ISSN:1066-7814    

DOI:10.1139/h94-042

出版商:NRC Research Press    

年代:1994

数据来源: NRC

ISSN:1066-7814    

DOI:10.1139/h94-043

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Movements that are performed with maximal velocity and acceleration can be considered ballistic actions. Ballistic actions are characterized by high firing rates, brief contraction times, and high rates of force development. A characteristic triphasic agonist/antagonist/agonist electromyographic (EMG) burst pattern occurs during ballistic movement, wherein the amount and intensity of antagonist coactivation is variable. In conditions of low-grade tonic muscular activity, a premovement EMG depression (PMD; or silent period, PMS) can occur in agonist muscles prior to ballistic contraction. The agonist PMD period may serve to potentiate the force and velocity of the following contraction. A selective activation of fast twitch motor units may occur in ballistic contractions under certain movement conditions. Finally, high-velocity ballistic training induces specific neuromuscular adaptations that occur as a function of the underlying neurophysiological mechanisms that subserve ballistic movement.Key words: electromyography, motor control, training adaptation, motor unit

ISSN:1066-7814    

DOI:10.1139/h94-030

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The Canadian Forces chemical defence protective clothing can induce an overwhelming strain on one's ability to regulate body temperature. Recently a number of investigations have been completed at the Defence and Civil Institute of Environmental Medicine that focused initially on understanding the interaction of metabolic rate, ambient temperature, and ambient vapour pressure on the severity of heat strain associated with wearing the protective clothing. This paper presents a summary of these initial studies together with an overview of different attempts to reduce heat strain during exercise in a hot environment. Factors such as improved aerobic fitness or a period of dry heat acclimation have little if any benefit on tolerance time while wearing the clothing during light or moderate exercise. The best solution to the problem of heat strain remains the use of microclimate conditioning (personal cooling), and these techniques have been successful for Naval and Air Force personnel. For our Land Forces, however, microclimate conditioning is not feasible until a lightweight high-energy power source is developed.Key words: thermoregulation, endurance training, heat acclimation, microclimate conditioning

ISSN:1066-7814    

DOI:10.1139/h94-031

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Nine elite male junior weightlifters (mean age 17.6 ± 0.3 yrs) performed weightlifting tests before (Test 1) and after (Test 2) 1 week of increased training volume (overreaching) and repeated the protocol after 1 year of their training program. Strength increased by Year 2 (p < 0.05) but did not change during either week of increased training volume. The 1-week overreaching stimulus resulted in attenuated exercise-induced testosterone concentrations during Year 1, but augmented exercise-induced testosterone concentrations during Year 2. Testosterone concentrations at 7 a.m. decreased for only Year 1. For both years, the 1-week overreaching stimulus increased Cortisol at 7 a.m., indicative of the increased training volumes. Testosterone/Cortisol was not affected by increased training volume for either year. One year of chronic weightlifting and prior exposure to the overreaching stimulus appears to decrease the detrimental effects of stressful training on the endocrine system.Key words: testosterone, Cortisol, weightlifting, overtraining

ISSN:1066-7814    

DOI:10.1139/h94-032

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Seven well-trained male long-distance runners were studied during a 100-km road race. Hematologic parameters, plasma electrolytes, glucose, lactate, urea, and creatinine content in plasma and the activity of the enzymes γ-glutamyltransferase and creatine kinase were determined before and after the race. A slight increase in hematocrit was found after the race, although the red blood cell count and hemoglobin concentration remained unchanged. Further, a significant rise in the number of white blood cells, lymphocytes, and neutrophils was found after the race. Postrun concentrations of plasma sodium and potassium increased significantly from 142 ± 7 to 161 ± 7 mmol∙L−1, and from 4.22 ± 0.37 to 5.15 ± 0.46 mmol∙L−1(p < 0.05), respectively. Plasma concentrations of lactate (1.29 ± 0.31 vs. 3.57 ± 1.22 mmol∙L−1), urea (6.09 ± 1.0 vs. 8.35 ± 1.35 mmol∙L−1), creatinine (73.4 ± 3.5 vs. 117.6 ± 19.4 μmol∙L−1), plasma creatine kinase (91.1 ± 25.1 vs. 2843 ± 2341 IU∙L−1), and γ-glutamyltransferase (20.28 ± 1.88 vs. 24.14 ± 4.09 IU∙L−1) increased significantly (p < 0.05) after the run. It was concluded that during ultralong-distance races, acute renal dysfunction and muscle damage could contribute to the observed hypernatremia and hyperkalemia.Key words: ultralong-distance races, hematological parameters, plasma electrolytes, plasma creatinine, c

ISSN:1066-7814    

DOI:10.1139/h94-033

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

This study documents the blood pressure responses to a progressive step test adapted from the Canadian Aerobic Fitness Test (CAFT). Subjects were administered the first five stages of the CAFT in a progressive and discontinuous manner. Mean heart rate, SBP, and ΔSBP increased linearly with exercise intensity, while mean diastolic blood pressure remained stable. The variables that contributed most to ASBP (Stage 3) in males were age and degree of participation in physical activity, and in females the variables were body weight and degree of participation. Criteria for the detection of an exaggerated (mean ΔSBP + 1 SD) and highly exaggerated (mean ΔSBP + 2 SD) SBP response were defined. Resting normotensive individuals who demonstrate an excessive exercise blood pressure response seem to do so at the lowest levels of stepping intensities. This step test protocol appears to be a useful and practical procedure for assessing the exercise blood pressure response in higher risk individuals.Key words: exercise testing, fitness appraisal, exercise hypertension, risk appraisal

ISSN:1066-7814    

DOI:10.1139/h94-034

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Entrainment of the breathing rhythm to that of the rhythm of limb movement during exercise has been shown to decrease oxygen consumption for cycling at a moderate workload. This study examined the effect of entrainment on oxygen consumption during treadmill walking at two workloads. For each workload, 8 subjects performed two exercise protocols consisting of walking on a treadmill for 8 min. For the first protocol they received no instructions, but for the second protocol they were instructed to coordinate one breath per auditory cue which was provided during the last 4 min of exercise. The auditory cue was transmitted as a click via headphones. It was derived from a foot switch and was designed to synchronize breathing to the walking pace at a respiratory frequency close to that observed in the first protocol. Entrainment and oxygen consumption were compared between the protocols for the last 4-min segments for each workload. These comparisons showed that the presence of the auditory cue significantly increased entrainment from 29 to 74%, but oxygen consumption was not significantly changed.Key words: breathing pattern, entrainment, exercise, locomotor-respiratory coupling, ventilation

ISSN:1066-7814    

DOI:10.1139/h94-035

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

In order to determine whether exercise mode affects recovery energy expenditure, 7 active men (average age 25 yrs) performed a control rest and three submaximal exercise bouts in counterbalanced order in separate weeks. The bouts, designed to involve three levels of eccentric muscular activity, included 60%jog (60 J), 60% downhill (−5%) jog (60 DH), 60% cycling (60 C), and a control session. Following a 24-hr period of regulated activity and diet, subjects exercised for 60 min.and RER were assessed during 48 hrs of regulated recovery. Total energy use was elevated following 60 C and 60 DH versus control, and fat energy use was elevated following 60 J, 60 DH, and 60 C versus control. For combined trials, the total energy use was higher at 1, 2, and 9 hrs postexercise. These results do not support the hypothesis that eccentric muscular activity affects the magnitude of recovery energy expenditure.Key words: energy expenditure, fat energy expenditure, excess postexercise oxygen consumption, exercise mode

ISSN:1066-7814    

DOI:10.1139/h94-036

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The mechanical twitch in response to increasing electrical stimulus intensity, delivered both over the motor point and motor nerve, was recorded in the first dorsal interosseous (FDI) and the adductor pollicis (AP), and only over the motor point in the soleus (Sol), lateral (LG), and medial (MG) gastrocnemius muscles of human subjects. The relationship between intensity of electrical stimulation (ES) and twitch torque showed a positive linear regression in all muscles. In the FDI and AP the relationship was not significantly different when ES was applied at the motor point or over the motor nerve. At small intensities of activation, ES induced larger twitch torques in the MG and LG, which contain a roughly equal proportion of slow and fast motor units (MUs) compared to the Sol, which is composed mainly of slow type fibres. Moreover, the relationship between ES intensity and twitch time-to-peak is best fitted in all muscles by a power curve that shows a greater twitch time-to-peak range in its initial part for muscles containing a larger proportion of fast MUs (LG, MG) than for muscles mainly composed of slow MUs (Sol). In conclusion, these results induced by ES at the motor point and/or over the motor nerve confirm the concept of a reversed sequence of MU activation, as compared to voluntary contractions, and document this viewpoint in muscles of different function and composition. The reversed sequence of MU activation is more clearly evident during motor point ES.Key words: muscle contraction, mechanical twitch, motor point, nerve

ISSN:1066-7814    

DOI:10.1139/h94-037

出版商:NRC Research Press    

年代:1994

数据来源: NRC