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Start Over Descriptor "contractile slowing" Topic fatigue
2 results on '"contractile slowing"'

1. The influence of muscle length on the fatigue-related reduction in joint range of motion of the human dorsiflexors.

Author

Cheng, Arthur J., Davidson, Andrew W., and Rice, Charles L.

Subjects
*RANGE of motion of joints, *FATIGUE (Physiology), *TETANUS, *YOUNG men, *ANAEROBIC infections, *JOINT physiology, *SKELETAL muscle physiology, *SKELETAL muscle, *COMPARATIVE studies, *CONVALESCENCE, *DYNAMICS, *KINEMATICS, *LEG, *RESEARCH methodology, *MEDICAL cooperation, *MUSCLE contraction, *MUSCLE strength, *RESEARCH, *TORQUE, *TRANSCUTANEOUS electrical nerve stimulation, *EVALUATION research, *MUSCLE fatigue, *ANATOMY
Abstract

The fatigue-related reduction in joint range of motion (ROM) during dynamic contraction tasks may be related to muscle length-dependent alterations in torque and contractile kinetics, but this has not been systematically explored previously. Twelve young men performed a repetitive voluntary muscle shortening contraction task of the dorsiflexors at a contraction load of 30% of maximum voluntary isometric contraction (MVC) torque, until total 40 degrees ROM had decreased by 50% at task failure (POST) to 20 degrees ROM. At both a short (5 degrees dorsiflexion) and long muscle length (35 degrees plantar flexion joint angle relative to a 0 degrees neutral ankle joint position), voluntary activation, MVC torque, and evoked tibialis anterior contractile properties of a 52.8 Hz high-frequency isometric tetanus [peak evoked torque, maximum rate of torque development (MRTD), maximum rate of relaxation (MRR)] were evaluated at baseline (PRE), at POST, and up to 10 min of recovery. At POST, we measured similar fatigue-related reductions in torque (voluntary and evoked) and slowing of contractile kinetics (MRTD and MRR) at both the short and long muscle lengths. Thus, the fatigue-related reduction in ROM could not be explained by length-dependent fatigue. Although torque (voluntary and evoked) at both muscle lengths was depressed and remained blunted throughout the recovery period, this was not related to the rapid recovery of ROM at 0.5 min after task failure. The reduction in ROM, however, was strongly related to the reduction in joint angular velocity (R(2) = 0.80) during the fatiguing task, although additional factors cannot yet be overlooked. [ABSTRACT FROM AUTHOR]

Published
2010
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2. INVESTIGATIONS INTO THE FATIGUE-RELATED REDUCTION IN TORQUE, SHORTENING VELOCITY, AND JOINT RANGE OF MOTION IN HUMANS

Author

Cheng, Arthur J.

Subjects
shortening velocity, contractile slowing, tibialis anterior, torque, fatigue, voluntary activation, dynamic contraction, triceps brachii, isometric contraction, range of motion, soleus
Abstract

Studies in humans and animals have derived much understanding of neuromuscular function from isometric (static) contractions. In comparison, fewer studies have evaluated dynamic contractions, which are relevant to everyday movements and activities of daily living. The primary purpose of this thesis was to investigate and compare the contributing factors to fatigue during different voluntary contraction tasks. The interpolated twitch technique is commonly used to assess voluntary activation, but with changes in muscle length, musculotendinous slackness can diminish the amplitude of electrically-evoked twitches used to calculate voluntary activation. This might result in erroneous measurements of voluntary activation. Chapter 2 describes an experiment in which at the short muscle lengths, when voluntary activation is 80% or lower, actual activation will be underestimated. Maximum voluntary isometric contraction (MVC) torque is often used to assess overall neuromuscular function, and any activity-induced decline in MVC torque is indicative of fatigue. However, a reduction in shortening velocity is also an important feature of fatigue. Results from Chapter 3 indicate that shortening velocity was an important and perhaps more sensitive measure of fatigue following both isometric and dynamic contraction tasks than MVC torque per se. These findings are further supported in Chapter 4, in which, following comparable repetitive shortening contraction tasks in two different muscles, shortening velocity was reduced to a greater extent at task failure but was restored more rapidly than MVC torque. Shortening contractions are also characterized by a fatigue-related reduction in joint range of motion (ROM) and it was suggested that the reduction in ROM might be due to length-dependent alterations in torque or contractile slowing with fatigue. Results iii presented in Chapter 5, suggest that length-dependent alterations in torque or contractile slowing cannot explain the fatigue-related reduction in dorsiflexion ROM. Thus, in addition to fatigue-related reductions in torque, decreases in shortening velocity and joint range of motion are important indicators of a fatigue-induced impairment in muscle shortening capacity.

Published
2010

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