Uncertainty of knee joint muscle activity during knee joint torque exertion: The significance of controlling adjacent joint torque

Dept. of Rehabilitation for Movement Functions, Research Institute NRCD, 4-1 Namiki, Tokorozawa, Saitama 359-8555, Japan.
Journal of Applied Physiology (Impact Factor: 3.06). 10/2005; 99(3):1093-103. DOI: 10.1152/japplphysiol.00365.2005
Source: PubMed


In the single-joint torque exertion task, which has been widely used to control muscle activity, only the relevant joint torque is specified. However, the neglect of the neighboring joint could make the procedure unreliable, considering our previous result that even monoarticular muscle activity level is indefinite without specifying the adjacent joint torque. Here we examined the amount of hip joint torque generated with knee joint torque and its influence on the activity of the knee joint muscles. Twelve healthy subjects were requested to exert various levels of isometric knee joint torque. The knee and hip joint torques were obtained by using a custom-made device. Because no information about hip joint torque was provided to the subjects, the hip joint torque measured here was a secondary one associated with the task. The amount of hip joint torque varied among subjects, indicating that they adopted various strategies to achieve the task. In some subjects, there was a considerable internal variability in the hip joint torque. Such variability was not negligible, because the knee joint muscle activity level with respect to the knee joint torque, as quantified by surface electromyography (EMG), changed significantly when the subjects were requested to change the strategy. This change occurred in a very systematic manner: in the case of the knee extension, as the hip flexion torque was larger, the activity of mono- and biarticular knee extensors decreased and increased, respectively. These results indicate that the conventional single knee joint torque exertion has the drawback that the intersubject and/or intertrial variability is inevitable in the relative contribution among mono- and biarticular muscles because of the uncertainty of the hip joint torque. We discuss that the viewpoint that both joint torques need to be considered will bring insights into various controversial problems such as the shape of the EMG-force relationship, neural factors that help determine the effect of muscle strength training, and so on.

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Available from: Kimitaka Nakazawa
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    • "The two other participants (5 and 10) exhibited a decrease in the modulus of the three measured muscles, suggesting compensation with VI. It is important to note that, although care was taken to minimize changes in body position throughout the experiment (see MATERIALS AND METHODS), we cannot exclude the contribution of the hip extensors to the knee extension torque produced, as previously reported by Nozaki et al. (2005). This is particularly important, as the elastographic measurements and the stimulation electrodes did not allow us to strap the right thigh. "
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    ABSTRACT: The present study aimed to investigate the effects of selective fatigue (i.e. one muscle of the quadriceps) on load sharing strategies during submaximal knee extensions. Shear wave elastography was used to measure muscle shear elastic modulus as this is considered to be an index of individual muscle force. Sixteen participants attended 2 experimental sessions that each involved 6 × 10 s knee extensions at 20% of maximal voluntary contraction (MVC) followed by a sustained submaximal isometric knee extension at 20% of MVC, until task failure (Tlim). Between the 10 s contractions and Tlim, participants were required to rest (5 min) for control session or underwent 5 min of electromyostimulation on vastus lateralis (EMS session). When compared to the control session, vastus lateralis shear elastic modulus values were significantly lower after EMS considering both the start of Tlim (54.6 ± 11.8 kPa vs. 68.4 ± 19.2; P=0.011) and the entire Tlim contraction (59.0 ± 14.0 vs. 74.4 ± 20.3 kPa; P=0.019). However, no significant differences were observed for the other recorded muscles (vastus medialis and rectus femoris, all P values=1), i.e., different patterns of changes were found between participants. In conclusion, this study demonstrates that pre-fatiguing a single agonist muscle does not lead to a consistent redistribution of load sharing among the quadriceps muscles between individuals. These results suggest that the central nervous system does not use a common principle among individuals to control load sharing when neuromuscular fatigue occurs.
    Full-text · Article · Nov 2013 · Journal of Neurophysiology
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    • "Stabiliser activation was not measured within the present study, but is thought to be important for optimal force expression [26]. For instance, Nozaki et al. [27] demonstrated that even during a relatively simple task such as an isometric knee extension used within the current study, that there was a large variation, both between and within-participants in the ability to stabilise the adjacent joint torque through effective inter-muscular coordination. The greater postural requirement for BL than UL strength tasks has been proposed as the mechanism accounting for the BLD in MVF [14]. "
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    ABSTRACT: Bilateral deficit (BLD) describes the phenomenon of a reduction in performance during synchronous bilateral (BL) movements when compared to the sum of identical unilateral (UL) movements. Despite a large body of research investigating BLD of maximal voluntary force (MVF) there exist a paucity of research examining the BLD for explosive strength. Therefore, this study investigated the BLD in voluntary and electrically-evoked explosive isometric contractions of the knee extensors and assessed agonist and antagonist neuromuscular activation and measurement artefacts as potential mechanisms. Thirteen healthy untrained males performed a series of maximum and explosive voluntary contractions bilaterally (BL) and unilaterally (UL). UL and BL evoked twitch and octet contractions were also elicited. Two separate load cells were used to measure MVF and explosive force at 50, 100 and 150 ms after force onset. Surface EMG amplitude was measured from three superficial agonists and an antagonist. Rate of force development (RFD) and EMG were reported over consecutive 50 ms periods (0-50, 50-100 and 100-150 ms). Performance during UL contractions was compared to combined BL performance to measure BLD. Single limb performance during the BL contractions was assessed and potential measurement artefacts, including synchronisation of force onset from the two limbs, controlled for. MVF showed no BLD (P = 0.551), but there was a BLD for explosive force at 100 ms (11.2%, P = 0.007). There was a BLD in RFD 50-100 ms (14.9%, P = 0.004), but not for the other periods. Interestingly, there was a BLD in evoked force measures (6.3-9.0%, P<0.001). There was no difference in agonist or antagonist EMG for any condition (P≥0.233). Measurement artefacts contributed minimally to the observed BLD. The BLD in volitional explosive force found here could not be explained by measurement issues, or agonist and antagonist neuromuscular activation. The BLD in voluntary and evoked explosive force might indicate insufficient stabiliser muscle activation during BL explosive contractions.
    Full-text · Article · Mar 2013 · PLoS ONE
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    • "Volunteers were encouraged to develop mental strategies, mostly involving visualization of the requested torque in a real-world scenario, which maximized the isolation of the torque. Feedback and instruction has a large influence on performance; Nozaki and colleagues, using a similar force cell apparatus, have shown that it is possible to reverse the associated torque at the hip joint during knee torque generation by providing verbal feedback about how to alter their strategy for generating knee extension (Nozaki et al., 2005). "
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    ABSTRACT: This study describes the use of a novel magnetic resonance imaging (MRI) compatible system capable of measuring isometric ankle, knee and hip joint torques in real-time during functional MRI (fMRI) testing in healthy volunteers. The motor representations of three isometric torques--ankle dorsiflexion, ankle plantarflexion and knee extension--were studied at two time points. The reliability of motor performance and fMRI-derived measures of brain activity across sessions was examined. Reproducible motor performance was observed for each of the tasks; torques of the requested amplitude, assisted by visual feedback, were generated at the relevant joint with good accuracy, both within and across the two sessions. Significant blood oxygen level dependent (BOLD) signal increases were observed in the left primary sensorimotor cortex (SM1) in the paracentral lobule and in secondary motor areas for all tasks. Within these areas there was substantial overlap of the motor representations though differential activation was observed in SM1, with greater activation of inferior paracentral lobule during knee extension than for either ankle task. Also, BOLD signal decreases were observed bilaterally within SM1 in the hand knob region for all tasks. No major session-related effects were identified at the group level. High intraclass correlation coefficients were observed for t-values of voxels in cortical motor areas for each contraction type for individuals, suggesting that fMRI-derived activity across time points was reliable. These findings support the use of this apparatus in serial studies of lower limb function.
    Full-text · Article · Aug 2008 · NeuroImage
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