Comparison of prolonged low-frequency force depression assessed using isometric torque and isotonic power following a dynamic fatiguing task

Paris, Michael T.; Zero, Alexander M.; Rice, Charles L.

doi:10.1007/s00421-022-05042-x

Cited by 4 publications

(2 citation statements)

References 32 publications

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“…The PAP response observed here was similar to prior reports from the dorsiflexors following an acute (<10 s) MVC (Baudry & Duchateau, 2004;Zero & Rice, 2021b). Furthermore, PLFFD assessed during the recovery from the sustained task was comparable to past reports in the human lower limb (Paris et al, 2022;Ruggiero et al, 2021;Skurvydas et al, 2016). During PAP, contractile properties are enhanced primarily due to increased Ca 2+ sensitivity and this effect is frequency dependent during isometric contractions (MacIntosh & Willis, 2000;Persechini et al, 1985;Sweeney et al, 1993;Vandenboom, 2017).…”

Section: Discussionsupporting

confidence: 88%

Acute and prolonged competing effects of activation history on human motor unit firing rates during contractile impairment and recovery

Zero,

Fanous,

Rice

2023

The Journal of Physiology

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The purpose of this study was to investigate the effect of inducing post‐activation potentiation (PAP) during prolonged low‐frequency force depression (PLFFD) on motor unit (MU) firing rates. In 10 participants, grouped firing rates of 3027 MUs from the tibialis anterior were recorded with tungsten microelectrodes. Baseline MU firing rates at 25% isometric maximal voluntary contraction (MVC) were ∼14 Hz. A 1 min dorsiflexion MVC reduced torque and maximal MU firing rates (36 Hz) by 49% and 52%, respectively. Following task completion, firing rates at 25% of baseline MVC torque and torque in response to electrically evoked (single twitch, 10 Hz and 50 Hz) stimulation were assessed before and after a 5 s MVC (to induce PAP) every 10 min for 60 min. From 10 to 60 min after task completion, the torque ratios (twitch:50 Hz and 10:50 Hz) were depressed (∼30%) relative to baseline (P < 0.001), indicating PLFFD; and firing rates were higher by ∼15% relative to baseline (P < 0.001). This occurred despite recovery of MVC rates (∼99%) and torque (∼95%) by 10 min (P > 0.3). Inducing PAP during PLFFD increased both low to high torque ratios (twitch and 10:50 Hz) by ∼200% and ∼135%, respectively (P < 0.001) and firing rates were ∼18% lower relative to PLFFD rates (P < 0.001), despite a speeding of evoked contractile properties (P = 0.001). Thus, firing rates appear strongly matched to alterations in torque, rather than contractile speed when modified by contractile history, and lower rates during PAP may be a mechanism to mitigate effects of PLFFD. The effect of activation history on contractile function demonstrates acute compensatory responses of motoneuron output. imageKey points Prolonged low frequency force depression (PLFFD) following a sustained 1 min isometric maximal voluntary contraction causes an increase in submaximal mean motor unit (MU) firing rates. Inducing post‐activation potentiation (PAP) during PLFFD, however, causes a reduction in mean submaximal MU firing rates to a level below those at baseline. The mean firing rate reduction during PAP occurs despite a speeding of evoked contractile properties and thus firing rates are more strongly matched to alterations in torque, rather than contractile speed when modified by various contractile histories. The reductions in firing rates during PAP may mitigate the effects of PLFFD during voluntary contractions. These results demonstrate that firing rates are highly responsive to opposing influences on the contractile state and can make rapid compensatory rate adjustments dependent on the active state of the muscle.

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Section: Discussionsupporting

confidence: 88%

Acute and prolonged competing effects of activation history on human motor unit firing rates during contractile impairment and recovery

Zero,

Fanous,

Rice

2023

The Journal of Physiology

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“…Peripheral nerve stimulation and ITT are frequently applied using static (i.e., isometric) contractions during and after a fatiguing task. However, fatigability is task dependent (5), and reductions in isometric torque may not be representative of decreases in power (torque-angular velocity) production during dynamic (i.e., shortening or lengthening) contractions (6)(7)(8). Thus, assessing peripheral and central factors after a dynamic fatiguing task by evaluating the isometric ITT or evoked isometric torque may not capture velocity-and power-dependent impairments within the neuromuscular system.…”

mentioning

confidence: 99%

Electrically Evoked Isotonic Plantar Flexion Contractions Are Impaired Less than Voluntary After a Dynamic Fatiguing Task

Paris

Kulkarni

Rice

2023

Medicine &Amp; Science in Sports &Amp; Exercise

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Purpose: Evaluating central and peripheral processes responsible for reduced power after dynamic fatiguing tasks are often limited to isometric torque, which may not accurately reflect dynamic contractile performance. Here, we compare voluntary and electrically evoked peak power (and its determinants: dynamic torque and velocity) and rate of velocity development (RVD) before and after a dynamic fatiguing task using concentric Plantar flexion contractions. Methods: Young (18-32 yr) males (n = 11) and females (n = 2) performed maximal-effort isotonic Plantar flexion contractions using a load of 20% isometric torque until an approximately 75% reduction in peak power. Voluntary and electrically evoked (300 Hz tibial nerve stimulation) contractions loaded to 20% and 40% isometric torque through 25°ankle joint range of motion were compared before and 0, 2.5, 5, and 10 min after task termination. Results: At task termination, peak power and RVD of voluntary contractions at both loads were reduced more (~40% to 50% reduction) than electrically evoked (~25% to 35% reduction) contractions (P < 0.001 and P = 0.003). Throughout the recovery period, electrically evoked peak power and RVD returned to baseline sooner (<5 min) than voluntary contractions, which were still depressed at 10 min. Reductions in peak power for the 20% load were equally due to impaired dynamic torque and velocity, whereas velocity was impaired more than dynamic torque (P < 0.001) for the 40% load. Conclusions: The relative preservation of electrically evoked power and RVD compared with voluntary contractions at task termination and quicker recovery to baseline indicates that the reductions in dynamic contractile performance after task termination are due to both central and peripheral processes; however, the relative contribution of dynamic torque and velocity is load dependent.

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Differential effects of stimulation frequency on isometric and concentric isotonic contractile function in human quadriceps

Zero,

Paris,

Rice

2024

Journal of Applied Physiology

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Electrically evoked contractions are used to assess the relationship between frequency input and contractile output to characterize inherent muscle function, and these have been done mostly with isometric contractions (i.e., no joint rotation). The purpose was to compare the electrically stimulated frequency and contractile function relationship during isometric (i.e., torque) with isotonic (i.e., concentric torque, angular velocity, and mechanical power) contractions. The knee extensors of 16 (5 female) young recreationally active participants were stimulated (~1-2.5s) at 14 frequencies from 1-100 Hz. This was done during four conditions, repeated on separate days, which were: isometric; and isotonic at loads of 0, 7.5 and 15% isometric maximal voluntary contraction (MVC). Comparisons across contractile parameters were made as a % of 100 Hz. Independent of the load, the mechanical power-frequency relationship was rightward shifted compared with isometric torque-, concentric torque- and velocity-frequency relationships (all p≤0.04). With increasing load (0-15% MVC) the isotonic concentric torque-frequency relationship was shifted leftward systematically from 15-30 Hz (all p≤0.04). Conversely, the same changes in load caused a rightward shift in the velocity-frequency relationship from 1-40 Hz (all p≤0.03). Velocity was leftward shifted of concentric torque in the unloaded isotonic condition from 10-25 Hz (all p≤0.03), but concentric torque was leftward shifted of velocity at 15% MVC isotonic condition from 10-50 Hz (all p≤0.03). Therefore, isometric torque is not a surrogate to evaluate dynamic contractile function. Interpretations of evoked contractile function differ depending on contraction type, load, and frequency which should be considered relative to the specific task.

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Comparison of prolonged low-frequency force depression assessed using isometric torque and isotonic power following a dynamic fatiguing task

Cited by 4 publications

References 32 publications

Acute and prolonged competing effects of activation history on human motor unit firing rates during contractile impairment and recovery

Acute and prolonged competing effects of activation history on human motor unit firing rates during contractile impairment and recovery

Electrically Evoked Isotonic Plantar Flexion Contractions Are Impaired Less than Voluntary After a Dynamic Fatiguing Task

Differential effects of stimulation frequency on isometric and concentric isotonic contractile function in human quadriceps

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