Electromechanical delay in isometric muscle contractions evoked by voluntary, reflex and electrical stimulation

Abstract

Electromechanical delay (EMD) in isometric contractions of knee extensors evoked by voluntary, tendon reflex (TR) and electrical stimulation (ES) was investigated in 21 healthy young subjects. The subject performed voluntary knee extensions with maximum effort (maximal voluntary contraction, MVC), and at 30%, 60% and 80% MVC. Patellar tendon reflexes were evoked with the reflex hammer being dropped from 60 degrees, 75 degrees and 90 degrees positions. In the percutaneous ES evoked contractions, single switches were triggered with pulses of duration 1.0 ms and of intensities 90, 120 and 150 V. Electromyograms of the vastus lateralis and rectus femoris muscles were recorded using surface electrodes. The isometric knee extension force was recorded using a load cell force transducer connected to the subject's lower leg. The major finding of this study was that EMD of the involuntary contractions [e.g. mean 22.1 (SEM 1.32) ms in TR 90 degrees; mean 17.2 (SEM 0.62) ms in ES 150 V] was significantly shorter than that of the voluntary contractions [e.g. mean 38.7 (SEM 1.18) ms in MVC, P < 0.05]. The relationships between EMD, muscle contractile properties and muscle fibre conduction velocity were also investigated. Further study is needed to explain fully the EMD differences found between the voluntary and involuntary contractions.

Effects of acute fatigue on the volitional and magnetically-evoked electromechanical delay of the knee flexors in males and females

“…While metabolically mediated increases in sensitivity of muscle contractile proteins to Ca 2+ may represent the processes underlying potentiated muscle force characteristics (Rassier and MacIntosh 2000), exercise-related changes to the compliance characteristics of the musculoskeletal system may represent the principal potentiating processes in the present study. This may be particularly true considering that the major proportion of EMD is accounted for by lengthening of the SEC (Komi 1979;Zhou et al 1995).…”

“…The net result following acute volitional muscle fatigue may be a 'reserve capacity' of unused motor units that can be deployed during perceived threat to the joint system. The utility of this preserved emergency capacity to the individual athlete may be dependent entirely, however, on the downregulation of these potential protective central and peripheral neuromuscular inhibitory mechanisms (Hopkins and Ingersoll 2000) that appear to limit access to the full capacity of large high threshold motor units under voluntary conditions (Tsuji and Nakamura 1988;Zhou et al 1995). This inhibition may be exemplified by the longer latencies associated with EMD V (e.g.…”

Voluntary Pilot Action Through Biodynamics for Helicopter Flight Dynamics Simulation

“…The actual muscle elongation demand is filtered by a low-pass filter that includes an electromechanical delay of about 50 ms, H NMD (s) (values between 10 and 120 ms are reported in the literature, see for example [45]). The filtered muscle elongation demand is added to the reference muscle elongation used in the quasi-steady approximation of the reflexive activation of Eq.…”

Influence of Simulated Microgravity on Mechanical Properties in the Human Triceps Surae Muscle in vivo

“…"Slack" tissues require more time from the moment of activation to the start of force generation, i.e. their EMD is longer and it is shortened when muscle stiffness is increased before muscle tension (Norman and Komi 1979;Vos et al 1991;Zhou et al 1995;Orizio et al 1999Orizio et al , 2003. Therefore, the EMD may become a criterion for the differences in stiffness of the musculo-tendinous complex (MTC) under different conditions.…”