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Biomedical subjects

D C McKenzie

Publications and source records attributed to D C McKenzie.

At least 19 recordsLinked to original sources
PubMed2000

Different effects of strenuous eccentric exercise on the accumulation of neutrophils in muscle in women and men.

The purpose of this study was to evaluate the sex differences in delayed onset muscle soreness (DOMS), torque, and accumulation of technetium-99m (Tc-99m) neutrophils in eccentric-exercised muscle. A group of 10 female and 12 male subjects took part in this study. The subjects completed a pre-test using the descriptor differential scale (DDS) to describe DOMS, and tests of concentric and eccentric torque of the right quadriceps. A volume of 100 ml of blood was taken by venipuncture for neutrophil labelling in the early morning of the exercise day. The Tc-99m neutrophils were re-infused intravenously before the eccentric exercise. The exercise stimulus consisted of 300 eccentric repetitions of the right quadriceps muscles. Radionuclide images of both quadriceps muscles (lateral views) were taken at 2 and 4 h. The DDS, and concentric and eccentric torques of the quadriceps were subsequently evaluated at 0 h, 2, 4, 20 and 24 h post-exercise. The presence of Tc-99m neutrophils was greater in the exercised leg than the non-exercised leg at 2 and 4 h post-exercise (P </= 0.013) and greater in the exercised leg of the women compared to the men at 2 h (P = 0.03). The DOMS had increased post-exercise (P < 0.001) and torque had decreased post-exercise (P </= 0.002) but the patterns were different between the sexes. We concluded that the sex influences the presence of Tc-99m neutrophils in the exercised muscle following eccentric exercise. In addition, different patterns of DOMS and torque were observed between the sexes after eccentric exercise, and require further investigation.

Adult↗
PubMed1999

Aerobic and anaerobic energy during a 2-km race simulation in female rowers.

The maximal aerobic power (VO2max) and maximal anaerobic capacity (AODmax) of 16 female rowers were compared to their peak aerobic power (VO2peak) and peak anaerobic capacity (AODpeak, respectively) during a simulated 2-km race on a rowing ergometer. Each subject completed three tests, which included a 2-min maximal effort bout to determine the AODmax, a series of four, 4-min submaximal stages with subsequent progression to VO2max and a simulated 2-km race. Aerobic power was determined using an open-circuit system, and the accumulated oxygen deficit method was used to calculate anaerobic capacities from recorded mechanical power on a rowing ergometer. The average VO2peak (3.58 l min(-1)), which usually occurred during the last minute of the race simulation, was not significantly different (P > 0.05) from the VO2max (3.55 l min(-1)). In addition, the rowers' AODmax (3.40 l) was not significantly different (P > 0.05) from their AODpeak (3.50 1). The average time taken for the rowers to complete the 2-km race simulation was 7.5 min, and the anaerobic system (AODpeak) accounted for 12% of the rowers' total energy production during the race.

Adult↗
PubMed1999

The effect of repeat exercise on pulmonary diffusing capacity and EIH in trained athletes.

PURPOSE: The purpose of this study was to determine the effects of repeated heavy exercise on postexercise pulmonary diffusing capacity (DL) and the development of exercise induced arterial hypoxemia (EIH). METHODS: 13 endurance-trained, male athletes (age = 27+/-3 yr, height = 179.6+/-5.0 cm, weight = 71.8+/-6.9 kg, VO2max = 67.0+/-3.6 mL x kg(-1) x min(-1) performed two consecutive, continuous exercise tests on a cycle ergometer to VO2max, separated by 60 min of recovery. Arterial oxygen saturation (%SaO2) was measured via ear oximetry, and resting DL was measured and partitioned by the single-breath method, before exercise and 60 min after each exercise bout. RESULTS: No significant differences resulted in VO2max, VE, peak heart rate (HR), or breathing frequency between exercise bouts (P > 0.05). There was a small but significant decrease (454-446 W; P < 0.05) in peak power output in the second test. %SaO2 decreased from resting values during both exercise tasks, but there was no difference between the minimum saturation achieved in test 1 (91.4) or test 2 (91.6; P > 0.05). After the initial exercise bout, significant decreases (P < 0.05) occurred in DL (11%), membrane diffusing capacity (DM) (11%) and pulmonary capillary volume (VC) (10%). Further decreases occurred in DL (6%; P < 0.05), DM (2%; P > 0.05), and VC (10%; P < 0.05) after the second exercise bout. CONCLUSIONS: These observations question the meaning of post exercise measurements of pulmonary diffusion capacity, and its components, relative to pulmonary gas exchange and pulmonary fluid accumulation during exercise. The fact that there was no further change in %SaO2 after the second test suggests that if any interstitial edema developed, it was of no clinical significance; alternatively, the changes in DL(CO) may be related more to redistribution of blood than the development of pulmonary edema.

Adult↗
PubMed1999

Markers of excessive exercise.

Overtraining is of serious concern to long-distance runners and will affect 65% of them at some time in their competitive career. The clinical presentation is nonspecific but the classical symptoms include fatigue, mood disturbances, frequent upper respiratory infections and injury, and a decrease in performance. Dysfunction of the hypothalamic pituitary axis from repeated stress, of a physical or nonphysical nature, represents the most likely pathogenesis of this condition. There is no single biological marker that is diagnostic of an overtrained state; however, several parameters deserve further study. The time to volitional fatigue on a cycle ergometer at an intensity of 110% of the individual anaerobic threshold represents a possible laboratory test. Salivary IgA holds promise as a useful immunoligical marker of the overtrained state and further research is needed to determine the validity of plasma glutamine as a blood marker. The most promising tool at present is a measure of the athlete's mood state, and several psychological tools can be used for this purpose.

Athletic Injuries↗
PubMed1999

Ventilation and locomotion coupling in varsity male rowers.

Ventilation and locomotion coupling (entrainment) has been observed and described in rowers during incremental exercise protocols but not during simulated race conditions. The purpose of this descriptive study was to examine ventilation and locomotion entrainment on a breath-by-breath and stroke-by-stroke basis in varsity male rowers during a maximal 2,000-m ergometer test. Eight of eleven rowers entrained ventilation at integral multiples of stroke rate (1:1, 2:1, or 3:1) for at least 120 consecutive seconds, with a 2:1 entrainment pattern being most common. In all 2:1-entrained subjects, inspiration occurred at catch and finish and expiration occurred during the latter portions of drive and recovery. In entrained and unentrained breaths from all rowers, peak flow rates and tidal volumes varied depending on when the breath was initiated during the stroke cycle. Entrained rowers made use of these differences and breathed in a pattern by which they avoided initiating breaths that resulted in reduced tidal volumes. The present data indicated that ventilation was impaired at stroke finish and not at catch, as hypothesized by some previous researchers. Ventilation also appeared to be subordinate to consistent locomotive patterns under race conditions.

Adult↗
PubMed1999

Exhaled nitric oxide during exercise.

Endogenously produced nitric oxide (NO) is detectable in the exhaled air of resting humans, and the amount of exhaled NO increases during exercise. It is believed that NO is likely to have an important role in the normal physiological response to exercise. Despite accumulating evidence of exhaled NO during exercise, the effects and relevance of NO to exercise are not yet completely understood. Scientific debate surrounds the site of NO production and the stimuli for production. Resolution of these controversial issues will explain the significance of exhaled NO during exercise.

Animals↗
PubMed1998

The time course of pulmonary diffusing capacity for carbon monoxide following short duration high intensity exercise.

We investigated the time course of changes in post-exercise pulmonary diffusing capacity for carbon monoxide (DLCO), membrane diffusing capacity (DM), and pulmonary capillary blood volume (VC) in highly trained (HT), moderately trained (MT) and untrained (UT) male subjects (n = 8/group). Subjects were assigned to groups based on their aerobic capacity from a preliminary VO2max test (HT > or = 65, MT = 50-60, UT < or = 50 ml x kg(-1) x min(-1)). Resting (BASE) DLCO, DM and VC were obtained, then subjects cycled to fatigue at the highest workrate attained during the preliminary tests. Diffusion measurements were then made at 1, 2, 4, 6 and 24 h. DLCO was depressed at 1 h, lowest at 6 h and approached BASE values at 24 h in all groups. The DLCO change was paralleled by a change in VC. Alterations to VC were similar between groups except at 24 h where MT and HT subjects had returned to BASE while UT did not. DM was significantly lower than BASE at 1, 2, 4, and 6 h, and was similar between groups. The changes in DLCO post-exercise appear to be primarily due to a decrease in VC. Comparable diffusion decrements were observed in all subjects. The results of this study suggest that post-exercise alterations in DLCO, DM and VC are not related to aerobic capacity.

Bicycling↗
PubMed1997

The asthmatic athlete: metabolic and ventilatory responses to exercise with and without pre-exercise medication.

To determine whether asthmatic athletes have normal physiological responses to exercise without pre-exercise medication, we studied 17 female and male asthmatic subjects, 9 highly trained (HT) and 8 moderately trained (MT) under 2 conditions: salbutamol (S) 200 micrograms taken via inhaler 15 minutes prior to exercise or placebo (PL). The exercise task was 4 continuous 5 minute increments representing 25, 50, 75 and 90% of the subject's VO2max.VO2, minute ventilation (VE), respiratory exchange ratio (RER), % saturation (SaO2), and HR were continuously measured during exercise. Blood lactate (LA) was measured each minute throughout exercise and recovery. Post-medication, exercise, and recovery measurements of peak expiratory flow rates (PEFR) were made using a Mini-Wright flow meter. No differences (p > 0.05) between treatment conditions were found at any stage of exercise with respect to VO2, VE, RER, HR and SaO2. However, among the HT group the mean HR for the 4 exercise conditions was significantly higher under PL (PL = 151.7;S = 147.2; p = 0.01). No difference was found in LA during exercise or in recovery. Pre-exercise PEFR was significantly higher when pretreatment was S(S = 582; PL = 545 l.sec-1; p = 0.003). During the exercise and recovery conditions mean PEFR measures were significantly higher (S = 600.1; PL = 569.6; p = 0.002) with the S treatment. Bonferroni's test detected a difference in PEFR measures between S and PL at 25% and 50% VO2max and 3 and 15 minutes into recovery. There was no difference in the physiological response to exercise between groups based on training status. It was concluded that although S affects the PEFR these asthmatic athletes do not have altered metabolic or ventilatory responses during this incremental exercise protocol.

Adult↗
PubMed1997

Force output and energy metabolism during neuromuscular electrical stimulation: a 31P-NMR study.

The purpose of this study was to determine the acute physiologic effects of two electrical stimulation protocols commonly used for muscle rehabilitation. Surface electrodes were used to provide 12 stimulations of the calf musculature. In protocol A the duty cycle was fixed at 1:1 (10-second stimulation: 10-second rest); for protocol B it was 1:5 (10-second stimulation: 50-second rest). We continuously recorded isometric plantarflexor force in six healthy male subjects during stimulation using a load cell connected to a foot pedal ergometer. Metabolic changes in the stimulated gastrocnemius muscle were monitored in the supine position using 31P-NMR spectroscopy (Phillips 1.5 tesla NMR machine). Relative changes in phosphocreatine (PCr), inorganic phosphate (Pi), and intracellular pH (pHi) were obtained during stimulation and recovery, using a 1.5 cm RF surface antenna. Over the 12 stimulations, protocol A produced a significantly (p < 0.001), greater force decline (protocol A: 30.4 +/- 1.3%, protocol B: 13 +/- 0.8%); a significantly (p < 0.005), greater increase in Pi/PCr (protocol A: 210%, protocol B: 50%); and a significantly (p <0.001), lower pHi (protocol A: 6.8 +/- 0.16, protocol B: 7.03 +/- 0.12). We conclude that the shorter duty cycle produces more fatigue throughout the stimulation period, possibly as a result of greater intracellular acidosis and reduced availability of the high energy phosphate PCr. The clinical application of this finding relates to the selection of a stimulation protocol that maximizes strength gains in atrophic vs healthy muscle.

Adult↗
PubMed1996

The relationship between test protocol and the development of exercise-induced hypoxemia (EIH) in highly trained athletes.

Healthy male endurance-trained cyclists [n = 11, age = 27.3 (3.9) years; mass = 73.0 (9.3) kg; height = 180.5 (6.9) cm; maximal oxygen consumption (VO2max) = 71.1 (5.8) ml.kg-1.min-1, mean +/- (SD)] were recruited to assess the relationship between test protocol and the development of desaturation of arterial hemoglobin with oxygen, during incremental exercise tests to maximal aerobic capacity (VO2max). All subjects demonstrated resting pulmonary function within normal limits [forced vital capacity (FVC) = 6.0 (0.9); forced expiratory volume (FEV1.0) = 4.9 (0.6); FEV1.0/FVC = 0.8 (0.1)] and completed three ramped VO2max tests (Mijnhardt KEM-3 electronically braked cycle ergometer) beginning at 0 W with increments of either 20,30 or 40 W.min-1. All periods of testing were separated by a minimum of 72 h. VO2max, peak minute ventilation (VEpeak) (Medical Graphics, CPX-D), peak heart rate (fcpeak), peak power output (Wpeak), and minimum percentage arterial oxyhemoglobin saturation (% SaO2min) (Omeda Biox 3740 pulse oximeter) were determined. There were no significant differences (p > 0.05) in VEpeak [191.5 (26.2), 196.0 (24.4), 194.3 (23.9) l.min-1] fcpeak [191.4 (7.0), 190.3 (5.5), 187.8 (5.9) beats.min-1], VO2max [5.0 (0.5), 5.1 (0.4), 5.1 (0.5) l.min-1] or %SaO2min [89.5 (1.5), 89.6 (1.3), 90.0 (2.3)] between protocols. The 20-W protocol [417 (27) W] demonstrated significantly lower Wpeak (P < 0.05) than the 30-W [434 (36) W] and 40-W [453 (38) W] protocols, indicating that peripheral fatigue may play an important factor in response to these tests. The results of this study demonstrate that arterial desaturation occurs as a result of intense exercise in highly trained athletes independent of the rate of attainment of VO2max.

Adult↗
PubMed1996

Pulmonary transit time and diffusion limitation during heavy exercise in athletes.

To investigate relationships between pulmonary transit times (PTT) and pulmonary diffusion limitation during exercise, 10 high aerobic capacity athletes (VO2max = 5.15 +/- 0.52 l.min-1) who had multiple inert gas elimination analysis evidence suggestive of diffusion disequilibrium were studied at rest and maximal exercise. Diffusing capacity for oxygen (DLO2) was calculated from the inert gas data. First pass radionuclide angiography was performed using 99mTechnecium labeled erythrocytes and whole lung PTT and pulmonary blood volume (PBV) were calculated. PTT decreased from 9.32 +/- 1.41 sec at rest, to 2.91 +/- 0.30 sec during exercise and was correlated with diffusion limitation suggested by the inert gases (r = -0.58, P < 0.05). PBV increased during exercise to over 25% of whole blood volume and correlated with DLO2 (r = 0.82, P < 0.01). These data suggest that diffusion limitation is related to shortened PTT in athletes and that maximal recruitment of PBV may defend against diffusion limitation.

Adult↗
PubMed1996

Comparison of aero-bars versus traditional cycling postures on physiological parameters during submaximal cycling.

The purpose of this investigation was to quantify the difference in energy expenditure between traditional cycling handlebars and aero-bars during outdoor submaximal cycling. Eleven trained cyclists (age = 29.3 +/- 1.9 years, weight = 69.4 +/- 3.8 kg, VO2max = 58.1 +/- 2.0 ml.kg-1.min-1) were randomly assigned a sequence of three hand positions: brake hoods (BH), drop-bars (DB), and aero-bars (AB). Subjects cycled at 30 km.h-1 in one position for 5 minutes, then recovered until HR fell below 120 bpm. This was then repeated for the other hand positions. All cycling was completed on a standard racing bike fitted with aero-bars. Tire pressure was held constant for all trials. A portable telemetric system (Cosmed K-2) was used to measure VO2, VE and heart rate (HR) during the trials. No statistical differences were observed between AB and DB. Significant differences (p < .05) were found between BH (VE = 66.1 +/- 2.7 L.min-1; HR = 152 +/- 4 bpm; VO2 = 1.56 +/- .15 L.min-1) and AB (VE = 61.3 +/- 2.8 L.min-1; HR = 146 +/- 4 bpm; VO2 = 1.31 +/- .10 L.min-1). AB provides an energy savings over the traditional BH cycling posture.

Adolescent↗
PubMed1996

Presence of WBC, decreased strength, and delayed soreness in muscle after eccentric exercise.

The purposes of this study were to assess the presence of 99mTc-labeled white blood cells (WBC) in exercised muscle compared with nonexercised muscle over time and to determine the time course of delayed onset muscle soreness (DOMS) and eccentric torque in 10 female subjects. A pretest was followed by 300 eccentric repetitions of the right quadriceps. DOMS and eccentric torque were measured at 2, 4, 20, 24, 48, and 72 h postexercise. Eccentric torque was also tested at 0 h. Radionuclide images of both quadriceps were taken at 2, 4, 20, and 24 h postexercise. The presence of 99mTc-WBC in the exercised muscle was significantly greater (P < 0.001) than in the nonexercised muscle. Eccentric torque declined at 0 and 24 h postexercise. DOMS peaked at 24 h postexercise. The presence of 99mTc-WBC in the exercised muscle in the first 24 h suggests that acute inflammation occurs as a result of exercise-induced muscle injury. The bimodal pattern of eccentric torque supports the hypothesis that more than one mechanism is involved.

Adult↗
PubMed1996

Altitude training for improvements in sea level performance. Is the scientific evidence of benefit?

Altitude training invokes physiological changes that are very similar to those caused by endurance training, As a result, it has been incorporated in the training regimes of elite athletes in an effort to improve sea level performance. Several training strategies, such as constant altitude exposure, intermittent altitude exposure or 'live high train low', have been used in an effort to incur an advantage in sea level performance over just sea level training alone. In spite of the accumulating scientific evidence that altitude training affords no advantage over sea level training, many coaches and athletes believe that it can enhance sea level performance for any athlete, whether endurance or power is the focus in their particular sport. However, altitude training may not be suitable for some athletes depending on their age, fitness level, health, iron status and the energy and technical requirements of their sport. The issue of whether altitude training enhances sea level performance remains a controversial topic.

Acclimatization↗
PubMed1996

Physical fitness and its relationship to other indices of health status in children with chronic arthritis.

OBJECTIVE: To compare aerobic and anaerobic fitness of a group of children w-th chronic arthritis with that of healthy controls, and to explore the relationship between physical fitness and other indices of health status in these children. METHODS: Thirty-one children aged 8 to 17 years with chronic arthritis of varying type and severity and 16 physically healthy controls participated in the study. Using a cycle ergometer, aerobic fitness was assessed by measuring peak oxygen uptake achieved in a 15 s period during exercise to volitional fatigue. Anaerobic fitness was assessed by measuring peak power in the legs in a 5 s period and total work completed (Wingate test). Joint pain experienced over the week before testing and during testing was measured using a 10 cm visual analog scale. Self-esteem was measured using the Self Perception Profile for Children Questionnaire. RESULTS: There were no significant differences between mean peak O2 uptake or mean peak anaerobic power for patients and controls; however, the mean values for both controls and patients were significantly lower than reported values for healthy children. Peak O2 uptake controlled for age, sex, and sum of skinfolds was negatively associated with disease severity, measured by physician global assessment (p = 0.04), but peak power was not. Neither aerobic nor anaerobic fitness were associated with disease activity measured by physician global assessment or active joint count, or with disease duration. There was a tendency for children with active arthritis to experience less pain during fitness testing than over the previous week (p = 0.06). Testing did not seem to exacerbate joint symptoms. Self-ratings of athletic competence were significantly correlated with peak O2 uptake achieved for children with arthritis (r = 0.43, p = 0.02), but not for controls. Global self-esteem was moderately correlated with self-rated athletic competence in controls (r = 0.49, p = 0.09), but was not in children with arthritis. CONCLUSION: In this sample of children, most of whom had limited joint involvement, we failed to demonstrate significant group differences in fitness between patients and controls. Disease severity may be related to fitness levels, but psychosocial factors may perhaps be more important determinants of fitness. Children with arthritis seem to have realistic perceptions of their own physical capabilities, and even those children who are less fit and perceive themselves as having less athletic competence do not appear to have lowered self-esteem.

Adolescent↗
PubMed1995

Ventilatory thresholds during wheelchair exercise in individuals with spinal cord injuries.

The ventilatory thresholds of 30 male wheelchair athletes were determined from their respiratory and metabolic responses to a continuously progressive exercise protocol to peak oxygen uptake on a wheelchair ergometer. The peak oxygen uptake (peak VO2), ventilatory threshold in 1 min-1 (VTL), and ventilatory threshold expressed as a percentage of peak VO2 (VT%) were measured for all subjects. Statistical analyses of selected subsamples were used to note sport and functional ability level differences in these variables. Analysis of peak VO2 by functional classification (old International Stoke Mandeville Games Federation system; classes 1A-5, plus an amputee class) indicated that paraplegic (classes 2-5) and the amputee class athletes (2.48 1 min-1) were higher than tetraplegic (classes 1A-1C) athletes (0.95 1 min-1). The paraplegic and amputee classes were combined for a comparison of peak VO2 by sport which showed that track athletes (2.80 1 min-1) were higher than basketball players (2.41 1 min-1) who were higher than athletes from other sports (1.88 1 min-1). The VTL analyses demonstrated differences similar to the peak VO2 analyses. The VT% analyses, however, showed no sport differences, but the tetraplegic athletes had higher VT% values (87%) than the paraplegic plus amputee group (69%).

Adult↗
PubMed1995

The metabolic cost of two kayaking techniques.

A common technique employed in flatwater kayak and canoe races is "wash riding", in which a paddler positions his/her boat on the wake of a leading boat and, at a strategic moment, drops off the wake to sprint ahead. It was hypothesized that this manoeuver was energy efficient, analogous to drafting in cycling. To study this hypothesis, minute ventilation (VE), heart rate (HR) and oxygen consumption (VO2) were measured in 10 elite male kayak paddlers (age = 25 +/- 6.5 yrs, height = 183.6 +/- 4.4 cm, mass = 83.9 +/- 6.1 kg) during steady-state exercise at a standardized velocity in conditions of "wash riding" (WR) and "non-wash riding" (NWR). The data were collected in field conditions using a portable telemetric metabolic system (Cosmed K2). Statistical analysis of the mean values for VE, VO2 and HR was performed using the Hotelling's T2 statistic and revealed significant (p < 0.05) differences between the WR and NWR trials for all three dependent variables. Mean values for VE (l/min) were WR = 113 +/- 16.5, NWR = 126.3 +/- 15.7; for VO2 (l/min) were WR = 3.22 +/- 0.32, NWR = 3.63 +/- 0.3; and for HR (bpm) were WR = 167 +/- 9.9, NWR = 174 +/- 8.0. It was concluded that wash riding during kayak paddling confers substantial metabolic savings at the speeds tested. This has implications for the design of training programs and competitive strategies for flatwater distance kayak racing.

Adult↗