Endurance time characteristics of human ankle dorsiflexors and plantarflexors

1995 ◽  
Vol 71 (2-3) ◽  
pp. 124-130 ◽  
Author(s):  
A. V. Shahidi ◽  
P. A. Mathieu
Keyword(s):  
Endurance Time ◽  
Human Ankle ◽  
Ankle Dorsiflexors

Muscle stiffness in human ankle dorsiflexors: intrinsic and reflex components

1988 ◽  
Vol 60 (3) ◽  
pp. 1110-1121 ◽  
Author(s):  
T. Sinkjaer ◽  
E. Toft ◽  
S. Andreassen ◽  
B. C. Hornemann
Keyword(s):  
Mechanical Response ◽  
Voluntary Contraction ◽  
Muscle Stiffness ◽  
Flexor Muscle ◽  
Muscle Properties ◽  
Decerebrate Cat ◽  
Human Ankle ◽  
Cross Bridges ◽  
Intrinsic Stiffness ◽  
Ankle Dorsiflexors

1. The purpose of this study was to evaluate the mechanical response to stretch in normal human ankle dorsiflexors at different levels of voluntary contraction. In an active muscle, the total mechanical response is the sum of the intrinsic response from the contractile apparatus, the response from passive tissues, and the reflex mediated response. Each of these components was investigated. 2. The total incremental stiffness was defined as the ratio between the torque increment and the amplitude of the stretch. In 14 subjects the total stiffness increased from approximately 0.6 N.m/deg to approximately 2.5 N.m/deg at 50% of MVC and remained constant (+/- 10%) from 30 to 80% of MVC. 3. The contribution to incremental stiffness from intrinsic muscle properties was measured during electrical stimulation of the deep peroneal nerve at 7-50 Hz. Intrinsic stiffness increased linearly with torque from approximately 0.5 N.m/deg to approximately 2.5 N.m/deg at 80% of MVC. 4. The reflex component (total minus intrinsic stiffness) had a maximum of 0.5-1.5 N.m/deg at 30-50% of MVC and was approximately zero at no and maximal contraction. For intermediate levels of contraction the reflex increased the stiffness with 40-100% of the intrinsic stiffness in this flexor muscle. 5. The reflex contribution to total stiffness began approximately 50 ms after onset of stretch and peaked 150-300 ms after onset of stretch. 6. Total, intrinsic, and reflex mediated stiffness were all nearly independent of the amplitude of stretch in the range from 2 to 7 degrees. The higher stiffness observed for 1 degree stretches could be due to "short range stiffness" of the cross bridges. 7. Stretching of a contracting muscle generates large force increments even for moderate amplitudes of stretch. Approximately half of this force increment is due to the stretch reflex, which makes the muscle stiffer than predicted from the intrinsic stiffness. These findings in human flexor muscles are surprisingly similar to previous findings in extensor muscles of the decerebrate cat.

An Evaluation of the Length-Tension Relationship in Elderly Human Ankle Dorsiflexors

1994 ◽  
Vol 49 (3) ◽  
pp. B121-B127 ◽  
Author(s):  
C. S. van Schaik ◽  
A. L. Hicks ◽  
N. McCartney
Keyword(s):  
Human Ankle ◽  
Ankle Dorsiflexors

Skin Cooling on Breath-Hold Duration and Predicted Emergency Air Supply Duration During Immersion

2020 ◽  
Vol 91 (7) ◽  
pp. 578-585
Author(s):  
Victory C. Madu ◽  
Heather Carnahan ◽  
Robert Brown ◽  
Kerri-Ann Ennis ◽  
Kaitlyn S. Tymko ◽  
...  
Keyword(s):  
Minute Ventilation ◽  
Hold Time ◽  
Whole Body ◽  
Breath Hold ◽  
Endurance Time ◽  
Skin Exposure ◽  
Breathing Apparatus ◽  
Air Supply ◽  
Skin Cooling ◽  
Breath Hold Duration

PURPOSE: This study was intended to determine the effect of skin cooling on breath-hold duration and predicted emergency air supply duration during immersion.METHODS: While wearing a helicopter transport suit with a dive mask, 12 subjects (29 ± 10 yr, 78 ± 14 kg, 177 ± 7 cm, 2 women) were studied in 8 and 20°C water. Subjects performed a maximum breath-hold, then breathed for 90 s (through a mouthpiece connected to room air) in five skin-exposure conditions. The first trial was out of water for Control (suit zipped, hood on, mask off). Four submersion conditions included exposure of the: Partial Face (hood and mask on); Face (hood on, mask off); Head (hood and mask off); and Whole Body (suit unzipped, hood and mask off).RESULTS: Decreasing temperature and increasing skin exposure reduced breath-hold time (to as low as 10 ± 4 s), generally increased minute ventilation (up to 40 ± 15 L · min−1), and decreased predicted endurance time (PET) of a 55-L helicopter underwater emergency breathing apparatus. In 8°C water, PET decreased from 2 min 39 s (Partial Face) to 1 min 11 s (Whole Body).CONCLUSION: The most significant factor increasing breath-hold and predicted survival time was zipping up the suit. Face masks and suit hoods increased thermal comfort. Therefore, wearing the suits zipped with hoods on and, if possible, donning the dive mask prior to crashing, may increase survivability. The results have important applications for the education and preparation of helicopter occupants. Thermal protective suits and dive masks should be provided.Madu VC, Carnahan H, Brown R, Ennis K-A, Tymko KS, Hurrie DMG, McDonald GK, Cornish SM, Giesbrecht GG. Skin cooling on breath-hold duration and predicted emergency air supply duration during immersion. Aerosp Med Hum Perform. 2020; 91(7):578–585.

Application of the endurance time methodology on seismic analysis and performance assessment of hydraulic arched tunnels

2021 ◽  
Vol 115 ◽  
pp. 104022
Author(s):  
Benbo Sun ◽  
Mingjiang Deng ◽  
Sherong Zhang ◽  
Chao Wang ◽  
Yang Li ◽  
...  
Keyword(s):  
Performance Assessment ◽  
Seismic Analysis ◽  
Endurance Time ◽  
And Performance

Design, Development, and Control of a Fabric-Based Soft Ankle Module to Mimic Human Ankle Stiffness

2019 ◽  
Author(s):  
Sunny Amatya ◽  
Amir Salimi Lafmejani ◽  
Souvik Poddar ◽  
Saivimal Sridar ◽  
Thomas Sugar ◽  
...  
Keyword(s):  
Design Development ◽  
Ankle Stiffness ◽  
Human Ankle ◽  
And Control

Reproducibility of velocity-dependent power: before and after lengthening contractions

2011 ◽  
Vol 36 (5) ◽  
pp. 626-633 ◽  
Author(s):  
Geoffrey A. Power ◽  
Brian H. Dalton ◽  
Charles L. Rice ◽  
Anthony A. Vandervoort
Keyword(s):  
Peak Power ◽  
High Reliability ◽  
Similar Amount ◽  
Shortening Velocity ◽  
Lengthening Contractions ◽  
Isokinetic Testing ◽  
Typical Error ◽  
Before And After ◽  
Absolute Reliability ◽  
Ankle Dorsiflexors

The determination of power using isokinetic testing has been shown to be highly reliable. However, isotonic and isokinetic testing involve specific mechanical constraints that likely necessitate different neuromuscular strategies. Therefore, the purpose here was to establish test–retest intrarater reliability (separated by 7 days) of loaded maximal shortening velocity and velocity-dependent power of the ankle dorsiflexors using the isotonic mode of the Biodex dynamometer (i) at baseline and (ii) throughout recovery following 150 high-intensity lengthening contractions. Intraclass correlation coefficients (ICC)2,1 with 95% CIs were used to determine relative reliability, whereas absolute reliability included typical error (TEM) and typical error expressed as a coefficient of variation (TEMCV). Twenty-four young men and women volunteered for the study. Maximal shortening velocity and power were determined with a fixed resistance set at 20% of maximal voluntary isometric contraction across 2 testing sessions separated by 7 days. ICCs were 0.93 and 0.98 for maximal shortening velocity and peak power, respectively. Following the lengthening contractions, ICCs indicated high reliability for maximal shortening velocity and peak power, 0.86 and 0.94, respectively, suggesting that a similar amount of fatigue was incurred on both days. Measures of absolute reliability for maximal shortening velocity and peak power also yielded high reliability. The isotonic mode is highly reliable when testing velocity-dependent power of the ankle dorsiflexors at baseline and following fatiguing lengthening contractions. The high reliability of this measure is encouraging and suggests that the isotonic mode can be used in various settings to track group changes before and after training and following fatigue and lengthening contractions.

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