Effects of Predictability of Load Magnitude on the Response of the Flexor Digitorum Superficialis to a Sudden Fingers Extension

Abstract

Muscle reflexes, evoked by opposing a sudden joint displacement, may be modulated by several factors associated with the features of the mechanical perturbation. We investigated the variations of muscle reflex response in relation to the predictability of load magnitude during a reactive grasping task. Subjects were instructed to flex the fingers 2–5 very quickly after a stretching was exerted by a handle pulled by loads of 750 or 1250 g. Two blocks of trials, one for each load (predictable condition), and one block of trials with a randomized distribution of the loads (unpredictable condition) were performed. Kinematic data were collected by an electrogoniometer attached to the middle phalanx of the digit III while the electromyography of the Flexor Digitorum Superficialis muscle was recorded by surface electrodes. For each trial we measured the kinematics of the finger angular rotation, the latency of muscle response and the level of muscle activation recorded below 50 ms (short-latency reflex), between 50 and 100 ms (long-latency reflex) and between 100 and 140 ms (initial portion of voluntary response) from the movement onset. We found that the latency of the muscle response lengthened from predictable (35.5±1.3 ms for 750 g and 35.5±2.5 ms for 1250 g) to unpredictable condition (43.6±1.3 ms for 750 g and 40.9±2.1 ms for 1250 g) and the level of muscle activation increased with load magnitude. The parallel increasing of muscle activation and load magnitude occurred within the window of the long-latency reflex during the predictable condition, and later, at the earliest portion of the voluntary response, in the unpredictable condition. Therefore, these results indicate that when the amount of an upcoming perturbation is known in advance, the muscle response improves, shortening the latency and modulating the muscle activity in relation to the mechanical demand.

Effects of Functional Electrical Stimulation Cycling of Different Duration on Viscoelastic and Electromyographic Properties of the Knee in Patients with Spinal Cord Injury

“…In particular, for each EMG signal, the TKEO was applied on the 20 Hz high pass filtered raw signal and the TKEO output was full wave rectified. To find the threshold that allowed to determine the onset time over the TKEO domain, we used formulas and procedures present in our previous work [ 44 ].…”

Postural Adjustments Following ACL Rupture and Reconstruction: A Longitudinal Study

“…If irregularities occurred for two or fewer trials, new trials were performed. Participants who performed incorrect trials more than two times were excluded from the analysis to minimise the learning effect [1]. Successive trials were separated by a minimum of 60 s. The participants were allowed to rest 5 min between series.…”

Stimulus Prediction and Postural Reaction: Phase-Specific Modulation of Soleus H-Reflexes Is Related to Changes in Joint Kinematics and Segmental Strategy in Perturbed Upright Stance

“…Second, when compensating for an unpredictable stimulus, proactive postural adjustments are absent and reactive compensatory responses predominate. Studies show a gradually increased sway path (Jacobs et al, 2008; Santos et al, 2010; Kanekar and Aruin, 2014a,b), augmented magnitude, timing differences (Aimola et al, 2014), variability of the postural response (Okai and Fujiwara, 2013; Kanekar and Aruin, 2014a,b), modified sensory processing (Kourtis et al, 2008), changes in neuromuscular activation reflected by delayed neuromuscular responses (McChesney et al, 1996), and modulated spinal (Burleigh-Jacobs et al, 1997) and supraspinal contributions (Adkin et al, 2006; Jacobs et al, 2008), which are also related to an increased fall and injury incidence (Mawston et al, 2007; Gehring et al, 2014; Pater et al, 2015). Furthermore, a shift in balance strategy could be observed.…”