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Biomedical subjects

W C Byrnes

Publications and source records attributed to W C Byrnes.

30 records · Page 2Linked to original sources
PubMed1987

Adaptation to exercise-induced muscle damage.

1. Serum creatine kinase (CK) and muscle soreness, common indicators of muscle damage, were assessed in 16 subjects after performance of two bouts of eccentric exercise spaced 7 days apart. The purpose was (1) to examine rapid muscle adaptation when the ipsilateral limb was exercised on the second bout and (2) to investigate possible central adaptations when the contralateral limb was exercised on the second bout. 2. The LSL group (n = 7) and the LOL group (n = 9) performed the exercise with the ipsilateral and the contralateral limb, respectively. Careful attention was paid to stabilization of the subject so that the contralateral limb was not active in isometric stabilization. 3. For the LSL group, a lower CK and soreness response was found on about 2 compared with bout 1. For the LOL group, no significant difference in CK response and soreness was found between bout 1 and bout 2. 4. No repeat bout effect was found when the contralateral limb was exercised; therefore central adaptation from performance of the first exercise was minimal. Because a lower repeated bout effect was found after bout 2 using the ipsilateral limb, it was concluded that an experimental design using ipsilateral muscle groups should provide a good model to study rapid muscle adaptation to exercise damage.

Adaptation, Physiological↗
PubMed1986

Levels of serum creatine kinase and myoglobin in women after two isometric exercise conditions.

The purpose of this study was to measure serum creatine kinase (CK) activity and serum myoglobin (MG) concentrations in women after two unilateral isometric knee extension exercises. Forty maximal voluntary contractions (MVC) were held for 10 s, with either a 5 s (10:5) or 20 s 10:20 exercise (349.4 +/- 66.1 mU . ml-1) and 6 h and MG values were measured pre, 0, 3, 6, and 18 h post exercise. For CK, the highest post exercise values were observed at 6 h following the 10:20 exercise (349.4 +/- 66.1 mU . ml-1) and 6 h following the 10:5 exercise (194.1 +/- 18.6 mU . ml-1). For MG, the highest values were found 3 h after the 10:20 exercise (148.9 +/- 61.7 ng . ml-1) and 6 h after the 10:5 exercise (67.3 +/- 10.9 ng . ml-1). Serum CK and MG levels were significantly greater (p less than 0.01) after the 10:20 exercise bout. The data demonstrate that CK and MG values for women increase significantly after isometric exercise. Since greater tension levels were maintained during the 10:20 exercise it is hypothesized that increased serum CK and MG values after isometric exercise may be related to the tension generated by the contracting muscle.

Adult↗
PubMed1986

Muscle soreness and serum creatine kinase activity following isometric, eccentric, and concentric exercise.

Serum creatine kinase (CK) activity and subjective ratings of muscle soreness were assessed in 28 college women following three different arm flexion exercise regimens. The subjects were randomly assigned to an eccentric, isometric, or concentric exercise regimen. Each regimen was equated for total work time and work-to-rest ratio. Blood samples for determination of serum CK activity and perceived soreness ratings were obtained prior to and 5, 10, and 25 h following each exercise. Significant increases in perceived soreness ratings were observed for each exercise regimen. The magnitude of the post-exercise increase in perceived soreness was greatest for the eccentric and the isometric exercises with minimal soreness following the concentric exercise. A small but significant increase in serum CK activity was observed following the three exercises (eccentric = 35.8%, concentric = 37.6%, isometric = 34.0%). The post-exercise serum CK increases did not differ significantly among the three regimens. The rise in serum CK activity suggests that muscle damage occurred during all three tasks. However, due to multiple factors which can affect serum CK levels, the increase in serum CK activity may not provide a sensitive indicator of the magnitude of the injury.

Creatine Kinase↗
PubMed1986

Delayed onset muscle soreness and training.

The perception of muscle soreness is probably due to the activation of free nerve endings around muscle fibers. These nerve endings serve as receptors of noxious stimuli associated with muscle damage. Modulation of soreness may take place at the peripheral receptor sites or at a central or spinal level. This multilevel modulation may explain the large intersubject variation in the perception of muscle soreness. The type of exercise that produces the greatest degree of soreness is eccentric exercise, although isometric exercise may also result in soreness. Eccentric exercise has been shown to produce muscle cellular damage and decrements in motor performance as well. Although training is considered to prevent muscle soreness, even trained individuals will become sore following a novel or unaccustomed exercise bout. Thus, training is specific to the type of exercise performed. Our laboratories have shown that the performance of a single exercise bout will have an effect on a subsequent similar bout given up to 6 weeks later. Thus, when a second bout of downhill running was given to subjects 6 weeks after the first bout, with no intervening exercise, less soreness developed, and muscle damage was estimated to be reduced. The explanation for this long-lasting prophylactic or "training effect" is currently under investigation in our laboratories.

Animals↗
PubMed1986

The reproducibility of VO2max, ventilatory, and lactate thresholds in elderly women.

The reproducibility of VO2max, ventilatory, and lactate thresholds in elderly women. Med. Sci. Sports Exerc., Vol. 18, No. 4, pp. 425-430, 1986. This investigation examined the reproducibility of maximal (VO2max) and submaximal measures of fitness for elderly women. Eight subjects [age (yr): mean = 80.6 +/- 3.7; range = 73-86] volunteered to repeat three continuous, incremental maximal effort treadmill tests. Blood lactate determinations were made for each increment from blood samples taken from an indwelling venous catheter located in the back of the hand. Average VO2max values (ml X min-1 X kg X l-1) were 13.21 + 1.95 for test 1, 13.44 +/- 1.83 for test 2, and 13.62 + 2.95 for test 3. In all but one subject, a threshold was not definable by either ventilatory or lactate measurements. Maximal lactate values were low, with the average values for tests 1, 2, and 3 being 1.89, 1.46, and 1.86 mmol X l-1, respectively. The data demonstrates that VO2max is reproducible for older women and can, therefore, be used for fitness assessment and exercise prescription. The use of ventilatory or lactate thresholds as submaximal measures of fitness or as minimal intensities for exercise prescription was determined not to be applicable for women in the eighth and ninth decades of life.

Aged↗
PubMed1985

Serum creatine kinase activity following forearm flexion isometric exercise.

The purpose of this study was to compare serum creatine kinase (CK) activity following two forearm flexion isometric exercise regimens differing in work to rest ratio, and examine the CK response to a repeated bout of isometric exercise. Eleven males were tested on two sessions (bouts) spaced 1 week apart. For bout 1, five subjects (group A) performed a forearm flexion isometric exercise consisting of 40 10-s maximal contractions with 20-s inter-trial rests (10:20), while six (group B) performed 40 maximal 10-s contractions with 5-s inter-trial rests (10:5). The increase in serum CK activity following the 10:20 exercise (143%) was significantly greater than that following the 10:5 exercise (52%). The 10:20 exercise was also associated with greater tension generation over trials. One week later, both groups performed a bout of 10:20 exercise. A substantial reduction in the serum CK response was found following this second bout. The data suggest that for bout 1 the isometric exercise associated with the greater overall tension levels resulted in the greater CK response. However, when the 10:20 exercise was repeated 1 week later, a substantial reduction in the CK response was found which was unrelated to the tension generated.

Adult↗
PubMed1985

Delayed onset muscle soreness following repeated bouts of downhill running.

Perceived muscle soreness ratings, serum creatine kinase (CK) activity, and myoglobin levels were assessed in three groups of subjects following two 30-min exercise bouts of downhill running (-10 degrees slope). The two bouts were separated by 3, 6, and 9 wk for groups 1, 2, and 3, respectively. Criterion measures were obtained pre- and 6, 18, and 42 h postexercise. On bout 1 the three groups reported maximal soreness at 42 h postexercise. Also, relative increases in CK for groups 1, 2, and 3 were 340, 272, and 286%, respectively. Corresponding values for myoglobin were 432, 749, and 407%. When the same exercise was repeated, significantly less soreness was reported and smaller increases in CK and myoglobin were found for groups 1 and 2. For example, the percent CK increases on bout 2 for groups 1 and 2 were 63 and 62, respectively. Group 3 demonstrated no significant difference in soreness ratings, CK activities, or myoglobin levels between bouts 1 and 2. It was concluded that performance of a single exercise bout had a prophylactic effect on the generation of muscle soreness and serum protein responses that lasts up to 6 wk.

Adult↗
PubMed1984

Submaximal exercise quantified as percent of normoxic and hyperoxic maximum oxygen uptakes.

Maximum oxygen uptake (VO2max) was measured in six college-aged males under normoxic (NVO2max) and hyperoxic (HVO2max; 70% oxygen) conditions. Subjects then randomly performed the following three 20-min submaximal exercise bouts: 75% normoxic VO2max under normoxia (NVO2N), 75% normoxic VO2max under hyperoxia (NVO2H), and 75% hyperoxic VO2max under hyperoxia (HVO2H). Metabolic parameters were obtained at 5-min intervals. Hyperoxia resulted in a 13% increase (P less than 0.01) in VO2max (NVO2max = 3.54 l X min-1 vs HVO2max = 4.00 l X min-1). Significant (P less than 0.05) decreases were observed in VE (ventilation) (13%), epinephrine (37%), norepinephrine (26%), and blood lactate (28%), with no change in oxygen uptake (VO2), carbon dioxide production (VCO2), or respiratory exchange ratio (R) during hyperoxia at the same absolute power output (NVO2N vs NVO2H). However, at the same relative power outputs (NVO2N vs HVO2H) no significant changes in VE, epinephrine, norepinephrine, or blood lactate were observed when hyperoxia and normoxia were compared.

Epinephrine↗
PubMed1979

Effect of hyperoxia on oxygen consumption in exercising ponies.

Published reports of oxygen consumption (VO2) during exercise in hyperoxia are equivocal. By and large, when measured at the lung using respiratory gas equations, VO2 is elevated in hyperoxia and, when measured at the blood-tissue level using the cardiovascular Fick (CVF) equation, it is unchanged. We sought to provide some insight into this problem by making through the use of both equations simultaneous determinations of VO2 during hyperoxia in exercising ponies. In normoxia, during treadmill exercise (115 m/min, 10% grade) of seven ponies, there was no difference in exercise VO2, whether it was measured by the Haldane transformation (HT) or CVF equations (P greater than 0.05). In hyperoxia, the exercise VO2 was significantly increased from the normoxia condition (P less than 0.05) when measured by the HT equation but not when measured by the CVF equation (P greater than 0.05). By use of the CVF equation as the method of choice for VO2 determinations in hyperoxia, the present data show no change in exercise VO2 in the hyperoxic condition.

Animals↗
PubMedDate not supplied

Commercial porters of eastern Nepal: health status, physical work capacity, and energy expenditure.

The purpose of the study was to compare full-time hill porters in eastern Nepal with part-time casual porters engaged primarily in subsistence farming. The 50 porters selected for this study in Kenja (elevation 1,664 m) were young adult males of Tibeto-Nepali origin. Following standardized interviews, anthropometry, and routine physical examinations, the porters were tested in a field laboratory for physiological parameters associated with aerobic performance. Exercise testing, using a step test and indirect calorimetry, included a submaximal assessment of economy and a maximal-effort graded exercise test. Energy expenditure was measured in the field during actual tumpline load carriage. No statistically significant differences were found between full-time and part-time porters with respect to age, anthropometric characteristics, health, nutritional status, or aerobic power. Mean VO2 peak was 2.38 +/- 0.27 L/min (47.1 +/- 5.3 ml/kg/min). Load-carrying economy did not differ significantly between porter groups. The relationship between VO2 and load was linear over the range of 10-30 kg with a slope of 9 +/- 4 ml O2/min per kg of load. During the field test of actual work performance, porters expended, on average, 348 +/- 68 kcal/hr in carrying loads on the level and 408 +/- 60 kcal/hr in carrying loads uphill. Most porters stopped every 2 min, on average, to rest their loads briefly on T-headed resting sticks (tokmas). The technique of self-paced, intermittent exercise together with the modest increase in energy demands for carrying increasingly heavier loads allows these individuals to regulate work intensity and carry extremely heavy loads without creating persistent medical problems.

Adult↗