Browsing by Subject "Force"

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Effects of varying the force levels and direction of force change on accuracy and force variability in a cyclic isometric pinch force tracking task
(2012-08) Park, Sangsoo; Abraham, Lawrence D.; Spirduso, Waneen
This study investigated how varying the required force level and the direction of force change produced by the thumb and index finger affect the accuracy and variability of a cyclic isometric pinch force-tracking task. Accuracy was examined by both absolute error and relative error for the minimum and maximum force levels and by root mean square error (RMSE) and normalized root mean square error (normalized RMSE) for the force direction reversals. Variability was represented by coefficient of variation of error (CVE). In this study, ‘maximum force’ was defined as the highest force level of a given target force range, and ‘minimum force’ was defined as the minimum force level of the target range. In addition, ‘force increasing to decreasing’ indicated that the track ball motion changed from increasing to decreasing, requiring the performer to exert increasing force up to the maximum force level and then decreasing force to follow the track ball moving toward the minimum force level. The phrase ‘force decreasing to increasing’ indicated the opposite force direction reversal. Eighteen healthy right handed adult volunteers (nine men and nine women; mean age ± SD, 28.3±1.22 and 26.4±1.74) participated in this study. The participants performed a cyclic isometric pinch force tracking task over three different force ranges. Force range 1 was from a minimum force of 3% of maximal voluntary contraction force (MVC) to a maximum force of 6% MVC. In force range 2, the range was from 6% to 12% MVC, and force range 3 was from 12% to 24% MVC. For each force range, five practice trials and ten actual test trials were performed. Rest periods of twenty seconds between trials and one minute between sets of trials (including between practice and actual test trials) were provided to minimize fatigue effects. Absolute error uniformly increased as a function of increasing force. However, the 3% target force level showed larger relative error compared to the 12% target force level (p < 0.05). Another finding of this study was that producing forces positioned at the minimum target level in a range yielded higher absolute error and relative error compared to the same forces when placed at the maximum target level of a different force range. In terms of the reversals, RMSE values were higher at the change from force deceasing to increasing than the opposite, as well as at higher force levels, while normalized RMSE values were greater at lower force levels. CVE was not significantly different between the two reversals in this study. This might indicate that poorer performance during the change from force decreasing to increasing could originate from the effort to maintain consistent performance and additional effort was not beneficial to increase accuracy for the change from force decreasing to increasing.
Muscle force potentiation and motor unit firing patterns during fatigue : effects of muscular endurance training
(2010-05) Mettler, Joni Ann; Griffin, Lisa; Abraham, Larry; Farrar, Roger; Jones, Theresa; Spirduso, Waneen
Muscular fatigue limits athletic performance as well as activities of daily living that require repetitive or sustained contractile activity. The decrease in force output or inability to maintain a given force level during fatigue occurs as the result of neural and muscle physiological factors. In contrast to muscle fatigue, potentiation is an increase in muscle force following voluntary muscle activity. The simultaneously occurring processes of potentiation and fatigue influence force output. The aims of this research were to investigate parameters used to potentiate muscle via electrical stimulation and voluntary contraction, and to better understand how muscle force is sustained, we studied single motor unit firing patterns and force potentiation following muscular endurance training. In study 1, electrical stimulation trains matched for pulse number of various frequencies and of increasing pulse number at a given frequency were administered to determine the effects of these stimulation parameters and of the force-time integral (FTI) produced during the train on potentiation magnitude. No difference in potentiation magnitude was found across trains of matched pulse number for frequencies of 15, 25, 30 and 50 Hz. Potentiation increased as pulse number increased and there was a positive correlation between potentiation and the FTI. In study 2, we measured maximal potentiation following conditioning contractions (CC) of 25%, 50% and 100% maximal voluntary contraction (MVC) and during a 25% MVC fatigue task, pre-post 8 weeks of muscular endurance training. Results showed significant potentiation for all CC intensities. Potentiation increased as CC intensity increased and CC duration required to achieve maximal potentiation decreased as CC intensity increased. Muscular endurance training resulted in increased maximal potentiation, and potentiation was greater during the fatigue task after training. Potentiation was also correlated to endurance time. In study 3, the effects of muscular endurance training on motor unit firing rates were investigated. There was a small increase in mean motor unit firing rates during the course of the fatigue task after training. This research contributes to our understanding of muscular force production and muscular endurance. The findings suggest that motor unit firing frequency and force potentiation may contribute to enhanced muscular endurance.
Precision pinch isometric force, force variability, accuracy, and task time among the fourth through eighth decades of life
(2011-05) Herring-Marler, Trenah Lannette; Abraham, Lawrence D.; Spirduso, Waneen Wyrick; Eakin, Richard T; Griffin, Lisa; Hunter, Diana
This dissertation encompassed three studies involving precision pinch strength and 5% submaximal fine-motor control. One hundred participants (30-79 years old) were divided into 10-year categories, with 10 males and 10 females in each decade. A Manual Force Quantification System containing a platform and force-transducer apparatus, along with a computer and visual monitor, was used. Each subject performed four tasks -- maximal voluntary isometric contraction (MVIC), force-matching, tracing, and tracking -- by applying force on the transducers with the thumb and index finger while attempting to produce a desired force level or task displayed on the computer monitor. The first study measured MVIC, accuracy (rRMSE, Root Mean Square Relative Error), and force variability (Coefficient of Variation, CV) during a 5% MVIC force-matching task. The second study measured accuracy (rRMSE), task time, and group variability during a 5% MVIC tracing task. The third study measured accuracy and group variability during a 5% MVIC tracking task. Tracing and tracking were each divided into six Segments (S1-S6), three of which (S1-S3) required the increasing application of force from 50g up to 5% MVIC and the remaining three (S4-S6) requiring a release of force from MVIC down to 1% MVIC. The force-matching and force-tracking task times were scaled to each participant's MVIC, while the tracing task was performed at the participant's self-selected speed. The participants were encouraged to be accurate but also to trace the target line as quickly as possible. Declines in precision pinch strength and force control began to occur in the 70s for easier force-control tasks and in their 60s for more advanced force-tracking tasks. Men were stronger than women at all age levels. Participants in their 30s were the fastest; those in their 40s, 50s, and 60s slowed down to be accurate; and those in their 70s moved faster but were the least accurate. Three segmental factors affected error and time: low force level, releasing as opposed to applying force, and location along the target line with respect to reversal or ending points. Finally, variables for females were more heterogeneous at earlier decades than for men, and the older the age group was, the greater the variable heterogeneity was.