Maximum Voluntary Contraction as a Function of Upper Extremity Posture in Females

2000 ◽  
Vol 44 (30) ◽  
pp. 5-441-5-444
Author(s):  
Kurt T. Hegmann ◽  
Arun Garg
Keyword(s):  
Perceived Exertion ◽  
Selection Process ◽  
Maximum Voluntary Contraction ◽  
Shoulder Girdle ◽  
Voluntary Contraction ◽  
Ratings Of Perceived Exertion ◽  
Job Tasks ◽  
Shoulder Flexion ◽  
Pain Ratings ◽  
Voluntary Contractions

Background: Little has been published on the maximum strength of the shoulder girdle as a function of varying postures. Such information may help aid in job design by better assessing the capabilities of workers. Methods: Female subjects (n=12) were required to hold a weight in place for 4 seconds in one of 6 different functional postures: 0/90 (shoulder flexion angle = 0° and included elbow angle = 90°), 30/90, 60/90, 90/120, 120/150 and 150/180. Postures and weights were chosen at random and measurements were repeated. Final weight adjustments were in increments of 0.1 lb. At least 3 minutes of rest between lifts was provided. Maximum voluntary contractions (MVCs) were required to be reproduced within 2 lbs. Dynamic lifting of the weight and holding in place MVCs (“lift and hold”), as well as only holding the weight in place MVCs (“hold only”) were assessed separately. Maximum voluntary torques were also computed and adjusted for arm weight. Ratings of perceived exertion (Borg CR-10) and pain ratings (0–10 scale) were obtained. Results: Maximum voluntary contractions varied greatly, with the strongest to weakest measurements approximating 2:1 ratios. For the 90/120 posture, lift and hold MVC was 14.6±3.0 lb. (range 9.5–19.0). The hold only MVC for 90/120 was 18.1±2.9 lb. (range 13.5–25.3). Similar variability occurred in all postures. Adjusted for arm weight, MVC for lift and hold at 90/120 was 18.1±3.3 lb, while hold only was 21.7±3.2 lb. Across all postures, hold only MVCs were greater than lift and hold MVCs by 4.3 lb. (26%). Lift and hold MVC torque at 120/150 was 217.2±39.3 in-lb. (range 157.5–266.8), while hold only was 280.6±38.0 in-lb. Across all postures, hold only maximum voluntary torques were greater than lift and hold torques by 25%. Except for the 0/90 and 150/180 postures, posture had little effect on hold only maximum voluntary torques. Borg CR-10 ratings averaged 6.6 for lift and hold and 6.9 for hold only (p>0.05). Posture had no effect on pain ratings, which averaged 0.8. Conclusions: Variability in female shoulder girdle lifting strength is substantial. Removing the lifting portion of job tasks likely substantially increases the percentage of workers capable of performing the tasks. Weakest postures are 90/120 and 120/150 and the female lift and hold MVC for those postures is 15 lb. (hold only 19 lb.). 30/90, 60/90 and 150/180 postures are equally strong; MVCs for lift and hold in those postures are 18 lb. (hold only 23 lb.). When overhead work is required, 150/180 posture appears preferable to 90/120 or 120/150. Some screening or selection process may be necessary on some jobs due to the degree of variability in strength.

Endurance time as a Function of the Percentage of Maximum Voluntary Contraction and Upper Extremity Posture in Healthy Females

2000 ◽  
Vol 44 (30) ◽  
pp. 5-437-5-440
Author(s):  
Arun Garg ◽  
Kurt T. Hegmann
Keyword(s):  
Upper Extremity ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Flexion Angle ◽  
Endurance Time ◽  
Shoulder Flexion ◽  
Healthy Females ◽  
Female Subjects

Endurance times were measured on 12 female subjects for seven different %MVCs and five different shoulder postures. Endurance time decreased nonlinearly with an increase in %MVC. It decresed with an increase in shoulder flexion angle up to 120° and then it increased. This study does not support the recommendation that weights corresponding to 5% of MVC, much less 20% of MVC as suggested by Rohmert, can be held indefinitely.

Acoustic myography for investigating human skeletal muscle fatigue

1991 ◽  
Vol 71 (4) ◽  
pp. 1422-1426 ◽  
Author(s):  
M. J. Stokes ◽  
P. A. Dalton
Keyword(s):  
Isometric Force ◽  
Maximum Voluntary Contraction ◽  
Force Production ◽  
Rectus Femoris ◽  
Quadriceps Muscle ◽  
Voluntary Contraction ◽  
Fatigued Muscle ◽  
Before And After ◽  
Acoustic Myography ◽  
Voluntary Contractions

Sounds produced during voluntary isometric contractions of the quadriceps muscle were studied by acoustic myography (AMG) in five healthy adults. With the subject seated, isometric force, surface electromyography (EMG), and AMG were recorded over rectus femoris, and the EMG and AMG signals were integrated (IEMG and IAMG). Contractions lasting 5 s each were performed at 10, 25, 50, 60, 75, and 100% of maximum voluntary contraction (MVC) force. Fatigue was then induced by repeated voluntary contractions (10 s on, 10 s off) at 75% MVC until only 40% MVC could be sustained. After 15 min of rest, the different force levels were again tested in relation to the fresh MVC. Both before and after fatiguing activity the relationships between force and IEMG [r = 0.99 +/- 0.01 (SD), n = 10] and force and IAMG (r = 0.98 +/- 0.02) were linear. After activity, however, the slopes of the regression lines for force and IEMG increased (P less than 0.01) but those for force and IAMG remained the same (P greater than 0.05). The present results clarify the relationship between AMG and isometric force in fatigued muscle without the problem of fatigue-induced tremor, which hampered previous studies of prolonged activity. This study contributes to the validation of AMG and shows that it is a potentially useful method for noninvasive assessment of force production and fatigue. Further studies to establish the origin of AMG activity are required before AMG can be accepted for use in neuromuscular physiology or rehabilitation.

Isometric Contraction of Arm Flexor Muscles as a Method of Evaluating Cardiac Vagal Tone in Man

1997 ◽  
Vol 92 (2) ◽  
pp. 175-180 ◽  
Author(s):  
M. Al-Ani ◽  
K. Robins ◽  
A. H. Al-Khalidi ◽  
J. Vaile ◽  
J. Townend ◽  
...  
Keyword(s):  
Heart Rate ◽  
Isometric Contraction ◽  
Maximum Voluntary Contraction ◽  
Young Male ◽  
Vagal Tone ◽  
Voluntary Contraction ◽  
Respiratory Cycle ◽  
Cardiac Vagal Tone ◽  
Flexor Muscles ◽  
Voluntary Contractions

1. We have previously shown that brief voluntary isometric contractions of upper arm flexor muscles performed for one respiratory cycle elicit a significant decrease in the R—R interval. The present study was designed to determine if similar changes are produced by non-voluntary electrically evoked contractions and, if so, to establish the consistency and repeatability of the associated changes in the R—R interval. 2. The heart rate (R—R interval) response to voluntary or non-voluntary brief isometric contraction equivalent to 40% of the maximum voluntary contraction was studied in 10 healthy young male subjects during controlled ventilation at supine rest. 3. The absolute values of R—R intervals occurring in any one of 10 arbitrary phases of a respiratory cycle were measured and plotted by a computer. 4. Both voluntary and non-voluntary contractions elicited similar changes in heart rate and R—R interval, which were greater during expiration than during inspiration. 5. This confirms our previous finding that the magnitude of the R—R interval changes, with brief isometric contraction, is positively related to the degree of cardiac vagal tone. 6. Analysis of the variability between repeated tests initiated in either inspiration or expiration revealed that there was significantly less variability with the electrically induced contraction. 7. It was concluded that electrically induced contractions of 40% maximal voluntary contraction are a viable alternative to voluntary contractions and provide a more controllable means of measuring cardiac vagal withdrawal.

Muscle temperature, contractile speed, and motoneuron firing rates during human voluntary contractions

1992 ◽  
Vol 73 (6) ◽  
pp. 2457-2461 ◽  
Author(s):  
B. Bigland-Ritchie ◽  
C. K. Thomas ◽  
C. L. Rice ◽  
J. V. Howarth ◽  
J. J. Woods
Keyword(s):  
Firing Rate ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Human Hand ◽  
Firing Rates ◽  
Hand Muscles ◽  
Fatigued Muscle ◽  
Contractile Parameters ◽  
Contraction And Relaxation ◽  
Voluntary Contractions

A study was made of motoneuron firing rates and mechanical contractile parameters during maximum voluntary contraction of human hand muscles. A comparison of muscles that had been fatigued after a 60-s maximum voluntary contraction (MVC) with muscles that were cooled by approximately 5 degrees C showed that the contractile properties, in particular the rates of contraction and relaxation, were similarly affected in both conditions. In contrast, the motoneuron firing rate was affected differently by the two treatments. In the case of the fatigued muscles the motoneuron firing rate was reduced by 36%, as was expected from previous studies, but in the case of the cooled muscles, there was no significant change in the motoneuron firing rate. We conclude that the reflex reduction in the motoneuron firing rate seen in the fatigued muscle is not triggered directly by a change in the mechanical properties of the muscle.

Physiological Versus Psychological Evaluation in Taekwondo Elite Athletes

2012 ◽  
Vol 7 (4) ◽  
pp. 322-331 ◽  
Author(s):  
Erika Casolino ◽  
Cristina Cortis ◽  
Corrado Lupo ◽  
Salvatore Chiodo ◽  
Carlo Minganti ◽  
...  
Keyword(s):  
Perceived Exertion ◽  
Selection Process ◽  
Elite Athletes ◽  
Training Period ◽  
Ratings Of Perceived Exertion ◽  
Technical Parameters ◽  
Psychological Measures ◽  
National Team ◽  
Blood Lactate Accumulation ◽  
National Training

Purpose:To anticipate outstanding athletic outcomes, the selection process of elite athletes simultaneously considers psychophysiological and technical parameters. This study aimed to investigate whether selected and nonselected athletes for the Italian national taekwondo team could be discriminated by means of sportspecific performances and psychophysiological responses to training.Participants:5 established Italian national athletes and 20 elite Italian taekwondo black belt athletes (9 women, 16 men; age 23.0 ± 3.1 y; body mass 67.0 ± 12.1 kg).Methods:To update the Italian national-team roster, the 20 elite athletes participated in a 1-wk selection camp (7 training sessions). Selected athletes (n = 10) joined established national athletes during the following 3-wk national training period (7 training sessions/wk). During the 1-wk selection camp, differences (P < .05) between selected and nonselected athletes in performances, heart-rate responses, blood lactate accumulation [La], subjective ratings of perceived exertion (session RPE), and mood were examined. During the 3-wk national training period, differences (P < .05) in mood between selected and established national athletes were investigated.Results:With respect to nonselected athletes, selected athletes responded better to training in terms of session RPE (P = .047) and [La] (P = .046). No difference in performance and mood between subgroups emerged. After the 3-wk national training period, differences (P = .035) emerged for confusion, with decreases in the established national athletes and increases for recently selected athletes.Conclusions:Session RPE and [La] seem to be more effective than psychological measures in discriminating between elite taekwondo athletes. Evaluation of mood could be effective in monitoring athletes’ response to national training.

Central and Peripheral Fatigue in Sustained Maximum Voluntary Contractions of Human Quadriceps Muscle

1978 ◽  
Vol 54 (6) ◽  
pp. 609-614 ◽  
Author(s):  
B. Bigland-Ritchie ◽  
D. A. Jones ◽  
G. P. Hosking ◽  
R. H. T. Edwards
Keyword(s):  
Maximum Voluntary Contraction ◽  
Central Fatigue ◽  
Quadriceps Muscle ◽  
Surface Emg ◽  
Voluntary Contraction ◽  
Peripheral Fatigue ◽  
Emg Activity ◽  
Limiting Factor ◽  
Extra Effort ◽  
Voluntary Contractions

1. The fatigue of force that occurs during the first 60 s of a maximum voluntary contraction of the human quadriceps has been examined by comparing the voluntary force with that obtained by brief tetanic stimulation at 50 Hz in nine healthy subjects. In three subjects the voluntary force declined in parallel with the tetanic force whereas in the remainder it fell more rapidly, suggesting that central fatigue was present. 2. For those subjects who showed little or no central fatigue, surface electromyograph (EMG) activity remained approximately constant while the force declined by about 60%. In the others, EMG activity and force declined in parallel but when an extra effort was made the subjects could briefly increase their force and this was accompanied by a proportionately greater increase in EMG activity (generally up to the original value). 3. It is concluded that in sustained maximum voluntary contractions of the quadriceps (a) central fatigue may account for an appreciable proportion of the force loss, (b) surface EMG recordings provide no evidence that neuromuscular junction failure is the limiting factor determining the loss of force in this muscle.

Activation of the insular cortex is affected by the intensity of exercise

1999 ◽  
Vol 87 (3) ◽  
pp. 1213-1219 ◽  
Author(s):  
J. W. Williamson ◽  
R. McColl ◽  
D. Mathews ◽  
M. Ginsburg ◽  
J. H. Mitchell
Keyword(s):  
Perceived Exertion ◽  
Insular Cortex ◽  
Voluntary Contraction ◽  
Distribution Data ◽  
Regional Cerebral Blood ◽  
Ratings Of Perceived Exertion ◽  
Perceived Effort ◽  
Leg Cycling ◽  
Intensity Of Exercise ◽  
Cuff Occlusion

The purpose of this investigation was to determine whether there were differences in the magnitude of insular cortex activation across varying intensities of static and dynamic exercise. Eighteen healthy volunteers were studied: eight during two intensities of leg cycling and ten at different time periods during sustained static handgrip at 25% maximal voluntary contraction or postexercise cuff occlusion. Heart rate, blood pressure (BP), perceived exertion, and regional cerebral blood flow (rCBF) distribution data were collected. There were significantly greater increases in insular rCBF during lower (6.3 ± 1.7%; P < 0.05) and higher (13.3 ± 3.8%; P < 0.05) intensity cycling and across time during static handgrip (change from rest for right insula at 2–3 min, 3.8 ± 1.1%, P < 0.05; and at 4–5 min, 8.6 ± 2.8%, P < 0.05). Insular rCBF was decreased during postexercise cuff occlusion (−5.5 ± 1.2%; P < 0.05) with BP sustained at exercise levels. Right insular rCBF data, but not left, were significantly related, with individual BP changes ( r 2 = 0.80; P < 0.001) and with ratings of perceived exertion ( r 2 = 0.79; P < 0.01) during exercise. These results suggest that the magnitude of insular activation varies with the intensity of exercise, which may be further related to the level of perceived effort or central command.

Psychophysical Measures of Exertion. Are They Muscle Group Dependent?

1995 ◽  
Vol 39 (10) ◽  
pp. 694-698
Author(s):  
Anpin ‘Max» Chin ◽  
Ram R. Bishu ◽  
Susan Hallbeck
Keyword(s):  
Upper Limb ◽  
Perceived Exertion ◽  
Maximum Voluntary Contraction ◽  
Subjective Assessment ◽  
Voluntary Contraction ◽  
Muscle Group ◽  
Muscle Groups ◽  
Male Subjects ◽  
Female Subjects

The purpose of the present study was to evaluate the applicability of the RPE (CR-10) scale for a number of physical exertions which employ only the upper limb with a variety of muscle group sizes and exertion levels. Ten female and ten male subjects performed pinch and pulling tasks in which four different muscle groups were engaged employing the finger, wrist, forearm and the whole arm. MVC (maximum voluntary contraction) exertion levels, RPE (Borg's CR-10 scale) value, and accuracy of the subjective assessment were measured. The results indicate that the accuracy of psychophysical measures are not muscle dependent although force generating capability is dependent on the muscle group involved. Female subjects were found more accurate in their perception of perceived exertion at lower levels of exertion than male subjects. It also appears that the RPE rating can be used to assess a variety of exertion levels accurately for a range of tasks, involving a range of muscle group sizes and location.

scholarly journals Using a System-Based Monitoring Paradigm to Assess Fatigue during Submaximal Static Exercise of the Elbow Extensor Muscles

Sensors ◽  
2021 ◽  
Vol 21 (4) ◽  
pp. 1024
Author(s):  
Kaci E. Madden ◽  
Dragan Djurdjanovic ◽  
Ashish D. Deshpande
Keyword(s):  
Perceived Exertion ◽  
Maximum Voluntary Contraction ◽  
Similarity Index ◽  
Performance Degradation ◽  
Voluntary Contraction ◽  
Dynamic Relationship ◽  
Extension Force ◽  
Synergistic Muscles ◽  
Dynamic Time ◽  
Changes Over Time

Current methods for evaluating fatigue separately assess intramuscular changes in individual muscles from corresponding alterations in movement output. The purpose of this study is to investigate if a system-based monitoring paradigm, which quantifies how the dynamic relationship between the activity from multiple muscles and force changes over time, produces a viable metric for assessing fatigue. Improvements made to the paradigm to facilitate online fatigue assessment are also discussed. Eight participants performed a static elbow extension task until exhaustion, while surface electromyography (sEMG) and force data were recorded. A dynamic time-series model mapped instantaneous features extracted from sEMG signals of multiple synergistic muscles to extension force. A metric, called the Freshness Similarity Index (FSI), was calculated using statistical analysis of modeling errors to reveal time-dependent changes in the dynamic model indicative of performance degradation. The FSI revealed strong, significant within-individual associations with two well-accepted measures of fatigue, maximum voluntary contraction (MVC) force (rrm=−0.86) and ratings of perceived exertion (RPE) (rrm=0.87), substantiating the viability of a system-based monitoring paradigm for assessing fatigue. These findings provide the first direct and quantitative link between a system-based performance degradation metric and traditional measures of fatigue.

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