Force Increase in a Repetitive Motor Task Inducing Motor Fatigue

Journal of Neurophysiology, 2010

We studied the effects of fatigue of the index finger on indices of force variability in discrete and rhythmic accurate force production tasks performed by the index finger and by all four fingers pressing in parallel. An increase in the variance of the force produced by the fatigued index finger was expected. We hypothesized that the other fingers would also show increased variance of their forces, which would be accompanied by co-variation among the finger forces resulting in relatively preserved accuracy of performance. The subjects performed isometric tasks including maximal voluntary contraction (MVC) and accurate force production before and after a 1-min MVC fatiguing exercise by the index finger. During fatigue, there was a significant increase in the root mean square index of force variability during accurate force production by the index finger. In the four-finger tasks, the variance of the individual finger force increased for all four fingers, while the total force variance showed only a modest change. We quantified two components of variance in the space of hypothetical commands to fingers, finger modes. There was a large increase in the variance component that did not affect total force and a much smaller increase in the component that did. The results suggest an adaptive increase in force variance by nonfatigued elements as a strategy to attenuate effects of fatigue on accuracy of multi-element performance. These effects were unlikely to originate at the level of synchronization of motor units across muscle compartments but rather involved higher control levels.

Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 2015

Muscle fatigue is associated with a higher risk of workplace injury, in particular during repetitive tasks. This study aimed to identify the effect of a complex force-time history (a task with multiple different submaximal effort levels) on fatigue accumulation and recovery during a handgrip task. We measured surface electromyography of the brachioradialis (BRD) and flexor carpi ulnaris (FCU) of ten right hand dominant females with no history of upper limb injury while they performed a complex submaximal visually targeted gripping task. The task consisted of 15%, 30%, 45%, 30%, and 15% maximum voluntary contraction (MVC) plateaus. Each plateau was held for 15s, followed by a 3s MVC and 3s of rest. The "pyramid" was repeated until fatigue criteria were met. Grip force, average EMG and mean power frequency (MnPF) for first cycle and fatigued last cycle, were compared. Post-plateau peak grip force was on average 20.5% MVC lower during the last cycle (p<0.01). Post-plateau ...

Experimental Brain Research, 1998

The goal of the study was to investigate forcesharing patterns in multi-finger tasks. Maximal normal force (MNF) as well as the force-time curves produced by individual fingers were measured in 10 young male subjects in three tasks: (1) holding an instrumented handle in a pad opposition with the thumb at seven different locations, from opposing the index finger (L 0 ) to opposing the little finger (L 6 ); (2) holding the handle in a pad opposition with the thumb at an individually selected comfortable location; and (3) pressing with the four fingers against the same handle fixed to the external support. We found that: (1) The moment due to the normal finger forces changed systematically when the thumb position varied from L 0 to L 5 / L 6 , and it was equal to zero at a certain middle position of the thumb, the neutral position. At this position, the shear force produced by the fingers was zero.

Proceedings of the 2020 CHI Conference on Human Factors in Computing Systems, 2020

Figure 1. Multiple sclerosis patients typically monitor the progression of their condition using specialized hardware to measure motor fatigue such as handgrip dynamometers (right). To allow such assessment to become more widely available and be performed more frequently, we propose a smartphone-based method to measure fatigability and assess motor fatigue (left). We show that our rapid alternating tapping task, over the first 30 seconds of a trial (center), is strongly correlated with a standard hand dynamometer for patients (ρ = 0.78) and the control group (ρ = 0.84).

Journal of Applied Biomechanics, 29:285-291

This study examined the influence of frequency and direction of force application on psychophysically acceptable forces for simulated work tasks. Fifteen male participants exerted psychophysically acceptable forces on a force transducer at 1, 3 or 5 repetitions per minute by performing both a downward press and a pull towards the body. These exertions were shown previously to be strength and balance limited, respectively. Workers chose acceptable forces at a lower percentage of their maximum voluntary force capacity during downward (strength limited) exertions than during pulling (balance limited) at all frequencies (4-11%, p = 0.035). Frequency modulated acceptable hand force; however only during downward exertions, where forces at five repetitions per minute were 13% less (p = 0.005) than those at one exertion per minute. This study provides insight into the relationship between biomechanically limiting factors and the selection of acceptable forces for unilateral manual tasks.

Frontiers in Physiology, 2019

During high intensity exercise, metabosensitive muscle afferents are thought to inhibit the motor drive command to restrict the level of peripheral fatigue to an individual's critical threshold. No evidence exists of an individual relationship between peripheral fatigue and the decrease in voluntary activation reached after prolonged all-out exercise. Moreover, there is no explanation for the previously reported large decrease in voluntary activation despite low metabolic stress during high force contractions. Thirteen active men completed two maximal intensity isokinetic knee extension tests (160 contractions) under conditions of low force-high velocity and high force-low velocity. Neuromuscular testing including maximal torque, evoked torque and voluntary activation, was done every 20 contractions. The exponential modeling of these variables over time allowed us to predict the stable state (asymptote) and the rate of decrease (curvature constant). For both high and low force contractions the evoked torque and voluntary activation asymptotes were negatively correlated (R 2 = 0.49 and R 2 = 0.46, respectively). The evoked torque asymptotes of the high and low force conditions were positively correlated (R 2 = 0.49). For the high force contractions, the evoked torque and voluntary activation curvature constant were negatively correlated (R 2 = 0.43). These results support the idea that a restrained central motor drive keeps peripheral fatigue under this threshold. Furthermore, an individual would show similar fatigue sensibility regardless of the force generated. These data also suggest that the decrease in voluntary activation might not have been triggered by peripheral perturbations during the first high force contractions.

Balkan Medical Journal, 2012

Background: The finger-tapping test is a commonly employed quantitative assessment tool used to measure motor performance in the upper extremities. This task is a complex motion that is affected by external stimuli, mood and health status. The complexity of this task is difficult to explain with a single average intertap-interval value (time difference between successive tappings) which only provides general information and neglects the temporal effects of the aforementioned factors. Aims: This study evaluated the time course of average intertap-interval values and the patterns of variation in both the right and left hands of righthanded subjects using a computer-based finger-tapping system.

IEEE Journal of Biomedical and Health Informatics, 2015

Sensory-motor performance is indicative of both cognitive and physical function. The Halstead-Reitan finger tapping test (FTT) is a measure of sensory-motor speed commonly used to assess function as part of a neuropsychological evaluation. Despite the widespread use of this test, the underlying motor and cognitive processes driving tapping behavior during the test are not well characterized or understood. This lack of understanding may make clinical inferences from test results about health or disease state less accurate because important aspects of the task such as variability or fatigue are unmeasured. To overcome these limitations, we enhanced the tapper with a sensor that enables us to more fully characterize all the aspects of tapping. This modification enabled us to decompose the tapping performance into 6 component phases and represent each phase with a set of parameters having clear functional interpretation. This results in a set of 29 total parameters for each trial, including change in tapping over time, and trial-to-trial and tapto-tap variability. These parameters can be used to more precisely link different aspects of cognition or motor function to tapping behavior. We demonstrate the benefits of this new instrument with a simple hypothesis-driven trial comparing single and dual-task tapping.

Journal of Neurophysiology

AND CONCLUSIONS 1. The activity of single motor units was recorded in the first dorsal interosseus muscle of human subjects while they performed an isometric ramp-and-hold maneuver. Motor-unit activity was characterized before and after fatigue by the use of a branched bipolar electrode that was positioned subcutaneously over the test muscle. Activity was characterized in terms of the forces of recruitment and derecruitment and the discharge pattern. The purpose was to determine, before and after fatigue, whether motor-unit activity was affected by the direction in which the force was exerted.

Behavior Research Methods, 2011

Motor speed is an important indicator and predictor of both cognitive and physical function. One common assessment of motor speed is the finger tapping test (FTT), which is typically administered as part of a neurological or neuropsychological assessment. However, the FTT suffers from several limitations including infrequent in-person administration, the need for a trained assessor and dedicated equipment, and potential short term sensory-motor fatigue. In this article, we propose an alternative method of measuring motor speed, with face validity to the FTT, that addresses these limitations by measuring the interkeystroke interval (IKI) of familiar and repeated login data collected in the home during a subject's regular computer use. We show significant correlations between the mean tapping speed from the FTT and the median IKIs of the non-dominant (r=0.77) and dominant (r=0.70) hands, respectively, in an elderly cohort of subjects living independently. Finally, we discuss how the proposed method for measuring motor speed fits well into the framework of unobtrusive and continuous in-home assessment.