摘要:

SUZUKI, S., K. KAIYA, S. WATANABE, and R. S. HUTTON. Contraction-induced potentiation of human motor unit discharge and surface EMG activity. Med. Sci. Sports Exerc, Vol. 20, No. 4, pp. 391-395, 1988. In quadrupeds, an electrically induced, moderate to high intensity brief muscle contraction potentiates autogenetic excitation and leads to enhanced recruitment and/or tonic firing frequency of a-motor neurons. To determine if similar adaptations occur in humans, single motor units (SMUs) and surface electromyographic activity (EMG) were recorded from the right biceps brachii before and immediately after a 5-s 25% or 50% maximum voluntary contraction (MVC), while subjects held a handle (0-1% MVC) attached to a force transducer or maintained a 2% MVC for 30-60 s. Of 26 SMUs recorded, 15 increased, 4 decreased, and 7 showed no change in firing frequency (mean increase: 5 imp/s,P<0.01). Twelve SMUs had lower recruitment force thresholds after contraction. There was no significant treatment effect for the % MVC intensity. The postcontraction surface EMG power spectrum broadened, increased in amplitude, and contained a higher frequency component than the control contraction power spectrum. Changes in recruitment and/or frequency coding were reflected in the raw EMG records. Findings agree with previous reports in animals of contraction-induced potentiation of subsequent submaximal muscle contractions. Such acute adaptations in spinal neuromuscular pathways would function to optimize force output to a submaximal range of neural input frequencies.

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

NIGG, B. M., M. R. YEADON, and W. HERZOG. The influence of construction strategies of sprung surfaces on deformation during vertical jumps. Med. Sci Sports Exerc, Vol. 20, No. 4, pp. 396-402, 1988. The purpose of this paper is to assess the influence of variations in the construction of area-elastic surfaces on the local deformation of these surfaces during an actual movement of athletes.Area-elastic surfaces were systematically varied in construction to allow the discussion of the influence of: (a) the number; (b) the spacing of the sleepers; (c) the material of the lowest sleeper; (d) variations of the second layer; (e) variations of the top surface; and (f) addition of a special padding element between the first and second sleepers on maximum deformation. Deformation data were collected using high-speed film from a group of recreational athletes and a group of national team athletes (volleyball) performing a drop jump.The differences in maximum deformation between the various surfaces tested were about 100% from the lowest to the highest value for the recreational athletes and about 1,000% for the national team athletes. The differences in deformation were primarily influenced by the number of sleepers used and/or by construction elements which are close to the top of the surface (top layer, second layer, add rubber padding, number of sleepers). The one sleeper system consistently had the lowest values of maximum deformation.

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

YEADON, M. R. and B. M. NIGG. A method for the assessment of area-elastic surfaces. Med. Sci. Sports Exerc, Vol. 20, No. 4, pp. 403- 407, 1988. A method is presented for the evaluation of area-elastic surfaces using two subject tests. Deformations and jump heights are determined for 12 sprung floor samples to accuracies of 0.12 mm and 0.4 cm respectively, using filming techniques. It is found that the deformation of a floor sample is dependent on both the subject group and the dimensions of the floor sample. The method showed significant differences in deformation values of the 12 floor samples but only small differences in jump heights.

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID

摘要:

MORGAN, W. P., D. L. COSTILL, M. G. FLYNN, J. S. RAGLIN, and P. J. O'CONNOR. Mood disturbance following increased training in swimmers. Med. Sci. Sports Exerc, Vol. 20, No. 4, pp. 408- 414, 1988. Twelve male swimmers were studied psychologically before, during, and after 10 d of increased training. Daily training distance was increased from 4,000 to 9,000 m · d−1, and intensity was maintained at 94% of &OV0312;O2max. Three of the swimmers were unable to tolerate the increased training load, and they did the same distance at slower speeds. Swimmers completed the Profile of Mood States, a muscle soreness scale, and a 24-h history each morning prior to the first of two daily training sessions. Changes across days were evaluated statistically with a one-way repeated measures ANOVA. Significant (P<0.005) increases occurred in the ratings of exercise intensity, muscle soreness, depression, anger, fatigue, and global mood disturbance, along with a reduction in general sense of well-being. Swimmers were classified as “responders“ or “non-responders” on the basis of distress patterns using separate physiological and psychological criteria, and these classifications were performed in a double-blind setting. Close agreement (89%) was achieved between the psychometric and physiological judgments, and the physiological results appear in related papers. It is concluded that significant psychometric changes occur with an intense 10-d training regimen, and these alterations resemble those observed in swimmers exposed to increased training across several months. These findings underscore the potential utility of monitoring mood states in the prevention of staleness.

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID

ISSN:0195-9131    

出版商:OVID    

年代:1988

数据来源: OVID