reported local RPE values that were greater (P < 0.05) than central ratings at the moderate to high exercise intensities. At 447 mm Hg, central and local RPE were similar in LAN. However, there was a significant correlation between acute mountain sickness (AMS) symptoms and central RPE (r = 0.875) across the five exercise intensities in LAN. The differences between the central and local RPE noted in MAN during their residence testing also persisted at 447 mm Hg. Thus, differentiated ratings of perceived exertion were similar in MAN at their residence altitude and at 4,270 m, but not in LAN subjects. Several factors, including AMS, may have contributed to this group difference in the RPE response.

Adult↗
PubMed1992

Oxygen consumption following exercise of moderate intensity and duration.

To study the effects of exercise intensity and duration on excess postexercise oxygen consumption (EPOC), 8 men [age = 27.6 (SD 3.8) years, VO2max = 46.1 (SD 8.5) ml min-1 kg-1] performed four randomly assigned cycle-ergometer tests (20 min at 60% VO2max, 40 min at 60% VO2max, 20 min at 70% VO2max, and 40 min at 70% VO2max). O2 uptake, heart rate and rectal temperature were measured before, during, and for 1 h following the exercise tests. Blood for plasma lactate measurements was obtained via cannulae before, and at selected times, during and following exercise. VO2 rapidly declined to preexercise levels following each of the four testing sessions, and there were no differences in EPOC between the sessions. Blood lactate and rectal temperature increased (P < 0.05) with exercise, but had returned to preexercise levels by 40 min of recovery. The results indicate that VO2 returned to resting levels within 40 min after the end of exercise, regardless of the intensity (60% and 70% VO2max) or duration (20 min and 40 min) of the exercise, in men with a moderate aerobic fitness level.

Adult↗
PubMed1992

Acute hormonal responses in elite junior weightlifters.

To date, no published studies have demonstrated resistance exercise-induced increases in serum testosterone in adolescent males. Furthermore, few data are available on the effects of training experience and lifting performance on acute hormonal responses to weightlifting in young males. Twenty-eight junior elite male Olympic-style weightlifters (17.3 +/- 1.4 yrs) volunteered for the study. An acute weightlifting exercise protocol using moderate to high intensity loads and low volume, characteristic of many weightlifting training sessions, was examined. The exercise protocol was directed toward the training associated with the snatch lift weightlifting exercise. Blood samples were obtained from a superficial arm vein at 7 a.m. (for baseline measurements), and again at pre-exercise, 5 min post-, and 15 min post-exercise time points for determination of serum testosterone, cortisol, growth hormone, plasma beta-endorphin, and whole blood lactate. The exercise protocol elicited significant (p less than or equal to 0.05) increases in each of the hormones and whole blood lactate compared to pre-exercise measures. While not being significantly older, subsequent analysis revealed that subjects with greater than 2 years training experience exhibited significant exercise-induced increases in serum testosterone from pre-exercise to 5 min post-exercise (16.2 +/- 6.2 to 21.4 +/- 7.9 nmol.l-1), while those with less than or equal to 2 years training showed no significant serum testosterone differences. None of the other hormones or whole blood lactate appear to be influenced by training experience.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Tennis: a physiological profile during match play.

Heart rate (HR), hematocrit, hemoglobin, blood glucose, and plasma concentrations of lactate, cortisol, and testosterone were monitored in 10 male subjects (Division I, 20.3 +/- 2.5 yrs, VO2max: 58.5 +/- 9.4 ml.kg-1.min-1) during singles tennis and a treadmill test. During the on-court session, HR was 144.6 +/- 13.2 beats.min-1 for the 85 min of play. Plasma lactate rose 50% from a post-warmup value of 1.6 +/- 0.6 mmol.l-1 to 2.3 +/- 1.2 mmol.l-1 during play (p greater than 0.05). Blood glucose slightly decreased (8%, p greater than 0.05) from a pre-exercise value of 4.6 +/- 0.8 mmol.l-1 as a result of the 10-min warmup. This was followed by a 23% rise (p less than 0.05) from 4.2 +/- 1.0 mmol.l-1 to 5.2 +/- 0.6 mmol.l-1, measured after the first 30 min of play. Blood glucose subsequently remained steady at slightly above the pre-exercise value. Plasma cortisol rose (9%, p greater than 0.05) during the warmup and subsequently decreased (p less than 0.05) from a post-warmup value of 558.2 +/- 285.2 nmol.l-1 to 337.1 +/- 173.3 nmol.l-1 (a 40% decrease), and remained decreased during recovery. Plasma testosterone rose 22% (p less than 0.05) from pre-exercise to recovery (13.5 +/- 3.8 nmol.l-1 and 16.5 +/- 2.6 nmol.l-1, respectively). Although tennis is characterized by periods of high-intensity exercise, the overall metabolic response resembles prolonged moderate-intensity exercise.

Adult↗
PubMed1991

Anaerobic power responses to amino acid nutritional supplementation.

To examine the effect of a nutritional supplement (ATP-E) on high intensity exercise performance, 23 physically active males volunteered to perform six Wingate Anaerobic Power tests. Tests were performed prior to and at 14 and 21 days during ATP-E or placebo ingestion. The experiment followed a double-blind and random-order design. Twelve subjects (responders, R) showed an increase in preexercise blood ATP on Day 14 of ATP-E ingestion compared to control measures. The remaining 11 subjects (nonresponders, NR) had no change in preexercise blood ATP. Peak power and mean power were unchanged for both R and NR subjects across the exercise tests, but R experienced a decrease (p < 0.05) in immediate post-exercise plasma lactate on Day 14 of ATP-E testing compared to their control measures. NR had no change in peak plasma lactate at any time during the study. The results suggest that short-term high intensity exercise performance was maintained in R with less reliance on anaerobic metabolism, and that response was evident following 14 days of ATP-E ingestion.

Adenosine Triphosphate↗
PubMed1991

Adrenal activation and the prolactin response to exercise in eumenorrheic and amenorrheic runners.

Adrenocorticotropic hormone (ACTH), cortisol, and prolactin responses following maximal and submaximal (40 min at 80% maximal O2 consumption) running were studied in eumenorrheic (ER; n = 8, 29.0 +/- 1.5 yr) and amenorrheic (AR; n = 8, 24.5 +/- 2.0 yr) runners. ER were studied in the early follicular and midluteal phases of the menstrual cycle. Physical, training, and gynecological characteristics were similar, and cardiorespiratory and metabolic responses to the exercises were indistinguishable in the groups. ACTH, cortisol, and prolactin data from the follicular luteal phases in ER were combined for comparison to AR, because no differences were noted between the menstrual phases at rest. Similar preexercise ACTH levels and responses following exercise occurred in both groups, but preexercise cortisol levels were elevated (ER = 293.1 +/- 46.3, AR = 479.6 +/- 42.4 nmol/l) and cortisol responses blunted in AR. Adrenal sensitivity was blunted in AR compared with ER after submaximal (ER = 121.9 +/- 17.4, AR = 51.7 +/- 13.6) and maximal exercise (ER = 27.9 +/- 9.2, AR = 12.1 +/- 3.8). Preexercise prolactin levels were reduced (ER = 16.4 +/- 2.7, AR = 10 +/- 2.3 micrograms/l), and prolactin responses to maximal exercises were blunted in AR, despite high lactate levels (11.4 +/- 0.4 mmol/l). We conclude that 1) control for menstrual phase in ER is important in studies of prolactin responses following exercise but not in studies of ACTH and cortisol responses following exercise, 2) cortisol responses following submaximal and maximal exercise in AR are blunted at the adrenal level, 3) prolactin responses following submaximal and maximal exercise are also blunted in AR, and 4) prolactin responses following exercise may be mediated by adrenal activation.

Adolescent↗
PubMed1991

The induction and decay of heat acclimatisation in trained athletes.

Heat acclimatisation/acclimation involves a complex of adaptations which includes decreased heart rate, rectal temperature, perceived exertion as well as increased plasma volume and sweat rate. These adaptations serve to reduce physiological strain, improve an athlete's ability to exercise in a hot environment, and reduce the incidence of some forms of heat illness. Few differences exist in the ability of men and women to acclimatise to heat. Typically, older runners do not perform in the heat as well as younger runners, but physical training can negate differences between these groups. Hormonal adaptations (e.g. aldosterone, vasopressin) during heat acclimatisation encourage fluid-electrolyte retention and cardiovascular stability. Athletes with high maximal aerobic power (VO2max) acclimatise to heat faster (and lose adaptations slower when they are inactive in a cool environment) than athletes with low VO2max values. Physical training in a cool environment improves physiological responses to exercise at high ambient temperatures. In attempting to optimise heat acclimatisation, athletes should maintain fluid-electrolyte balance, exercise at intensities greater than 50% VO2max for 10 to 14 days, and avoid factors (e.g. sleep loss, infectious disease) which are known to reduce heat tolerance. Once acclimatisation has been achieved, inactivity results in a decay of favourable adaptations, after only a few days or weeks.

Adaptation, Physiological↗
PubMed1991

Middle age male distance runners: physiological and psychological profiles.

This study investigated 4 research questions addressing exercise capabilities and psychological characteristics of middle-age (30 to 50 years) male runners. Subjects provided an extensive running history, completed the Multidimensional Anger Inventory, completed the Myers-Briggs Type Indicator, and performed a treadmill running test to volitional exhaustion. Another aspect of the study compared anticipatory and posttest reactions to the treadmill test experience to actual test results. The findings suggest that these runners have common personality profiles, that long-term involvement in running and training is associated with a positive sense of self, and that lifelong aerobic exercise is associated with high cardiovascular fitness. Although the research design does not permit causal or predictive conclusions, the study provides valuable additional baseline information for physicians and fitness professionals who serve middle aged male runners.

Adult↗
PubMed1990

Effects of menstrual phase and amenorrhea on exercise performance in runners.

There are few well controlled studies in terms of subject selection, menstrual classification, and exercise protocol that have examined both maximal and submaximal exercise responses during different phases of the menstrual cycle in eumenorrheic runners and compared these runners to amenorrheic runners. Thus, the purpose of this study was to measure selected physiological and metabolic responses to maximal and submaximal exercise during two phases of the menstrual cycle in eumenorrheic runners and amenorrheic runners. Eight eumenorrheic runners (29.0 +/- 4.2 yr) and eight amenorrheic runners (24.5 +/- 5.7 yr) matched for physical, gynecological, and training characteristics were studied. The eumenorrheic runners performed one maximal and one submaximal (40 min at 80% VO2max) treadmill run during both the early follicular (days 2-4) and midluteal (6-8 d from LH surge) phases. The amenorrheic runners performed one maximal and one submaximal (40 min at 80% VO2max) treadmill run. Cycle phases were documented by urinary luteinizing hormone and progesterone assays and by plasma estradiol and progesterone assays. No differences were observed in oxygen uptake, minute ventilation, heart rate, respiratory exchange ratio, rating of perceived exertion, time to fatigue (maximal), and plasma lactate (following the maximal and submaximal exercise tests) between the follicular and luteal phases in the eumenorrheic runners and the amenorrheic runners. We conclude that neither menstrual phase (follicular vs luteal) nor menstrual status (eumenorrheic vs amenorrheic) alters or limits exercise performance in female athletes.

Adolescent↗
PubMed1989

Substrate and hormone responses to exercise following a marathon run.

The aim of this study was to examine selected substrate and hormone responses to 30-min treadmill runs performed several days before and after a competitive marathon (42.2 km) to determine the time course for return of altered responses to pre-race levels. Six experienced male runners (30.8 +/- 9.1 years) ran at their predicted race pace (77.1% +/- 4.1% of VO2max) 8-7 days prior (S-1) to the Boston Marathon and 2-3 (S-2), 6-7 (S-3), and 13-14 days (S-4) post-marathon. All 30-min runs were performed in the morning at a constant time for each subject following a 12-h fast. Blood samples were drawn immediately before and immediately after (within 1 min) the 30-min runs. Post-exercise glucose responses were higher (P less than 0.05) during S-2 and S-3 compared with S-1 values. S-2 post-exercise lactate concentrations were also higher than the corresponding S-1 value. Pre-exercise free fatty acid (FFA) levels during S-4, and the post-exercise FFA values during S-2, S-3, and S-4, were lower (P less than 0.05) than the corresponding S-1 concentrations. Pre- and post-exercise alanine levels during S-2 were higher (P less than 0.05) than the S-1 values. Both pre- and post-exercise insulin levels during S-2, S-3, and S-4 were greater (P less than 0.05) than corresponding S-1 concentrations. Glucagon concentrations were unchanged across all sessions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Menstrual status and plasma vasopressin, renin activity, and aldosterone exercise responses.

The effects of menstrual cycle phase (early follicular vs. midluteal) and menstrual status (eumenorrhea vs. amenorrhea) on plasma arginine vasopressin (AVP), renin activity (PRA), and aldosterone (ALDO) were studied before and after 40 min of submaximal running (80% maximal O2 uptake). Eumenorrheic runners were studied in the early follicular and midluteal phases determined by urinary luteinizing hormone and progesterone and plasma estradiol and progesterone assays; amenorrheic runners were studied once. Menstrual phase was associated with no significant differences in preexercise plasma AVP or PRA, but ALDO levels were significantly higher during the midluteal phase than the early follicular phase. Plasma AVP and PRA were significantly elevated at 4 min after the 40-min run in the eumenorrheic runners during both menstrual phases and returned to preexercise levels by 40 min after exercise. Plasma ALDO responses at 4 and 40 min after exercise were higher in the midluteal phase than the early follicular phase. Menstrual status was associated with no significant differences in preexercise AVP or PRA; however, ALDO levels were significantly higher in the amenorrheic runners. After exercise, responses in the amenorrheic runners were comparable with the eumenorrheic runners during the early follicular phase. Thus, submaximal exercise elicits significant increases in plasma AVP and PRA independent of menstrual phase and status. However, plasma ALDO is significantly elevated during the midluteal phase, exercise results in a greater response during this menstrual phase, and amenorrheic runners have elevated resting levels of ALDO.

Adolescent↗
PubMed1989

Training responses of plasma beta-endorphin, adrenocorticotropin, and cortisol.

The purpose of this study was to examine the effects of three different run training programs on plasma responses of beta-endorphin (beta-EP), adrenocorticotropin (ACTH), and cortisol to maximal treadmill exercise. Subjects were randomly assigned to one of three training groups: sprint intervals (SI) (N = 8), endurance (E) (N = 10), or combination (C) (N = 7). Training was monitored for 10 wk, and maximal treadmill exercise tests were administered pre-training and after 2, 4, 6, 8, and 10 wk of training. Blood samples were obtained (pre-training and after 10 wk) before, immediately after, and 5 and 15 min following the maximal exercise tests. All groups significantly (P less than 0.05) increased maximal oxygen consumption values at 8 and 10 wk of the training period. Significant exercise-induced increase in plasma beta-EP, ACTH, cortisol, and blood lactate were observed for both pre- and post-training tests in all training groups. The SI group demonstrated significant post-training increases in beta-EP, ACTH, cortisol, and 5 min post-exercise blood lactate concentrations in response to maximal exercise. No training-induced hormonal changes were observed for the E group. While exercise-induced increases were observed, the C group exhibited significant post-training reductions in plasma responses of beta-EP, ACTH, and blood lactate concentrations in response to maximal exercise. Still, resting and post-exercise increases in plasma cortisol concentrations were significantly higher in magnitude in the post-training test. Lactate was significantly correlated with beta-EP (r = 0.72), ACTH (r = 0.70), and cortisol (r = 0.64).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗
PubMed1988

Exercise testing in the evaluation of human responses to powerline frequency fields.

The present study used exercise testing to examine the effects of 60-Hz electric and magnetic field exposure. Eleven males, 21-29 years, were tested during four experimental sessions (counterbalanced order and double-blind design). These included either 45-min exercise (50% of VO2 max) or no-exercise periods followed by either real field (9-kV/m, 16-A/m) or sham exposure for 2 h in a 60-Hz human exposure facility. Exercise produced a decrease in plasma volume and increases (p less than 0.05) in lactic acid, cortisol, growth hormone and testosterone levels, but these were not different under real and sham field conditions during the 2-h recovery periods. During no-exercise sessions, cardiac interbeat interval was increased (p less than 0.05), i.e., heart rate was slower, when subjects were exposed to real fields. Our results suggest that future studies should focus on evaluation of the effects of 60-Hz fields on the entire process of exercise-induced activation and recovery.

Adult↗