Effect of fatigue on force fluctuations in knee extensors in young adults

Abstract

This study investigated the hypothesis that fatiguing exercises led to increased force fluctuations during submaximal isometric knee extensions and to decreased accuracy and steadiness in the time and frequency domains. Sixteen young adults (eight males, eight females) were tested, in a seated posture with 90°knee flexion, to assess their ability to reproduce target extensor torques set at 15 per cent and 20 per cent of their maximum voluntary isometric contraction, both before and after fatiguing exercises. Normalized mean (NMAE) and peak (NPAE) of the absolute error were both used to quantify accuracy, whereas normalized standard deviation of the absolute error (NSAE) was used to quantify steadiness of the torque trials in the time domain. Mean and median power frequencies (MnPF, MdPF) and normalized peak power (NPkP) were used to assess the spectral structure of the torque signals. NMAE, NSAE and NPAE all showed excellent intra-as well as intersession reliabilities (intraclass correlation values greater than 0.75 and low standard error of measurement values), demonstrating repeatability of the test set-up. NMAE, NSAE and NPAE increased significantly postfatigue (greater than 42%), together with a shift towards higher frequency (MnPF and MdPF) components, indicating that the set-up was sensitive enough to detect the decreased force accuracy and steadiness of the musculature after fatigue. Increased force variability in both the time and frequency domains could therefore explain decreased steadiness after fatigue.

Increase in joint stability at the expense of energy efficiency correlates with force variability during a fatiguing task

“…Increases in muscular cocontraction and stiffness with force variability spurred us to examine the relationship between w and force variability. Similar to Reeves et al (2008) and Singh et al (2010), we found that force variability measures in the time domain (F CV ) increased with fatigue for all contraction intensities. Furthermore, we found that greater F CV corresponded with increased cocontraction intensity for 8 of the 10 windows.…”

“…We found that F MPF decreased with fatigue and contraction intensity. Singh et al (2010) in F MPF with contraction intensity, but found that F MPF increased with fatigue. Differences between our studies include the examined joint (elbow vs. knee) and tested contraction intensities (40%, 70%, and 100% vs. 15% and 20%).…”

“…During fatiguing isometric contractions, many researchers have noted increases in force variability (Reeves et al, 2008;Singh et al, 2010) and muscle cocontraction (Psek and Cafarelli, 1993;O'Brien and Potvin, 1996;Potvin and O'Brien, 1998;Reeves et al, 2008). There is evidence that cocontraction may help stabilize our joints during load-bearing tasks (Lee et al, 2006;Potvin and O'Brien, 1998;Reeves et al, 2008), but is energetically costly and increases the rate of fatigue (Hogan, 1984;Cholewicki and McGill, 1996).…”

Kinematic measures for assessing gait stability in elderly individuals: a systematic review

“…Here, stability parameters not only provide information regarding the noise present in the motor task performance, but also explicitly quantify the performance of the dynamic error correction. On the other hand, variability during specific tasks results from noise present in the motor task and in the environment [56][57][58]. In addition, variability will increase at a given noise level when error corrections are less effective.…”

The virtual physiological human: computer simulation for integrative biomedicine I

“…Levels of investigation range from the tissue level, as in 'Trabecular bone remodelling simulation considering osteocytic response to fluid-induced shear stress' (Adachi et al 2010) and 'In silico design of treatment strategies in wound healing and bone fracture healing' (Geris et al 2010), to the whole organ, as in 'Predicting the yield of the proximal femur using highorder finite-element analysis with inhomogeneous orthotropic material properties' (Yosibash et al 2010) and 'Mechanical testing of bones: the positive synergy of finite-element models and in vitro experiments' (Cristofolini et al 2010) or even the entire organ system, as in 'Influence of fatigue on the simulated relation between the amplitude of the surface electromyogram and muscle force' (Dideriksen et al 2010) and 'Effect of fatigue on force fluctuations in knee extensors in young adults' (Singh et al 2010). All papers share the integrative approach that is characteristic of VPH research.…”